How to solve the problem that the inner end face of thin flange is easy to be quenched
The flange shaft is shown in Figure 1, with a material of 40Cr and a total length of 215 mm. the diameter of the shaft body part is 60 mm, the length is 210 mm, the cylindrical outer surface is quenched, the depth of the hardened layer is 1-3 mm, and the hardness is 45-50 HRC. the flange part has a diameter of 90 mm, the thickness is only 5 mm, the inner end surface is quenched, the depth of the hardened layer is 1-3 mm, and the hardness is 45-50 HRC. induction The quenching method is vertical scanning quenching, starting from the inner face of the flange and scanning from the bottom up. In the induction quenching process, the flange part is very easy to be heated, over-burning, the phenomenon of hardening, can not meet the technical requirements. After several adjustments to the process parameters, the effect is not obvious. This requires an alternative way to take a new approach to solve the problem of the flange edge being quenched through.
Figure.1 flange shaft quenching requirements
Analysis of the cause
Flange shaft cylinder of the solid thick, high material heat capacity, in the induction quenching process, the use of penetration heating (i.e. quenching heating layer is less than the induction current thermal penetration depth). The temperature distribution of the penetration quenching heating layer, in order from the outside to the inside: the surface superheat layer, quenching heating layer (full austenite layer), heating transition layer.
The depth of the surface superheated layer is very small and negligible, and the value is taken as 0.
The quench heating layer will continue to advance deep into the column until it reaches the depth of induction current penetration. According to the technical requirements of the flange shaft cylindrical part of the heat treatment layer depth of 1-3mm, the actual quenching layer depth of the flange shaft quenching control at about 2mm is most appropriate.
Heating transition layer is much smaller than the quenching heating layer, the general layer depth of induction current penetration depth of 0.25-0.3 times, that is, the depth of about 1mm.
In order to achieve the best quenching efficiency, the induction current penetration depth should be about 4mm is more suitable, then: the total heating heat flow expansion depth ≈ surface superheat layer depth + over the induction current penetration depth + heating transition layer depth ≈ 0 + 4 + 1 ≈ 5 (mm) Similarly, when the inductor heated to the inner surface of the flange, the total heating layer depth of 5mm, and the thickness of the flange is also 5mm. therefore, the flange is heated through The quenching will be quenched through, resulting in the scrapping of the part.
The solution measures
According to the analysis of the above reasons, to solve the flange shaft is quenched through the problem, one is to change the structure of the parts to increase the thickness of the flange, does not produce the phenomenon of quenching, this program is obviously not feasible, because the parts diagram can not be changed; Second, the heat of the outer surface of the flange will be exported by means of heat transfer, so as to ensure that the inner surface of the flange shaft quenching layer depth.
Measure one: water cooling heat transfer, as shown in Figure 2. Make a cooling water box, set with water inlet and outlet, the water inlet is passed into the cooling quenching fluid. The outer face of the flange shaft is in direct contact with the cooling quenching fluid, and its heat is absorbed by the cooling quenching fluid and flows out from the outlet of the cooling water box. The gap between the inner hole of the water box and the outer diameter of the flange is 0.1-0.3mm. Adjust the flow rate of the water box inlet and outlet so that the flow rate of the inlet is slightly larger than the flow rate of the outlet, the water will not splash out from the gap, and if a little water gushes out, it does not affect the quenching effect.
Figure.2 flange shaft water cooling device
1. support base; 2. quenching water inlet; 3. water spray ring; 4. flange shaft; 5. on the top; 6. sensor; 7. water box; 8. quenching water outlet; 9. under the top; 10. spindle
Measure 2: Steel tooling for heat transfer, as shown in Figure 3. The special tooling is used to place the flange shaft. The outer face (bottom face) of the flange shaft is in direct contact with the tooling, and the heat of the flange is transferred to the tooling; the bottom face and outer diameter of the flange are in direct contact with the tooling, thus absorbing the heat of the flange. The height of the outer ring of the tooling is 0.1-0.3mm lower than the height of the flange, so that the magnetic field generated by the inductor is induced to the upper face of the outer circle of the tooling, which disperses the magnetic flux at the outer circle of the flange, thus making the depth and shape of the hardened layer of the inner end face of the flange shaft meet the technical requirements. And the heat on the tooling will be taken away by the quenching liquid, which will not produce the accumulation of thermal energy and will not affect the mass production.
Figure.3 Flange shaft quenching tooling
1. inductor; 2. flange shaft; 3. upper center; 4. quenching water jet; 5. workpiece; 6. spindle.
In taking the way of heat conduction with the help of external cooling, three aspects should be considered: First, the technical requirements of heat treatment of the parts must be met; second, to improve the efficiency of the induction quenching process; third, to reduce the production cost of the device and the cost of use.
The two solutions compared
In the induction hardening production, we have compared two solutions.
(1) The use of water cooling, through contact with the quenching fluid will be flange shaft flange heat export, which has the effect of increasing its heat capacity.
Advantages: It meets the technical requirements of heat treatment of flange shaft and has a better thermal conductivity.
Disadvantages: the structure of the cooling device is more complex, the production cost is higher.
(2) Heat transfer by steel tooling is used to carry away the heat loaded to the flange through heat conduction of the tooling and dispersion of the induced magnetic flux.
Advantages: meet the technical requirements of heat treatment of flange shaft, the structure of the device is simpler, the production cost is lower, and the cost of use is low.
Disadvantages: The upper end face of the workpiece outer circle is easily burned after being repeatedly heated by fire.
By comparing the two methods, the solution of induction quenching by using steel workpiece heat transfer and decentralized magnetic field, which has a simpler structure of the workpiece and lower production and use costs, prevails.
The heat pattern of the sample block shown in Figure 4 is less than perfect, but the hardened layer depth test results meet the technical requirements for heat treatment of flanged shafts. For official production, the hardened layer depth is controlled at about 2mm.
Figure.4 Sample block
Conclusion
For flange shafts with relatively large differences in geometry, the flange edge with relatively thin material thickness is extremely easy to be quenched during the induction hardening process. The main reason is that the heat capacity is not enough. When the process parameters can not be adjusted to solve the problem, we must find a way to load the heat to the flange side of the heat conduction by means of external cooling, indirectly improve the heat capacity of the flange shaft body, so that the depth of the inner surface of the flange hardened layer to meet the technical requirements of heat treatment.
Source: China Flanges Manufacturer – Yaang Pipe Industry (www.pipelinedubai.com)