Секция 3/Отраслевое машиностроение

Zharkevich O.M., Nurzhanova O.A.

Improving the quality of restoration of stocks of mechanical supports

 

Large volume of coal mining determines intensive exploitation of mechanical supports that tightens the requirements for their reliability and durability in Kazakhstan. About 75% of stocks of mechanical supports are repairable, but they were culled in major repairs. Therefore, appropriate alternative to the production of replacement stocks is re-using of worn-out stocks after repair.

Plasma spraying is often used to restore the stocks of mechanical supports.

The mathematical model of the technological parameters of plasma spraying is developed in program ANETR 5 to improve the quality of the restored stock and improve physical and mechanical properties of the coating and the choice of powder is justified.

The following criteria for optimization of plasma spraying are accepted: y1 is hardness of sprayed coating, y2 is tension and y3 is adhesion.

Ten factors were selected before drawing up of a matrix table of experiments: x1 - the content of propane in the plasma-forming gas,%; x2 - nickel powder,%; x3 – chromium powder,%;  x4 - silicon powder,%; x5 - speed of the plasma jet, m/s ; x6 - powder consumption, g/min; x7 - arc voltage, V; x8 - current strength, A; x9 - rotational speed parts, rev/min; x10 - spraying distance, mm, which vary in (max) and (min) levels.

The mathematical model is obtained according to the program ANETR 5 defines the relationship between hardness and shaping factors of it:

          (1)

tension and shaping factors of it:

      (2)

adhesion and shaping factors of it:

       (3)

The significance of each factor and the required number of them are determined with the help of clustering method.

It is experimentally proved, that the composition of the powder affects to  the physic-mechanical properties of sprayed coatings. Results of studies of physical and mechanical properties of the coating allowed to justify the following multi-component powder compositions: PG-19M-01, M4H1.0, PN70H15S3R2, PNH51015, PZHRV, etc. Technological regimes of plasma spraying have been developed for providing stocks of mechanical supports fatigue failure resistance and wear resistance at the level of new stocks.

Spraying metal layer, compensating wear, is fed with the powder composition witch fraction 72-100 mm in the ratio of nickel Ni = 60-80%; chromium Cr = 17% silicon Si = 3%; Ti = 2%, B2 = 3 %; aluminum Al = 5%, flow rate of carrier gas - 1,5 g/sec, flow rate of plasma gas (air + СзН8) - 1 g/sec, the current strength of the arc-200-280A, voltage-160-180V, spraying distance - 100 -120 mm, traverse the plasma torch – 3,5 - 4,0 mm/rev; diameter of  burner nozzle – 6 - 7 mm, spraying angle – 60 - 900, rotation frequency of product - 45-60 rev / min, flow rate of coating material - 4-5 kg / h, the thickness of the underlayer – 0,1 – 0,2 mm.

The series of experiments determined mechanical parameters of the coating (the wear rate, hardness, coating, adhesive strength) after spraying plasma coating according to the chosen regimes (Table 1).

 

Table 1 - Mechanical parameters of the plasma coating

Name of parameter

Value of the parameter

Wear rate, m /thousand m • h

0,05

Hardness of coating HV, MPa

5300

Adhesive strength, kg/cm2

14

Residual stresses, MPa

80

Alpha

It was established experimentally that the wear affected the stress concentration.

Hardness of the coating indicated that the high values ​​of heat input spraying of refractory components were provided. Residual stresses in the plasma coating were not significant compared with a yield that did not lead to cracking. Adhesive strength was satisfactory.

Summing up, we can conclude that the regimes of spraying, based on a mathematical model, and the powder composition may be recommended to improve the quality and durability of renewable stocks of mechanical supports.

 

References:

 

1. Kudinov V. Plasma coating. – M.: Nauka, 1977. - 192 p.

2. Barvinok V.A. Managing stress state and properties of plasma coatings. - M.: Mashinostroenie, 1990. - 384 p.

3.                      Lyubimov V.V., Voevodin A.A., Yerokhin A.L. Formal Order for Search of the Principle Structure there of Multilayer Coatings at Their Designing // Phisica status solidi, 145(1994). P. 565-574.

4.                      Savinkin V. Investigation of influence of the selected coating material on the physic-mechanical properties of parts, reduced plasma deposition // Bulletin of the Academy of Military Sciences. № 3 (28). - 2009. P.345-351.