TWI575170B - Ball screw device - Google Patents

Description

Ball screw device

The present invention relates to a ball screw device, and more particularly to a ball screw device suitable for use in an injection molding machine.

The ball screw device is roughly classified into an injection molding machine application and a transportation/positioning application. In recent years, in order to reduce the weight of automobile parts, it is one of the methods to investigate the resinization of parts. Under such a demand, the output required for the injection molding machine is increased, and the apparatus is inevitably enlarged. Therefore, it is more and more important to suppress the long life of the large-sized ball screw device as much as possible.

As the performance sought by the ball screw device, the movement of the axial direction is stably performed for the first time, and for this reason, it is sought not to change the shape of the spiral groove for a long time. The change in the shape of the screw shaft is caused by the peeling or abrasion of the surface defect of the raceway surface, and the dimensional change caused by the expansion or contraction of the steel. In other words, it can be said that the screw shaft having excellent peeling resistance, abrasion resistance, and dimensional stability is a ball screw device of good quality.

However, it is not easy to manufacture products that satisfy all of these durability at a high level. Since the ball screw device is used as a thrust source in the injection molding machine, the ball screw device needs to repeatedly load a high stress, so it is necessary to improve the peeling resistance. In the ball screw device, since the nut moves in the axial direction with respect to the screw shaft, it is easy to mix foreign matter, and in addition, when the ball is scratched by the circulating part of the nut, the surface property of the rolling element is easily deteriorated, so that it is common. It is called the surface starting type peeling of Peeling. Regarding the peeling of this form, it is effective to optimize the residual Worth iron of the screw shaft raceway surface, and use a carburizing place for this purpose. Reason. However, the residual Worthite iron is liable to change to the granulated iron in the long-term use, and the dimensional difference may be caused by the expansion due to the difference in density. Therefore, when carburization treatment is performed to improve the peeling resistance, it is necessary to allow a certain degree of reduction in dimensional stability.

On the other hand, high frequency heat treatment is used when focusing on the case of dimensional stability. In the high-frequency heat treatment, the surface of the steel material is heated by induction heating, whereby only the necessary portion can be quenched. As a method of manufacturing the screw shaft by high-frequency heat treatment, the round bar including the steel material is subjected to groove processing and then applied to the hardened layer. The method and the method of performing groove processing after imparting a hardened layer to the round bar. In either method, the hardened layer which produces a dimensional change is only the surface of the screw shaft, and an performance equal to or higher than that of the carburizing treatment can be expected. However, the peeling resistance is not easily improved by the high frequency heat treatment. In the high-frequency heat treatment, since heat is generated on the surface, overheating easily occurs on the surface, and cracking is likely to occur due to overheating in a steel material having a large amount of carbon. Therefore, in the case of high-frequency heat treatment, medium carbon steel is generally used, and SAE 4150 based on 0.5% C is actually used as the screw shaft. However, the amount of residual Worstian iron which is effective for peeling depends on the carbon content in the steel, and the life extension effect is hardly expected in the carbon content of about 0.5% by mass.

Further, for the high-frequency heat treatment in the manufacturing process of the screw shaft, for example, Patent Documents 1 and 2 can be referred to.

Further, in the ball screw device for an injection molding machine, if the use environment is severe, special peeling may occur. This peeling is caused by the change of the structure called "white peeling" as a starting point, and is considered to be caused by intrusion of hydrogen into the steel. Hydrogen is considered to be originally present in steel, and is generated by decomposition of lubricating oil or the like during use and intrusion into steel. On the other hand, if white peeling occurs, the amount of iron in the remaining Worthfield increases, and the effect of long life is weakened.

[Previous Technical Literature]

Patent Document 1: Japanese Laid-Open Patent Publication No. 2010-90924

Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-299720

As described above, it is difficult to achieve dimensional stability and to improve peeling resistance and wear resistance and to achieve a long life. Moreover, the white peeling of hydrogen has not yet been explored. Accordingly, an object of the present invention is to provide a screw shaft which has more excellent dimensional stability, peel resistance including white peeling, and wear resistance.

