Sliding nut and slide screw device

Abstract

To provide a sliding nut of a slide screw device having excellent sliding characteristics such as seizure resistance and wear resistance even under a high load condition while enabling low cost, and a slide screw device.SOLUTION: A sliding nut 3 moves relatively while sliding on an axis of a screw shaft as the screw shaft rotates in a sliding screw device, and is composed of a metal outer ring 4 made of metal, and a resin inner ring 5 that is integrally provided on an inner peripheral part of the metal outer ring 4. An interface with the resin inner ring 5 in the metal outer ring 4 is a cylindrical surface. The resin inner ring 5 has a female screw that is screwed onto the screw shaft. A thickness of the cylindrical surface of the metal outer ring 4 at a screw groove bottom part 5b of the female screw is 0.1 mm or more and less than 1.0 mm. At least the cylindrical surface of the metal outer ring 4 is an etched surface, and fine irregularities on the surface are impregnated with a resin of the resin inner ring 5.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a sliding nut of a sliding screw device and a sliding screw device using the sliding nut.

Background Art

[0002] A sliding screw device that converts rotational motion into linear motion or linear motion into rotational motion has the advantage of being able to be designed more compactly compared to a ball screw device, and is widely used in feed devices and positioning devices of industrial machines. In a sliding screw device using a metal nut such as a copper alloy, there is a concern about torque increase and seizure due to the exhaustion of the applied oil or grease, so regular maintenance is required. In addition, it cannot be used in an environment where oil or grease cannot be applied, such as in a vacuum or underwater. Therefore, sliding screw devices using resin nuts have been developed for the purpose of being usable without lubrication and maintenance-free.

[0003] As an example of making the entire nut or the screw groove portion that becomes the sliding portion made of resin, for example, a screw groove portion (or the entire nut) that is screwed onto a screw shaft is formed from a PPS resin composition obtained by blending at least polytetrafluoroethylene (hereinafter referred to as PTFE) resin and a non-melting organic resin powder at 280°C with polyphenylene sulfide (hereinafter referred to as PPS) resin. A resin nut has been proposed (see Patent Document 1). In addition, a sliding screw device is provided with a screw shaft and a nut that relatively moves while sliding on the axis of the screw shaft as the screw shaft rotates, and an aromatic polyimide resin powder coating film is formed on at least the female screw portion of the nut. It has been proposed (see Patent Document 2).

[0004] In addition, as an example of a structure composed of a metal part and a resin part, for example, a flanged nut that is screwed onto a screw shaft and relatively moves in the axial direction with respect to the screw shaft. The outer peripheral portion including the flange is formed of metal, and the inner peripheral portion that is screwed onto the screw shaft is formed of a lubricious resin, and a means for preventing rotation and coming off between these outer peripheral portion and inner peripheral portion is provided. A flanged nut has been proposed (see Patent Document 3).

[0005] As another method for manufacturing a resin nut, an injection mold is used which includes a fixed mold having a molding surface for molding one end surface of the resin nut, or one end surface and its vicinity, a movable mold having a cavity for molding the remaining outer surface of the resin nut and being axially movable with respect to the fixed mold, and a core pin provided on the movable mold and having a spiral groove formed on its outer diameter surface for forming a thread groove. After filling the mold with molten resin to mold the resin nut, a manufacturing method has been proposed in which the mold is opened and the core pin is rotated to remove the resin nut (see Patent Document 4).

[0006] However, although the resin nut of Patent Document 1 can be used without lubrication, there are concerns about the strength of the attachment parts such as the flange or the tooth roots of the internal thread part under high loads, and it is difficult to use.

[0007] On the other hand, in the screw device of Patent Document 2, since the main body is made of metal or ceramics, no deformation of the nut occurs even under high loads. However, in the formation of the powder coating film of aromatic polyimide resin, the resin is not completely melted or in a molten flow state, and it is also difficult to apply a high pressure in a high-temperature state, so a dense resin film cannot be formed. Therefore, when used under high loads, the wear of the resin film is large, and there is a possibility that the adhesion (shear adhesion strength) to the nut main body part is not sufficient. Also, it is not easy to accurately and uniformly form the powder coating film of the resin on the internal thread part of the nut.

[0008] Furthermore, in the flanged nut of Patent Document 3, although the outer peripheral part of the nut is made of metal, the inner peripheral part including the internal thread part is made of synthetic resin. Therefore, the mechanical strength of the tooth roots of the internal thread part is equivalent to that of the resin nut of Patent Document 1, and in use under high loads, there is a possibility that the internal thread part and the joint part between the metal and the resin may be deformed, etc.

