EP1612291A1

EP1612291A1 - Multistage continuous carburizing and quenching furnace and continuous carburizing and quenching method

Info

Publication number: EP1612291A1
Application number: EP05013682A
Authority: EP
Inventors: Shohei c/o Fuji Jukogyo Kabushiki Kaisha Shintani
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 2004-06-25
Filing date: 2005-06-24
Publication date: 2006-01-04
Anticipated expiration: 2025-06-24
Also published as: EP1612291B1; JP4540406B2; DE602005004448D1; JP2006009087A; DE602005004448T2

Abstract

A carburizing zone 11, a diffusion zone 12, and a temperature lowering zone 13 are sequentially disposed in a furnace. The furnace interior is divided into first- to fourth-stage carburizing furnace areas I to IV by first- to fourth-stage transport roller conveyors 14-1 to 14-4 and carrying-out roller conveyors 15-1 to 15-5. Heat treatment pallets 50 on which metallic materials are respectively placed are loaded into the respective carburizing furnace areas I to IV in accordance with a preset order of the carburizing furnace areas at an interval corresponding to a quenching cycle, so as to perform uniform carburizing without variations in the respective carburizing furnace areas I to IV. The heat treatment pallets 50 from temperature lowering zones 13-1 to 13-4 in the respective carburizing furnace areas I to IV are immersed in a quenching medium in a quenching zone 21 in the aforementioned order of the carburizing furnace areas, so as to perform uniform quenching without variations.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims foreign priority based on Japanese Patent Application No. P.2004-187556, filed on June 25, 2004, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a carburizing and quenching furnace and a carburizing and quenching method used in carburizing and quenching, and more particularly to a multistage continuous carburizing and quenching furnace and a continuous carburizing and quenching method.