In order to solve the above problems, the inventors have obtained the following findings through careful research. First, in order to improve the resistance against peeling other than white peeling, it is effective to control the amount of residual Worth iron, and it can be achieved by high carbonization of steel. On the one hand, in order to increase the amount of surface residual Worthite iron and ensure the dimensional stability, the mechanism of the dimensional change was investigated in detail, and it was found that the size of the wire was changed to the axis as in the case of the carburized steel. Although the equi-directionality of both the radial direction and the axial direction occurs, the core portion is based on the thermally stable ferrite-rich iron phase, and the volume is secured by a certain amount or more, and hardly changes in the axial direction. The dimensional stability sought by the ball screw device is related to the axial direction, and this phenomenon can be used to balance life and dimensional stability.

Further, although it is not mainstream in the ball screw device for injection molding machines, when a screw shaft is produced by high-frequency heat treatment, a hardened layer may be applied to the round bar, and then groove processing may be performed. By ensuring a certain degree of hardenability by high carbonization, it is possible to ensure a necessary depth of the hardened layer by adding a general amount of alloying elements, and further to secure a core region necessary for dimensional stability in the depth of the hardened layer.

However, the combination of high carbon steel and high frequency heat treatment has problems of quenching cracking and cracking when bent. The former can be avoided by frequency conditions and strict temperature management, but it is difficult to avoid the fact that the latter is difficult to perform bending correction. When quenching, the structure will change from the Worthite iron to the granulated iron, which will inevitably cause thermal deformation due to the difference in density. By providing the hardened layer as described above and performing the groove processing, the deformation can be reduced, but the deformation can be reduced. In the ball screw device for an injection molding machine, in order to secure a shape necessary for a mechanical component, a high-frequency heat treatment is often performed after the groove processing. Therefore, the deformation caused by the heat treatment appears as a bending of the screw shaft, and must be bent by bending. Processing corrects it. Since the screw shaft is formed with a groove, the groove bottom is greatly deformed during the bending process, and if the allowable amount is exceeded, the crack is generated. Therefore, the influence of the structure on the bending strength was investigated in detail, and as a result, it was found that the amount of the carbide at the bottom of the groove was set to be constant or more. This is because the pinning effect of carbides keeps the crystal grains fine, and the steel is high carbon steel, and the amount of carbon is as high as 1% by mass. Therefore, the more the amount of carbides, the less the amount of carbon dissolved in the substrate, and the toughness is ensured. The reason.

Further, when the white peeling was examined, it was found that by limiting the amount of hydrogen in the steel in the state before use, white peeling can be suppressed, and only ordinary peeling is caused, and it is substantially harmless.

The present invention has been accomplished based on this understanding, and provides the following ball screw device.

(1) A ball screw device comprising: a screw shaft having a spiral groove on an outer peripheral surface; a ball nut having a spiral groove on an inner peripheral surface opposite to a spiral groove of the screw shaft; and a plurality of a ball inserted between the two spiral grooves and circulated by a ball circulation path provided in the ball screw; and the ball screw device is characterized in that the screw shaft is a high carbon bearing steel or a heat hardening The steel material having a Ms point of 172° C. or lower and calculated by the following formula 2 and having a DI value of 2.8 or more is obtained, and the ratio of the effective hardened layer having a hardness in the radial direction of HV500 or more is 60% or less. The non-hardened layer with a hardness of less than HV500 is a metal structure containing a ferrite grain phase and a sulphur carbon iron phase. The average residual Worthite iron in the radial direction section is 4.5% or less, and the hydrogen content of the spiral groove rolling surface is 0.61 ppm or less. The carbide area ratio of the bottom is 1.5% or more, and the amount of residual Worthite iron from the track surface to the depth of 50 μm is 5 to 40% by volume: Formula 1 = 550-361 [C]-39 [Mn]-20 [Cr]-17 [Ni]-5[Mo]

Equation 2=(0.2[C]+0.14)×(0.64[Si]+1)×(4.1[Mn]+1)×(2.33[Cr]+1)×(3.14[Mo]+1)×(0.52 [Ni]+1)

(In the formula, [C], [Si], [Mn], [Cr], [Mo], [Ni]) steel materials, C, Si, Mn, Cr, Mo, Ni (content%) .