[0009] As a sliding screw for solving such problems, there is known a sliding nut characterized in that the nut body is made of molten metal, and a resin layer of a resin composition having a synthetic resin as a base resin is formed by injection molding on the surface of the female screw portion that engages with the screw shaft in the nut body (see Patent Document 5). The sliding nut described in Patent Document 5 has a nut body made of molten metal, and a resin layer of a resin composition having a synthetic resin as a base resin is formed by injection molding on the surface of the female screw portion that engages with the screw shaft in the nut body. Therefore, the mechanical strength of the attachment portion such as the flange of the nut and the tooth base of the female screw portion is high, and it will not be deformed even under high loads. In addition, since it has excellent heat dissipation properties, softening of the synthetic resin portion can be suppressed. As a result, the true contact area on the friction surface of the resin is reduced, the frictional force and frictional heat are reduced, and there are advantages of reducing wear and suppressing an increase in the friction surface temperature.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0011] Regarding the manufacturing method of the sliding nut described in Patent Document 5, due to the shape of the inner diameter portion of the nut body, for example, it is necessary to perform the manufacturing method described in Patent Document 4 or a manufacturing method in which, after injection molding a resin layer on the nut body, a predetermined female screw shape is formed by machining.

[0012] However, in the manufacturing method described in Patent Document 4, the injection mold is complex and expensive. As a result, the sliding nut and the ball screw device tend to be expensive. Further, in the manufacturing method of forming a resin layer on the nut main body and then forming a predetermined female thread shape by machining, it is necessary to synchronize the female thread shape of the nut main body with the feed of the lathe, and the female thread machining was not easy.

[0013] The present invention has been made in view of such circumstances, and an object thereof is to provide a sliding nut of a ball screw device and a ball screw device that can be manufactured at low cost and have excellent sliding characteristics such as seizure resistance and wear resistance even under high load conditions.

Means for Solving the Problems

[0014] The sliding nut of the present invention is a sliding nut that moves relatively while sliding on the axis of a screw shaft as the screw shaft rotates in a ball screw device, or a sliding nut that rotates the screw shaft by moving relatively while sliding on the axis of the screw shaft. The sliding nut is composed of a metal outer ring formed of metal and a resin inner ring integrally provided on the inner peripheral portion of the metal outer ring. The interface between the metal outer ring and the resin inner ring is a cylindrical surface. A female thread that engages with the screw shaft is formed on the resin inner ring. The thickness from the bottom of the thread groove of the female thread to the cylindrical surface of the metal outer ring is 0.1 mm or more and less than 1.0 mm. At least the cylindrical surface of the metal outer ring is an etched surface, and the resin of the resin inner ring infiltrates into the fine irregularities of the surface.

[0015] A retaining structure for the resin inner ring is provided at at least one inner diameter side end in the axial direction of the metal outer ring.

[0016] As the retaining structure, the metal outer ring has an inclined surface that expands in diameter toward the outside in the axial direction, and the resin inner ring has an enlarged diameter portion formed to expand in the radial direction along the inclined surface.

[0017] It is characterized in that the etching amount calculated by the following formula (1) on the etching treatment surface is larger than 5 μm. Etching amount (μm) = Weight reduction amount (g) / (Surface area (cm 2 ) × Specific gravity (g / cm 3 )) × 10000 ··· (1)

[0018] In the resin inner ring, the thickness at the bottom of the thread groove is characterized by being more than 0.5 mm and less than 1.0 mm.

[0019] The sliding nut of the present invention is characterized in that it can be preferably provided for a ball screw device.

Effect of the Invention

[0020] The sliding nut of the present invention is composed of a metal outer ring which is the nut main body part and a resin inner ring integrally provided on the inner peripheral part of the metal outer ring. Therefore, it has higher strength than a resin sliding nut and can be used even under high loads. Also, since a thread is formed on the resin inner ring for screwing with the screw shaft, it has excellent slidability and can move smoothly. Furthermore, since the thickness from the bottom of the thread groove of the thread to the cylindrical surface of the metal outer ring is 0.1 mm or more and less than 1.0 mm, sliding heat can be effectively dissipated, wear of the sliding surface of the thread is suppressed low, and durability is improved. As a result, high-speed operation is also possible.

[0021] Also, at least the cylindrical surface of the metal outer ring is an etching treatment surface, and the resin of the resin inner ring has infiltrated into the fine irregularities of that surface. Therefore, the adhesion strength between the metal outer ring and the resin inner ring is improved. Furthermore, since the contact area between the resin inner ring with the thread formed and the metal outer ring becomes large, heat is easily transmitted, and the heat dissipation property of the sliding heat is further improved. Also, since the interface between the resin inner ring and the metal outer ring in the metal outer ring is a cylindrical surface, the thread can be formed by tapping, and the manufacture of the sliding nut becomes easy. Also, it leads to shortening of time and reduction of cost associated with manufacturing, and cost reduction is possible.

