Reasonably add the recycled materials

Pinhole size reflects the spatial distribution density of pinholes and is an important factor affecting the air tightness of castings. There are many pinholes in the castings due to the combined effects of the micro pores and oxidation inclusions in the recycled materials. The scrap rate of individual castings in production is relatively high. Due to energy saving and consumption reduction, the actual production of scrap parts for recycling, as well as a substantial increase in the recycling amount of runner, will also lead to poor airtightness of castings

Therefore, the classification, treatment and use of recycled materials should be strictly controlled when producing castings with air tightness requirements, so that the proportion of recycled materials and new materials can be used in strict proportion when meeting the quality requirements. Otherwise, excessive use of recycled materials will increase the degree of pinhole of castings in subsequent production, failing to meet the requirements of air tightness, which is not conducive to the assurance of casting quality

Select a reasonable filling degree of the pressure chamber

When the diameter of the punch and the die casting machine are selected, the weight of the metal liquid contained in the pressure chamber is also a certain value, but the weight requirements of the metal liquid poured each time for different castings are different. If the volume of metal liquid poured into the pressure chamber is insufficient (i.e., the filling degree of the pressure chamber is low), the gas in the pressure chamber cannot be eliminated as soon as possible during injection. With the high-speed push of the injection piston, the disordered flow in turbulent state is formed, which is easy to get involved in the gas, leading to defects such as air holes and insufficient pouring. At the same time, due to the existence of too much oxide skin in the pressure chamber, it is easy to form a diaphragm inside the casting, which leads to the reduction of local strength of the casting, and leakage is very easy to occur under the action of large leakage test pressure. Therefore, the reasonable filling degree of the pressure chamber can effectively reduce the porosity defects in the castings, thereby reducing the air leakage rate of the castings

Because aluminum alloy has a severe tendency of oxidation and gas absorption, and it directly contacts with furnace gas or the outside atmosphere during the smelting process, if the control is slightly improper during the smelting process, aluminum alloy will easily absorb gas and form pores, most commonly pinholes. Pinholes usually refer to precipitation pores less than 1mm in the casting, which are mostly circular and unevenly distributed on the whole section of the casting, especially in the thick section of the casting and the part with low cooling rate. According to the distribution and shape characteristics of precipitation pores in aluminum alloys, pinholes can be divided into three categories

1. Reticular pinholes: in low magnification tissues, pinholes are densely connected to form a network, with a few large holes. It is not convenient to check the number of pinholes per unit area, nor to measure the diameter of pinholes

2. Dotted pinholes: in the macrostructure, pinholes are round and dot shaped, with clear and discontinuous outlines, and can count the number of pinholes per square centimeter of area and measure their diameters. This kind of pinhole is easily distinguished from shrinkage cavity, shrinkage porosity, etc

3. Comprehensive stomata: it is the middle type of punctate pinholes and reticular pinholes. From the perspective of macrostructure, there are many large pinholes, but they are not dots but polygonal

The production practice of aluminum alloy metal die casting has proved that the main gas component of aluminum alloy forming pores due to air suction is hydrogen, and there is no certain rule to follow for its rising, usually all or most aluminum alloy die castings in a furnace have pinholes; Materials are no exception. All kinds of aluminum alloys easily produce pinholes

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Aluminum die casting is a kind of die casting parts. It is a kind of die-casting mechanical die-casting machine with a casting mold installed. The aluminum or aluminum alloy heated to liquid is poured into the feeding port of the die-casting machine. After die-casting by the die-casting machine, aluminum parts or aluminum alloy parts with the shape and size limited by the mold are cast. Such parts are usually called aluminum die castings. Aluminum die castings have different names in different places, such as aluminum die casting parts, die-casting aluminum parts, die-casting aluminum parts, die-casting aluminum, aluminum die castings, aluminum alloy die-casting parts, etc