JPH10192816A - Apparatus for reducing volume of waste plastic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a waste plastic material surely from being caught between a treatment container and a piston by installing the piston reciprocating in the container in a pressurizing part for reducing the volume of the material by pressurizing the material beginning to be softened and attaching a sliding member to the side of the piston. SOLUTION: In volume reducing treatment, first compressed air is supplied into a pressurizing actuator 4 to start the compression of a waste plastic material 28 which is melted by circulating high temperature gas in a hot air circulating furnace 11 through a piston 25a. After the end of the compression of the material 28, the compressed air in the actuator 4 is released to the atmosphere to bring down the piston 25a. Since a radius of curvature smaller than the inside radius of a treatment container 2 is provided on a surface on which sliding members 29a attached to three places at equal intervals in the circumferential direction above and below the circumference of the piston 25a, and one sliding member 29a contacts with one point, a trouble in which the circumferential side of the piston 25a is caught in a way is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for reducing the volume of a waste plastic material which is heated and softened to reduce the volume of waste plastic material such as styrene foam generated at homes, offices, shops and the like.

[0002]

2. Description of the Related Art Conventionally, a large amount of waste has been discharged from homes, business establishments, stores, and the like. Due to a shortage of processing facilities such as incineration landfills and an increase in processing costs including collection and transportation. Measures are urgent. As a countermeasure, reducing the amount of waste is the fundamental solution, but the use of resources through recycling is also very effective. Above all, waste plastic materials are attracting attention as targets for recycling because the raw materials are valuable energy resources such as petroleum, and they do not rot even if they are landfilled, and are bulky. Among them, especially Styrofoam,
Because of its light weight, cushioning property, low cost, and the like, it is frequently used as a distribution container, and its alternative material has not been found so far. Therefore, it is strongly desired to reuse the material for recycling. However, when the styrofoam or the like is collected and collected at one place for recycling, there is a problem that the bulky bulk increases the transportation cost, which increases the overall recycling cost. For this reason, a volume reduction processing method and a volume reduction processing device that are installed in places where waste plastic materials are generated, such as homes, business offices, and stores, to reduce the volume thereof have been proposed. This volume reducing device softens styrene foam and the like by heating to form a softened solid. The softened solid obtained by reducing the volume is collected by a trader and recycled at a recycling factory.

However, in the method of reducing the volume of styrofoam or the like by heating, it is necessary to heat the styrofoam or the like until the styrofoam or the like softens, and in some cases, melts. Since the exhaust gas containing styrene gas and flammable gas such as butane gas contained in the styrene foam is generated with odor, not only is the styrene gas vaporized but also unpleasant during the volume reduction operation. Consideration was needed for safety measures.

Therefore, the following techniques have been conventionally proposed as an improvement of the volume reduction processing method. This technology circulates heated air in a processing vessel, catalyzes the circulated air, heats and compresses the waste plastic material, and recovers it.It aims to reduce the volume and deodorize waste plastic material. is there.

[0005] A conventional waste plastic material volume reducing device will be described below. FIG. 5 is an overall view of a conventional waste plastic material volume reducing device. In FIG. 5, reference numeral 1 denotes a waste plastic material volume reducing device main body, a heat-resistant container 22, a processing container 2 in which the waste plastic material 28 is stored and softened, and a pressurization for directly compressing and reducing the volume of the waste plastic material 28. A section 3 and a hot air circulation path 11 for circulating high-temperature gas are provided. The heat-resistant container 22 has a structure in which hot air at the above-mentioned temperature, mostly about 160 ° C., does not leak out of the waste plastic material volume reducing device 1, and is made of a heat-resistant plastic material such as polyamide. It is a stainless steel plate or the like.

In order to use this waste plastic material volume reducing device at a store such as a supermarket, it is appropriate that the volume of the processing container 2 is about 80 to 200 liters.

[0007] The reason is that the installation area is not so large if the size is about this size, and the movement is easy. On the other hand, instead of increasing the recovery rate of the waste plastic material 28 or increasing the number of waste plastic material reduction devices due to the enlargement of the store, the time required for one volume reduction operation is shortened to increase the throughput. This is more economical. In this case, a waste container may be provided on the side of the waste plastic material reducing device so that the waste plastic material 28 is temporarily stored.