[0022] Since a resin inner ring retaining structure is provided at at least one inner diameter side end portion in the axial direction of the above-mentioned metal outer ring, for example, separation of the resin inner ring from the metal outer ring can be prevented even during long-term use under harsh conditions. Also, separation of the resin inner ring can be prevented even when an extreme load is applied in the axial direction of the sliding nut. Furthermore, as a retaining structure, the metal outer ring has an inclined surface that expands in diameter toward the outside in the axial direction, and the resin inner ring has an expanded diameter portion formed to expand in the radial direction along the inclined surface. Therefore, for example, compared with the case where the retaining structure is a non-inclined surface, the heat dissipation effect of sliding heat does not decrease, and the wear resistance of the thread sliding surface can be maintained. Also, when an extreme load is applied in the axial direction of the sliding nut, the load transmitted from the metal outer ring to the resin inner ring can be easily dispersed, and the wear resistance of the thread sliding surface can be maintained.

[0023] Since the etching amount calculated by the above formula (1) on the above etching treatment surface is larger than 5 μm, as shown in the examples described later, the adhesion strength of the resin inner ring can be improved, and it can also cope with high loads.

[0024] In the resin inner ring, since the resin thickness at the bottom of the thread groove is more than 0.5 mm and less than 1.0 mm, it is possible to suppress variations in wear resistance while ensuring the heat dissipation of sliding heat.

[0025] Since the sliding screw device of the present invention includes the sliding nut of the present invention, it is excellent in sliding characteristics such as seizure resistance and wear resistance even under high load conditions, and cost reduction is possible.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0027] An embodiment of the sliding screw device of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view of the sliding screw device, and FIG. 2 is an axial cross-sectional view of an example of the sliding nut. The sliding screw device 1 of the present invention includes a screw shaft 2 and a sliding nut 3 of the present invention that is screwed into the screw groove of the screw shaft 2 and relatively moves while sliding on the screw shaft. The rotational motion of the screw shaft 2 is converted into the linear motion of the sliding nut 3. In addition, by rotating the sliding nut 3 at the same position, it is also possible to apply a linear motion to the screw shaft 2.

[0028] As the screw shaft 2, a metal shaft such as stainless steel, carbon steel, or an iron-based metal such as these with zinc plating, nickel plating, steel-chromium plating, etc., or an aluminum alloy, or a resin shaft such as polyimide (PI) resin or phenolic resin can be used. Corrosion-resistant metals or resins such as alloys such as stainless steel and aluminum alloy are preferable because rust does not occur, and are also suitable because rust prevention treatment can be omitted. In the present invention, corrosion-resistant metals that can ensure dimensional accuracy and have excellent durability are most preferable.

[0029] Examples of the processing method of the screw shaft 2 include forging, cutting, grinding, etc., and any processing method may be used. Considering the sliding characteristics such as wear resistance under high load conditions, it is preferable that the surface roughness of the contact surface between the screw shaft and the sliding nut is small. When the surface roughness of the screw shaft is 0.1 μm Ra or less, the digging-up wear of the sliding nut due to the convexity of the screw shaft surface is very small. In particular, a surface roughness of 0.05 μm Ra or less is optimal.

[0030] The screw shaft 2 can be used without lubrication. Also, when emphasizing lower frictional properties rather than maintenance-free, a lubricant such as oil or grease may be used at the sliding part between the screw shaft 2 and the sliding nut 3. In this case, a linear groove in the axial direction may be formed on the sliding surface of the sliding nut with the screw shaft so that wear debris is retained therein to take measures to suppress abrasive wear.

[0031] The sliding nut 3 may be provided with a flange at one end as shown in Fig. 1. Also, a flange may be provided at the central portion in the axial direction of the sliding nut, or may be provided between one end and the central portion in the axial direction. Note that the flange is not necessarily essential. As shown in Fig. 2, the sliding nut 3 is composed of a metal outer ring 4 made of metal and a resin inner ring 5 provided integrally on the inner peripheral portion of the metal outer ring 4. A female screw for screwing with the screw shaft is formed on the resin inner ring 5. The surface of the female screw is in direct sliding contact with the screw shaft 2 (see Fig. 1). The sliding nut 3 has a nut main body portion composed of the metal outer ring 4. The inner peripheral surface 4a of the metal outer ring 4 is a cylindrical surface. That is, the interface between the metal outer ring 4 and the resin inner ring 5 is a cylindrical surface. Note that the cylindrical surface is a concept that includes not only a straight cylindrical surface but also a structure in which protrusions or recesses for preventing detachment or rotation are provided on the cylindrical surface.

[0032] In Fig. 2, the inner peripheral surface 4a of the metal outer ring 4 is an etched surface subjected to etching treatment. Fine irregularities smaller than the micron size are formed on the etched surface, and the resin of the resin inner ring 5 has infiltrated into the fine irregularities. Specifically, by injection molding the resin for forming the resin inner ring 5 on the inner peripheral surface 4a of the metal outer ring 4, the molten resin enters the fine irregularities, and when the resin solidifies, the metal outer ring 4 and the resin inner ring 5 are firmly joined. Furthermore, the true joint area between the resin inner ring 5 and the metal outer ring 4 increases, and since they are in close contact, the sliding heat generated on the surface of the resin female screw is easily transmitted to the metal outer ring 4.