Carburizing and quenching treatment is extensively performed for metallic materials (ex. Steel alloy, steel) of mechanical parts and the like for which toughness, wear resistance, and fatigue strength are required. In the carburizing and quenching treatment, gas carburizing treatment using a carburizing gas is widely used. The gas carburizing treatment is heat treatment in which a metallic material, i.e., a member to be treated, is heated to a high temperature in a carburizing gas atmosphere to thereby allow carbon to diffuse and infiltrate into the surface of the metallic material. As a result of the subsequent quenching treatment, its interior comes to excel in toughness, while its surface becomes hard and wear resistance is obtained.
Here, in the quenching treatment in which a metallic material is immersed in a quenching medium, the quenching transformation is generally completed by immersing the metallic material in the quenching medium for 5 minutes or thereabouts, and the time required for a quenching cycle is 10 minutes or thereabouts. On the other hand, since 30 to 60 minutes or thereabouts is required as the carburizing cycle, there is a large difference between the time required for the quenching cycle and the time required for the carburizing cycle. The entire cycle of the continuous carburizing and quenching treatment is set in accordance with the carburizing cycle, and the standby time is set between the quenching cycles, so that efficient continuous carburizing and quenching treatment is made difficult.
Meanwhile, in such continuous carburizing treatment, by using a long continuous carburizing furnace in which a carburizing zone is formed on the upstream side inside the furnace and a diffusion zone is formed on the downstream side inside the furnace, it is practiced to carburize the surfaces of the metallic materials in the carburizing zone while the metallicmaterials are being transported by a common transporting apparatus. Subsequently, it is practiced to diffuse carbon into the interior of each metallic material in the diffusion zone. However, a long continuous carburizing furnace is required to effect the carburizing and carbon diffusion while the metallic materials are being sequentially transported by a common transporting apparatus. A long installation site is required to install that continuous carburizing furnace.
Accordingly JP-A-10-204607 discloses a continuous carburizing furnace in which zone the metallic materials are sequentially transported by a single transporting apparatus in the carburizing, whereas in the diffusion zone the metallic materials carburized in the carburizing zone are transported in a distributed manner by a plurality of transporting apparatuses so as to diffuse carbon into the metallic materials in parallel on the plurality of transporting apparatuses, thereby making the diffusion zone short.
In addition, JP-A-2001-207253 discloses a continuous carburizing furnace structured by a common transporting apparatus for sequentially transporting metallic materials and a carburizing furnace in which a carburizing zone fitted for the carburizing treatment of metallic materials requiring a deep carburizing depth is formed, wherein the metallic materials are sequentially transported by the transporting apparatus, and in a case where a metallic material requiring a shallow carburizing depth follows a metallic material requiring a deep carburizing depth, that metallic material requiring the shallow carburizing depth is carried in by taking an interval with respect to the precedingmetallic material by the difference in the time expended in the carburizing treatment. When the metallic material requiring the shallow carburizing depth passes through the carburizing zone, the metallic material is transported in such a manner as to shorten the interval ahead. The metallic materials requiring various different carburizing depths can thus be subjected to carburizing treatment continuously in the single carburizing furnace.
Further, disclosed in Fig. 11 is a multistage continuous carburizing furnace of related art. In the related multistage continuous carburizing furnace, heat treatment pallets 101 with metallic materials placed thereon are stacked in a plurality of stages. The plurality of heat treatment pallets 101 stacked in stages are transported simultaneously within a carburizing zone 103 of a carburizing furnace 102 by a transporting apparatus 106 such as a conveyor. The respective metallic materials placed on the plurality of heat treatment pallets 101 stacked in stages are simultaneously subjected to carburizing and carbon diffusion. After the metallic materials are annealed in a temperature lowering zone 105, the plurality of stacked heat treatment pallets 101 with the carburized metallic materials placed thereon are simultaneously subjected to oil quenching by being immersed in oil, i.e., a quenching medium, in a quenching zone 107.
According to the continuous carburizing furnace disclosed in JP-A-10-204607, in the carburizing zone the metallic materials are sequentially transported by the single transporting apparatus, whereas in the diffusion zone the carburizedmetallic materials are transported in a distributed manner by the plurality of transporting apparatuses so as to diffuse carbon, there by making it possible to shorten the continuous carburizing furnace.
However, since the plurality of transporting apparatuses are disposed in parallel in the diffusion zone, the widthwise length of the diffusion zone becomes long. In addition, since the metallic materials are sequentially transported by the single transporting apparatus to perform carburizing in the carburizing zone, efficient carburizing treatment cannot be obtained. Thus, it is apprehended that productivity declines.
On the other hand, according to the continuous carburizing furnace disclosed in JP-A-2001-207253, the metallic materials requiring various different carburizing depths canbe subjected to carburizing treatment continuously in the single carburizing furnace. However, since the metallic materials are sequentially transported by the single transporting apparatus to perform carburizing, efficient carburizing treatment cannot be obtained. Thus, it is apprehended that productivity declines.
Meanwhile, according to the multistage continuous carburizing furnace shown in Fig. 11, the heat treatment pallets 101 with the metallic materials placed thereon are stacked in multiple stages. The plurality of heat treatment pallets 101 stacked in multiple stages are transported simultaneously within the carburizing zone 103 of the continuous carburizing furnace 102. The metallic materials placed on the plurality of heat treatment pallets 101 are simultaneously subjected to carburizing and carbon diffusion. Further, the metallic materials placed on the plurality of heat treatment pallets 101 stacked in multiple stages are simultaneously subjected to quenching treatment in the quenching zone 107. Thus, carburizing and quenching treatment can be performed efficiently.
However, since the respective metallic materials placed on the plurality of stacked heat treatment pallets 101 are simultaneously carburized in the carburizing zone 103, the flow of the carburizing gas in the carburizing zone 103 is affected by the stacked heat treatment pallets 101. In addition, variations occur in the flow of the carburizing gas depending on the positions of the stacked heat treatment pallets 101, i.e., the stages, and variations also occur in the carburizing temperature in consequence of the disturbance of the carburizing gas. Further, variations occur in the amount of carbon infiltrating into the surface of the metallic material placed on the heat treatment pallet 101 in each stage. These variations constitute factors making it impossible to attain stable uniform carburizing treatment.
Furthermore, in the quenching zone 107, the metallic materials respectively placed on the stacked heat treatment pallets 101 are immersed in the oil in the state of being stacked in stages so as to be quenched. Therefore, a time lag occurs in the timing of charging the metallic materials into the oil during quenching between the lower- and upper-stage heat treatment pallets 101. Hence, owing to various effects of the oil, a cooling difference occurs between the metallic material placed on the heat treatment pallet 101 in the lowermost stage and the metallic materials placed on the heat treatment pallets 101 in the higher stages, so that a difference occurs in the progress of the transformation. Thus, variations occur in the deformation entailed in quenching among the metallic materials, and it is apprehended that the dimensional accuracy of the quenched metallic materials becomes stable.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been devised in view of the above-described aspects. The object of the present invention is to provide a multistage continuous carburizing and quenching furnace and a continuous carburizing and quenching method which excel in productivity, make it possible to obtain stable uniform carburizing treatment, and make it possible to ensure dimensional accuracy and perform high-quality carburizing and quenching.
In accordance with one or more embodiments of the present invention, a continuous carburizing and quenching furnace is provided with a multistage carburizing furnace including a carburizing zone, a diffusion zone, a temperature lowering zone, wherein the carburizing zone, the diffusion zone and the temperature lowering zone are sequentially arranged continuously from an upstream side to a downstream side of a furnace interior, and a plurality of transporting apparatuses respectively continuing from the carburizing zone to the temperature lowering zone, wherein the plurality of transporting apparatuses partition the furnace interior into multiple-stage carburizing furnace areas respectively continuing from the carburizing zone to the temperature lowering zone; a workpiece loading apparatus disposed on the upstream side of the multistage carburizing furnace, wherein heat treatment pallets, on which metallic materials to be carburized and quenched are respectively placed thereon, are sequentially loaded to the workpiece loading apparatus in accordance with a preset order of the carburizing furnace areas and at an interval corresponding to a quenching cycle; and a quenching zone disposed on the downstream side of the multistage carburizing furnace, wherein the heat treatment pallets with carburized metallic materials thereon are sequentially immersed in a quenching medium in the quenching zone, in a continuous quenching cycle from the temperature lowering zone of each of the carburizing furnace areas in accordance with the preset order of the carburizing furnace areas.
