JP2000238097A - Sealing member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent incomplete sealing and to enhance durability by providing an outer shell member having a dynamic frictional coefficient of a steel of a specific value or below, and an inner member made of a material or a structure having elasticity and disposed in the outer shell member. SOLUTION: The sealing member is constituted of its outer shell member 22 of a material or a structure having excellent slidability, low dynamic coefficient and self-lubricity and constituted of its inside inner member 23 of a material or a structure having elasticity. As the material of the member 22, an ethylene tetrafluoride resin having 0.2 or below of the coefficient to a screw 2 of a steel material or a polyacetal resin or the like is used. The member 23 is obtained by bending a metal plate in a substantially U shaped section, and formed in a ring state as seen in plan. Here, the member 23 has a moderate elasticity, and the sealing member is broadened to an output. Thus, a problem of durability is eliminated, and sealability can be assured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealing member for reducing or evacuating the inside of a cylinder of a molding machine, or for filling the inside of a cylinder with an inert gas.

[0002]

2. Description of the Related Art Conventionally, in injection molding or extrusion molding of resin, metal, glass, or the like, (1) in order to avoid contact with air (oxygen) so that oxidation does not occur, or (2) in voids. In order to prevent air bubbles called from entering the molded product, that is, degas the gas (air, moisture, residual solvent, low molecular weight monomer, etc.) existing in the material or in the gap between the materials. For this reason, it is known that the inside of a cylinder of a molding machine is decompressed or evacuated, or the cylinder is filled with an inert gas for such purposes.

For example, JP-A-2-252513, JP-A-6-190891, JP-A-8-579
No. 17 describes an apparatus for reducing or evacuating the inside of an injection cylinder.

Japanese Patent Application Laid-Open No. 7-9489 describes that the inside of an injection cylinder is made airtight and filled with an inert gas.

[0005]

However, in the above-mentioned conventional example, although there is a description that the gap between the screw of the injection cylinder and the cylinder body is sealed by a seal member, there is no description about the material and structure thereof.

In general, it is conceivable to use a sealing member such as an O-ring. However, for example, a screw in an injection cylinder moves in a complicated manner such as a forward motion at the time of injection and a retreating motion while rotating at the time of metering. Therefore, there is a problem of durability of the O-ring seal.

As a countermeasure against the durability problem, it is conceivable to use a sealing member made of a self-lubricating material such as ethylene tetrafluoride (Teflon). Then, 0.2m in the radial direction
The shaft runout of about m occurs, and the above-mentioned ethylene tetrafluoride (Teflon) has poor elasticity, so it cannot follow the shaft runout, the seal becomes incomplete, and air enters the injection cylinder. There was a problem that would.

Therefore, as described in Japanese Patent Application Laid-Open Nos. Hei 4-238011 and Hei 7-155917, there is a proposal to make the whole rear of the injection cylinder an airtight chamber that is cut off from the outside air. However, since there is practically no space near the rear end of the injection cylinder of the injection molding machine, there are drawbacks such as difficulty in mounting and an increase in the size of the apparatus.

Accordingly, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a sealing member which can prevent incomplete sealing and has high durability.

Another object of the present invention is to provide a seal member which can be attached to a rear end portion of a cylinder of an ordinary molding machine without increasing a portion to be sealed.

[0011]

Means for Solving the Problems The above-mentioned problems are solved,
In order to achieve the object, the seal member according to the present invention includes:
A seal member for maintaining airtightness in an injection cylinder of an injection molding machine, wherein an outer shell member having a coefficient of kinetic friction against steel of 0.2 or less and an outer shell member are arranged inside the outer shell member to improve elasticity. And an internal member made of a material or a structure having the same.

Further, in the seal member according to the present invention, the material of the outer shell member is an ethylene tetrafluoride resin.

Further, in the seal member according to the present invention, the material of the outer shell member is a polyacetal resin.

Further, in the seal member according to the present invention, the material of the internal member is metal.

Further, in the seal member according to the present invention, the internal member is formed to have a substantially U-shaped cross section.

Further, in the seal member according to the present invention, the internal member is formed in a coil spring shape.

Further, in the seal member according to the present invention, the material of the internal member is rubber.

Further, in the seal member according to the present invention, the outer shell member is formed to have a substantially U-shaped cross section.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to injection molding of a thermoplastic resin will be described below in detail with reference to the accompanying drawings.

FIG. 1 is an overall schematic view of an injection cylinder of an injection molding machine to which a seal member according to one embodiment of the present invention is attached.

In FIG. 1, 1 is an injection cylinder, 2 is a screw, 3 is a band heater, and 4 is a nozzle. 5
Is an air vent hole for reducing the pressure or vacuum in the injection cylinder, or an inert gas supply hole for filling the inside of the injection cylinder with an inert gas.

Reference numeral 6 is a hopper, 7 is a rotary shutter, and 8 is a sensor for detecting the storage state of material pellets.

