U.S. patent number 3,598,381 [Application Number 04/802,434] was granted by the patent office on 1971-08-10 for continuous carburizing furnace.
This patent grant is currently assigned to Holcroft & Company. Invention is credited to Edward C. Bayer, Donald J. Schwalm.
United States Patent |
3,598,381 |
Schwalm , et al. |
August 10, 1971 |
CONTINUOUS CARBURIZING FURNACE
Abstract
A continuous carburizing furnace comprising a heating chamber
having inlet door means through which, when open, work can be fed
into the chamber, a carburizing chamber, interconnecting door means
between the chambers through which, when open, work can be fed from
the heating chamber to the carburizing chamber, first feeding means
for feeding work fed into the heating chamber into a transfer
position within said chamber, second feeding means for feeding work
from the transfer position through the interconnecting door means
when open to a feed position in the carburizing chamber, third
feeding means for feeding work from the feed position towards
outlet door means of the furnace and means for operating the
interconnecting door means when at least the inlet door means are
closed.
Inventors: |
Schwalm; Donald J. (Northville,
MI), Bayer; Edward C. (Dearborn, MI) |
Assignee: |
Holcroft & Company
(Livonia, MI)
|
Family
ID: |
25183707 |
Appl.
No.: |
04/802,434 |
Filed: |
February 26, 1969 |
Current U.S.
Class: |
266/97; 266/249;
266/132; 266/252; 432/53; 266/133; 266/251; 266/259; 432/56 |
Current CPC
Class: |
C23C
8/06 (20130101) |
Current International
Class: |
C23C
8/06 (20060101); C21d 009/00 () |
Field of
Search: |
;266/5,5T,5E,24
;148/16.5 ;263/36,37,38,6,8 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Meister; James M.
Claims
What we claim as our invention is:
1. A continuous carburizing furnace comprising a heating chamber
containing a noncarburizing gaseous atmosphere which prevents
scaling or decarburization, inlet door means through which, when
open, work can be fed into said heating chamber, a carburizing
chamber containing a carburizing atmosphere, a diffusion chamber at
the outlet end of said carburizing chamber containing an atmosphere
adjusted to be in equilibrium with the desired carbon content in
the surface of the work, interconnecting door means between the
chambers through which, when open, work can be fed from the heating
chamber to the carburizing chamber, first feeding means for feeding
work fed into the heating chamber into a transfer position within
said chamber, second feeding means for feeding work from the
transfer position through the interconnecting door means when open
to a feed position in the carburizing chamber, third feeding means
for feeding work from the feed position towards outlet door means
of the furnace and means for operating the interconnecting door
means when at least the inlet door means are closed, said feeding
means and said door-operating means being automatically operable at
predetermined times throughout a treatment cycle.
2. A furnace according to claim 1 wherein said outlet door means
are situated at an outlet of said diffusing chamber which is in
constant communication with said carburizing chamber, the operating
means for said interconnecting door means being operable when both
said inlet and said outlet door means are closed.
3. A furnace according to claim 1 wherein the outlet door means are
situated at the outlet of a diffusing chamber which is separated
from the carburizing chamber by a second interconnecting door
means, the latter being provided with operating means operable when
the outlet door means are closed, and when either one or both of
the first said interconnecting door means and the inlet door means
are closed, there being further provided a fourth feed means to
feed work from the carburizing chamber into the diffusing chamber
through the second interconnecting door means, and a fifth feed
means to feed work in the diffusing chamber towards the outlet door
means.
4. A furnace according to claim 3, wherein the heating chamber and
the carburizing chamber are arranged in generally parallel but
transversely offset relation, and with the downstream end of the
former overlapped longitudinally with the upstream end of the
latter, to provide for communication between the two chambers
through said interconnecting door means.
5. A furnace according to claim 4 wherein the first feeding means,
second feeding means, and third feeding means each comprise a
pusher device for engaging the work, or a work support, to advance
same longitudinally of the heating chamber, in the case of the
first feeding means, to advance same transversely of the heating
chamber and the carburizing chamber through the interconnecting
door means in the case of the second feeding means, and to advance
same longitudinally of the carburizing chamber in the case of the
third feeding means.
6. A furnace according to claim 4 wherein an access door means is
provided to provide communication to the overlapping end sections
of the heating and carburizing chambers.
7. A furnace according to claim 4 wherein the diffusing chamber is
situated adjacent to the downstream end of the carburizing chamber,
and in transversely offset relation thereto, and wherein said
fourth feeding means comprises a pusher device for moving the work
transversely of the carburizing chamber through said second
interconnecting door means.
