Surface hardness and mechanical properties of gray cast iron for valves

With the rapid development of valve manufacturing industry, the professional production of domestic valve enterprises is becoming stronger and stronger, and gradually formed valve machining and assembly enterprises and valve casting production bases. According to incomplete statistics, 90% of the castings of domestic valve casting enterprises are purchased, and some foreign well-known valve casting companies also purchase a large number of castings in China for assembly and export. At present, the materials of low-pressure valve pressure parts are mainly gray cast iron. How to control the quality of valve gray cast iron has become the key and foundation of producing high-quality valve castings. At the same time, convenient, fast and accurate detection and acceptance of large quantities of valve castings is also a common problem to be solved by valve casting manufacturers and casting manufacturers.

ZHY casting is a low-pressure valve manufacturing company integrating valve casting and valve machining. At the same time, it also provides valve iron castings for other valve companies. Through the practice and repeated comparison in recent years (pouring test bar to measure the tensile strength, compared with the hardness in the valve body), a series of fast and convenient testing methods with hardness as the acceptance standard are summarized. According to the actual production, the valve casting below pn10dn600 is specified as HT200. Above DN700 is HT250, which mainly tests the hardness of valve body and bonnet of valve pressure castings. The testing position is specified on the machined surface of the inlet and outlet flange of the valve body and the machined surface of the small outlet flange of the valve cover. The testing instrument is a portable hardness instrument (adjusted with a fixed hardness instrument). The specific parameters are DN < 100, ≥ 175hb. DN100 ~ 400 , ≥170HB 。 DN500 ~ 600 , ≥165HB 。 DN700 ~ 800 ,≥175HB 。 DN900 ~ 1 200 , ≥170HB 。 DN >1 200 , ≥165HB 。

Taking the surface hardness of gray cast iron of valves as the standard for the acceptance of their mechanical properties, it is convenient to detect, reliable, fast and practical. All relevant valve casting manufacturers can formulate hardness acceptance parameters acceptable to both parties according to different production conditions of casting manufacturers, so as to more effectively control the quality of valve castings, so as to improve and improve the product performance and quality of low-pressure valve castings.