RU2595175C2 - Method to strengthen cylindrical helical compression springs - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention can be used in production of springs of steel. Method includes operations of winding, hardening, tempering, grit blasting and pre-stressing of spring that is followed by cold-hardening of inner surface of springs using hardening device. Latter comprises three deforming rollers arranged relative to each other at an angle of 120°. Force-hardening of spring inner surface is created due to turn of each of deforming rollers on angle, the value of which depends on the preset radial force. Cold-hardening is performed at rotation of the spring at the rate of not more than 10 rpm.

EFFECT: higher fatigue strength and durability of helical springs is taking effect, reduced noise, vibration and drawing force in machining, higher period of resistance of the hardening device is taking effect too.

1 cl, 2 dwg

Description

The invention relates to methods for changing the physical structure of ferrous metals, namely their surface hardening by deformation by cold working, and can be used in the manufacture of steel springs.

The prior art method for increasing the fatigue strength of elastic elements - coil springs, torsion bars, leaf springs, used in the manufacture of these parts - surface treatment by a stream of shot, called bead-blasting [1, 2].

The application of this method for coil springs made of steel is provided by regulatory documents (GOST 13764-86, GOST 1452-2011). In this method, the spring is fed into the chamber along the rotating rotating shafts, where it is exposed to the flow of shots for several minutes (the flight speed of the pellets is 70-120 m / s, the diameter of the pellets is 0.8-1.2 mm). The fraction flow is formed in the shot blasting machine of the shot blasting machine [3, 4].

When shot blasting, under the influence of impacts of pellets, plastic deformation of the surface layers of the metal of the spring turns occurs - hardening to a depth of 0.1-0.4 mm. In this layer, hardness increases, residual compressive stresses are created, which generally complicates the nucleation of a fatigue crack during operation of the springs and increases their service life until fracture.

The disadvantages of the known method of hardening are its relatively high complexity and low efficiency. During axial loading, the stress springs arising in the material of the coil are unevenly distributed along the length and cross section - the layers on the outer and inner surfaces of the coil are most stressed. In this case, the stresses on the inner surface of the coil of the spring are greater than on the outer surface by 1.4–1.6 times [5].

The magnitude of this inequality depends on the design parameters of the spring - the magnitude of the curvature of the coil. An increased level of stresses on the inner surface of the coil of the spring leads to the fact that the fatigue crack originates on the inner surface of the coil. Therefore, in order to effectively strengthen the springs during shot blasting, the inner layers of the spring should be processed most intensively. This can be done only with springs having relatively small diameters of the spring and the rod from which it is wound, and a large inter-turn gap (more than 2–3 times the diameter of the rod). With these design parameters, the fraction flow reaches the inner surface of the coil of the spring and makes them riveted.

In springs having large diameters and a small inter-turn gap (less than or equal to the diameter of the bar), the fraction flow practically does not reach the inner surface of the coils and does not harden them. The specified type includes tension springs (there is no inter-turn clearance) and coil springs of railway carriages. For such springs, the efficiency of shot blasting is insignificant, since it neutralizes only existing defects on the outer surface of the coil, and destruction develops from its inner surface.

Closest to the claimed technical solution is a method of hardening the inner surface of a coil of a spring (RU 2462519, IPC C21D 9/02, C21D 7/06, B21F 35/00, published on 09.27.2012), namely, options for its implementation by pulling the mandrel and by the impact of the rollers on the coil of the spring under the action of centrifugal force [6].

In the first case, a mandrel is inserted inside the spring fixed on the lathe, and in the second case, a reinforcing head with rollers. When processing a door spring, rotation is set with a small number of revolutions (20-30 rpm), and in the second case, the reinforcing head receives rotation from an additional electric motor and the revolutions are selected depending on the mass of the shock elements (about 800-1000 rpm). After 2-3 seconds, the longitudinal feed of the mandrel (head) is turned on to process the inner surface of all the turns of the spring. After processing, the rotation stops, and the tool is removed from the spring.

The disadvantages of the method carried out in the first embodiment include the following:

- when pulling the mandrel, a small part of the inner surface of the turn is processed;

- there are significant traction when processing large-sized springs;

- the geometry of the coil changes, for example, flats appear on the inner surface of the coil.

The disadvantages of the method carried out in the second embodiment include increased noise, strong vibrations during processing, and relatively low resistance of the shock elements.

