JPS5821708Y2 - Screw head with backflow prevention valve - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a screw head with a check valve for an injection molding machine.

In an injection molding machine, a screw head with a backflow prevention valve is used to prevent backflow when the molten resin metered and accumulated at the tip of the cylinder is injected and filled into the mold under high pressure by the screw. This is a very important part in order to obtain a stable molded product while keeping it to a minimum.

However, although there are some differences depending on the resin used, screw heads are generally manufactured at high temperatures of 200 to 300℃ and 1000℃.
It is used under extremely harsh environments and conditions, such as operating at high pressures of ~2000 kg/cm2 and without lubrication.

Therefore, a major problem is that the sliding parts wear out.

In particular, glass fiber-reinforced plastics, flame-retardant plastics, and the like have come into widespread use recently, and wear has become an even bigger problem.

Furthermore, corrosion caused by flame-retardant plastics is added to this wear, causing important parts such as screw heads, rings, and barrels to become unusable within a short period of time.

The present invention aims to solve the above-mentioned problems. First, a conventional screw head with a check valve will be explained based on FIGS. 1 to 4 of the accompanying drawings.

In order to prevent backflow during injection, it is necessary to provide a check valve at the front of the screw.

Various types of screw heads with check valves are known, but they can basically be represented by the four types shown in FIGS. 1 to 4.

Based on the shape of the check valve, it can be divided into the backflow method shown in Figures 1.2 and 4, and the check ball method shown in Figure 3. The purpose is to allow the molten resin to freely flow forward during metering, and to separate the molten resin in front of the screw from the resin in the screw groove during the injection and pressure holding periods.

In the example shown in FIG. 1, a screw head 4 is fixed to the tip of a screw 2 in a barrel 1 via a pusher 3, and a ring 5 is arranged around the outer circumference of the screw head 4.

A plurality of straight or spiral flights 6 are provided at the tip of the screw head 4 to form a resin passage 7 and to come into contact with the front end surface of the ring 5.

The outer diameter of the ring 5 is such that it is difficult to cause backflow through the gap with the inner diameter of the barrel 1, but the inner diameter of the ring 5 is dimensioned to provide a sufficient clearance between the inner diameter of the screw head and the outer diameter of the screw head. Thereby, a resin passage 8 is formed.

Further, the total length of the ring 5 is shorter than the distance between the front end of the pusher 3 and the rear end of the flight 6 by a predetermined length,
The ring 5 can be moved in the axial direction by that length.

This screw head works as follows.

The material plasticized and melted by the screw 2 is transferred to the ring 5
A resin passage 9 is formed between the presser metal 3 and the ring 5 by pushing forward, a resin passage 8 is formed between the inner diameter part of the ring 5 and the outer diameter part of the screw head 4, and the screw head 4
The resin passes through the resin passage 7 at the tip of the screw head 4 and is measured and accumulated at the tip of the screw head 4.

Next, the ring 5 is pushed back by the injection pressure generated by the forward movement of the screw 2, contacts the pusher 3, and closes the resin passage 9 to prevent backflow.

In the example shown in FIG. 2 (the barrel is not shown in FIGS. 2 to 5), a groove is cut out in the front end of the ring 10 to form the resin passage 11, and the front end of the screw head 12 is It has a conical enlarged diameter portion 13.

Other points are similar to the example shown in FIG. That is,
The only difference between the example in FIG. 1 and the example in FIG. 2 is whether the resin passages 7, 11 are provided on the screw head side or on the ring side, and the rings 5, 10 are not connected to the screw head. Basically, they are the same thing.

Therefore, since the operation is also the same as in the example shown in FIG. 1, the explanation will be omitted.

The advantage of the screw head of the type shown in FIGS. 1 and 2 is that since the rings 5 and 10 hardly rotate, there is no wear on the inner diameter of the barrel or the outer diameter of the rings. The gap between the two can be reduced, and the injection efficiency can be increased.

On the contrary, the disadvantage of this type of screw head is that it is necessary to provide a resin passage on one of the contact surfaces between the screw head 4, 12 and the rings 5, 10, so the contact area is reduced and The screw head 4, 1 rotates to
2 and the rings 5 and 10, which hardly rotate, come into contact under high surface pressure.

Therefore, the side where the resin passage is provided rapidly wears out.

That is, in the example shown in FIG. 1, the flight portion 6 of the screw head 4 wears out, and eventually the ring 5 falls off to the tip side of the screw head 4, resulting in an accident.

Further, on the side shown in FIG. 2, the tip of the ring 10 is severely worn, and the resin passage 11 disappears within a short period of time, making it impossible to plasticize.

In the example shown in FIG. 3, a ball 18 is arranged in a chamber 17 that communicates the screw side passage 15 and the tip side passage 16 in the screw head 14.

This allows the resin to flow from passage 15 to passage 16, but prevents its reverse flow.

In the example shown in FIG. 4, the enlarged diameter portion 20 of the screw head 19
A plurality of grooves 21 are provided on the outer periphery of the ring 22, and a plurality of pawls 23 that engage with the grooves 21 are provided at the front end of the ring 22.

The gap between the groove 21 and the pawl 23 becomes a resin passage.

The effect of preventing backflow is similar to the example shown in Figs. 1 and 2, but the major difference is that the ring 22 rotates together with the screw head 19, and the outer diameter of the ring and the inner diameter of the barrel are separated. It means moving.

The advantages and disadvantages of the screw head shown in FIGS. 3 and 4 are completely opposite to the advantages and disadvantages of the screw head shown in FIGS. 1 and 2.

That is, in the example of FIG. 3, there is no ring and the part corresponding to the ring is integral with the screw head, and in the example of FIG. 4, the ring 22 rotates together with the screw head 19, so the first and second In the case of the example shown in the figure, the wear of the contact surface between the screw head and the ring, which was a problem, is not a problem at all.

