The method of preparation of the surfaces of the parts

 

(57) Abstract:

Before coating thermal spraying the surface of the product is subjected to electro-processing tool for performing a reciprocating movement in a plane perpendicular to the plane of the work surface. The treatment is carried out by the instrument's profile, allowing you to contact the processing of 1/4 of the surface with periodic off the electric current. 2 C. p. F.-ly, 1 tab., 2 Il.

The invention relates to mechanical engineering, in particular to thermal methods of coating, for example, in the repair and restoration of parts of hardened steel.

The known method of surface preparation [1, 2] including shot blasting the surface.

This method allows you to provide the necessary roughness when machining parts with low hardness, but when machining hardened steel components necessary for high adhesion surface roughness is not ensured.

Closest to the proposed invention is a method of surface preparation of parts [3] mainly of hardened steel prior to coating deposition, IEP form a machining surface of the workpiece by the tool with the profile, corresponding to the profile of the recesses, and deletion at the site of contact of the tool and parts electric current to the local melting of the latter when the pressure of the tool 50 to 80 kgf/cm2and moving it along a helical line.

The disadvantages of the known method is relatively low adhesion due to the coincidence of the direction of the turns of the roll with the direction of the tangential stresses at the coating conditions of friction, seeking in the process to tear sprayed coating from the substrate, and reduction in fatigue strength of the workpiece due to the formation on its surface connected by a helix of stress concentrators.

The invention aims to improve the adhesion without significant reduction in fatigue strength.

The solution of this problem is achieved by the fact that the treatment is carried out by the instrument's profile, allowing you to contact the processing of 1/4 workpiece surface, and the shifting shall be reciprocating in a plane perpendicular to the treated surface with periodic off the electric current. The electric current turns off before moving the instrument wars with the prototype allows to make a conclusion, because the relief in the proposed method, the tool is formed with a profile that provides for brief contact with a multitude of local melting and forcing the metal at the points of contact of the tool with the surface of the part not related to each other, not by squeezing the tool moving relative to the workpiece along a helical line formed in the process craters will not be linked which is not reduced to a significant reduction in fatigue strength. The increase in the area of the substrate surface due to its processing tool, which increases the lengths of the guide and a generatrix line of the surface (Fig. 1) allows to increase the adhesion strength of the coating.

In Fig. 1 shows a diagram of the formation of the surface.

The surface details are not processed (Fig. 1A). The surface area to be processed is calculated by the formula:

S1= 2Rh1(1)

where S1surface area (m2);

R radius (m);

h1the length of the conventional forming surface (m).

Since 2R=l1, (2)

where l1the length of the conventional guide surface (m).

The expression (1) takes the form:

S1<

The surface area is calculated by the formula:

S2l2h2(4)

where l>2the length of the conventional guide surfaces treated by the method described in the prototype (m);

h2the length of the conventional forming surface processed by the method described in the prototype (m).

Since l2l1h2> h1,

the area of the surface of the substrate processed by the method described in the prototype, there will be more square untreated surface.

S2> S1< / BR>
The surface details are processed by the proposed method (Fig. 1B).

The area of the formed surface is calculated by the formula:

S3l3h3(5),

where S3the area of the surface of the substrate processed by the proposed method (m2);

l3the length of the conventional guide surfaces treated by the proposed method (m);

h3the length of the conventional forming surface processed by the proposed method (m).

Since l3> l2h3h2,

the area of the surface of the substrate processed by the proposed method, more surface area of the raw and processed by the method described in protot mm. The samples are tempered at the facility HDTV at a depth of 1.5-3.0 mm to hardness RC 56-62. Before deposition, the samples were divided into five groups. Their surfaces were subjected to various kinds of processing.

To generate the surface profile of the samples of the first group used the tool that represents the punch with a concave working surface. The length of the arc describing the working surface of the tool is equal to 1/4 of the circumference of the workpiece. The radius of the arc describing the working surface of the tool is equal to 1/2 the diameter of the surface of the workpiece. On the working surface of the tool, made of a refractory alloy VL-4 is cut tetradecene teeth with a pitch of 2.5 mm, the Radius of the top of the teeth is 0.8 mm

Tool performing reciprocating motion in the plane perpendicular to the plane of the workpiece, for one revolution of the workpiece in contact with it 4 times with a pressure of 50-80 kg/cm2. On the part and the tool was applied current 500-550 And when the voltage 2-6 C. In order to prevent the formation of an electric arc with the disengagement of the tool from the surface, before beginning its upward movement, the electric current is turned off.

The processing of the above-described method electric current is shut off immediately after contact of the tool with the workpiece and local melting of the surface. Next tool, continuing to move down, deformed cooling the metal, thereby procrea surface.

Surface treatment of samples of the third group was made by the method described in the prototype.

Surface samples of the fourth group were subjected to blast processing.

Samples of the fifth group were not treated.

Flame spraying parts of the first four groups was performed with the powder feeding PLUS-25 (GOST 21448-75), when the particle size of 5-100 μm and the coefficient of its use 70-80% of the Distance of the torch from the workpiece during the coating within 50-100 mm, the flow rate of plasma gas (argon) 2-C m3/PM

Samples of the fifth group did not nubilalis.

The deposited samples were polished up to a diameter 50,8 mm

The adhesion strength was determined by the force tangential shear segment size of 10 x 5 mm

On fatigue strength in torsion sample was tested on the installation of the MIND-4. For a database of tests taken 1,2x107loading cycles.

The results of the tests are presented in the table and shown in Fig. 2, which presents the adhesion strength of the coating and fatigue strength of specimens.

the second strength of the coating without significant reduction in fatigue strength of the part. It can be recommended to use the invention in mechanical engineering, in particular when restoring worn parts.

1. The way to prepare the surface before coating thermal spraying, including Electromechanical processing surface of the workpiece by the tool at a pressure of 50 to 80 kgf/cm by passing electric current at the site of contact to melting and movement of the tool, wherein the treatment is carried out by the instrument's profile, allowing you to contact the processing of 1/4 workpiece surface, and the shifting shall be reciprocating in a plane perpendicular to the processed surface with periodic off the electric current.

2. The method according to p. 1, characterized in that the electric current is disconnected before moving the instrument up.

3. The method according to p. 1, characterized in that the electric current is shut off after the contact of the tool with the surface.

 

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