U.S. patent application number 09/757877 was filed with the patent office on 2001-08-16 for device and product of pressing two mold portions together and controlling an internal pressure so as to create a hollow cone.
This patent application is currently assigned to U.S. Philips Corporation. Invention is credited to Selten, Wilhelmus N.M., Tuin, Hermanus N., Van Roosmalen, Martinus P.W..
Application Number | 20010013231 09/757877 |
Document ID | / |
Family ID | 8210868 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013231 |
Kind Code |
A1 |
Selten, Wilhelmus N.M. ; et
al. |
August 16, 2001 |
Device and product of pressing two mold portions together and
controlling an internal pressure so as to create a hollow cone
Abstract
A method and device for the manufacture of a hollow cone (37)
with a cone tip (31) whereby a parison of viscous material (35) is
molded into the shape of the hollow cone. An escape space (11)
becomes accessible to the material in the vicinity of a cone tip to
be formed. The moment the pressure present in the material in the
vicinity of the cone tip to be formed exceeds a previously defined
value. Breaking-off of the cone tip during or after molding is
prevented by this. The hollow cone is suitable inter alia for use
in a cathode ray tube.
Inventors: |
Selten, Wilhelmus N.M.;
(Eindhoven, NL) ; Van Roosmalen, Martinus P.W.;
(Eindhoven, NL) ; Tuin, Hermanus N.; (Eindhoven,
NL) |
Correspondence
Address: |
Jack E. Haken
c/o U.S. PHILIPS CORPORATION
Intellectual Property Department
580 White Plains Road
Tarrytown
NY
10591
US
|
Assignee: |
U.S. Philips Corporation
|
Family ID: |
8210868 |
Appl. No.: |
09/757877 |
Filed: |
January 10, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09757877 |
Jan 10, 2001 |
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08938938 |
Jul 22, 1996 |
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6205817 |
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08938938 |
Jul 22, 1996 |
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08441713 |
May 15, 1995 |
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08441713 |
May 15, 1995 |
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08106007 |
Aug 13, 1993 |
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Current U.S.
Class: |
65/168 ; 65/140;
65/170; 65/182.2 |
Current CPC
Class: |
C03B 11/06 20130101 |
Class at
Publication: |
65/168 ; 65/140;
65/170; 65/182.2 |
International
Class: |
C03B 040/04; C03B
011/10 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 20, 1992 |
EP |
92202545.7 |
Claims
1. A method of manufacturing a hollow cone provided with an open
side and a cone tip remote from the open side, whereby a parison of
viscous material is brought into a first mould part after which the
parison of material is moulded into the desired shape of the hollow
cone by means of a second mould part, characterized in that an
escape space for the material becomes accessible in the vicinity of
the cone tip to be formed and adjoining the first mould part the
moment the pressure present in the material in the vicinity of the
cone tip to be formed exceeds a previously defined value.
2. A method as claimed in claim 1, characterized in that the escape
of the material into the escape space is prevented by means of a
gas pressure applied in the escape space until the pressure present
in the material has become greater than the gas pressure.
3. A method as claimed in claim 2, characterized in that after the
parison of material has been introduced into the first mould part,
the parison is kept floating in the first mould part by means of
the gas pressure until moulding starts.
4. A method as claimed in claim 2 or 3, characterized in that the
formed cone is pressed from the first mould part by means of the
gas pressure after moulding.
5. A method as claimed in claim 2, 3 or 4, characterized in that
the gas pressure is adjustable during the manufacture of the hollow
cone.
6. A device suitable for carrying out the method as claimed in
claim 1, 2, 3, 4 or 5, which device is provided with a first and a
second mould part which are displaceable relative to one another,
characterized in that the device is provided with an escape space
with closing possibility which merges into the first mould
part.
7. A device as claimed in claim 6, characterized in that the escape
space is provided with a gas pressure connection.
8. A device as claimed in claim 7, characterized in that the escape
space is funnel-shaped, a comparatively large open side of the
escape space merging into the first mould part and a comparatively
small open side of the escape space being connected to the gas
connection.
9. A cone manufactured by the method as claimed in claim 1, 2, 3, 4
or 5.
10. A cathode ray tube provided with a cone as claimed in claim 9.
Description
[0001] The invention relates to a method of manufacturing a hollow
cone provided with an open side and a cone tip remote from the open
side, whereby a parison of viscous material is brought into a first
mould part after which the parison of material is moulded into the
desired shape of the hollow cone by means of a second mould
part.
