The home appliance industry has always been the most widely used industry of stainless steel in Western developed countries, including a large number of industrial clusters such as refrigerators, washing machines, dishwashers, microwave ovens, electric ovens, disinfection cabinets, and small household appliances.
In the household electrical appliance industry, a large amount of stainless steel is the inner tube of an automatic washing machine, the inner and outer shell of a microwave oven, and the inner lining of the refrigerator, and ferritic stainless steel is mostly used. my country’s microwave ovens, refrigerators, air conditioners, TVs, etc. are already the most competitive products in the world, and the development and application of stainless steel in the domestic appliance industry have broad prospects.
In 2012, the consumption of stainless steel in the home appliance industry was about 1.04 million tons, accounting for 14% of the country’s total consumption. The industry is expected to grow steadily at a rate of 10% for a period of time in the future. By 2015, the consumption of stainless steel in the home appliance industry will reach 1.5 million tons.
Classification of Home Appliances
Household appliances, short for household appliances, refer to appliances driven by electrical energy (or mechanized actions), which can help perform household chores, such as cooking, food preservation, or cleaning. In addition to the family environment, it can also be used in companies or industries. Environment. Basically, household appliances are divided into large household appliances (white household appliances, black household appliances) and small household appliances.
Black household appliances: household appliances that bring people entertainment and leisure. They are generally equipped with electronic components and circuit boards, including televisions, video recorders, stereos, VCDs, DVDs, mobile phones, etc.
White goods: household appliances that reduce people’s labor intensity, improve the living environment, and improve material living standards. They mainly work by converting electrical energy into heat and kinetic energy through motors, including washing machines, dishwashers, microwave ovens, refrigerators, and some Kitchen Appliances.
Small household appliances: generally refer to household appliances that take up relatively small power resources, or the body itself is relatively small, mainly including electric irons, electric kettles, soymilk machines, etc.
With the improvement of people’s living standards, the pursuit of the quality of home appliances is also rising. The widespread use of stainless steel in the home appliance industry is increasing day by day. At present, it is mainly concentrated in white goods such as washing machines, dishwashers, microwave ovens, refrigerators, kitchen appliances, and a variety of small home appliances.
Second, the selection of stainless steel materials for household appliances
1. Surface Selection
The main types of stainless steel surface finishing used in home appliances are 2B, BA0, BA1, and NO.4. The surface gloss of the first three is in increasing order, while No. 4 is a polished surface (commonly known as wire drawing). The surface of NO.4 is mostly used in the outer door panels of medium and large household appliances, such as refrigerator panels, microwave oven panels, etc.;
BA1 is mostly used in the visible cavities of small household appliances and medium and large computers, such as electric kettle shells, washing machine drums, etc.; 2B is more used Used in various stainless steel parts of low-end appliances and non-visible parts of high-end appliances.
The surfaces of 2B, BA1, and NO.4 are all used directly, and sometimes we may see that some household appliances are used with mirror-like stainless steel. This is because the manufacturer has polished the stainless steel, in this case, the BA0 surface is the best choice. BA0 surface is a product with a brightness between 2B and BA. The process path includes both bright annealing and the traditional 2B process.
It has the advantages of good gloss, high resolution, and low price. Due to the special process of BA0 products, the probability of defects is greatly reduced. The surface defects of the products are minimal, the color is uniform, and they have a certain degree of gloss. A mirror effect can be achieved with slight polishing. If you choose 2B, the polishing cost will be high, and if you choose BA1, the material cost will increase, which is not ideal.
Household appliances require that the stainless steel surface has no defects that affect the use. The existence of defects such as press-in and scratches seriously affects the visual beauty of the product, and the damage to the brand value is immeasurable. The stainless steel used in home appliances has strict process control standards and surface quality inspection standards in the manufacturing process.
