definition:
The casting is a metal molded object obtained by various casting methods, that is, the smelted liquid metal is poured into a pre-prepared mold by pouring, injecting, inhaling or other casting method, and after cooling, after falling sand, cleaning and then Processing, etc., the resulting article with a certain shape, size and performance.
Casting history:
Casting applications have a long history. Ancient people used castings for coins, rituals, weapons, tools, and some living utensils. In modern times, castings are mainly used as blanks for machine parts, and some precision castings can also be directly used as parts of machines. Castings account for a large proportion in mechanical products. For example, in tractors, the weight of castings accounts for 50-70% of the weight of the whole machine, 40-70% of agricultural machinery, and 70-90% of machine tools and internal combustion engines. Among all kinds of castings, the most used castings are mechanical, the shape is the most complicated, and the amount is also the largest, accounting for about 60% of the total casting output. Followed by metal ingot molds for metallurgy and engineering pipes.
Castings are also closely related to daily life. For example, door handles, door locks, radiators, water pipes, iron pans, gas hobs, irons, etc., which are often used, are castings.
Casting classification:
There are many classification methods for castings: according to the different metal materials used, they are divided into steel castings, cast iron parts, cast copper parts, cast aluminum parts, cast magnesium parts, cast zinc parts, and cast titanium parts. Each type of casting can be further divided into different types according to its chemical composition or metallographic structure. For example, cast iron parts can be divided into gray iron castings, ductile iron castings, vermicular graphite iron castings, malleable iron castings, alloy cast iron fittings, etc.; according to different molding methods, castings can be divided into ordinary sand castings, metal castings, and die castings. , centrifugal castings, continuous castings, investment castings, ceramic castings, electroslag remelting castings, bimetal castings, etc. Among them, ordinary sand castings are the most widely used, accounting for about 80% of all castings. Non-ferrous metal castings such as aluminum, magnesium and zinc are mostly die-casting parts.
Casting properties and uses:
Castings have excellent mechanical and physical properties. They can have a variety of different strength, hardness, and toughness properties. They can also have one or more special properties, such as wear resistance, high temperature resistance, low temperature, corrosion resistance, etc. .
Castings are available in a wide range of weights and sizes. The lightest weight is only a few grams, the heaviest is 400 tons, the thinnest wall is only 0.5 mm, the thickest can be more than 1 meter, and the length can range from a few millimeters to a dozen meters. It can meet the requirements of different industrial sectors.
Casting quality:
It mainly includes appearance quality, intrinsic quality and quality of use. Appearance quality refers to the surface roughness, surface defects, dimensional deviation, shape deviation and weight deviation of the casting; the intrinsic quality mainly refers to the chemical composition, physical properties, mechanical properties, metallographic structure of the casting, and the holes, cracks, inclusions existing in the casting. Segregation and other conditions; the use of quality refers to the working durability of the casting under different conditions, including wear resistance, corrosion resistance, chilling heat, fatigue, shock absorption and other properties as well as machinability, weldability and other process properties.
Casting quality has a major impact on the performance of mechanical products. For example, the wear resistance and dimensional stability of machine tool castings directly affect the accuracy of the machine tool to maintain the life; the size of the impeller, the housing and the internal cavity of the hydraulic pump, the accuracy of the profile and the surface roughness directly affect the pump. And the hydraulic system's working efficiency, energy consumption and cavitation development; the strength of the internal combustion engine cylinder block, cylinder head, cylinder liner, piston ring, exhaust pipe and other castings and the resistance to chilling heat, directly affect the working life of the engine. There are many factors affecting the quality of castings. The first is the design and craftability of castings. When designing, in addition to determining the geometry and size of the casting according to working conditions and metal material properties, the rationality of the design must be considered from the perspective of casting alloy and casting process characteristics, namely obvious dimensional effect and solidification and shrinkage. Problems such as stress, to avoid or reduce the occurrence of defects such as segregation, deformation, cracking of the casting. The second is to have a reasonable casting process. That is, according to the structure, weight and size of the casting, casting alloy characteristics and production conditions, select the appropriate parting surface and shape, core making method, reasonable setting of casting ribs, cold iron, riser and casting system. To ensure the quality of castings. The third is the quality of raw materials for casting. Metal furnace materials, refractory materials, fuels, fluxes, modifiers, and materials such as foundry sand, sand binders, coatings, etc., are substandard, which may cause defects such as pores, pinholes, slag inclusions, and sanding of castings, affecting the appearance quality of castings. And internal quality, serious castings will be scrapped. The fourth is the process operation, it is necessary to formulate reasonable process operation procedures, improve the technical level of workers, and make the process procedures correctly implemented.
In casting production, the quality of castings is controlled and tested. First, we must formulate the technical rules and technical conditions for the control and inspection of raw materials and auxiliary materials to each specific product. Each process is strictly controlled and tested according to the technical code and technical conditions. Finally, the quality of the finished castings is checked. Be equipped with reasonable testing methods and appropriate inspectors. Generally, for the appearance quality of the casting, the comparative sample can be used to judge the surface roughness of the casting; the fine crack of the surface can be inspected by the coloring method and the magnetic powder method. The internal quality of the casting can be checked and judged by means of audio, ultrasound, eddy current, X-ray and gamma ray.
How to repair the casting defects:
Due to a variety of factors, castings often have defects such as pores, pinholes, slag inclusions, cracks, and pits. Commonly used repairing equipment are argon arc welding machines, resistance welding machines, cold welding machines, and the like. For casting defects that are not required for quality and appearance, it can be repaired with a welding machine such as a argon arc welding machine that generates a large amount of heat and a high speed. However, in the field of precision casting defect repair, due to the great influence of argon welding heat, the deformation of the casting, the hardness reduction, the blisters, the local annealing, the cracking, the pinhole, the abrasion, the scratch, the undercut, or the bonding force are insufficient. Secondary defects such as stress damage. The cold welder has overcome the above shortcomings. Its advantages are mainly in the small heat affected zone. The castings do not need to be preheated, and are cold-welded at room temperature, so there is no deformation, undercut and residual stress, no local annealing, no change of the metal of the casting. Organizational status. Therefore, the cold welder is suitable for surface defect repair of precision castings. The welding repair range of cold welding is the process of repeated melting and stacking of Φ1.5-Φ1.2mm welding repair points. In the process of repairing large area defects, the repair efficiency is the only factor that restricts its widespread application. For large defects, a composite application of a conventional weld repair process and a casting defect repair machine is recommended. Sometimes we don't have a lot of defects, so we don't have to invest a lot of cost. We can fix it with some repairing agents. It is convenient and simple. For example, iron materials, we can use (Jin Sucheng) JS902 to fix it. If you can't use it, you can use it later, which can save costs for our manufacturers. Let our foundry put more money into improving the quality of the product itself, and let users create more wealth.
How to test the hardness of castings:
The properties of the casting itself directly affect the quality of the processing, and the hardness value is an important indicator for determining the casting processing. 1. Brinell hardness: mainly used to determine the hardness of castings, forgings, non-ferrous metal parts, hot-rolled billets and annealed parts, the measurement range is ≯HB450. 2. Rockwell hardness: HRA is mainly used for high hardness test pieces, and the hardness and surface hardness of HRC67 or higher, such as cemented carbide and nitrided steel, are measured. The measurement range is HRA>70. HRC is mainly used for the hardness measurement of steel parts (such as carbon steel, tool steel, alloy steel, etc.) after quenching or tempering, and the measurement range is HRC20~67. 3. Vickers hardness: used to determine the hardness of thin and steel parts, can also be used to determine the hardness of surface hardened parts such as carburizing, **, nitriding.
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