(2) The ball screw device according to the above aspect (1), wherein the hardness (HRC) of the surface of the raceway surface of the screw shaft and the residual Worthite iron amount (γ R) from the raceway surface to a depth of 50 μm satisfy the following formula 3 and Equation 4: Equation 3: γ R+0.15×HRC-19.1≧0

Formula 4: γ R+21.2×HRC-1176≧0.

(3) The ball screw device according to the above aspect (1) or (2), wherein the old Worth iron having a groove bottom of the screw shaft has a particle diameter of 30 μm or less.

The ball screw device of the present invention heat-treats a specific steel material, and (a) the ratio of the effective hardened layer, (b) the metal structure of the non-hardened layer, (c) the average residual Worthite iron amount, and (d) rolling The amount of hydrogen on the surface, (e) the area ratio of the carbide at the bottom of the groove, and (f) the amount of residual Worthite from the track surface to the depth of 50 μm is set to a specific range, and the screw shaft has more dimensional stability than ever before. Contains the peel resistance of white peeling and abrasion resistance. Therefore, it is useful especially for the ball screw device for injection molding machines, and has high performance and long life.

Figure 1 is a graph showing the relationship between the Ms point and the life ratio.

Figure 2 is a graph showing the relationship between the DI value and the life ratio.

Fig. 3 is a graph showing the relationship between the amount of Worstian iron on the surface and the life ratio.

Fig. 4 is a graph showing the relationship between hardness and the amount of Worstian iron remaining on the surface.

Fig. 5 is a graph showing the relationship between the value of Formula 3 and the life ratio.

Fig. 6 is a graph showing the relationship between the value of Formula 4 and the life ratio.

Fig. 7 is a graph showing the relationship between the area ratio of the effective hardened layer and the dimensional change rate in the axial direction.

Fig. 8 is a graph showing the relationship between the area ratio of carbides at the bottom of the groove and the ratio of the flexural strength.

Fig. 9 is a graph showing the relationship between the value of the formula 5 and the bending strength ratio.

Fig. 10 is a graph showing the relationship between the amount of hydrogen and the life ratio.

Fig. 11 is a graph showing the relationship between the value of Expression 6 and the life ratio.

Hereinafter, the present invention will be described in detail with reference to the drawings.

The ball screw device of the present invention comprises: a screw shaft having a spiral groove on an outer circumferential surface; a ball nut having a spiral groove on an inner circumferential surface opposite to a spiral groove of the screw shaft; and a plurality of balls And interposed between the two spiral grooves, and can be circulated by a ball circulation path provided on the ball screw; and the ball screw device is made of a specific high carbon steel bearing and heat treated. Forming an effective hardened layer on the surface. Further, the ball or the ball nut is not limited except for the screw shaft.

In other words, as the material of the screw shaft used in the present invention, a high carbon bearing steel or a steel material having a Ms point of 173° C. or lower and having a DI value of 2.8 or more calculated by the following formula 2, which is calculated by the following formula 1, is used.

Formula 1=550-361[C]-39[Mn]-20[Cr]-17[Ni]-5[Mo]

Equation 2=(0.2[C]+0.14)×(0.64[Si]+1)×(4.1[Mn]+1)×(2.33[Cr]+1)×(3.14[Mo]+1)×(0.52 [Ni]+1)

(In the formula, [C], [Si], [Mn], [Cr], [Mo], [Ni]) steel materials, C, Si, Mn, Cr, Mo, Ni (content%)

The high-carbon bearing steel or the steel material satisfying Formula 1 and Formula 2 is not limited, but is preferably a bearing steel containing 0.6% by mass or more of carbon and further containing chromium and manganese as essential components. When the carbon content is less than 0.6% by mass, the heat treatment quality specified in the present invention cannot be obtained, so it is preferably 0.6% by mass or more. More preferably, the carbon content is set to 0.95 mass%. on. Further, although the upper limit of the carbon content is not limited, when it exceeds 2% by mass, coarse carbides remain, which affects the life resistance and the like. The high-carbon bearing steel contains approximately 1% by mass of carbon, and even if a necessary amount of carbon of about 0.5% by mass is dissolved in the base during quenching, a sufficient amount of carbide can remain on the raceway surface, and wear resistance can be improved.

