RU2072911C1 - Limit wrench - Google Patents

Abstract

FIELD: mechanical engineering. SUBSTANCE: limit wrench has friction pair composed of stepped mandrel 2 and sleeve 5. Mandrel 2 is mounted in bearings 3,4. Sleeve 5 is supported by adjusting screw 6 and is locked against rotation relative to casing 1 by retainer 9. Spring 8 is mounted on mandrel 2 between mandrel bead and end of inner race of bearing 3. Torque is transmitted to working head 10 from casing 1 through friction pair 5,2. When predetermined extreme tightening torque is reached, sleeve 5 and casing 1 are rotated relative to fixed mandrel 2 and head 10. EFFECT: increased efficiency, wider operational capabilities, simplified construction and enhanced reliability in operation. 2 dwg

Description

 The invention relates to devices for calibrated tightening of threaded connections and can be used in various industries.

 Known limit key containing a cam disk with a working head, a swinging bridge, a flat spring, a micrometric screw pair. In the key, one end of the bridge interacts with the disk, and the other with the spring. The spring stiffness is controlled by moving along the handle of the spring support using a screw pair with a reading of the maximum torque on the scale.

 The disadvantage of this design is that between the working head of the cam disc and the axis of the handle there is a certain distance (shoulder). When a force is applied to the handle due to the presence of this shoulder, a lateral moment acts on the axis of the cam disc, tending to turn it to the side. The cam disk is mounted in the bearings and this lateral moment leads to an increase in friction in the bearings and distortion of the transmitted moment. That is, a high accuracy of the key is not ensured.

 There is a known limit torque clutch in which rotation from the shaft is transmitted to the sleeve, in which a working spring abuts against one end, setting the magnitude of the transmitted maximum torque, the second end of the spring rests on the control ring, which is fixedly mounted in the clutch housing by the antennae and nut. During the operation of the clutch, one end of the spring rotates along its support with sliding friction, which reduces the accuracy of the clutch.

 After the operator enters the screwdriver blade into the slot of the nipple, the transmitted torque increases and the ball bearings rise along the screw profile of the cam. Together with ball bearings, the sleeve also rises up, compressing the spring. In this case, the sleeve moves along the shaft and key with sliding friction, which also helps to reduce the accuracy of the coupling.

 Thus, despite the presence of nine rolling bearings in the clutch, it is not free from sliding friction, the presence of which significantly affects the accuracy of operation since the coefficient of sliding friction of steel over steel is 30.150 times greater than the coefficient of friction of rolling steel over steel.

 Of the known keys, the closest in technical essence to the claimed one is the limiting friction key containing a driven shank, body, polished steel disks between which ferrodo rings are placed. The friction force between the disks is created by a spring, the tension of which is regulated by screwing the handle onto the housing.

The disadvantages of this key include the fact that when working in its design, sliding friction occurs in several places (except for friction pairs):
between the mating diameters of the (outer) shank and (hole) of the handle from the radial reaction of the transmitted moment. Moreover, the shank with splines additionally increases the sliding friction;
between the mating diameters of the (outer) shank and (hole) of the housing from the radial reaction of the transmitted moment.

 Due to the presence of sliding friction during operation in a known manner, high accuracy of operation is not ensured.

 The aim of the invention is to improve the accuracy of operation of the key limit torque.

 This goal is achieved by the fact that in the known limit key containing a spring-loaded friction pair installed in the housing with an adjusting screw and a replaceable working head, according to the invention, the friction pair is made up of a step mandrel contacted by the ends installed in the rolling bearings and a cup stopping from turning in housing retainer and resting on the adjusting screw, and the spring is mounted on the mandrel completely between the inner ring of the bearing and the shoulder of the mandrel. In this design, sliding friction occurs in only one place: between the ends of the glass and the mandrel, thereby reducing the number of factors affecting the accuracy of the key, which distinguishes the claimed invention from the prototype.

 In FIG. 1 shows a general view of the proposed limit key, in FIG. 2 section A A in figure 1.

 The limit key contains a stepped cylindrical housing 1, a stepped mandrel 2 installed in the rolling bearings 3 and 4 of the housing 1 and pressed flat end to the flat end of the cup 5 resting on the adjusting screw 6, which is locked by a nut 7. The spring 8 mounted on the mandrel 2 abuts at the end of the inner ring of the rolling bearing 3 and the shoulder of the mandrel. The glass 5 is stopped from rotation relative to the housing 1 by the latch 9. In the axial hole and the groove of the step mandrel 2, a replaceable working head 10 is mounted, fixed by a screw 11.

где f_пр приведенный коэффициент трения;
f коэффициент трения скольжения;
Q усилие прижима;
d диаметр отверстия в оправке 1;
D диаметр торца оправки 1.The flat end face of the 1st mandrel, pressed against the end of the cup 5, forms a friction pair, the friction moment of which can be calculated by the formula [4]

where f _{pr the} reduced coefficient of friction;
f slip friction coefficient;
Q clamping force;
d the diameter of the holes in the mandrel 1;
D The diameter of the end of the mandrel 1.

 The limit key works as follows.

 When calibrating the key, the adjusting screw 6 is wrapped and moves the cup 5 and the stepped mandrel 2 in the axial direction. In this case, the spring 8 is compressed, and the clamping force of the flat end of the mandrel 2 to the end of the cup 5 increases. Upon reaching the specified limit torque, the adjusting screw 6 is locked with a nut and closed with a lid.

 When the screw (nut) is tightened with a limit wrench, the torque from the housing 1 is transmitted through a flat friction pair (end of the cup 5, end of the step mandrel 2) to the working head 10. When the specified tightening torque is reached, the cup 5 with the housing 1 are rotated relative to the stationary step mandrel 2 and working head 10. Together with the housing 1, the outer rings of the rolling bearings 3 and 4 are rotated relative to the stationary inner rings.

 Thus, the supply of the limit key with a flat friction pair using dry friction (for example, steel on steel) allows you to calculate the dimensions of the key according to a given value of the limiting moment. The use of rolling bearings in combination with the installation of a stepped mandrel in them with a spring resting on the end of the inner ring of the rolling bearing and the mandrel flange increases the accuracy of the key, because it completely eliminates sliding friction (except for the working friction pair. In addition, wear of the friction pair will not affect the key’s performance during long-term operation.

Claims (1)

 A limit key containing a spring-loaded friction pair with an adjusting screw installed in the housing and a replaceable working head, characterized in that the friction pair is composed of a step mandrel in contact with the ends installed in the rolling bearings, and a cup resting on the adjusting screw against rotation in the housing, and the spring is mounted on the mandrel ugly between the inner ring of the bearing and the shoulder of the mandrel.

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