An appropriate number of side outlets 18 for hot air are provided on the side surface of the processing container 2, and an opening / closing lid 6 provided with an O-ring elastic body 5 is provided on the upper surface side. This opening / closing lid 6
Is opened when the waste plastic material 28 is charged into the processing melter, and is closed and closed when softening and reducing the volume in the processing vessel 2. Further, the pressurizing section 3 is movable up and down and is provided on the lower side of the processing container 2.
The volume of the waste plastic material 28 which has started to be softened by a high-temperature gas of about 60 ° C. is reduced by applying a surface pressure to the open / close lid 6.
The pressurizing section 3 is reciprocated by the pressurizing actuator 4 and the pressurizing actuator 4, and the waste plastic material 28
, Which is directly pressurized.

The pressurizing actuator 4 is a rubber balloon-like air bag that can expand and contract, and is inflated by air fed from an air pump 21 to push up a piston 25 to reduce the volume of the waste plastic material 28, and thereafter, a pressure regulating valve. 13 is opened to discharge the air accumulated inside and return the pressurizing section 3 to its original position. At the time of volume reduction, the waste plastic material 28 does not leak outside due to the O-ring-shaped elastic body 5. The air pressure sent at this time is 0.1 to 0.2K
g / cm ² may be sufficient. For example, if the area of the piston 25 is 1000 cm ² , a pressing force of about 100 Kg can be obtained.

As described above, the structure of the pressurizing section is relatively simple, the exhaust capacity of the air pump 21 may be small, the weight is light, the noise can be suppressed, and the air pump 2
The exhaust capacity of 1 can be small, the weight is light, the noise can be reduced, and it can be installed in a store such as a supermarket. 7 is a blower with a blowing volume of about 2500 liters /
It has a capacity of about one minute, and is provided in a hot air circulation path 11 communicated with the processing container 2 to circulate a high-temperature gas through the processing container 2. The hot air circulation path 11 is provided with a heating unit 8 which is an electric heater for heating the circulating gas, and a first temperature sensor 9 near the hot air discharge port 10 of the hot air circulation path 11.

Reference numeral 12 denotes a discharge path, a part of which is provided in communication with the hot air circulation path, for branching a part of the circulating high-temperature gas and discharging it as exhaust gas to the outside of the system. When the waste plastic material 28 is styrofoam, this exhaust gas is a mixture of foaming gas such as butane, toluene and xylene, and flammable gas such as styrene monomer gas vaporized at the time of volume reduction treatment of about several thousand ppm. It is. The flammable concentration of these flammable gases is 80,000 ppm or more, and this exhaust gas does not burn in the processing vessel 2 in a normal volume reduction process.
Therefore, an oxidizing unit 14 is provided in the discharge path 12 to oxidize the exhaust gas to be burned without flame. The oxidizing section 14 includes a catalyst heating section 16 as an electric heater and a catalyst heating section 16.
Oxidation catalyst 1 that promotes oxidation of exhaust gas heated by
5 and a second temperature sensor 17 for detecting the temperature of the heated exhaust gas. The oxidation catalyst 15 is, for example, a platinum-containing compound supported on a mullite ceramic containing aluminum oxide, silicon oxide or the like as a main component.

The combustible exhaust gas is heated by the catalyst heating unit 16 to a temperature higher than the activation temperature of the catalyst, and the combustible components passing therethrough are easily oxidized and smokelessly burned. The exhaust gas that has undergone smokeless combustion is exhausted from the exhaust port 20 to the outside of the system through the exhaust passage 12. The discharge path 12 is made of a material excellent in thermoelectricity so that the heat of the processing gas can be easily carried.

Reference numeral 23 denotes an air suction port provided in the heat-resistant container 22, and constantly sucks air from outside during hot air circulation. The amount of the sucked air and the amount of the processing gas discharged from the discharge passage 12 are balanced, thereby preventing the flammable gas in the discharged plastic material volume reducing device main body 1 from becoming too high in concentration. I have. The control unit 24 controls the operation of the waste plastic material volume reducing device, and controls the temperature of the circulating high-temperature gas, the amount of circulating air, the pressure in the pressurizing unit 3, and the like. Reference numeral 27 denotes an exhaust fan for radiating heat generated in the waste plastic material volume reducing device 1 to the outside of the system.

