Abstract:
The continuous carburizing furnace of this invention provides a furnace, a lift mechanism and a plurality of pushers. A furnace has a carburizing zone and a plurality of regions including a first region and a second region at the upstream side of said carburizing zone. The second region and the first region being disposed successively along a direction of conveyance of workpieces loaded upon a tray in this order. The lift mechanism lowers a tray in some region, among the plurality of regions, other than the region most to the upstream side in the direction of conveyance. A plurality of pushers includes a first pusher and a second pusher. The first pusher pushes a tray in said first region to said carburizing zone. The second pusher pushes a tray in said second region to said first region. A plurality of pushers are arranged the lower, the further towards the downstream side in said direction of conveyance is the position at which they push said trays.

Description:
CROSS REFERENCE 
       [0001]    This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2007-031780 filed in Japan on Feb. 13, 2007, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a continuous carburizing furnace which performs a plurality of processes, including a carburizing process, successively upon a workpiece, the subject for processing, which is being conveyed in an ambient atmosphere which includes a carburizing gas. 
         [0003]    With a continuous carburizing furnace, a heating zone, a carburizing zone, a diffusion zone, a cooling zone, and so on are provided within the furnace. A workpiece which has been loaded upon a tray is subjected to processing in each of these zones, while the tray is conveyed from a transport entrance of the furnace towards a removal aperture thereof. 
         [0004]    As methods for conveying the workpiece within the furnace, both the tray pusher method and the roller hearth method are available. With a continuous carburizing furnace which utilizes the tray pusher method, as for example disclosed in Japanese Laid-Open Patent Publication 2004-10945, a tray most to the upstream side is pushed by a pusher from the transport entrance towards the removal aperture, and thereby a plurality of trays are conveyed while being kept in mutual contact. On the other hand, with a continuous carburizing furnace which utilizes the roller hearth method, a large number of hearth rollers which are arranged across the floor of the furnace are rotationally driven, so that the trays are shifted over these hearth rollers. 
         [0005]    It is necessary to apply mutually different levels of heating energy to the heating zone and to the carburizing zone within the furnace. Furthermore, the carburizing zone receives an input of a carburizing gas. In order to enhance the product quality of the workpiece after carburizing processing, it is necessary to keep the temperature and the ambient atmosphere in each zone constant; and, to this end, it has been contemplated to selectively isolate the heating zone, in which the temperature differences with the previous and successive zones are most conspicuous, with intermediate doors which are opened and closed as required. 
         [0006]    With the roller hearth method, it is possible to adjust the gaps between the various trays in a simple and easy manner by controlling the rotation of the hearth rollers. Due to this, continuous carburizing furnaces which utilize the roller hearth method, and in which intermediate doors are installed between the heating zone and the carburizing zone, are nowadays widespread. 
         [0007]    However, with a continuous carburizing furnace which utilizes the roller hearth method, it is necessary to drive the large number of hearth rollers from the exterior, and a considerable amount of thermal energy is wasted by thermal diffusion from the side walls of the furnace in which the shafts of the hearth rollers are supported. Furthermore, it becomes necessary to oscillate the hearth rollers by rotating them forwards and backwards periodically in order to prevent deflection of the hearth rollers due to the loadings imposed upon them from the trays, so that the drive control of the rollers becomes troublesome. Moreover, the maintenance of this large number of hearth rollers also becomes complicated and troublesome. Yet further, the size of the furnace is increased due to the provision of the gaps between the plurality of trays. 
         [0008]    On the other hand, with a continuous carburizing furnace which utilizes the tray pusher method, it is possible to eliminate the above described shortcomings of the roller hearth method; and, by changing the stroke of the pusher, it is possible to provide a gap between the tray which is most towards the upstream side and the tray in front of it. However, a purge chamber which is provided with an intermediate door between itself and the heating zone is present at the transport entrance side of the furnace, and it is not possible to bring in the next tray to this purge chamber until the previous tray has been conveyed from the heating zone to the carburizing zone, so that the time period between bringing in trays becomes long. 
