Dalian Xinmiao Casting Industry Co., Ltd. — Providing Casting Solutions for You
What are the advantages of gray iron castings, and what are the acceptance criteria?
2020-07-08
Gray iron castings are produced using the lost-foam, resin-bonded sand casting process, equipped with a large gas-fired tempering furnace, artificial aging, and quenching-and-tempering to relieve internal stresses, thereby enhancing the dimensional accuracy of the finished castings. During the finish machining of the machine bed, prolonged cutting operations cause the spindle to heat up, leading to thermal deformation that adversely affects the final machining accuracy. For high-precision and large-scale machine tools, machining errors caused by thermal deformation account for approximately 40% to 70%. Since thermal deformation can only be mitigated but not completely eliminated, under given machine tool conditions, the primary approach is to control the cutting parameters in order to stabilize the machine tool’s operating temperature and thus prevent temperature fluctuations from compromising machining accuracy. The main measures for controlling temperature variations during bed machining include:
1) Prior to finish machining, the machine tool must undergo a period of no-load operation. Only after the temperature rise has stabilized, the entire machine tool system has reached thermal equilibrium, and the positions of all machine tool components have become relatively stable may finish machining be carried out.
2) After semi-finishing, due to the relatively large cutting parameters and significant temperature rise caused by the machine tool, direct finishing should be avoided; instead, the machine should be run at no-load for a period of time before proceeding with finishing.
3) During the multiple passes of finish machining, in order to ensure consistent temperature rise, the cutting parameters must be kept essentially constant.
(1) Higher compressive and tensile strengths.
(2) Excellent precision stability.
(3) High elastic modulus.
(4) Excellent wear resistance.
(5) Better shock absorption.
(6) Excellent machinability.
(7) Good casting performance.
(8) Higher dimensional accuracy and lower surface roughness.
Large gray iron castings shall be inspected and accepted after pouring in accordance with the following acceptance criteria:
1. Chemical composition standards for castings;
2. Mechanical property standards for castings: tensile strength and hardness values;
3. Metallographic standards for castings, including carbide content, pearlite content, and graphite length, among others;
4. Dimensional requirements for castings;
5. Performance requirements for castings, such as pressure testing and leak detection;
Previous article:
Next article:
