U.S. patent number 3,779,684 [Application Number 05/273,367] was granted by the patent office on 1973-12-18 for continuous curing apparatus.
This patent grant is currently assigned to Dunlop Holdings Limited. Invention is credited to Hugh Lorain Folkes.
United States Patent |
3,779,684 |
Folkes |
December 18, 1973 |
CONTINUOUS CURING APPARATUS
Abstract
An apparatus for heating and compressing an elongated article ls
provided. The invention comprises the use of a plurality of
individual press units which are heated; the press units are moved
into heating and compression relationship with opposed surfaces of
the article; each press unit is moved successively into engagement
with the article and into contacting end to end relationship with
the previous press unit, the units being moved relative to the
surface only in a direction perpendicular to the surfaces when in
contact with the surfaces; the press units and the article are
moved stepwise in the direction of the length of the article; the
press units are continuously maintained in contact with the article
until the end of the heating and compressing cycle; with the press
unit finally successively being moved out of engagement with the
thus produced elongated article.
Inventors: |
Folkes; Hugh Lorain (St.
Leonards'-on-Sea Sussex, EN) |
Assignee: |
Dunlop Holdings Limited
(London, EN)
|
Family
ID: |
27258990 |
Appl.
No.: |
05/273,367 |
Filed: |
July 20, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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45604 |
Jun 12, 1970 |
3714317 |
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775347 |
Nov 13, 1968 |
|
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28290 |
Apr 22, 1970 |
|
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592131 |
Nov 4, 1966 |
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Foreign Application Priority Data
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Nov 25, 1967 [GB] |
|
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53716/67 |
Jul 14, 1966 [GB] |
|
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31657/66 |
Nov 10, 1965 [GB] |
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47594/65 |
|
Current U.S.
Class: |
425/233; 425/383;
425/406; 425/47; 425/385; 425/394 |
Current CPC
Class: |
B29D
29/00 (20130101); B29C 43/26 (20130101); B29C
43/44 (20130101); B29K 2021/00 (20130101); B29L
2031/709 (20130101) |
Current International
Class: |
B29C
43/22 (20060101); B29C 43/26 (20060101); B29C
35/02 (20060101); B29C 43/44 (20060101); B29D
29/00 (20060101); B29C 35/00 (20060101); B29d
029/00 (); B29h 007/22 () |
Field of
Search: |
;264/231,280,347
;425/233,47,384,385,394,407,408,453,406 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Spicer, Jr.; Robert L.
Parent Case Text
RELATED U.S. APPLICATIONS
This application is a division of my copending application Ser. No.
45,604 now U.S. Pat. No. 3,714,317, filed June 12, 1970 which is in
turn a continuation-in-part of my copending applications Ser. No.
775,347, filed Nov. 13, 1968 (now abandoned), and 28,290 filed Apr.
22, 1970 (now abandoned), the latter application being a
continuation of my now abandoned application Ser. No. 592,131,
filed Nov. 4, 1966.
Claims
I claim
1. A curing press unit for curing elongated articles comprising a
plurality of press units each having a pair of platens, a first
station having press means for bringing press units in curing
relationship with successive portions of an article to be cured,
means for moving press units in curing relationship with an article
to be cured in a stepwise manner through the curing unit, a second
station for succesively moving the press units out of curing
relationhip with the article at a second station, means for the
press unit to move the platens of two successive press units in a
direction perpendicular to the surface of an article being cured in
such a manner that in a first stage of operation of the press means
the forward end of a platen of one press unit is pressed against
said article so as to incline the platen relative to the
longitudinal direction of the article, and in a second stage of
operation of the press means the rearward end of said platen is
pressed against said article to dispose said platen parallel to the
other platen of the pair of platens, the press means having means
such that simultaneous with the second stage of operation the
neighboring forward end of a platen of the next successive unit is
pressed against said article.
2. A curing press unit according to claim 1 in which the press
means comprises first and second pressure plates for engagement
with two successive press units, the pressure plates being
pivotally mounted so that the forward end of each pressure plate
can be moved towards the article being cured independently of the
rearward end thereof.
3. A curing unit according to claim 2 in which the press means
comprises a thrust member for urging the pressure plates into
engagement with the press units, the thrust member comprising a
tapered portion for engagement with the first pressure plate and an
untapered portion for engagement with the second pressure plate,
and auxiliary press means being provided independent of the tapered
thrust member to urge the forward end of the second pressure plate
towards the article being cured.
4. A curing unit according to claim 3 in which the auxiliary press
means comprises a press head pivotally connected to the forward end
of the second pressure plate and arranged to exert a substantially
uniform compressive thrust on the press unit immediately ahead of
the press unit engaged by the second pressure plate.
Description
This invention relates to the curing of elongated articles, and in
particular to the curing of rubber and plastic belting and like
elongated articles.
The production of extremely long belting is of ever increasing
importance, being necessary for moving pedestrian sidewalks and
ramps which are being installed in increasing numbers in areas
which have heavy pedestrian traffic. Exemplary of such uses is to
avoid the necessity of forcing passengers at airports from walking
from the terminal building to the departure gates and in providing
upward ramps at modern sports stadiums. It will be clearly
appreciated that a continuous belt of considerable length is
required for such moving sidewalks and ramps. Uniformity in these
belts is most important, as variations may result in a space
between the sides of the moving sidewalk housing and the belt. In
such a case, it is possible that a person's leg could become
trapped, resulting in serious injury.
The method for curing elongated belting generally used in the prior
art comprises the use of large up-stroke presses, usually steam
heated. A moving table is arranged to run the full length of the
press and is of heavy box section design for minimum deflection.
The platens are made from steel plate accurately machined and
polished on the working surfaces.
The platens are divided into a number of chests. With the exception
of the two end chests, the remainder are inter-connected to allow
efficient circulation of steam or water. Conveniently the two end
chests are isolated from the remainder, so that they can be
maintained at a lower temperature to provide for an overlap between
each press charge.
It is extremely important in the prior art process that the
temperature of the platens is constant and controllable to ensure
uniformity of cure. It is also important that the belt receives
uniform compression over the whole platen area to obtain maximum
adhesion of the plies and covers, and also to produce a belt of
uniform cross-section, which is essential for correct tracking of
the belt in service. Without correct tracking the aforementioned
dangerous problem of a gap between the belt and the side track may
result.
Hydraulic gripping and stretching gear is also fitted to the press
so that stretch can be applied prior to curing to limit the amount
of elongation which will occur in service, stretch being maintained
during curing.
The uncured belting is supported in a roll adjacent to the press
and a leader consisting of a piece of cured belting is attached to
the end by means of belt fasteners. At the same time the
temperature of the press platens is adjusted to the required
temperature.
Longitudinal molding irons (full press length) of the required
thickness to allow the necessary compression of the uncured belt
are placed on the bottom platen. A sufficient number of these irons
are used to form a frame to give the final width of the belt, when
lateral pressure, either mechanical or hydraulic, is applied from
the sides of the press.
The end of the leader is drawn through the press to a position
where the cured belt is eventually formed into a roll.
The first charge of the belt is drawn centrally into the press.
Stretching equipment consisting of clamps fitted at each end of the
press (one being movable) are closed onto the belt and a
predetermined percentage of stretch applied. The press is closed on
low hydraulic pressure, and lateral pressure is applied to the belt
edges, followed after an interval by the application of high
pressure. The hydraulic pressure, rate of application, delay and
cure cycles will vary according to the type and grade of belt, for
example, from 12 minutes at 50 psi steam for a thin belt to 48
minutes at 30 psi steam for a belt one inch thick.