Next, the operation of this conventional waste plastic material volume reducing device will be described. The lid 6 is opened, and the waste plastic material 28 is put into the processing container 2. Next, when the operation is started by closing and closing the opening / closing lid 6 and pressing an operation switch (not shown), the blower 7 and the catalyst heating unit 16 are energized under the control of the control unit 24. When the temperature of the exhaust gas heated by the catalyst heating unit 16 rises to about 300 ° C., the second temperature sensor 17 detects the temperature and transmits it to the control unit 24. Here, the control unit 24 energizes the heating unit 8 to start heating. At this time, if the temperature of the circulating gas rises to a predetermined temperature, the first temperature sensor 9 detects this and transmits a detection signal to the control unit 24 to automatically control the temperature to the set temperature. This control temperature range is often around 100-
The temperature is in the range of 160 ° C., which is changed depending on the type of the waste plastic material 28, and a heating pattern suitable for it is set. Further, the temperature of the exhaust gas heated by the catalyst heating unit 16 is controlled so as to be maintained at about 500 ° C. by a detection signal from the second temperature sensor 17.

The high-temperature gas becomes hot air and is discharged from the hot-air discharge port 10 into the processing container 2 as shown by an arrow b, and heats and softens the waste plastic material 28 put into the processing container 2. Next, the high-temperature gas is discharged from the side discharge port 18 as shown by an arrow c, flows through a gas flow path 19 formed between the inner surface side of the heat-resistant container 22 and the outer surface side of the processing container 2, and is taken in by the blower 7. It reaches the mouth and is circulated through the hot air circulation path 11 as shown by the arrow d.

When the waste plastic material 28 in the processing container 2 is heated by a high-temperature gas, the apparent volume occupied by the waste plastic material 28 is reduced, and in addition, in the case of, for example, styrene foam, The foaming gas contained in the portion is separated, and the volume of the styrene is reduced due to vaporization of part of the styrene. That is, when heated, the waste plastic material 28 contracts while substantially maintaining its original shape, significantly reduces the bulk, starts softening from the softened portion, and reduces the volume. Then, in order to further reduce the volume and increase the volume reduction rate, the material is compressed by the pressurizing unit while heating with a high-temperature gas, together with the start of softening. However, in the case of a PET bottle or the like, if heating proceeds too much, it crystallizes and becomes hard, so it is necessary to finish pressurizing by then. When the pressure adjusting valve 13 is closed and the air pump 21 is operated, air is pressure-fed to the pressurizing actuator 4 composed of an air bag or the like, and the piston 25 moves as shown by an arrow g, and the waste plastic material 28 in the processing vessel 2 is moved. Is compressed between the opening and closing lid 6 to reduce the volume. The waste plastic material 28 whose volume has been reduced and its volume has been reduced is collected, collected for several days, and collected and recycled by a collection company.

As described above, in this volume reduction processing apparatus, the vertically movable piston provided at the bottom of the processing vessel is pushed up by using air pressure, and the waste plastic material softened by heating is compressed and sandwiched between the open / close lid. It is a method of reducing the volume.

[0018]

However, in such a conventional waste plastic material volume reducing apparatus, when the piston moves up and down, the inner periphery of the processing container and the outer periphery of the piston slide, so that the smooth vertical movement is achieved. In order to enable this, it is necessary to provide a certain gap between the processing vessel and the piston.If the gap is too large, the waste plastic material softened at the time of compression occurs. There is a problem that the processing container and the piston must be strictly controlled for dimensional accuracy (especially roundness in the case of a circular container) and surface roughness because the container is caught by the processing container when descending.

Therefore, the present invention solves the above-mentioned conventional problems, in which the waste plastic material does not bite between the processing container and the piston, and the piston is caught in the processing container and cannot move. It is an object of the present invention to provide a compact and lightweight waste plastic material volume reduction device that is easy, safe, sanitary, and economical in volume reduction operation without strictly controlling the dimensional accuracy of the processing container and the piston. Things.

