JPS6360805B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a rolling press hardening device. Rolling press hardening is a method of hardening the workpiece under pressure from the outside, so it can reduce distortion during hardening, so it is suitable for axially symmetrical parts such as pins and shafts, and other axially symmetrical parts. This is a quenching method that is relatively frequently used for quenching parts with . First, to explain the outline of this hardening device, as shown in FIG.
3, and the heated workpiece A is placed between these rollers 1, 2, and 3. roller 1,
As shown in FIG. 2, 2 and 3 include shaft parts 4, 5, and 6, which are formed to have a larger diameter than the shaft parts 4, 5, and 6, and which apply pressure by contacting the surface of the workpiece A. A so-called cylindrical grooving roller having pressurizing parts 7, 8, and 9 is used; however, as shown in FIG.
A so-called spiral groove cutting roller in which rollers 8 and 9 are arranged in a spiral may be used. The workpiece A is rotated by the rollers 1, 2, and 3, and is also pressurized from the outside.
Water spray nozzle 10,1 disposed between 3
The surface is quenched by the water jetted from 0 and 10. Since the workpiece A is hardened while being pressurized from the outside in this way, the bend in the axial direction is corrected during the process, and as described above, the distortion during hardening can be made extremely small. By the way, in the conventional hardening equipment mentioned above,
It is known that when a material with poor hardenability is hardened, there is a problem in that the surface hardness distribution along the axial direction of the hardened product becomes non-uniform. For example, Fig. 4 shows the axial surface hardness distribution of a specimen made of carbon steel having the components shown in Table 1, which was hardened using a conventional cylindrical groove roller.
Figure 5 shows a similar hardness distribution when hardening is carried out using a cylindrical grooving roller as the pressure roller and a spiral grooving roller oriented in opposite directions as the receiving roller. In the former case
It is clear that there is a large variation between HRC52 and 63, and in the latter case HRC57 and 64.