[0033] Examples of the etching process include, for example, chemical etching, plasma etching, etc. Among these etching processes, chemical etching in which complex and intricate fine irregularities are formed is preferred. By the etching progressing not only in the vertical direction of the processing surface but also in the horizontal direction, three-dimensionally intricate fine irregularities can be formed, and it is easy to exhibit a strong anchor effect.

[0034] Examples of the chemical etching process include acidic solution treatment (sulfuric acid, nitric acid, hydrochloric acid, etc., or a mixture with other solutions), alkaline solution treatment (sodium hydroxide, potassium hydroxide, etc., or a mixture with other solutions), and methods such as the Amalfa treatment manufactured by Meck and the NMT treatment manufactured by Taisei Plus can be applied. The shape of the fine irregularities varies depending on the concentration, processing time, post-treatment, etc., but in order to enhance the binding property due to the anchor effect, it is preferable to have fine irregularities with a concave pitch of several nm to several tens of μm. When performing the Amalfa treatment manufactured by Meck, it is preferable that at least the surface that is the interface between the resin inner ring and the metal outer ring is aluminum-based or copper-based. If it is copper-based, the metal outer ring can be made of iron-based, and the surface that is the interface with the resin inner ring can be copper-plated. Also, the metal outer ring can be made of a melted metal of aluminum-based or copper-based.

[0035] From the viewpoint of improving the binding strength of the resin inner ring 5 to the metal outer ring 4, the etching amount on the etching surface (etching amount per 1 cm of the surface to be etched) is preferably greater than 5 μm. The etching amount can be calculated by the following formula (1). 2 The etching amount (μm) = weight reduction amount (g) / (surface area (cm²) × specific gravity (g / cm³)) × 10000 ··· (1) Etching amount (μm) = weight reduction amount (g) / (surface area (cm²) 2 ) × specific gravity (g / cm³) 3 ) × 10000 ··· (1)

[0036] In the above formula (1), the "weight reduction amount" is the value obtained by subtracting the weight of the metal outer ring after the etching treatment from the weight of the metal outer ring before the etching treatment. The "surface area" is the area of the surface to be etched. For example, in FIG. 2, when not masked, it is the total surface area of the metal outer ring before the etching treatment (including the areas of the inner peripheral surface, the outer peripheral surface, and the flange surface). The "specific gravity" is the specific gravity of the metal outer ring.

[0037] The etching amount calculated from the above formula (1) is preferably 7 μm or more, more preferably 8 μm or more, and may be 10 μm or more. Note that when the etching amount becomes large to a certain extent, it becomes difficult to observe an improvement in the adhesion strength. Therefore, the etching amount is, for example, 20 μm or less, and may be 15 μm or less.

[0038] In the chemical etching treatment, a plurality of solutions (chemicals) may be combined and used, or stepwise treatment may be performed.

[0039] As shown in FIG. 2, in the sliding nut 3, the internal thread that is screwed onto the screw shaft is formed of resin. In FIG. 2, the internal thread is composed of a thread crest 5a formed to protrude toward the inner diameter side and a thread groove bottom 5b, and the thread crest 5a and the thread groove bottom 5b are alternately arranged along the axial direction. Note that the shape of the thread crest 5a is not particularly limited, and in addition to the trapezoidal shape as shown in FIG. 2, it may be a triangular shape, a rectangular shape, or a Gothic arc shape. Further, although the thread groove bottom 5b is formed as a flat surface in FIG. 2, its shape is not particularly limited, and it may be a V-shaped or U-shaped or the like.

[0040] In FIG. 2, in the resin inner ring 5, the resin thickness t a in each thread crest 5a arranged along the axial direction of the sliding nut 3 b is constant, and the resin thickness t a in each thread groove bottom 5b b is constant. Further, the resin thickness t a in the thread crest 5a is thicker than the resin thickness t b in the thread groove bottom 5b (t ais the vertical distance from the apex of the thread 5a to the bottom of the thread groove 5b. The resin thickness t at the bottom 5b of the thread groove b is the vertical distance from the bottom 5b of the thread groove to the inner peripheral surface 4a of the metal outer ring 4.

[0041] As shown in FIG. 2, the resin thickness t at the bottom 5b of the thread groove b is formed to be thin. Specifically, the resin thickness t b is 0.1 mm or more and less than 1.0 mm. If the resin thickness t b is less than 0.1 mm, the durability of the bottom 5b of the thread groove may decrease. If the resin thickness t b is 1.0 mm or more, sufficient heat dissipation of the sliding heat cannot be ensured, and the wear amount of the sliding surface may increase. The resin thickness t b is preferably 0.2 mm or more and less than 0.9 mm, and more preferably 0.3 mm or more and less than 0.8 mm. Further, from the viewpoint of suppressing variations in wear resistance, more preferably more than 0.5 mm and less than 0.8 mm.

