JP2948710B2 - Sliding screw for feed mechanism - Google Patents

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 for 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 for a feeder or a positioning device of an industrial machine is required to have a characteristic of a low friction coefficient and a relatively small wear coefficient. 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 Application Laid-Open No.
No.-314274 ).

[0003]

However, even conventional sliding screws for a feed mechanism made of a material obtained by adding a polytetrafluoroethylene resin and a phenol resin cured product to a thermoplastic polyimide resin as a filler, still have sufficient wear resistance. Was not improved, and neither the coefficient of friction nor the wear resistance was satisfactory.

[0004] On the other hand, under conditions of use requiring severe heat resistance, such as reaching the glass transition temperature (Tg = 240 ° C) of the polyimide resin for the sliding screw for the feed mechanism, the polyimide resin material is subjected to heat treatment. Crystallinity 25%
It is also known to use with increased heat resistance.

[0005] However, in this case, since the molded product shrinks by 2 to 5% (shrinkage ratio) by the crystallization treatment, there is a problem that the screw efficiency is reduced.

Accordingly, the present invention solves the above-mentioned problems and provides a slide screw for a feed mechanism having required heat resistance and sliding characteristics, and sufficiently excellent wear resistance. It is an object of the present invention to reduce the shrinkage ratio before and after such a treatment even if more excellent heat resistance is obtained by the crystallization treatment, and to keep the precision of the shape and the screw efficiency from decreasing.

[0007]

In order to solve the above-mentioned problems, according to the present invention, 50 to 90% by weight of a thermoplastic polyimide resin represented by the following formula and a non-phenol resin-based raw material are obtained by graphitization. 100 parts by weight of a resin composition comprising 50 to 10 parts by weight of graphite having a fixed carbon amount of 97% or more, 5 to 20 parts by weight of an ethylene tetrafluoride resin, and 5 to 30 parts by weight of a powdered cured phenol resin. Is adopted as a sliding screw for a feed mechanism made of a polyimide-based resin composition containing

[0008]

[0009]

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The graphite having a fixed carbon content of 97% or more may be flake-like natural graphite. The details are described below.

First, the thermoplastic polyimide resin represented by the formula (2) used in the present invention is obtained by reacting an aromatic ether diamine represented by the following formula (3) with at least one tetracarboxylic dianhydride. It is obtained by dehydration cyclization of a polyamic acid.

[0012]

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Among such polyimide resins, commercially available polyimide resins (R _{1 to} R ₄ in the above formula (2))
Are all hydrogen) as manufactured by Mitsui Toatsu Chemicals:
AURUM.

Next, in the present invention, the fixed carbon amount is 97%.
The above graphite may be natural flaky graphite produced from underground or artificial graphite. Of natural graphite,
Experiments have shown that flaky graphite having an average particle size of about 10 μm is particularly preferred for achieving the intended object of the present invention. As artificial graphite, for example, it is preferable that coke derived from pitch is solidified with tar or pitch, fired at about 1200 ° C., and then placed in a graphitization furnace to grow crystals at a high temperature of about 2300 ° C. Raw materials for artificial graphite include pitch, coal tar, coke, wood raw materials, furan resin,
Polyacrylonitrile or the like 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 separately added phenol resin cured product.

The fixed carbon in the graphite component is a component remaining after quantifying and removing water, ash, and volatile components in industrial analysis of a coal test method. It contains oxygen and nitrogen. If the amount of fixed carbon is less than 97%, satisfactory results cannot be obtained in both the wear resistance and the shrinkage of the molded article before and after the crystallization treatment.

The mixing ratio of the 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. If the amount of graphite exceeds 50% by weight, the melt viscosity of the composition increases and melt molding becomes difficult. If the amount is less than 10% by weight, hardening with improved abrasion resistance cannot be sufficiently obtained. Because.

The ethylene tetrafluoride resin used in the present invention is preferably in the form of a powder in order to be uniformly mixed in the composition. For example, molding powder, fine powder or γ-ray etc. What was crushed by electron beam irradiation may be used. The mixing ratio of the tetrafluoroethylene resin is 5 to 20 parts by weight based on 100 parts by weight of the above-mentioned composition of the thermoplastic polyimide resin and graphite. When the amount is less than 5 parts by weight, sufficient sliding properties are not provided to the added thermoplastic polyimide resin composition, and when the amount exceeds 20 parts by weight, the original mechanical strength of the thermoplastic polyimide resin is impaired. Because.