In accordance with one or more embodiments of the present invention, a carburizing treatment for effecting carburizing into surfaces of the metallic materials and carbon diffusion into interiors of the metallic materials is performed by sequentially transporting the metallic materials through the carburizing zone, the diffusion zone, and the temperature lowering zone, a quenching treatment for effecting quenching is performed by immersing the carburized metallic materials in the quenching medium in the quenching zone, and the carburizing treatment and the quenching treatment are continuously performed.
In accordance with one or more embodiments of the present invention, the transporting apparatuses which partition the furnace interior into the multiple-stage carburizing furnace areas allow a circulation of an air stream between adjacent ones of the carburizing furnace areas.
In accordance with one or more embodiments of the present invention, the transporting apparatuses are roller conveyors.
In accordance with one or more embodiments of the present invention, the continuous carburizing and quenching furnace is provided with a plurality of opening/closing partitioning means. The plurality of opening/closing partitioning means respectively provided at an upstream end of each of the carburizing furnace areas, between the carburizing zone and the diffusion zone, and between the diffusion zone and the temperature lowering zone so as to partition into the respective zones.
In accordance with one or more embodiments of the present invention, eachofthepluralityofopening/closingpartitioning means is opened, when the heat treatment pallets with the metallic materials placed thereon pass therethrough, so as to allow a movement of the heat treatment pallets.
In accordance with one or more embodiments of the present invention, the continuous carburizing and quenching furnace is provided with a quenching elevator provided to the quenching zone and disposed on the downstream side of the multistage carburizing furnace. The quenching elevator immerses in the quenching medium the heat treatment pallet which is carried from the temperature lowering zone of each of the carburizing furnace areas in accordance with the preset order of the carburizing furnace areas and on which the carburized metallic material is placed, so as to quench the metallic material. The quenching elevator carries out the heat treatment pallet with the quenched metallic material placed thereon.
In accordance with one or more embodiments of the present invention, a continuous carburizing and quenching method, for continuously performing carburizing treatment for effecting carburizing into surfaces of metallic materials and carbon diffusion into interiors of the metallic materials and quenching treatment for immersing the carburized metallic materials in a quenching medium, is performed in a continuous carburizing and quenching furnace including a multistage carburizing furnace in which a carburizing zone, a diffusion zone, and a temperature lowering zone are sequentially arranged continuously from an upstream side to a downstream side of a furnace interior, and including a plurality of transporting apparatuses for partitioning the furnace interior into multiple-stage carburizing furnace areas respectively continuing from the carburizing zone to the temperature lowering zone. The method comprises sequentially loading heat treatment pallets on which the metallic materials to be carburized and quenched are respectively placed, in accordance with a preset order of the carburizing furnace areas and at an interval corresponding to a quenching cycle, on an upstream side of a transporting apparatus in the carburizing furnace area; sequentially transporting the metallic materials by the transporting apparatus through the carburizing zone, the diffusion zone, and the temperature lowering zone, so as to performe the carburizing treatment; and sequentially immersing in the quenching medium the heat treatment pallets, with carburized metallic materials thereon, in a continuous quenching cycle from the temperature lowering zone of each of the carburizing furnace areas in accordance with the preset order of the carburizing furnace areas, so as to perform the quenching treatment.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
According to one or more embodiments of the present invention, the heat treatment pallets on which the metallic materials to be carburized are respectively placed thereon are loaded into the respective carburizing areas in a preset order of the carburizing furnace areas and at an interval corresponding to the quenching cycle, so as to perform carburizing treatment concurrently in the respective carburizing zones and diffusion zones in the respective carburizing areas. After the metallic materials are annealed in the respective temperature lowering zones, the heat treatment pallets with the metallic materials placed thereon are immersed in the quenching medium in the quenching cycle from the temperature lowering zone of each of the carburizing furnace areas in accordance with the preset order of the carburizing furnace areas so as to perform the quenching treatment of the metallic materials. Therefore, quenching treatment can be sequentially performed without an interruption in the continuous quenching cycle. Thus, carburizing and quenching treatment excelling in productivity can be obtained.
Furthermore, as the heat treatment pallets in the state of being flatly loaded are transported through the carburizing zones and the diffusion zones in the respective carburizing areas by the respective transporting apparatuses, there are not variations in the amount of carbon infiltrating into the surfaces of the metallic materials loaded on the heat treatment pallets and in the carbon diffusion, so that satisfactory carburizing treatment can be effected concurrently. In addition, since the heat treatment pallets on which the metallic materials annealed in the temperature lowering zones are respectively placed thereon are separately immersed in the quenching medium, a fixed timing of charging into the quenching medium can be ensured, and a cooling difference ceases to occur among the metallic materials. Since the variation in the deformation entailed in quenching among the metallic materials is suppressed, the dimensional accuracy of the treated metallic materials becomes stable, thereby making it possible to ensure high-quality carburizing and quenching treatment. In addition, the carburizing areas divided by the transporting apparatuses are arranged in multiple stages. Consequently, it is possible to reduce the widthwise length of the multistage continuous carburizing furnace 1, and a reduction of its installation site can be expected.
According to one or more embodiment of the present invention, the flow of the air stream including the carburizing gas between adjacent ones of the carburizing zones in the respective carburizing furnace areas is not affected by the transporting apparatuses, and the temperature and atmosphere of the entire carburizing zone in the furnace canbe controlled to satisfactory conditions. At the same time, the flow of the air stream between adjacent ones of the diffusion zones in the respective carburizing furnace areas is not affected by the transporting apparatuses, and the temperature and atmosphere of the entire diffusion zone in the furnace can be controlled satisfactorily.
According to one or more embodiment of the present invention, the transporting apparatuses which allow the circulation of the air stream between adjacent ones of the carburizing furnace areas can be easily formed by existing roller conveyors.
According to one or more embodiment of the present invention, the opening/closing partitioning means are provided at the upstream end of each of the carburizing furnace areas, between the carburizing zone and the diffusion zone, and between the diffusion zone and the temperature lowering zone to partition into the respective zones and are adapted to open when the heat treatment pallets with the metallic materials placed thereon pass therethrough. Therefore, the temperature and atmosphere in the carburizing zones and the diffusion zones in the furnace can be effectively controlled to satisfactory conditions.
According to one or more embodiment of the present invention, the quenching zone is provided with the quenching elevator disposed on the downstream side of the multistage carburizing furnace and adapted to immerse in the quenching medium the heat treatment pallet which has been carried in from the temperature lowering zone of each of the carburizing furnace areas in accordance with the preset order of the carburizing furnace areas and on which the carburized metallic material is placed, so as to quench the metallic material, and adapted to carry out the heat treatment pallet with the quenched metallic material placed thereon. Therefore, quenching treatment can be effected easily.
According to one or more embodiment of the present invention, the heat treatment pallets on which the metallic materials to be carburized are respectively placed thereon are loaded into the respective carburizing areas in a preset order of the carburizing furnace areas and at an interval corresponding to the quenching cycle, so as to perform carburizing treatment concurrently in the respective carburizing zones and diffusion zones in the respective carburizing areas. After the metallic materials are annealed in the respective temperature lowering zones, the heat treatment pallets from the temperature lowering zone of each of the carburizing furnace areas are immersed in the quenching medium in the quenching cycle in accordance with the preset order of the carburizing furnace areas so as to perform the quenching treatment of the metallic materials. Therefore, quenching treatment can be sequentially performed without an interruption in the continuous quenching cycle. Thus, it is possible to perform carburizing and quenching treatment excelling in productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic explanatory diagram of a multistage continuous carburizing furnace illustrating an outline of the multistage continuous carburizing furnace and a continuous carburizing method in accordance with one or more embodiments of the present invention.
Fig. 2 is an explanatory process diagram of the carburizing method using the multistage continuous carburizing furnace.
Fig. 3 is an explanatory process diagram of the carburizing method using the multistage continuous carburizing furnace.