[0042] The resin thickness t a , t b may be made to the required thickness by injection molding, or may be finished to the required resin thickness by machining after injection molding.

[0043] Another example of the sliding nut of the present invention will be described with reference to FIGS. 3 and 4. FIG. 3 is a cross-sectional perspective view of the sliding nut, and FIG. 4 is an enlarged view around the retaining structure. In these figures, mainly the configurations different from those of the sliding nut in FIG. 2 will be described. Note that FIG. 3 shows a state in which a screw shaft is screwed into the sliding nut 6. Further, in FIG. 4, for convenience, a part of the metal outer ring 7 and the resin inner ring 8 is shown by hatching.

[0044] As shown in Fig. 3, the sliding nut 6 is composed of a metal outer ring 7 made of metal and a resin inner ring 8 provided integrally on the inner peripheral portion of the metal outer ring 7. A female thread for screwing onto the screw shaft is formed on the resin inner ring 8. In the sliding nut 6, a retaining structure for the resin inner ring 8 is provided at the inner diameter side ends on both axial sides of the metal outer ring 7. Specifically, as the retaining structure, the metal outer ring 7 has an inclined surface 7b that expands in diameter toward the outer side in the axial direction, and the resin inner ring 8 has an enlarged diameter portion 8c that expands in the radial direction along the inclined surface 7b. In the sliding nut 6, since the enlarged diameter portion 8c of the resin inner ring 8 is axially caught by the metal outer ring 7, it is possible to prevent the resin inner ring 8 from coming off. Note that the retaining structure may be provided only on one side in the axial direction, but it is preferably provided on both sides.

[0045] Further, the inclined surface 7b is subjected to an etching treatment, and since the resin of the enlarged diameter portion 8c impregnates into the fine irregularities of the inclined surface 7b, it is possible to more effectively prevent the resin inner ring 8 from coming off.

[0046] As shown in Fig. 3, in the metal outer ring 7, the inclined surface 7b is formed over the entire circumference. Also, the enlarged diameter portion 8c of the resin inner ring 8 is formed over the entire circumference. By forming the inclined surface 7b over the entire circumference, when a load is applied to the sliding nut 6 in the axial direction, it is easy to disperse the load transmitted from the metal outer ring 7 to the resin inner ring 8, which in turn leads to an improvement in the wear resistance of the sliding surface. Note that in the sliding nut 6, although a structure for preventing rotation between the metal outer ring 7 and the resin inner ring 8 is not provided, since the cylindrical surface (including the inclined surface 7b) of the metal outer ring 7 is an etched surface and is firmly joined to the resin of the resin inner ring 8, it is not necessary to provide such a structure.

[0047] As shown in Fig. 4, the radial depth t of the retaining structure in the metal outer ring 7 c (in Fig. 4, the radial depth of the inclined surface 7b) is preferably 0.3 mm to 2.0 mm. If the radial depth t c is less than 0.3 mm, it is difficult to exhibit the retaining effect, and if the radial depth t cIf it is larger than 2.0 mm, the heat dissipation of the sliding heat may decrease, which may lead to premature wear of the sliding surface and the like.

[0048] Further, the inner peripheral surface of the enlarged diameter portion 8c of the resin inner ring 8 is a tapered surface that expands as it goes toward the outer side in the axial direction. This facilitates the assembly when the screw shaft is screwed into the screw hole of the sliding nut 6.

[0049] Note that, as the retaining structure in the metal outer ring, any structure in which the resin inner ring is caught in the axial direction with respect to the metal outer ring may be used. In addition to the inclined portions as shown in FIGS. 3 and 4, a rectangular recess, a trapezoidal recess, or the like may be used. Further, the retaining structures may be provided at intervals (for example, at equal intervals) in the circumferential direction, and in this case, the anti-rotation function is also provided.

[0050] The materials of each part of the sliding nut will be described below.

[0051] Since the metal constituting the metal outer ring has a high thermal conductivity, molten metal is preferred. Specifically, as the material of the metal, iron, aluminum, aluminum alloy, copper, or copper alloy is preferably used. By adopting these materials, in the metal outer ring, the required thermal conductivity and load resistance can be ensured, and the sliding heat generated on the sliding surface can be easily dissipated from the metal outer ring to the outside, and it can be used even under high load.

[0052] As the iron, general structural carbon steel (such as SS400), mechanical structural carbon steel (such as S45C), stainless steel (such as SUS303, SUS316), etc. can be used. Further, these irons may be plated with zinc, nickel, copper, or the like. However, when applying corrosion-resistant plating such as zinc plating or nickel plating, masking is performed on the surface that becomes the interface with the resin inner ring.

