Abstract:
The fastening torque control tool for a fastening device herein includes a base portion which is fixed onto a head portion of the fastening device in a way that restricts relative rotation around the device&#39;s axis. The tool has an operational portion which is integrally provided with the base portion on the same axis. The operational portion is fixed into a fastening instrument to turn the fastening device in a way that restricts relative rotation around the axis. The control tool also contains a separating portion for separating the operational portion from the base portion when a fastening torque, which is applied to the operational portion, reaches a predetermined level. The separating portion is formed between the base portion and the operational portion.

Description:
BACKGROUNDS OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fastening torque control tool of a fastening device for making constant the fastening torque by a fastening material, that is the joint strength, in fastening by use of the fastening material such as a bolt or a screw. 
     2. Description of the Related Art 
     As illustrated in FIG.  5  and FIG. 6, for example, in a case  3  consisting of a top box  1  and a bottom box  2  coming into contact with the top box  1 , the top box  1  is connected to the bottom box  2  by a plurality of bolts  4  which act as fastening devices and which extend through the top box  1 , in the conventional technique. 
     In these drawings, a concave portion  5  is formed on the top surface of the top box  1 , and a through hole  6  of a smaller diameter than that of the concave portion  5  is formed continued from the concave portion  5 . A tapped hole  7  positioned along the same axis as that of the through hole  6  is formed on the inside of the bottom box  2 . After bringing the bottom box  2  into contact with the top box  1 , the bolt  4  as the fastening device is inserted into the concave portion  5  and the through hole  6 . The bolt  4  is screwed down into the tapped hole  7  of the bottom box  2 , thereby connecting both boxes  1  and  2 . 
     The bolt  4 , that is, for example, a hexagon socket head cap screw, is screwed by a hexagonal wrench  8  as a fastening instrument. 
     This fastening method requires management of the fastening torque, in some cases, in order to prevent the occurrence of disadvantages such as looseness after fastening. Management of the fastening torque is also required to make the fastening forces of a plurality of fastening devices uniform. 
     The above-mentioned torque control is performed by using a tool provided with a torque control function, such as a torque wrench, in the manufacturing line or the assembly line of a factory. 
     Under present conditions, however, at the assembly time or maintenance time in the site, the above-mentioned tool provided with the torque control function is rarely used. The torque control cannot help relying on the sense of a worker, and the constant fastening torque cannot be always obtained. 
     Even if fastening can occur with the tool provided with the torque control function in the factory, there is a possibility that the fastening will be performed by a torque other than the established torque. Moreover, once it is fastened, it is impossible to confirm the fastening torque. 
     SUMMARY OF THE INVENTION 
     To solve the conventional problem, an object of the present invention is to provide a fastening torque control tool of a fastening device capable of confirming the fastening torque of the fastening device that has been fastened, regardless of whether the fastening occurs at the factory or at the site. 
     According to one aspect of the invention, a fastening torque control tool of a fastening device comprises 
     a base portion fixed into a head portion of the fastening device in a way of restricting relative rotation around its axis, and 
     an operational portion, integrally provided with the base portion on the same axis, which a fastening instrument to turn the fastening device is fixed into in a way of restricting relative rotation around the axis, 
     wherein a separating portion for separating the operational portion from the base portion when a fastening torque applied to the operational portion reaches a predetermined value is formed between the base portion and the operational portion. 
     In the preferred construction, the separating portion is formed by making thin a connected portion of the operational portion and the base portion as a thin portion. 
     In another preferred construction, the separating portion is formed by making thin a connected portion of the operational portion and the base portion as a thin portion, and 
     the thin portion is formed on the whole circumference of the operational portion. 
     In another preferred construction, the separating portion is formed by making thin a connected portion of the operational portion and the base portion as a thin portion, and 
     the thin portion is formed at a plurality of positions at predetermined intervals in the circumferential direction of the operational portion. 
     In another preferred construction, the base portion is formed so as to be attached to the head portion of the fastening device in a state of the operational portion being separated. 
     In another preferred construction, the base portion is formed so as to be attached to the head portion of the fastening device in a state of the operational portion being separated, and 
     the separating portion is formed by making thin a connected portion of the operational portion and the base portion as a thin portion. 
