To reduce the cost, the nesting process of 9Crl8 stainless steel bearing ring has been tried, and good results have been achieved.

9Crl8 is a commonly used martensitic stainless steel. The steel has good corrosion resistance in weak corrosive medium and under the condition that the temperature does not exceed 30 ℃. It is one of the commonly used steels for rolling bearings. Because of its narrow forging temperature range and poor plasticity, single piece reverse extrusion process is often used to produce bearing rings, which is a waste of materials and low productivity. In order to reduce the cost, the nesting process of 9Crl8 stainless steel bearing ring has been tried, and good results have been achieved.

1. Forging Heating Specification

The equilibrium structure of 9Crl8 steel at room temperature is martensite plus carbide. When heated to more than 950 ℃, it becomes a single austenite. When the heating temperature is higher than 1,150 ℃, it appears ferrite and enters a two-phase state. It is very easy to crack during deformation. Therefore, the forging temperature range of this stainless steel is 1,120 ℃ for initial forging and 950 ℃ for final forging. Electric furnace heating is adopted to ensure the quality of forgings.

Figure 1 original process heating specification

Figure 2 improved process heating specification

The heating specification of the original process is shown in Figure 1. The material section is heated to 800 ℃ with the furnace for 30 min, then raise the temperature to 1,120℃ and keep the temperature for 30 min. Due to the long time of high temperature heating, the coarse austenite forms coarse martensite in the subsequent process, the plasticity is greatly reduced, and the impact resistance of the bearing ring is reduced. After that, the heating specification is changed to as shown in Figure 2. The material section is heated in the furnace at 1,000 ℃ and kept warm for 20 min, and then quickly heated to 1,120 ℃ and kept warm for 15 min to start forging. The effect is good.

2. Determination of Forging Process

The conventional nesting process of bearing ring is shown in Figure 3. This process has the following problems for 9crl8 stainless steel nesting, and forging cracks are easy to appear on the outer diameter surface and bottom surface of the nesting core. The cause of the crack is due to the poor plasticity of 9Crl8 stainless steel. When the single piece reverse extrusion process is adopted, the crack is avoided because the material is in a very high three-dimensional compressive stress state. The key problem of pre extrusion forming is to increase the pre extrusion forming quality of forgings. The process flow is shown in Figure 4. The structure diagram of stew extrusion die is shown in Figure 5.

Fig. 3 conventional nesting process flow

Fig. 4 technological process of stewing extrusion preform

Fig. 5 structure of stewing and extrusion die

After repeated experiments, the diameter d₁ of the stewing extrusion punch and the inner diameter d₂ of the core die are kept at d₁-d₂ = 0.1 ~ 0.3 mm. And H₁-H₂ = 0.5mm is appropriate, which not only ensures the height of the outer ring and the filling of the outer circle fillet, but also ensures the metal weight required by the inner ring.

3. Cooling and Lubrication

The serious wear of die is another factor affecting the mass production of 9Crl8 stainless steel bearing ring. The inner ring reverse extrusion die produces about 150 forgings, and the wear amount is up to 1mm. Moreover, the bottom cutting punch is easy to stick, so that the production cannot continue. The main reasons are the poor thermal conductivity and fluidity of 9Crl8 stainless steel and the mold heating block. In order to solve this problem, tap water is used for forced cooling and water agent graphite is used to lubricate the mold in production. The service life of dies has been increased from less than 150 to more than 2,000.

4. Conclusion

It is feasible for 9Crl8 stainless steel bearing ring to adopt stewing extrusion nesting process, and the effect of energy saving and material saving is remarkable. Taking 6204 / 01 sets of 6205 / 02 as an example, the production of 10,000 pieces can save 660kg of steel, which is 16,500 yuan according to the current price of 25 yuan / K. Moreover, only one heating and blanking can produce two products, saving 600 yuan per 10,000 pieces of energy, which has significant economic benefits.

More about FRC Stainless steel bearings:

Stainless steel bearings provide a several notable benefits when other materials pose problems. Notably, stainless steel offers greater chemical and corrosion resistance, along with better stability in high temperature environments. These benefits make stainless steel bearings a great fit for applications in demanding environments or specialty circumstances.

FRC stainless steel ball bearings can be supplied with food grade lubricants, water resistant or chemically resistant lubricants as well as high temperature lubricants to withstand up to 300°C. Stainless steel will cope with much higher temperatures than chrome steel.

Stainless steel bearings are suitable for use in mildly corrosive environments as the steel is corrosion resistant but it is affected by seawater and stronger acids or alkalis. For higher loads and speeds, we stock a range of full ceramic bearings.

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