The element which improves the hardenability by chromium is preferably contained in an amount of 0.9% by mass or more. However, if too much chrome causes a decrease in workability, it is preferably 2% by mass or less. Manganese is also an element that improves hardenability similarly to chromium. It is preferably added in an amount of 0.2% by mass or more. However, if too much manganese causes a decrease in workability, it is preferably 2% by mass or less.

Further, it is preferred to contain molybdenum. As shown in the examples to be described later, the wear resistance can be further improved by setting the value of Formula 1 relating to the content of chromium and manganese together with the content of molybdenum steel to a specific range. It is presumed that the carbide is hardened by the incorporation of chromium, manganese and molybdenum into the carbide.

Specifically, JSI G 4805 high carbon chromium steel, ISO 683-17 bearing steel, SUJ2-5 steel, 100CrMnSi6-4 steel, etc. are exemplified, but it is preferably SUJ2-5 steel and 100CrMnSi6-4 steel.

Next, the thermosetting treatment includes a round rod of such a high carbon bearing steel, and an effective hardened layer having a hardness of HV500 or more is formed in the surface portion. Although the carburization treatment may be performed as the heat hardening treatment, it is preferably a high-frequency heat treatment in which a round rod material including the steel material is inserted into a coil connected to a high-frequency power source to cause a high frequency. Current flows in the coil. Thereby, the eddy current flows on the surface of the round bar material due to the high frequency electromagnetic field, so that the surface of the round bar material is heated. Next, the coil material is heated over the entire length by moving the coil in the axial direction of the round rod material. After heating, the round bar raw material is sprayed with an aqueous solution in which a water-soluble quenching liquid is dissolved, and the like.

The effective hardened layer was placed in the cross section of the screw shaft, and the volume ratio was set to 60% or less. That is, the processing conditions (frequency or loss) are adjusted according to the steel composition or the diameter of the screw shaft, such that the depth from the surface of the effective hardened layer is 60% or less with respect to the diameter of the screw shaft. Out, heating time).

The ratio of the effective hardened layer is 60% or less, which means that the ratio of the non-hardened layer having a hardness of less than HV500 is 40% or more. The non-hardened layer contains the ferrite phase and the ferritic carbon-iron phase. However, since the iron content of the ferrite phase is very low, there is almost no change even in long-term use, and the hard layer of the surface layer is limited. As a result of the core, even if the amount of the surface-remaining Worthite iron generated by the heat treatment is increased, the dimensional change in the axial direction hardly occurs. In order to obtain such an effect, the proportion of the non-hardened layer may be 40% or more, and 60% or more is more effective.

Further, the average residual Vostian iron content in the radial direction section was 4.5% by volume. If the average residual Vostian iron amount exceeds 4.5% by volume, the dimensional change rate will increase.

Further, in the groove bottom, by setting the carbide area ratio to 1.5% or more, preferably 5.6% or more, a particularly excellent bending strength can be obtained in the bending test of the later-described embodiment, and the bending correction can be prevented. The rupture is effective. Further, in order to prevent cracking, the old Worthite iron having a groove bottom is preferably finer in particle diameter, and specifically preferably 30 μm or less, more preferably 18 μm or less.

In addition, the amount of residual Worthite iron (the amount of surface residual Worthite iron) which is 50 μm deep from the raceway surface is 5 to 40% by volume. In the ball screw device, since the screw shaft is exposed, it is likely to be peeled off due to foreign matter, and in order to suppress the dimensional change on the one hand and to increase the life of the foreign matter, the amount of the remaining Worstian iron is 5 to 40% by volume. It is preferably set to 9.7 to 35 vol%.

Further, in order to prevent white peeling, the amount of hydrogen on the rolling surface was set to 0.61 ppm or less. The smaller the amount of hydrogen, the better, and it is preferably 0.2 ppm or less.

