CH711031B1 - Method for producing guide rails for a linear roller bearing. - Google Patents

Abstract

The invention relates to a method for producing guide rails (11) for a linear rolling bearing, wherein a steel strand material (12) is provided which has a constant starting cross-sectional shape (13), having a length of at least 10 m, at least in some areas wherein the strand material (12) is successively passed through a heating device (15) and a rolling device (16) at a constant transport speed, wherein the strand material (12) in the heating device (15) is heated to an austenitizing temperature at the austenite structure is present in the steel, wherein the strand material is plastically deformed in the rolling apparatus, wherein the temperature of the strand material (12) to the end of the rolling device (16) is so high that austenite is present. According to the invention, the strand material (12) is cooled immediately after it has passed through the rolling device (16) to form martensite in its curable areas, whereby the strand material (12) is subsequently ground (20) to the finished guide rail (12) obtained, between the said plastic deformation (16) and said loops (20) no further form-changing processing takes place on the surfaces to be ground of the guide rail (12).

Description

Description [0001] The invention relates to a method for producing a guide rail according to the preamble of claim 1.

In DE 10 2008 008 632 A1 a method for the production of guide rails for a linear roller bearing is described as prior art. In this case, a blank is first hot rolled, so that it receives by plastic deformation a cross-sectional shape, which comes close to the final cross-sectional shape of the guide rail. Typically, this blank is made of a hardenable steel, so that the running surfaces of the finished guide rail have a sufficiently high hardness. The blank is heat-treated after being hot-rolled so that it is not cured so that the further production steps can be carried out. These manufacturing steps include a cold drawing process in which the cross-sectional shape of the blank is changed by plastic deformation at room temperature to approximate the final cross-sectional shape of the guide rail except for an economical grinding allowance. The cold drawn blank is typically surface hardened by heating its edge zones to the austenitizing temperature by means of an inductive heating device, which are then quenched to form a martensite texture. The hardened blank is then ground to obtain the finished guide rail.

The advantage of the present invention is that the proposed manufacturing process is less expensive.

According to the invention, a method for producing guide rails for a linear roller bearing is proposed, wherein a strand material made of steel is provided which has a constant initial cross-sectional shape, wherein it has a length of at least 10 m, wherein it is curable at least in some areas, wherein the strand material successively passing through a heating device and a rolling device at a constant transport speed, wherein the strand material in the heating device is heated to an austenitizing temperature at which austenitic structure is present in the steel, whereby the strand material in the rolling device is plastically deformed, the temperature of the strand material remaining up to The end of the rolling device is so high that austenite is present, the strand material, immediately after it has passed through the rolling device, is cooled so that martensite in the curable areas is formed, wherein the strand material is then ground to obtain the finished guide rail, wherein between said plastic deformation and the said loops no further form-changing processing takes place on the surfaces to be ground of the guide rail. In contrast to the prior art, the strand material is already hardened immediately after hot rolling, whereby the heat required for hot rolling is utilized. The process step of cold drawing is completely eliminated.

Hardenable steels such as C45E or 56 NiCrMoV 7 are preferably used as steel. However, it is also conceivable to use feedstock steels which are curable exclusively in the carburized surface region. The steel grade is preferably chosen so that after the heat treatment phase-pure martensitic structure is present. The said structure should preferably be fine needles and without coarse grain formation and further without crack networks.

As far as a strand material with a length of at least 10 m is mentioned, this is to be understood in particular a strand material, which is produced continuously in a previous process step. It is also referred to as an endless strand material, it being understood that the length of this strand material is limited by the finite duration of the said preceding process step.

The proposed cooling can be done by unregulated cooling of the ambient air or by a controlled cooling, in particular using a cooling device depending on the steel grade used. By means of the preferred controlled cooling, the tempera ture course during cooling can be adjusted so that the least possible distortion of the strand material arises during martensite formation.

In the dependent claims advantageous refinements and improvements of the invention are given.

The provided strand material may have a circular starting cross-sectional shape with a diameter between 20 mm and 90 mm. It is preferable to use a hot-rolled wire as a strand material. Most preferably, the surface of the said wire chip is processed lifting, in particular by means of peeling and / or grinding. As a result, the areas of the provided strand material are removed, which may contain surface defects after hot rolling or their carbon content changed in an undesirable manner, in particular reduced.