Fig. 4 is an explanatory process diagram of the carburizing method using the multistage continuous carburizing furnace.
Fig. 5 is an explanatory process diagram of the carburizing method using the multistage continuous carburizing furnace.
Fig. 6 is an explanatory process diagram of the carburizing method using the multistage continuous carburizing furnace.
Fig. 7 is an explanatory process diagram of the carburizing method using the multistage continuous carburizing furnace.
Fig. 8 is an explanatory process diagram of the carburizing method using the multistage continuous carburizing furnace.
Fig. 9 is an explanatory process diagram of the carburizing method using the multistage continuous carburizing furnace.
Fig. 10 is an explanatory process diagram of the carburizing method using the multistage continuous carburizing furnace.
Fig. 11 is an explanatory diagram of a related multistage continuous carburizing furnace.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Figs. 1 to 10, a description will be given to a multistage continuous carburizing furnace and a continuous carburizing method in accordance with one or more embodiments of the invention.
Fig. 1 is a schematic explanatory diagram of a multistage continuous carburizing furnace 1 in accordance with one or more embodiments of the invention. Reference numeral 10 denotes a multistage carburizing furnace. In the multistage carburizing furnace 10, a carburizing zone 11 is arranged on the upstream side inside the furnace, and a diffusion zone 12 and a temperature lowering zone 13 are continuously formed on the downstream side of the carburizing zone 11.
A first-stage transport roller conveyor 14-1, which serves as a first-stage transporting apparatus, is disposed continuously on a furnace bottom of the multistage carburizing furnace 10 in such a manner as to extend from an upstream end of the carburizing zone 11 to a downstream end of the diffusion zone 12. Second- to fourth-stage transport roller conveyors 14-2 to 14-4, which serve as second- to fourth-stage transporting apparatuses, are sequentially disposed at equal intervals above the first-stage transport roller conveyor 14-1. These first-to fourth-stage transport roller conveyors 14-1 to 14-4 are respectively driven independently.
The interior of the carburizing zone 11 is divided into first- to fourth-stage carburizing zones 11-1 to 11-4 in order from the lower side by these first- to fourth-stage transport roller conveyors 14-1 to 14-4.
In the first-stage carburizing zone 11-1, unillustrated stoppers are provided for stopping and retaining heat treatment pallets 50, which are transported sequentially from the upstream side to the downstream side by the first transport roller conveyor 14-1, at the respective stop positions including a first stop position 11-1a to a sixth stop position 11-1f. Further, a pallet detection sensor 11-1s is provided for detecting the presence or absence of the heat treatment pallet at the first stop position 11-1a.
Similarly, in the second- to fourth-stage carburizing zones 11-2 to 11-4 as well, unillustrated stoppers are respectively provided for stopping and retaining the heat treatment pallets 50, which are transported by the second-to four-stage transport roller conveyors 14-2 to 14-4, at the respective stop positions including first stop positions 11-2a, 11-3a, and 11-4a to sixth stop positions 11-2f, 11-3f, and 11-4f. Further, pallet detection sensors 11-2s to 11-4s are provided for detecting the presence or absence of the heat treatment pallets 50 at the respective first stop positions 11-2a to 11-4a.
In the same way as the carburizing zone 11, the interior of the diffusion zone 12 is divided into first- to fourth-stage diffusion zones 12-1 to 12-4 in order from the lower side by the first- to fourth-stage transport roller conveyors 14-1 to 14-4. These first- to fourth-stage transport roller conveyors 14-1 to 14-4 are constituted by existing roller conveyors for a carburizing furnace, and a plurality of rollers disposed with intervals provided therebetween are rotatively driven to transport the heat treatment pallets 50 with the loaded metallic materials placed thereon. Circulation of an air stream such as a carburizing gas is allowed through the rollers.
In the first-stage diffusion zone 12-1, stoppers (not shown) are provided for stopping and retaining the heat treatment pallets 50, which are transported sequentially from the upstream side to the downstream side by the first transport roller conveyor 14-1, at the respective stop positions including a first stop position 12-1a to a third stop position 12-1c. Similarly, in the second- to fourth-stage diffusion zones 12-2 to 12-4 as well, unillustrated stoppers are respectively provided for stopping and retaining the heat treatment pallets 50, which are transported by the second- to four-stage transport roller conveyors 14-2 to 14-4, at the respective stop positions including first stop positions 12-2a, 12-3a, and 12-4a to third stop positions 12-2c, 12-3c, and 12-4c.
A first-stage carrying-out roller conveyor 15-1, which makes up the first-stage transporting apparatus together with the first-stage transport roller conveyor 14-1, is disposed in the temperature lowering zone 13 in such a manner as to continue from the downstream side of the first-stage transport roller conveyor 14-1. Second- to fourth-stage carrying-out roller conveyors 15-2 to 15-4, which make up the second- to fourth-stage transporting apparatuses, are sequentially disposed at equal intervals above the first-stage carrying-out roller conveyor 15-1 in such a manner as to respectively continue from the second- to fourth-stage transport roller conveyors 14-2 to 14-4. The interior of the temperature lowering zone 13 is divided into first- to fourth-stage temperature lowering zones 13-1 to 13-4 in order from the lower side by the first-to fourth-stage carrying-out roller conveyors 15-1 to 15-4. These first- to fourth-stage carrying-out roller conveyors 15-1 to 15-4 are driven independently.
Doors 16-1, 17-1, 18-1, and 19-1, which are opening/closing partitioning means for partitioning the furnace interior into the respective zones, are openably provided at the upstream end serving as an entrance for the first-stage carburizing zone 11-1, between the downstream end of the first-stage carburizing zone 11-1 and the upstream end of the first-stage diffusion zone 12-1, between the downstream end of the first-stage diffusion zone 12-1 and the upstream end of the first-stage temperature lowering zone 13-1, and at the downstream end of the first-stage temperature lowering zone 13-1. A first-stage carburizing furnace area I is formed by the first-stage carburizing zone 11-1, the first-stage diffusion zone 12-1, and the first-stage temperature lowering zone 13-1.
Similarly, doors 16-2, 17-2, 18-2, and 19-2, which are opening/closing partitioning means for partitioning the furnace interior into the respective zones, are openably provided at the upstream end serving as an entrance for the second-stage carburizing zone 11-2, between the downstream end of the second-stage carburizing zone 11-2 and the upstream end of the second-stage diffusion zone 12-2, between the downstream end of the second-stage diffusion zone 12-2 and the upstream end of the second-stage temperature lowering zone 13-2, and at the downstream end of the second-stage temperature lowering zone 13-2. A second-stage carburizing furnace area II is formed by the second-stage carburizing zone 11-2, the second-stage diffusion zone 12-2, and the second-stage temperature lowering zone 13-2.
Doors 16-3, 17-3, 18-3, and 19-3 are openably provided at the upstream end of the third-stage carburizing zone 11-3, between the third-stage carburizing zone 11-3 and the third-stage diffusion zone 12-3, between the third-stage diffusion zone 12-3 and the third-stage temperature lowering zone 13-3, and at the downstream end of the third-stage temperature lowering zone 13-3. A third-stage carburizing furnace area III is formed by the third-stage carburizing zone 11-3, the third-stage diffusion zone 12-3, and the third-stage temperature lowering zone 13-3. Similarly, doors 16-4, 17-4, 18-4, and 19-4 are openably provided at the upstream end of the fourth-stage carburizing zone 11-4, between the fourth-stage carburizing zone 11-4 and the fourth-stage diffusion zone 12-4, between the fourth-stage diffusion zone 12-4 and the fourth-stage temperature lowering zone 13-4, and at the downstream end of the fourth-stage temperature lowering zone 13-4. A fourth-stage carburizing furnace area IV is formed by the fourth-stage carburizing zone 11-4, the fourth-stage diffusion zone 12-4, and the fourth-stage temperature lowering zone 13-4.
The carburizing zone 11 is partitioned from the diffusion zone 12 as the respective upstream doors 16-1 to 16-4 are closed and the respective downstream doors 17-1 to 17-4 are closed. At the same time, the interior of the carburizing zone 11 is partitioned into the first- to fourth-stage carburizing zones 11-1 to 11-4 by the first- to fourth-stage transport roller conveyors 14-1 to 14-4 which are capable of ensuring the flowof the air streambetween adj acent ones of the carburizing furnace areas I and II, II and III, and III and IV .
The diffusion zone 12 is partitioned from the carburizing zone 11 by closing the upstream doors 17-1 to 17-4, is partitioned from the temperature lowering zone 13 by closing the downstream doors 18-1 to 18-4, and is partitioned into the respective first- to fourth-stage diffusion zones 12-1 to 12-4 by the respective first- to fourth-stage transport roller conveyors 14-1 to 14-4.
A quenching zone 21 for subjecting the carburized metallic materials to oil quenching by charging them in oil, i.e., a quenching medium, is arranged on the downstream side of the multistage carburizing furnace 10 in which the first-stage carburizing area I, the second-stage carburizing area II, the third-stage carburizing area III, and the fourth-stage carburizing area IV are arranged in a state of being stacked in stages.
A carrying-in elevator 25 is disposed on the upstream side of the multistage carburizing furnace 10. The carrying-in elevator 25 is a workpiece loading means for loading into the first- to fourth-stage carburizing zones 11-1 to 11-4 the heat treatment pallets 50 carried in by a carrying-in conveyor 29 serving as a carrying-in means.