[0053] As for aluminum, A1050, A1100, etc. can be used, and as for aluminum alloys, A2017, A2024, A5056, A6061, etc. can be used. Since they have excellent machinability, A2017 and A2024 are preferred. Also, aluminum alloy die castings (such as ADC12) and aluminum alloy castings (such as AC4B) can be used. In order to improve the corrosion resistance of aluminum, anodizing treatment may be performed. However, when performing anodizing treatment, masking is carried out on the surface that becomes the interface with the resin inner ring.

[0054] As for copper, C1100, etc. can be used, and as for copper alloys, C3604, etc. can be used. From the viewpoints of machinability and environmental properties, C6801, C6802, etc. with lead of 0.1% or less and cadmium of 0.0075% or less are preferred. Also, copper alloy castings (such as CAC406) can be used.

[0055] The metal of the metal outer ring preferably has a thermal conductivity of 50 W / (m·K) or more. For example, the above-mentioned aluminum, aluminum alloys, copper, and copper alloys can be mentioned. Since the higher the thermal conductivity of the metal, the easier it is to dissipate sliding heat, 100 W / (m·K) or more is more preferred.

[0056] The synthetic resin forming the resin inner ring is based on an injection-moldable synthetic resin, and a synthetic resin with excellent lubrication characteristics is preferred. Also, a synthetic resin with high heat resistance is preferred so that the sliding nut can be used in a part with a high ambient temperature. Such synthetic resins include, for example, aromatic polyether ketone-based resins such as polyether ether ketone (PEEK) resin, polyether ketone (PEK) resin, and polyether ketone ether ketone ketone (PEKEKK) resin, polyacetal (POM) resin, PPS resin, injection-moldable thermoplastic PI resin, polyamideimide (PAI) resin, polyamide (PA) resin, injection-moldable fluororesin, etc. These synthetic resins may be used alone or may be a polymer alloy mixed with two or more types. Among these synthetic resins, PEEK resin, thermoplastic PI resin, PPS resin, PA resin, etc. are particularly preferred.

[0057] The synthetic resin forming the resin inner ring preferably does not contain fibrous inorganic fillers such as glass fibers, carbon fibers, and whiskers. When the resin inner ring contains a fibrous inorganic filler, when the sliding nut relatively reciprocates while sliding on the axis of the screw shaft as the screw shaft rotates, the ends of the fibers may become edges and cause wear and damage to the mating screw shaft, or when the sliding nut reciprocates, the ends of the fibers may be repeatedly stressed and cause fatigue wear of the resin.

[0058] The synthetic resin forming the resin inner ring preferably contains a PTFE resin. By containing the PTFE resin, low friction can be achieved, sliding heat can be reduced, and excellent friction and wear characteristics can be obtained even under high loads. As the PTFE resin, any of molding powder by suspension polymerization method, fine powder by emulsion polymerization method, and recycled PTFE may be adopted.

[0059] The synthetic resin forming the resin inner ring preferably contains graphite. By containing graphite, the friction and wear characteristics can be improved. In addition, since the thermal conductivity is high, it is easy to dissipate the sliding heat to the metal outer ring. Graphite is roughly classified into natural graphite and artificial graphite, and further includes flaky, granular, spherical, etc., and any of them can be used. In order to increase the elastic modulus of the synthetic resin, improve the wear resistance and creep resistance, and obtain more stable low friction, flaky graphite is preferred.

[0060] The synthetic resin forming the resin inner ring preferably contains organic resin powders such as thermosetting PI resin, phenolic resin, and wholly aromatic polyester resin. By containing the organic resin powder, the friction and wear characteristics can be improved. In addition, the elastic modulus of the synthetic resin can be increased, the wear resistance and creep resistance can be improved, and more stable low friction can be obtained.

[0061] The synthetic resin forming the resin inner ring preferably contains 10 to 40% by volume of PTFE resin with respect to the whole synthetic resin without containing fibrous inorganic compounding materials, and more preferably contains 3 to 30% by volume of graphite or organic resin powder. Thereby, even under high load, it has a low coefficient of friction, less deformation and wear of the resin inner ring, less damage to the mating screw shaft, and also has high resistance to oil and the like.

[0062] In addition, well-known resin compounding materials may be blended with the synthetic resin to the extent that the effects of the present invention are not inhibited. Examples of such compounding materials include friction property improvers such as boron nitride, molybdenum disulfide, and tungsten disulfide, thermal conductivity improvers such as carbon powder and metal oxide powder, and colorants such as carbon powder, iron oxide, and titanium oxide. Further, granular inorganic fillers such as calcium carbonate, calcium sulfate, mica, and talc, and aramid fibers and the like can be mentioned.

[0063] The means for mixing and kneading the above raw materials is not particularly limited. Only the powder raw materials can be dry-mixed with a Henschel mixer, ball mixer, ribbon blender, Lodige mixer, ultra-Henschel mixer, etc., and then melt-kneaded with a melt extruder such as a twin-screw extruder to obtain molding pellets. Further, side feeding may be employed when melt-kneading with a twin-screw extruder or the like. Further, heat treatment such as annealing treatment may be performed to improve physical properties.

