Continuous type atmosphere heat treating furnace

A continuous heat treating furnace for heat treating a ferrous metal work in a protective atmosphere, including a furnace separated into a charge chamber and a heat treating chamber by a partition door and provided with a transport device for transporting the work. A first heating device, a recirculating fan and a gas purge device are provided in the charge chamber, while a second heating device is provided in the heat treating chamber supplied with the protective atmosphere, whereby the work is preheated through convectional heat transfer in the charge chamber simultaneously with high-temperature purging of the charge chamber and then, is heat treated under the protective atmosphere in the heat treating chamber.

BACKGROUND OF THE INVENTION 
The present invention generally relates to continuous type heat treating 
furnaces such as a continuous type gas carburizing furnace, a continuous 
type non-oxidizing hardening furnace, a continuous type annealing furnace, 
etc. and more particularly, to a continuous type gaseous atmosphere heat 
treating furnace employing a protective atmosphere. 
In heat treatment such as carburizing, carbonitriding, non-oxidizing 
hardening, bright annealing, etc., it has been conventionally so arranged 
that a protective atmosphere suitable for heat treatment of ferrous metal 
works, for example, a carburizing gas, an endothermic gas, an exothermic 
gas, a mixture of the endothermic gas and the exothermic gas, etc. is 
drawn into the furnace such that the heat treatment is performed under the 
protective atmosphere. Continuous type atmosphere heat treating furnaces 
to be used for such heat treatment include a charge vestibule or a 
discharge vestibule designed for protecting atmosphere in the furnaces. 
The charge vestibule or the discharge vestibule, which is of a steel 
structure, is provided with a proper purge means and is substantially 
maintained at ambient temperatures. Accordingly, the known furnaces have 
such a drawback that in the case where the charge or discharge vestibule 
is subjected to gas purging at the time of transfer of the works from the 
charge vestibule to a heat treating chamber or transfer of the works from 
the heat treating chamber to the discharge vestibule, a purge gas in an 
amount four to six times a capacity of the charge or discharge vestibule 
is required to be used, thereby making the gas purging uneconomical. 
Furthermore, the known furnaces have such a disadvantage that since the 
works are heated from ambient temperatures in the heat treating chamber, 
the heat treating chamber itself is required to be made large in size, 
thus resulting in poor thermal efficiency of the heat treating chamber. 
Meanwhile, in the case of gas carburizing, non-oxidizing hardening, etc. in 
which a combustible protective atmosphere is introduced into the heat 
treating chamber during the heat treatment, it has been so arranged that 
the atmosphere in the heat treating chamber is supplied into the charge or 
discharge vestibule so as to subject the charge or discharge vestibule to 
gas purging. In this case, the purge gas (combustible gas) is exhausted 
from the furnaces and burned off in the environment outside the furnace 
and thus, is not effectively utilized. Moreover, in gas carburizing, 
non-oxidizing hardening, etc., the works are washed by using 
trichloroethylene (trichlene) or are cleaned through heating thereof prior 
to loading of the works into the furnaces in order to remove from the 
works impurities such as oil, etc. adhering thereto. A cleaning apparatus 
for cleaning the works through heating thereof, i.e., for removing 
impurities such as oil, etc. from the works through heating thereof is 
proposed in Japanese Patent Publication No. 2588/1983. This prior art 
cleaning apparatus is separately provided forwardly of a continuous 
furnace so as to remove impurities such as cutting oil, etc. From the 
works through heating thereof. Subsequently, after the charge vestibule of 
the continuous furnace has been subjected to gas purging for about 20 to 
30 min., the works are loaded into the heat treating chamber (gas 
carburizing chamber). Consequently, this prior art continuous furnace has 
such inconveniences that amount of the consumed purge gas increases, that 
heat possessed by the works at the time of cleaning of the works through 
heating thereof is not effectively utilized and that the production cost 
rises. 
SUMMARY OF THE INVENTION 
Accordingly, an essential object of the present invention is to provide a 
continuous type atmosphere heat treating furnace whose production cost is 
low and in which a purge gas required therefor is not only reduced in 
amount but effectively utilized, with substantial elimination of the 
disadvantages inherent in conventional heat treating furances of this 
kind. 
Another important object of the present invention is to provide an 
atmosphere heat treating furnace of the above described type in which a 
heating time period is reduced for the purpose of energy saving through 
utilization of heat of cutting oil, etc. adhering to works to be treated. 