In addition to the above, since the screw shaft exerts a high contact surface pressure with the rolling elements, the hardness (HRC) of the surface of the raceway surface is preferably as high as possible, and between the amount of residual Worthite (γ R) remaining on the surface. It is preferable to satisfy the following formula 3 and formula 4.

Equation 3: γ R+0.15×HRC-19.1≧0

Equation 4: γ R+21.2×HRC-1176≧0

[Examples]

The invention is further illustrated by the following examples, but the invention is not limited thereto.

(Test 1)

A high-carbon bearing steel including the alloy composition shown in Table 1 and a rod-shaped test piece in which the diameter of the grinding was determined in consideration of the cutting margin of the grinding were prepared, and the moving quenching was performed at a frequency of 100 to 200 kHz. Subsequently, the mixture was tempered at 160 to 200 ° C for 2 hours, and 200 μm was removed from the surface of the black skin by polishing, and then subjected to a life test under the following conditions. Further, in order to reproduce the peeling of the ball screw device, as described below, the rolling elements are used in which the balls having poor surface roughness are used in advance. Further, the Ms point is calculated from the following formula 1. The results are shown in Table 2 and FIG. 1, but are shown as relative values (life ratio) with respect to Comparative Example 2.

Formula 1=550-361[C]-39[Mn]-20[Cr]-17[Ni]-5[Mo]

<Test conditions>

. Test piece...φ 12.6mm, rod test piece

. Rolling body...Material: SUJ2, size: 1/2 inch, surface roughness: 0.3μmRa

. Face pressure...5.5GPa

. Lubrication...oil bath lubrication, VG68

Note) The unit of each element content is % by mass, and the rest is iron and unavoidable impurities.

As shown in Table 2 and FIG. 1, in the examples 1 to 5, the life extension effect was confirmed, so that the Ms point was 173 ° C or lower.

(Test 2)

As shown in Table 3, a rod-shaped test piece containing the steel material shown in Table 1 was used, and the rod-shaped test piece was subjected to mobile quenching by a high-frequency heat treatment at a frequency of 30 to 100 kHz, and then subjected to a reaction at 160 to 200 ° C for 2 hours. The fire treatment was carried out for the same life test as Test 1 after being removed by grinding from the surface of the black skin by 4 mm. Moreover, the DI value was calculated from the following formula 2. The results are shown in Table 3 and FIG. 3, but are shown as relative values (life ratio) with respect to Comparative Example 3.

Equation 2=(0.2[C]+0.14)×(0.64[Si]+1)×(4.1[Mn]+1)×(2.33[Cr]+1)×(3.14[Mo]+1)×(0.52 [Ni]+1)

As shown in Table 3 and FIG. 2, in the examples 6 to I0, the life extension effect was confirmed, so that the DI value was 2.8 or more. Further, the DI values of Example 6 and Example 8 were almost the same, but the life of Example 8 was longer. This is considered to be caused by the difference in quality between the two cutting margin positions. That is, in the sixth embodiment, the steel material A (Ms point: 155 ° C) was used, and in the eighth embodiment, the steel material C (Ms point: 172 ° C) was used. Therefore, it is understood that the heat treatment quality of a certain level or more must be obtained for the life extension effect. It is affected by both the DI value and the Ms point.

(Trial 3)

As shown in Table 4, a rod-shaped test piece containing the steel material shown in Table 1 was used, and high-frequency heat treatment and groove processing were carried out to prepare a screw shaft. Next, the hardness of the surface of the produced screw shaft raceway surface and the amount of Worstian iron remaining on the surface were measured. Further, a ball screw device was produced using the produced screw shaft, and the same life test as in Test 1 was carried out. The results are shown in Table 4, but are shown as relative values (life ratio) with respect to Comparative Example 6. Figure 3 graphically shows the relationship between the life ratio and the average residual Vostian iron content.