[0064] The sliding nut of the present invention can be obtained, for example, by setting a metal outer ring (nut main body part) having an etching treatment on its surface in an injection molding die, injecting and molding synthetic resin onto this metal outer ring, and then forming a predetermined female screw shape by machining (such as tapping). By insert molding in this way, the resin inner ring can be firmly bonded to the inner peripheral surface of the metal outer ring without gaps without using an adhesive.

Example

[0065] [Example 1] As the sliding nut with the dimensions described in Fig. 5, A5056 (aluminum alloy) was used for the metal outer ring. A through hole with a diameter of φ13.2 mm is provided on the central axis of the metal outer ring, and 45-degree inclined surfaces are provided as an anti-loosening structure at the inner diameter portions at both axial ends of the metal outer ring (see Fig. 4). The length of the inclined surface is 1 mm in the axial direction. The entire surface of this metal outer ring was subjected to etching treatment without masking. As the etching treatment, an amorphization treatment manufactured by Meck was performed, and A-10101 (pretreatment) and A-10156 (roughening treatment) were used for the chemical solution. The etching amount calculated from the following formula (1) was 6 μm. Etching amount (μm) = weight reduction amount (g) / (surface area (cm 2 )) × specific gravity (g / cm 3 )) × 10000 ··· (1) In the above formula (1), the "weight reduction amount" was 0.0614 g, the "surface area" was 38.803 cm 2 and the "specific gravity" was 2.64 g / cm 3 .

[0066] Also, the following raw materials were dry-blended using a Henschel dry mixer and melt-kneaded using a twin-screw extruder to produce pellets of a PPS resin composition. Using these pellets, the etched metal outer ring was placed in a mold, and the PPS resin composition was insert-molded into the inner diameter portion of the metal outer ring. For the insert-molded nut, a female thread was processed by tapping on the central axis to produce a nut test piece. In the resin inner ring, the resin thickness at the bottom of the thread groove was 0.55 mm, and the resin thickness at the thread crest was 1.49 mm. (1) PPS resin: 60% by volume (2) Thermosetting PI resin powder: 15% by volume (3) PTFE resin: 25% by volume

[0067] [Comparative Example 1] Comparative Example 1 is a resin sliding nut (without molten metal). Using the pellets produced in Example 1, a sliding nut with the dimensions described in Fig. 5 was injection-molded, and tapping was performed in the same manner as in Example 1 to produce a nut test piece.

[0068] [Comparative Example 2] As the sliding nut having the dimensions shown in FIG. 5, A5056 (aluminum alloy) was used for the metal outer ring. A female screw shape was formed in the inner diameter portion of this metal outer ring, and an etching process with an etching amount of 6 μm was performed on this inner peripheral surface in the same manner as in Example 1. Insert molding was performed using the pellets produced in Example 1, and then a nut test piece with a resin layer thickness of 0.3 mm (uniform) was produced by machining the resin along the female screw of the metal outer ring.

[0069] A forged screw shaft made of SUS304 was assembled to each nut test piece, and the following wear test was conducted.

[0070] Test 1: Wear test The nut test pieces of Example 1 and Comparative Example 1 were respectively assembled to the vertically installed screw shaft. Under the following Condition 1, the nut test piece was reciprocated with an axial load applied, and continuous operation was performed until the total movement distance reached 5000 m. During the test, the axial wear amount (wear amount of the screw tooth surface) was measured over time. The results are shown in FIG. 6(a). Also, the surface temperature of the screw shaft was measured after 100 m and 500 m. <Condition 1> Axial load: 300 N Rotation speed: 300 min -1 Stroke: 150 mm Nut movement distance: 5000 m Lubrication: Dry Temperature: Room temperature

[0071] As shown in FIG. 6(a), in Example 1, the axial wear amount was significantly reduced compared to Comparative Example 1. Also, the surface temperature of the screw shaft after 100 m was 98°C in Example 1 and 175°C in Comparative Example 1, and the surface temperature of the screw shaft after 500 m was 80°C in Example 1 and 210°C in Comparative Example 1.

[0072] <Condition 2> For the sliding screw test pieces of Example 1 and Comparative Example 2, the axial load was 1200 N and the rotation speed was 100 min -1Except for setting to this, continuous operation was performed under the same conditions as Condition 1. The results are shown in Fig. 6(b).

[0073] As shown in Fig. 6(b), the axial wear amounts of Example 1 and Comparative Example 2 were equivalent. Also, the surface temperature of the screw shaft after 100 m was 70°C for Example 1 and 62°C for Comparative Example 2, and the surface temperature of the screw shaft after 500 m was 67°C for Example 1 and 48°C for Comparative Example 2. Note that Comparative Example 1 could not be tested because the flange part was damaged when an axial load (1200 N) was applied.