At the end of the cycle the press is opened, the lateral pressure
released and the belt is drawn through the press, leaving
approximately 12 inches of the end of the charge at the exit end of
the press.
The process is then repeated until the required length of belting
has been cured.
It will be readily appreciated that there are practical
difficulties which present serious drawbacks to the conventional
method of the prior art to which no satisfactory solution has
hitherto been found.
The use of a single press means that the method is essentially a
"batch" process in that when any particular length of article has
been cured, the press must be opened and the cured portion of the
article withdrawn from the press, thereby drawing behind a portion
of uncured material with the boundary between cured and uncured
material being advanced to the forward end of press before the
latter is closed and the curing cycle repeated. This method is not
only time consuming, but furthermore difficulties arise in the
exact alignment of the uncured portion while within the press,
resulting in problems of double-curing or under-curing of the end
of the portions cured in each batch treatment.
A further major disadvantage of the conventional method is that
considerable time is wasted due to the fact that the curing process
must be interrupted when the press is opened and not resumed until
the press is closed on the succeeding portion of uncured material.
The fact that the prior art "batch" process does not allow
continuous production and therefore restricts the amount of belting
which can be produced in a particular time period, is very
unsatisfactory, especially in view of the large capital cost of the
machinery used.
Further disadvantages arise from the size and weight of the presses
and particularly, of the moving parts. In a conventional form of
press, known as the "column type," a typical platen size is 32 feet
.times. 84 inches, giving an effective length of 28 feet, and an
effective width of 80 inches. In this press, the moving table is
actuated by 24 hydraulic rams, each of 153/4 inches diameter, and
the total weight of the presses is 420 tons. Another form of press,
known as the "plate Frame walk-in type," has a typical platen size
of 36 feet .times. 65 inches, giving an effective length of 30 feet
and an effective width of 60 inches. Again, a large number of
hydraulic rams are used to actuate the moving table and the total
weight of the press is 300 tons.
It will be thus appreciated that conventional presses are large,
heavy and expensive items. To increase output, presses with even
larger platens have been proposed. However, the larger the press,
the more difficult and expensive it is to ensure that the platens
are accurately machined and assembled and that uniform compression
occurs over the whole of the platen area.
An object of this invention is therefore to provide an improved
process and apparatus for curing rubber and plastic belting and
other elongated articles.
A further object of this invention to provide belting of excellent
uniformity, and which can be produced with greater economy than
previously possible through the provision of a continuous belting
process.
The objects of this invention are achieved through the apparatus
and method of the present invention. In its broadest aspect, the
present invention provides a method of curing an elongated article,
comprising pressing the article in a press comprising a number of
press units, the press units being successively engaged with the
article at a first station and moving in engagement with the
article to a second station where the press units are successively
disengaged and returned to the first station.
In a particular embodiment of the invention, on completion of a
curing operation and being disengaged from the article at the
second station, the press units are employed to execute a further
curing operation in the course of returning to the first station.
The further curing operation may comprise transfer of the press
units to, and successive engagement of the press units with, an
article at a third station and movement of the press units in
engagement with this article to a fourth station where the press
units are successively disengaged and transferred to the first
station.
To avoid gaps between cured portions of the article, the press
units are moved into contacting end to end relationship, and also
the movement of the press units, relative to the article, is in a
direction perpendicular to the surface of the article once the
press units are in contact with the article.
When curing certain articles of a plastic consistency, it has been
found that as a press unit is moved into contact with the article,
a small amount of material forming the article is pushed out at the
reat edge of the unit. The next press unit has to compress this
extra material and as a result more material is pushed out at the
rear edge of this next unit. This action become progressive.
By moving the press units into contact with the article in a
particular manner, expulsion of material can be avoided. Thus
according to a further embodiment of the invention, pressure is
applied by the press units to successive contiguous portions of an
elongated article to be cured, the pressure exerted on each portion
of the article by its respective press unit initially substantially
greater in the region of the forward end of the said portion of the
article than in the remainder of that portion of the article.
Pressure is then applied or increased in the remainder of that
portion of the article in a progressive manner from the forward end
to the rearward end thereof, the pressure being applied or
increased in the region of the rearward end of the said portion of
the article substantially simultaneously with the initial exertion
of pressure in the region of the forward end of the next following
contiguous portion of the article.
The invention can be used for curing articles other than belting
and like material. Thus the invention can be used in the
manufacture of laminated material, such as plywood, and boarding
such as fibre-board, insulating board and other products which
require pressure and heat treatment during production.
In this specification the term "curing," and derivatives thereof,
refers to heat treatment to produce a change of state and
specifically in relation to rubber and similar materials refers to
vulcanisation thereof. A further example is the application of
pressure and heat to convert material in one form into another, as
for instance to convert a pasty or liquid material to a solid
self-supporting form.
Various embodiments of the invention will now be described by way
of example, in conjunction with the accompanying diagrammatic
drawings, in which:
FIGS. 1 to 4 are plan-view representations of a sequence of
successive steps in the curing of two lengths of conveyor belting
in two parallel presses;
FIG. 5 shows a transverse cross-section through a continuously
heated press unit, having its own compressive force-applying means,
in engagement with an article being cured;
FIG. 6 shows a section of the line VI--VI of FIG. 5;
FIG. 7 shows a longitudinal cross-section through part of two
adjacent press units of the type shown in FIGS. 5 and 6, each
having its own compressive force-applying means;
FIG. 8 shows a transverse cross-section through a press unit
designed for intermittent heating and for use with fixed
presses;
FIG. 9 shows a longitudinal cross-section through part of two
adjacent press units of the type shown in FIG. 8 showing the
platens clamped end to end;
FIG. 10 shows a vertical cross-section through a single daylight
fixed press having re-heating means in the form of hot plates, for
the platens of the press units, a press unit being shown in
position;
FIG. 11 is a plan view representation of a stage in the course of
continuous curing of two conveyor belts side by side at the same
level, employing single daylight fixed presses;
FIG. 12 shows another plan view of two curing units of a different
form;
FIG. 13 shows a cross-sectional view taken on the line 13--13 in
FIG. 12;
FIGS. 14 and 15 illustrate fragmentary cross-sectional views
illustrating further details;
FIG. 16 shows a pressing station A in FIG. 12 in a side elevational
view at right angles to a length of belting being cured;
FIGS. 17, 18, 19 and 20 show diagrammatic cross-sectional views
taken on the line 17--17 in FIG. 12 illustrating a sequence of
movements during operation of a pressing station, and in which a
series of clamps is indicated for maintaining pressure on an
article being cured after the article emerges from the pressing
station;
FIG. 21 is a longitudinal cross-section through a press unit
otherwise similar to that of FIGS. 8 and 9, but designed to be
spaced apart from adjacent press units during a curing
operation;
FIG. 22 is a vertical cross-section through a double daylight fixed
presses, two press units shown in position;
FIG. 23 is a representation of a stage in the course of continuous
curing of a single length of conveyor belting using double daylight
fixed presses;
FIG. 24 is a representation of an elevation of the apparatus shown
in FIG. 23.
The invention is described herein with particular reference to the
curing of conveyor belting, but as indicated above, the invention
is applicable to the curing of rubber and plastics and other
elongated articles in general.
