1、NEW DESIGN OF MACHINE WRENCH FOR DRILLING AND DRIVING PIPESAt the All-Union Research Institute of Petroleum Machinery investigations were carried out revealing the regularities of the transmission of torque by machine wrenches based on different schemes. It was thereby established that the clamping
2、forces of the jaws exerted by the machine wrench at torques of 30-40 kNm suffice for transmitting much higher torques (80 kNm). In connection with that it therefore becomes possible to reduce the weight of the wrenches and increase their reliability by reducing the intensity of the clamping of the s
3、panner jaws on the pipes in proportion to the increase of torque. Of course, at the initial stage of loading a clamping force has to be ensured that makes slippage of the wrench impossible. However, machine wrenches of traditional design do not ensure the necessary regularity of the change of forces
4、 in the gripping links of the wrench. The characteristics of the intensifying mechanisms of wrenches based on different schemes are presented in i.It should be borne in mind that contact of the wrench with the pipe occurs at large values of the angles of rotation of the lever. Then, as the drawing f
5、orce on the lever of the wrench increases, the angle becomes smaller, i.e., the process of tightening the thread proceeds from right to left (see Fig. i).The most efficient combination of intensifying mechanisms can be obtained in wrenches with link gear and hinged mechanism. When the pipe is grippe
6、d first, the link mechanism acts (curve i); its zone of action is limited by the size of the slit in the lever. Then comes the transition to operation by the hinged four-link mechanism (curve 2) ensuring the highest coefficients of intensification. When the end face of the lever comes up against the
7、 final gripping link, intensification proceeds by the scheme of the crank and connecting rod mechanism (curve 4) with a connecting rod of variable length. Thus, in the case under consideration, tightening of the wrench links on the pipe begins at an intensification coefficient i = 18-20, which incre
8、ases to i = 42-45, and ends with i = 12-13.With wrenches with hinged scheme the process of tightening ends with the coefficient of intensification i 25 (curves 2, 3). This also explains why these wrenches weigh 20%2 more than wrenches with link gear and hinged mechanism.Another substantial advantage
9、 of the link gear and hinged wrench should be mentioned: the wider range of working angles of rotation of the lever: -15 e 30 .For wrenches with the hinged scheme -5 18 because of the unreliable gripping with i 18-20 at the onset of the process and the better operation of such wrenches by the scheme
10、 of the crank and connecting rod mechanism (curve3).The results of our investigations were made the basis for working out the multihinge machine wrench KMB 108-2112 for drilling pipes with torque limiter 3. The special feature of the design of these wrenches consists in the reduction of the coeffici
11、ent of intensification to one-half or one-third when the process of tightening the wrench on the pipe is concluded; this is the result of a braking force being applied to the end face of the lever by means of a special torque limiter.The wrench operates on the link gear and hinge mechanism scheme. T
12、he torque limiter, a part with a groove of wedge-shaped section, is hinged to the drawing link of the gripping part of the wrench. On the end face of the lever there is a rack with the same section as the groove of the torque limiter.The wrench begins to operate by the link gear scheme; when the mot
13、ion is limited in the slide groove, it operates by the scheme of the hinged four-link mechanism, and when approximately half the maximal drawing force is attained, it operates by a scheme where the rack of the lever fits tightly into the groove of the torque limiter.Thanks to the effective braking o
14、f the wrench lever at the last stage, it forms with the drawing link of the gripping part a two-armed lever with the ratio of the arms approximately equal to three, which corresponds to the coefficient of intensification of the fifth scheme (see Fig. i). Thus in the wrench KMB 108-212 a rational com
15、bination of the operating regimes was effected: with large intensification (i _ 45) at the beginning of the process with small drawing loads on the lever (to attain reliable cohesion between the wrench and the pipe) and with considerable reduction of the intensification when high drawing loads are a
16、ttained (to prevent overloading of the wrench). Strain-gauge measurements showed that in that case the maximal stresses in the links of the wrench are reduced by one third to one half.A prototype of the wrench KMB 108-212, calculated for a nominal torque of 80 kN was tested on a test bench of the Azerbaidzhan Institute of Petroleum Machinery with a torque of 207.5 kN-m. The efficiency of the wrench was not impaired in any way. In 1985 series