The powdery cured phenol resin used in the present invention is prepared by adding a known filler as necessary to a novolak-type or resol-type phenol resin produced by using a formalin-generating compound as a phenol. Alternatively, a cured product may be obtained by adding a crosslinking agent such as hexamine and heating to obtain a cured product, and then pulverized. The production method is described in JP-A-57-1770011 and JP-A-58-177001.
No. 17114, and 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.
m and a particle size of 80% by weight or more and 150 μm or less are preferable. Because, when the particle diameter exceeds 150 μm, the mutual adhesion between the particles of the powder is insufficient at the time of molding, and the mechanical strength such as abrasion resistance and bending strength of the molded body is reduced. This is because it is not preferable. Then, the cured phenolic resin used in the present invention needs to be sufficiently cured.
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 if the methanol solubility exceeds 20% by weight, foaming occurs during molding, and voids and minute cracks occur in the molded body.

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

The polyimide resin composition for a sliding material according to the present invention can be mixed with various known additives listed below as long as the object of the present invention is not impaired. Of course.

That is, glass fiber,
Carbon fiber, boron fiber, silicon carbide fiber, carbon whisker, asbestos, metal fiber, rock wool, etc. Flame retardant, antimony trioxide, magnesium carbonate, calcium carbonate, etc. Electric property improver, clay, mica, etc. , As an anti-cracking agent, asbestos, silica, graphite, etc., as a thermal conductivity improver, iron, zinc, aluminum, copper and other metal powders, etc., as other fillers, glass beads, glass balloons, calcium carbonate, alumina, Talc, diatomaceous earth,
It is a hydrated alumina, shirasu balloon, various metal oxides, inorganic pigments, etc., and is a natural or synthetic compound 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 a melt mixer, or a Henschel mixer, a ball mixer, a ribbon blender may be used in advance. Or two or more types may be mixed simultaneously using a general-purpose mixer such as The mixing temperature in that case is usually 250 to 420
° C, preferably 300-400 ° C. In addition, the molding method of the slide screw for the feed mechanism can employ compression molding, sintering molding, or the like. A uniform molten blend can be formed, and injection molding or extrusion molding can also be performed.

[0024]

The sliding screw for a feed mechanism according to the present invention is made of a heat-resistant polyimide resin as a matrix and is added with a tetrafluoroethylene resin which is particularly excellent in the effect of reducing the coefficient of friction. In addition, the powdered phenol resin cured product and the fixed carbon amount are
By adding the graphite in a predetermined amount, the abrasion resistance is improved, and the shrinkage ratio before and after the crystallization treatment is reduced to 1% or less, and the molding accuracy and the screw efficiency are improved. That is, the slide screw for the feed mechanism of the present invention is a male screw.
Generated by frictional resistance between the thread surfaces of the screw and female screw
The torque value is reduced and the so-called screw efficiency is improved
Thus, a more accurate feeding operation can be performed.

[0025]

EXAMPLES The raw materials used in Examples and Comparative Examples are collectively as follows.

In addition, all the mixing ratios are% by weight.
The abbreviations are shown in brackets.

(1) Thermoplastic polyimide resin [TPI-1] manufactured by Mitsui Toatsu Chemicals: AURUM # 450 (2) Thermoplastic polyimide resin [TPI-2]: Meldin A (3) Flaky natural graphite [flaky Graphite] Nippon Graphite: ACP (99.5% fixed carbon) (4) Cured powdered phenol resin [PF] Kanebo: Bellpearl C2000 (average particle size: 48 μm) (5) Ethylene tetrafluoride resin PTFE] KTL610 manufactured by Kitamura Co., Ltd. [Examples 1 to 4, Comparative Example 1] Raw materials were blended at the ratio shown in Table 1 and dry-mixed, and then mixed using a twin-screw extruder.
The pellets are extruded and granulated under the conditions of 0 to 400 ° C., and the obtained pellets are supplied to an injection molding machine, and the cylinder temperature is set to 370 to 4
00 ° C, injection pressure 1000 kg / cm ² , mold temperature 15
Injection molding is performed under the condition of 0 to 200 ° C., and a test piece having a required shape or a shape shown in FIG.
A test female screw having a length of 4 mm and a lead of 2.4 mm was formed.