In the arrangement shown in FIG. 1 two identical presses 1 and 2
each consist of a number of identical press units, in the present
example six press units, the units of press 1 extending between a
first station S1 and a second station S2 and being 1B, 1C, 1D, 1E,
1F and 1G, and the units of press 2 extending between a third
station S3 and a fourth station S4 and being 2B, 2C, 2D, 2E, 2F and
2G. The units of each press are in contiguity with each other,
i.e., in end-to-end contact, each have an upper platen (shown in
FIGS. 1 to 4) and a lower platen (not shown), the two platens
having means (not shown) to urge them towards each other by
hydraulic or other suitable power. Edge irons 3 are provided for
engagement with the edges of the belting and heating means (not
shown), such as steam pipes, provided for raising the unit to a
suitable curing temperature and maintaining it at that temperature.
At the stage shown in FIG. 1 the pressure applied to urge together
the platens of units 1G and 2G which have just been added to the
presses 1 and 2 at the first and third stations S1 and S3
respectively, is less than that applied to the platens of the other
units of the presses.
The conveyor belting 4 of press 1 consists of a series of portions;
an uncured portion 4A which has not yet entered the press, a number
of portions (not shown) within the press units and a further
portion 4B of cured belting which has left the press. Similarly the
conveyor belting 5 of press 2 consists of an uncured portion 5A,
portions (not shown) within the press units and a cured portion
5B.
Fixed clamps 7 and 8 and longitudinally movable clamps 6 and 9 are
provided for producing and holding the longitudinal tension
required during curing. Similarly the tension means for the
reinforcement of belting 4 consists of fixed clamps 11 and 12 and
longitudinally movable clamps 10 and 13. Each clamp consists of a
pair of horizontal jaws, one of which is movable vertically by
hydraulic or other means so that the jaws can be closed upon and
hold the belt, or opened to allow the belt to pass between them. It
will be seen that the fixed clamp of each pair is on the press side
of each of the pairs of clamps.
The lower platens (which support the belting) are themselves
carried on horizontal tables (not shown in FIGS. 1 to 4). Fixed
base members 14, 15 are provided between the stations, on which
press units can be transferred from the second station S2 to the
third and from the fourth S4 to the first S1. In FIG. 1 press unit
1A, with its edge irons, is supported by fixed base member 14 and
is in the course of being transferred from the second station S2 to
the third station S3. Similarly press unit 2A, supported by fixed
base member 15, is in the course of being transferred from the
fourth station S4 to the first station S1.
In FIG. 1 the tension in the reinforcement of the belting 4 is
provided by clamps 10 and 13 which are shut firmly on the belting,
clamps 11 and 12 being open. Similarly, the tension in the
reinforcement of belting 5 is provided by clamps 6 and 9 which are
shut firmly on the belting, clamps 7 and 8 being open. The arrow
associated with clamps in FIG. 1 show the movement that took place
in the immediately preceding step of the method.
In FIG. 2 the presses 1 and 2 consist respectively of press units
1C, 1D, 1E, 1F and 1G, and 2C, 2D, 2E, 2F and 2G (1G and 2G being
still pressed against the belting at a lower pressure than the
other units). Press unit 2B has arrived at the fourth station S4,
its platens having been separated. The portion 16 of the belting
from which unit 2B has been released is in a fully cured condition.
Similarly, press unit 1B has arrived at the second station S2, the
belting portion 17 being in a fully cured condition. The press
units 1A and 2A, which in FIG. 1 were supported by turntables not
shown in FIG. 1 but shown in FIG. 2 as 18 and 19, have been turned
through 180.degree. on the turntables and forwarded respectively
towards the third and first stations, the upper and lower platens
of each unit being situated respectively above and below the
belting but without yet being closed on the belting.
The belting 4 is now held in tension by clamps 11 and 12 while
belting 5 is held in tension by clamps 7 and 8. Clamps 10 and 13
have each been moved to the right, while in an open condition, and
similarly clamps 6 and 9 have been moved to the left while open.
Clamps 10 and 6 each initially move a distance somewhat less than
the width of a press unit, the actual distance moved being such
that when clamps 10 and 6, together with clamps 13 and 9, are
closed on the belting, and clamps 7, 8, 11 and 12 are opened,
clamps 10 and 6 are moved a further distance to bring the total
distance moved by these clamps up to that equalling the width of a
press unit, and at the same time applying the correct tension to
the belting 4 and 5. The relative proportions of the initial
movement and the further movement are selected to provide the
desired tension in the belting.
With reference to FIG. 3, press 1 now consists of press units 1C,
1D, 1E, 1F, 1G and 2A, and press 2 consists of press units 2C, 2D,
2E, 2F, 2G and 1A, press units 1A and 2A having been added
respectively to the tails of presses 2 and 1, their platens closed
on the belting and their temperature raised. Press units 1G and 2G,
which in FIG. 2 were shown as being at low pressure, now have that
pressure increased to that of press units 1C, 1D, 1E and 1F and
units 2C, 2D, 2E and 2F respectively. Press units 1B and 2B have
been forwarded respectively to turntables 18 and 19 for rotation
through 180.degree. and if necessary change of side irons 20 and 21
represent respectively the means for changing the edge irons of the
press units between successive curing operations thus making it
possible to use the press continuously without stopping production
when one belt is completed and one of a different thickness and
width is started and making it possible to press two different
sizes of belt on the two presses. The rotation is made to avoid the
steam lines or other connections becoming crossed. The main steam
line (not shown) feeding presses 1 and 2 preferably lies between
the two presses, and if rotation through 180.degree. of the press
units being transferred were not made, it would result in the steam
lines of the transferred press units being on the outer side of the
press with consequent inconvenience in operation.
As described previously, clamps 6 and 10 are shown as having been
moved a further short distance respectively from clamps 7 and 11,
as indicated by the arrows touching clamps 6 and 10. Before this
movement was made clamps 6 and 10 were shut firmly on the belting
and consequently the belt portions 22 and 23 are subjected to a
tension substantially the same as the tension in the belting within
the press. 24 and 25 represent preheating means to preheat the
uncured belting before it is fed to the presses and thereby to
increase the output of the presses, but this is an optional feature
and the success of the method of the invention is not dependant
upon it.
FIG. 4 shows the press units in the same order as shown in FIG. 3,
but iron-changing means 20 and 21 and the heaters 24 and 25 are not
shown.
The stage illustrated in FIG. 4 is that immediately following the
movement (by means of hydraulic or other power) of belting 5 and
its press units 2C, 2D, 2E, 2F, 2G and 1A towards the right of the
drawing by an amount equal to the width of a press unit. This
movement has been accompanied by opening clamps 7 and 8 so as to
release the belting and moving clamps 6 and 9 towards the right by
a distance equal to the width of a press unit. Similarly, movement
of the belting 4 and its press units 1C, 1D, 1E, 1F, 1G and 2A
towards the left-hand side of the drawing has been accompanied by
opening clamps 11 and 12 and moving clamps 10 and 13 towards the
left by a distance equal to the width of a press unit.
It will be seen that the disposition of the press units of presses
1 and 2, the press units in transfer across the fixed base members
14 and 15 and the tension clamps 6, 7, 8, 9, 10, 11, 12 and 13 is
the same in FIG. 4 as in FIG. 1 and that the cycle illustrated in
FIGS. 1-4 has resulted in the emergence from the press of one fully
cured portion of width equal to the length of a single press unit.
Consequently, the first stage of the next cycle of the method is
represented by FIG. 2 and so on.
In the specific process described above each cycle results in the
whole of the belting portions within press units being cured to the
same extent and at any particular stage of the cycle the contiguous
portions within the press units constituting the press at that time
are in states of cure which range from the almost fully cured state
of the portion in the press unit at the head of the press near
stations S2 or S4 to a state of only very slight, if any, cure of
the portion within the press unit at the tail of the press near
stations S1 or S3. It will be seen, therefore, that the conditions
of temperature and pressure used to effect cure are preferably
selected so that a belting portion in any particular press unit
reaches the fully cured state at the time when its press unit is to
be detached from the head of the press. Where the material being
cured is one which is susceptible to "over cure," care has to be
taken to select conditions which avoid that state.