The technical problem to which the invention is directed is to increase the manufacturability of the hardening method, as well as to increase the fatigue strength and durability of coil compression coil springs made of steel.

This problem is solved due to the fact that the method of hardening cylindrical helical compression springs, including winding, hardening, tempering, shot peening and gouging, differs from the known ones in that at the final stage after gouging, the inner surface of the springs is hardened by rolling in the hardening device containing at least three deforming rollers located relative to each other at an angle of 120 °, while the force required to carry out the work of hardening the internal rhnosti spring, is provided by a rotation of each of the deforming rollers at an angle.

A positive technical result provided by the indicated combination of features is an increase in the fatigue strength and durability of coil cylindrical springs, as well as a decrease in noise, vibration, pulling forces during processing, an increase in the durability period of the deforming tool, which generally increases the adaptability of the hardening method.

The method is illustrated by drawings, where in FIG. 1 shows the workable spring, as well as the hardening device necessary for implementing the method, FIG. 2 - the processed spring, as well as the hardening device, left view.

The method is as follows.

The spring 1, which has undergone operations of winding, hardening, tempering, and gouging, is fixed in the clamping device 2, which is installed in the lathe chuck. The reinforcing device 3, containing at least three deforming rollers 4 mounted on the axes, is mounted on a support of a lathe. At the beginning of work, the reinforcing device is inserted into the spring to be processed, while the deforming rollers 4 are in an inoperative position: between the axis of each of the rollers and the axis of their rotation there is a certain eccentricity e. depends on the required value of the radial force P _RAD ). Then the spring begins to rotate with a small number of revolutions (up to 10 rpm), the longitudinal feed of the hardening device is provided automatically due to the angle of inclination of the helix of the generatrix of the spring (self-tightening). After processing the spring, the rotation is stopped and the reinforcing device is removed from the spring. After the described operation, the spring undergoes control and painting operations.

In the process of rolling in with deforming rollers, a hardened layer (a layer of material with increased mechanical characteristics) is created on the inner surface of the coil, and residual compression stresses arise.

An increase in the yield strength leads to an increase in the level of stresses causing the initiation of a fatigue crack on the inner surface of the coil, and the residual compressive stresses add up with tensile stresses arising under operational loads, reducing the latter. In addition, residual compressive stresses neutralize stress concentrators, which have a depth comparable to the propagation depth of residual compressive stresses. All this together has a strengthening effect - the level of permissible operating voltages and the service life of the springs increase.

Information sources

1. Luzgin N.P. Spring Manufacturing: A Textbook for Preparing Workers in Production. - 2nd ed., Revised. and add. - M .: Higher. School, 1980; Ostroumov V.P. The production of coil cylindrical springs - M.: Mechanical Engineering, 1970.

2. Odintsov L.G. Hardening and finishing of parts by surface plastic deformation. M .: Engineering, 1987.

3. GOST 13764-86. Cylindrical helical springs of compression and tension from steel of circular cross section. Classification. Enter 07/01/88. - M .: Standartinform, 2007.

4. GOST 1452-2011. Springs are cylindrical screw trolleys and shock-traction devices of rolling stock of railways. Technical conditions Enter 01/01/2012. - M .: Standartinform, 2011.

5. Ponomarev S.D., Andreeva L.E. Calculation of the elastic elements of machines and devices. - M.: Mechanical Engineering, 1980; GOST R 54326-2011. Spring suspension springs of railway rolling stock. Test methods for cyclic durability.

6. Pat. 2462519, Russian Federation, IPC C21D 9/02, C21D 7/06, B21F 35/00. The method of hardening cylindrical coil springs / Shavrin O.I .; applicant O.AND. Shavrin; patent holder SPC "Spring". No. 20111115786/02; declared 04/20/2011; publ. 09/27/2012, Bull. Number 27. 7 sec .; silt

Claims (1)

A method of hardening cylindrical compression helical springs, including winding the spring, hardening, tempering, shot blasting, covering and hardening the inner surface of the spring, characterized in that the hardening is carried out by means of a hardening device made in the form of three deforming rollers located at an angle of 120 ° relative to friend and with an eccentricity between the axis of the roller and the axis of its rotation, which is introduced into the work spring, the deforming rollers are brought into operation by turning angle, the value of which is determined by the specified value of the radial force hardening, and carry out the rotation of the spring with a number of revolutions per minute of not more than 10 until hardening, after which the rotation of the processed spring is stopped and the hardening device is output.

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