JPH06193701A - Sliding screw for feed mechanism - Google Patents

Abstract

PURPOSE:To obtain a sliding screw having excellent heat-resistance, wear- resistance, and sliding characteristics by forming the screw out of a polyimide resin composite, which is obtained by mixing a specific resin with another resin composite consisting of a specific thermoplastic polyimide resin and specific graphite. CONSTITUTION:A sliding screw, which is used for a feed gear or a positioning device for an industrial machine, is manufactured by forming a polyimide resin composite into a required shape, which is obtained by mixing both a tetra- fluoroethylene resin (5 to 20weight%) and a hardened and pulverulent phenolic resin (5 to 30weight%) with a resin composite (100weight%) consisting of a thermoplastic polyimide resin (50 to 90weight%) as shown in a general formula on the right and graphite (50 to 10weight%) which is obtained by graphitizing a non-phenolic resin material and which has fixed carbon content of at least 97%. In the formula, 'X' denotes a group selected out of a hydrocarbon radical of a directly coupled type or the number of carbons of which is 1 to 10, while 'Y' denotes a quadrivalent radical selected out of an aliphatic group the number of carbons of which is at least two and a cyclic aliphatic group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slide screw for a feed mechanism used in a feed device or a positioning device of an industrial machine.

[0002]

2. Description of the Related Art Generally, a sliding screw for a feed mechanism used in a feeder or a positioning device of an industrial machine is required to have characteristics such as a low friction coefficient and a relatively small wear coefficient. Then, for example, a material obtained by adding a tetrafluoroethylene resin and a powdered phenol resin cured product as a filler to a thermoplastic polyimide resin (Japanese Patent Laid-Open No. Sho 63-63).
No. 314712).

[0003]

However, even a conventional sliding screw for a feed mechanism, which is made of a material obtained by adding a tetrafluoroethylene resin and a cured phenol resin to a thermoplastic polyimide resin as a filler, still has a sufficient wear resistance. However, neither the coefficient of friction nor the wear resistance was satisfactory.

On the other hand, under the usage conditions that require severe heat resistance such that the sliding screw for the feed mechanism reaches the glass transition temperature (Tg = 240 ° C.) of the polyimide resin, the polyimide resin material is heat treated. Crystallinity 25%
It is also known that the heat resistance is increased for use.

However, in this case, since the molded product shrinks by 2 to 5% (shrinkage rate) by the crystallization treatment, there is a problem that the screw efficiency is lowered.

In view of the above, the present invention solves the above-mentioned problems, and makes the sliding screw for the feed mechanism to have the required heat resistance and sliding characteristics and to have sufficiently excellent wear resistance. Even if even more excellent heat resistance is obtained by the crystallization treatment, it is an object to reduce the shrinkage ratio before and after such treatment, and not reduce the shape accuracy and screw efficiency.

[0007]

In order to solve the above-mentioned problems, in the present invention, it is obtained by graphitizing 50 to 90% by weight of a thermoplastic polyimide resin represented by the following formula and a non-phenol resin raw material. 5 to 20 parts by weight of a tetrafluoroethylene resin and 5 to 30 parts by weight of a powdered phenol resin cured product, to 100 parts by weight of a resin composition consisting of 50 to 10% by weight of graphite having a fixed carbon amount of 97% or more. The composition was adopted as a slide screw for a feed mechanism made of a polyimide resin composition containing

Note

[0009]

[Chemical 2]

The graphite having a fixed carbon content of 97% or more may be scaly natural graphite. The details will be described below.

First, the thermoplastic polyimide resin represented by the above formula 2 used in the present invention is obtained by the reaction of one or more tetracarboxylic dianhydrides with the aromatic ether diamine represented by the following formula 3. It is obtained by dehydration cyclization of polyamic acid.

[0012]

[Chemical 3]

Of such polyimide resins, commercially available products of polyimide resins (R _{1 to} R ₄ in the above formula 2) are used.
Are all hydrogen), manufactured by Mitsui Toatsu Chemicals Inc .:
AURUM is mentioned.

