With the development of the lost foam casting, people pay more attention to the lost foam casting. It is reported that the refractory material is the aggregate composition of the lost foam coating, a lot of variety of refractory materials, usually choose the following five:
The main components of zircon powder are ZrO2 and SiO2, namely, the zirconium silicate. Its high degree of fire resistance, is now used for lost foam casting the best one of the anti sand. Cast steel castings and large cast iron parts, the use of such refractory materials, can reduce the workload of the cleaning of the casting, to obtain a smooth surface of the castings.
The main component of quartz powder is SiO2. Because the quartz powder has different crystal form transformation under different temperature conditions, the volume change of the quartz powder is changed, thereby reducing the use value of the quartz powder. Generally used to cast columns of cast iron and aluminum, copper and other non-ferrous metal parts. The EPC is mainly used in small, so the common application of quartz powder.
Alumina is corundum powder, the main component is Al2O3. It is also a kind of excellent performance of refractory materials, can be used to cast steel castings and large cast iron parts.
Graphite powder is one of the refractory materials used in the production of cast iron. It has a high degree of fire resistance, but it is easy to be oxidized. Its thermal expansion coefficient is very low, generally within 50 x 10-7.
Kyanite refractoriness at 1800 degrees, and kyanite in high temperature 1100-1450 degree gradually transformed into mullite, mullite 1800 is still stable, 1810 degrees is decomposed into corundum. Kyanite has relatively low price, is the ideal substitute for mineral corundum materials.
Various mechanical and engineering structures are composed of a number of components. These components work to bear the role of the force, in order to ensure that the components in the working conditions and the use of life during the normal work, to meet the following requirements:
1. Have enough strength
It is a prerequisite for the normal operation of the component to ensure that the component does not occur under the external force, so the strength of the component is the ability to resist the damage under the action of external forces.
2. Have enough stiffness
The deformation caused by the member under the external force should be within the allowable limit. The capacity of the member to resist deformation under the action of external force, that is, the stiffness of the member.
3. Have enough stability
Some slender members (or thin-walled members) in the axial pressure to reach a certain value, will lose the original balance of the form and the loss of work ability, this phenomenon is known as instability. Stability refers to the ability of the component to maintain the balance of the original form.
The strength, stiffness and stability of the components are related to the mechanical properties of the materials used, and the mechanical properties of the materials must be determined by experiments. In addition, some practical engineering problems can not be solved by theoretical analysis, which must depend on the experimental methods.
The actual engineering structure in many load-bearing components such as bridges, automobile transmission shaft, the beam and column, the length of the size is far greater than the cross-sectional dimensions, this kind of component in the study of mechanics of materials, often referred to as a bar, all the centroid of cross section of the rod connecting line, called the axis for the bar, if the axis is a straight line, it is called straight rod; axis curve is called curved bar. Rod shape and size of all cross section are the same as with rod; different called variable cross-section bar. The mechanics of materials research uniform bar.
EPC coating is the role of support and protection to prevent infiltration of metal foam model, sand and sand, absorption and decomposition products and make the cavity formation and decomposition of gas through the coating, maintain the integrity of the foam model after evaporation, and keep the liquid metal heat will not soon be distributed. Therefore the use of EPC coating can reduce the surface roughness of EPC casting, to ensure the accuracy of the castings, reduce or prevent the casting sand, sand holes, porosity, permeability, cold insulation, metal casting, no carbon deposition defects. So the EPC coatings should have sufficient refractoriness, certain mechanical strength, proper insulation and thermal conductivity, suitable permeability and absorption liquid decomposition products, smooth surface, and not enough brushing performance and foam model of chemical reaction etc..
Function analysis of lost foam casting coating
Casting coating can prevent the penetration and thermochemical sticky sand, formation of castings improve the stiffness of EPC foam model, prevent buried type deformation, contribute to the decomposition of gas foam pattern heat rapid discharge effect, then disappear why EPC coating brought together so many functions, we will analysis from the following six aspects.
