How to solve the problem that the inner end face of long weld neck flange is easy to be hardened?
The material of the long weld neck flange as shown in the figure is 40Cr, and the total length is 215mm. The diameter of the shaft body is 60mm and the length is 210mm. The outer surface of the cylinder is quenched, the hardened layer depth is 1-3mm, and the hardness is 45-50HRC. The diameter of the long welding neck flange part is 90mm, the thickness is only 5mm, the surface of the inner end surface is hardened, the hardened layer depth is 1-3mm, and the hardness is 45-50hrc. Induction hardening is a vertical scanning quenching, starting from the inner end of the long weld neck flange, from bottom to top scanning quenching. In the process of induction quenching, the long weld neck flange part is easily heated and burned, resulting in quenching, which cannot meet the technical requirements. After many times of adjustment of process parameters, the effect is not obvious. This requires a new approach to solve the problem of hardening the flange edge in a new way.
Figure.1 quenching requirements of long welding neck flange
The entity of the cylinder with long high-necked flange is thick, and the heat capacity of the material is relatively high. In the process of induction quenching, penetration heating is adopted (that is, the quenching heating layer is smaller than the induction current heat penetration depth). The temperature distribution of penetrating quenching heating layer, from outside to inside in order: surface overheating layer, quenching heating layer (full austenitic layer), heating transition layer.
The depth of the overheated surface layer is very small, which can be ignored, and the value is 0.
The quenching heating layer will constantly advance to the column body in depth until it reaches the penetration depth of the induction current. According to the technical requirements of the heat treatment layer depth of the cylinder part of the long weld neck flange, it is most suitable to control the actual hardened layer depth of the long weld neck flange to be about 2mm when quenching.
The heating transition layer is far less than the quenched heating layer, and its general layer depth is 0.25-0.3 times of the penetration depth of the induction current, I .e. the depth is about 1mm.
In order to achieve the best quenching efficiency, it is more suitable that the penetration depth of induction current should be about 4mm, then: the extension depth of total heating heat flow ≈ the depth of the surface overheated layer + the penetration depth of the over-induction current + the depth of the heating transition layer ≈ 0+4+1 ≈ 5(mm) is the same, when the sensor is heated to the internal end face of the flange, the total depth of the heating layer is 5mm, and the thickness of the flange is 5mm. Therefore, the flange is heated through, and it will be quenched during quenching, resulting in the scrap of the parts.
According to the analysis of the above reasons, to solve the problem of the flange of the long weld neck flange is quenched, one is to change the structure of the part, increase the thickness of the flange, do not produce the phenomenon of quenching, this scheme is obviously infeasible because the part drawing cannot be changed. The second is to export the heat from the outer end of the flange through heat conduction, so as to ensure the depth of the hardened layer of the inner end face of the long weld neck flange.
Measure 1: Water cooling heat transfer, as shown in the figure. Manufacture a cooling water box with water inlet and water outlet inlet to cool quenching liquid. The outer end of the long weld neck flange directly contacts with the cooling quenching liquid, and its heat is absorbed by the cooling quenching liquid 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 of the water box inlet and outlet so that the flow of the water inlet is slightly larger than that of the outlet, and the water will not splash out from the gap, if a little water flows out, it will not affect the quenching effect.
Figure.2 long weld neck flange water cooling device
1. Support seat, 2. Quenching water inlet, 3. Water spray ring, 4. Long high neck flange, 5. Go to the top, 6. Sensor, 7. Water box, 8. Quenching outlet, 9. Under the top, 10. Spindle
Measure 2: Heat Transfer of steel tooling, as shown in the figure. The special tooling is used to place the long weld neck flange. The bottom surface of the outer face of the long weld neck flange directly contacts the tooling, and the heat of the flange is conducted to the tooling; The bottom surface and the outer diameter of the flange directly contact with the tooling, so as to absorb the heat of the flange. The height of the outer ring of the tooling is 0.1-0.3mm lower than that of the flange, which makes the magnetic field generated by the sensor induce to the upper end face of the outer circle of the tooling, dispersing the magnetic flux at the outer circle of the flange, so that the depth and shape of the hardened layer of the inner end face of the long weld neck flange can meet the technical requirements. 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 long weld neck flange quenching tooling
1. Sensor, 2. Long high neck flange, 3. Top, 4. Quenching sprinkler, 5. Tooling, 6. Spindle
When adopting the way of external cooling and heat conduction, it should be considered from three aspects: first, it must meet the requirements of heat treatment technology of parts; Second, it is necessary to improve the efficiency of induction quenching; the third is to reduce the production cost and use cost of the device.
The comparison of two solutions
In induction quenching production, we compared the two solutions.
- (1) by using water cooling, the heat of the long-high neck flange is derived through the contact with quenching liquid, which has the effect of increasing its heat capacity.
- Advantages: it meets the technical requirements of heat treatment for long weld neck flanges, and has good heat conduction effect.
- Disadvantages: the structure of the cooling device is complex and the production cost is high.
- (2) adopt the way of steel frock heat transfer, take away the heat loaded into the flange through the heat conduction of frock and dispersed induction magnetic flux.
- Advantages: it meets the technical requirements of heat treatment of long weld neck flange, and the structure of the device is relatively simple, the production cost is relatively low, and the use cost is low.
- Disadvantages: after the upper side of the outer circle of the tooling is heated repeatedly, it is easy to burn out.
By comparing the two ways, adopting the way of steel tooling’s heat transfer and dispersive magnetic field to conduct induction quenching tooling has a simple structure, and the production and use costs are also relatively low. This scheme is dominant.
As shown in figure 4, the hot-mode sample block is not perfect, but the hardened layer depth detection result meets the requirement of heat treatment technology of long weld neck flange. For formal production, the depth of hardened layer is controlled at about 2mm.
Figure.4 sample blocks
For long welding neck flanges with large geometric shape difference, in the process of induction hardening, the flange edge with relatively thin material thickness is easy to quench. The main reason is that its heat capacity is not enough. When adjusting process parameters can not solve the problem, we should think of a way to export the Heat loaded on the flange side by means of external cooling and heat conduction, indirectly improve the heat capacity of the long weld neck flange body, so that the hardened layer on the inner surface of the flange deeply meets the technical requirements of heat treatment.
Author: Liu Junhui
Source: China Long Weld Neck Flange Manufacturer – Yaang Pipe Industry (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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