Next, the fixed carbon content in the present invention is 97%.
The above graphite may be natural flake graphite produced from the ground or artificial graphite. Out of natural graphite
Experiments have shown that scaly graphite having an average particle size of about 10 μm is particularly preferable for achieving the intended purpose of the present invention. The artificial graphite is preferably, for example, one in which coke derived from pitch is solidified with tar or pitch, baked at about 1200 ° C., placed in a graphitizing furnace, and crystals are grown at a high temperature of about 2300 ° C. In addition, as a raw material of artificial graphite, pitch, coal tar, coke, wood raw material, furan resin,
Polyacrylonitrile is used, and phenol resin is not used as a raw material. This is because it is not preferable to use it together with a phenol resin cured product added separately.

Here, the fixed carbon in the graphite component is the remaining component obtained by quantitatively removing water, ash and volatile matter in the industrial analysis of the coal test method, and contains a small amount of hydrogen containing carbon as the main component. It contains oxygen and nitrogen. When the fixed carbon content is less than 97%, satisfactory results cannot be obtained for both wear resistance and shrinkage of the molded product before and after the crystallization treatment.

The mixing ratio of the above-mentioned thermoplastic polyimide resin and graphite is 50 to 90% by weight of the thermoplastic polyimide resin and 50 to 10% by weight of graphite having a fixed carbon amount of 97% or more. This is because when the amount of graphite added exceeds 50% by weight, the melt viscosity of the composition becomes large, making it difficult to perform melt molding, and when the amount added is less than 10% by weight, improvement in wear resistance and hardening cannot be sufficiently obtained. Because.

Next, the tetrafluoroethylene resin used in the present invention is preferably in a powder form so as to be uniformly mixed in the composition. For example, molding powder, fine powder, or γ-rays after molding and firing are used. It may be pulverized by electron beam irradiation. The blending ratio of the tetrafluoroethylene resin is 5 to 20 parts by weight based on 100 parts by weight of the composition of the thermoplastic polyimide resin and graphite. Because, if the amount is less than 5 parts by weight, the added thermoplastic polyimide resin composition does not have sufficient sliding properties, and if the amount exceeds 20 parts by weight, the mechanical strength inherent to the thermoplastic polyimide resin is impaired. Because.

The powdery phenolic resin cured product used in the present invention comprises a novolac type or resol type phenolic resin produced by using a formalin-generating compound for phenols, if necessary, with a known filler, and as it is. Alternatively, it may be obtained by adding a crosslinking agent such as hexamine and heating it to obtain a cured product, which is then crushed. The manufacturing method is disclosed in JP-A-57-17701 and JP-A-58-1.
As disclosed in Japanese Patent No. 7114 and the like, examples of commercially available products include Bell Pearl manufactured by Kanebo Co., Ltd.

Here, these phenolic resins are heat infusible powdery resins, and specifically have an average particle size of 50 μm.
The particle size is preferably m or less, and 80% by weight or more and 150 μm or less. This is because when the particle size is larger than 150 μm, the mutual adhesion of the powder particles to each other is insufficient at the time of molding, and the mechanical strength such as wear resistance and bending strength of the molded article decreases. This is because it is not preferable. And, the phenol resin cured product used in the present invention is required to be sufficiently cured. For example, when the degree of curing is used as a scale to display the solubility in methanol,
Its solubility is 20% by weight or less, preferably 15% by weight or less, and more preferably 5% by weight or less. This is because when the solubility of methanol exceeds 20% by weight, foaming occurs during molding, resulting in voids and microcracks in the molded body.

The compounding ratio of such a cured phenol resin is 5 to 30 parts by weight based on 100 parts by weight of the composition comprising the thermoplastic polyimide resin and the above graphite. This is because, if the amount is less than 5 parts by weight, the effect of abrasion resistance cannot be obtained, and if the amount is more than 30 parts by weight, not only the melt viscosity of the composition becomes high and melt molding is not possible, but also the friction coefficient cannot be reduced. is there.

The polyimide resin composition for a sliding material according to the present invention may contain various known additives as listed in the following to the extent that the object of the present invention is not impaired. Of course.

