Precision casting is a kind of casting technology with little or no cutting. It is an excellent technology in the casting industry. Its application is very wide, not only suitable for various types of alloy casting, and the production of casting dimensional accuracy, surface quality is higher than other casting methods, even other casting methods are difficult to cast complex, high temperature resistant, not easy to process casting, can be cast by precision casting. So what do we need to pay attention to in precision casting?
Surface treatment method
Stainless steel has unique strength, high wear resistance, superior corrosion resistance and not easy to rust and other excellent characteristics. Therefore, it is widely used in the industry, food machinery, mechanical and electrical industry, household appliances industry and home decoration, finishing industry. The use of stainless steel development prospects will be more and more broad, but the use of stainless steel development largely depends on its surface treatment technology development degree.
1.Mirror processing, is to the outer layer of stainless steel polishing, according to the technique can also be divided into physical and chemical polishing, can also be done in a small part of the field polishing, after mirror processing of stainless steel will become more high-grade, fashion.
2.Sandblasting, which is also a common outer processing technology on the market, it is the use of air compression power, make the spray material high-speed spray to the construction of the outer layer, so that the outer layer of the workpiece shape change, it can improve the viscosity of the connector, so that the outer layer of processing parts become more smooth and balanced.
3.Chemical treatment, it is mainly the use of chemistry and electricity in stainless steel outer layer with stable compounds, such as electroplating is a class of chemical treatment.
4.Surface coloring, coloring techniques can be used to bring rich color to the outer layer of stainless steel, it can not only make the color of stainless steel become a variety of, but also can improve its wear resistance, corrosion resistance effect.
5.Surface drawing treatment, we often can see it in the decoration of the house, can be made into straight lines, threads, ripples and other forms, and feel good, smooth and exquisite, excellent wear resistance, is widely used in electronics, home, mechanical equipment and other fields.
6.Spraying, it and the above coloring disposal nature is not the same, because the material is different, some spraying may make the stainless steel outer oxide film damage, but some spraying can change the color at the same time to change its feel.
From the above content we can see that there are many methods of stainless steel surface treatment, and each method can bring the effect is not the same, when we carry out the construction, we must understand their characteristics and their own needs, choose the right implementation, so as to achieve the purpose at the same time to avoid a lot of unnecessary trouble.
Passivation treatment is the last process step in chemical cleaning, is a key step, its purpose is to prevent corrosion of materials. Such as the boiler after pickling, water washing, rinsing, the metal surface is very clean, very active, very easy to suffer corrosion, so must immediately passivation treatment, so that the cleaning of the metal surface protective film, slow down the corrosion.
The purpose of passivation treatment
The formation of passivation or passivation film on the surface of stainless steel alloys is a natural phenomenon when the clean surface contains oxygen, and the formation of passivation film may be enhanced by chemical treatment of the stainless steel surface.
A prerequisite for chemical passivation process preparation is a cleaning procedure. This procedure includes all operations necessary to remove surface contaminants (oil, grease, etc.) to ensure the metal’s strong corrosion resistance, prevent product contamination, and achieve the required surface condition. Z final chemical passivation is to remove iron ions or other contaminants from the surface of the alloy, so that the alloy in a Z strong corrosion resistance state.
Passivation of stainless steel with strong corrosion resistance in the standard (such as 316L) is the most beneficial and important. Passivation can be used to reduce iron ion concentration and enhance chromium content depending on the user’s choice.
In passivation, it must be recognized that the best passivation treatment or any surface treatment only gives the alloy a Z strong corrosion resistance under certain circumstances. In other words, alloy materials have inherent corrosion resistance limits, the best passivation treatment can not replace alloy materials to meet the higher corrosion resistance required for certain occasions.
1.Why should the metal surface be passivated?