It is understood that the steel material G used in Comparative Example 6 is difficult to increase the amount of Worstian iron remaining on the surface by high-frequency heat treatment, and the life extension effect cannot be confirmed. On the other hand, in the steel materials A, B, C, D, and E used in the examples 11 to 37, the output was increased by the high-frequency heat treatment, and the amount of Worstian iron remaining on the surface was increased, and it was set to 9.7 vol% or more. A sufficient life extension effect is obtained, and it is preferably set to 13% by volume or more.

Further, in the range where the amount of the Worstian iron remaining on the surface was 13% by volume or more, it was found that there was a variation in the life. As a result of the review, it was found that there is a correlation between surface residual Worthite iron content and hardness (HRC). In Fig. 4, for the comparative example and the embodiment in which the life ratio is 1.6 or more, the relationship between the hardness of each person and the amount of Worstian iron remaining on the surface is graphically displayed.

Further, it has been found that there is a correlation between Formula 3 or Formula 4 expressed by the surface residual Worthite iron content and hardness (HRC) and the life ratio. The value of the formula 3 and the value of the formula 4 are shown in Table 4, and the relationship between the value of the formula 3 and the life ratio is graphically shown in Fig. 5, and the relationship between the value of the formula 4 and the life ratio is graphically shown in Fig. 6. As shown in the figure, the values of the formula 3 and the value of the formula 4 are all 0 or more, and the life extension effect can be obtained. Equations 3 and 4 are converted into relational expressions relating to the amount of surface residual Worthite iron, and are represented by a straight line in Fig. 4 and a comparison of the curve "X". For example, either one is outside the range enclosed by two straight lines associated with Equation 3 or Equation 4. That is, in terms of life extension, it is preferred to simultaneously satisfy Formula 3 and Formula 4.

(Test 4)

As shown in Table 5, a rod-shaped test piece containing the steel material shown in Table 1 was used for high-frequency heat treatment to prepare a screw shaft having a different ratio of effective hardened layers. For the screw shaft to be produced, the ratio (%) of the effective hardened layer, the amount of Worstian iron (% by volume) remaining on the surface, and the average residual Worthite iron (% by volume) were measured. In addition, the surface residual Worthite iron amount is a residual Worthite iron amount of 50 μm deep from the surface of the raceway surface, and the surface layer of 50 μm from the track surface is removed, and then measured by X-ray. Further, a metal structure was obtained by chemical analysis of a core portion (a region having a hardness less than HV500). Further, after the high-frequency heat treatment and before the tempering at a low temperature for a predetermined period of time, the dimensional change rate in the axial direction was measured, and the relative value (size change ratio) with respect to Comparative Example 9 was determined. The results are shown in Table 5, and the relationship between the effective hardened layer ratio and the axial direction dimensional change rate is graphically shown in FIG.

In Examples 38 to 45, even if the ratio of the effective hardened layer was increased, the dimension in the axial direction hardly changed. On the other hand, in Comparative Examples 7 to 9, as the ratio of the effective hardened layer increases, the dimension in the axial direction also increases. In any of the examples, the ratio of the effective hardened layer was 60% or less, and it was found that the dimensional stability was excellent by setting the ratio of the effective hardened layer to 60% or less.

Further, Comparative Example 9 is a model in which the screw shaft of the conventional ball screw device is used, and even if the amount of Worstian iron remaining on the surface is small, it is irrelevant, and the dimensional change amount is the same as that of Examples 38 to 45. From this, it can be said that setting the average Worthfield iron residual amount to 4.5% by volume or less is also effective for dimensional stability.

Further, in Examples 38 to 45, the amount of Worstian iron remaining on the surface was 5 to 40% by volume, and the dimensional change rate was small. From this, it can be said that it is also effective to set the surface residual Worthite iron amount to 5 to 40% by volume.

Further, as a result of the chemical analysis of the core, except for Comparative Example 9, any of the above was a ferrite containing a ferrite phase and a ferritic carbon phase.

