RU2129937C1 - Process of mechanized plasma surfacing of parts - Google Patents

Abstract

FIELD: plasma surfacing of parts, manufacture of articles with coatings. SUBSTANCE: stable thermal conditions for formation of coat are created thanks to preliminary heating of surface of article by plasma arc in zone of first lateral surfacing roller. Heating is conducted to temperature of ultimate thermal saturation under specified parameters of surfacing ( thickness of coat, width and frequency of oscillations, width of surfacing roller and surface spacing ). Procedure for computation of temperature of ultimate thermal saturation, power of arc and duration of preliminary heating is established. Process provides for manufacture of quality coats with same depth of surfacing, composition and structure. EFFECT: improved efficiency of process. 2 dwg, 1 tbl

Description

 The technical field to which the invention relates. The invention relates to a coating technique for the purpose of hardening and restoration of parts.

 The prior art. Modes of plasma surfacing by an oscillating plasmatron are usually chosen without taking into account the thermal conditions of coating formation / M.G. Rosenberg, G.A. Pozdeev. Determination of the main parameters of plasma-powder surfacing. Welding Production, 1989, N12, p.52-53; Yu.F. Zotov, E.P. Gordienko. The condition for the surfacing continuity during the harmonic movement of the heating source. Welding Production, 1993, N1, pp. 14-15 /. The arc power is selected experimentally from the conditions for the formation of a transverse seam at the initial temperature of the product. However, during the process, the surface temperature along the front of the deposit increases, which leads to an increase in the size of the weld, the penetration depth and the degree of mixing of the coating materials and the base. The coating is heterogeneous in composition, structure and physico-mechanical properties. Sometimes, before surfacing, parts are preheated in a furnace or with an acetylene-oxygen flame / E.S. Komarchenkova et al. Structure and properties of anti-corrosion wear-resistant coatings made by plasma surfacing with powders. Welding Production, 1987, N2, p. 4-5; V.O. Muktepavel, H.E. Khatskin. Plasma surfacing of the sealing surface of the exhaust valve of a diesel engine. Welding Production, 1989, N4, p. 2 /. This technique reduces, but does not exclude, the instability of thermal conditions of coating formation.

 SUMMARY OF THE INVENTION It consists in creating stable thermal conditions for the formation of a coating during vibrational surfacing, which is ensured by the plasma arc heating of the product surface in the area of the first transverse weld inlet weld to the temperature of the maximum heat saturation for the specified surfacing parameters (coating thickness, width and frequency of oscillation, width of the surfacing bead and step of surfacing )

 Information confirming the possibility of carrying out the invention.

где g - эффективная тепловая мощность дуги;
Δt - - продолжительность действия дуги на элементарном участке;
R_i - радиус-вектор в подвижной системе координат, т.е. расстояние от центра элементарного участка до пятна дуги;
cρ - - удельная объемная теплоемкость материала наплавляемого изделия;
t - время действия дуги;
a - коэффициент температуропроводности.If we divide the trajectory of the oscillatory motion of the arc spot over the surface of the deposited part into elementary sections and consider them as instantaneous heat sources, then the temperature along the surfacing front can be determined by the total thermal effect of all elementary sections of the previously deposited transverse rollers

where g is the effective thermal power of the arc;
Δt - is the duration of the arc in the elementary section;
R _i is the radius vector in the moving coordinate system, i.e. the distance from the center of the elementary section to the arc spot;
cρ - is the specific volumetric heat capacity of the material of the deposited product;
t is the duration of the arc;
a is the coefficient of thermal diffusivity.

То же на периферии полосы в точке b:

где t_i - полупериод, продолжительность одного поперечного перемещения плазмотрона;
i - порядковый номер поперечного шва;
k - общее количество поперечных швов.For harmonic (sinusoidal) vibrations when dividing the transverse passage into four elementary sections (Fig. 1), the expression of the surface temperature in front of the plasma arc in the center of the deposited strip (point a) takes the form:

The same on the periphery of the strip at point b:

where t _i - half-life, the duration of one transverse movement of the plasma torch;
i - serial number of the transverse seam;
k is the total number of transverse seams.