If found convenient, the press units can move during transfer
between presses, on a semi-circular path between the two base
members or on a path which is partly curved and partly straight. In
that event, the rotation of the units through 180.degree. during
transfer from the second or fourth to the third or first station
respectively is effected by the curved path and turntables can be
dispensed with.
As shown in FIGS. 5 to 7 a press unit 26 comprises horizontal
rectangular platens 27 and 28 between which is located a portion 29
of conveyor belting. The press unit 26 further comprises insulation
layers 30 and 31 to reduce the loss of heat from the platens during
curing and tables 32 and 33 which ensure a uniform compressive
force on the conveyor belting during curing, the arrangmeent being
such that the platens are sandwiched between the insulating layers
which are themselves sandwiched between the tables.
The lower table 33 is supported by a support member 34 slidably
located on rails 35 and 36 formed on fixed base member 37. The
rails 35 and 36 are located in corresponding grooves 38 and 39
formed in support member 34, so that the whole press unit may slide
along the fixed base member 37 during curing. Motive power to cause
the press unit to slide thus is derived from an external fluid
pressure operated means and is applied to the press units through
drive brackets 40 and 41.
Upper table 32 is secured to two support brackets 42 and 43
extending upwardly from the table having mounted at their upper
ends axles 44 and 45 one on each bracket, extending at right angles
to the sides of the press unit, two pairs of wheels 46 and 47 being
rotatably mounted, one pair on each axle, to engage overhead guide
rails (not shown) at second station S2 or fourth station S4 at the
end of a curing operation.
To control the width and thickness of the portion of belting 29
being cured, and to produce straight edges thereon, the press unit
26 is provided with two edge irons 48 in the form of plates having
straight edges and adapted to be positioned with one edge of each
iron in engagement with one edge of the portion of belting 29. The
edge irons each have formed therein two openings 49 to provide
locating sockets for fluid pressure operated means (not shown) to
urge the irons into engagement with the belting, two series of
apertures 50 being provided to co-operate with pins 51 associated
with the upper platen 27 to hold the edge irons in the required
position after engagement with the belting as described above. Two
further apertures 52 in the form of slots adjacent each end of the
iron are provided for a purpose to be described.
The press unit 26 is provided with four similar piston and cylinder
assemblies 53 operable by fluid pressure to draw together the two
platens, thereby exerting compressive forces on the belting 29
being cured. The piston and cylinder assemblies are all mounted on
the upper rectangular table 32, one near each corner thereof in
order that at least one assembly should be located adjacent each
edge of the opposite side edges 54 and 55 (FIG. 5) of the upper
platen 27.
Each piston and cylinder assembly 53 comprises a piston rod 56
attached at one end to a piston (not shown) and having an abutment
57 at the other end, the piston rod being arranged to extend
through the apertures 52 formed in the edge irons 48, and
corresponding alignable apertures in the tables 32, 33, insulation
layers 30, 31, platens 27, 28 and the support member 34.
In FIG. 5, the piston rod 56 is shown fully extended outwardly from
the cylinder. In order that, on admission of fluid pressure to the
cylinder and withdrawal of the piston rod into the cylinder, the
platens may be urged together, removable means in the form of a
swingable locking piece 58A (only one being shown in FIG. 6) is
provided for each piston and cylinder assembly to engage the
abutment 57 and prevent withdrawal thereof so that the tables 32,
33 and thereby the platens 27, 28 are squeezed between the
cylinders and the abutments of the assemblies 53.
Control panels 59 and 60, one on each side of the press unit 26 are
provided to control the supply of fluid pressure to the various
cylinders on the unit, valves (not shown) on the panels being
operated by rods and cams (not shown) at appropriate points in the
course of any given curing operation.
The various connections necessary for the supply of steam, cold
water, hydraulic power and other requirements to the press units
are made to the inner side of the press units with respect to the
closed circuit path which they follow, by means of flexible pipes
(not shown) and a services conveyor.
In the apparatus shown in FIGS. 5 to 7 adjacent press units are
secured end-to-end during curing of the belting by means of two
fluid-operated latch mechanisms 61 on each press unit, mounted
horizontally, one on each side edge of each table adjacent one end
of each side edge. Each latch mechanism comprises a hinge 62 on
which a cylinder 63 is mounted, swingable in the plane of the
table. A piston (not shown) is located in each cylinder 63, and has
a piston rod 64 with an abutment 65 at the free end thereof. Each
latch mechanism further comprises a latch portion 66 in the form of
two separate raised members 67 arranged so that piston rod 64 can
pass between them by swinging cylinder 63 on hinge 62. When fluid
pressure is supplied to cylinder 63, the piston is urged toward the
hinge end of the cylinder 63, and abutment member 65 engages raised
members 67 of the adjacent press unit 68 thereby urging the units
together.
Edge irons 48 are each provided with a rectangular guide slot 69
extending parallel to the end edges of the edge iron, in each of
which is located a corresponding guide lug 70 attached to lower
platen 28, this provision being to ensure that the edge irons are
always positioned parallel to the side edges of the platens,
thereby ensuring substantially straight edges are formed on the
belt through-out its length.
A curing operation employing the apparatus shown in FIGS. 1 to 7
will now be described.
In FIG. 1, press unit 1A, which for the purpose of describing this
sequence of operations will be considered to be the press unit 26
of FIG. 7, but as will be explained more fully hereafter may be of
a modified design, is shown midway between the second station S2
and the third station S3. At this point unit 1A is turned through
an angle of 180.degree. on turntable 18 (FIG. 2) and then is moved
towards station S3 where the belting 5A is located between platens
27 and 28. Unit 1A then moves up to unit 2G as shown in FIG. 2,
latch mechanism 61 secures it to unit 2G and edge irons 48 engage
the sides of the belt, and are located in position by pins 51.
Assemblies 53 close the platens on the belt under low pressure. The
platens, being continuously steam-heated are already hot, and
curing begins. Curing proceeds under increasing pressure from
piston and cylinder assemblies 53 as the belt and attached press
units move slidably and stepwise through the press supported on the
fixed guide member 37 as already described, in conjunction with the
appropriate clamping operations of clamps 6, 7, 8, 9, 10, 11, 12
and 13.
During curing, appropriate adjustments to fluid pressures and other
control operations are effected by engagement of the controls of
panels 59 and 60, for example by levers and cams suitably
positioned as the press unit slides along fixed base member 37.
As unit 1A reaches station S4, the pressure on the platens is
released, the latch mechanism disengaged, the edge irons released,
and wheels 46 and 47 engage fixed overhead guide rails (not shown)
causing the upper part of the press unit to be disengaged from the
belt. The parts of the press unit are then moved sideways, to
station S1, being turned through an angle of 180.degree. during
such movement, ready to engage with the belt 4, thus completing one
curing operation.
FIGS. 8 and 9 show a modified press unit arranged to be heated
intermittently and used in conjunction with means independent of
the press unit for applying a suitable compressive force to the
belt.
As previously described, pressure is applied to the platens
progressively, in that initially the pressure is relatively low,
then being increased up to a maximum compressive force which is set
by various requirements, for example to squeeze the rubber into the
interstices of the tensile member, and to produce a uniform
surface. However, it has been found that this maximum compressive
force need not be applied throughout the remaining curing time of
the belting. It is sufficient for the compressive force to be built
up during the first part of the curing cycle, and may be reduced
thereafter for the remainder of the operation, to a magnitude
sufficient to overcome pressure produced between the platens, for
example by the formation of steam from moisture present in the
article being cured.
