What factors determine the shrinkage of Castings
Castings performance and industrial production applications have a great relationship, so for its performance has a high demand. Sometimes the same batch of Castings cast, the size of the existence of a deviation, largely caused by shrinkage, so determine the process parameters are the basis for the production process. Castings in the sand Castings conditions under the Castings shrinkage of 2.6% to 2.7%, but it varies with the size of the cast and wall thickness. The thicker the metal, the stronger the thermal effect of the metal on the mold, the less the strength of the cast material, the loss of strength to the Castings shrinkage, and the Castings has a greater contraction in the mold, and the shrinkage is high. Otherwise the low shrinkage value. The larger the size of the Castings, the greater the obstruction caused by the Castings and the Castings itself, the less shrinkage. On the contrary simple shape of the small pieces of high shrinkage. For the wear-resistant steel should be found in the Castings shrinkage value (ie, the ordinate value) multiplied by the correction factor. The shrinkage of the Castings is related to the size of the Castings, the wall thickness and the structure, so these factors should be taken into account during processing.
We have to use the Castings before the test in advance to detect whether the device is suitable for the current application, there is no damage, etc., we have to be equipped with a reasonable detection method and the appropriate testing staff for the finished product for quality inspection.
1, the appearance of the Castings can be used to compare the sample to determine the surface roughness of the Castings, the surface of the fine cracks can be colored, magnetic powder method.
2, the internal quality of the cast, available audio, ultrasound, eddy current, X-ray and γ-ray and other methods to check and judge.
Castings should ensure that during transport and storage without corrosion and no mechanical damage, should be accompanied by a certificate, the certificate should be marked with the drawings meet the drawings or the relevant technical standards and the requirements.
Slagging defects refers to the dry sand, paint and other inclusions in the Castings process with the molten iron into the Castings and the formation of defects. White or dark gray inclusions spots, single or piece distribution, white quartz sand particles, black and gray slag, paint, foam model pyrolysis residues and other inclusions. This defect is commonly known as "into the sand" or "slag", in the Castings production of the defect is a very common flaw.
In the Castings after the box is not cleared before the cold, according to Castings and Castings system surface conditions, that can be determined whether there is no sand and slag defects. If the gates, sprues, runners, runners and gate surfaces or joints and the surface of the Castings are in serious or cracked sticky sand, the Castings are of the view that the Castings are slag and sand. Such Castings, especially plate, round cake Castings machine processing surface will have white, black and gray spots defects. If the operation of the process control is not strict, seriously affecting the quality and order to complete the progress.
The quality of the Castings not only includes the use of quality and quality of the content, as well as the appearance of quality. The appearance quality refers to the Castings surface roughness, appearance defects, scale error, shape error, component error; the use of quality refers to the Castings of the Castings In the same conditions, the work of durable, including wear, corrosion resistance, resistance to cold heat, fatigue, shock absorption and other functions, as well as cutting, solderability and other process functions.
Castings because of a variety of factors, often showing the pores, pinholes, slag, cracks, pits and other shortcomings. Commonly used repair equipment for the argon arc welding machine, resistance welding machine, cold welding machine. On the quality and appearance of the Castings requirements of the shortcomings can be used argon arc welding machine and other large heat, fast welding machine to repair.
Castings the quality of the mechanical product function or there is a great impact. For example, the impeller of each type of pump, the shell and the scale of the inner part of the hydraulic parts, the accuracy of the line and the roughness of the surface directly affect the operation efficiency of the pump and hydraulic system, the energy consumption and the development of the cavitation; Cylinder head, cylinder liner, piston ring, exhaust pipe and other pieces of copper strength and resistance to chilling heat, a direct impact on the engine operating life.