In order to accomplish these objects according to one preferred embodiment 
of the present invention, there is provided a continuous heat treating 
furnace for heat treating a ferrous metal work in a protective atmosphere, 
comprising: a furnace which is lined with refractories; a loading door 
which is provided at one end of said furnace; a discharge door which is 
provided at the other end of said furnace such that said work is loaded 
into and discharged out of said furnace through said loading door and said 
discharge door, respectively; a partition door for separating said furnace 
into a charge chamber and a heat treating chamber arranged in this order 
in a processing sequence of said continuous heat treating furnace such 
that said protective atmosphere is supplied into said heat treating 
chamber; a transport means for transporting said work from said one end to 
said other end of said furnace; said partition door and said transport 
means being provided in said furnace; a first heating means for 
maintaining a temperature in said charge chamber at a first predetermined 
value; a recirculating fan for agitating an atmosphere in said charge 
chamber; a gas purge means for purging said charge chamber at the time of 
loading of said work into said charge chamber; said first heating means, 
said recirculating fan and said gas purge means being provided in said 
charge chamber; and a second heating means for maintaining a temperature 
in said heat treating chamber at a second predetermined value, which is 
provided in said heat treating chamber, whereby said work, while said 
charge chamber is being purged at high temperatures by said gas purge 
means, is preheated through convectional heat transfer in said charge 
chamber by said first heating means and said recirculating fan and then, 
is heat treated under said protective atmosphere in said heat treating 
chamber.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, there is shown in FIGS. 1 and 2, a 
continuous type gaseous atmosphere heat treating furnace K1 according to a 
first embodiment of the present invention. The furnace K1 includes a 
furnace 1. The furnace 1 is separated into a charge chamber 3 and a heat 
treating chamber (annealing chamber) 15 by a partition door 2. In the 
charge chamber 3, a heater 4 acting as an indirect heating means is 
provided. Furthermore, a recirculating fan 5 and a gas purge means 6 are 
provided at a top wall of the charge chamber 3. The gas purge means 6 is 
constituted by a supply pipe 7 for introducing N.sub.2 gas into the charge 
chamber 3 and a discharge pipe 8. Meanwhile, a heater 16 is provided in 
the heat treating chamber 15. A plurality of recirculating fans 17 are 
provided at a top wall of the heat treating chamber 15. 
The furnace K1 further includes a discharge vestibule 19 provided with a 
gas purge means (not shown). A loading door 20 and a discharge door 21 
are, respectively, provided at opposite ends of the furnace 1. The furnace 
K1 includes conveyor roller units 22a to 22d and 22f which are driven 
independently of one another for transporting the work W to be treated. 
Namely, the conveyor roller unit 22a is provided in the charge chamber 3, 
while the conveyor roller units 22b, 22c and 22d are provided in the heat 
treating chamber 15. Meanwhile, the conveyor roller unit 22f is provided 
in the discharge vestibule 19. 
An annealing process of the furnace K1 of the above described arrangement 
will be described, hereinbelow. Initially, a temperature in the charge 
chamber 3 is raised to a predetermined value, for example, 500.degree. C. 
by the heater 4. Then, the work W is loaded from a loading table 25 into 
the charge chamber 3 upon opening of the loading door 20. The work W is 
preheated through convection by the recirculating fan 5 while being 
conveyed at low speed upon low-speed rotation of the conveyor roller unit 
22a. At the same time, N.sub.2 gas is fed into the charge chamber 3 from 
the supply pipe 7 so as to purge the charge chamber 3. After the work W 
has been preheated in the charge chamber 3 for a predetermined time 
period, the work W is transferred from the charge chamber 3 to the heat 
treating chamber 15 at high speed upon opening of the partition door 2 and 
synchronous rotations of the conveyor roller units 22a and 22b. 
Subsequently, the work W is conveyed towards the discharge vestibule 19 so 
as to be heated, soaked and cooled under protective atmosphere in the heat 
treating chamber 15 and finally, is discharged out of the furnace K1 via 
the discharge vestibule 19. 
