Technical requirements for normalizing of castings and causes of high hardness after normalizing and preventive and remedial measures
① The casting clamping method and charging capacity shall meet the requirements of the process card of the precision casting, and it is not allowed to bring loose sand into the furnace;
② The castings of different steel grades shall not be normalized in the same furnace;
③ The temperature difference of equipment is required to be no more than 10 ℃;
④ Before the casting is put into the furnace, the furnace temperature shall not be lower than 600 ℃;
⑤ The heating temperature and holding time meet the requirements of the process card of the investment casting;
⑥ The casting is air cooled after being discharged, and forced cooling in any way is not allowed;
⑦ The furnace door shall not be opened in the process of casting heat preservation;
⑧ The casting without gate is not allowed to be normalized.
The causes of high hardness after normalizing and the preventive and remedial measures are as follows:
(1) low heating temperature or insufficient holding time. The preventive measure is to normalize according to the process, and the remedial measure is to normalize once again;
(2) improper cooling mainly refers to too fast cooling speed. The preventive measure is natural cooling after normalizing, and the remedial measure is to conduct a normal normalizing again.
On 2018-08-08 11:45:46