Reference numeral 21 denotes a seal member for sealing a gap between the screw 2 and the injection cylinder 1, and reference numeral 20 denotes a fixing member for fixing the seal member.

Material pellets 9 dried in hopper 6
Is melted by heat from the band heater 3 in the injection cylinder 1, kneaded and measured by the screw 2, and then injected from the nozzle 4 into a mold (not shown). The sensor 8 detects that the material pellet 9 on the screw 2 has been reduced.
Sends a signal to the rotary shutter 7
Is rotated to drop the material pellets 9 in the grooves in the rotary shutter 7.

Here, when the material pellet 9 is melted,
If air (oxygen) exists in or around the material pellets 9, an oxidation problem occurs. Alternatively, air entrainment may occur during weighing. Also,
If there is a gas component (air, moisture, residual solvent, low molecular weight monomer, etc.) in the material pellets, there also arises a problem that bubbles called voids are mixed into the molded product. Therefore, measures are taken to reduce or reduce the pressure in the injection cylinder 1 of the injection molding machine.

At this time, a portion from the rotary shutter 7 to the inside of the injection cylinder 1 is depressurized or evacuated by a vacuum pump (not shown) connected to the air vent hole 5.

If the problem of voids can be counteracted by the conditions of back pressure at the time of measurement and the shape of the screw, only the problem of oxidation of the material is caused. This problem is caused by filling the injection cylinder with an inert gas. It is solved by the technique of keeping. At this time, the part from the rotary shutter 7 to the inside of the injection cylinder 1 is filled with the inert gas by the inert gas supply means connected to the inert gas supply hole 5.

Here, nitrogen gas is generally used as the inert gas.

Since the nozzle 4 side of the injection cylinder 1 is filled with the molten material, air does not enter from the nozzle 4. Further, since the rotary shutter 7 is provided on the hopper 6 side, air does not enter from here. Therefore, there is a possibility that air may enter in the gap between the injection cylinder 1 and the screw 2 behind the injection cylinder 1. The seal member 21 is disposed at this portion to prevent air from entering.

Here, the seal structure on the hopper 6 side includes a slide shutter in addition to the rotary shutter 7 shown in FIG. 1. In particular, when the inside of the injection cylinder 1 is decompressed or evacuated, the slide When the shutter is opened, the atmosphere that has been decompressed or evacuated returns to atmospheric pressure.
It is better to take measures such as doubling.

FIG. 2 is a detailed view of the vicinity of the seal member 21 of FIG. 1, and FIG. 3 is a perspective view of the seal member 21. In FIG. 3, the outer shell member 22 constituting the outer surface is shown in a partially cut-off state so that the internal structure of the seal member 21 can be clearly understood.

The outer shell member 22 of the seal member 21
It is made of a self-lubricating material having excellent slidability and a low coefficient of dynamic friction, and the inner member 23 inside is made of an elastic material or structure.

The material of the outer shell member 22 needs to have a low dynamic friction coefficient with respect to the screw 2 (made of steel). When the durability of the seal material was examined for various seal materials having different dynamic friction coefficients with respect to steel, good results were obtained with materials having a dynamic friction coefficient of 0.2 or less.

Specifically, as shown in FIG. 5, polyacetal resin, polyethylene resin, ethylene tetrafluoride resin,
Nylon resin is preferred.

Of the above four kinds of seal materials, ethylene tetrafluoride resin or polyacetal resin is preferable in consideration of heat resistance, dimensional stability, abrasion resistance, chemical resistance and the like.

It is further desirable to add a filler to the above-mentioned materials in order to increase the abrasion resistance. Examples of the filler include carbon graphite, glass fiber, molybdenum disulfide, polyethylene, and polyester elastomer.

The ethylene tetrafluoride resin is usually called Teflon. Teflon TFE (ethylene tetrafluoride-propylene hexafluoride copolymer) or Teflon PFA (ethylene tetrafluoride-perfluoroalkyl vinyl ether) is used. The effects obtained with copolymers such as (copolymers) and other modified products are almost the same.

Next, as for the material of the inner member 23 of the seal member 21, the metal plate shown in FIGS. 2 and 3 is formed by bending a metal plate into a substantially U-shaped cross section and making it a ring shape in plan view. Things. Among metals, it is desirable to use SUS (stainless steel) in consideration of corrosion resistance.

FIG. 4 shows an example in which rubber is used as the inner member 24. In this case, a commercially available O-ring was used.

In either case, the inner member 23,
24 has a moderate elasticity, so that the sealing member 2
1 spreads outward, and the screw 2 can sufficiently follow a radial runout of about 0.2 mm when the screw 2 is advanced, rotated, or retracted, and the sealing property can be secured.

The outer shell member 22 of the seal member 21 is formed in a substantially U-shape having an opening 25 as shown in FIGS. 2 to 4, thereby further following the radial deflection. be able to. In this case, the portion to be sealed may be a substantially U-shaped shape, and may be a shape in which the other portion is combined with the substantially U-shaped shape.