Referring now to FIGS. 3 to 7, there is shown a continuous type atmosphere 
heat treating furnace K2 according to a second embodiment of the present 
invention. In the same manner as the furnace K1, the furnace K2 includes 
the furnace 1 which is separated into the charge chamber 3 and the heat 
treating chamber 15 by the partition door 2. The heat treating chamber 15 
is further separated into a heating chamber 15a, a carburizing chamber 15b 
and a cooling chamber 15c by partition doors 2a and 2b. The furnace K2 
further includes a hardening apparatus 23 following the cooling chamber 
15c. Meanwhile, the furnace K2 includes the conveyor roller units 22a, to 
22f which are driven independently of one another for transporting the 
work W. Namely, the conveyor roller units 22a, 22b and 22f are provided in 
the charge chamber 3, the heating chamber 15a and the cooling chamber 15c, 
respectively. The carburizing chamber 15b is provided with three conveyor 
roller units, i.e., an inlet conveyor roller unit 22c, a central conveyor 
roller unit 22d and an outlet conveyor roller unit 22e. The central roller 
unit 22d is further divided into a plurality of, for example, three roller 
segments 22d1, 22d2 and 22d3 as shown in FIG. 5. It is to be noted that 
the conveyor roller units 22a, 22b and 22f provided in the charge chamber 
3, the heating chamber 15a and the cooling chamber 15c, respectively can 
be rotated not only forwardly but reversely so as to reciprocate the work 
W in the charge chamber 3, the heating chamber 15a and the cooling chamber 
15c. 
Meanwhile, the charge chamber 3 is provided with the heater 4 acting as an 
indirect heating means, the recirculating fan 5, an air supply pipe 9 for 
burning off cutting oil, etc. adhering to the work W and a radiant tube 
14. The radiant tube 14 is coupled, at one end thereof disposed outwardly 
of the furnace K2, with a discharge pipe 11 for discharging exhaust gas. 
The discharge pipe 11 is communicated with the charge chamber 3. the 
radiant tube 14 is provided, at its portion coupled with the discharge 
pipe 11, with a pilot burner 12 and an air inflow tube 14a for introducing 
combustion air into the radiant tube 14. A purge gas, (a combustible gas 
in the heat treating chamber 15), which is drawn into the charge chamber 3 
through a gap 3a between the partition door 2 and the inner face of the 
wall of the furnace 1, is exhausted from the furnace K2 by way of the 
discharge pipe 11 and the radiant tube 14. Namely, the gas purge means 6 
is constituted by the gap 3a and the radiant tube 14. Meanwhile, a 
combustion means 10 for burning the combustible gas is constituted by the 
air supply pipe 9, the air inflow tube 14a, the pilot burner 12, the 
charge chamber 3 and the radiant tube 14, with the charge chamber 3 and 
the radiant tube 14 acting as combustion chambers for the combustible gas. 
Furthermore, each of the heating chamber 15a, the carburizing chamber 15b 
and the cooling chamber 15c constituting the heat treating chamber 15 is 
provided with the heater 16, the recirculating fan 17 and a gas generator 
18 for generating an endothermic gas that acts as a carrier gas. 
As shown in FIG. 5, the furnace 1 is lined with refractories and the 
furnace K2 includes a plurality of driving devices for driving the 
conveyor roller units 22a to 22f, respectively. Accordingly, the conveyor 
roller units 22a to 22f are driven independently of one another by the 
driving devices so as to transport the work W in the furnace K2 at speeds 
shown in FIG. 5. FIGS. 6 and 7 show constructions of the radiant tube 14 
in detail. 
Hereinbelow, a continuous gas carburizing process of the work W having 
cutting oil, etc. adhering thereto in the above described continuous type 
gaseous atmosphere heat treating furnace K2 of the roller hearth 
arrangement will be described. Initially, a temperature in the charge 
chamber 3 is raised to a predetermined value, for example, about 
800.degree. C. by the heater 4. Subsequently, upon opening of the loading 
door 20, the work W is loaded from the loading table 25 into the charge 
chamber 3. The work W disposed in the charge chamber 3 is reciprocated in 
the charge chamber 3 upon forward and reverse rotations of the conveyor 
roller unit 22a and, at the same time, is preheated through convection by 
the heater 4 and the recirculating fan 5. During this time period, the 
cutting oil, etc. adhering to the work W are vaporized through heating 
thereof. In the charge chamber 3, this vaporized oil is subjected to 
complete combustion together with the combustible gas supplied into the 
charge chamber 3 by a predetermined amount of air introduced into the 
charge chamber 3 from the air supply pipe 9. This combustion gas is 
exhausted out of the furnace K2 by way of the discharge pipe 11 and the 
radiant tube 14. When the above described operation for vaporizing from 
the work W through heating thereof the cutting oil or the like adhering 
thereto has been completed, supply of air into the charge chamber 3 from 
the air supply pipe 9 is stopped. Thereafter, the charge chamber 3 is 
purged by using atmosphere (combustible gas) of the heat treating chamber 
15 flowing into the charge chamber 3 through the gap 3a between the 
partition door 2 and the inner face of the wall of the furnace 1. Before 
being exhausted from the furnace K2 by way of the discharge pipe 11 and 
the radiant tube 14, the purge gas is burnt in the radiant tube 14 upon 
ignition of the burner 12 connected, outwardly of th furnace 1, with the 
radiant tube 14 and upon introduction of air into the radiant tube 14 from 
the air inflow tube 14a and the heat of combustion is utilized for heating 
in the charge chamber 3. 
