Common defects and prevention methods of the hotte

Common defects and prevention methods of induction heating quenching

Name: insufficient hardness or soft spots, soft bands

causes:

1. The carbon content of steel for quenching parts is too low

2. Serious surface oxidation and decarburization

3. Coarse grains of original structure. The pearlescent volume in the original structure of nodular iron castings is too small

4. The heating temperature is too low or the heating time is too short

5. The cooling water pressure is too low, the cooling water volume is insufficient, or the cooling is not timely

6. The height of the induction ring is not enough, and there is oxide skin in the sensor

7. The distance between the bus bars is too large

8. The rotation speed of the part is inconsistent with the moving speed of the part (or sensor), Forming soft belts

9. The angle of the water spray hole of the sensor is inconsistent

10. The position of the part in the sensor is eccentric or the part is severely bent

11. There are impurities in the quenching medium, and the emulsifier is aging

prevention methods:

1. The mass fraction of carbon in the induction heating quenched parts is generally greater than 0.4%, and the material composition is tested in advance

2. Before quenching, clean the oil stain on the surface of the parts Spots and oxide scales

3. Control the intercalation degree of the original tissue. Nodular iron castings need normalizing treatment before induction heating and quenching, so that the volume fraction of pearlite is greater than 70%

4. Appropriately increase the quenching temperature, so that the ferrite in the steel can be fully dissolved to obtain a single austenite. Toray industries is the world's largest PPS supplier organization or appropriately extend the quenching and heating time

5. Increase the water pressure, increase the flow of cooling water, and spray water for cooling in time after heating

6. Appropriately increase the height of the sensor, Regularly clean the sensor

7. Adjust the distance between busbars to be 1~3mm

8. Adjust the rotational speed of parts and the moving speed of parts (or sensors), when the moving speed of parts ν When it is 1~24mm/min, the rotating speed of the part n=60v can avoid the formation of quenching soft belt

9. If the adjustment is not good, the inductor needs to be replaced

10. Adjust the relative position of the part and the inductor to make the gap between each side equal. Facing the impact of the new round of technological revolution and industrial revolution, the part is severely bent and straightened before quenching

11. Change medium

Name: quenching cracking

cause:

1. Carbon content in steel High manganese content

2. There are many inclusions in the steel, which are in shape, with segregation of components and more harmful elements

3. The heating temperature is too high and the temperature is uneven. The sharp corners, grooves and circles on the parts are mainly used for medical equipment, educational institutions, administrative buildings, stores, hotels and industrial facilities, and the stress concentration at the holes

4. The cooling speed is too large and uneven

5. The quenching medium is improperly selected

6. Tempering is not timely, Insufficient tempering

7. High material hardenability

8. Repaired parts have not been annealed and normalized

9. Unreasonable part structure design and improper technical requirements

prevention methods:

1. The carbon content and manganese content of parts should not exceed the upper limit. During trial quenching, process parameters and quenching medium can be adjusted

2. High carbon steel and high carbon alloy steel need spheroidizing annealing before induction heating quenching, check the content and distribution of non-metallic inclusions, and the blank must be repeatedly forged

3. Adjust electrical parameters, reduce electric power per unit area, and shorten heating time. Before quenching, use asbestos rope or metal bar to block grooves and holes; Sharp corner rounding; Leave a non hardening area at the shaft end

4. Reduce the water pressure, reduce the amount of water spray, and shorten the water spray time

5. Use a quenchant with low cooling capacity. Use oil, polyvinyl alcohol aqueous solution or other emulsifiers as quenchant for alloy steel

6. Temper in time after quenching, and the retention between quenching and tempering shall not exceed 4H for carbon steel or cast iron, and 0.5h for alloy steel. In case of insufficient tempering, appropriately extend the tempering time

7. When the material hardenability is high, the quenching medium with slow cooling can be selected

8. The repaired parts must be annealed and normalized before induction heating and quenching

9. It is suggested that the design department should modify the unreasonable structural design, Propose practical process requirements

Name: quenching distortion

cause:

shaft and rod parts:

the hardening layer is uneven, and usually the parts are bent to the side with shallow hardening layer or no hardening layer

the hardening layer of long strip parts is asymmetric

gears: the inside of cylindrical gears is also generally reduced by 0.01~0.05mm, The outer diameter is unchanged or reduced by 0.01~0.03mm

for thin-walled gears with the ratio of inner diameter to outer diameter less than 1.5, the inner hole and outer diameter tend to swell, and the double gear has a bell mouth

the tooth shape change is that the tooth thickness is generally manifested as the middle concave 0.002~0.005mm

the change of the common normal line is generally 0.02~0.05mm (tends to swell when quenching, tends to shrink when quenching)

the gear wall thickness is uneven, There will be great differences in the change of the common normal line of each part

there is also keyway distortion inside

prevention methods:

bearing rod parts:

the workpiece rotates concentrically with the inductor

quenching during heating, straightening after tempering

the hardening layer is symmetrical

straightening after quenching and tempering

gear wheel:

on the premise of meeting the requirements of the hardening layer, use a larger specific power to shorten the heating time

end face capping, Prevent premature cooling of the inner hole

after the gear blank is processed, first carry out a high-frequency normalizing, and then process the inner hole and milling teeth, which can significantly reduce the shrinkage of the inner hole to 0.005~0.02mm

the design should be reasonable, the process route should be arranged correctly, so that the gear wall thickness is uniform and the shape is symmetrical

choose the appropriate cooling method, Use mild cooling medium

all parts of the gear should be designed as symmetrical as possible

leave grinding allowance or increase pre shrinkage

gears with keyway in the inner hole should be subject to high-frequency quenching first, and then insert keyway (end)