In the past, one of our customers used a box furnace for the overall heat treatment of the gun barrel tail seat. Under the quenching temperature, due to the oxidation and decarburization on the surface, the hardness of the heat treatment was uneven. In addition, the shape of the gun barrel tail seat is asymmetric, quenching deformation is difficult to correct. To do this, they purchased KQG – 60 type transistor intermediate frequency induction heating equipment, we made the special sensor for its design, not only ensure the two locking groove heat at the same time but also effectively control the heating position, prevent waste thin wall surrounding the place too hot melt quality problem, for transistor intermediate frequency induction heating equipment successfully applied in barrel tailstock local heat treatment.
1. Process principle
(1) The gun barrel tailstock replaces the box furnace with the transistor-type if induction heating method. With the advantages of safety, reliability, and energy saving of the transistor IF induction heating equipment, it can not only guarantee the hardness requirements of local heat treatment of the workpiece but also prevent the problem of deformation out of tolerance.
(2) The heating effect of the workpiece is not only dependent on the working current of the induction coil, but also directly related to the shape of the induction coil, the material of the workpiece, and the shape factor. The problem of overheated molten waste at the peripheral thin wall caused by induction heating of new equipment must be solved for the inner hole of the barrel tail seat relative to two locking slots. To this end, we designed and manufactured a sensor with a shape like a gourd, which not only ensures the simultaneous heating of the two locking slots but also effectively controls the heating position to prevent the quality problem of excessive hot melting at the peripheral thin wall, thus ensuring the successful application of the new equipment in the local heat treatment of the barrel tail seat.
2. The proposal of a new process of intermediate frequency induction hardening for gun barrel tailstock
To meet the requirements of energy saving and consumption reduction, vacuum tube type high frequency equipment is gradually phased out, and transistor type medium frequency equipment is used in the local heat treatment of barrel tail base, so as to solve the problem of uneven hardness and out-of-tolerance deformation of overall heat treatment of barrel tail base before. Our company’s newly developed pump gun barrel tail seat heat treatment is more difficult, the original use of converter overall heating quenching, due to the box furnace heating oxidation decarbonization, resulting in uneven hardening hardness. In addition, due to its asymmetry, the heat treatment deformation is seriously out of tolerance and difficult to correct. For this, we adopt KQG – 60 transistor intermediate frequency induction equipment to local heating of the barrel the tailstock, by heating the piece to be hardened in symmetrical two locking groove tube hole, started using conventional sensors for blocking fossa fracture to the thin wall surrounding the burning-out waste, to solve this problem, we passed the test design special sensors, ensures that the new equipment in the barrel tailstock local heat treatment of successful application solved the barrel tailstock uneven quenching hardness and heat treatment deformation problem as a whole.
3. Feasibility analysis of a new technology of intermediate frequency induction heating for barrel tailstock
(1) on the basis of electromagnetic induction, the “proximity effect” and the basic principle of heat conduction, barrel tailstock local induction heat treatment, heat treatment can be adopted by controlling the output current, and the heating time, ensure that the barrel tailstock tube hole symmetry, after two locking slot in induction heating quenching hardness of the product performance requirements: 45 ~ 50 HRC,
(2) The gun barrel tail seat sensor. The hardness of the local heat treatment of the gun barrel tail seat is required to be greater than 45HRC. The wall thickness of the induction part is 4.5mm, while the surrounding wall thickness is only 1.5mm.In this regard, we designed a special sensor, which is shaped like a bottle gourd and USES the arc induction heating inside the bottle gourd to heat two locking slots in the tail seat.
4. New process scheme of intermediate frequency induction quenching for gun barrel tailstock
Through heat treatment process test and trial production, the new intermediate frequency quenching process for gun barrel tailstock is improved and introduced as follows:
(1) Material of gun barrel tail seat: 42CrMo.
(2)Induction quenching equipment: KQG-60 intermediate frequency equipment.
(3) Design and manufacture of gun barrel tail seat sensor, it is shaped like a gourd, with the arc induction heating inside the gourd tail seat two locking groove, adjacent to the locking nest at the thin wall just gourd mouth and bottom side, away from the sensor copper pipe without overheating.
(4) Input power: 60kVA.
(5) Output oscillating current: 1000A.
(6) For induction heating, the quenching heating temperature was changed from (860±10) ℃ to (870±10) ℃ in order to ensure that the workpiece was heated uniformly, organized well and the technological parameters were adjusted. Induction heating time: 15 ~ the 20s.
(7) Quenching cooling medium: quick quenching oil to ensure that the local induction quenching hardness is greater than 55HRC.
(8) Tempering equipment is RJJ-35 well furnace, with 100 pieces of furnace capacity, tempering temperature of 180±10℃, and holding time of 1.5 ~ 2h.
5. Comparison of new and old processes
(1) The original process of barrel tailstock adopts box furnace to heat as a whole, and there are oxidation and decarburization on the surface, resulting in uneven hardness; Since the adoption of the new medium frequency induction local heat treatment technology, the test and trial production show that the workpiece has no oxidation and decarburization, and the hardness is uniform, reaching 45 ~ 50HRC, which meets the design requirements.
(2) The original process of barrel tail seat adopts a box furnace to heat as a whole. After quenching, the deformation is 0.15 ~ 0.2mm, making straightening difficult; Since the adoption of the new process of intermediate frequency induction local heat treatment, the test and trial production show that the local heat treatment of the workpiece has no deformation and out-of-tolerance phenomenon, and all meet the design requirements.