When purging of the charge chamber 3 has been completed, the work W, which 
has been cleaned through heating thereof and has been preheated in the 
charge chamber 3, is transferred from the charge chamber 3 to the heating 
chamber 15a upon opening of the partition door 2 and synchronous forward 
rotations of the conveyor roller units 22a and 22b. After the work W has 
been transferred from the charge chamber to the heating chamber 15a, the 
partition door 2 is closed and the work W is heated substantially to a 
carburizing temperature while being reciprocated upon forward and reverse 
rotations of the conveyor roller unit 22b. In the meantime, the next work 
W is loaded into the charge chamber 3 such that preheating of the work W 
(cleaning of the work W through vaporization of the cutting oil or the 
like) and purging of the charge chamber 3 are preformed in the same manner 
as described above. After heating of the work W in the heating chamber 
15a, the work W is transferred from the heating chamber 15a to the 
carburizing chamber 15b upon opening of the partition door 2a and 
synchronous forward rotations of the conveyor roller unit 22b in the 
heating chamber 15a and the inlet conveyor roller unit 22c in the 
carburizing chamber 15b. Subsequently, the work W is sequentially 
transported towards the outlet conveyor roller unit 22e by the central 
conveyor roller unit 22d so as to be subjected to carburizing and 
diffusing in the carburizing chamber 15b. Then, the next work W is 
transferred from the charge chamber 3 to the heating chamber 15a upon 
closing of the partition door 2a, opening of the partition door 2 and 
synchronous forward rotations of the conveyor roller units 22a and 22b. 
Thereafter, when the preceding work W transferred to the carburizing 
chamber 15b has been displaced away from the inlet conveyor roller unit 
22c, the next work W in the heating chamber 15a is transported upon 
opening of the partition door 2a and synchronous forward rotations of the 
conveyor roller units 22b and 22c so as to come close to the preceding 
work W. Subsequently, in the same manner as described above, the work W is 
transported through the charge chamber 3, the heating chamber 15a and the 
carburizing chamber 15b so as to be subjected to carburizing. When the 
foremost work W has reached the outlet conveyor roller unit 22e of the 
carburizing chamber 15b, the work W is transferred to the cooling chamber 
15c upon opening of the partition door 2b and synchronous forward 
rotations of the conveyor roller units 22e and 22f. In the cooling chamber 
15c, the work W is cooled to a hardening temperature while being 
reciprocated upon forward and reverse rotations of the conveyor roller 
unit 22f. After the work W has been cooled to the hardening temperature, 
the work W is transferred from the cooling chamber 15c to the hardening 
apparatus 23 upon opening of the discharge door 21 and forward rotation of 
the conveyor roller unit 22f. After the work W has been subjected to 
hardening in the hardening apparatus 23, the work W is discharged out of 
the furnace K2. 
Referring further to FIG. 8, there is shown a furnace K2' which is a first 
modification of the furnace K2. The furnace K2' includes the partition 
doors 2 and 2b but is not provided with the partition door 2a. Thus, the 
heat treating chamber 15 of the furnace K2' is separated into the 
carburizing chamber 15b and the cooling chamber 15c by the partition doors 
2 and 2b. In the carburizing chamber 15b, the work W is heated to the 
carburizing temperature and is subjected to carburizing and diffusing 
while being maintained at the carburizing temperature. Then, the work W is 
maintained at the hardening temperature in the cooling chamber 15c. Since 
other constructions of the furnace K2' are substantially similar to those 
of the furnace K2, detailed description thereof is abbreviated for the 
sake of brevity. It can be, needless to say, also so arranged as shown in 
FIG. 5 that the central conveyor roller unit 22d of the carburizing 
chamber 15b is further divided into a plurality of roller segments. 
