Abstract:
A less expensive cooler for a machine tool comprises a main spindle ( 3 ), a housing ( 1 ) rotatably supporting the main spindle ( 3 ) via bearing ( 2 ), and a tube ( 11 ) wound around the housing ( 1 ) for passing a cooling mist therethrough.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a cooler for a machine tool.  
           [0003]    2. Desription of the Art  
           [0004]    In conventional machine tools, a main spindle is rotatably supported by a housing via a bearing, so that heat generated by the rotation of the main spindle is conducted to the housing. Therefore, a cooler for cooling the housing is provided in such a machine tool. One example of such a cooler is the structure for cooling a spindle unit as shown in FIG. 4 which is disclosed in Japanese Unexamined Patent Publication No. 6-31585 (1994). The spindle unit includes a housing  31 , a spindle cylinder  32  fixed within the housing  31 , and a main spindle  33  rotatably supported in the housing  31  via a bearing unit  34  and an upper bearing (not shown). The cooling structure of the spindle unit includes a cooling liquid channel defined between a helical groove  35  formed in an outer peripheral surface of the main spindle  33  and a bearing inner cylinder  36  of the bearing unit  34 , and another cooling liquid channel defined between a helical groove  37  formed in an outer peripheral surface of the spindle cylinder  32  and the housing  31 . In FIG. 4, the spindle unit further includes a cooling liquid supply path  38 , a cooling liquid drain path  39 , a cooling liquid inlet port  40  and a cooling liquid outlet port  41 . In general, a cooling liquid is supplied to the respective cooling liquid channels by a cooling liquid supply unit which has an orifice for flow rate control, a sensor for temperature control and the like.  
           [0005]    However, a cooling liquid supply unit specifically designed for supplying the cooling liquid to the cooling liquid channels in the spindle unit cooling structure is quite expensive, thereby making the machine tool itself more expensive.  
           [0006]    In view of the foregoing, it is an object of the present invention to provide a less expensive cooler for a machine tool.  
         SUMMARY OF THE INVENTION  
         [0007]    In accordance with the present invention to achieve the aforesaid object, there is provided a cooler for a machine tool, which comprises a main spindle, a housing rotatably supporting the main spindle via a bearing, and a channel provided in association with the housing for passing a cooling mist therethrough.  
           [0008]    In the inventive machine tool cooler having the main spindle and the housing rotatably supporting the main spindle via the bearing, the channel for passing the cooling mist therethrough is in association with the housing. Therefore, the housing can be cooled by passing the cooling mist through the channel in association with the housing and taking heat away from the housing by evaporation of the cooling mist. In addition, the cooling mist can easily be generated with the use of a cooling liquid supply unit and a compressed air supply unit, both typically included in the machine tool. More specifically, a tank containing a cooling liquid, a lubricating liquid or a mixture of the cooling liquid and the lubricating liquid for cooling or lubricating a tool, and a pump for supplying the cooling liquid or the like from the tank to a cooling liquid injection nozzle typically are provided in the machine tool as the cooling liquid supply unit. In addition, an air compressor for supplying compressed air to eject the cooling liquid or the like from the cooling liquid injection nozzle typically is provided in the machine tool as the compressed air supply unit. Therefore, the generation of the cooling mist can easily be achieved by mixing the cooling liquid supplied from the cooling liquid supply unit with the compressed air supplied from the compressed air supply unit so as to produce the cooling liquid in mist form. By thus employing the cooling liquid supply unit and the compressed air supply unit provided in the machine tool, the need for providing a relatively expensive cooling liquid supply unit specifically designed for the cooling of the housing can be obviated which thereby reduces the cost of the machine tool.  
           [0009]    Where the channel comprises a tube helically wound around the housing in the inventive machine tool cooler, the channel can be formed from a less expensive tubular material.  