On the other hand, a quenching elevator 27 is disposed on the downstream side of the multistage carburizing furnace 10. By means of this quenching elevator 27, the heat treatment pallets 50 which have been carried out by the first- to fourth-stage carrying-out roller conveyors 15-1 to 15-4 of the respective first- to fourth-stage temperature lowering zones 13-1 to 13-4 are collected, are lowered, and are immersed in the oil, i.e., the quenching medium, in the quenching zone 21 for a predetermined time, thereby performing the oil quenching of the metallic materials. In addition, the arrangement provided is such that, after the quenching treatment, the heat treatment pallets 50 are raised by the quenching elevator 27 and are carried out from the multistage continuous carburizing furnace 1 by such as a carrying-out roller conveyor 30 serving as a carrying-out means.
Next, referring to the explanatory process drawings shown in Figs. 2 to 10, a description will be given of the method of carburizing treatment using the multistage continuous carburizing furnace 1 thus constructed.
Here, in the quenching in which a carburized metallic material is immersed in a quenching medium, the quenching transformation is generally completed by immersing the metallic material in the quenching medium for 5 minutes or thereabouts, and the time required for a quenching cycle is 10 minutes or thereabouts. Therefore, a description will be given by citing as an example the case where the quenching cycle is set to 10 minutes.
The doors 16-1 to 16-4 on the upstream side of the multistage carburizing furnace 10, the doors 17-1 to 17-4 for partitioning into the carburizing zone 11 and the diffusion zone 12, the doors 18-1 to 18-4 for partitioning into the diffusion zone 12 and the temperature lowering zone 13, and the doors 19-1 to 19-4 on the downstream side of the multistage carburizing furnace 10 are closed, thereby partitioning the interior of the multistage carburizing furnace 10 into the carburizing zone 11, the diffusion zone 12, and the temperature lowering zone 13.
A carburizing gas is supplied into the carburizing zone 11 whose entrance on the upstream side is closed by the doors 16-1 to 16-4 and whose downstream side is closed by the doors 17-1 to 17-4, and is circulated throughout the entire carburizing zone 11. At the same time, the temperature and atmosphere in the carburizing zone 11 are controlled to preset conditions by temperature control and the like. The interior of the carburizing zone 11 is divided into the first- to fourth-stage carburizing zones 11-1 to 11-4 by these first- to fourth-stage transport roller conveyors 14-1 to 14-4 which are capable of ensuring the flow of the air stream including the carburizing gas. Therefore, this control makes it possible to provide control such that the temperature and atmosphere in the entire the carburizing zone 11 ranging from the first-stage carburizing zone 11-1 to the fourth-stage carburizing zone 11-4 are set in conditions free of nonuniformityor in satisfactory conditions in which the occurrence of nonuniformity of the temperature and atmosphere is suppressed to a remarkable degree without being affected by the arrangement of these transport roller conveyors 14-1 to 14-4.
Similarly, the temperature and atmosphere in the diffusion zone 12 whose upstream side is partitioned from the carburizing zone 11 by the closed doors 17-1 to 17-4 and whose downstream side is partitioned from the temperature lowering zone 13 by the closed doors 18-1 to 18-4 are controlled topreset conditions. The interior of the diffusion zone 12 is divided into the first- to fourth-stage diffusion zones 12-1 to 12-4 by the first- to fourth-stage transport roller conveyors 14-1 to 14-4 which are capable of ensuring the flow of the air stream. Therefore, this control makes it possible to provide control such that the temperature and atmosphere in the entire the diffusion zone 12 ranging from the first-stage diffusion zone 12-1 to the fourth-stage diffusion zone 12-4 are set in conditions free of nonuniformity or in satisfactory conditions in which the occurrence of nonuniformity of the temperature and atmosphere is suppressed to a remarkable degree without being affected by the arrangement of these transport roller conveyors 14-1 to 14-4.
In addition, the temperature and atmosphere in the temperature lowering zone 13 whose upstream side is partitioned from the diffusion zone 12 by the closed doors 18-1 to 18-4 and whose downstream side is closed by the doors 19-1 to 19-4 are controlled to preset conditions suitable for temperature lowering. The interior of the temperature lowering zone 13 is divided into the first- to fourth-stage temperature lowering zones 13-1 to 13-4 by the first- to fourth-stage carrying-out roller conveyors 15-1 to 15-4 which are capable of ensuring the flow of the air stream. Therefore, this control makes it possible to control the interior of the entire temperature lowering zone 13 ranging from the first-stage temperature lowering zone 13-1 to the fourth-stage temperature lowering zone 13-4 to the satisfactory temperature and atmosphere without being affected by the arrangement of these carrying-out roller conveyors 15-1 to 15-4.
In the state in which the temperature and atmosphere in the respective zones of the carburizing zone 11, the diffusion zone 12, and the temperature lowering zone 13 of the multistage carburizing furnace 10 are maintained and controlled to satisfactory conditions, the heat treatment pallets 50 on which the metallic materials to be carburized are placed are loaded sequentially into the first- to fourth-stage carburizing zones 11-1 to 11-4 in the preset order of carburizing furnace areas, e.g., the first-stage carburizing furnace area I, the second-stage carburizing furnace area II, the third-stage carburizing furnace area III, and the fourth-stage carburizing furnace area IV. Then, the metallic materials are subjected to carburizing treatment while the heat treatment pallets 50 with the metallic materials placed thereon are being transported through the respective carburizing furnace areas I to IV for the respective first to fourth stages. The heat treatment pallets 50 are carried out sequentially from the first- to fourth-stage temperature lowering zones 13-1 to 13-4 in the order of the carburizing furnace areas, and are subjected to quenching treatment in a continuous quenching cycle in the quenching zone 21.
To give a specific description of this carburizing and quenching treatment, first, if the it is detected by the pallet detection sensor 11-1s that the heat treatment pallet 50 is absent, the heat treatment pallet 50 which has been carried in by the carrying-in roller conveyor 29 and on which the metallic material to be carburized is placed is loaded on the first-stage transport roller conveyor 14-1 in the first-stage carburizing furnace area I through the entrance with the door 16-1 opened by the carrying-in elevator 25, and is held at that first stop position 11-1a by the stopper. Subsequently, the door 16-1 is closed, and the carburization of the metallic material placed on the loaded heat treatment pallet 50 is started.
After the lapse of 10 minutes, which corresponds to the quenching cycle, subsequent to the loading of the heat treatment pallet 50 at the first stop position 11-1a in this first-stage carburizing zone 11-1, if it is detected by the pallet detection sensor 11-2s that the heat treatment pallet 50 is absent at the first stop position 11-2a in the second-stage carburizing zone 11-2, the heat treatment pallet 50 on which the ensuing metallic material to be carburized is placed is loaded on the second-stage transport roller conveyor 14-2 through the entrance with the door 16-2 opened by the carrying-in elevator 25, and is held at that first stop position 11-2a. The door 16-2 is then closed, and the carburization of the loaded metallic material is started.
Similarly, after the lapse of 10 minutes subsequent to the loading of the heat treatment pallet 50 in the second-stage carburizing zone 11-2, if it is detected by the pallet detection sensor 11-3s that the heat treatment pallet 50 is absent at the first stop position 11-3a in the third-stage carburizing zone 11-3, the heat treatment pallet 50 on which the metallic material to be carburized is placed is loaded on the third-stage transport roller conveyor 14-3 by the carrying-in elevator 25, and is held at that first stop position 11-3a. Further, after the lapse of 10 minutes subsequent to the loading of the heat treatment pallet 50 in the third-stage carburizing zone 11-3, if it is detected by the pallet detection sensor 11-4s that the heat treatment pallet 50 is absent at the first stop position 11-4a in the fourth-stage carburizing zone 11-4, the heat treatment pallet 50 on which the metallic material to be carburi zed is placed is loaded on the fourth-stage transport roller conveyor 14-4 by the carrying-in elevator 25, and is held at that first stop position 11-4a.
After 10 minutes subsequent to the sequential loading of the heat treatment pallets 50 at the respective first stop positions 11-1a to 11-4a in the first-stage carburizing zone 11-1 to the fourth-stage carburizing zone 11-4, i.e., after the lapse of 10 minutes subsequent to the loading of the heat treatment pallet 50 in the fourth-stage carburizing zone 11-4, the holding of the heat treatment pallet 50 at the first stop position 11-1a in the initially loaded first-stage carburizing furnace area I is released. This heat treatment pallet 50 is transported to the second stop position 11-1b by the first-stage transport roller conveyor 14-1, and is held at the second stop position 11-1b. Then, if the pallet detection sensor 11-1s detects that the heat treatment pallet 50 is absent at the first stop position 11-1a, the heat treatment pallet 50 is loaded on the first-stage transport roller conveyor 14-1 by the carrying-in elevator 25, and is held at the first stop position 11-1a.
After 10 minutes subsequent to the loading of the heat treatment pallet 50 at the first stop position 11-1a in the first-stage carburizing zone 11-1, the holding of the heat treatment pallet 50 being held at the first stop position 11-2a in the second-stage carburizing zone 11-2 is released. This heat treatment pallet 50 is transported to the second stop position 11-2b by the second-stage transport roller conveyor 14-2, and is held at the second stop position 11-2b. Then, if the pallet detection sensor 11-2s detects that the heat treatment pallet 50 is absent at the first stop position 11-2a, the heat treatment pallet 50 is loaded on the second-stage transport roller conveyor 14-2 by the carrying-in elevator 25, and is held at the first stop position 11-2a.