[0074] From the results of Condition 1 and Condition 2 in the above wear test, it was confirmed that the axial wear amount is affected by sliding heat. The sliding screw test piece of Example 1 showed equivalent wear resistance while being easier to manufacture and capable of cost reduction compared to the sliding screw test piece of Comparative Example 2.

[0075] Test 2: Examination of the resin thickness at the bottom of the screw groove By changing the inner diameter dimension of the metal outer ring, the resin thickness at the bottom of the screw groove of the resin inner ring was set to three levels (0.3 mm, 0.7 mm, 1.0 mm), and sliding screw test pieces of Example 2 to Example 3 and Comparative Example 3 were produced. Using these, continuous operation was performed under Condition 1, and the axial wear amount after 3000 m elapsed was measured. For each level, the test was carried out with n = 1 to 2. The results are shown in Fig. 7.

[0076] As shown in Fig. 7, when the resin thickness at the bottom of the screw groove of the resin inner ring was 1.0 mm, the heat dissipation of sliding heat became insufficient and the axial wear amount increased significantly. On the other hand, in Example 2 and Example 3 where the resin thickness at the bottom of the screw groove was less than 1.0 mm, the axial wear amount was significantly suppressed to 0.08 mm or less, and particularly in Example 3, the variation was also small.

[0077] Test 3: Examination of the etching amount Using the same metal outer ring as in Example 1, without processing the anti-loosening structure and without masking this metal outer ring, the same etching treatment as in Example 1 was performed on the entire surface. Regarding the degree of treatment, etching amounts defined by the above formula (1) were prepared at three levels (5 μm, 7 μm, 10 μm). Next, a PPS resin composition similar to that in Example 1 was injection-molded onto the inner peripheral surface of the metal outer ring to produce an adhesion strength test piece composed of the metal outer ring and the resin inner ring. Note that no threaded insert was processed on this adhesion strength test piece.

[0078] As shown in FIG. 8, only the resin inner ring 13 of the adhesion strength test piece 11 was axially loaded with the press-fitting jig 14, and the strength at which the metal outer ring 12 and the resin inner ring 13 were peeled off was defined as the adhesion strength. The results are shown in FIG. 9.

[0079] As shown in FIG. 9, when the etching amount on the etched surface was 5 μm, the adhesion strength was extremely low. In contrast, when the etching amount was 7 μm, the adhesion strength was greatly improved to 5 MPa or more, and in the case of 10 μm, the variation was further reduced.

Industrial Applicability

[0080] The sliding screw device provided with the sliding nut of the present invention can achieve cost reduction and has excellent sliding characteristics such as seizure resistance and wear resistance even under high load conditions. Therefore, it can be suitably used as a sliding screw device used under high load and high temperature conditions in industrial machines and the like.

Explanation of Signs

[0081] 1 Sliding screw device 2 Screw shaft 3 Sliding nut 4 Metal outer ring 4a Inner peripheral surface 5 Resin inner ring 5a Thread 5b Thread groove bottom 6 Sliding nut 7 Metal outer ring 7a Inner peripheral surface 7b Inclined surface 8 Resin inner ring 8c Diameter-expanded part 11 Adhesion strength test piece 12 Metal outer ring 13 Resin inner ring 14 Press-fitting jig

Claims

1. In a sliding screw device, a sliding nut that moves relatively while sliding on the axis of the screw shaft as the screw shaft rotates, or a sliding nut that rotates the screw shaft by moving relatively while sliding on the axis of the screw shaft, wherein the sliding nut is composed of a metal outer ring formed of metal and a resin inner ring integrally provided on the inner peripheral portion of the metal outer ring, the interface between the metal outer ring and the resin inner ring is a cylindrical surface, a female screw that engages with the screw shaft is formed on the resin inner ring, and the thickness from the bottom of the screw groove of the female screw to the cylindrical surface of the metal outer ring is 0.1 mm or more and less than 1.0 mm, at least the cylindrical surface of the metal outer ring is an etched surface, and the resin of the resin inner ring infiltrates into the fine unevenness of the surface, and a sliding nut characterized by this.

2. The sliding nut according to claim 1, wherein a retaining structure for the resin inner ring is provided at at least one inner diameter side end portion in the axial direction of the metal outer ring.

3. As the retaining structure, the metal outer ring has an inclined surface that expands in diameter toward the outside in the axial direction, and the resin inner ring has an expanded diameter portion formed so as to expand in the radial direction along the inclined surface. The sliding nut according to claim 2, characterized by this.

4. The sliding nut according to claim 1 or claim 2, wherein the etching amount calculated by the following formula (1) on the etched surface is larger than 5 μm. Etching amount (μm) = Decrease in weight (g) / (Surface area (cm ２ ) × Specific gravity (g / cm ３ )) × 10000... (1)

5. The sliding nut according to claim 1 or claim 2, wherein in the resin inner ring, the thickness at the bottom of the screw groove exceeds 0.5 mm and is less than 1.0 mm.

6. A sliding screw device comprising the sliding nut according to claim 1 or claim 2.

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