According to the rules of heat aging process and the characteristics of high precision of our casting, this operating procedure is formulated
1. Preparation before prescription
A) the casting shall be cleaned before aging and there shall be no sundries
B) check whether all parts of the furnace body, flue, air duct, gate trolley, blower and dragging mechanism are normal.
C) check and calibrate the thermocouple instrument at each measuring point to make it in normal working condition.
D) prepare pad iron and tooling according to casting characteristics
2. The furnace
A) every time the furnace is loaded, the casting thickness and structural complexity coefficient should be close to each other, so as to facilitate the selection of appropriate process parameters.
B) we should grasp the principle that big does not crush small and heavy does not crush light.
C) casting discharge and support
1. Casting discharge shall be conducive to uniform heating and normal flow of furnace gas.
2. Castings shall not be placed on key parts and key surfaces, such as bed guide rail surface
3. In order to prevent deformation caused by the dead weight of the workpiece and add new stress, the maximum support distance of the pad iron shall not be greater than 1/3 of the maximum width of the casting, and the upper and lower pad iron shall not be staggered during layering
4. The casting shall be no less than 100mm away from the trolley face, no less than 400mm away from the furnace top, no less than 50mm away from the casting layer, no less than 100mm away from the adjacent casting, no less than 200mm away from the platform door
5. Castings should be placed smoothly and neatly on the pad iron, not too high or too wide
6. After the inspection personnel pass the inspection, check the sand truck seal normally and start the truck into the furnace;The walls of the furnace are aligned and the seams are sealed with asbestos or mud
7. Heat, keep warm and cool
A) heating, heat preservation and cooling process axis is shown in the figure above
B) the temperature of casting shall not exceed 200℃ and the heating speed shall not be greater than 100℃/ hour. If there are many miscellaneous activities such as working table and body shell, the heating speed shall be less than 60℃/ hour, and the temperature difference between the three measuring points in the heating process shall be less than 100℃/ hour
C) heat preservation: the heat preservation time is generally 5 hours, if the furnace load is large, the heat preservation time should be appropriately extended, and the temperature difference between the three temperature measurement points should be controlled within 60 degrees during the heat preservation process
D) temperature should be controlled below 70℃/ hour in general, and below 50℃/ hour in case of less miscellaneous work.They come out at less than 200℃
E) in order to facilitate inspection and analysis, the situation of the furnace shall be truthfully filled into the heat aging process record sheet, which shall be submitted together with the recording paper to the inspectors for preservation and future reference
A) pull out the thermocouple before baking to avoid damage.
B) take out the oven twice in winter, and pull it out at intervals of 30 minutes
After discharging the aging part of the large furnace, the inspectors should be notified and the next procedure can be carried on after the signature of the inspection according to the relevant provisions
10. Safe production
A) operate electrical and mechanical parts and follow relevant operating rules.
B) clean flammable materials around the aging furnace after work, and turn off the main power supply
D) tempering treatment for stress relief (artificial aging)
Stress relief is to remove the stress caused by the rough machining of some parts and the stress caused by the straightening, in order to ensure the stability of precision and lay a good foundation for the next process of heat treatment to reduce deformation.
1. Eliminate machining stress
Aging temperature is generally between 120-180℃, 4 -6 hours of insulation, its purpose is to stabilize the residual austenite and reduce machining stress, so as to make the size stable.The 38CrMoAL grinding wheel spindle of our factory is an exception. Its aging temperature is 240±10℃ and the insulation is 6-12 hours.
2. Eliminate alignment stress
C) the blank should be straightened after tempering and bending, and its stress-relieving temperature should be lower than the tempering and tempering temperature of 30-50℃.
Quenching parts after straightening the elimination of the temperature to do not reduce its hardness for the principle, generally 160-300℃, in drying or oil bath treatment