Forging Heating Method

Generally, the forging heating in which the amount of burning loss is 0.5% or less is less oxidative heating, and the heating in which the amount of burning loss is 0.1% or less is referred to as non-oxidizing heating. Less oxidation-free heating can reduce metal oxidation and decarburization, and can also significantly improve the surface quality and dimensional accuracy of forgings and reduce mold wear. Less oxidation-free heating technology is an indispensable supporting technology for precision forging. At present, this technology has yet to undergo a lot of research work in China.

 

There are many ways to achieve less oxidation-free heating. The commonly used and fast-developing methods are rapid heating, medium protection heating and less oxidizing flame heating. machining part

 

—, rapid heating

Rapid heating includes rapid heating and convection rapid heating, induction electric heating, and contact electric heating in a flame furnace. The theoretical basis for rapid heating is that when the metal blank is heated at a technically possible heating rate, the superposition of temperature stress, residual residual stress and tissue stress generated inside the billet is insufficient to cause cracking of the billet. This method can be used for small-sized carbon steel ingots and blanks for general forging of simple shapes. Since the above method has a high heating rate, the heating time is short, and the oxide layer formed on the surface of the billet is thin, so that the purpose of oxidation is small.

When induction heating, the amount of burning of the steel is about 0.5%. In order to achieve the requirement of no oxidation heating, a protective gas can be introduced into the induction heating furnace. The shielding gas is an inert gas such as nitrogen, argon, helium or the like, and a reducing gas such as a mixture of CO and H2, which is specially prepared by a protective gas generating device. cnc 

Since rapid heating greatly shortens the heating time, the degree of decarburization can be significantly reduced while reducing oxidation, which is different from the less oxidizing flame heating, which is one of the greatest advantages of rapid heating. plastic part

 

2, liquid medium protection heating

 

Common liquid protection media are molten glass, molten salt, and the like. The salt bath furnace heating described in the first section of Chapter 2 is a type of liquid medium protection heating.

 

Figure 2-24 shows a pusher type semi-continuous glass bath furnace. In the heating section of the furnace, a high-temperature molten glass is melted in the bottom of the furnace, and the billet is heated after being continuously pushed through the glass liquid. Due to the protection of the glass liquid, the billet is not oxidized during the heating process, and after the billet is pushed out of the glass liquid, the surface is on the surface. Attached to a thin layer of glass film, it not only prevents secondary oxidation of the billet, but also lubricates it during forging. This method is fast and uniform in heating, has good oxidation and decarburization effects, and is easy to operate, and is a promising less oxidation-free heating method.
3, solid medium protection heating (coating protection heating)

 

A special coating is applied to the surface of the blank. When heated, the coating melts to form a dense and airtight coating film. It is firmly bonded to the surface of the blank to isolate the blank from the oxidizing furnace gas to prevent oxidation. After the billet is discharged, the coating can prevent secondary oxidation and has a heat insulating effect, which can prevent the surface temperature drop of the billet and can act as a lubricant during forging.

 

The protective coating is divided into a glass coating, a glass ceramic coating, a glass metal coating, a metal coating, a composite coating, and the like according to its composition. The most widely used is the glass coating.

 

Glass coatings are suspensions of a certain composition of glass powder, plus a small amount of stabilizer, binder and water. Before use, the surface of the blank should be cleaned by sandblasting, etc., so that the surface of the coating and the blank can be firmly bonded. Coatings are applied by dip coating, brush coating, spray gun spraying and electrostatic spraying. The coating is required to be uniform. The thickness is appropriate. Generally, it is 0.15 to 0.25 mm. If the coating is too thick, it is easy to peel off, and it is too thin to protect. After coating, it is naturally dried in the air and then placed in a low temperature drying oven for drying. It is also possible to preheat the billet to about 120 ° C before coating, so that the wet powder is dried immediately after application, and adheres well to the surface of the blank. The pre-forging heating can be carried out after the coating is dried.

 

In order to provide good protection and lubrication of the glass protective coating, the coating should be properly melted, viscous and chemically stable. When the various distribution ratios of the glass are different, the above physical and chemical properties are different. Therefore, the use depends on the type of metal material and the level of forging temperature. Choose the right glass ingredients.

 

The glass coating protection heating method has been widely used in the production of titanium alloy, stainless steel and superalloy aviation forgings in China.