There are many factors influencing the formation of casting defects from the perspectives of defect types and possible causes of stainless steel investment castings, and the quality control of each link will affect the final casting quality. Stainless steel casting manufacturer can control the casting quality strictly from the following three aspects based on the the casting defects happened in the stainless steel investment casting production practice.
1. Raw Material Control
The surface layer material has an important influence on the surface quality of stainless steel castings owing to its direct contact with the alloy melt. Zircon sand neutral refractory material should be selected as the surface layer material, the ZrSiO4 content of zircon sand should be high, and the content of oxide impurities such as K, Na, Ca and Mg should be controlled. 1 to 2 zircon sand suppliers should be fixedly selected so as to ensure the stability of casting quality, and the zircon sand should be entrusted to the corresponding research institutions for testing. The specific requirements should be in accordance with the Ministry of Aviation Industry standards HB534921986, and pass the defined acceptance?criteria.
The supply of alloy raw materials and auxiliary materials should have a relatively stable channel. The charging materials should be strictly controlled, and the charging materials should be cleaned without rust before entering the furnace. The operating procedures should be strictly followed in order to to avoid the introduction of impurities into the alloy melt.
2. Coating and Dewaxing Control
(1) To conduct strict coating slurry quality control and monitor the gelation time of the binder extract in the coating slurry regularly, and give up the coating that has deteriorated resolutely, especially the surface coating.
(2) To ensure that the thermal conductivity and permeability of the shell are good, and to ensure that the surface layer of the wax mold melts before the wax mold expands as a whole; meanwhile, the perfect permeability of the shell surface layer should be guaranteed, and to relieves the tension generated by the thermal expansion of the wax mold on the shell and prevents the shell from cracking.
(3) To improve the shell drying rate. The dryer the shell, the higher the shell strength, and the stronger the ability of the wax mold to expand when subjected to dewaxing, the less likely the shell is to crack. Meanwhile, the suitable drying rate of the shell also makes it possible that there is less residual moisture in the shell.When dewaxing, abnormal boiling caused by the high temperature of steam will not occur , thus avoiding local damage and cracking of the shell.
3. Roasting, Smelting and Pouring Control
(1) A shell with full-roasting .
(2) Deoxidation and slag removal treatment should be sufficient during alloy smelting, and to ensure that the slag inclusions on the surface oxide of the melt should be cleaned in time. A reducing atmosphere around the cast shell can be artificially created if necessary, such as sprinkling sawdust into the cast shell that has just been poured. At the same time, it is also necessary to avoid adding excessive deoxidizer to prevent the increasing of non-metallic inclusions in the molten steel. For example, ferromanganese and ferrosilicon are often used as stainless steel deoxidizers, and they react in molten steel to form MnO and SiO2, and the melting point of SiO2 is higher. It is difficult to remove suspensions in melting steel and easily react with metals to form non-metallic inclusions of silicate series, which is one of the main sources of surface black spot defects.
(3) To control the appropriate pouring temperature. A sufficiently high pouring temperature must be adopted in order to ensure that the molten steel fills the cavity and obtains a good casting surface quality. However, it is likely to exacerbate the oxidation of the surface alloying elements if the pouring temperature is too high, thereby causing other defects such as surface pitting. Therefore, a lower casting temperature should be adopted to obtain a well-defined casting.
CFS Stainless Steel Foundry is the professional stainless steel investment casting manufacturer, we have rich experience in casting stainless steel with investment casting method. If you met unsolved casting defects and would like to look for an alternative stainless steel casting supplier, pls contact our company!