           [0010]    Where the channel is provided within the housing in the subject machine tool cooler, the housing can be cooled from its interior with a more advantageous cooling effect. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a sectional view illustrating a machine tool cooler according to one embodiment of the present invention;  
         [0012]    [0012]FIG. 2 is a sectional view illustrating a machine tool cooler according to another embodiment of the present invention;  
         [0013]    [0013]FIG. 3 is a sectional view illustrating a machine tool cooler according to further another embodiment of the present invention; and  
         [0014]    [0014]FIG. 4 is a sectional view illustrating a machine tool cooler according to the prior art. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    Embodiments of the present invention will hereinafter be described in detail with reference to the attached drawings.  
         [0016]    [0016]FIG. 1 is a sectional view illustrating a cooler for a machine tool in accordance with one embodiment of the present invention. In this embodiment, the machine tool is a numerically controlled (NC) lathe. In FIG. 1, a generally cylindrical housing  1  fixed to a headstock (not shown) has a center through-hole  1   a , and a pair of bearings  2  are fixed to longitudinally opposite portions of the inner periphery of the center through-hole  1   a . A generally cylindrical main spindle  3  within through-hole  1   a  is rotatably supported by the bearings  2 . A chuck (not shown) is provided at one end (a right end in FIG. 1 ) of the main spindle  3 . A pulley  4  is fixed around the other end portion (a left end portion in FIG. 1) of the main spindle  3 , and is coupled to a rotation shaft (not shown) of a motor via a belt  5 . A draw bar and the like (not shown) are provided in the center through-hole  3   a  of the main spindle  3 . In FIG. 1, an annular fixture  6  is fitted around the main spindle  3 .  
         [0017]    The machine tool includes a cooling liquid supply unit (not shown) including a tank containing a cooling water (cooling liquid) such as tap water and a pump for supplying the cooling water from the tank to a cooling water injection nozzle (not shown). The machine tool further includes a compressed air supply unit (not shown) including an air compressor for supplying compressed air to the cooling water injection nozzle. During machining, the cooling water and the compressed air are supplied from the cooling liquid supply unit and the compressed air supply unit, respectively, to the cooling water injection nozzle, so that the cooling water from the cooling water injection nozzle is sprayed over a machining part (including a machining surface of the tool and a machined surface of a workpiece).  
         [0018]    The housing  10  has a helical groove  10  formed in an outer peripheral surface thereof, and a tube  11  such as a flexible tube is helically wound around the housing  1  along the groove  10 . One end of the tube  11  is connected to a bifurcated connection tube  12  (one example of mist generating means), and the other end of the tube is open to the atmosphere. The bifurcated connection tube  12  has a confluent portion  13  connected to the one end of the tube  11 , and two branch portions  14 ,  15  branched from the confluent portion  13 . The branch portions  14  is connected to the cooling liquid supply unit via a hose or the like, and the branch portion  15  is connected to the compressed air supply unit via a hose or the like.  
         [0019]    When the cooling liquid supply unit and the compressed air supply unit are operated in the machining of a workpiece, cooling water is supplied from the cooling liquid supply unit to the cooling water injection nozzle and to the branch portion  14  of the bifurcated connection tube  12 , and compressed air is supplied from the compressed air supply unit to the cooling water injection nozzle and to the branch portion  15  of the bifurcated connection tube. Then, the cooling water is sprayed over the machining part from the cooling water injection nozzle. On the other hand, the cooling water and the compressed air respectively supplied to the branch portions  14  and  15  merge and mix with each other in the confluent portion  13 , so that the cooling water is disintegrated into minute water particles in a mist form. The resultant cooling mist flows into the tube  11  helically wound around the housing  1 . The water particles of the mist evaporate while passing through the tube  11  to cool the housing  1 , and discharge from the other end of the tube  11  into the atmosphere.  
         [0020]    In this embodiment, the housing  1  is cooled by passing the cooling mist through the tube  11  helically wound around the housing  1  and withdrawing heat from the housing by the evaporation of the cooling mist. In addition, the cooling mist may be generated by employing the cooling liquid supply unit and the compressed air supply unit already provided in the machine tool. Although the tube  11  is required, the cooler is inexpensive since there is no need to provide a cooling mist supply unit specifically designed for the cooling of the housing. Further, tap water can be used as the cooling water and, hence, even if the cooling mist passed through the tube  11  is discharged from the other end of the tube  11  into the atmosphere, there is no adverse influence on the environment. Furthermore the tube  11  has a simple construction with the other end thereof being open to the atmosphere.  