8. A furnace according to claim 7 wherein the fifth feeding means
provided in said diffusing chamber is in the form of a rotary
hearth.
9. A continuous carburizing furnace comprising heating and
carburizing chambers through both of which work can be fed in a
direction longitudinally of the chambers and which are arranged in
generally parallel transversely offset relation to each other with
the downstream end of the former adjacent to the upstream end of
the latter; inlet, interconnecting, and outlet door means
controlling communication into the heating chamber, between the
chambers and out of the carburizing chamber respectively; and
first, second and third feeding means for continuously feeding the
work through the heating chamber, therefrom to the carburizing
chamber and through the carburizing chamber respectively; and a
control system coordinating operation of the door means and feeding
means to maintain at least one of said door means closed at any
given instant in the feeding cycle.
10. A furnace according to claim 9 wherein the outlet door means
are situated at an outlet of a diffusing chamber communicating with
the carburizing chamber, the operating means for the
interconnecting door means being operable when both the inlet and
the outlet door means are closed.
Description
BACKGROUND OF THE INVENTION
The invention relates to heat treating furnaces, particularly to
continuous carburizing. The invention also relates to the method of
heat treating, especially carburizing. In this specification, the
word carburizing is intended to include carbonitriding.
Continuous carburizing is carried out using the gas carburizing
method and the carburizing is carried out in three stages. Firstly,
the work is heated to carburizing temperature in a gaseous
atmosphere which prevents scaling or decarburization. Secondly, the
work is heated in an atmosphere which has been carbon enriched
which causes carbon to penetrate into the work. The length of time
which the work is exposed to the carbon enriched atmosphere
controls the depth of penetration of the carbon. Thirdly, the work
is subjected to a diffusion period during which the carbon content
of the atmosphere is adjusted to be in equilibrium with the desired
carbon content in the surface of the work. The diffusion period
allows the high surface carbon which is produced during the
carburizing period to diffuse to produce a case upon the work which
has the required carbon gradient from the interior of the work to
the external surface thereof.
In previously known continuous carburizing furnaces, all three of
these stages are carried out in what amounts to a single chamber.
This is usually an elongated chamber in which the work is fed in at
one end and is removed at the other. Since the chamber is usually
full of work, inlet and outlet doors at the ends of the chamber
have to be open at the same time to enable new work to be fed in
and carburized work to be removed and as a result the atmosphere in
the chamber migrates from one section to another.
It is thus difficult, in prior known furnaces, precisely to
determine the boundaries of the heating, carburizing and diffusing
zones. Since the degree of carburization depends on the time which
the work is in the carburizing atmosphere and since this is
determined in turn by the rate of feed of work through the chamber,
migration of the carburizing atmosphere from the carburizing zone
has an effect on the rate at which carburization is effected. This
makes it difficult, inter alia, to control the carburizing depth in
components of different section passing through the furnace, and
even in different parts of the same component presenting different
sections respectively.
Prior furnaces are controlled by controlling the carbon enrichment
of the atmosphere in the various sections of the furnace but since
the atmosphere can migrate from one section to another it is
difficult to maintain entirely the desired atmosphere in each
section. It is therefore necessary, to some extent, to run prior
art furnaces on a trial and error basis.
The object of the present invention is to enable closer control to
be obtained over the carburizing process.
According to one aspect of the invention, we provide a continuous
carburizing furnace comprising a heating chamber having inlet door
means through which, when open, work can be fed into the chamber, a
carburizing chamber, interconnecting door means between the
chambers through which, when open, work can be fed from the feeding
chamber to the carburizing chamber, first feeding means for feeding
work fed into the heating chamber into a transfer position within
said chamber, second feeding means for feeding work from the
transfer position through the interconnecting door means when open
to a feed position in the carburizing chamber, third feeding means
for feeding work from the feed position towards outlet door means
of the furnace and means for operating the interconnecting door
means when at least the inlet door means are closed.
By this arrangement, the interconnecting door means can be closed
when it is desired to feed new work into the feeding chamber. The
inlet door means can then be opened and the work can be fed in.
Since the interconnecting door means are closed, there will be no
migration of atmosphere from the heating chamber to the carburizing
chamber. When the work is in the heating chamber, the inlet door
means can be closed and the interconnecting door means can be
opened and work can be fed from the heating chamber to the
carburizing chamber. There may be a small migration of atmosphere
from one chamber to the other, but since the inlet door means is
closed, there will be no air or gas flow tending to cause such
migration.