[0020]

SUMMARY OF THE INVENTION In order to solve the above-mentioned object, a waste plastic material reducing apparatus according to the present invention is provided at the bottom of a processing vessel to reduce the volume of a waste plastic material that has started to soften by pressurizing. A hot air circulation passage communicating with the pressure section, the processing vessel and circulating a high-temperature gas for softening the waste plastic material, and a discharge passage communicating with the hot air circulation passage and discharging a part of the high-temperature gas circulating through the hot air circulation passage. A blower provided in the hot air circulation path and a heating unit for heating the gas, a piston reciprocating in the processing vessel is provided in the pressurizing unit, and a sliding member is provided on a side surface of the piston. And

Accordingly, the waste plastic material does not bite between the processing container and the piston, the piston does not get caught in the processing container and cannot move, and the dimensional accuracy of the processing container and the piston is improved. It is possible to provide a compact and lightweight waste plastic material volume reducing device that is simple, safe, sanitary, and economical in volume reduction operation without strict control.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a processing container provided with an opening / closing lid and capable of softening waste plastic material inside, and a waste plastic provided at the bottom side of the processing container and having started softening. A pressurizing unit that pressurizes and reduces the volume of the material, a hot air circulation path that communicates with the processing vessel and circulates a high-temperature gas for softening the waste plastic material, and a high-temperature gas that communicates with the hot air circulation path and circulates in the hot air circulation path A discharge path for discharging a part of the gas, a blower provided in the hot air circulation path, and a heating unit for heating the gas, and the pressurizing unit is provided with a piston that reciprocates in the processing container, By providing a sliding member on the side surface of the piston, the piston is prevented from being caught.

According to a second aspect of the present invention, since a dish-shaped member having a tapered outer periphery is provided at the upper part of the piston, the waste plastic material is interposed between the inner periphery of the processing container and the side surface of the piston. It has the effect of preventing intrusion.

According to a third aspect of the present invention, the sliding members are arranged at regular intervals in the circumferential direction on the side surface of the piston, so that the friction between the inner periphery of the processing container and the side surface of the piston is reduced. In addition to enabling smooth vertical movement, the dimensional accuracy of the processing container and the piston can be easily controlled.

According to a fourth aspect of the present invention, since the sliding member is formed of a deformable spring-like member, the dimensional accuracy of the processing container and the piston can be more easily controlled.

According to a fifth aspect of the present invention, the sliding member is formed of a spherical member rotatable between the processing container and the piston, so that the friction between the inner periphery of the processing container and the side surface of the piston is further reduced. This allows the piston to move up and down smoothly.

According to a sixth aspect of the present invention, since the sliding member is coated with a low-friction member, the friction between the inner periphery of the processing container and the side surface of the piston is further reduced, so that the piston can move up and down smoothly. Is what makes it possible.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1, 2, 3, and 4. FIG.

(Embodiment 1) FIG. 1 is an overall view of a waste plastic material volume reducing apparatus according to Embodiment 1 of the present invention. In FIG. 1, 1 is a waste plastic material volume reducing device main body, 2 and 3a are pressure units, 4 is a pressure actuator, 5 is an O-ring elastic body, 6 is an opening / closing lid, 7 is a blower, and 8 is a blower. A heating unit, 9 is a first temperature sensor, 10 is a hot air discharge port, 11 is a hot air circulation path, 12 is a discharge path, 12a is a discharge port, 13 is a pressure regulating valve, 14 is an oxidizing unit, 15 is an oxidation catalyst, and 16 is A catalyst heating unit, 17 is a second temperature sensor, 18
a is a side discharge port, 19 is a gas flow path, 20 is an exhaust port, 21
Is an air pump, 22 is a heat-resistant container, 23 is an air inlet, 2
4 is a control part, 25a is a piston, 27 is a gallery part,
28 is a waste plastic material. Since the components denoted by the same reference numerals as those in FIG. 5 have basically the same operation as the conventional waste plastic material volume reducing device, the detailed description is omitted by referring to the description of FIG.