[0002] The invention also relates to a device suitable for carrying
out the method according to the invention, which device is provided
with a first and a second mould part which are displaceable
relative to one another.
[0003] The invention further relates to a cone manufactured by the
method according to the invention and to a cathode ray tube
provided with such a cone.
[0004] The term "viscous material" is understood to mean a material
such as glass or synthetic resin with a viscosity of
10.sup.2-10.sup.7 Pa.s.
[0005] A method and a device suitable for manufacturing a cone are
known from German Patent DE-C2 2734773.
[0006] During the manufacture of a cone, the parison of material is
introduced into the first mould part and then pressed into the
desired shape by means of the second mould part. The first mould
part has a funnel shape and the parison is introduced into a
comparatively narrow portion of the funnel shape. The cone tip is
formed in the narrowest portion of the funnel shape during
moulding. The required wall thickness in the vicinity of the cone
tip of the cone to be shaped is comparatively small compared with
the rest of the cone. During moulding, the material is pressed into
the narrowest portion of the first mould part, from which a portion
of the material is pressed towards the wider portion of the first
mould part through interspacings between the first and second mould
parts. During moulding, the distance between the first and second
mould parts becomes increasingly smaller, so that the material is
forced to flow through ever narrower interspacings towards the
wider portion of the funnel shape. Furthermore, a thin skin of
cooled material is formed against the mould parts during moulding.
This renders the interspacings through which material can flow even
narrower. Comparatively high compression forces are necessary for
forcing the material through these narrow interspacings. It is
possible for the cone tip to break off from the rest of the cone
with these high compression forces. This breaking of the cone tip
is the result of the excessive pressure on the material which has
already cooled down.
[0007] A solution proposed for this problem in the known device is
a better temperature control in that the wall thickness of the
mould parts in the vicinity of the cone tip to be formed is at
least twice as thin as the wall thickness of the remaining portions
of the mould parts.
[0008] A disadvantage of the known device is that the determination
of the required wall thicknesses is inconvenient because new mould
parts are to be manufactured each time for changing the wall
thicknesses.
[0009] The invention has for its object to provide a simple method
for the manufacture of a hollow cone by which the said
disadvantages are avoided.
[0010] According to the invention, the method is for this purpose
characterized in that an escape space for the material becomes
accessible in the vicinity of the cone tip to be formed and
adjoining the first mould part the moment the pressure present in
the material in the vicinity of the cone tip to be formed exceeds a
previously defined value.
[0011] The material which during moulding cannot or can hardly flow
through the interspacings between the mould parts towards the wider
portion of the funnel shape anymore will try to escape to the
escape space. The entrance to the escape space, however, is blocked
until the pressure in the material in the vicinity of the cone tip
exceeds a previously defined value and the escape space becomes
accessible. The pressure in the material in the vicinity of the
cone tip in this way never becomes higher than a predetermined
value.
[0012] A blocking mechanism which is comparatively easy to provide
and in which the previously defined value of the admissible
pressure in the material in the vicinity of the cone tip can be
easily changed in an embodiment of the method according to the
invention is characterized in that the escape of the material into
the escape space is prevented by means of a gas pressure applied in
the escape space until the pressure present in the material has
become greater than the gas pressure.
[0013] The desired gas pressure level is experimentally determined,
while the gas pressure may be readily changed so as to optimize the
moulding process.
[0014] An alternative embodiment of the method according to the
invention is characterized in that, after the parison of material
has been introduced into the first mould part, the parison is kept
floating in the first mould part by means of the gas pressure until
moulding starts.
[0015] The time between the moment the viscous parison of material
is introduced into the first mould part and the start of the
moulding process in practice is a few seconds. A cold layer arises
in the parison in all locations where the parison touches the walls
of the mould part, because the parison transfers heat to the colder
mould part. The formation of the cold layer, especially in
locations where the cone to be formed has a comparatively thin
wall, means that the required compression force is comparatively
great. Sagging of the parison by its own weight is prevented in
that the parison is kept floating in the mould part until moulding
starts, so that the contact surface area between the parison and
the mould part remains comparatively small and only a comparatively
small cold layer is formed before moulding starts. Owing to this
measure, the required compression force is comparatively small,
which contributes to the prevention of cone tip fracture.