     In another preferred construction, the base portion is formed so as to be attached to the head portion of the fastening device in a state of the operational portion being separated, 
     the separating portion is formed by making thin a connected portion of the operational portion and the base portion as a thin portion, and 
     the thin portion is formed on the whole circumference of the operational portion. 
     In another preferred construction, the base portion is formed so as to be attached to the head of the fastening device by being fixed into the head of the fastening device in a pressed state, when the operational portion is separated. 
     In another preferred construction, the base portion is formed so as to be attached to the head of the fastening device by being fixed into the head of the fastening device in a pressed state, when the operational portion is separated, and 
     the separating portion is formed by making thin a connected portion of the operational portion and the base portion as a thin portion. 
     In another preferred construction, the base portion is formed so as to be attached to the head portion of the fastening device by an adhesive agent applied to a connected portion of the base portion with the head portion of the fastening device and, in a state of the operational portion being separated. 
     In another preferred construction, the base portion is provided with a marking function for marking the fastening device when the base portion is fixed into the fastening device. 
     In another preferred construction, the base portion is provided with a marking function for marking the fastening device when the base portion is fixed into the fastening device, and 
     the separating portion is formed by making thin a connected portion of the operational portion and the base portion as a thin portion. 
     In another preferred construction, the base portion is provided with a marking function for marking the fastening device when the base portion is fixed into the fastening device, and 
     the base portion is formed so as to be attached to the head portion of the fastening device in a state of the operational portion being separated. 
     In another preferred construction, the base portion is provided with a marking function for marking the fastening device when the base portion is fixed into the fastening device, and 
     the marking function is executed by applying colorant on the connected surface of the base portion with the fastening device and attaching the colorant to the head of the fastening device when the base portion is fixed into the head of the fastening device. 
     In another preferred construction, the head of the fastening device is a hexagonal pole, and a hexagonal socket to fix the head therein is formed on the base portion of the fastening torque control tool. 
     In another preferred construction, the head of the fastening device is a hexagonal pole, and a hexagonal socket to fix the head therein is formed on the base portion of the fastening torque control tool, and 
     the separating portion is formed by making thin a connected portion of the operational portion and the base portion as a thin portion. 
     In another preferred construction, the head of the fastening device is a hexagonal pole, and a hexagonal socket to fix the head therein is formed on the base portion of the fastening torque control tool, and 
     the base portion is formed so as to be attached to the head portion of the fastening device in a state of the operational portion being separated. 
     In another preferred construction, the head of the fastening device is a hexagonal pole, and a hexagonal socket to fix the head therein is formed on the base portion of the fastening torque control tool, and 
     the fastening instrument is a hexagonal wrench, and a hexagonal socket to fix the fastening instrument therein is formed on the operational portion of the fastening torque control tool. 
     In another preferred construction, the head of the fastening device is a hexagonal pole, and a hexagonal socket to fix the head therein is formed on the base portion of the fastening torque control tool, 
     the fastening instrument is a hexagonal wrench, and a hexagonal socket to fix the fastening instrument therein is formed on the operational portion of the fastening torque control tool, and 
     the separating portion is formed by making thin a connected portion of the operational portion and the base portion as a thin portion. 
     Also, the head of the fastening device is a hexagonal pole, and a hexagonal socket to fix the head therein is formed on the base portion of the fastening torque control tool, 
     the fastening instrument is a hexagonal wrench, and a hexagonal socket to fix the fastening instrument therein is formed on the operational portion of the fastening torque control tool, 
     the separating portion is formed by making thin a connected portion of the operational portion and the base portion as a thin portion, and 
     the base portion is formed so as to be attached to the head portion of the fastening device in a state of the operational portion being separated. 
     Other objects, features and advantages of the present invention will become clear from the detailed description given herebelow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiment of the invention, which, however, should not be taken to be limitative to the invention, but are for explanation and understanding only. 
