Common defects in induction heating quenching and

2022-06-16
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Common defects and prevention methods of induction heating quenching

Name: insufficient hardness or soft spots, soft bands

causes:

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

2. serious surface oxidation and decarburization

3. coarse grains in 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 inductor

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 inductor), Forming soft strips

9. the angle of the water spray hole of the inductor is inconsistent

10. the position of the part in the inductor 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, the oil stain on the surface of the parts shall be cleaned Spots and oxide scales

3. control the intercalation degree of the original structure. The nodular iron castings shall be normalized before induction heating and quenching to make the volume fraction of pearlite greater than 70%

4. the quenching temperature shall be appropriately increased to make the ferrite in the steel fully dissolved to obtain a single austenite. Toray industries is the world's largest PPS supplier organization or the quenching and heating time shall be appropriately extended

5. increase the water pressure, increase the cooling water flow, and spray water for cooling after heating

6. appropriately increase the height of the inductor, Regularly clean the sensor

7. adjust the distance between bus bars to be 1~3mm

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

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

10. adjust the relative position of parts and inductors so that the gaps on all sides are equal to face the impact of the new round of technological revolution and industrial revolution, and the parts should be straightened before quenching due to severe bending

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. The stress is concentrated at the holes

4. the cooling speed is too large and uneven

5. the quenching medium is improperly selected

6. the tempering is not timely, Insufficient tempering

7. high material hardenability

8. the repaired parts have not been annealed and normalized

9. the structural design of the parts is unreasonable and the technical requirements are improper

prevention methods:

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

2. spheroidizing annealing shall be carried out for high carbon steel and high carbon alloy steel before induction heating quenching to check the content and distribution of non-metallic inclusions. 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. Oil, polyvinyl alcohol aqueous solution or other emulsifiers shall be used as quenchant for alloy steel

6. tempering shall be carried out in time after quenching. The retention time 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. in case of high material hardenability, the quenching medium with slow cooling can be selected

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

9. it is suggested that the design department should modify the unreasonable structural design and put forward practical process requirements

Name: quenching distortion

cause:

shaft and rod parts:

uneven hardened layer, Generally, the parts bend to the side with shallow hardening layer or no hardening layer

the hardening layer of long strip parts is asymmetric

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

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

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

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

the gear wall thickness is uneven, and the common normal line change of each part will be greatly different

the internal keyway distortion

prevention method:

bearing rod parts:

the workpiece and the sensor rotate concentrically

heating quenching at, Straightening after tempering

symmetry of hardened layer

straightening after quenching and tempering

gear:

on the premise of meeting the requirements of hardened layer, adopt larger specific power, shorten heating time

end face capping to prevent premature cooling of inner hole

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

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

select an appropriate cooling method, use a mild cooling medium

design each part of the gear as symmetrical as possible

leave grinding allowance or increase the pre shrinkage

for gears with keyway in the inner hole, carry out high-frequency quenching of the gear first, and finally insert the keyway (end)

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