It is therefore possible to pass the press units, one at a time,
through a fixed press which builds up the maximum compressive force
on the press units, after which latches are engaged, to lock the
platens together. The press units then pass from the press, the
latches retaining the platens together and thus maintaining
pressure on the belt. Depending upon the material being cured,
there may be a variation in the pressure between the platens, and
this pressure may even reduce to zero by the end of the cycle.
While such fixed presses need to be of substantial construction, as
they only have to accept one press unit at a time the size of the
fixed presses can be much smaller than conventional belting
presses.
FIGS. 8 and 9 illustrate a press unit, 71 for use with a fixed
press and for intermittent heating. Press unit 71 comprises platens
72 and 73 between which is located a portion 74 of a length of
conveyor belting. Edge irons 75 similar to the irons 48 employed in
the press 26 depicted in FIGS. 5 to 7 are provided, with edge iron
pins 76 associated with upper platen 72 co-operating with a series
of apertures (not shown) formed in each edge iron as previously
described in connection with edge irons 48.
Lower platen 73 is provided with a pair of right-angled mild steel
angles 77 one limb of each of which is secured to one side edge
face of the platen. The other limb extends laterally from the
platen 73, with its upper surface in the same plance as that of the
belt-contacting surface of platen 73.
A second pair of right-angled mild steel angles 78 of smaller gauge
metal then the angles 77 is located in the angle between the limbs
of the angles 77, and between the angles 77 and the angles 78 is a
right-angled section layer of insulating material 79, to minimise
the loss of heat from the platen. The assembly of platen angles and
insulation material being secured together to form a unified
structure.
Mild steel angles 78 serve as guide and support surfaces for the
press unit and engage guide wheels 80 rotatable in a horizontal
plane, and support wheels 81 rotatable in a vertical plane mounted
on right-angled support brackets 82 fixed to and extending along
the length of the press with a base 83. Between support brackets
82, and fixed to base 83 is a layer of insulation 84, the
arrangement being such that the platens are supported by support
wheels 81 so that there is an air gap between the upper surface of
insulation layer 84 and the lower surface of platen 73.
Upper platen 72 is also provided with a pair of right-angled mild
steel angles 85 corresponding to the angles 77, one limb of each of
which is secured to one side edge face of the platen 72, the other
limb extending laterally with its lower surface in the plane of the
belting contacting surface of platen 72.
The platens 72 and 73 of press unit 71 are of such a thickness that
their thermal capacity is sufficient for the curing of the belt in
the time of the curing cycle, without requiring any further
addition of heat. For example it has been found that the thermal
capacity of a 3-inch thick platen is more than sufficient for the
purpose of vulcanising a 1-inch thick belt.
Heat is supplied to the platens at re-heat stations by bringing the
platens into contact with hot metal plates as will be described
hereafter. Other satisfactory methods of re-heating the platens
include the use of infra-red heating units and direct heating by
gas flames of the outer surfaces of the platens which surfaces do
not contact articles to be cured.
Employment of an intermittent supply of heat has the advantage that
before the platen is brought into contact with the article to be
cured, it can be heated to a temperature higher than that normally
used for the curing of the article so that heat penetrates from the
surface of the article to its centre portion more quickly, thus
providing a shorter curing time. The loss of heat from the surface
of the platen to the article cools the platen surface so that
over-curing of the article can be avoided.
As press unit 71 moves along the press in the course of a curing
operation, heat losses from the upper surface of upper platen 72
are minimised by the provision of a stationary canopy 86 extending
along most of the length of the press and having a lining 87 of
insulating material.
Two lifting lugs 88 are secured to each angle 85 at the side of
press unit 71 whereby the upper platen may be lowered and lifted by
external means (not shown) as required to engage and disengage the
belting 75 at the beginning and end of a curing operation.
A sequence of operations during curing, employing press units as
already described with reference to FIGS. 8 and 9 and fixed presses
89 which incorporate platen reheating apparatus (see FIG. 10) will
now be described with reference to FIG. 11.
In FIg. 11 the arrangement and general mode of operation of press
units 71 (only one being numbered), clamps 90 for tensioning the
belts 91 and 92 and pre-heat stations 93 for pre-heating the belt
are as previously described with reference to FIGS. 1 to 4.
At the first station S1 in FIG. 11, the belt 91 is located between
the platens 72 and 73 of press units 71 (FIG. 10). Edge irons
engage the edges of the belt and the press unit is secured to its
adjacent unit by screw-threaded unit clamping means 100 operated by
external means. Locating pins 101, one on each side of each press
unit and passing through apertures formed in angles 77 and 85
ensure accurate alignment of the platens. The press unit is then
moved on wheels 81 and guided by wheels 82 to fixed press 89 (see
FIG. 10) where by operation of piston and cylinder assembly 94
mounted on base 95, movable lower table 96 slidably mounted on
guide members 97 is urged towards upper table 98 thereby causing
hot plates 99, insulated from the tables by insulating layers 102,
to engage the platens and the press unit to be lifted off wheels
81.
While the press unit 71 is under compression in fixed press 89,
platen clamping means in the form of four platen clamping screws
103, two at each side edge of the press unit and passing through
angles 77 and 85, are operated by external means so that on
emergence of the press unit from the fixed press the platens are
retained at substantially the proximity they assumed in the fixed
press.
After a predetermined interval the press unit leaves the fixed
press 89 and moves in stages in a manner similar to that already
described in connection with FIGS. 1 to 4, towards the second
station S2. Curing continues as heat is conducted from the platens
to the portion of belting with which they are engaged, while the
unit rides along on supporting wheels 81 under the canopy 86.
At the second station the unit is released from its adjacent unit
by releasing the unit clamping means 100, compression is released
by releasing clamping screws 103, and locating pins 101 and edge
iron pins 76 are disengaged all by external means (not shown), and
the upper platen lifted away from the belt by means of lugs 88. The
lower part of the unit is moved away from the belt, and the whole
unit transferred to the third station S3 but without being turned
round since this is unnecessary because no flexible connections
such as steam pipes are made to the press unit. At the third
station S3, the sequence of operations just described is repeated
and the press unit moves with the belt 92 to the fourth station and
thence back to the first station again.
As previously stated, where curing certain articles of a plastic
consistency, there is a tendency for material to be squeezed out
from between the platens, at the rear end of the press unit. FIGS.
12 to 22 illustrate an embodiment of the invention in which
pressure is applied by the press units to successive contiguous
portions of the article being cured, in such a manner that pressure
is applied, or increased, in the rearward zone of one portion as
pressure is applied to the forward zone of the next succeeding
portion. The press units are arranged so that successive platens
are in end contact with one another, and squeezing out of material
is thus avoided.
As seen in FIG. 12, there are first and second identical curing
units 201. 202 each comprising a plurality of identical press units
203 extending between two stations in contiguous head to tail
relationship and in engagement with respective portions of
reinforced rubber conveyor belting.
The press units 203 are successively brought into alignment with a
length of belting 204 at a position 205, and successively engaged
with successive contiguous portions of the length of belting 204 at
a pressing station 225 constituting a first station of the first
curing unit 201 and move in engagement with the belting to a second
station 206 at the other end of the first curing unit where they
are successively disengaged from the belting and transferred
through a position 207 to a pressing station 225 constituting a
first station of the second curing unit 202. Here the press units
are successively engaged with successive contiguous portions of
another length of belting 208 and moved in engagement with the
belting to a second station 209 at the other end of the second
curing unit where they are then successively disengaged from the
belting and returned to the position indicated by numeral 205 to
commence another identical sequence of operations.