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

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

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

(3) Shrinkage 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 (a gate opening diameter of 2.5 mm from the center of the inner diameter).
20 mm), and these were subjected to step heating to 320
A crystallization heat treatment at 2 ° C. for 2 hours was performed, and the shrinkage ratio before and after this heat treatment was examined.

(4) Screw Efficiency As shown in FIG. 1, a female screw 1 (made of SUS303, cutting process) 2 having an effective diameter of 6.2 mm, a pitch of 2.4 mm, and a lead of 2.4 mm was used as the female screw 1 for testing. 2a). 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 a screw efficiency calculation formula shown below to obtain a screw efficiency η.

Note: η = R · Q · tan β / M tan β = n · p / π · d (where R: effective screw shaft diameter / 2, Q: axial load, n:
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 female screw 1 for test is fixed integrally with the holding cylinder 3 while holding the male screw 2 with a shaft. The rotation power is transmitted from the motor 5 via the conduction belt 4 to rotate at 2 rpm. At this time, the axial load is applied vertically downward to the male screw 2 by the weight 6 of 1 kg. This torque M is measured by a strain gauge 8 connected to a strain amplifier (not shown). The end of the leaf spring 7 can be moved up, down, left, and right by a pair of rollers 9 that are in point contact with each other at right angles.

[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 amount of 97% or more was not blended had a high coefficient of friction and a high wear coefficient, and a shrinkage rate of crystallization treatment of 3. It was 8%, which was far short of its intended purpose.

On the other hand, in Examples 1 to 4 in which both the components and the mixing ratio satisfy all the conditions, both the coefficient of friction and the coefficient of wear are small, and the shrinkage by crystallization treatment is as low as less than 1.0%. The screw efficiency did not decrease before and after the crystallization treatment, showing excellent characteristics as a sliding screw for the feed mechanism.

[0038]

According to the present invention, as described above, a polyimide resin is used as a matrix, an ethylene tetrafluoride resin, which is particularly excellent in the effect of reducing the friction coefficient, is added to the matrix, and a powdered phenol resin cured product and fixed carbon are added. Since the sliding screw for the feed mechanism is made of a polyimide resin composition to which a predetermined amount of graphite is added in a predetermined amount or more, the sliding screw has excellent sliding characteristics and excellent wear resistance. Even if more excellent heat resistance is obtained by the heat treatment, there is an advantage that the shrinkage ratio is small and the screw shape precision and screw efficiency are extremely excellent.

[Brief description of the drawings]

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

FIG. 2 is a longitudinal sectional view illustrating a screw efficiency measuring device.

[Explanation of symbols]

 Reference Signs List 1 internal thread 2 external thread 2a shaft 3 holding cylinder 4 conduction belt 5 motor 6 weight 7 leaf spring 8 strain gauge 9 roller

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code FI C08L 61:06) (56) References JP-A-63-152762 (JP, A) JP-A-63-314274 (JP, A) JP-A-5-170937 (JP, A) JP-A-5-271538 (JP, A) JP-A-6-192573 (JP, A) JP-A-6-193628 (JP, A) (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08L 79/00-79/08 F16H 25/24 CA (STN) REGISTRY (STN)

Claims (2)

(57) [Claims] A slide for a feed mechanism comprising a male screw and a female screw.
In the screw, the female screw is formed from 50 to 90% by weight of a thermoplastic polyimide resin represented by the following formula and 50 to 10% by weight of graphite having a fixed carbon amount of 97% or more obtained by graphitizing a non-phenol resin-based material. Molded with a polyimide resin composition in which 5 to 20 parts by weight of an ethylene tetrafluoride resin and 5 to 30 parts by weight of a powdered cured phenol resin were mixed with 100 parts by weight of a resin composition. feed mechanism for sliding screw you with. Note: 2. The sliding screw for a feed mechanism according to claim 1, wherein the graphite having a fixed carbon amount of 97% or more is scaly natural graphite.