After 10 minutes subsequent to the loading of the heat treatment pallet 50 at the first stop position 11-2a in the second-stage carburizing zone 11-2, the holding of the heat treatment pallet 50 being held at the first stop position 11-3a in the third-stage carburizing zone 11-3 is released. This heat treatment pallet 50 is transported to the second stop position 11-3b by the third-stage transport roller conveyor 14-3, and is held at the second stop position 11-3b. Then, if the pallet detection sensor 11-3s detects that the heat treatment pallet 50 is absent at the first stop position 11-3a, the heat treatment pallet 50 is loaded on the third-stage transport roller conveyor 14-3 by the carrying-in elevator 25, and is held at the first stop position 11-3a.
After 10 minutes subsequent to the loading of the heat treatment pallet 50 at the first stop position 11-3a in the third-stage carburizing zone 11-3, the holding of the heat treatment pallet 50 being held at the first stop position 11-4a in the fourth-stage carburizing zone 11-4 is released. This heat treatment pallet 50 is transported to the second stop position 11-4b by the fourth-stage transport roller conveyor 14-4, and is held at the second stop position 11-4b. Then, if the pallet detection sensor 11-4s detects that the heat treatment pallet 50 is absent at the first stop position 11-4a, the heat treatment pallet 50 is loaded on the fourth-stage transport roller conveyor 14-4 by the carrying-in elevator 25, and is held at the first stop position 11-4a.
Similarly, while the heat treatment pallets 50 loaded sequentially at the first stop positions 11-1a to 11-4a by the first- to fourth-stage transport roller conveyors 14-1 to 14-4 are being intermittently transported, the presence or absence of the heat treatment pallets 50 is confirmed by the pallet detection sensors 11-1s to 11-4s, and the heat treatment pallets 50 are repeatedly loaded on the first- to fourth-stage transport roller conveyors 14-1 to 14-4 in the order of the carburizing furnace areas.
As a result, the heat treatment pallets 50 loaded on the first-stage transport roller conveyor 14-1 are intermittently transported sequentially among the respective stop positions including the first to sixth stop positions 11-1a to 11-1f in the first-stage carburizing zone 11-1. Then, during this transport, the metallic materials loaded on the heat treatment pallets 50 are carburized in the first-stage carburizing zone 11-1. Further, the metallic materials loaded on the heat treatment pallets 50 are intermittently moved sequentially among the first to third stop positions 12-1a to 12-1c in the first-stage diffusion zone 12-1 to diffuse carbon in the metallic materials, and are subsequently transported to the first-stage temperature lowering zone 13-1.
Here, each of the heat treatment pallets 50 is stopped and held for 40 minutes at the respective stop positions including the first to sixth stoppositions 11-1a to 11-1f in the first-stage carburizing zone 11-1 by the first-stage transport roller conveyor 14-1, thereby making it possible to ensure the carburizing cycle of 240 minutes in the first-stage carburizing zone 11-1. In addition, each of the heat treatment pallets 50 is stopped and held for 40 minutes at the respective stop positions including the first to third stop positions 12-1a to 12-1c in the first-stage diffusion zone 12-1, thereby making it possible to ensure the diffusion cycle of 120 minutes in the first-stage diffusion zone 12-1. It should be noted that the doors 16-1 to 16-4, 17-1 to 17-4, 18-1 to 18-4, and 19-1 to 19-4 are opened only during the passing of the heat treatment pallets 50, and are normally closed.
Similarly, the heat treatment pallets 50 loaded on the second- to fourth-stage transport roller conveyors 14-2 to 14-4 are intermittently transported sequentially among the respective stop positions from the first stop positions 11-2a to 11-4a to the sixth stop positions 11-2f to 11-4f in the second- to fourth-stage carburizing zones 11-2 to 11-4. Then, the metallic materials loaded on the heat treatment pallets 50 are carburized in the second- to fourth-stage carburizing zones 11-2 to 11-4. Further, the metallic materials loaded on the heat treatment pallets 50 are intermittently moved sequentially among the respective stop positions from the first stop positions 12-2a to 12-4a to the third stop positions 12-2c to 12-4c in the respective diffusion zones 12-2 to 12-4 to diffuse carbon in the metallic materials in the second- to fourth-stage diffusion zones 12-2 to 12-4, and are subsequently transported to the respective second- to fourth-stage temperature lowering zones 13-2 to 13-4, as shown in Fig. 3.
Here, as for each heat treatment pallet 50, the carburizing cycle of 240 minutes can be ensured in the carburizing zone 11, and the diffusion cycle of 120 minutes can be ensured in the diffusion zone 12.
Further, the heat treatment pallets 50 on which the carburized and diffused metallic materials are placed are intermittently carried in sequentially from the first- to fourth-stage diffusion zones 12-1 to 12-4 to the first- to fourth carrying-out roller conveyors 15-1 to 15-4 disposed in the first- to fourth-stage temperature lowering zones 13-1 to 13-4 in accordance with the order of the carburizing furnace areas at the interval of loading of the heat treatment pallets 50 into the first- to fourth-stage carburizing zones 11-1 to 11-4, i.e., at the interval of 10 minutes corresponding to the quenching cycle.
After the metallic material placed on the heat treatment pallet 50 carried into the first-stage temperature lowering zone 13-1 is annealed for 40 minutes in the first-stage temperature lowering zone 13-1, the heat treatment pallet 50 in the first-stage temperature lowering zone 13-1 is carried out by the first-stage carrying-out roller conveyor 15-1 onto the quenching elevator 27 which is on standby after having been raised to the position of the first-stage temperature lowering zone 13-1, as shown in Fig. 4. The quenching elevator 27 with the heat treatment pallet 50 placed thereon is lowered, as shown in Fig. 5, to immerse the heat treatment pallet 50 in the oil, i.e., the quenching medium, in the quenching zone 21, thereby subjecting the metallic material to oil quenching. Upon completion of the quenching transformation of the metallic material after the lapse of the preset immersing time, the heat treatment pallet 50 is raised from the quenching zone 21 by the quenching elevator 27, is transferred onto the carrying-out roller conveyor 30, and is carried out. This quenching cycle is set to 10 minutes.
In interlocked relation to the transfer, or after the transfer, of the heat treatment pallet 50 from this first-stage temperature lowering zone 13-1 onto the quenching elevator 27, the heat treatment pallets 50 being held at the first to sixth stop positions 11-1a to 11-1f in the first-stage carburizing zone 11-1 by the first-stage transport roller conveyor 14-1 are respectively transported sequentially to the respectively adjacent second stop position 11-1b to first stop position 12-1a in the first-stage diffusion zone 12-1, as shown in Fig. 6. Similarly, the heat treatment pallets 50 being held at the first to third stop positions 12-la to 12-1c in the first-stage diffusion zone 12-1 are respectively transported sequentially to the adjacent second stop position 12-1b to first-stage temperature lowering zone 13-1. In due course of time, if the pallet detection sensor 11-1s detects that the heat treatment pallet 50 is absent at the first stop position 11-1a, a new heat treatment pallet 50 with the metallic material placed thereon is loaded on the first-stage transport roller conveyor 14-1 by the carrying-in elevator 25, and is held at the first stop position 11-1a.
Next, after the metallic material placed on the heat treatment pallet 50 is annealed in the second-stage temperature lowering zone 13-2, the heat treatment pallet 50 in the second-stage temperature lowering zone 13-2 is carried out by the second-stage carrying-out roller conveyor 15-2 onto the quenching elevator 27 which is on standby at the position of the second-stage temperature lowering zone 13-2, as shown in Fig. 7. The quenching elevator 27 with the heat treatment pallet 50 placed thereon is lowered, as shown in Fig. 8, to immerse the heat treatment pallet 50 in the oil in the quenching zone 21, thereby subjecting the metallic material to oil quenching. After the lapse of the preset immersing time, the heat treatment pallet 50 is raised from the quenching zone 21 by the quenching elevator 27, is transferred onto the carrying-out roller conveyor 30, and is carried out.
At this time, in interlocked relation to the transfer, or after the transfer, of the heat treatment pallet 50 from this second-stage temperature lowering zone 13-2 onto the quenching elevator 27, the heat treatment pallets 50 being held at the first to sixth stop positions 11-2a to 11-2f in the second-stage carburizing zone 11-2 by the second-stage transport roller conveyor 14-2 are respectively transported sequentially to the respectively adjacent second stop position 11-2b to first stop position 12-2a in the second-stage diffusion zone 12-2, as shown in Fig. 8. In addition, the heat treatment pallets 50 being held at the first to third stop positions 12-2a to 12-2c in the second-stage diffusion zone 12-2 are respectively transported sequentially to the adjacent second stop position 12-2b to second-stage temperature lowering zone 13-2. In due course of time, if the pallet detection sensor 11-2s detects that the heat treatment pallet 50 is absent at the first stop position 11-2a, a new heat treatment pallet 50 with the metallic material placed thereon is loaded on the first-stage transport roller conveyor 14-2 by the carrying-in elevator 25, and is held at the first stop position 11-1a.
In the same way as described above, after the metallic material placed on the heat treatment pallet 50 is annealed in the third-stage temperature lowering zone 13-3, the heat treatment pallet 50 in the third-stage temperature lowering zone 13-3 is carried out by the third-stage carrying-out roller conveyor 15-3 onto the quenching elevator 27 which is on standby at the position of the third-stage temperature lowering zone 13-3, as shown in Fig. 9. Subsequently, the quenching elevator 27 with the heat treatment pallet 50 placed thereon is lowered to immerse the heat treatment pallet 50 in the oil in the quenching zone 21, thereby subjecting the metallic material to oil quenching. After the lapse of the preset immersing time, the heat treatment pallet 50 is raised from the quenching zone 21 by the quenching elevator 27, is transferred onto the carrying-out roller conveyor 30, and is carried out.