(Test 5)

As shown in Table 6, a rod-shaped raw material (diameter: 12.8 mm) containing the steel material shown in Table 1 was used, and a groove of 1.5R was formed on the circumference of the central portion in the longitudinal direction. The groove depth is 1.5 mm and the groove width is 3 mm. Thereafter, high-frequency heat treatment was performed at a frequency of 10 to 30 kHz to prepare a screw shaft. For the screw shaft thus produced, the area ratio of the carbide at the bottom of the groove and the crystal grain size of the old Worthite iron were measured. The results are shown in Table 6.

Further, the produced screw shaft was subjected to a 4-point bending test to measure the bending strength. The results are shown in Table 6, but are shown as relative values (retraction strength ratio) with respect to Comparative Example 10 which is based on the current product. Further, the relationship between the carbide area ratio and the bending strength ratio at the bottom of the groove is graphically shown in Fig. 8. Further, it is confirmed that the screw shaft of either of them generates a crack from the bottom of the groove, and the crack does not stop until the screw shaft is broken.

In Comparative Example 10, the current steel material was used, and the same quality as the current one was used. In Comparative Example 11, the bending strength was lowered as compared with Comparative Example 10. In Comparative Example 11, the setting output of the high-frequency heat treatment was increased and the amount of carbon dissolved was increased, and the deformation ability of the substrate was lowered.

In Examples 46 to 56, the set output was further lowered as compared with Comparative Example 11, and the bending strength was equal to or higher than that of the conventional Comparative Example 10. The flexural strength generally tends to be higher as the hardness is lower. In the case where high carbon steel is used as in the present invention, as in the case of Comparative Example 11, when the amount of carbon dissolved is increased, the amount of the soft tissue remaining is increased. The hardness is lowered, so it is not suitable as an evaluation index. As an appropriate evaluation index, the solid solution amount of carbon in the granulated iron of the methadine is not simple, but it is not simple to quantitatively determine the solid solution amount. In the present invention, since the bearing steel is used, the amount of solid solution carbon can be determined by subtracting the amount of undissolved carbon, that is, the amount of remaining carbide, from the amount of carbon of the raw material. When the amount of residual carbide is large, that is, the amount of solid solution carbon is small, the bending strength is improved. From Examples 46 to 56, it is known that the area ratio of the carbide at the bottom of the groove is 1.5% or more, and the same resistance as the current one can be obtained. strength.

Further, when investigating the correlation between the flexural strength and the particle size of the old Worthite, it can be said that the comparison of the comparative example 11 with the examples 46 to 56 is that the particle size of the old Worthite iron at the bottom of the groove is set to 30 μm. the following.

Further, from the results of the above, it was found that there is a correlation between the value of the following formula 5 relating to the cell area ratio of the groove bottom and the particle size of the old Worthfield iron, and the bending strength ratio. The value of the formula 5 is shown in Table 6, and the relationship with the bending strength ratio is graphically shown in Fig. 9. When the value of the formula 5 is 22 or more, preferably 35 or more, the bending strength can be increased.

Formula 5 = groove bottom carbide area ratio +50 - old Worthite iron particle size

(Test 6)

Based on the above test results, a ball screw device BS6316-10.5 (nominal: JIS B1192 63×16×300-Ct7) was produced and mounted on a ball screw endurance tester manufactured by Nippon Seiko Co., Ltd. for durability test. The test conditions are as follows. Further, in Examples 57 to 61, high-frequency heat treatment was carried out, and in Examples 62 and Comparative Example 12, carburization treatment was carried out to adjust the amount of concentrated gas, thereby adjusting the amount of hydrogen on the raceway surface. The amount of hydrogen is cut off from the orbital surface of the screw shaft before the test, and after forming the surface of the orbital surface on the surface of the 10 mm square cube, the temperature is raised from room temperature to 400 ° C and the total amount of hydrogen released by the hydrogen analyzer is measured. The value. The life indicates the relative value (life ratio) of the calculated life of the ball screw device using the screw shaft including the steel G. The results are shown in Table 7. Further, in Table 7, the DI value, the Ms point, and the surface residual Worthite iron amount of the produced screw shaft are described together with the amount of hydrogen. In addition, the relationship between the amount of hydrogen and the lifetime ratio is shown graphically in FIG.