[Table] When parts with large variations in surface hardness are used, parts with low surface hardness may be selectively abraded, and surface compressive residual stress and strength may be partially reduced. ,the result,
A problem arises in that the durability of the product is significantly reduced. This invention was made in view of the above, and its purpose is to provide a hardened product with high surface hardness and a uniform surface hardness distribution along the axial direction even if the material has poor hardenability. The purpose of the present invention is to provide a rolling press hardening device that can perform the following steps. The present inventors compared the hardness distribution when using a cylindrical grooving roller and when using a helical grooving roller, and found that the hardness distribution was slightly improved when the helical grooving roller was used. After focusing on the fact that there is a tendency to
It has been found that this is because the frequency of contact with the second and third pressurizing parts 7, 8, and 9 is different. In other words, while the cooling water is sprayed onto the surface of the workpiece, the parts of the rollers 1, 2, and 3 that frequently come into contact with the pressurizing parts 7, 8, and 9 are not cooled rapidly and complete hardening is not performed. That means no. The reason why the hardness distribution is improved when using the spiral grooving roller as described above is that the surface of the workpiece comes into contact with the pressure parts 7, 8, and 9 of the rollers 1, 2, and 3 less frequently. It is assumed that this is because they are getting used to it. Therefore, the rolling press hardening apparatus of the present invention based on the above knowledge has a pressure roller and a set of receiving rollers, and each of these rollers has a pressure section that contacts the outer periphery of the steel workpiece. formed at intervals,
In a rolling press hardening device in which a workpiece is placed between rotating rollers and hardened while rotating under pressure, between one set of rollers arbitrarily selected from three rollers, There is an overlapping part where the contact part of the pressure part of one roller to the outer periphery of the workpiece and the part of the contact part of the pressure part of the other roller to the outer periphery of the workpiece overlap each other. The pressing part of each roller is arranged so that the length in the axial direction is about 4 mm or less. The numerical value of 4 mm here is a value that has been experimentally and theoretically confirmed as a value that can achieve the purpose of the present invention. Next, specific embodiments of the present invention will be described in detail with reference to the drawings. First, a first embodiment of the present invention is shown in FIGS. , 3 is substantially the same as the known device described above. In this case, the pressure roller 1 and both receiving rollers 2 and 3 are both connected to the shaft portions 4, 5, and 6, and have diameters larger than the shaft portions 4, 5, and 6, and are equally spaced relative to the shaft portions 4, 5, and 6. It has pressurizing parts 7, 8, and 9 arranged at intervals. These pressurizing parts 7, 8, and 9 are all parts that come into contact with the outer periphery of the workpiece A, but in this case, each pressurizing part 7,
The width W of 8 and 9 is larger than one-third of the arrangement pitch P of each pressure section. The pressing portions 7, 8, and 9 of the rollers 1, 2, and 3 are arranged at the same pitch and offset by one-third of a pitch in the axial direction. Therefore, when viewed from the side perpendicular to the axial direction (Fig. 6a)
The pressure units 7, 8, and 9 are arranged alternately so that some of them overlap each other in the vertical direction, and one roller is attached to the peripheral side of the workpiece A. a portion a that contacts only the pressurizing parts 7, 8, and 9;
The portion b that contacts the pressing portions 7, 8, and 9 of any two rollers coexists. In this invention, the width of the portion b of the workpiece that contacts the pressure parts 7, 8, and 9 of the two rollers, that is, the vertical overlap width of each pressure part 7, 8, and 9 is an important factor. Become. Therefore, various experiments were conducted in which the width of this portion b was varied. For example, if the diameter of the pressure part 7 of the pressure roller 1 is 75 mm, the diameter of the pressure parts 8, 9 of the receiving rollers 2, 3 is 115 mm, and the width of each pressure part 7, 8, 9 is 15 mm, Diameter 20~70mm
Tests were conducted using the processed article A while varying the pitches P of the pressurizing parts 7, 8, and 9. As a result, in all tests, the pressurizing parts 7, 8,
If the overlap width in the vertical direction of 9 is 4 mm or less, the surface hardness of the processed product is high, and there is no variation in surface hardness distribution along the axial direction, and the overlap width is 4 mm.
It has become clear that when the hardness exceeds this value, the hardness distribution suddenly fluctuates. For example, when the vertical overlap width of each of the pressurizing parts 7, 8, and 9 is 4 mm, the surface hardness distribution along the axial direction is extremely good as shown in Fig. 7 (steel material composition is table 1
(same as shown in ). Therefore, in both cases, the limit value of the overlap width at which variations in hardness distribution occur is 4.
We investigated the reason why it is mm.
Figure 8 shows the cooling curve (calculated value) at a predetermined distance from the cooled end surface when the steel surface heated to 850°C is rapidly cooled with water. , 1 second after the start of cooling, the temperature at the cooled end surface is approximately 120℃, and the temperature is 2 mm from the cooled end surface.
It is clear that the temperature decreases to about 430°C at a distant position and to about 680°C at a position 4 mm away from the cooling end face. By the way, in carbon steel
The nose of the CCT diagram usually shows about 1 second after the start of cooling.
If the temperature is around 450℃ and the cooling rate is faster than this, a complete martensitic structure can be obtained, but
It is said that if the cooling rate is slower than this, a part of the steel will contain a bainitic structure and complete hardening will not be possible. From this and the above cooling curve, it can be seen that complete hardening can be achieved by heat conduction if the distance from the cooled end face is within about 2 mm. By the way, this is 2 of the items to be processed A.
Considering the part b that contacts the two pressurizing parts 7, 8, and 9, even if the cooling water does not work effectively, this part b should be approximately 2 mm from the end surface of the pressurizing parts 7, 8, and 9, i.e. Approximately 4mm considering both end faces
Within this range, effective hardening can be performed by heat conduction from the end surfaces of the pressurizing parts 7, 8, and 9.
From the above, when the width of the part b where the processed product A contacts the pressure parts 7, 8, and 9 of the two rollers exceeds 4 mm, the sudden variation in hardness distribution occurs because cooling water is effective. It is thought that this is because when the cooling effect cannot be applied to the pressurizing parts 7, 8, 9, the cooling effect due to heat conduction from the end surfaces of the pressurizing parts 7, 8, 9 does not reach the central part thereof. Furthermore, as shown in FIG. 6, if the pressure parts 7, 8, and 9 of the two rollers are arranged so that they overlap in the vertical direction, it is possible to prevent scratches from occurring on the surface of the processed product due to contact with the roller surfaces. It becomes possible. The rolling press hardening device of the present invention is constructed as described above. Accordingly, even if the material has poor hardenability, the hardened product can be hardened and The surface hardness distribution along the axial direction can be made uniform without variation. Further, since the contact portions of the pressurizing portions on the workpiece are overlapped with each other, it is possible to prevent scratches caused by contact with the roller surface even when the pressurizing force is large.

[Brief explanation of drawings]

Figures 1 to 5 are diagrams showing known techniques, in which Figure 1 is a principle diagram of a rolling press hardening device, and Figure 2 is a diagram showing the principle of a rolling press hardening device.
3 and 3 are explanatory diagrams each showing the roller shape, FIGS. 4 and 5 are graphs each showing the quenching hardness distribution by a conventional device, and FIGS. 6 to 8 are diagrams for explaining the present invention. FIGS. 6a and 6b are explanatory diagrams of an example of the arrangement of pressure parts, FIG. 7 is a graph showing the quenching hardness distribution according to the arrangement of the pressure parts, and FIG.
The figure is a graph showing the relationship between elapsed time and temperature during quenching. A... Workpiece, 1... Pressure roller, 2, 3... Receiving roller, 7, 8, 9... Pressure section.

Claims (1)

[Claims] 1 It has a pressure roller and a set of receiving rollers, and each of these rollers is formed with a pressure part that contacts the outer periphery of the steel workpiece at intervals, and the workpiece is placed between the rotating rollers. In a rolling press hardening device that hardens a product while rotating it under pressure, between one set of rollers arbitrarily selected from three rollers, the pressure part of one roller is used to harden the product. There is an overlapping part where the contact part to the outer periphery of the processed product and the contact part to the outer periphery of the processed product by the pressure part of another roller overlap each other, and the length in the axial direction of this overlap part is about 4 mm or less A rolling press quenching device characterized in that the pressure section of each roller is arranged so that