         [0021]    [0021]FIG. 2 is a sectional view illustrating a machine tool cooler according to another embodiment of the present invention. This embodiment differs from the embodiment shown in FIG. 1 in that the tube  11  is not wound around the housing  1  along the groove  10  formed in the outer peripheral surface of the housing  10 , but rather a cylindrical body  20  is fitted around the housing  1  in a liquid tight manner so as to close the circumferential open side of the groove  10 . Thus, a helical channel  21  is defined between the groove  10  and an inner peripheral surface of the cylindrical body  20 . One end of the channel  21  is connected to a bifurcated connection tube (mist generating means)  12  via a hose  22 , and the other end of the channel is open to the atmosphere. In this embodiment, other components are the same as in the embodiment of FIG. 1, and like components are denoted by like reference characters. This embodiment has similar functions and effects as the embodiment of FIG. 1.  
         [0022]    [0022]FIG. 3 is a sectional view illustrating a machine tool cooler according to a further embodiment of the present invention. This embodiment diffes from the embodiment shown in FIG. 1 in that a plurality of channels  25  (only one channel  25  is shown in FIG. 3) are within the housing  1 . One end of each of the channels  25  is connected to a bifurcated connection tube (mist generating means)  12  and the other end of each of the channels  25  is open to the atmosphere. Therefore, the tube  11  is not wound around the housing  1  along the groove  10 . In this embodiment, other components are the same as in the embodiment of FIG. 1, and like components are denoted by like reference characters. This embodiment has similar functions and effects as the embodiment of FIG. 1. However, the housing  1  can be cooled from its interior with a more advantageous cooling effect.  
         [0023]    In the embodiments described above, the groove  10  is formed in the outer peripheral surface of the housing  1 , but the formation of the groove  10  is not necessarily required. Further, any of various cooling liquids and lubricating liquids may be used alone or as a mixture instead of the cooling water in the aforesaid embodiments. In the embodiment shown in FIG. 3, the channels  25  may be helically formed in the housing  1 .  
         [0024]    Although the pulley  4  fixed around the other end portion of the outer periphery of the main spindle  3  is coupled to the rotation shaft of the motor via the belt  5  for driving the main spindle  3  in the embodiments described above, a motor incorporating the main spindle  3  may be employed to drive the main spindle.  
         [0025]    The inventive machine tool cooler is applicable not only to a numerically controlled (NC) lathe, but also to any of various other machine tools such as machining centers and grinding machines.  
         [0026]    In the machine tool cooler according to the present invention, the housing can be cooled by passing the cooling mist through the channel provided in association with the housing which removes heat from the housing by the evaporation of the cooling mist. In addition, the cooling mist can easily be generated with the use of a cooling liquid supply unit and a compressed air supply unit typically provided in the machine tool. More specifically, a tank containing a cooling liquid, a lubricating liquid or a mixture of the cooling liquid and the lubricating liquid for cooling or lubricating the tool and/or workpiece, and the pump for supplying the cooling liquid or the like from the tank to the cooling liquid injection nozzle typically are provided in the machine tool as the cooling liquid supply unit, and further an air compressor for supplying compressed air to eject the cooling liquid or the like from the cooling liquid injection nozzle typically is provided in the machine tool as the compressed air supply unit. Therefore, the generation of the cooling mist easily can be achieved by mixing the cooling liquid supplied from the cooling liquid supply unit with the compressed air supplied from the compressed air supply unit to produce the cooling liquid into a mist form. By thus employing the cooling liquid supply unit and the compressed air supply unit already provided in the machine tool, the need for providing a relatively expensive cooling liquid supply unit specifically designed for the cooling of the housing can be obviated thereby reducing the cost of the machine tool.  
         [0027]    Where the channel comprises a tube helically wound around the housing in the inventive machine tool cooler, the channel can be formed from an inexpensive tubular material.  
         [0028]    Where the channel is provided within the housing in the inventive machine tool cooler, the housing can be cooled from its interior with a more advantageous cooling effect.