As shown in FIG. 13, each press unit 203 comprises a pair of thick
metal platens 210, 211 for engagement with the belting 204 and 208.
Holding means in the form of a series of clamps (not shown) are
moved to prevent separation of the platens and thereby maintain any
desired compressive forces on the belting during a curing operation
as the press unit passes between the first and second stations of
the two curing units 201 and 202.
To control the width and thickness of the portion of belting being
cured by each press unit 203 and to produce straight edges on the
belting, each press unit is provided with two edge irons 212 in the
form of metal slats have straight side edges and arranged to be
positioned with one edge of each iron in engagement with one edge
of its respective portion of belting. Angle members 214 are
attached to the sides of the platens 210, 211 to provide support
and location for the edge irons.
Power operated means (not shown) independent of the press units is
provided to force the edge irons 212 into engagement with the edges
of the belting after the platens 210, 211 have engaged the belt at
the commencement of each curing operation at the first stations
225. To maintain the separation of the edge irons and therefore to
control the width of the belting throughout each curing operation,
each press unit is provided with locking means for the edge irons
comprising a pair of locking pins 213 (see FIG. 14) mounted at each
side of the press unit, each pin being seated in aligned holes
formed in a first pair of right angled mild steel angles 214. The
mild steel angles are secured in back-to-back relation, one to each
side edge of each platen so that in the assembled state of the
platens they constitute a T-shaped structure, the pins 213 being
seated in holes formed in the two limbs one from each mild steel
angle, which are back-to-back.
Each locking pin 213 is locatable in any one of a series of
apertures formed in its associated edge iron 212 at a corresponding
position along the length thereof, the apertures of each series
being spaced apart across the width of the edge iron. When the edge
irons have been forced to have their required separation at the
first station 225, they are maintained at this separation by
locating the locking pins in the apertures in the edge irons
appropriate to this separation.
Generally, in other respects, the press units 203 are similar in
form to the press units 71 illustrated in FIGS. 8 and 9, and
therefore further detailed descriptions of the press units 203 is
not considered necessary.
Two iron change units 215 are provided between the two curing units
201, 202, one at each end thereof, where the edge irons required in
the curing of one belt are changed, if necessary, for those
required for the other belt. Thus, if desired, the two belts 204
and 208 may be of different widths and thickness.
As each belt passes through its respective curing unit, it is
maintained under a predetermined steady longitudinal tensile load
by means of tension units 216 located one at each end of each
press.
Each tension unit 216 comprises a longitudinally fixed clamp 218,
219, and a longitudinally movable clamp 217, 220. By engagement of
the clamps with and disengagement of the clamps from the belt and
movement of the movable clamps, at appropriate times, the belt is
moved stepwise through the curing unit under substantially constant
tension.
The operation of the clamps of the tensioning units 216, is as the
operation of the clamps 6 to 13 of the arrangement illustrated in
FIGS. 1 to 4 and will not be further described, it being understood
that the purpose of the units 216 is to provide for tensioning of
the belting 204 and 208, and maintaining such tension, while
permitting movement of the belting through the curing units 201 and
202.
To support and guide the press units for longitudinal movement with
the belting during curing, support and guide wheels are provided at
spaced apart positions along both sides of each press. The support
wheels 221 (see FIG. 13) are mounted for rotation about horizontal
axes parallel to the planes in which the press unit platens 210,
211 lie and engage support surfaces extending along the length of
each press unit, one of each side thereof. Guide wheels (not shown)
are mounted for rotation about vertical axes and engage guide
surfaces also extending along the length of each press unit one on
each side thereof.
To support and guide the press units for longitudinal movement with
the belting during curing, support and guide wheels are provided at
spaced apart positions along both sides of each press. The support
wheels 221 (see FIG. 13) are mounted for rotation about horizontal
axes parallel to the planes in which the press unit platens 210,
211 lie andengage support surfaces extending along the length of
each press unit, one on each side thereof, whereas the guide wheels
222 (see FIG. 15) are mounted for rotation about vertical axes and
engage guide surfaces also extending along the length of each press
unit one on each side thereof.
The support and guide surfaces of each press unit are constituted
by a second pair of angle members 223 mounted one of each side of
the lower platen 211 of each press unit 203 and insulated from the
first mild steel angle 214 secured thereto, by a layer 224 of
insulating material.
Similar means is provided for supporting and guiding the press
units 203 during transfer from one curing unit to the other.
The pressing stations 225, which respectively constitute the first
station of each curing unit will now be described.
As shown in FIG. 16, each pressing station 225 comprises thrust
means for simultaneously applying pressure through three successive
press units within the pressing station to three contiguous
portions of the belting. It is sufficient however, for the success
of the invention for a pressing station to accommodate only two
press units as will be explained hereafter.
The thrust means comprises a vertically movable base member
designated as a whole by the reference numeral 226 and equal in
length to three press units, on which the platens of three press
units are supported while in the pressing station, and first and
second vertically movable press heads each designated as a whole by
the respective reference numerals 227, 228. The vertical movement
of the base member 226 lifts the press units off their support
wheels 221 (not shown in FIG. 16) so that the wheels are not
subjected to loads arising from the pressure applied to the belting
in the pressing station. Pressure is applied to the belting within
the three press units by vertically downward movement of the press
heads 227, 228.
The press heads 227, 228 are fluid pressure operated. The first
press head 227 comprises two portions, a parallel portion 243 and a
tapered portion 242. Each portion is approximately equal in length
to one press unit and the tapered portion 242 is at the end at
which the belting enters. Mounted below the press head 227 are two
pressure plates 230 and 231. The pressure plates are in two parts,
an upper part and a lower part, the lower part being heated and
insulated from the upper part by a layer of insulation 247. The
pressure plates 230 and 231 are of the same thickness and are of
constant thickness.
Mounted below press head 228 and rigidly attached thereto is a
pressure plate 228a, comprised of two parts, upper and lower,
separated by an insulation layer 247. The overall thickness of
press head 288 and pressure plate 228a is the same as that of the
parallel portion 243 of the press head 227 plus pressure plate
231.
The manner in which the two pressure plates 230, 231 of the first
press head are mounted below will now be described:
At the end of the first press head 227 at which the belt 204 enters
the pressing station, the rearward end of the first pressure plate
230 is pivotally connected to the first press head 227 by a link
joint at each side thereof, each link joint comprising two hinge
members 232 one rigidly secured to the first pressure plate and the
other rigidly secured to the press head and a rigid link 233
interconnecting the two hinge members and pivotally secured thereto
at each end.
Three pairs of side plates 234, 235, 236 are rigidly secured one
plate to each side of the first and second pressure plates 230 and
231 and one plate to each side of the second pressure plate 228a
respectively.
The side plates 234, 235, 236 extend downwardly to the level of the
belt 204 being cured, where they are pivotally interconnected, as
described below.
The rearward ends 237 of the side plates 236 of the pressure plate
228a are pivotally connected to the forward ends 238 of the side
plates of the second pressure plate 231 of the first press head
227. The pivot is at the level of the belting but this can be
varied as described later. Thus a downward movement of the second
press head 228 effects a similar downward movement of the forward
end of the second pressure plate 231 of the first press head
227.