Although the stainless steel element is clean before installation and the passivation film is intact, the passivation film in the weld and heat affected zone (HAZ) can be destroyed during welding. In passivation films, the content of chromium is usually higher than that of iron. When the metal melts, the concentration of iron increases while the content of chromium decreases, which disturbs the distribution of chromium, iron and oxygen in the weld and in the heat-affected zone.
This may reduce corrosion resistance if oxidation and contamination (especially iron) from heat generated during manufacture is not removed. Post-welding passivation removes free iron ions and helps restore the passivation layer, but does not remove the oxidation color caused by heat. The removal of thermal oxidation color requires a stronger acid than the nitric or citric acid used for passivation. Because passivation is usually used only after welding of already installed piping systems, welding procedures specify ways to mitigate thermal oxidation formation.
Production, cutting, bending and other pollutants will lead to reduced corrosion resistance, such as embedded iron filings, hot printing, welding flux on the electrode, arc damage, paint, marks, exposure to carbon steel or iron environment is particularly harmful. By removing contaminants, especially free iron, passivation helps to restore stainless steel damaged during production to its original dullness.
2.When must passivation
The passivation treatment must be performed in the following situations: After welding and fabrication, the user may specify the passivation treatment of the components that have been welded and electrolytically polished after welding; The components of the newly loaded system need passivation treatment after welding.
Common passivation process
As the most important industrial material in the construction of national economy, steel is widely used in automobile manufacturing, metallurgy, hardware, household appliances, construction, machinery and other industries. However, the surface layer of iron and steel materials in the wet, hot and other complex environment, easy to rust, affect the use, appearance, coating and other properties, so in some steel production line requirements of steel materials necessary passivation treatment. At present, our main processing technology is pottery.
Ceramic processing technology
The passivation treatment of fluozirconate can form inorganic film based on zirconia, known as ceramic film, application is relatively mature, to achieve no phosphating treatment. ZrO2 inorganic non-metallic material with wear resistance, high temperature resistance, corrosion resistance and other characteristics, is mainly used in aluminum alloy surface treatment and other fields.
ZrO2 conversion film technology is mainly processed by condensing deposition on the metal surface into a nano-zirconia ceramic film coating in fluozirconate solution: (Me represents Fe, Zn, Al, Mg and other substrates)
Its main advantages are: Mechanical, acid and alkali resistance, good thermal stability, stable tank easy to control, and the original coating process and coating equipment is basically compatible, the process process is brief, film forming rate within 30s, less sediment, no COD, BOD, no phosphate, stable quality, process parameters can realize automatic control, greatly reduce the water consumption, reduce waste slag, wastewater discharge treatment, Reduce energy consumption, manpower, equipment maintenance costs; Moreover, it is suitable for mixed line processing and widely used in highly automated painting shop and automotive pretreatment.
Excellent salt spray corrosion resistance after passivation treatment; The adhesion of the ceramic film on the surface with epoxy resin coating and polyurethane coating is 0 grade. However, it also has some disadvantages, such as the time and pH of ceramic film forming, thin ceramic film layer, and poor corrosion resistance of bare film compared with phosphating film.
The development of precision casting equipment in China is relatively late, and it requires a strong precision process. In theory and practice, we should strengthen the understanding of precision casting process, constantly add common sense, enrich practical experience, straighten out the whole precision casting production process, and cast more powerful quality products.
In the use of precision casting equipment, the foam model in the filling process to go through liquefaction, decomposition, which produces a lot of small molecules of gas and foam ash, these substances are harmful to the human body, the operator must strictly follow the operation manual in daily work, whether it is the actual operation or auxiliary protective goods, must be carried out according to the requirements. In the production process, master the operating steps, with rigorous work attitude to complete the task, safe production. Mould material directly affects the appearance quality of precision casting. Paraffin stearic acid is the early application of the mold, but the softening point is low, the strength is not high, is a low temperature mold, the line shrinkage is larger. According to this situation, people have carried on the improvement and the development of new mold. Domestic has developed a series of die materials for different product objects and different precision casting process requirements.