In recent years, the casting technology of aluminum alloy castings has been greatly developed. The output of aluminum castings has been increasing year by year. Now it has been more and more widely used in weapons, aviation, aerospace, textile and other fields. strict. Among all the characteristics of casting quality, internal quality is the key factor that determines the overall quality of the casting. At the same time, the level of internal quality of the aluminum castings also reflects the pros and cons of the level of casting technology. Therefore, the control of quality defects in castings is the goal that casting technicians must always solve and improve.
1. The concept of internal quality
Generally speaking, the internal quality of aluminum castings refers to the degree to which the internal defects of the castings meet the requirements of relevant standards. These defects generally include cracks, pinholes, pores, shrinkage, porosity, segregation and inclusions. Due to the existence of these defects, the physical properties, mechanical properties and metallographic structure of the casting will often change, which will bring the use of the casting Serious hidden dangers. Therefore, internal quality is the primary control factor for casting production and inspection.
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2. Characteristics of internal quality defects
(1) Internal quality defects are often hidden inside the casting, which cannot be inspected by ordinary visual methods, and often requires special methods and equipment to complete.
(2) Judgment of internal quality defects, inspectors need to provide professional knowledge training and have certain practical work experience.
The requirements of the two standards for internal defects are the same and different, mainly due to different industries, the use requirements are different, but the basic requirements and inspection methods are the same, the high quality aluminum casting manufacturer described below.
3. GB / T9438-1999 requirements
(1) Casting inspection type. The standard stipulates that the internal quality inspection must be carried out for the type I castings; the internal quality inspection is only carried out when the users require the inspection for the type II and III castings.
(2) Several standards cited in the internal quality inspection of this standard
① GB / T11346—1989 X-ray inspection of aluminum alloy castings for pinhole (round) classification. This standard specifies the classification of round pinholes in aluminum alloy castings. It is divided into two groups A and B according to the thickness of transillumination. The component A is suitable for castings with a thickness of <13mm and the component B is suitable for transillumination. For castings with a thickness of 13-50mm, each group has 8 reference films.
②HB6578—1992 Standard reference radiographic film for inspection of aluminum and magnesium alloy castings. The standard classifies internal quality defects in more detail. There are 6 major categories of pores, pinholes, shrinkage holes, looseness, inclusions, and segregation. Each category is divided into 8 grades of reference film.
③JB / T7946.3—1999 cast aluminum alloy pinhole. The standard stipulates the classification principle and evaluation method of the low pinhole degree of cast aluminum alloy. The standard divides the pinhole degree into 5 levels.
(3) Inspection methods X-ray nondestructive testing; low magnification test inspection.
(4) Specific requirements for inspection
① Inspect the internal quality of castings first according to the technical requirements of the aluminum casting compressor body drawings.
② Cracks are not allowed inside the casting.
③ If there is no clear stipulation, for pinhole defects, Class I castings, hydraulic parts, and pneumatic parts shall be accepted as Class 2 in the GB / T11346-1989 standard. Partial Class 4 pinholes are allowed, but generally shall not exceed the inspection area 25%. When the air-tightness test meets the design requirements, it is allowed to be accepted at level 3. Type Ⅱ castings are accepted as pinholes in grade 3.
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