In interlocked relation to the transfer, or after the transfer, of the heat treatment pallet 50 from this third-stage temperature lowering zone 13-3 onto the quenching elevator 27, the heat treatment pallets 50 being held at the first to sixth stop positions 11-3a to 11-3f in the third-stage carburizing zone 11-3 and at the first to third stop positions 12-3a to 12-3c in the third-stage diffusion zone 12-3 by the third-stage transport roller conveyor 14-3 are respectively transported sequentially to the respectively adjacent second stop position 11-3b in the third-stage carburizing zone 11-3, third stop position 12-3c in the third-stage diffusion zone 12-3, and third-stage temperature lowering zone 13-3. In due course of time, if the pallet detection sensor 11-3s detects that the heat treatment pallet 50 is absent at the first stop position 11-3a, as shown in Fig. 10, a new heat treatment pallet 50 with the metallic material placed thereon is loaded on the third-stage transport roller conveyor 14-3 by the carrying-in elevator 25, and is held at the first stop position 11-3a.
Subsequently, after the metallic material placed on the heat treatment pallet 50 is annealed in the fourth-stage temperature lowering zone 13-4, the heat treatment pallet 50 in the fourth-stage temperature lowering zone 13-4 is carried out by the fourth-stage carrying-out roller conveyor 15-4 onto the quenching elevator 27 which is on standby at the position of the fourth-stage temperature lowering zone 13-4. Then, the quenching elevator 27 is lowered to immerse the heat treatment pallet 50 in the oil in the quenching zone 21, thereby subjecting the metallic material to oil quenching. After the lapse of the preset immersing time, the heat treatment pallet 50 is raised from the quenching zone 21 by the quenching elevator 27, is transferred onto the carrying-out roller conveyor 30, and is carried out.
In interlocked relation to the transfer, or after the transfer, of the heat treatment pallet 50 from this fourth-stage temperature lowering zone 13-4 onto the quenching elevator 27, the heat treatment pallets 50 being held at the first to sixth stop positions 11-4a to 11-4f in the fourth-stage carburizing zone 11-4 and at the first to third stop positions 12-4a to 12-4c in the fourth-stage diffusion zone 12-4 by the fourth-stage transport roller conveyor 14-4 are respectively transported sequentially to the respectively adjacent second stop position 11-4b in the fourth-stage carburizing zone 11-4, third stop position 12-4c in the fourth-stage diffusion zone 12-4, and fourth-stage temperature lowering zone 13-4. In due course of time, if the pallet detection sensor 11-4s detects that the heat treatment pallet 50 is absent at the first stop position 11-4a, a new heat treatment pallet 50 with the metallic material placed thereon is loaded on the fourth-stage transport roller conveyor 14-4 by the carrying-in elevator 25, and is held at the first stop position 11-4a.
Thus, the heat treatment pallets 50 with the metallic materials placed thereon are loaded sequentially into the first-to fourth-stage carburizing zones 11-1 to 11-4 of the multistage carburizing furnace 10 in the order of the carburizing furnace areas at the interval corresponding to the quenching cycle. While the heat treatment pallets 50 are moved through the first- to fourth-stage carburizing zones 11-1 to 11-4 and the first- to fourth-stage diffusion zones 12-1 to 12-4, carburizing and carbon diffusion are carried out continuously, and the heat treatment pallets 50 are sequentially transported to the first- to fourth-stage temperature lowering zones 13-1 to 13-4 where the metallic materials are annealed. Then, the heat treatment pallets 50 on which the metallic materials annealed in the first- to fourth-stage temperature lowering zones 13-1 to 13-4 are sequentially immersed in the oil in the quenching zone 21 by the quenching elevator 27 in accordance with the order of the carburizing furnace areas so as to quench the metallic materials, thereby continuously performing the series of carburizing and quenching treatment.
Accordingly, the interior of the carburizing zone 11 and the interior of the diffusion zone 12 of the continuous carburizing furnace 10 thus constructed in accordance with the embodiment are partitioned into the first- to fourth-stage carburizing zones 11-1 to 11-4 and the first- to fourth-stage diffusion zones 12-1 to 12-4 by the first- to fourth-stage transport roller conveyors 14-1 to 14-4 which are capable of ensuring the circulation of the air stream. Therefore, the flow of the air stream including the carburizing gas is not affected by the first- to fourth-stage transport roller conveyors 14-1 to 14-4, and the temperature and atmosphere of the entire carburizing zone 11 ranging from the first-stage carburizing zone 11-1 to the fourth-stage carburizing zone 11-4 can be controlled to satisfactory conditions. Similarly, the temperature and atmosphere of the entire diffusion zone 12 ranging from the first-stage diffusion zone 12-1 to the fourth-stage diffusion zone 12-4 can be controlled satisfactorily.
Through the interiors of the first- to fourth-stage carburizing zones 11-1 to 11-4 and the first- to fourth-stage diffusion zones 12-1 to 12-4 thus held in the satisfactory conditions, the heat treatment pallets 50 with the metallic materials placed thereon are transported in a state of being flatly loaded for each stage without being stacked in stages by the first- to fourth-stage transport roller conveyors 14-1 to 14-4. Therefore, the atmosphere in the first- to fourth-stage carburizing zones 11-1 to 11-4, such as the flow of the carburizing gas and the carburizing temperature, can be maintained to fixed levels. Hence, the variation in the amount of carbon infiltrating into the surface of the metallic material placed on each heat treatment pallet 50 in the first- to fourth-stage carburizing zones 11-1 to 11-4 is small. Also, the temperature and atmosphere inside the first- to fourth-stage diffusion zones 12-1 to 12-4 are maintained to fixed levels, and the variation in the amount of carbon dispersed into the interior of the metallic material placed on each heat treatment pallet 50 in the first- to fourth-stage diffusion zones 12-1 to 12-4 is small. Thus, satisfactory carburizing treatment can be concurrently obtained efficiently and continuously.
Furthermore, the heat treatment pallets 50 on which the metallic materials annealed in the first- to fourth-stage temperature lowering zones 13-1 to 13-4 are respectively placed thereon are charged into the oil as single heat treatment pallets 50 without being stacked in stages to effect quenching. Therefore, a time lag does not occur in the timing of charging into the oil, and a cooling difference ceases to occur among the metallic materials placed on the respective heat treatment pallets 50. Since there is no difference in the progress of the quenching transformation, the variation in the deformation entailed in quenching among the metallic materials is suppressed, so that the dimensional accuracy of the treated metallic materials becomes stable, thereby making it possible to ensure high-quality carburizing and quenching treatment.
In addition, the heat treatment pallets 50 with the metallic materials placed thereon are loaded sequentially into the first-to fourth-stage carburizing zones 11-1 to 11-4 and the first-to fourth-stage diffusion zones 12-1 to 12-4 in the preset order of the carburizing furnace areas at the interval corresponding to the quenching cycle. Carburizing treatment is performed concurrently in the first- to fourth-stage carburizing zones 11-1 to 11-4 and the first- to fourth-stage diffusion zones 12-1 to 12-4, and after the metallic materials are annealed in the first- to fourth-stage temperature lowering zones 13-1 to 13-4, quenching treatment can be performed without an interruption in a continuous quenching cycle. Thus, carburizing and quenching treatment excelling in productivity can be obtained.
Furthermore, the interior of the carburizing zone 11 and the interior of the diffusion zone 12 of the continuous carburizing furnace 10 are partitioned to form the first- to fourth-stage carburizing zones 11-1 to 11-4 and the first-to fourth-stage diffusion zones 12-1 to 12-4 by the first-to fourth-stage transport roller conveyors 14-1 to 14-4 to form the first-stage carburizing area I, the second-stage carburizing area II, the third-stage carburizing area III, and the fourth-stage carburizing area IV in multiple stages. Further, the carrying-in elevator 25 is disposed on the upstream side of the continuous carburizing furnace 10, and the quenching elevator 27 is disposed on the downstream side thereof. Consequently, it is possible to reduce the widthwise length of the multistage continuous carburizing furnace 1, and a reduction of its installation site can be expected.
In the above-described embodiment, the heat treatment pallets 50 are loaded from the carrying-in elevator 25 in the order of the first-stage carburizing zone 11-1 and the second-, third-, and fourth-stage carburizing zones 11-2, 11-3, and 11-4 in accordance with the preset order of the carburizing furnace areas, and the heat treatment pallets 50 are carried out onto the quenching elevator 27 in the order of the first-stage temperature lowering zone 13-1 and the second-, third-, and fourth-stage temperature lowering zones 13-2, 13-3, and 13-4 so as to perform quenching treatment sequentially. However, the heat treatment pallets 50 may be loaded into the first-to fourth-stage carburizing zones 11-1 to 11-4 in accordance with another order of the carburizing furnace areas. In this case, the order in which the heat treatment pallets 50 are carried out onto the quenching elevator 27 from the first-to fourth-stage temperature lowering zones 13-1 to 13-4 is also changed in correspondence with the loading order.
In addition, although in the above-described embodiment the first- to fourth-stage transporting apparatuses are formed by roller conveyors, the first- to fourth-stage transporting apparatuses may also be formed by other types of transporting apparatuses, such as tact conveyors, which allow the passage of the air steam.
Furthermore, although in the above-described embodiment a description has been given of the case in which the carburizing areas are formed by the four-stage carburizing areas I to IV in the first to fourth stages, the carburizing areas may be formed by two-stage, three-stage, or five-stage, or other plural-stage carburizing areas.
It will be apparent to those skilled in the art that various modifications and variations can be made to the described preferred embodiments of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover all modifications and variations of this invention consistent with the scope of the appended claims and their equivalents.