         [0009]    Moreover, by providing a plurality of pushers whose pushing angles in plan view are mutually orthogonal, and by changing the direction of conveyance of the trays within the furnace in a zigzag manner, it is possible to create a gap between a pair of trays, during their passage through the furnace. However, in this case, the shape of the furnace in plan view cannot be made to be linear, so that the area which the device occupies is increased in size. 
         [0010]    The objective of the present invention is to supply a continuous carburizing furnace which operates according to the tray pusher method, with which, while maintaining the shape in plan view of the conveyance path as being a straight line, the conveyance path for trays with workplaces loaded upon them is made to include a plurality of stages at the upstream side of the carburizing zone, and with which, by providing a plurality of pushers which push the trays at each stage, it is made possible to establish gaps between each of the trays being successively conveyed and the next one, in order to allow the operation of intermediate doors which are installed. 
       SUMMARY OF THE INVENTION 
       [0011]    The continuous carburizing furnace of this invention provides a furnace, a lift mechanism and a plurality of pushers. A furnace has a carburizing zone and a plurality of regions including a first region and a second region at the upstream side of said carburizing zone. The second region and the first region being disposed successively along a direction of conveyance of workpieces loaded upon a tray in this order. The lift mechanism lowers a tray in some region, among the plurality of regions, other than the region most to the upstream side in the direction of conveyance. A plurality of pushers includes a first pusher and a second pusher. The first pusher pushes a tray in said first region to said carburizing zone. The second pusher pushes a tray in said second region to said first region. A plurality of pushers are arranged the lower, the further towards the downstream side in said direction of conveyance is the position at which they push said trays. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a plan sectional view of a continuous carburizing furnace according to an embodiment of the present invention; 
           [0013]      FIG. 2  is a side sectional view of this continuous carburizing furnace; and 
           [0014]      FIGS. 3A through 3E  are schematic side cross sectional views for explanation of the operation of the principal portions of this continuous carburizing furnace. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    In the following, an embodiment of the present invention will be described in concrete terms with reference to the drawing.  FIG. 1  is a plane sectional view showing an example of a continuous carburizing furnace according to an embodiment of the present invention. And  FIG. 2  is a side sectional view of this continuous carburizing furnace. 
         [0016]    This continuous carburizing furnace  100  continuously performs, as one example, pre-processing, heating processing, carburizing processing, diffusion processing, cooling processing, and quenching processing upon workpieces which are loaded upon trays to during conveyance along a conveyance path which is shaped as a straight line in plan view. This continuous carburizing furnace  100  is a continuous carburizing furnace employing a hybrid method, and conveys trays which are loaded with a large number of workpieces through pre-processing, heating processing, carburizing processing, and diffusion processing by a tray pusher method, and then conveys them through cooling processing and quenching processing by a roller hearth method. And this continuous carburizing furnace  100  comprises a furnace main body  1 , a lift mechanism  2 , pushers  3  and  4 , intermediate doors  5  through  8 , an introduction door  9 , a roller hearth  10 , a quenching device  11 , and a removal device  12 . 
         [0017]    The furnace main body  1  is the “furnace” of the Claims, and, in plan view, is made as a rectangle of approximately constant width, extending along the direction of conveyance of trays  200 , as shown by an arrow sign X. A purge chamber  21 , a heating chamber  22 , a carburizing zone  23 , a diffusion zone  24 , and a cooling zone  25  are arranged in that order in the furnace main body  1 , along the direction of the arrow sign X. The purge chamber  21  and the heating chamber  22  correspond to the “plurality of regions” of the Claims. 
         [0018]    In this example, in the purge chamber  21 , heat at approximately 400° C. is applied to a workpiece which is loaded upon a tray  200  in an ambient atmosphere which has been isolated from the external air, and pre-processing such as degreasing processing and so on is performed thereupon. The purge chamber  21  is not to be considered as being limited by the above; any configuration will be acceptable, provided that it is one with which it is possible to replace the ambient atmosphere therein. 
         [0019]    In the heating chamber  22 , the workpiece is subjected to preliminary heat application at approximately 900° C. in an ambient atmosphere of a carrier gas such as RX gas or the like. 