According to a further aspect of the invention, we provide a
continuous method of carburizing comprising passing work into a
heating chamber in which the work is heated in a noncarburizing
atmosphere, passing the work from the heating chamber to a
carburizing chamber in which the work is heated in a carburizing
atmosphere, passing the work from the carburizing chamber into a
diffusing chamber and subsequently out of the diffusing chamber,
characterized in that migration of the atmospheres between the
heating and carburizing chambers is controlled by cutting off
communication between the heating and carburizing chambers during
the time that work is fed into the heating chamber.
Where the carburizing chamber and the diffusing chamber are in
communication, the heating and carburizing chambers will be put out
of communication also while the work is removed from the diffusing
chamber. This may occur simultaneously with the feed of work into
the heating chamber. Alternatively, feed of work into the heating
chamber may be effected at a different (nonoverlapping) time with
feed of work out of the diffusing chamber.
The invention will now be described in detail by way of example
with reference to the accompanying drawings in which:
FIG. 1 is a plan view of a complete carburizing plant including a
carburizing furnace embodying the invention.
FIG. 2 is a longitudinal vertical section through the heating
section of the furnace shown in FIG. 1.
FIG. 3 is a transverse section of the heating section of the
furnace.
FIG. 4 is a longitudinal, vertical section of the carburizing
section of the furnace.
FIG. 5 is a transverse cross section of the carburizing section of
the furnace.
FIG. 6 is a fragmentary view of a modification in which a rotary
hearth diffuser is provided, and
FIG. 7 is a schematic circuit diagram of a control system for the
door and feed means of the furnace.
Referring to FIG. 1, the carburizing furnace is indicated generally
at 10. The carburizing plant also includes a quench tank 11 which
is conveniently of the type described in patent specification No.
987,338; a washer 12 and a tempering furnace 13 which may be
electric. A conveyor 14 conveys the work from the quench tank to
the washer, a conveyor 15 which conveys the work from the washer to
the tempering furnace and a conveyor 16 conveys the work from the
tempering furnace. The conveyor 16 leads to a length of conveyor 17
from which the work can be unloaded and onto which fresh work is
loaded. The work is supported in jigs and the jigs are mounted on
trays. The jigs are so arranged that the whole of the surface of
the work which is required to be carburized is open to the
carburizing atmosphere when the work is in the carburizing chamber.
A further length of conveyor 18 leads from the conveyor 17 to
introduce new work into the furnace.
The furnace comprises a heating section indicated generally at 19,
a carburizing section indicated generally at 20, and a diffusing
section indicated generally at 21. The carburizing section 20 and
the diffusing section 21 form parts of the same chamber.
Referring first to the heating section 19 and thus to FIGS. 1, 2,
and 3, the section comprises a supporting framework having vertical
side members 22 and an upper horizontal frame 23. A chamber is
formed within the framework having sidewalls 24 of refractory
material, a base 25 and a roof 26 also of refractory material. End
walls 27 and 28 are also provided and are likewise formed of
refractory material. Extending between the sidewalls 24 are a
number of pairs of radiant tube burners some of which are indicated
at 29 and which exhaust into duct work indicated generally at 30.
The heating chamber includes two spaced tracks 31 to receive work
which is indicated in FIG. 3 by two trays 32 carrying work loads
occupying positions indicated at 33. Some of the radiant tube
burners 29 are above the work and some below as is clearly seen
from FIGS. 2 and 3.
The work may be arranged in one or more rows and typically as seen
in FIG. 1 is arranged in two rows, each of the rows being supported
on one of the tracks 31. The work is introduced into the heating
chamber through inlet door means indicated at 34 in FIG. 1. A tray
of work occupying a position indicated at 35 in FIG. 1 is fed
through a door 36 into a vestibule 37 so that it assumes the
position 38. From this position it is pushed by means of a pusher
39 through the inlet door means 34 to the interior of the heating
chamber to assume a position indicated at 40a or 40.
Mounted at the bottom of the end wall 27 is a first feed means
comprising two pushers 41 which may be mechanically linked, and are
arranged side by side so that one of the pushers can engage a tray
in the position 40a and the other of the pushers can engage a tray
in the position 40. The pushers then push the tray into the
appropriate row shown in FIG. 1 and push the row to the right in
that figure.