     In the drawings: 
     FIG. 1 is an exploded perspective view showing the fastening structure of a case according to one embodiment of the present invention; 
     FIG. 2 is a cross-sectional view of an important portion showing the fastening structure of a case according to one embodiment of the present invention; 
     FIG. 3 is a cross-sectional view showing the fastening structure of a case in the state before fastening, with one portion omitted therefrom, according to one embodiment of the present invention; 
     FIG. 4 is a cross-sectional view showing the fastening structure of a case in the state after fastening, with one portion omitted therefrom, according to one embodiment of the present invention; 
     FIG. 5 is an exploded perspective view showing the fastening structure of the conventional case; 
     FIG. 6 is a cross-sectional view showing an important portion of the fastening structure shown in FIG.  5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment of the present invention will be discussed hereinafter in detail with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be obvious, however, to those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures are not shown in detail in order to prevent any unnecessary obscuring of the present invention. 
     As illustrated in FIG. 1, this embodiment will be described while applying the present invention to a case  12  consisting of a top box  10  and a bottom box  11  which is fastened to the top box  10  by using a plurality of hexagonal bolts  13  acting as fastening devices. 
     A plurality of concave portions  14 , receiving each head portion  13   a  of each bolt  13  therein, are formed on the top box  10  of the case  12 . As illustrated in FIG. 2, a through hole  15 , for inserting a screw portion  13   b  of the bolt  13  therein, is formed continued from the concave portions  14 . 
     A tapped hole  16 , for inserting the screw portion  13   b  of the bolt  13  after it is inserted into the through hole  15  of the top box  10 , is formed at a portion of the bottom box  11  corresponding to the concave portion  14  of the top box  10 . 
     A fastening torque control tool  17  related to the embodiment is installed on the head of the bolt  13 . 
     The fastening torque control tool  17  related to the embodiment comprises: a base portion  17   a  which is fixed to the head portion  13   a  of the bolt  13  in a way that restricts the relative rotation around the axis  27 ; and an operational portion  17   b  to which a fastening instrument  18  to turn the bolt  13  is fixed in a way that restricts the relative rotation around the axis  27 . A separating portion  17   c , for separating the operational portion  17   b  from the base portion  17   a  when the fastening torque applied to the operational portion  17   b  reaches a predetermined value, is formed between the base portion  17   a  and the operational portion  17   b , in a basic way (as shown in FIG.  4 ). 
     Describing the details of these portions, the fastening torque control tool  17  is made of a synthetic resin. A hexagonal socket  19  having the same shape as the sectional shape of the head portion  13   a  of the bolt  13  is formed on the base portion  17   a  thereof. The correspondence in the shape of the hexagonal socket  19  and the head portion  13   a  allows the hexagonal socket  19  to engage the head portion  13   a  of the bolt  13 . 
     In this embodiment, the hexagonal socket  19  is formed in the same shape as the head portion  13   a  but is a little smaller than the head portion  13   a ; when fixing the base portion  17   a  into the head portion  13   a , the base portion  17   a  is fixed to the head portion  13   a  in a pressed way. Therefore, when fixing the fastening torque control tool  17  onto the bolt  13 , it is stuck fast to the bolt  13 . 
     A hexagonal socket  20  for fixing the fastening instrument  18  is formed on the operational portion  17   b  when a hexagonal wrench is used as the fastening instrument  18  as illustrated in FIG. 1; this fixes the fastening instrument  18  into the operational portion  17   b  in a way that restricts the relative rotation of the operational portion  17   b.    
     Further, in this embodiment, the separating portion  17   c  is formed by making thin the continued portion from the base portion  17   a  and the operational portion  17   b ; the thin separating portion  17   c  acts as a stress-concentrating portion. 
     This thin separating portion  17   c  is formed either all around the circumference of the operational portion  17   b  or at several positions around the circumference of the operational portion  17   b  at some interval  26 . The shape of the thin separating portion  17   c  is properly established in consideration of: (a) the defined fastening torque necessary for separating the base portion  17   a  from the operational portion  17   b ; (b) the thickness of the operational portion  17   b ; and (c) the material of the fastening torque control tool  17 . 
     Namely, it should be a shape causing a breaking stress to the separating portion  17   c  when the fastening torque reaches the predetermined value, as mentioned above. 