Therefore, the first embodiment will be described in detail with reference to FIG. FIG. 2A is a detailed view of the pressing unit 3a according to the first embodiment, and FIG. 2B is a cross-sectional view taken along the line AA. 29a is a sliding member,
3 are attached at equal intervals in the circumferential direction on the upper and lower sides of the outer peripheral side surface. The sliding member 29a has a cylindrical shape, and the diameter of the cylinder is larger than the lateral length of the side discharge port 18a so as not to fit into the side discharge port 18a provided in the processing container 2. The surface in contact with the container 2 has a radius of curvature smaller than the inner diameter of the processing container 2. The material of the sliding member 29a is a copper alloy, an aluminum alloy, a fluororesin or the like having a low coefficient of friction.

The sliding member 29a is mounted on the piston 25a, and the gap between the processing containers 2 is set to 0.5 mm to 1.0 mm on one side in consideration of slidability and dimensional change due to thermal expansion.
About 5 mm is provided. Reference numeral 30 denotes a dish-shaped member attached to the upper part of the piston 25a, and its material is 1 mm thick.
Stainless steel plate or the like, and the outer peripheral portion having a width of about 10 mm is bent upward by about 45 ° to about 60 °. The gap between the dish-shaped member 30 and the processing vessel 2 is about 1 mm larger than the gap between the sliding member 29a and the processing vessel 2 so that the dish-shaped member 30 and the processing vessel 2 do not come into contact with each other.

The operation of the pressurizing section 3a during the volume reduction process will be described with reference to FIGS. 2 (a) and 2 (b). When the volume reduction process is started, compressed air is sent from the air pump 21 (FIG. 1) to the pressurizing actuator 4, and the piston 25a moves to the arrow g.
To start compressing the waste plastic material 28. At this time, since the waste plastic material 28 is softened by heating, the material in the vicinity of the processing container 2 can easily enter the gap with the piston 25a, but the outer periphery of the dish-shaped member 30 becomes tapered. Waste plastic material 2
There is no bite to pick up the 8.

Subsequently, when the compression of the waste plastic material 28 is completed, the operation of the air pump 12 is stopped, and the compressed air in the pressurizing actuator 4 is released to the atmosphere by the pressure regulating valve 13, so that the waste plastic material 28 Due to the gravity of the piston 25a or the like, the piston 25a goes down. At this time, the sliding member 29a and the processing container 2 which are attached at three places at equal intervals in the circumferential direction above and below the outer periphery of the piston 25a come into contact with each other and slide, but the surface of the sliding member 29a which contacts the processing container 2 is Since the radius of curvature is smaller than the inner diameter of the processing container 2, one sliding member 29a is inscribed at one point, that is, only six points are inscribed as a whole. Therefore, unlike the conventional example, the outer peripheral side surface of the piston 25a is in surface contact with the inner surface of the processing container 2, and the piston 25a does not easily fall due to friction alone due to friction, and is not caught in the middle. Also, piston 2
In the case of 5a, only the portion to which the sliding member 29a is attached needs to be dimensionally controlled.

Further, by using an inexpensive material such as cast iron as the material of the sliding member 29a and coating it with a low friction material such as fluororesin, the sliding property can be greatly improved while keeping the material cost low.

(Embodiment 2) Next, Embodiment 2
Will be described in detail with reference to FIG. FIG. 3A is a detailed view of a pressing unit 3b according to the second embodiment, and FIG.
(B) is the AA sectional view. Reference numeral 29b denotes a sliding member, which is attached to three places at equal intervals in the circumferential direction above and below the outer periphery of the piston 25b. Sliding member 29b is 1m thick
m, and a portion in contact with the processing container 2 has a deformable semi-arc shape, and the radius of curvature of the arc is such that it does not fit into the side discharge port 18 a provided in the processing container 2. The length is larger than the lateral length of the side discharge port 18a. The outer diameter of the sliding member 29b is larger than the inner diameter of the processing container 2 in a state where the sliding member 29b is mounted on the piston 25b. And comes into contact with the processing container 2. The sliding member 29b is the piston 25
The outer diameter of the sliding member 29b within the dimensional tolerance between the piston 25 and the processing container 2 can be lowered by gravity even when the amount of deformation of the semicircular portion of the sliding member 29b within the dimensional tolerance of the piston 25b is maximum. The size is as large as possible. 30 is a piston 25b
Embodiment 1 is a dish-shaped member attached to the upper part of
The description is omitted here.