<Test conditions>

. The outer diameter of the screw shaft: 63mm

. Lead: 16mm

. Ball diameter: 12.7mm

. Test load: 300kN

. Maximum rotation speed: 3200min ^-1 (Dn: 200,000)

. Raw material of screw: SCM420

. Separating membrane material: 66 nickel-iron alloy

. Cycle mode: overflow pipe mode

. Lubricant: "YS2 Lubricant" manufactured by LUBE Co., Ltd.

As shown in Table 7, in Examples 57 to 62, the Ms point was 173 ° C or lower, the DI value was 2.8 or more, the surface residual Worthite iron amount was 5 to 40% by volume, and the orbital surface hydrogen amount was 0.61 ppm or less. Each has a lifetime that is more than twice the calculated lifetime.

Further, it has been found that there is a correlation between the value of the formula 6 and the life ratio expressed by the amount of hydrogen on the orbital surface and the surface residual Worthite iron. The value of Formula 6 is also shown in Table 7, and the relationship between the value of Formula 6 and the life ratio is graphically shown in Fig. 11. If the value of Formula 6 is 40.2 or less, the life extension ratio can be expanded.

Equation 6 = (amount of hydrogen on the orbital surface) × 15 + surface residual Worthite iron

The present invention has been described in detail with reference to the preferred embodiments thereof.

This application is based on a Japanese patent application filed on May 30, 2014 (Japanese Patent Application No. 2014-112386), and a Japanese patent application filed on June 10, 2014 (Japanese Patent Application No. 2014-119697), 2014 Japanese patent application filed on the 4th of the month (Japanese Patent Application No. 2014-224033), Japanese patent application filed on January 26, 2015 (Special Wish 2015-012610), Japanese patent filed on January 27, 2015 The entire contents of these applications are incorporated herein by reference.

[Industrial availability]

The ball screw device of the present invention is excellent in dimensional stability and has excellent peeling resistance and abrasion resistance including white peeling, and is therefore particularly useful for a ball screw device for injection molding machines, and has high performance and long life. .

Claims (3)

A ball screw device comprising: a screw shaft having a spiral groove on an outer peripheral surface; a ball nut having a spiral groove on an inner circumferential surface opposite to a spiral groove of the screw shaft; and a plurality of balls And the like is interposed between the two spiral grooves, and can be circulated by a ball circulation path provided in the ball screw; and the screw shaft is a high carbon bearing steel or a heat hardening process is calculated by the following formula 1: A steel having a Ms point of 172° C. or lower and having a DI value of 2.8 or more calculated by the following formula 2; and a ratio of an effective hardened layer having a hardness of HV500 or more in the radial direction section of 60% or less, and a hardening of a hardness of less than HV500; The layer is a metal structure containing a ferrite iron phase or a stellite carbon iron phase, and the average residual Worthite iron content in the radial direction section is 4.5% or less, and the hydrogen content of the spiral groove rolling surface is 0.61 ppm or less, and the groove bottom carbide area ratio is For 1.5% or more, the amount of residual Worthite iron from the orbital surface to a depth of 50 μm is 5 to 40% by volume: Formula 1 = 550-361 [C]-39 [Mn]-20 [Cr]-17 [Ni]-5 [ Mo] Formula 2 = (0.2 [C] + 0.14) × (0.64 [Si] + 1) × (4.1 [Mn] + 1) × (2.33 [Cr] + 1) × (3.14 [Mo] + 1) × (0.52[Ni ]+1) (wherein the contents of C, Si, Mn, Cr, Mo, and Ni in the [C], [Si], [Mn], [Cr], [Mo], [Ni]) steel materials ( quality%)). The ball screw device of claim 1, wherein the hardness (HRC) of the surface of the orbital surface of the screw shaft and the amount of residual Worthite iron (γ R) from the orbital surface to a depth of 50 μm satisfy the following formulas 3 and 4: Formula 3: γ R+0.15×HRC-19.1≧0 Formula 4: γ R+21.2×HRC-1176≧0. The ball screw device according to claim 1 or 2, wherein the old Worth iron having a groove bottom of the screw shaft has a particle diameter of 30 μm or less.