[0016] A further embodiment of the method according to the
invention is characterized in that the formed cone is pressed from
the first mould part by means of the gas pressure after
moulding.
[0017] The removal of the moulded cone from the first mould part is
facilitated thereby.
[0018] It is noted that the use of compressed air for stripping the
formed cone from the mould part is known per se from German Patent
Application DE 2001977. In the method according to the invention,
however, the gas pressure is used both for preventing cone tip
fracture and for removing the formed cone from the mould part.
[0019] A yet further embodiment of the method according to the
invention is characterized in that the gas pressure is adjustable
during the manufacture of the hollow cone.
[0020] This renders it possible to adapt the gas pressure to the
desired pressure at any moment during cone manufacture. The
relevant pressure gradient is experimentally determined.
[0021] The invention also has for its object to provide a device
for the manufacture of a hollow cone by which the disadvantages of
the known device are avoided.
[0022] The device according to the invention suitable for carrying
out the method according to the invention is for this purpose
characterized in that an escape space with closing possibility
merges into the first mould part.
[0023] The escape space is not accessible to the parison of
material until the moment the pressure in the material exceeds a
previously defined value. The term "with closing possibility" in
relation to the escape space in this connection is accordingly
understood to mean that the escape space can be blocked in such a
manner that no material can escape into the escape space.
[0024] An embodiment of a device suitable for carrying out the
method according to the invention, in which the escape space is
initially kept inaccessible by means of gas pressure until the
pressure in the material has become greater than the gas pressure,
is characterized in that the escape space is provided with a gas
pressure connection.
[0025] The desired gas pressure is applied in the escape space
through the gas pressure connection. The use of gas for rendering
the escape space temporarily inaccessible has the advantage that no
moving mechanical parts need be used in and around the hot escape
space (400.degree. C.). Moving parts may cause malfunctioning and
are subject to wear.
[0026] A further embodiment of a device suitable for carrying out
the method according to the invention is characterized in that the
escape space is funnel-shaped, a comparatively large open side of
the escape space merging into the first mould part and a
comparatively small open side of the escape space being connected
to the gas connection.
[0027] Owing to the funnel-shaped escape space, the cone can be
readily pressed from the escape space and the mould part after
moulding.
[0028] The invention is explained in more detail with reference to
the drawing, in which
[0029] FIG. 1 diagrammatically shows an embodiment of a device
according to the invention, FIG. 1a showing a cross-section and
FIG. 1b a plan view of a detail of the device shown in FIG. 1a,
[0030] FIG. 2 diagrammatically shows a cross-section of an
alternative embodiment of a device according to the invention,
[0031] FIGS. 3a and 3b show the manufacture of a cone according to
the prior art,
[0032] FIGS. 4a and 4b show the manufacture of a cone by a method
according to the invention,
[0033] FIG. 5 shows the pressure gradient of the gas pressure
applied in the escape space during manufacture of a cone, and
[0034] FIG. 6 shows a cone manufactured by the method according to
the invention.
[0035] FIG. 1 shows a device 1 which forms part of a moulding press
which is known per se. The device is provided with a first mould
part 3 and a second mould part 5 which is displaceable relative to
the first mould part 3 along an axis 7. The first mould part 3
comprises a funnel-shaped portion 9 and an escape space 11. The
escape space 11 is connected to a gas connection 15 through a
gas-transmitting filter 13. The gas-transmitting filter 13 is
provided with comparatively small channels 17 which run parallel to
the axis 7.
[0036] A parison of heated glass with a viscosity of
10.sup.3-10.sup.4 Pa.s is introduced into the first mould part 3,
upon which the second mould part 5 is displaced in the direction of
the arrow 19 and the glass parison is moulded into the desired
shape between the two mould parts. Different positions of the
second mould part 5 are indicated with broken lines. Gas is
introduced into the escape space 11 through the gas connection 15
and a gas pressure is adjusted such that the glass cannot flow into
the escape space. The gas may be air, nitrogen, or some other
gaseous medium.
[0037] In those locations where the glass lies against the mould
parts the glass will cool down comparatively strongly and a thin
layer of glass 21 of comparatively high viscosity will be formed.