An uninterrupted strand material can be provided by successively welding finite pieces of strand material together at the ends. Preferably, it is contemplated that said finite pieces are provided coiled up, being unwound from the spools and bent into a straight shape prior to welding. The resulting material stresses are eliminated by the subsequent heating to the Austenitisierungstemperatur and the associated Rekristalli-sierungsvorgang.

The corresponding welding points can be cut out before the grinding of the strand material, where they are not used to produce a guide rail. In the area of the welds, a reduced quality of the finished guide rail must be expected, which is why these pieces are discarded from the outset, the steel material preferably being recycled. Preferably, it is envisaged to choose the distances of the welding points so that they are slightly larger than an integer multiple of the length of the pieces of strand material, which are ground in one operation at the end of the proposed method.

In the heating device, a magnetic heating and / or an induction heating and / or a conductive heating of the strand material can take place. The induction heating preferably takes place frequency-controlled. In a preferred embodiment, a magnetic heating is combined with a subsequent low-frequency induction heating. All proposed types of heating have in common that the heating is very fast. It should be noted that the time in which the strand material is transported from the beginning of the heating device to the end of the rolling device is inherently very short. The strand material therefore has the high austenitizing temperature only over a very short period of time. Accordingly, the period during which the carbon in near-surface layers of the strand material can chemically react with the ambient air is very short. It comes therefore at most to very low Abkohlungen. By using a protective gas atmosphere in the area of the heating and / or rolling device, unwanted changes in the surface of the strand material can be reduced to a minimum.

The heating device may heat the strand material over its entire cross-section to a temperature which is at least equal to said Austenitisierungstemperatur. Accordingly, low material stresses arise in the strand material in the rolling device. A delay of the strand material is not to be feared. It should be noted that during induction heating, the strand material only heats up to the austenitizing temperature at the surface during the conventional production process.

The strand material is heated in the heating device preferably at most 2/3 of its melting temperature. As a result, a very accurate cross-sectional shape of the strand material can be produced in the rolling device. It should be noted that the cost-effectiveness of the method according to the invention increases if only a very small material removal occurs during the final grinding of the strand material. Accordingly, it is preferred if a very accurate cross-sectional shape of the guide rail is made in the rolling apparatus which is very close to the desired end shape of the guide rail.

The rolling apparatus may comprise a plurality of rolling stands. Preferably, the total required plastic deformation is evenly divided among many rolling stands, so that in each rolling mill only a very small plastic deformation takes place, which in turn can be performed very accurately. Preferably takes place at the last in the transport direction rolling mill plastic deformation, which is smaller, preferably significantly smaller than the plastic deformation of the first rolling mill in the transport direction. The individual rolling stands preferably each have a separate drive which is speed-controlled. Most preferably, the drive comprises an electric motor, in particular a synchronous motor. In the speed control of the drives preferably the force is taken into account, preferably as a controlled variable, which acts on the strand material in the transport direction. Preferably, the strand material is placed under tension. Said force is preferably calculated taking into account the drive torques of the drives and / or the drive currents of the electric motors.

The Schleifaufmass, which is removed during the grinding of the strand material, is preferably at most 0.5 mm.

The extruded material provided may have a higher carbon content on the surface than in the interior. This material condition is preferably achieved by carburizing the strand material. That it is preferably enclosed in a carbonaceous environment, in particular in carbon powder, and heat-treated there.

It is understood that the features mentioned above and those yet to be explained not only in the combination specified, but also in other combinations or alone, without departing from the scope of the present invention.

The invention will be explained in more detail below with reference to the accompanying drawings. It shows:

1 is a rough schematic representation of an inventive process sequence;

Fig. 2. a cross-section of the rolled strand material; and

FIG. 3 is a continuous time-temperature conversion graph of 56NiCRMoV 7 steel. FIG.

Fig. 1 shows a rough schematic representation of an inventive method sequence. The process begins by providing a strand material 12, which preferably has a circular starting cross-sectional shape 13 with a diameter between 20 mm and 90 mm. The strand material 12 is first passed through a heating device 15, which operates by way of example inductively. The corresponding electrical coil surrounds the strand material 12 helically. It is fed with an alternating electrical current which induces eddy currents in the strand material 12. The ohmic resistance of the strand material 12 in conjunction with said eddy currents leads to rapid heating of the strand material. The distribution of the eddy currents and thus the temperature distribution can be influenced by the frequency of the injected alternating current and the shape of the induction coils. At high frequencies, the heating takes place predominantly on the surface of the strand material 12. Preferably, the strand material 12 is heated over its entire cross section to the austenitizing temperature, so that over the entire cross section there is a good plastically deformable austenite structure.