         [0020]    In the carburizing zone  23 , a carrier gas such as RX gas or the like and an enrichment gas such as a hydrocarbon gas or the like are supplied, and carburizing processing is performed by applying heat to the workpiece at approximately 930° C. to 950° C. in an ambient atmosphere of carburizing gas. 
         [0021]    In the diffusion zone  24  diffusion processing is performed, in order to diffuse the carbon which has been loaded by the carburizing processing onto the surface of the workpiece, into the interior of the workpiece. 
         [0022]    In the cooling zone  25 , the workpiece is cooled and soaked to a temperature of approximately 850° C., which is the temperature before the start of quenching processing. 
         [0023]    The lift mechanism  2  is disposed in the heating chamber  22 , and comprises a lift stage  31 , which constitutes a portion of the floor surface of the heating chamber  22 , and a raising and lowering cylinder  32 . 
         [0024]    By raising and lowering the lift stage  31  with the raising and lowering cylinder  32  (which is hydraulically driven), this lift mechanism  2  displaces the conveyance path of the trays  200  downwards. The lift mechanism  2  could also raise and lower the lift stage  31  with a pneumatic drive system or a motor drive system. 
         [0025]    The floor surface of the purge chamber  21  is higher than the floor surfaces of the carburizing zone  23  and of subsequent zones. As compared with the conveyance path from an introduction stage  13  to the interior of the purge chamber  21 , the conveyance path for the trays  200  from the carburizing zone  23  onwards is lower, so that the conveyance path in the furnace main body  1  is structured in two stages, an upper stage and a lower stage. 
         [0026]    In the heating chamber  22 , the lift mechanism  2  lowers the trays  200 , which are to be displaced from the upper stage conveyance path for the trays  200  to the lower stage conveyance path. 
         [0027]    The pushers  3  and  4  are the “plurality of pushers” of the Claims. The pusher  3  is the “first pusher” of the Claims, and pushes the trays  200  in the direction of the arrow sign X from the introduction stage  13  to the purge chamber  21 , and from the purge chamber  21  to the heating chamber  22 . And the pusher  4  is the “second pusher” of the Claims, and pushes the trays  22  in the direction of the arrow sign X from the heating chamber  22  to the carburizing zone  23 . 
         [0028]    The intermediate doors  5 ˜ 8  are the “plurality of intermediate doors” of the Claims. The intermediate door  5  opens and closes between the purge chamber  21  and the heating chamber  22 . The intermediate door  6  opens and closes between the heating chamber  22  and the carburizing zone  23 . The intermediate door  7  opens and closes between the diffusion zone  24  and the cooling zone  25 . The intermediate door  8  opens and closes between the cooling zone  25  and the quenching device  11 . And the introduction door  9  opens and closes a transport entrance  21 A of the purge chamber  21 . 
         [0029]    Due to these intermediate doors  5  and  6 , it is possible selectively to mutually isolate the purge chamber  21  and the heating chamber  22 , and the heating chamber  22  and the carburizing zone  23 . It is accordingly made possible to maintain mutually different ambient atmospheres and temperatures in the purge chamber  21 , the heating chamber  22 , and the carburizing zone  23 . 
         [0030]    The roller hearth  10  comprises a plurality of hearth rollers  10 A, and a motor not shown in the figures which supplies rotatory power to this plurality of hearth rollers  10 A. The plurality of hearth rollers  10 A are arranged at approximately equal intervals so as to constitute a floor surface from a portion of the diffusion zone  24  on its downstream side via the cooling zone  25  to a portion of the quenching device  11  on its upstream side. Both end portions of each of these hearth rollers  10 A are passed through the side walls of the furnace main body  1  so as to be exposed to the exterior of the furnace main body  1 , and are supported rotatably by bearings not shown in the figures. And the rotation of the motor is transmitted to the one end portions of each of these hearth rollers  10 A. 