When the internal member is made of metal, FIG.
In FIG. 3, the inner member 23 has a substantially U-shaped shape like the outer shell member 22, but may have a shape such as a coil spring.

Further, the internal member 23 may be any elastic member, and may be a member other than metal and rubber, or may be a composite of metal and rubber.

Here, in FIG. 2 and FIG.
Faces the right side, that is, the side opposite to the nozzle 4. This is convenient when the pressure in the injection cylinder 1 is reduced or evacuated. This is because the flat portion 26 on the opposite side of the opening 25 comes into close contact with the rear end face of the injection cylinder and seals the gap between the injection cylinder 1 and the fixed member 20. Since the injection cylinder 1 and the fixing member 20 do not move, an O-ring 28 is inserted between them as shown in FIGS.
It is better to prevent air from entering.

On the other hand, when the injection cylinder 1 is filled with the inert gas, the pressure inside the injection cylinder 1 is higher than the atmosphere outside the injection cylinder 1. Therefore, the opening 25 of the seal member 21 is opened by the positive pressure. It is more convenient that the opening 25 is directed to the left side, that is, the nozzle side, so as to bring about an effect of further improving the sealing performance.

2 and 4, the seal member 21 is arranged at the rear end face of the injection cylinder 1. However, a notch is formed in the screw 2, and the seal member 21 is mounted in the notch. There is also a method of sealing with the inner surface of the injection cylinder 1. However, in general, the surface roughness of the inner surface of the cylinder is coarser than the surface roughness of the screw surface, and from the viewpoint of the durability and sealing properties of the sealing member, as shown in FIGS. Therefore, it is desirable to dispose the seal member 21 outside the screw 2. In this case, the surface roughness of the screw surface is 2
μm (2S) or less (desirably 1.6 μm (1.6S)
It is preferable that the surface is hardened. As the hardening treatment, for example, in addition to heat treatment such as quenching, it is effective to apply hard chrome plating or coating such as TiN or TiCN.

By adopting the sealing structure as shown in FIGS. 1, 2 and 4, it is small and can be attached to a normal molding machine, thereby preventing the apparatus from becoming large.

In this embodiment, injection molding of a thermoplastic resin has been described. However, the present invention can be applied to a thermosetting resin, an extrusion molding, and a molding machine of metal, rubber, glass, or the like. is there.

The seal member 21 may be coated with a lubricant called vacuum grease. There is an advantage that durability is further improved by applying a lubricant.

A dust seal or the like is provided before and after the seal member 21, and abrasion powder of the seal member 21 or the screw 2 and a lubricant such as the grease attached to the surface of the seal member 21 enter the injection cylinder 1. When the gap between the injection cylinder 1 and the screw 2 or between the fixing member 20 and the screw 2 is wide, a gap may be reduced by inserting a backup ring or the like. It is informative.

[0051]

As described above, according to the present invention,
Even in the complicated movement of the screw in the cylinder, for example, the forward movement at the time of injection, or the backward movement while rotating at the time of weighing, there is no durability problem, and it occurs at the time of forward movement, rotation and backward movement of the screw. , 0.2 in the radial direction
It is possible to follow the shaft runout of about mm, and there is an effect that the seal does not become incomplete.

Further, by making the shape of the seal member a substantially U-shaped shape having an opening, it is possible to make the shape more resilient in terms of shape, and to prevent the screw shaft from oscillating in the radial direction. On the other hand, there is an effect that the sealing property is further improved.

Further, there is an effect that the portion to be sealed does not become large and can be mounted near the rear end of the cylinder of a normal molding machine.

[Brief description of the drawings]

FIG. 1 is an overall schematic view of an injection cylinder of an injection molding machine according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a part of a seal member of FIG. 1;

FIG. 3 is a perspective view of a seal member.

FIG. 4 is a view showing a modification of the seal member.

FIG. 5 is a diagram showing a coefficient of kinetic friction and durability of a material of an outer shell member against steel.

[Description of Signs] 1 Injection cylinder 2 Screw 9 Material pellet 20 Fixing member 21 Sealing member 22 Outer shell member 23, 24 Internal member 25 Opening

Claims (8)

[Claims] 1. A seal member for maintaining airtightness in an injection cylinder of an injection molding machine, wherein the outer shell member has a dynamic friction coefficient against steel of 0.2 or less, and is disposed inside the outer shell member. And an internal member made of a resilient material or structure. 2. The seal member according to claim 1, wherein the material of the outer shell member is an ethylene tetrafluoride resin. 3. The seal member according to claim 1, wherein a material of the outer shell member is a polyacetal resin. 4. The seal member according to claim 1, wherein a material of the internal member is metal. 5. The seal member according to claim 4, wherein the internal member is formed to have a substantially U-shaped cross section. 6. The seal member according to claim 4, wherein the inner member is formed in a coil spring shape. 7. The seal member according to claim 1, wherein a material of the inner member is rubber. 8. The seal member according to claim 1, wherein the outer shell member is formed to have a substantially U-shaped cross section.