Subsequently, the strand material 12 is guided by a rolling device 16. Contrary to the illustration, several rolling stands are actually present, which are arranged one behind the other in the transport direction 10, wherein they each cause a slight plastic deformation on the strand material 12. The rolls of the individual rolling stands can process the strand material 12 from different sides. It may, for example, be thought that a rolling stand processes only the side surfaces 21, with an immediately following rolling mill only the head and the foot surface 22; 23 processed in particular with respect to the transport direction 10 last rolling stand can be thought that a total of at least four rollers act simultaneously on the strand material 12, wherein they at the associated four sides 21; 22; 23 each cause only a slight plastic deformation. At the end of the rolling apparatus, the strand material 12 has the cross-sectional shape marked with the number 14, which coincides with the final cross-sectional shape after the grinding 20 except for a small grinding allowance of, for example, 0.3 mm.

After the rolling device 16, the strand material 12 is passed through a cooling device 17. The cooling device 17 may, for example, have a multiplicity of spray nozzles 18, which are arranged distributed in a ring around the strand material 12. Via the spray nozzles 18, the strand material 12 can be sprayed, for example with water or oil, to cool it. It can be thought that the strand material 12 at the end of the cooling device 17 has a temperature which is still considerably above room temperature, the final cooling takes place at room temperature in the period in which the cut guide rails 12 stored before grinding, become ,

To the cooling device is followed by a separator 19, for example, a fast-rotating cutting wheel whose axis of rotation 27 is aligned parallel to the strand material 12 and to the transport direction 10. With the separator 19, finite pieces of the strand material 12 are cut off, which can be processed well in a grinding machine. Typically, these pieces are 6 meters long.

After cutting, the pieces of strand material are ground on a plurality of different grinding machines or grinding devices. The number of grinding machines is chosen so that the process can run continuously without 19 unprocessed pieces of strand material accumulate after the separator and without any individual grinding machines remain unused. In Fig. 1, the grinding machines are shown simplified by two profile grinding wheels 20.

Fig. 2 shows an Ouerschnitt 14 of the rolled strand material 12. The Ouerschnittsform 14 is designed with respect to a plane of symmetry 25 mirror-symmetrical. The top surface 22 is slightly curved convexly after rolling, being ground flat during grinding. On the two side surfaces 21 are each two raceways 24 for rolling elements. In the case of the finished guide rail, it is particularly important that these raceways 24 are hardened so that the corresponding linear roller bearing has a long service life. In the present case, concave curved tracks 24 for spherical rolling elements are shown. However, the method according to the invention is equally applicable to even raceways for circular cylindrical rolling elements. In principle, any number of raceways 24 can be produced with the method according to the invention. In the context of the final grinding, in particular the raceways 24 are machined with very high accuracy so that the finished linear roller bearing has a high guiding accuracy.

Attention is still on the support areas 26 on the foot surface 23 of the guide rail. With the support areas 26, the guide rail is in the installed state to a parent assembly. As can be seen, the bearing surfaces 26 are not completely flat after rolling. This unevenness is also eliminated during the final grinding process.

Fig. 3 shows a continuous time-temperature conversion graph of the steel 56 NiCRMoV 7, which is purely exemplary suitable for carrying out the method according to the invention. In the horizontal, the cooling time t is plotted logarithmically in seconds. In the vertical, the temperature T of the strand material is plotted in ° C. In the diagram are two typical cooling curves 31; 32 registered, which arise when you cool the strand material with different intensity. The cooling curves 31; 32 are each characterized by a cooling time t8 / 5, which indicates the time in seconds in which the temperature falls from 800 ° C to 500 ° C. Next, the martensite line 30 is located, which in the present case is 245 ° C. This line 30 separates the area marked A in which austenite structure exists from the area marked M in which martensite is present.

In the process control of the cooling process is preferably to ensure that no slow cooling takes place below the martensite line 30, so that possible forms no carbide precipitates. This self-priming effect would lead to a decrease in hardness and, in interaction with micro-stresses in the microstructure, favors the formation of microcracks.

The cooling above the martensite line 30 is of less critical importance, since, as shown by the example 58 NiCrMoV 7, the carbon remains dissolved in supercooled martensite.

