Wed, 01 Aug 2018 03:41:21 +0000
Nitrogen treatment of mold
The shallow nitriding layer will shorten the wear – resistant life of the hardened layer. Reasons for the shallow nitriding layer of the mould: (1) the time of the mould nitriding is too short, the nitriding temperature is too low, the temperature distribution in the effective heating area of the nitriding furnace is not uniform, the nitrogen concentration in the first stage of the nitriding process is not properly controlled (the ammonia decomposition rate is too high or too low), etc. (2) the oil pollution was not removed before the mold was put into the furnace, too much oil was put into the furnace, and the distance between the molds was too close.
(2) strengthen the sealing of the nitriding furnace to ensure the normal circulation of nitrogen atmosphere in the furnace. And control the decomposition of ammonia according to the technical requirements
(3) secondary nitriding can be carried out on the molds with insufficient nitriding layer, and the nitriding can be supplemented strictly in accordance with the second stage of nitriding technology.
The hardness of the nitriding layer of the lining and mould is not uniform or soft
The uneven nitriding layer or soft spot of the mould will make the performance of the mould unstable when it is used, and the weak area will wear out more at first, causing the early damage and failure of the whole mould, seriously affecting the service life of the mould. Causes of uneven hardness or soft spots:
(1) the temperature in the nitriding furnace is not uniform due to unbalanced heating on and off the nitriding furnace or unobstructed air flow. (2) partial blockage of ammonia gas into the pipeline, affecting nitrogen atmosphere in the furnace; The ammonia gas circulation in the furnace is bad. (3) the surface oil was not cleaned well before the mold was loaded into the furnace.
(4) too many molds are loaded in the nitriding furnace, or the molds in the furnace are too small and partially exposed. Preventive measures:
(1) strictly control the furnace temperature in the upper and lower areas of the nitriding furnace so as to keep it in the same temperature zone at all times. (2) clean the ammonia inlet pipe regularly to keep the pipe free.
(3) before installing the mould, it is necessary to use such degreasing as gasoline or alcohol, and the surface of the mould after cleaning shall not be contaminated with oil or other dirt.
(4) when the mold is loaded into the furnace, a certain distance shall be maintained between the molds, and the working face of the mold shall be strictly protected from contact and overlap. (5) the atmosphere circulation in the furnace should be sufficient, the nitriding furnace should be well sealed, and the air leakage muffle tank should be replaced timely. Oxidation color on the surface of the molar and molds after nitriding