The rearward ends 239 of the side plates 235 of the second pressure
plate 231 of the first press head 227 are pivotally connected to
the forward ends 240 of the side plates 234, of the first pressure
plate 230 of the first press head, and the two joints therebetween
are each supported by a support arm 241 pivotally connected at one
end to the two side plates 234, 235 at the joint therebetween, and
pivotally connected at its other end to the upper tapered thrust
member midway along the length thereof.
The first and second pressure plates 230, 231 positioned below the
tapered and parallel portions 242 and 243 respectively, are each of
the same length as one press unit, so that for a given downward
movement of the first press head 227, the second pressure plate 231
will experience a generally uniform thrust over its whole upper
surface, whereas although the first pressure plate 230 will receive
substantially the same thrust at its forward end as the second
pressure plate, the thrust decreases towards the rearward end of
the first pressure plate where it is comparatively small. As a
result of the pivotal mounting of the said first and second
pressure plates, the downward thrusts applied to the upper platens
10 of the press units below the two pressure plates correspond to
the thrusts received by the two pressure plates themselves.
To ensure that the links 233 only support the pressure plate 230
and do not apply any pressure thrusts on actuation of the press
head 227, when the press head 227 is raised there is a small gap
between the top surface of the pressure plate 230 and the
undersurface of the press head 227. Also one of the pairs of hinge
members 232 has the pivot holes slightly elongated to allow some
vertical movement between the pressure plate 230 and thepress head
227.
The second press head 228 applies a substantially uniform thrust to
the upper platen 210 of its respective press unit.
To allow the pivotal movements of the two pressure plates, 230, 231
of the first press head 227, forward and rearward edges of the
pressure plates are spaced apart as shown in FIG. 16. Alternatively
they can be chamferred.
The operation of the pressing stations will now be described with
reference to FIGS. 17 to 20 of the drawings. FIGS. 17 to 20 are
purely diagrammatic and many parts shown in FIG. 16 have been
omitted for clarity.
The belting 204 and press units compressing platens 210, 211 move
stepwise through the pressing stations 225, moving forward by the
length of one press unit in each step, the two press heads 227, 228
executing one complete downward and upward movement before the belt
and press units move on.
FIG. 17 illustrates the situation with both press heads raised and
the belting and press units having moved forward the distance of
one press unit. When the belting and press units are correctly
positioned, the press heads come down into contact with the press
units (FIG. 18). On further movement of the press heads, press unit
C and its respective portion of uncured belting is compressed first
between the first pressure plate 230 and the base member 226 (see
FIG. 19). This causes the belting 204 to achieve at the forward end
of the press unit C the thickness required in the fully cured
belting, but at the rearward end the belting is hardly compressed,
if at all.
Next, the pressing station is opened and the press unit C, with the
belting, is moved one press unit length further into the pressing
station (see FIG. 20) to the position of press unit B in FIG. 17,
and a further press unit D takes its place between the first
pressure plate and the base member.
It is believed that it is not necessary for this specification to
include drawings showing the press unit C undergoing the next stage
of compression in the pressing station, because press unit C is
then as shown in FIG. 20, in the position occupied by press unit B
in FIGS. 17 to 19, and undergoes the sequence of operations
executed on press unit B in FIGS. 17 to 19. Accordingly, this next
stage will be described with reference to press unit B in FIGS. 17
to 19.
When the first press head 227 is forced downwardly, as shown in
FIGS. 18 and 19, the press unit B is compressed at its rearward end
substantially simultaneously with the initial exertion of
compressive forces on the next following contiguous portion of
belting by the forward end of the next following press unit.
Thus the belting within the press unit B is brought to its required
final thickness at the stage illustrated in FIG. 19, and clamps are
suitably tightened to maintain the desired compressive forces on
the belting.
Since the initial exertion of appreciable compressive forces at the
rearward end of the press unit within the pressing station does not
occur until the press unit is positioned below the second pressure
plate 231 of the first press head 227 (see press unit B in FIGS. 18
and 19), and this occurs substantially simultaneously with the
initial exertion of compressive forces on the forward end of the
next following press unit (see press unit C in FIG. 18 and 19), the
tendency for soft hot rubber to be squeezed out from between the
platens at the rearward end of the press unit is smaller than when
there is no simultaneous compression at the forward end of the next
following press unit.
On commencing curing of a length of belting, some rubber may tend
to be squeezed out from between the forward ends of the platens of
the first press unit on the belt, but if this occurs the short
length of affected belting can be discarded and from then onward
the problem will not arise again with the remainder of that length
of belting.
The second press head 228 engages each press unit 203 successively
but since the belting in the press units has by then already been
subjected to substantially the required degree of compression, very
little or no further compression occurs at this stage. However, by
virtue of the arrangement of the pivoted side plates 234, 235, 236,
the forward end of the second pressure plate 231 of the first press
head 227 is always at substantially the same distance from the base
member 226 of the pressing station as the second press head 228 and
therefore during the initial exertion of compressive forces on the
rearward end of any given press unit, the compressive forces at the
forward end thereof are maintained and there is no tendency for
soft hot rubber to be squeezed in a forward direction in this
stage.
The second press head 228 constitutes means, independent of the
first press head 227 to urge the forward end of the second pressure
plate 231 towards the belting being cured, and the maintenance,
when required, of compressive forces at the forward end of each
press unit is the main function of the second press head.
Accordingly if desired the second press head can be dispensed with
and replaced by equivalent means such as fluid pressure operated
ram acting on the forward ends of the side plates 235 of the second
pressure plate 231. However, the second press head 228 does also
serve to maintain uniform compressive forces over the whole area of
belting within the press unit which is engaged by the second press
head at any given time. Thus, provision of the second press head
allows the clamps which are provided for each press unit to be of
relatively light construction, and to be designed to act on the
press unit platens around the edges thereof only. Although such
clamps are adequate to maintain pressure on the belting after it
has passed through the pressing station, on their own the clamps
would be incapable of maintaining uniform pressure on a portion of
belting when the preceding contiguous portion of belting is being
compressed in a pressing station, since in such circumstances the
pressure of hot fluid rubber can be sufficient to cause buckling of
the platens of a press unit which is clamped only at its edges.
Further, by holding its associated press unit in firm head to tail
relationship with the next following press unit, the second press
head 228 also serves to prevent the two press units separating
longitudinally under the pressures of hot fluid rubber and thereby
effectively stretching the belting. Thus the inclusion of a second
press head in the pressing stations although not essential is
nevertheless desirable.
Heat is supplied to the platens of the press units during the time
that they are under compression in the pressing stations 225, so
that each press unit is reheated at the beginning of each curing
operation.
The heat is transferred to the platens of the press units by
contact between the platens and heated portions of the thrust
means. Thus certain portions of both the base member 226 and the
press heads 227, 228 are continuously heated by electricity, steam,
or any other convenient source of heat. The supply of heat to two
press heads and to the base member is limited to the lower portions
and upper portions respectively thereof, which engage the press
units. The heated portions of the press heads are insulated from
the remainder thereof by insulation layers 247, as previously
described, to minimise heat loss, and a similar insulation layer
248 is provided below the heated portion of the base member.
Heat losses from the press units on emerging from the pressing
station 225 during a curing operation are minimised by providing
tunnels 249 each having a lining 250 of insulating material (see
FIG. 13). The tunnels closely surround the press units and extend
along the length of their respective curing unit 201, 202 so that
the press units pass therethrough during each curing operation.
The supply 251 (FIG. 12) of uncured belting at one end of each
curing unit may be simply in the form of a roll of uncured belting
mounted for rotation on an axle, or, the curing unit may be
positioned at one end of a belting production line in which case
the uncured belting enters the press immediately after it has been
assembled from, for example, a rubber-frictioned textile
reinforcement and superimposed rubber covering layers.