In FIG. Figure 2 shows the dependence of the temperature before the arc in the middle (T _a ) and at the periphery (T _b ) of the deposited strip on the number of transverse passages during surfacing with harmonic oscillations of the plasma torch (oscillation width - 15 mm, surfacing step - 1.6 mm, frequency) oscillations - 30 min ^-1 , arc power - 2575 W).

At the beginning of the process, the temperature along the surfacing front increases rapidly with an increase in transverse passages, and then stabilizes under conditions of limiting heat saturation. Coating defects usually occur on an increasing portion of the heat saturation curve under unstable thermal conditions for the formation of a weld bead. An unstable surfacing section can be eliminated if the surface of the part in the zone of the first transverse roll is heated to the temperature of maximum heat saturation. The surfacing sequence includes:
1. The inclusion of the mechanism of transverse oscillations of the plasma torch.

 2. After heating the surface in the zone of the input transverse roller to a temperature corresponding to the limiting heat saturation of the process, the actual surfacing starts, the device for longitudinal movement of the product and powder supply are turned on.

 In order to implement the described process, it is necessary to determine the arc power and the temperature of the maximum heat saturation at the specified surfacing parameters (coating thickness, width and frequency of oscillations, width of the surfacing bead and step of surfacing), as well as the duration (number of oscillations or time) of the preheating.

то при плазменно-порошковой наплавке

где g' - эффективная тепловая мощность, необходимая для расплавления порошка;
g'' - эффективная тепловая мощность, необходимая для расплавления (подогрева) поверхности основы на ширину наплавляемого валика;
B - ширина наплавляемого валика;
V - скорость наплавки;
Т_пл - температура плавления материала основы;
Т₀ - начальная температура детали;
Т_ф - температура предельного теплонасыщения по фронту наплавки;
θ_ф - относительная температура предельного теплонасыщения.If accept
g = g '+ g'', (3)

in plasma powder surfacing

where g 'is the effective thermal power needed to melt the powder;
g '' is the effective thermal power required to melt (heat) the surface of the substrate to the width of the weld bead;
B is the width of the weld bead;
V is the deposition rate;
T _PL - the melting temperature of the base material;
T ₀ - the initial temperature of the part;
T _f - temperature limit heat saturation along the front of the surfacing;
θ _f is the relative temperature of the limiting heat saturation.

Calculation Sequence:
1) determination of θ _f from the limit value (1) or (2);
2) the definition of g '' by (6);
3) the definition of g according to (3);
4) the definition of T _f according to (5);
5) determination of the duration of preheating (the number of transverse passages) according to (1) or (2) with a surfacing step equal to zero.

 The table shows the printout on the PC display of the results of the calculation of the regime of plasma-powder surfacing with harmonic (sinusoidal) oscillations of the plasma torch. The first two lines are the specified surfacing parameters entered by the operator, the remaining parameters are calculated. The design mode provides not only stable formation of surfacing rollers and uniformity of coating, but also the highest thermal efficiency of surfacing at specified parameters.

Claims (1)

The method of mechanized plasma surfacing of parts, in which the process is carried out with transverse oscillations of the plasma torch, characterized in that the surfacing is carried out in the mode of maximum heat saturation, for which the surface of the part in the area of the first transverse roller is preheated by a plasma arc to a temperature T _{f of} maximum heat saturation, which is determined depending on operational parameters
T _f = f (v, B, T _pl , q ′, cρ, N),
where v is the velocity of the plasma torch;
B is the width of the weld bead;
T _PL - the melting temperature of the base or deposited material;
q 'is the effective thermal power required to melt the deposited powder;
cρ is the specific volumetric heat capacity of the base material;
N is the oscillation frequency of the plasma torch.

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