The glass which has not yet cooled down so strongly is pressed down
and up through an interspacing 23 present between the layers 21 in
the direction of the arrows 25, 27, respectively. The compression
force P required for this increases in proportion as the
interspacing 23 becomes narrower. At a certain moment the pressure
in the glass in the vicinity 29 of the cone tip to be formed will
become greater than the gas pressure prevailing in the escape space
11. From that moment the glass will flow into the escape space 11.
After moulding, the second mould part 5 is displaced in a direction
opposite to the arrow 19. The moulded cone is subsequently pressed
from the first mould part 3 by the gas pressure. The escape space
11 is funnel-shaped to facilitate stripping of the moulded cone
from the first mould part 3.
[0038] The gas-transmitting filter 13 is provided with channels 17
whose cross-sectional dimensions (0,05-0,3 mm) are so chosen that
the glass cannot penetrate these channels owing to its viscosity
when it is pressed against the gas-transmitting filter 13. In
practice, the aim will be to prevent this by means of a good
pressure control.
[0039] FIG. 2 shows an alternative embodiment of an escape space 11
provided in the first mould part 3. The solid gas-transmitting
filter 13 situated in the escape space 11 is provided with four
channels 17 at its circumference which are connected to the gas
connection 15 via a chamber 33.
[0040] FIGS. 3a and 3b diagrammatically show an aspect of glass
moulding according to the prior art. FIG. 3a shows a mould part 3
into which a glass parison 35 has been introduced. It then takes a
few seconds in practice before moulding is started. During this
time the glass parison 35 sinks into the bottom position of the
mould part 3 under its own weight. This is shown in FIG. 3b. A
comparatively cold layer 21, which increases in thickness during
moulding, arises in all locations where the glass touches the mould
part 3. The compression force required becomes comparatively high
at the end of the moulding process owing to the presence of the
cold layer 21 in that portion of the first mould part 3 where the
cone to be formed has comparatively thin walls.
[0041] FIGS. 4a and 4b diagrammatically show glass moulding by the
method according to the invention. FIG. 4a shows a mould part 3
into which a glass parison 35 has been introduced. A gas is brought
into the escape space 11 below the glass parison 35 through the gas
connection 15 at such a pressure that the glass parison 35 remains
as it were in a floating state. The formation of a cold layer 21 is
then limited to a few spots where the parison lies against the
mould part, so that no cold layer has yet been able to form near
the cone tip to be moulded at the beginning of the moulding
process. As a result the interspacing between the mould parts 3, 5
through which glass can continue to flow is greater than in the
case of moulding according to the prior art, and the required
compression force P at the end of the moulding process is
accordingly lower.
[0042] FIG. 5 shows the pressure gradient of the gas pressure
provided in the escape space 11 during the manufacture of a cone.
Time is plotted on the horizontal axis and pressure on the vertical
axis. Cone manufacture is subdivided into four phases. At the
beginning of phase I, the parison of material is brought into the
first mould part and the parison is kept floating during phase I by
means of the gas pressure p1. In phase II, the parison is moulded
into the desired shape with a constant compression force, during
which the pressure in the escape space is increased to p2. The
pressure p2 provided is between 3 and 100 bar, depending on the
size of the cone to be moulded and the wall thickness of the cone
in the vicinity of the cone tip to be formed. After moulding,
pressure is reduced to zero bar by gauge, after which during phase
III the formed cone is cooled down. In phase IV, the cone is
pressed from the first mould part by means of the gas pressure
p3.
[0043] FIG. 6 shows a cone 37 manufactured by the method according
to the invention. The cone tip 31 is comparatively long, i.e.
compared with cones manufactured by the known methods. The cone
wall thickness in the vicinity of the portion 29 of the cone tip 31
is approximately 1 to 10 mm.
[0044] The cone may be used, for example, in a cathode ray tube,
the tip 31 formed at the cone being removed and a neck-shaped
element being fastened in the opening formed thereby. An electron
gun is subsequently fastened in this neck-shaped element. When a
cone manufactured by the method according to the invention is used,
fewer rejects occur in the manufacture of a cathode ray tube than
with the use of a known cone. This is probably caused by the fact
that the material in the narrow portion of the cone contains fewer
mechanical stresses than the known cone, so that fastening of the
electron gun to the cone leads less quickly to material fracture in
the cone.
[0045] The method of manufacturing a hollow cone may also be used
for other products such as funnels, and products having a hollow,
conical projection.
[0046] The escape space may be blocked, not only by means of gas
pressure, but also, for example, by means of a spring-loaded
mechanical valve which opens automatically when the pressure
exerted thereon exceeds a previously defined value.
* * * * *