With the above configuration, the sliding member 2
Since there is no need to provide a gap between 9b and the processing container 2, there is no need to tighten the dimensional accuracy between the piston 25b and the processing container 2, and processing of the piston 25b and the processing container 2 becomes extremely easy.

(Embodiment 3) Next, Embodiment 3
Will be described in detail with reference to FIG. FIG. 4A is a detailed view of the pressing unit 3c according to the third embodiment.
(B) is the AA sectional view. Reference numeral 29c denotes a sliding member which has a spherical shape and is rotatably held in a state where it is inserted into the processing container 2 in three holes provided at equal intervals in the circumferential direction above and below the outer periphery of the piston 25c. Have been. The material of the sliding member 29c is stainless steel or the like, and its surface is polished. The diameter is set to be larger than the lateral length of the side discharge port 18a so as not to be stuck in the side discharge port 18a provided in the processing container 2. 30 is a piston 25
This is a dish-shaped member attached to the upper part of c, which is the same as that of the first embodiment, and will not be described here.

With the above configuration, the sliding member 2
Since there is no need to provide a gap between 9c and the processing container 2, there is no need to tighten the dimensional accuracy of the piston 25c and the processing container 2, and processing of the piston 25c and the processing container 2 becomes extremely easy.

Further, since the sliding member 29c is rotatable between the piston 25c and the processing container 2, frictional resistance is small,
The piston 25c can move up and down more smoothly.

[0040]

As is apparent from the above description, the waste plastic material volume reducing apparatus of the present invention has a simple structure and the waste plastic material does not bite between the processing container and the piston, and the piston is caught on the processing container. Nothing. Also, there is no need to strictly control the dimensional accuracy of the processing container and the piston, and processing of the processing container and the piston becomes extremely easy.

[Brief description of the drawings]

FIG. 1 is an overall view of a waste plastic material volume reducing device according to a first embodiment of the present invention.

FIG. 2 is a detailed view of a pressing unit according to the first embodiment of the present invention.

FIG. 3 is a detailed view of a pressing unit according to the second embodiment of the present invention.

FIG. 4 is a detailed view of a pressing unit according to the third embodiment of the present invention.

FIG. 5 is an overall view of a conventional waste plastic material volume reducing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Waste plastic material volume reduction apparatus main body 2 Processing container 3, 3a, 3b, 3c Pressurizing part 4 Pressurizing actuator 5 O-ring elastic body 6 Opening / closing lid 7 Blower 8 Heating part 9 First temperature sensor 10 Hot air outlet 11 Hot air Circulation path 12 Discharge path 12a Discharge port 13 Pressure regulating valve 14 Oxidation unit 15 Oxidation catalyst 16 Catalyst heating unit 17 Second temperature sensor 18 Side discharge port 19 Gas flow path 20 Processing gas exhaust port 21 Air pump 22 Heat resistant container 23 Air intake port 24 Control part 25a, 25b, 25c Piston 27 Exhaust fan 28 Waste plastic material 29a, 29b, 29c Sliding member 30 Dish member

Claims (6)

[Claims] A processing container provided with an opening / closing lid and capable of softening waste plastic material therein; a pressurizing unit provided at a bottom side of the processing container to pressurize and reduce the volume of the softened waste plastic material; A hot air circulation path communicating with the processing container and circulating a high-temperature gas for softening waste plastic material, and a discharge path communicating with the hot air circulation path and discharging a part of the high-temperature gas circulating through the hot air circulation path, A heating unit for heating the gas and the blower provided in the hot air circulation path,
A waste plastic material volume reducing device, wherein a piston that reciprocates in the processing container is provided in the pressurizing unit, and a sliding member is provided on a side surface of the piston. 2. A waste plastic material reducing device according to claim 1, wherein a dish-shaped member having a tapered outer periphery is provided on an upper part of said piston. 3. The waste plastic material reducing apparatus according to claim 1, wherein the sliding members are arranged at equal intervals in a circumferential direction on a side surface of the piston. 4. A waste plastic material reducing device according to claim 1, wherein said sliding member is formed of a deformable spring-like member. 5. The waste plastic material reducing device according to claim 1, wherein said sliding member is constituted by a spherical member rotatable between said processing container and said piston. . 6. An apparatus according to claim 1, wherein said sliding member is coated with a low friction member.