     While, colorant  21  is applied to the inside of the hexagonal socket  19  of the base portion  17   a  into a predetermined thickness, as illustrated in FIG. 3, this colorant  21  is attached to the surface of the head portion  13   a  when fixing the base portion  17   a  to the head portion  13   a  of the bolt  13 , which works as a marking function in this embodiment. For example, even if the fastening torque control tool  17  is removed away after completing fastening of the bolt  13 , checking the color attached to the head portion  13   a  makes it possible to confirm the fastening has been performed by using the fastening torque control tool  17 . 
     The function of the embodiment, having the structure above described, will now be described. 
     After fixing the base portion  17   a  of the fastening torque control tool  17  into the head portion  13   a  of the bolt  13  to hold fast, the fastening instrument  18  is fixed into the hexagonal socket  20  of the operational portion  17   b  of the fastening torque control tool  17 . 
     Thus, the screw portion  13   b  of the bolt  13  is inserted into the tapped hole  16  of the bottom box  11  via the concave portion  14  and the through hole  15  on the top box  10 , and the bolt  13  is rotated by the fastening instrument  18  through the fastening torque control tool  17 , thereby screwing the bolt  13  to the bottom box  11 . 
     If this rotation of the bolt  13  is continued, the top box  10  will be connected to the bottom box  11  by a predetermined pressure and the fastening torque applied by the fastening instrument  18  will be increased. 
     When the fastening torque reaches a predetermined value, the stress caused in the separating portion  17   c  of the fastening torque control tool  17  reaches the breaking stress; as a result, the operational portion  17   b , into which the fastening instrument  18  is fixed, is separated from the base portion  17   a.    
     Here, as the base portion  17   a  is attached to the head portion  13   a  of the bolt  13 , the base portion  17   a  is left on the head portion  13   a  of the bolt  13  even after the operational portion  17   b  is separated. Therefore, by confirming the presence of the base portion  17   a , it is possible to confirm easily and surely that the fastening has been performed by the predetermined fastening torque at the fastening work time. 
     Further, in this embodiment, since the colorant  21  is applied to the base portion  17   a , even if the base portion  17   a  is removed for some reason, the marking caused by the colorant  21  left behind on the head portion  13   a  of the bolt  13  makes it possible to confirm that the fastening has been performed by the above-mentioned predetermined fastening torque. 
     As mentioned above, according to this embodiment, it is possible to perform the fastening by a constant fastening torque and confirm the fastening torque even after the fastening work. 
     Accordingly, whether the fastening work has been completed well or not can be determined even after the fastening work is completed. 
     Each shape and measure of each component as shown in this embodiment is only one example, and it may be changed depending on various requirements. 
     For example, although the base portion  17   a  is pressed onto the head portion  13   a  in this embodiment (as a means for attaching the base portion  17   a  to the head portion  13   a  of the bolt  13 ), an adhesive agent can be used to attach the base portion  17   a  to the head portion  13   a , thereby attaching both by using the adhesive power of the adhesive agent. 
     Although the description has been made, by way of example, with respect to a structure having a hexagonal socket  19  on the base portion  17   a  into which head portion  13   a  of the bolt  13  is fixed, it is also possible to use a protruding portion of a hexagonal pole, extending from the base portion  17   a , which is to be fixed into a hexagonal hole formed on the head cap screw; the shape of the socket in the head cap screw would be changed to correspond to the shape of the fastening device to be used. 
     This change in the shape is properly applied also to the operational portion  17   b  depending on the shape of the fastening instrument  18 . 
     As above-described, it is possible to perform the fastening with a constant fastening torque and to confirm the fastening torque even after the fastening work is completed. 
     Therefore, whether the fastening work has been done well or not can be verified even after the fastening work. 
     Although the invention has been illustrated and described with respect to an exemplary embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without departing from the spirit and scope of the present invention. Therefore, the present invention should not be understood as limited to the specific embodiment set out above, rather, it should be interpreted to include all possible embodiments which can be embodied within a scope encompassed by the features set out in the appended claims, and equivalents thereof.