12 Practical Experiences in Heat Treatment Workshop

(1) Regularly replenish the quenching oil and quenching liquid and replace the slags.

Generally, the quenching oil shall be replenished (added) every three months, and the slag of large oil tanks in the circulation room and outdoors shall be excavated and cleaned every year.

The quenching liquid shall be replaced as a whole to ensure the cooling characteristics.

In order to meet the needs of cooling temperature, the quenching oil and quenching liquid are equipped with a cooling system.

Air cooling radiator or water cooling are both effective.

For parts with strict requirements that affect the cooling effect of the cooling medium at low temperatures, heating devices are required.

(2) The mesh belt furnace regularly cleans the carbon deposits in the hopper to reduce the bending of parts and extend the service life of the mesh belt.

Usually, the hopper is cleaned every month to remove the carbon deposits stuck on the inner surface (four corners and inner surface).

Fig. 1 shows the carbon deposits and valves cleaned.

Each shift shall check the operation and damage of the mesh belt. Once the mesh belt is found to be damaged (broken, torn, etc.), see Fig. 2.

The damaged mesh belt shall be replaced in a timely manner to eliminate product deformation and waste.

Fig. 1 Carbon Deposits+Valves Cleaned by Mesh Belt Furnace
Fig. 2 Damaged heating mesh belt (part)

(3) Continuously improve the production efficiency of heat treatment, reduce the labor intensity of employees by increasing the furnace loading, and use highly automated heat treatment equipment (such as mesh belt furnace production line, automatic nitriding line, gas furnace, pusher furnace, vibrating bottom furnace, etc.) to ensure that the heat treatment needs of different automobile parts (quenching and tempering treatment, solution treatment, carburizing and nitrocarburizing treatment, etc.) are met.

Increase the charging capacity of mesh belt furnace or pusher furnace to improve production efficiency and realize effective utilization of heat energy.

The production efficiency is improved by 2-3 times by increasing the heating charge of parts and adopting the method shown in Fig. 3 and Fig. 4.

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Such parts (such as valves, rods, steel tappets, standard parts, bearings, piston pins, etc.) are placed in such a way that the radiant tubes of the mesh belt furnace are arranged at the upper and lower positions, which can achieve rapid and uniform heating without the problem of impermeability.

Fig. 3 Placement of rod parts on the mesh belt
Fig. 4 Arrangement of Fork Products on the Mesh Belt

(4) Special automatic straightening equipment shall be vigorously promoted.

Valves are intensive products, which have the characteristics of large production batch, short cycle, and inevitable deformation of heat treatment and shot blasting.

Manual straightening of valves is inefficient, labor intensive, and requires a large number of operators, which is a difficult problem in the valve heat treatment industry.

The problem is solved by using the special valve straightening machine.

Parts are straightened with special machinery, such as shafts, rods, valves, etc., and tempering treatment is canceled, which can save the secondary heating and shot blasting process.

The one-time straightening has high qualification rate, saves a lot of manpower, reduces the labor intensity of operators, and has significant economic benefits.

It is an unusually effective measure and method, which is the only way to improve the labor productivity of heat treatment.

(5) The hanging shot blasting machine has broad application prospects.

After nitriding, the products were originally crawler shot blasting machine, but about 12% of the products were seriously bruised;

The use of small rotary sandblasting machine has a large amount of labor, and the consumption of spare parts is relatively serious, so it is not used much;

The use of hoisting completely avoids the generation of waste products.

The valve has high cleanliness, good appearance quality, and is equipped with a dust suction device, which has significant economic benefits.

(6) The automatic sorter used for valves is directly used for sorting after mechanical alignment.

The technical requirements are to detect the straightness of the rod, the runout of the disc cone or the end face of the disc, automatically detect, and separate the qualified and unqualified products.

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It has the characteristics of high production efficiency (6000 pieces of each equipment per shift) and stable quality.

(7) Stepped quenching or isothermal quenching is adopted to reduce the deformation of parts.

According to the material and technical requirements of parts, adopting the best heat treatment and cooling process can not only reduce the heat treatment deformation of parts, but also achieve energy conservation and environmental protection.

For parts that require surface blackening after heat treatment, use the nitrate bath for grading or isothermal treatment, which can complete the blackening treatment and clean the surface.

It should be noted that the cooling water jacket should be placed in the salt bath to control the temperature of the salt bath.

(8) Reduce the rework treatment of products (control the hardness, grain size, penetration depth, etc. of finished products and processes).

For the classified treatment of reworked products to achieve the purpose of energy saving and consumption reduction, it should be noted that when formulating the heat treatment process, the technical requirements should be stricter than those specified in the drawings, so that even if the quality of the process does not meet the technical requirements, there is still room to meet the requirements of the drawings.

In addition, according to the product requirements, it can be comprehensively considered whether to conduct heat treatment again.

(9) Heat treatment of tappets saves energy.

After the cast iron tappet is heated and cooled by oil in the salt bath furnace, it needs to clean the oil and residual salt in the bottom socket and then conduct low-temperature tempering treatment.

Clean it with hot water without cleaning agent.

Control the water and salt in the bottom socket to prevent rust.

The effect is obvious. At the same time, the pit is very clean after shot blasting.

(10) Adopt the packing method and special equipment to reduce the deformation of parts, so as to realize the control of the deformation and quality of parts.

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Due to the low height of the material box, the overlapping of parts will not cause bending, and it is convenient to load and discharge materials.

For parts that are easy to be deformed by heat treatment, a large amount of overlapping under heating state should be reduced, and at the same time, extrusion, distortion, etc. should be prevented.

Improve the qualification rate of nitrogen valve repair and reduce manufacturing cost.

Especially for valves whose rods have been processed to finished products, special process equipment is required to ensure that the finished rods will not be subject to nitrogen treatment, thus saving the special requirements that some conical surfaces will not be processed anymore.

(11) Optimize the process and shorten the process flow of parts.

After the electric upsetting and pressing of the valve, the threading frame shall be annealed or aged;

The threading frame for stress relief annealing before valve nitriding is processed by machining, and directly carried out in the mesh belt furnace or box furnace after being sent to the heat treatment process, which saves secondary clamping and reduces manual and valve deformation.

(12) Accelerate the melting speed of nitriding salt bath and oxidizing salt bath.

Pour the nitrided salt or oxidized salt on the slag catcher and then sink it into the middle of the salt bath, which is more than twice as long as directly sinking the salt into the bottom of the furnace tank.

This method has a significant energy-saving effect.

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