Method of manufacturing of ball bearing's rings by rolling-out of the blanks from bearing's steel using a roll-out machine

Background of the invention

This invention concerns the method of manufacturing of ball bearing's rings by roll- out of the blanks from bearing's steel using a rolling-out machine

State of the art

Ball bearing's rings are usually manufactured by hot rolling-oout at the forging temperature or by cold rolling-out.

By hot rolling-out the starting material are blanks forged either by hammer forging or by die forging. The forges which manufacture ball bearing's rings are usually equipped with roll-out machines of various types of different suppliers. The rolling- out of blanks is done at the forging temperatures above 850 ⁰ C, for bearing steel typically between 1050 ⁰ C - 850 ⁰ C.

Disadvantages of this technology are big material allowances and tolerances which have to balance the manufacturing inaccuracies, shrinkage, decarburisation, surface defects arising not only by rolling-out but also by forging. There is higher energy consumption because the furnaces are set at 1100 ⁰ C and due to high temperature there is heat-stressing of the tools and the machine, there is lower accuracy in shapes and dimensions, less efficient use of materials, and in many cases a less appropriate orientation of material fibres, which are disrupted by the subsequent machining.

Cold rolling-out at temperatures below 400 ^C C is relatively new technology where the material is shaped, respectively rolled-out, either at the temperature of the surroundings, or at slightly elevated temperatures. The rolling-out is made using a

special rolling-out machine. As the blank there is a lathe-turned ring of an appropriate shape.

Cold rolling-out therefore enables the lower materials allowance, the higher dimensional accuracy, and more efficient use of material. The rolled-out shape is precice and corresponds approximately to the shape of the completely finished ring, so the orientation of fibres is very good considering the subsequent strains in the bearing ring. By the cold rolling-out process the material is strengthened.

But there is the disadvantage because the material has to have a uniform structure appropriate for cold rolling-out. The material has to be soft annealed with some arrest at the annealing temperature. Cold rolling-out also includes greater strains on the machine due to necessity of higher forming power and higher forming work. This means greater demands on the quality of the tools, which have to endure higher stresses. There is a non-uniform deformation strain in the material which results in dimention deformations and ovality of the ring after tempering.

The aim of the invention is to eliminate the above mentioned disadvantages and to achieve lover forming work, lower energy consumption, better exploitation of the material, lower weight of the blanks, longer tool life, and lower material allowances and tolerances and evetually to aenable rolling-out of rings of greater dimensions.

Feature of the invention

The above mentioned disadvantages are considerably eliminated by the use of the method of manufacturing of ball bearing's rings by rolling-out of the blanks from bearing's steel using a roll-out machine according to the invention, where the blank is heated at the temperature between 600 °C and 800 ⁰ C before being rolled-out.

In a preferred embodiment the blank is heated at the temperature between 700 ⁰ C and 720 ⁰ C before being rolled-out.

In another preferred embodiment the rolled -out blanks are blanks from hammer forging or die forging or the rolled-out blanks are lathe-turned blanks or the rolled-out blanks are rings divided from thick-walled tubes.

The advantage of this solution is lower energy costs in a comparison to forged rolling.out, less forming work in a comparison with cold rolling-out, better exploitation of material, lower weight of the blanks in a comparison to the heat rolling-out, longer tool life, and lesser material allowances and lower tolerances in a comparison with forged rolling-out. Forge scale formation and decarburisation is minimal and they have a negligible effect on turning allowances. This solution also enables to manufacture rings of greater dimensions in a comparison wit cold rolling-out.

Preferred embodiment of the invention

The invention concerns the technology of manufacturing of ball bearing's rings by use of ,,semi-hot" rolling-out of the blanks The proposed technology effectively utilises the advantages of both of the above described technologies from state of the art while eliminating their disadvantages.

The principle is that the rolling-out takes place at temperatures between 600 to 800 ⁰ C. Advantageous temperature is in the range of 700 - 720 ⁰ C. As the starting material for the blanks of thick-walled tubes or die forged blanks are used. These blanks are lethe-turned to the necessary shape and volume. The turned ring is then placed in an induction heater where it is heated up to the required temperature, e.g. of 720 ⁰ C. The unloading from the heater is monitored by a thermometer which controls temperature maintenance so that only a blank with the proper temperature is put into the rolling-out machine.

The transfer between the heater and the roll-out machine is proceeded by a robot. The rolling-out process is programmable and is computer controlled and stored in its memory. This guarantees the repeatability and accurate reproduction of the profile. After rolling-out, the ring is taken out of the machine and placed on a cooling-after conveyor which enable uniform and controled cooling to the temperature of about 300 ⁰ C.

The advantage of this solution is lower energy costs in a comparison to forged rolling.out, less forming work in a comparison with cold rolling-out, better exploitation of material, lower weight of the blanks in a comparison to the heat rolling-out, longer tool life, and lesser material allowances and lower tolerances in a comparison with forged rolling-out. Forge scale formation and decarburisation is minimal and they have a negligible effect on turning allowances. This solution also enables to manufacture rings of greater dimensions in a comparison wit cold rolling-out.

This proposed new technology of rolling-out of blanks using "semi-hot" conditions utilises the technological advantages of both technologies known from the state of the art while eliminating their disadvantages. The optimal temperature for implementing the methods outlined in the invention is between 700 - 720 ⁰ C, where the material's deformational resistance is half of the value in a comparison with cold material and there is improved plasticity of the material. <CύTv