In addition to the above common surface defects, there is a kind of “place gold” defect that needs to be strictly avoided in stainless steel for household appliances. Here is the definition of this defect: the stainless steel surface is coated with a film and then the protective film is torn off. There will be bright white fine metal particles on the surface, which is in a “shiny” state, which is a “placer gold” defect. This defect is different from common manufacturing defects, and it only occurs in ferritic stainless steel. Generally, it occurs mostly in 430 steel.
Because the surface requirements of stainless steel for household appliances are extremely high, the measures of covering the surface with a protective film are adopted in the processing and manufacturing of household electrical appliances. If there is a “place gold” defect, the negative impact will be great.
There are many controversies about the cause of this defect. One thinks that it is caused by surface roughness, and the other thinks it is caused by intergranular corrosion. There is no conclusion yet, and there is no effective control method so far. From the perspective of material usage, the “placer gold” defect does not affect the internal performance of the material but damages the appearance of the surface. One way is to wipe the surface metal particles with a clean cloth to wipe away the defects.
2. Performance Selection
According to the processing methods of household appliances and the requirements of finished product acceptance, the requirements for the existence of stainless steel materials are mainly summarized into four categories: plate type requirements, mechanical performance requirements, welding performance requirements, and corrosion resistance requirements.
Board type requirements. Home appliances are mostly assembled from various parts, and the stainless steel shearing distribution center is required to flatten the coils into cut-to-length materials before the parts are processed. The provided cut-to-length material requires a flat plate shape to ensure an effective fit to the mold.
Sometimes the stainless steel coil will be warped after being cut into small pieces, which is the result of the release of the internal stress of the steel plate. There are two reasons for the internal stress: the strip steel is not sufficiently annealed and the internal stress has not been eliminated, or the original coil has a poor shape and is forced to be leveled by a straightening machine. Under the above circumstances, the material has accumulated a certain amount of internal stress.
When cut into small pieces, part of the internal stress will be released and the plate shape will return to a warped shape. The warped steel plate is forcibly processed, and the mold will be damaged if it fails. Therefore, it must be avoided.
Mechanical performance requirements. Different home appliance parts have different degrees of processing deformation and have different requirements on the mechanical properties of stainless steel materials. The popular 430 material can be selected for the shallow stamping parts, and the 430L, 439, 430LN/430LNT/430J1L, 443NT, and even 304 stainless steel grades can be selected according to the actual situation for the parts with complicated deformation.
Welding performance requirements. For parts with welding processing, both welding efficiency and weld strength need to be considered. After ordinary 430 weldings, the weld seam structure has coarse grains, the weld seam is brittle, and easy to crack, which cannot meet the welding process.
Due to the ultra-low carbon and nitrogen control and the addition of niobium and titanium trace elements, the 430LNT steel has significant grain refinement in the weld area, high weld strength, and no harmful phase precipitation. It is the first choice for welding parts. In addition, 439 and 430J1L steel grades are also widely used for welding.
Corrosion resistance performance requirements. Scientifically speaking, stainless steel is a kind of steel that is not easy to rust, and rust will inevitably occur under certain conditions. However, ordinary consumers, believe that the stainless steel products they buy should not show rust, which is public perception. Therefore, two aspects should be considered in actual production. One is to select materials reasonably according to the use environment, and the other is to avoid the introduction of rust conditions during the product manufacturing process.
In the former, the steel grade should be reasonably selected according to the use environment of the product and the assembly location of the components. The stainless steel of each brand of commonly used household appliances has different electrochemical pitting potentials. The stainless steel used in household appliances rusts, which basically shows pitting corrosion. The pitting potential is a characterization of the resistance of a material to pitting.
The larger the value, the less likely the material is to pit corrosion under the same external environment. In the latter case, it is necessary to strictly prevent the intrusion of corrosive media during the processing and assembly of the components. In particular, once the medium containing chloride ions contaminates the surface of stainless steel, it is very easy to cause pitting corrosion. Therefore, processing the stainless steel surface after coating it with a protective film, using demineralized water to clean the stainless steel surface, and paying attention to cleaning the residual grinding slag after surface grinding is all effective and feasible measures.