When a tray reaches a transfer position 42 or 43 in the heating
chamber, it is then advanced by a second feed means comprising a
pusher 44 movable transversely of the rows in the heating chamber
through interconnecting door means 45 into the carburizing chamber
20. Although, again, the work can be arranged in more than one row
in the carburizing chamber, it is shown in FIG. 1 arranged in a
single row. After displacement by pusher 44 each tray will then be
in the position 59a ready for movement along the carburizing
chamber.
The carburizing chamber is constructed in a similar manner to
heating chamber having a steel framework with uprights 45 and an
upper and lower horizontal frame 46 and 47 respectively. The
chamber has sidewalls 48, a roof 49, a base 50 and end walls 51 and
52. These walls are all formed with refractory material. A track 53
is shown in FIG. 5 is provided for a single row of trays.
Adjacent to the base of the end wall 52 is a third feed means
comprising a pusher 55 which can be operated to advance the trays
along the carburizing chamber. The carburizing chamber had radiant
tube burners such as indicated at 56 arranged above the work and
these radiant tube burners exhaust into duct means 57.
Part way along the carburizing chamber there is a baffle 58
extending from the roof of the chamber to adjacent the top of the
work on the trays and this baffle divides the chamber into the
carburizing section 20 and the diffusing section 21.
Upon arrival at the position 59, each tray can be pushed by means
of a pusher 60 through outlet door means 61 into the quench tank 11
lowerator platform.
The heating chamber is provided with a central roof fan 62 and the
carburizing chamber with two such fans 63. Various access doors are
provided, thus there is a first access door 64 in the vestibule 37,
an access door 65 in the heating chamber opposite to the inlet door
means 34, access doors 66 in the heating chamber in the end wall
28, an access door 67 in the carburizing chamber opposite to the
interconnecting door means 45 and an access door 68 in the end wall
51 of the carburizing chamber.
In the modification illustrated in FIG. 6, a diffusing chamber 70
is provided at the downstream end of the carburizing chamber 71 in
laterally offset relation thereto. The diffusing chamber is not
permanently in communication with the carburizing chamber, such
communication being controlled by a second interconnecting door
means 73.
The carburizing chamber itself is equipped with heating elements in
the form of radiant tube burners 74, and the feed means provided in
the diffusing chamber for advancement of the work trays to an
outlet door means 75 comprises a rotary hearth or platform 76 which
may be driven continuously or intermittently as required.
In this modification the carburizing chamber includes three
trackways 71a 71b 71c for rows of work trays advanced in this case
by a feed means similar to that shown at 55 in FIG. 1, but
including three separate pusher devices, one for each of the
trackways.
A discharge pusher device operating laterally of the trackways is
provided at 77 and operates in a manner similar to the pusher
device 60 already mentioned.
Upon emergence from the outlet door means 75, the work supporting
trays are moved along a conveyor 78 which may be a roller
conveyor.
For effecting operation of each of the door means and the feeding
means in the required sequence, each of these means is provided
with an individually energized operating device which may be either
pneumatic or electrical.
Conveniently the door means are operated by pneumatic piston and
cylinder units, and the feed means, that is to say each pusher
device, is operated by means of an electric motor.
The arrangement is illustrated schematically in FIG. 7, wherein the
various doors, conveyors, and pushers are shown connected to
respective operating devices designated by a like numeral of
reference with a suffix a .
An electrical timing circuit 80 provides the requisite output
signals to control operation of each operating device at the
required time.
Where the operating devices are pneumatic piston and cylinder
units, the requisite control may be effected by means of a solenoid
valve controlled by an electrical signal from the timing circuit,
and in the case where the operating device is an electric motor,
the timing circuit can supply the requisite signal to operate
switch means for the electric motor.
The operation of the furnace is as follows:
It is assumed that the outlet door means 61 has just closed after
the pusher 60 has moved the tray containing the work load from the
position 59 onto the platform of the quench tank 11 preparatory to
lowering said platform. All other door means of the furnace at this
time will be closed, the positions 38, 39, 40, 42, 43, 59a and 59
will all be vacant.
To effect advancement of the work through the furnace the inlet
door means 36 is opened and a tray containing a work load is moved
from the position 35 to the position 38 in the inlet vestibule 37
by a beam and pawl feeding means incorporated in the conveyor
18.
