¡¡¡¡In polysilicon, coal chemical industry, power plant ash, mud and boiler slag discharge and other material in the pipeline, valve sealing parts not only by the seal parts of sliding friction and wear, and bear high temperature and high hardness, high speed impact gas-solid two phase mixture, and the high pressure fluid caused by flash and cavitation, resulting in damage, increase the valve failure. Therefore, powder conveying harsh working conditions, such as abrasion resistance became an important valve performance appraisal indicators.
2 analysis
According to the conditions and mechanism of friction and wear a variety of different forms, common are abrasive wear, adhesive wear, fatigue wear and corrosion wear and tear, and the erosion wear, etc.
Characterization of the wear performance of the commonly used parametric wear volume and wear rate, wear, abrasion resistance and relative wear resistance, etc. Abrasive wear resistance is the basic requirement of surfaces must have high hardness (surface hardness should exceed the abrasive hardness), at the same time should also be in the working temperature has good oxidation resistance ability, the effective way to control or minimize wear and tear is increasing material hardness and abrasion resistance. Sintered tungsten carbide with high intensity, surface finish can also be very high, when paired with other materials used, the friction coefficient is smaller than steel, can significantly reduce the interface friction, effectively reduce operating torque.
Three characteristics
Overall sintered tungsten carbide is made from a mixture of tungsten and carbon heating, most of the tungsten carbide hardness is very high, the microhardness is second only to diamond, melting point 2870 ¡æ, boiling point 6000 ¡æ, relative density 15.63 (18 ¡æ), high temperature is not easy to decompose, good oxidation resistance. Usage survey on the spot, tungsten carbide in abrasive wear and erosion wear and abrasion of abrasion resistance than the tool steel, stainless steel, iron and brass contour 100 times, 2 ~ 3 times higher than steel rigidity, 4 ~ 6 times higher than the cast iron and brass and shock resistance are similar to those of hardened tool steel.
4 application
Such as coal gasification and polysilicon high temperature and high pressure, corrosive and slurry containing solid particles and powder, such as working conditions, the routine use of hard seal ball valve, venturi blackwater control valve, the control valve of pulverized coal, the disc of the valve and gate valve disc and seat respectively applied by spraying tungsten carbide seal. Because of the tungsten carbide coating thickness < 2 mm, < < 60 HRC, coating and substrate, hardness 1000 psi. Spraying usually under 10000 ¡æ high temperature conditions, operating conditions of construction. Valve life is difficult to ensure that a 10000 - cycle, cant meet the coal chemical pulp and polycrystalline powder system stable production requirements for a long period of time. Spraying intensity of tungsten carbide, on the other hand, mainly provided by the substrate material, when two kinds of material linear expansion coefficient is bigger, use is limited by temperature and is difficult to more than 450 ¡æ.
New hard seal ball valve (figure 1), venturi blackwater control valve (figure 2), pulverized coal control valve (figure 3), disc valve (figure 4) and slide valve disc and seat are made whole sintering tungsten carbide seal, valve performance was improved obviously.
Figure 1 new hard sealing ball valves
Figure 2 venturi blackwater control valve
(1) high hardness. > 80 HRC hardness, can withstand the coal-water slurry, coal powder, silicon powder and so on multiphase particles of high speed scouring.
(2) high temperature resistant. Can work for a long time in the high temperature of 750 ¡æ condition, strength, adhesion strength and thermal expansion is not subject to the limits of temperature, fully meet the coal chemical industry and so on high temperature condition.
(3) resistance to high pressure. Overall sintered tungsten carbide transverse rupture strength of 4000 mpa, is more than 10 times the strength of steel and conventional 25 mpa in under the condition of pressure levels of work for a long time.
(4) corrosion resistance. Overall sintered tungsten carbide chemical stability, even in the case of heating, insoluble in water. Dont work with hydrochloric acid and sulphuric acid, or even not be dissolved in aqua regia, enough to satisfy the coal chemical industry, etc. The special requirements of special industries on the corrosion performance.
(5) wear resistance. Integral sintered tungsten carbide characteristics of high hardness and high stability etc. To ensure the good wear resistance, seal materials meet the coal powder, organic silicon, etc (silicon powder grain hardness of 62 HRC) medium wear special requirements.
Figure 3 coal control valve
Figure 4 disc valve
(6) resistance to erosion. Conventional valve using sprayed tungsten carbide coating as sealing surface, the valve internals under serious erosion, usually under the working condition of 250 ¡æ, 1 months to present honeycomb, complete loss function. Using integral sintered tungsten carbide as control of a venturi blackwater control valve, the control valve of pulverized coal, under the temperature of 450 ¡æ (the rest of the working condition of the same) the service life of up to 12 months. Frequently open disk valve and gate valve switch number > 300000 times, completely satisfy the requirement of the coal chemical industry, etc. 8000 h long period running.
(7) high temperature performance flexible action. Sphere and valve seat with for whole sintering tungsten carbide, the linear expansion coefficients of conventional steel 1/3 ~ 1/2, effectively avoid the phenomenon of conventional high temperature card plug valve and ensure the high temperature and poor working conditions of their excellent performance.
(8) low friction. Using sintered tungsten carbide antifriction gaskets, not only prolong the service life of high temperature gaskets, given its low coefficient of friction, usually only the conventional matching material of 1/3 ~ 1/2, greatly reduce the friction between the two, reduces the valve operating torque.