FIG. 9 shows a combustion means 10' which is a modification of the 
combustion means 10 for burning the combustible gas in the charge chamber 
3 of the furnaces K2 and K2'. The combustion means 10' for burning the 
combustible gas includes a combustion chamber 13 formed at one end portion 
of the radiant tube 14, which one end portion projects out of the furnace 
1. Consequently, the vaporized cutting oil and the combustible gas which 
is produced at the time of purging of the charge chamber 3 and operation 
of the furnace K2 are subjected to complete combustion in the combustion 
chamber 13 by the pilot burner 12 and through introduction of combustion 
air into the combustion chamber 13 and then, are exhausted out of the 
furnace K2 via the radiant tube 14. 
Meanwhile, FIG. 10 is a heating chamber 15a' which is a modification of the 
heating chamber 15a of the furnace K2. In the heating chamber 15a', the 
conveyor roller unit 22b of the heating chamber 15a of the furnace K2 is 
divided into a plurality of, for example, two segments, i.e., conveyor 
roller units 22b1 and 22b2 driven independently of each other such that a 
plurality of, i.e., two works W in this case, are accommodated in the 
heating chamber 15a'. 
It is to be noted that the roller hearth type transport means is employed 
for transporting the work W in the above described embodiments of the 
present invention but can be replaced by any other transport means of tray 
pusher type, etc. 
As is clear from the foregoing description, in the present invention, the 
charge chamber provided with the heating means and the recirculating fan 
is employed in place of the prior art charge vestibule by separating the 
work loading side of the furnace by the use of the retractable partition 
door. 
Accordingly, in accordance with the present invention, since the work can 
be preheated through convection in the charge chamber simultaneously with 
purging of the charge chamber, the work can be preheated uniformly and 
rapidly, thereby resulting in reduction of the heating time period of the 
work. 
Furthermore, in accordance with the present invention, since the charge 
chamber is purged at high temperatures, amount of the purge gas consumed 
therefor can be reduced drastically. For example, it was found that when 
the charge chamber is set at a temperature of 800.degree. C., a necessary 
amount of the purge gas is reduced to about 29% of that of the prior art 
charge vestibule held at ambient temperatures. 
Moreover, in accordance with the present invention, since the combustion 
means for burning the combustible gas is provided in the charge chamber, 
the work can be cleaned through heating thereof in the charge chamber in 
the case where a combustible protective atmosphere for a gas carburizing 
process, a non-oxidizing heating process, etc. is used in the continuous 
type gaseous atmosphere heat treating furnace. Thus, heat possessed by the 
work at the time of cleaning of the work through heating thereof can be 
effectively used. Furthermore, heat of combustion of the combustible gas 
at the time of cleaning of the work through heating thereof and the 
combustible gas in the heat treating chamber can be used as a part of the 
heat source of the charge chamber. Consequently, the heating time period 
of the work in the heating chamber can be reduced due to the effect of 
preheating of the work, thereby resulting in saving of energy. 
Meanwhile, in the present invention, it can be so arranged that the 
transport means of the continuous type atmosphere heat treating furnace is 
of roller hearth type and the furnace is a continuous type gas carburizing 
furnace, namely, the furnace is separated into the charge chamber, the 
heating chamber, the carburizing chamber and the cooling chamber or into 
the charge chamber, the carburizing chamber and the cooling chamber by the 
partition doors and the conveyor roller units driven independently of one 
another are, respectively, provided in the chambers such that the work is 
reciprocated during the heating process for heating the work of the 
carburizing temperature and the cooling process for cooling the work to 
the hardening temperature. Thus, in accordance with the present invention, 
the work is uniformly heated so as to prevent nonuniform carburizing of 
the work and is uniformly cooled with consequent elimination of nonuniform 
hardening of the work. Furthermore, since heating of the work to the 
carburizing temperature and cooling of the work to the hardening 
temperature can be performed rapidly, it becomes possible to reduce the 
length of the furnace. 
In addition, in accordance with the present invention, since the central 
conveyor roller unit of the carburizing chamber is constituted by a 
plurality of the roller segments, vacant regions in the carburizing 
chamber can be reduced at the time of change of the carburizing conditions 
and thus, the carburizing conditions can be changed efficiently. 
Although the present invention has been fully described by way of example 
with reference to the accompanying drawings, it is to be noted here that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, unless otherwise such changes and modifications depart 
from the scope of the present invention, they should be construed as being 
included therein.