Claims

A continuous carburizing and quenching furnace comprising:
a multistage carburizing furnace including:
a carburizing zone;

a diffusion zone;

a temperature lowering zone, wherein the carburizing zone, the diffusion zone and the temperature lowering zone are sequentially arranged continuously from an upstream side to a downstream side of a furnace interior; and

a plurality of transporting apparatuses respectively continuing from the carburizing zone to the temperature lowering zone, wherein the plurality of transporting apparatuses partition the furnace interior into multiple-stage carburizing furnace areas respectively continuing from the carburizing zone to the temperature lowering zone;

a workpiece loading apparatus disposed on the upstream side of the multistage carburizing furnace, wherein heat treatment pallets, on which metallic materials to be carburized and quenched are respectively placed thereon, are sequentially loaded to the workpiece loading apparatus in accordance with a preset order of the carburizing furnace areas and at an interval corresponding to a quenching cycle; and

a quenching zone disposed on the downstream side of the multistage carburizing furnace, wherein the heat treatment pallets with carburized metallic materials thereon are sequentially immersed in a quenching medium in a continuous quenching cycle from the temperature lowering zone of each of the carburizing furnace areas in accordance with the preset order of the carburizing furnace areas.
The continuous carburizing and quenching furnace according to claim 1, wherein a carburizing treatment for effecting carburizing into surfaces of the metallic materials and carbon diffusion into interiors of the metallic materials is performed by sequentially transporting the metallic materials through the carburizing zone, the diffusion zone, and the temperature lowering zone,
a quenching treatment for effecting quenching is performed by immersing the carburized metallic materials in the quenching medium in the quenching zone, and

the carburizing treatment and the quenching treatment are continuously performed.
The continuous carburizing and quenching furnace according to any one of claims 1 and 2, wherein the transporting apparatuses which partition the furnace interior into the multiple-stage carburizing furnace areas allow a circulation of an air stream between adjacent ones of the carburizing furnace areas.
The continuous carburizing and quenching furnace according to any one of claims 1 to 3, wherein the transporting apparatuses are roller conveyors.
The continuous carburizing and quenching furnace according to any one of claims 1 to 4, further comprising:
a plurality of opening/closing partitioning means, respectively provided at an upstream end of each of the carburizing furnace areas, between the carburizing zone and the diffusion zone, and between the diffusion zone and the temperature lowering zone so as to partition into the respective zones.
The continuous carburizing and quenching furnace according to claim 5, wherein each of the plurality of opening/closing partitioning means is opened, when the heat treatment pallets with the metallic materials placed thereon pass therethrough, so as to allow a movement of the heat treatment pallets.
The continuous carburizing and quenching furnace according to any one of claims 1 to 6, further comprising:
a quenching elevator provided to the quenching zone and disposed on the downstream side of the multistage carburizing furnace,

wherein the quenching elevator immerses in the quenching medium the heat treatment pallet which is carried from the temperature lowering zone of each of the carburizing furnace areas in accordance with the preset order of the carburizing furnace areas and on which the carburized metallic material is placed, so as to quench the metallic material, and

the quenching elevator carries out the heat treatment pallet with the quenched metallic material placed thereon.
A continuous carburizing and quenching method for continuously performing carburizing treatment for effecting carburizing into surfaces of metallic materials and carbon diffusion into interiors of themetallicmaterials and quenching treatment for immersing the carburized metallic materials in a quenching medium, wherein the method is performed in a continuous carburizing and quenching furnace including a multistage carburizing furnace in which a carburizing zone, a diffusion zone, and a temperature lowering zone are sequentially arranged continuously from an upstream side to a downstream side of a furnace interior, and including a plurality of transporting apparatuses for partitioning the furnace interior into multiple-stage carburizing furnace areas respectively continuing from the carburizing zone to the temperature lowering zone, the method comprising:
sequentially loading heat treatment pallets on which the metallicmaterials tobe carburized and quenched are respectively placed, in accordance with a preset order of the carburizing furnace areas and at an interval corresponding to a quenching cycle, on an upstream side of a transporting apparatus in the carburizing furnace area;

sequentially transporting the metallic materials by the transporting apparatus through the carburizing zone, the diffusion zone, and the temperature lowering zone, so as to performe the carburizing treatment; and

sequentially immersing in the quenching medium the heat treatment pallets, with carburized metallic materials thereon, in a continuous quenching cycle from the temperature lowering zone of each of the carburizing furnace areas in accordance with the preset order of the carburizing furnace areas, so as to perform the quenching treatment.