CS255611B1 - Method of protection against contact corrosion of metal friction surfaces - Google Patents

Abstract

The method of protection against contact corrosion of metal friction surfaces consists in electrolytically applying a nickel-graphite layer with a thickness of 0.001 to 1.00 mm, a microhardness of 250 to 350 HVm and a graphite content of 2 to 4% by weight to at least one of the friction surfaces. At least one metal plate can be inserted between the third surfaces, onto which a nickel-graphite layer is electrolytically applied on both sides.

Description

The invention relates to a method of protection against contact corrosion of metal friction surfaces, in particular for blades of axial turbo-compressors.

The fatigue strength and durability of some types of blades of axial turbo compressors is significantly reduced by insufficient resistance of the hinges to the simultaneous effect of mechanical fatigue and contact corrosion. During cyclic loading of these blades by bending vibrations during resonant fatigue tests, alternating cyclic deformation with high amplitude occurs at stress-exposed points of the hinges. This is inevitably accompanied by repeated mutual shifts of the surface layers of the hinge and the groove for the test block hinge. In conjunction with the high specific pressure in the contact surface, the displacements lead to intensive contact corrosion of the hinge surface layer and thus to a reduction in local resistance to mechanical fatigue. At critical points of the hinge, continuing cyclic stress causes fatigue crack formation and propagation to the point where the hinge is depreciated due to insufficient residual bending stiffness due to the lack of residual bending stiffness.

In the fatigue test, the described case is associated with the loss of a part, usually a substantial part of the information we expect from the experiment. Both the scoop (often very expensive) and the costly test process are therefore largely devalued. However, breakage of the blade during operation of the turbocharger due to the fatigue fracture of the hinge would have even more serious consequences.

Contact corrosion can be slowed down to some extent by some technological modifications to the hinge seating surfaces, such as ballotination or electroplating by a layer of copper Cu and other metals. At high values of specific pressures and bending stresses in the hinge, combined with a high number of load oscillations, these measures prove to be ineffective and cannot prevent hinge fatigue fractures. The problem of contact corrosion in the clamping of test specimens during fatigue tests is not limited to blade hinges. It also appears in tests of bodies of simpler shapes, eg prismatic beams or beams of constant strength.

The disadvantages of the above-mentioned disadvantages are eliminated by the method of protection against contact corrosion of metal friction surfaces according to the invention, which consists in that a nickel-graphite layer with a thickness of 0.001 to 1.00 mm with 2-4% by weight is electrolytically applied to at least one friction surface. graphite, wherein the microhardness of the nickel-graphite layer is 250 to 350 HVm.

The nickel-graphite layer can be electrolytically applied either directly to the lateral abutment surfaces of, for example, the blade hinge or block groove or to the surfaces of the auxiliary plate-planks inserted between the blade hinge and the groove. Said method entails a number of advantages in practical application, since there is no difficulty in metallizing bulky bodies, including the protection of those parts of the surface that must be immersed in the plating bath but in which the nickel-graphite layer is undesirable. ?

The material, shape and dimensions of the plates can be selected in a wide range depending on the type of use and secondary properties desired.

The electrolytically formed layer is sufficiently strong so that it does not break even under long-term stress, even if the alternating tension of the hinge lies in the region of the fatigue limit of the material. The nickel-graphite layer permanently mechanically separates the surface of the two friction surfaces from one another.

The excellent self-lubricating properties of the nickel-graphite layer prevent seizure and contact corrosion. The life of the test specimens increased by an average of 10 times.

The proposed method of protection against contact corrosion has been tested in the fatigue tests of the blades with very good results. Detected excellent combination of nickel-graphite and 17CrNi2 chromium steels against seizing and contact corrosion at high specific pressures and mastering the technology of depositing homogeneous nickel-graphite layers on the surface of virtually all technically significant metallic materials except aluminum alloys together with temperature and corrosion resistance of said layer opens the possibility of using the indicated technical solution in a much wider field of applications, eg in:

- bearing housings operating at high pressures and temperatures

- damping elements (friction vibration dampers)

- other structural elements with sliding, friction or contact surfaces.

The proposed method is documented by the following examples.

Example 1

The turbo-compressor blade with a chord profile of 185 mm length with trapezoidal suspension was clamped in the groove of the electromagnetic vibrator block. In the fatigue test by alternating symmetrical bending in resonance mode, with the stress amplitude at the fatigue limit of the paddle steel used, after 5x10 trh oscillations, a fatigue crack occurred, caused by frictional corrosion in the bearing surface of the blade hinge. After plating the hinge and groove of the blade with a 0.03 mm nickel-graphite layer with a graphite content of 2.5 to 3.5% by weight. graphite, under the same test conditions g

lifetime extended to 50x10 oscillations.

Example 2

Because the galvanic treatment of the surface of large components is difficult (for example, large plating devices are required), another alternative approach has been proposed and successfully tested by inserting thin metal plates between the clamping groove surfaces and the blade hinge surfaces. of brass, bronze or steel of a thickness of 0,8 mm, coated on both sides with a galvanically deposited nickel-graphite layer (content 2,5 to 3,5% by weight of graphite) with a thickness of 0,05 mm. The fatigue test on an electromagnetic vibrator revealed an increase in blade resistance to friction corrosion from 5.10 ^ to 50.10 kmit.

Claims (2)

Method for protection against contact corrosion of metallic friction surfaces, characterized in that a nickel-graphite layer having a thickness of 0.001 to 1.00 mm, a microhardness of 250 to 350 HVm and a graphite content of 2 to 4% is electrolytically applied to at least one of the friction surfaces. weight. Method according to claim 1, characterized in that at least one metal plate is placed between the friction surfaces, on which a nickel-graphite layer is electrolytically applied on both sides.