         [0031]    The quenching device  11  comprises an outlet door  41 , a lift mechanism  42  and an oil tank  43 . The outlet door  41  opens and closes between the quenching device  11  and the removal device  12 . The lift mechanism  42  comprises a lift stage  42 B which can be raised and lowered freely, and which comprises a plurality of rollers  42 A. A tray  200  which has been brought into the cooling zone  25  is mounted upon this lift stage  42 B. The oil tank  43  is disposed below the conveyance path of the tray  200 , and stores quenching oil. The lift mechanism  42  lowers the lift stage  42 B with a tray  200  mounted upon it, and dips the tray  200  into the oil tank  43 . Thereby a workpiece which is loaded upon the tray  200  is abruptly cooled by the quenching oil. 
         [0032]    The removal device  12  comprises a plurality of rollers  51  and a removal door  52 . This plurality of rollers  51  constitutes a conveyance surface within the removal device  12  for a tray  200 . And the removal door  52  controls the opening and closing of a removal outlet  12 A of this removal device  12 . 
         [0033]      FIGS. 3A through 3E  are schematic side cross sectional views for explanation of the operation of the principal portions of this continuous carburizing furnace according to an embodiment of the present invention. In the following, the explanation will only focus attention upon the operations related to the intermediate doors  5  and  6  and the introduction door  9  during the processing for bringing in the trays  200  to the purge chamber  21 , the heating chamber  22 , and the carburizing zone  23 ; and explanation of the operation of the other doors will be omitted. 
         [0034]    Before a tray  200  is brought in, the intermediate doors  5  through  8  and the introduction door  9  are in their closed positions, so that the conveyance path is interrupted at the positions where these doors are disposed. Furthermore, due to considerations of safety, the lift mechanism  2  is waiting in its position with the lift stage  31  lowered. 
         [0035]    After a first tray  200 A with a large number of workpieces loaded upon it has been mounted upon the introduction stage  13 , as shown in  FIG. 3A , the introduction door  9  is shifted to its open position so that the transport entrance  21 A is opened, and the tray  200 A is pushed in the direction of the arrow sign X by the pusher  3 . Thereby the tray  200 A is brought in from the introduction stage  13  to the purge chamber  21 . After the tray  200 A has been brought into the purge chamber  21 , the introduction door  9  is shifted to its closed position, so that the purge chamber  21  is closed. And degreasing processing is performed, in which the workpieces which are loaded upon the tray  200 A are heated up to a predetermined temperature within an ambient atmosphere which is isolated from the external atmosphere, so that oil and grease and so on adhering to their surfaces are burnt away. 
         [0036]    After this degreasing processing has been completed, as shown in  FIG. 3B , along with the lift mechanism  2  shifting the lift stage  31  to its upper position and stopping it there, the intermediate door  5  is shifted to its opened position so that the purge chamber  21  and the heating chamber  22  are communicated together, and then the tray  200 A is pushed by the pusher  3  in the direction of the arrow sign X. Thus the tray  200 A is brought in from the purge chamber  21  to the heating chamber  22 , and is mounted upon the lift stage  31 . After the tray  200 A has thus been brought within the heating chamber  22 , the intermediate door  5  is shifted to its closed position, and thereby the communication between the purge chamber  21  and the heating chamber  22  is interrupted. The workpieces which are loaded upon the tray  200 A are then subjected to pre-heating processing by the application of heat, so as to heat them up to a predetermined temperature within an ambient atmosphere of carrier gas. 
         [0037]    While this pre-heating processing is being performed upon the workpieces which are loaded upon the first tray  200 A, a second tray  200 B is mounted upon the introduction stage  13 , the introduction door  9  is shifted to its opened position so as to open up the transport entrance  21 A, and the tray  200 B is pushed by the pusher  3  in the direction of the arrow sign X. Thus, the tray  200 B is brought into the purge chamber  21  from the introduction stage  13 . After the tray  200 B has been brought into the purge chamber  21 , the introduction door  9  is shifted to its closed position, so that the purge chamber  21  is closed. And the workpieces which are loaded upon the tray  200 A are then subjected to degreasing processing by the application of heat at a predetermined temperature within an ambient atmosphere which is isolated from the external atmosphere. 