On emerging from its respective curing unit the belting passes
through a trim unit 252 (FIG. 12) for the removal of rubber
flashing, and after cooling is ready for service.
If it is found desirable, a reheating station 253 (see FIG. 12) may
be provided near the end of each curing unit to supply heat to the
platens of the press units shortly before the press units reach the
second station of the respective curing unit and are removed from
the belting. Heat is supplied to the platens of the press units in
the reheating stations by contact between the platens and heated
metal blocks.
Also, leakage of soft hot rubber from between the forward and
rearward ends of the press units may be further reduced by the
provision of two steel bands (not shown) of the same width as the
belt, sandwiching the belt between them during curing and moving
along the press with the belting. Thus, pressure is applied to the
belting through the steel bands by the platen of the press units.
The belts are at all times supported for their full area by the
pressure plates.
Each steel band is in the form of an endless loop which is held in
the correct position relative to the belting by the press units and
which on emerging from the press with the cured belting is guided
back to the other end of the press by large diameter pulleys or
rollers.
Alternatively, instead of the steel bands described above, means
may be provided for positively forcing the platens of successive
press units together in a longitudinal direction so that the
forward end of one press unit is more firmly engaged with the
rearward end of the next press unit and so on, so that leakage of
rubber between the said ends is minimised. This may be achieved
simply by arranging that the pivotal joints between the side plates
236 of the second press head 228 and the side plates 235 of the
second pressure plate 231 of the first press head 227 are higher
with respect to the base member 226 than the corresponding joints
between the side plates of the two pressure plates 230, 231 of the
first press head.
The advantages provided by the modifications, as described above in
relation to FIGS. 12 to 20 is as follows:
First, by reducing or eliminating the squeezing out of soft hot
rubber from between the platens of the press units at the forward
and rearward edges thereof the operation of the press as a whole is
improved since rubber squeezed out from one press unit tends to
interfere with the operation of adjoining press units. Further the
quality of the cured article produced by the curing units is
improved, since formation of irregularities and ribs on the
surfaces thereof by rubber squeezed out from between the platens,
is avoided.
Secondly, because there is a gradual transition from small or zero
compressive forces at one end of a pressing station to relatively
large compressive forces at the other end thereof, an appreciable
step in belt thickness is never formed by the curing units as it is
in conventional belt presses, and therefore kinking of the belt
reinforcement and associated irregularities in the belt surface are
avoided.
The use of steel bands sandwiching the belt between them to reduce
further the leakage of soft hot rubber from between the press unit
platens and to give an improved finish to the belt, is associated
with the advantage referred to in the preceding paragraph. Such
steel bands cannot be employed in presses where any appreciable
step in belt thickness is produced during curing, since such a step
would cause kinking of the steel bands which would rapidly become
useless.
The present abutting forward allows such steel bands to be used,
and when they are used they eliminate the formation of thin films
of rubber flashing on the upper and lower surfaces of the belt
through leakage of rubber between the abuttingforward and rearward
edges of the platens of successive press units which might occur.
Unlike the rubber flashing which is formed at the edges of the belt
as a result of rubber leaking between the platens and the edge
irons, which is easily removed in the trim units, films of rubber
on the upper and lower surfaces of the belt are not easily removed
and therefore it is a clear advantage to avoid their formation.
The press unit 304 shown in FIG. 21 is designed for use in the
apparatus represented in FIGS. 23 and 24, using the double daylight
fixed press of FIG. 22. This apparatus is intended to be used where
it is not convenient to provide for simultaneous cure two belts
having more or less the same curing time and length, as is
desirable for the apparatus described above. The press unit 304 is
a modification of the press unit 71 of FIGS. 8 and 9 in that it is
arranged so that during a curing operation units of this type are
spaced apart from one another along a length of the article being
cured. Consequently there is no screw-threaded unit clamping means
corresponding to that of press unit 71 (FIG. 9). At each end of
press unit 304 there are provided four substantially L-shaped end
pieces 305, each secured to an end surface of one of the platens
through an intermediary insulation layer 306 by one of the limbs of
the L, the other limb serving to extend longitudinally of the belt
contacting surface of the platen but being shaped so that these
extended surfaces provided by adjacent end pieces slope away from
each other.
Insulated from the hot platens by the insulating layers 306, the
end pieces 305 remain relatively cold (water cooling being used if
required), and thereby ensure that at each end of the press unit,
there is a strip 307 of the belt, extending across the belt which
is under compression but which is substantially unheated thus
preventing hot viscous rubber from being squeezed out from the ends
of the unit and avoiding consequent irregularities on the surface
of the belt at the ends of the press unit.
Other features of press unit 304 are substantially the same in
structure and function as those of press unit 71 of FIGS. 8 and 9
and are numbered accordingly.
Fixed press 308 comprises a horizontal base 309, side members 310
secured thereto in vertical positions, a fixed upper table 311
secured to the upper ends of side members 310, an upper moving
table 312 and a lower moving table 313 both slidably located on
side members 310 between the base and the fixed upper table, and a
fluid-operated piston and cylinder assembly 314 located between the
lower moving table and the base.
As shown in FIGS. 23 and 24 the belt 315 extends in an upper run
through tensioning clamps 316, belt pre-heat station 317, a first
station S1, the upper daylight of double daylight fixed press 308,
through a second station S2 to rollers 318, and in a lower run from
rollers 318 through pre-heat station 319, third station S3, the
lower daylight of double daylight fixed press 308 through fourth
station S4 and tensioning clamps 320. Thus the first and second
stations are at one level and the third and fourth stations at
another level and the belt is arranged to move in two runs, one
above the other, one run between the first and second stations and
the other run between the third and fourth stations.
Tensioning clamps 316 and 320 operate in the same way as clamps 6,
7, 8 and 9 of FIGS. 1 to 4. On engaging the belt at station S1
press unit 304 with pre-heated platens moves to the upper daylight
of fixed press 308 where it is compressed by operation of piston
and cylinder assembly 314 and its platens clamped together. The
press unit then moves stepwise to station S2 where it is disengaged
from the belt, transferred laterally to iron charging station 321
and then to re-heat station 322 which is at the level of the lower
run of the belt where its platens are re-heated. At station S3 it
engages a substantially uncured portion of the belt 305, thereby
filling in an uncured `gap,` passes to the lower daylight of fixed
press 308 where it is compressed again, its platens clamped
together and it begins another curing operation. At station S4 the
press unit is again disengaged from the belt and transferred via
iron charging station 323 and re-heat station 324 to the upper run
and back to station S1, where another cycle of operations
begins.
As a result of the sequence of operations just described, in a
press comprising a series of press units, the belting leaving
station S2 is in the form of a series of fully cured portions
separated by uncured portions shorter in length by a small amount
than a press unit. The further curing operations on the lower run
of the belt cure these uncured portions of the belt, thus producing
a fully cured belt.
The embodiments of the invention described above have several major
advantages over previous systems of curing. They can be operated
continuously without the need to stop when one length of belt is
completed and another started; the belt being manufactured is
continuously under pressure until curing is completed: changing of
the means to form the edges of the belt and determine the thickness
is easily carried out automatically if required; difficulties
caused by partial curing at the end of a stationary press are
eliminated; pre-heating can be more expeditiously effected; the
labour required is reduced and more accurate belts can be produced
owing to the alignment facilities provided and the greater ease
with which it is possible to manufacture and maintain the surfaces
of the press units in a truly flat condition compared with the
large surfaces required for existing presses.
* * * * *