Casting and Rolling Composite Technology of 42CrMo Bearing Ring Blank

Abstract: There are many forging processes and high costs for the 42CrMo oversized bearing ring blank. This article introduces the process flow and various process parameters of producing bearing ring blanks using the casting and rolling composite process. Through inspection, it is shown that the mechanical properties, impact energy, and hardness of the ring blanks processed by the casting and rolling composite process meet the relevant technical requirements.

Keywords: Extra large bearings; 42CrMo; Forging; Rolling and rolling; Casting and rolling composite process; performance testing

At present, the bearing industry mostly uses 42CrMo steel ring forgings as blanks for oversized bearing rings. The processing process of bearing ring forgings is as follows: steelmaking → ingot casting → cutting off the ingot cap and tail → ingot heating → forging → upsetting → hole expanding → secondary heating → rolling. There are many processing procedures and high costs for forging blanks. In order to reduce the processing process of the blank and reduce production costs, the casting ring part+rolling composite forming process is adopted instead of the original process. Using conventional smelting and pouring processes to cast circular castings, the circular castings are then rolled and processed into rough bearing rings, and then normalized and quenched to obtain mechanical properties that meet technical requirements.

1. Process flow

The processing process for producing oversized bearing ring blanks using casting and rolling composite technology is as follows: smelting → casting (casting into circular castings) → heating of casting ring parts → rolling → normalizing → turning processing → quenching and tempering treatment.

1.1 Smelting

(1) Smelting method: Electric arc furnace smelting.

(2) Feeding coefficient: 1.184 (the proportion of scrap iron required to be added per ton of casting, excluding alloy element content). (3) Alloy element ratio: Mo 5 kg/t, Cr 18 kg/t, Si 5.5 kg/t, Mn 12 kg/t, Al 1.2-1.5 kg/t.

(4) Smelting temperature: 1680-1700 ℃.

(5) Smelting time: 3.5-4 hours.

(6) After the furnace material is fully melted, conduct a rapid analysis in front of the furnace, measure and adjust the chemical composition of the steel liquid. The chemical composition of the steel liquid should meet the requirements of Table 1.

(7) After the chemical composition of the molten steel is adjusted to be qualified, pour the molten steel from the smelting furnace into the ladle.

Table 1 Chemical Composition of ZG42CrMo Steel Liquid          w,%

(8) Remove the slag floating on the ladle, and then use a portable thermometer to measure the temperature of the molten steel. Let the temperature of the molten steel stand at 1550-1560 ℃, and the quenching time of the molten steel before casting should not be less than 3 minutes.

1.2 Casting

(1) Molding sand formula: water glass 7% -9%, bentonite 1% -1.5%, and the rest are quartz sand.

(2) Molding sand mixing process: Use a sand mixer to mix dry quartz sand with bentonite, dry mix for 8-10 minutes, then add water glass, mix for 10-15 minutes, and produce sand for molding.

(3) Shape: After the molding sand is mixed, it should be immediately shaped according to the process requirements to avoid hardening of the molding sand.

(4) Pouring temperature: 1550-1560 ℃.

(5) Pouring speed: 65-70 kg/s.

(6) Pouring time: approximately 15 seconds (depending on the size of the casting).

(7) Insulation time: The casting is insulated with sand mold for 22 hours.

(8) Cut the sprue and riser when the casting ring is cooled to 400-500 ℃.

1.3 Rolling

Heat the casting ring to 1150 ℃, with a heating speed of 150 ℃/h, and a holding time of 4-5 hours before rolling. The axial rolling force of the ring rolling machine is 0-200 t, and the radial rolling force is 0-250 t.

1.4 Normalization

To refine the structure of the rolled parts, they should be subjected to normalizing treatment. The normalizing process is to heat them up at a heating rate of 30-70 ℃/h to (650 ± 5) ℃, keep them warm for 1 hour, then heat them up at a rate of 50-100 ℃/h to 860-880 ℃, keep them warm for 8-9 hours, and then air cool them out of the furnace. The process curve is shown in Figure 1.

Figure 1 Normalizing Process Curve

1.5 Tempering

In order to ensure the mechanical properties of oversized bearings, the rolled parts are subjected to quenching and tempering treatment. The process route of quenching and tempering treatment is: heating at a rate of 30-70 ℃/h to (650 ± 5) ℃, holding for 1 hour, and then heating at a rate of 50-100 ℃/h to (840 ± 5) ℃, holding for 2.5 hours before quenching out of the furnace. After quenching, tempering should be carried out in a timely manner (within 2 hours). The workpiece should be heated to (580 ± 5) ℃ at a heating rate of 30-70 ℃/h in the tempering furnace, and left for 6 hours for air cooling. The process curve is shown in Figure 2.

Figure 2 Tempering Process Curve

2. Technical requirements and inspection results

In order to verify whether the mechanical properties of the 42CrMo oversized bearing ring blank produced by the casting and rolling composite process can meet the technical requirements, the casting and rolling composite parts after quenching and tempering treatment are dissected, and their mechanical properties and impact energy are tested after dissection. The requirements for mechanical properties and impact energy in JB/T5000.6-1998 "General Technical Conditions for Heavy Machinery (Steel Castings)", JB/T6396-2006 "Technical Conditions for Large Alloy Structural Steels", and Q/LYCC (B) 0014 "Technical Conditions for Ordering 42CrMo Steel Ring Forgings for Wind Turbine Bearings", as well as the mechanical properties and impact energy inspection results of cast and rolled composite parts, are shown in Table 2. From Table 2, it can be seen that the mechanical properties, impact energy, and hardness of the ring blank produced by the casting and rolling composite process all exceed the technical requirements of JB/T 6396-2006 and Q/LYCC (B) 0014.

3. Conclusion

The experimental results indicate that the production of 42CrMo oversized bearing ring blanks using the casting and rolling composite process is completely feasible. The new casting and rolling composite process reduces production processes such as forging, upsetting, hole expanding, and secondary heating, greatly reducing production costs.

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