         [0038]    Until the pre-heating processing has been completed upon the workpieces which are loaded upon the tray  200 A, the lift stage  31  is kept lowered to its downward position, along with the tray  200 A, as shown in  FIG. 3C . 
         [0039]    When the pre-heating processing upon the workpieces which are loaded upon the tray  200 A has been completed, as shown in  FIG. 3D , the intermediate door  6  is shifted to its opened position so that the heating chamber  22  and the carburizing zone  23  are communicated together, and then the tray  200 A is pushed by the pusher  4  in the direction of the arrow sign X. Thus the tray  200 A is brought into the carburizing zone  23  from the heating chamber  22 . After the tray  200 A has been brought into the carburizing zone  23 , the intermediate door  6  is shifted to its closed position so that the heating chamber  22  and the carburizing zone  23  are isolated from one another. And then carburizing processing is performed upon the workpieces which are loaded upon the tray  200 , by application of heat so as to raise them to a predetermined temperature within an ambient atmosphere of carburizing gas. 
         [0040]    After having brought the tray  200 A into the carburizing zone  23 , the intermediate door  6  is shifted to its closed position (refer to  FIG. 3E ). By the above, one cycle of processing to bring a tray  200  into the carburizing zone  23  is completed. 
         [0041]    Subsequently, when the operations shown in  FIGS. 3B through 3D  are performed, and when the tray  200 B is brought into the carburizing zone  23  from the heating chamber  22 , then the tray  200 A is pushed by the tray  200 B and is shifted within the carburizing zone  23  in the direction of the arrow sign X. And, as the operations shown in  FIGS. 3B through 3E  are repeated, the plurality of trays  200  in the carburizing zone  23  and the diffusion zone  24  are shifted in the direction of the arrow sign X due to their state of being in mutual contact. 
         [0042]    By providing the lift mechanism  2  in the heating chamber  22 , the conveyance path for the trays  200  is structured in two stages, an upper stage and a lower stage, so that, on the upper stage conveyance path from the introduction stage  13  through the purge chamber  21  to the heating chamber  22 , the trays  200  are pushed by the upper stage pusher  3 , while, on the lower stage conveyance path from the heating chamber  22  to the carburizing zone  23 , the trays  200  are pushed by the lower stage pusher  4 . According to this structure, on the upstream side of the carburizing zone  23  in the conveyance path, between each pair of trays  200  which are being conveyed, it is possible to establish a suitable gap for installation of the intermediate door  6 . 
         [0043]    It is also possible to convey the plurality of trays  200  within the carburizing zone  23  in mutual contact, if the purge chamber  21  and the heating chamber  22  on the upstream side of the carburizing zone  23  in the conveyance path are arranged in a state in which it is possible to mutually isolate them by the intermediate doors  5  and  6 . And it is possible, while shortening the overall length of the furnace, and while keeping the area which it occupies compact, to perform pre-processing in the purge chamber, pre-heating processing in the heating chamber  22 , and carburizing processing upon a large number of workpieces in the carburizing zone, in a uniform manner. 
         [0044]    While, in the embodiment described above, the purge chamber  21  and the heating chamber  22  were disposed on the upstream side of the carburizing zone  23  in the conveyance path, the present invention is not limited to the case in which such processing is performed in the two regions; it would also be acceptable for these to be regions in which other types of processing are performed. Moreover, it would also be possible to implement the present invention in a similar manner, with three or more regions being provided. In this case, the same number of pushers as the number of regions would be arranged in upper and lower stages, lift mechanisms would be provided to each of the regions with the exception of the region most towards the upstream side, and the same number of stages of conveyance path as the number of regions would be provided as upper and lower stages. 
         [0045]    It should be understood that, in the above described explanation of an embodiment of the present invention, all of the features are shown by way of example, and should not be considered as being limitative of the present invention. The scope of the present invention is not to be defined by any of the features of the embodiment described above, but only by the scope of the appended Claims. Moreover, equivalents to elements in the Claims, and variations within their legitimate and proper scope, are also to be considered as being included within the range of the present invention.