Lost foam casting coatings with these six characteristics
1. High strength and stiffness to prevent deformation and damage to the dry sand;
2. High refractory performance to prevent the casting of the casting surface sticky sand;
3. Excellent permeability, can be quickly derived from the appearance of gasification products;
4. Strong adhesion to prevent the production process of coating cracking or even off;
5. Good coating and hanging, can be used to facilitate the use of a certain thickness of the coating;
6. Good sintering and peel off, that is, after casting, forming the coating shell which is easy to peel off automatically, so as to obtain the surface finish.
Fan impeller wear and abrasive composition, particle size, concentration, shape, impact velocity, impact angle, gas chemical composition, properties, temperature and humidity and other factors. And the flow of gas inside the impeller is not uniform and accelerates the wear and tear. As to prevent the impeller wear measures: one is to reduce dust and corrosive gas into the fan, this must be the transformation of the fan operation system; two is to make local wear uniform wear, it needs to improve the wear resistance of the impeller. High hardness and good wear resistance can be used to improve the wear resistance of the impeller. This will not only bring difficulties to the impeller manufacturing process, but also from an economic point of view is not reasonable. Therefore, it is an economical and reasonable solution to improve the surface quality of the fan impeller, to weld or spray welding (spray) wear layer and to add a layer of lining board to the blade.
Coating anti abrasion coating
The main anti - wear coatings are resin anticorrosive and wear-resistant coating, rubber anticorrosive and wear-resistant coating, silica, water glass and ceramic anticorrosive and wear-resistant materials, etc..
In order to make the 890 wear resistant compound can be used on the impeller of the fan, we have carried out some experiments with the company of Chesterton. 890 wear resistant compound is a ceramic composite metal surface from abrasion for repair and protection, and combined with the wear resistance and the parent material force of this kind of compounds are good. But the 890 wear compound coating thickness must reach 6mm or more thick, this is not appropriate, the rotor some narrow channel or start more stringent requirements as a layer of wear-resistant liner to solve the fan impeller wear also exist such problems in leaves.
Surfacing of blade surface
Surfacing is the selection of a certain welding rod (or welding wire), manual arc (or automatic welding) welding in the blade easy to wear parts, to improve the quality of the blade surface, to protect the blade and improve the blade life. The blade surfacing electrode in general use D217, D237, D317B, D707 and D717, D217 and D237 belong to the Ma steel welding metal abrasion resistance, there is certain, but the welding crack tendency greatly. D317B surfacing material is composed of a large number of tungsten carbide (WC) is a kind of hardfacing alloy particle distribution formed on the metal substrate, the melting point of WC and the hardness is very high, so the weld metal hardness is very high hardness and impact resistance, HRC = 60, smaller crack tendency of surfacing metal. As for the D237 and D317B welding rod of our company in Ma'anshan Steel Corp sintering fan impeller has been carried out on the comparison test, the test results show that the D317B welding rod welding resistance to wear and impact resistance is better than D237. D217, D237 and D317B electrode has been successfully used in our company's sintering fan impeller, the use of the various steel companies are also good.
Surface spray welding (spray)
Spray welding process is a process that uses heat source to spray and melt on the surface of the work piece to form a dense spray welding layer. Wear resistance of the spray welding powder basically all is the use of Ni-Cr-B-Si series of nickel base spray welding powder. The spray welding layer basic organization is a solid solution of Ni-Cr-Fe, at the same time, there are a lot of boron compounds and tungsten carbide, the uniform distribution of WC particles in Ni based spray layer, these particles are uniform and discontinuous, but can form a hardness of HRC70 skeleton. Ni base material is filled in the skeleton, in the wear debris, can withstand high abrasive wear. Spray welding surface hardness is HRC55 ~ 70, the basic component is Ni60%+WC35%. My company in the two phase of the project in the application of the technology, and then in the Panzhihua Steel Corp, Steel Corp, Anshan, Ma'anshan Steel Corp, Steel Corp and other Steel Corp in the application, the use of good results. In 2001, also in the Wuhan Iron and Steel Corporation IDF rotor spray welding and partial spraying WC powder, the effect is good. Some nickel based powder and nickel based cemented carbide have been developed in Harbin Welding Research Institute.