After austenitizing at 860 ° C, martensite with a hardness of 770HV is achieved by te / 5 = 7.5 sec (first cooling curve 31). After a holding period of 400 seconds, just above the martensite line 30 and further cooling, as in accordance with the first cooling curve 31, a hardness arises, as in the first cooling line 31. The latter cooling process is shown with the third cooling line 33. The optically unequal appearing first and third cooling curves 31; 33 in Fig. 3 are due to the logarithmic scale. The cooling with te / 5 = 153 sec. According to the second cooling curve 32 leads to lower hardness. Now, if the cooling accelerates from 280 ° C according to the third cooling curve 33, the hardness is higher again.

For the steel C45E, which is also suitable for carrying out the method according to the invention, the conditions shown with reference to FIG. 3 also arise in principle.

In order to simplify the temperature control from the rolling heat, however, it is also possible to start from a steel with a low carbon content. After the appropriate conditioning of the hot-rolled wire (surface defects, diameter, carburization and / or carburization), this wire may e.g. be brought back into coil form. These coils with surface-processed wire rod can be easily heat-treated, i. a chemical modification of the near-surface layers are subjected. Preferred by carburization, the carbon content of the steel can be increased so that with appropriate cooling from the rolling heat surface hardened components are present, which can be used as a starting material for rails. Carbon content as well as case hardening depth are to be adjusted so that the conditions already mentioned are met on rolling-loaded components. The procedural processing of such heat-treated coils (with chemical modification of the surface) is similar to the procedure already described.

In both cases, the measurement of the hot-rolled and hardened guide rail pre-material can be chosen so that if required simple mechanical processes (milling, planing, scraping, grinding, ...) can be used to target non-heat treated areas of profile guide rails adjust.

[0034] t cooling time T temperature 10 transport direction 11 guide rail 12 strand material 13 starting cross-sectional shape 14 rolled cross-sectional shape 15 heating device 16 rolling device 17 cooling device 18 spray nozzles 19 separating device 20 grinding device 21 side surface of the guide rail 22 top surface of the guide rail 23 foot surface of the guide rail 24 raceway 25 symmetry plane

Claims (10)

claims 1. A method for producing guide rails (11) for a linear rolling bearing, wherein a strand material (12) made of steel is provided, which has a constant starting cross-sectional shape (13), wherein it has a length of at least 10 m, wherein it is curable at least partially wherein said strand material (12) is successively passed through a heating device (15) and a rolling device (16) at a constant transport speed, wherein said strand material (12) in said heating device (15) is heated to an austenitizing temperature at said austenite structure in said steel wherein the strand material is plastically deformed in the rolling apparatus, wherein the temperature of the strand material (12) to the end of the rolling device (16) is so high that austenite is present, the strand material (12) immediately after the rolling device (16) has been passed, is cooled so that in its curable areas Ma The strand material (12) is then ground (20) to obtain the finished guide rail (12), wherein between the said plastic deformation (16) and said loops (20) no further form-changing processing to be sanded Surface of the guide rail (12) takes place. 2. The method according to claim 1, characterized in that the provided strand material has a circular starting cross-sectional shape (13) with a diameter between 20 mm and 90 mm. A method according to any one of the preceding claims, characterized in that a continuous strand material (12) is provided by successively welding finite pieces of strand material together at the ends. 4. The method according to claim 3, characterized in that the corresponding welding points are cut out before the grinding (20) of the strand material, wherein they are not used for the production of a guide rail (12). 5. The method according to any one of the preceding claims, characterized in that in the heating device (15) takes place, a magnetic heating and / or an induction heating and / or a conductive heating of the strand material (12). 6. The method according to any one of the preceding claims, characterized in that the heating device (15) heats the strand material over its entire cross-section to a temperature which is at least equal to said Austenitisierungstemperatur. 7. The method according to any one of the preceding claims, characterized in that the strand material (12) in the heating device (15) is heated to at most 2/3 of its melting temperature. 8. The method according to any one of the preceding claims, characterized in that the rolling device (16) has a plurality of rolling stands. 9. The method according to any one of the preceding claims, characterized in that the Schleifaufmass, which is removed in the final grinding (20) of the strand material, at most 0.5 mm. 10. The method according to one of the preceding. Claims, characterized in that the provided strand material (12) on the surface has a higher carbon content than in the interior.