That is, as a reinforcing agent, glass fiber,
Carbon fibers, boron fibers, silicon carbide fibers, carbon whiskers, asbestos, metal fibers, rock wool, etc. Flame retardant improvers such as antimony trioxide, magnesium carbonate, calcium carbonate, etc. Electrical property improvers such as clay, mica, etc. , Asbestos, silica, graphite, etc. as cracking resistance improver, iron, zinc, aluminum, copper and other metal powders as thermal conductivity improver, other fillers such as glass beads, glass balloons, calcium carbonate, alumina, Talc, diatomaceous earth,
Hydrated alumina, shirasu balloon, various metal oxides, inorganic pigments, etc., which are natural or synthetic compounds stable at 300 ° C. or higher.

The means for mixing the raw materials used in the present invention described above is not particularly limited, and the raw materials may be individually supplied to the melt mixer, or a Henschel mixer, a ball mixer, a ribbon blender in advance. Two or more types may be simultaneously mixed using a general-purpose mixer such as. The mixing temperature in that case is usually 250 to 420.
C., preferably 300 to 400.degree. Further, as a method of molding the slide screw for the feed mechanism, compression molding, sintering molding, etc. can be adopted, and injection molding or extrusion molding can be performed by forming a uniform melt blend.

[0024]

The sliding screw for the feed mechanism of the present invention has a heat-resistant polyimide resin as a matrix, and a tetrafluoroethylene resin, which is particularly excellent in the effect of reducing the friction coefficient, is added to it, so that it has excellent heat resistance and friction characteristics. In addition, the powdered phenolic resin cured product and the fixed carbon amount are the specified%.
By adding the above graphite in a predetermined amount, the abrasion resistance is improved, and the shrinkage ratio is reduced to 1% or less before and after the crystallization treatment, so that the molding accuracy and the screw efficiency are excellent.

[0025]

[Examples] The raw materials used in Examples and Comparative Examples are summarized below.

The mixing ratios are all weight%,
Abbreviations are shown in [].

(1) Thermoplastic Polyimide Resin [TPI-1] Mitsui Toatsu Chemical Co., Ltd .: AURUM # 450 (2) Thermoplastic Polyimide Resin [TPI-2]: Meldine A (3) Scale Natural Graphite [Scale Graphite] Nippon Graphite Co., Ltd .: ACP (fixed carbon amount 99.5%) (4) Phenolic resin cured product [PF] Kanebo Co., Ltd .: Bell Pearl C2000 (average particle size 48 μm) (5) Tetrafluoroethylene resin [ PTFE] KTL610 manufactured by Kitamura Co., Ltd. [Examples 1 to 4, Comparative Example 1] Raw materials were blended in a ratio shown in Table 1 and dry-mixed, and then 37 using a twin-screw melt extruder.
It is extruded and granulated under the condition of 0 to 400 ° C., the obtained pellets are supplied to an injection molding machine, and the cylinder temperature is 370 to 4
00 ° C, injection pressure 1000 kg / cm ² , mold temperature 15
Injection molding was carried out under the condition of 0 to 200 ° C., and a test piece having a required shape or an effective diameter of 6.2 mm and a pitch of 2.
A test internal thread having a length of 4 mm and a lead of 2.4 mm was molded.

The obtained test piece or female screw was subjected to crystallization heat treatment at 320 ° C. for 2 hours by step heating, and (1) friction coefficient before and after crystallization treatment, (2) wear coefficient,
Tests of (3) shrinkage ratio and (4) screw efficiency were conducted, and the obtained results are shown in Table 2.

(1) Coefficient of friction Using a thrust type friction / wear tester (manufactured by our company), surface pressure 5.0 kg / cm ² , sliding speed 128 m / min, mating material S
The friction coefficient at UJ2, no lubrication, and operating time of 60 minutes was obtained.

(2) Wear coefficient Using the tester used for measuring the friction coefficient, the surface pressure is 5.0 k
g / cm ² , sliding speed 128 m / min, mating material; SUJ
2. Abrasion coefficient × 10 ⁻¹⁰ (cm ³ / kgf · m) was obtained from the wear test results in the non-lubricated state, the amorphous state after 100 hours of operation, and the state after the crystallization treatment.

