RU2497652C1 - Method of hardening abrasive wheels - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to machine building and may be used for hardening abrasive wheels operated at increased speeds or in force grinding. Abrasive wheel is shaped and subjected to thermal processing. Residual compression strain is created by application of detonation coating on wheel side surfaces. Coating depth is selected to make compression compensate tensile stress originating in running wheel.

EFFECT: guaranteed structural strength.

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Description

The invention relates to a reinforcing technology for processing parts and specifically to methods for hardening abrasive wheels operating at high speeds or during power grinding.

A similar method is known [1], in which, to obtain circles of increased strength, a mixture of grinding grains with moisturizers, binders and fillers is prepared, a mixture and a reinforcing fiberglass mesh are placed in a mold, a metal sleeve is placed at the mounting hole of the grinding wheel, the grinding wheel is formed, it is removed from the mold and heat treated. At the same time, a second mixture of grinding grains with moisturizers, binders and fillers is prepared, in which needle-plate shapes pre-ordered by the shape of the grinding grains are used, having granularity lower than the first mixture and a predetermined controlled shape factor, and the second mixture is placed in the press a form with laying the first mixture and reinforcing fiberglass meshes, the second mixture being placed in the concentric zone at the landing hole of the grinding wheel, limited by its limiting diameter wear and tear.

The disadvantage of this method is the inability to obtain high degrees of internal compression stresses that compensate for tensile stresses arising in a rotating circle, which does not guarantee high structural strength of the abrasive wheels.

As a prototype, the method described in the patent [2] was selected in which the abrasive wheel is formed, subjected to heat treatment, and in the zone adjacent to the hole, a structure is denser than the structure of the rest of the circle, while creating a dense structure adjacent to the hole, take a metal mandrel, the coefficient of thermal expansion of the material of which is higher than the coefficient of thermal expansion of the material of the ligament of the circle, insert it into the hole of the circle, and heat treatment is carried out from the condition of tightness m I am waiting mandrel and the wall of the hole circle and creating the residual stress of compression.

The disadvantage of the prototype is the impossibility of creating residual compressive stresses on the periphery of the circle, and also that dangerous tensile circumferential stresses may appear in the abrasive wheel due to the wedging action of the metal mandrel.

The technical result of the present invention is to ensure guaranteed structural strength of abrasive wheels by creating residual compressive stresses that compensate for tensile stresses in a rotating circle.

The technical result is achieved by the fact that the circle is shaped, subjected to heat treatment and create residual compression stresses, while the residual compression stresses are obtained by applying a detonation coating to the side surfaces of the circle, and the coating thickness is selected so that the generated compression stresses compensate for tensile stresses arising in a rotating circle.

It is known that when the abrasive wheels rotate, radial σ _τ and circumferential σ _t stresses arise in them [3], which can be calculated by formulas (1) and (2), respectively.

where γ is the density of the material of the circle, kg / m ³ ; ω is the angular velocity of the circle, s ^-1 ; g is the acceleration of gravity, m / s ² ; µ is the Poisson's ratio; R _n - the outer radius of the grinding wheel, mm; r _in - the inner radius of the grinding wheel, mm; r is the current radius of the grinding wheel, mm

These stresses in conjunction with tensile residual stresses that may form during the manufacturing of abrasive wheels, lead to the risk of destruction of the abrasive wheels during operation.

When spraying detonation coatings in the base material, compressive residual stresses are created that arise as a result of crystallization and cooling (as well as thermal compression) of the coating layer formed by the flow of molten particles. In the coating itself, tensile stresses are created that can be calculated using the Kingeri formula [4]

where E is the modulus of elasticity of the coating material, MPa; α is the thermal coefficient of linear expansion, K ^-1 ; ΔT is the difference between the initial (melting point) and the final coating temperature, K.

Taking into account the difference in coating thicknesses h _n (mm) and the substrate h _к (mm), compression stresses equal to

Thus, using an abrasive wheel as a basis by applying a detonation coating on its side surfaces, full compensation of tensile circumferential and radial stresses is possible, provided that the coating thickness satisfies the condition

where h _b is the thickness of the coating applied to each side surface of the abrasive wheel, mm

In this case, guaranteed structural strength of the abrasive wheel will be ensured. In addition, the detonation coating will provide hardening of the side surfaces of the circle during grinding.

The method is implemented in the following steps:

- The abrasive wheel, after molding and heat treatment, is placed in the manipulator of the detonation unit.

- Set the manipulator to move according to a program that ensures the application of a detonation coating on the side surface of the abrasive wheel, with a layer thickness that meets condition (5).

- Turn the abrasive wheel in the manipulator, ensuring the application of a detonation coating on the other side surface of the abrasive wheel, with a layer thickness that meets the condition (5).

An example implementation of the method. Strengthened the abrasive wheel brand 25AF46L6V35. The outer diameter of the circle is 150 mm, the inner diameter is 32 mm, and the thickness is 20 mm. The rotation frequency of the circle is 4500 min ^-1 . The calculation of radial and circumferential stresses arising in a rotating circle (figure 1). Calculation of the required coating thickness (corundum) on the side surfaces of the abrasive wheel showed that the maximum coating thickness is 11.8 μm. Considering that the thickness of one layer of the sprayed coating spot is 13 μm (Fig.2), the sides of the circle were coated with a corundum coating 13 μm thick. This provided guaranteed stresses (circumferential and radial) of compression of the circle during its rotation.

Figure 1 shows the change in stress depending on the abrasive wheel: 1 - circumferential stress; 2 - radial stresses.

Figure 2 shows the change in the estimated coating thickness depending on the radius of the abrasive wheel.

Literature

1. RF patent No. 2349446. A method of manufacturing grinding wheels of increased strength on a bakelite bond / V. Korotkov Publ. 03/20/2009, bull. No. 8.

2. RF patent No. 2113341. The method of hardening abrasive wheels / Kravchenko B.A., Nosov N.V., Samarin Yu.P. Publ. 06/20/1998

3. Feodosiev V.I. Resistance of materials: textbook for technical colleges - 9th ed., Rev. - M .: Nauka, 1986 .-- 512 s.

4. Kingery U.D. Introduction to ceramics. - M .: Stroyizdat, 1969 .-- 456 p.

Claims (1)

A method of hardening abrasive wheels, including the formation of a circle, heat treatment and the creation of residual compressive stresses, characterized in that the residual compressive stresses are created by applying a detonation coating to the lateral surfaces of the circle, the thickness of which provides compensation for tensile stresses arising in the rotating circle.

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