However, in the example of FIG. 3, the wear between the inner diameter part of the barrel and the outer diameter part of the screw head 14 similarly
In the illustrated example, wear between the inner diameter of the barrel and the outer diameter of the ring 22 becomes a problem.

When this wear increases, backflow becomes severe and injection becomes impossible.

As described above, in the conventional device, when the ring is not connected to the screw head as shown in Figs. 1 and 2, wear of the contact surface between the screw head and the ring becomes a problem.
As shown in FIGS. 3 and 4, when the ring or the ring equivalent rotates together with the screw head, wear of the contact surface between the ring and the inner diameter of the barrel becomes a problem.

In order to deal with this problem, a method of overlaying or thermal spraying a wear-resistant material on the sliding parts has recently been adopted, which can extend the service life by two to three times.

However, since the problem has not been fundamentally solved, it is ultimately impossible to prevent similar problems from occurring.

Moreover, this method is not only expensive and time consuming, but also unstable in quality.

Therefore, the object of the present invention is to provide a screw head with a check valve that eliminates the above-mentioned drawbacks of conventional screw heads.

Hereinafter, the present invention will be described in the fifth and sixth figures of the attached drawings showing the embodiments thereof.
This will be explained based on the diagram.

Diameter d.

A screw head 26 having a main body portion 24 and a collar portion 25 having a diameter d2 is fixed to the tip of the screw 2 via a pusher 3.

A ring 27 having an outer diameter d3 and an inner diameter d1 is arranged between the collar-shaped portion 25 and the pusher 3, but its total length is shorter than the distance between the collar-shaped portion 25 and the pusher 3, so the difference is can be moved only in the axial direction.

Note that the diameter d1 is the diameter d.

The resin passage 28 is larger than the ring 27 and the main body portion 24 of the screw head 26, while the diameter d3 is large enough to prevent backflow from occurring through the gap between the ring 27 and the main body portion 24 of the screw head 26. The dimensions are as follows.

Further, the diameter d2 is slightly smaller than the diameter d3.

The optimum difference differs depending on the resin, but is usually 0.2~
It is about 1 mm.

A plurality of resin passage holes 29 are provided in the collar-shaped portion 25 of the screw head 26, and the resin passage holes 29 are annular resin passages 28 formed by the ring 27 and the main body portion 24 of the screw head 26. , that is, within the projected area of the resin passage 28 projected onto the collar portion 24 in the axial direction.

Next, the operation of this screw head will be explained.

The material plasticized and melted by the screw 2 is
A resin passage 30 is formed between this and the presser metal 3 by pushing the screw head 7 forward, a resin passage 28 is formed by the inner diameter of the ring 27 and the outer diameter of the screw head main body portion 24, and the screw head 26. brim-shaped part 25
The resin is measured and accumulated at the tip of the screw head 26 through a plurality of resin passage holes 29 provided in the screw head 26 .

Next, the ring 27 is pushed back backward by the injection pressure generated at the tip as the screw 2 moves forward, and the ring 27 is pushed back.
The resin passage 30 between the rear end of the resin member 7 and the presser metal 3 is closed to prevent backflow.

When feeding the material through the passages 30.28 and 29 to the tip of the screw head 26, the ring 27 is not connected to the screw head 26 and is free.
The ring hardly rotates, and the inner diameter part of the barrel and the outer diameter part of the ring do not move and wear out.

Therefore, the gap between the inner diameter part of the barrel and the outer diameter part of the ring is maintained as initially set, and stable molding work can be performed.

That is, the drawbacks of the conventional devices shown in FIGS. 3 and 4 are eliminated.

On the other hand, in this case, the front end surface of the ring 27 and the screw
The contact portion of the rad 26 with the collar-shaped portion 25 will move, but in the present invention, no resin passage is provided on the contact surface, and the entire surface is in effective contact. Compared to conventional products, it is possible to reduce the pressure to almost a fraction of that, and the occurrence of wear is largely prevented.

In addition, the outer diameter d2 of the collar-shaped portion 25 of the screw head 26
is slightly smaller than the outer diameter of the ring 27, so even when the screw head 26 rotates, it will not come into contact with the inner diameter of the barrel and cause wear.

Therefore, the drawbacks of the conventional devices shown in FIGS. 1 and 2 are eliminated.

As explained below, according to the present invention, a screw head with a check valve that combines only the advantages of conventional devices can be obtained by a simple configuration of the screw head and the ring.

As a result, wear on the sliding parts between the barrel inner diameter and the ring outer diameter and between the screw head and the ring can be significantly reduced, making it possible to perform stable molding operations over a long period of time. can.

[Brief explanation of the drawing]

1 to 4 are sectional views showing conventional screw heads, FIG. 5 is a sectional view of a screw head with a check valve according to the present invention, and FIG. 6 is a left side view of FIG. 5. 2...Screw, 3...Pushing metal, 24.
...Body part, 25...Brim-shaped part, 2
6...Screw head, 27...Nong, 28...Resin passage, 29...Resin passage hole.

Claims (1)

[Scope of utility model registration request] A flange-shaped portion 25 having a slightly smaller diameter than the ring 27 is provided at the tip of a screw head with a check valve of an injection molding machine, and a ring 27 is provided between the flange-shaped portion 25 and the presser metal 3 at the tip of the screw 2. is disposed so as to be movable in the axial direction, and the collar portion 25 has a position on the extension line of the annular resin passage 28 formed by the outer diameter portion of the main body portion 24 of the screw head 26 and the inner diameter portion of the ring 27. A sukunoyu head characterized in that a plurality of resin passage holes 29 are provided in the sukunoyu head.