(3) Shrinkage ratio A thrust washer type test piece having an outer diameter of 66.5 mm, an inner diameter of 37 mm and a thickness of 2 mm (from the center of the inner diameter to the gate opening diameter of 2.5
20 pieces that were formed by disc gate molding with a diameter of 10 mm and the inner diameter was cut.
Crystallization heat treatment was performed at 2 ° C. for 2 hours, and the shrinkage ratio before and after this heat treatment was examined.

(4) Screw Efficiency As shown in FIG. 1, a male screw (made of SUS303, cutting work) 2 (shaft) having an effective diameter of 6.2 mm, a pitch of 2.4 mm and a lead of 2.4 mm 2a included). Then, the female screw 1 and the male screw 2 are attached to a screw efficiency measuring device as shown in FIG.
(Gf · cm) was measured, and this was substituted into the formula for calculating the screw efficiency shown below to determine the screw efficiency η.

Note η = RQtan β / M tan β = np / πd (where R: screw shaft effective diameter / 2, Q: axial load, n:
The number of threads, p: pitch, d: effective diameter, M: friction torque. Here, the screw efficiency measuring device of FIG. 2 will be briefly described. The test female screw 1 is integrally fixed to the holding cylinder 3 while holding the male screw 2 with the shaft, and the holding cylinder 3 is Rotational power is transmitted by the motor 5 via the conduction belt 4 to rotate at 2 rpm. At this time, since the axial load is vertically downwardly applied to the male screw 2 by the weight 6 of 1 kg, the torque M due to the frictional resistance between the screw surfaces appears as the distortion of the leaf spring 7. This torque M is measured by a strain gauge 8 connected to a strain amplifier (not shown). The end portion of the leaf spring 7 can be vertically and horizontally moved by a pair of rollers 9 which are in point contact with each other in an orthogonal manner.

[0034]

[Table 1]

[0035]

[Table 2]

As is clear from the results shown in Table 2, Comparative Example 1 in which graphite having a fixed carbon content of 97% or more was not compounded had both a high friction coefficient and a high wear coefficient, and a shrinkage ratio of 3. It was 8%, which did not reach the intended purpose.

On the other hand, Examples 1 to 4, which satisfy all the conditions for the compounding ingredients and the compounding ratios, have small friction coefficient and wear coefficient, and have a low shrinkage rate of less than 1.0% due to crystallization treatment. The screw efficiency did not decrease before and after the crystallization process, and showed excellent characteristics as a sliding screw for a feed mechanism.

[0038]

As described above, the present invention uses a polyimide resin as a matrix, to which a tetrafluoroethylene resin having a particularly excellent effect of reducing the friction coefficient is added, and a powdered phenol resin cured product and fixed carbon are further added. Since the amount is a sliding screw for a feed mechanism made of a polyimide resin composition containing a predetermined amount of graphite in a predetermined amount or more, this product has excellent sliding properties and excellent wear resistance, and also has a crystal structure. Even if superior heat resistance is obtained by the chemical treatment, there is an advantage that the shrinkage rate is small and the screw shape precision and screw efficiency are extremely excellent.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a slide screw for a feed mechanism according to an embodiment.

FIG. 2 is a vertical cross-sectional view illustrating a screw efficiency measuring device.

[Explanation of symbols]

 1 Female Screw 2 Male Screw 2a Shaft 3 Holding Tube 4 Conduction Belt 5 Motor 6 Weight 7 Leaf Spring 8 Strain Gauge 9 Roller

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Claims (2)

[Claims] 1. A thermoplastic polyimide resin represented by the following formula in an amount of 50 to 90% by weight, and a graphite having a fixed carbon amount of 97% or more obtained by graphitizing a non-phenolic resin raw material.
Molded with a polyimide resin composition in which 5 to 20 parts by weight of a tetrafluoroethylene resin and 5 to 30 parts by weight of a powdered phenol resin cured product are mixed with 100 parts by weight of a resin composition consisting of 0% by weight. Sliding screw for feeding mechanism. Note: 2. The sliding screw for a feed mechanism according to claim 1, wherein the graphite having a fixed carbon content of 97% or more is flaky natural graphite.