The inlet door means 36 then closes and upon arrival at the closed
position the inlet door means 34 is opened. The tray containing or
supporting the work load is then moved, at right-angles to its
direction of advancement by the conveyor 18 through the opening
afforded by the open door means 34 into either the position 39, or
the position 40, according to which of the two rows of trays in the
heating section 19 of the furnace is due for advancement (that is
to say the track which was not advanced in the preceding cycle of
operations). In some cases, however, both rows of trays may be
advanced together where the carburizing section has tracks for
accommodating same.
The twin pusher 41 is then operated, and that driving element
thereof which is aligned with the position 39 or 40 into which the
tray has been delivered, will thereby cause the end tray of the
associated track to be delivered into the position 42 or 43 as the
case may be.
The interconnecting door means 45 is then opened and the pusher 44
is operated to move the tray occupying the position 42, or the
position 43, through the opening afforded by the door means 45 into
the position 59a. It will be noted that the direction of movement
of the tray in this direction is at right angles in its direction
of advancement through the heating section 19 and through the
carburizing and diffusing sections 20 and 21 of the furnace.
The interconnecting door means 45 now closes, and the pusher 55 is
operated to advance all the trays and work loads situated in the
sections 20 and 21 to bring the foremost and its work load into the
position 59, leaving a vacant space at the position 59a upon
retraction of this pusher. The outlet door means 61 is then opened
and the pusher 60 operated to move the tray and work load occupying
the position 59 to the platform of the quench tank 11 after which
the outlet door means 61 closes to complete the cycle of
operation.
The interconnecting door means 45 is opened only when the inlet
door means 34 and outlet door means 61 are both closed.
In the modified form of furnace illustrated in FIG. 6, a suitable
connection would be provided from the timing circuit to operate the
second interconnecting door means 73 and the outlet door means 75
in the required timed relationship, with the other door means and
with the feeding means of the furnace. In this case, the second
interconnecting door means may be open concurrently with the first
interconnecting door means, provided that the outlet door means 75
is closed. Alternatively, if the outlet door means 75 is open
concurrently with the first interconnecting door means between the
heating and carburizing chambers, then the second interconnecting
door means 73 should be closed at this time.
In any of the foregoing arrangements there is less tendency for the
atmosphere of one of the sections to migrate into the successive
section. The atmosphere in the heating section 19 is thus
maintained as noncarburizing atmosphere. The atmosphere in the
carburizing section is maintained as a carburizing atmosphere.
Consequently, each work load is subjected to carburizing for a
precisely determined time and in precisely determined atmospheric
conditions, namely, those in the carburizing section 20. The
carburizing time is a predetermined fraction of a fixed cycle time
determined by the timing circuit.
This enables greater accuracy than heretofore to be attained in
respect of the depth of carburizing of the work.
Off setting of the sections 19, 20 and possibly 21 in directions
transverse to the direction of advancement of the trays and work
loads through each of these sections and the provision of feeding
means such as a pusher operating at right angles at its direction
of advancement, enables the interconnecting door means to close
without requiring any longitudinal spacing to be maintained between
successive trays. This is an advantage in the feeding means in
effecting longitudinal displacement through each section of the
furnace can be in the form of a pusher, and the provision of
spacing between successive trays is not necessary.
It will be understood that although, as illustrated, it is
convenient in many cases in successive sections of the furnace to
be offset from each other horizontally, it would be within the
scope of the invention to adopt some other arrangement where this
is found to be necessary or advantageous in any particular case.
For example, such sections can be offset vertically, or both
vertically and horizontally.
A further improvement in control as to the depth of gradient of
carburization can be achieved by employment of automatic means for
controlling the atmosphere primarily in the carburizing section 20
but also if desired in the heating and diffusing sections.
If in the event of a breakdown of the furnace, only the work in the
carburizing chamber 20 will be affected, and even in respect of
this work the extent of carburization will be known through
knowledge of its residence time in the carburizing section before
breakdown. This permits the selected carburizing treatment to be
achieved in respect of this work upon restoration of the furnace to
operable conditions.
Although the foregoing description to the drawings and for the
construction of furnace shown therein, advancement of the trays and
work loads has been effected by means of pushers, it will be
understood that the invention may be applied to constructions of
furnace wherein advancement is effected by other forms of feed
means, for example, such feed means may comprise one or more belt
or slat conveyors. Alternatively one or more of the sections of the
furnace may comprise a rotary chamber mounted for rotation about
longitudinally extending axis and provided internally with a
helical formation, such as a rib, to effect advancement of a tray
carrying a work load axially through the chamber in response to
rotation thereof.
* * * * *