JPH07156227A - Backflow preventive device for injection molding machine - Google Patents

Abstract

PURPOSE:To prevent the backflow in the injection dwelling process and minimize the unevenness of weight and dimension of a molded product by forming a second molten material flow path by means of a large diameter section on the front of a screw main body and a short cylindrical section of a rear end of backflow preventive ring and fitting the ring idly when the backflow preventive ring is moved back to shut off the second molten material flow path. CONSTITUTION:A backflow preventive ring 1 is pushed out by a molten material in the platicizing process, and a front end face 1b of the ring is brought into contact with a ring step face 4d of a screw head main body 4a to form a second molten material flow path C between the rear end of a short cylinder section 1c and the front end of a large diameter section 2c of a press bar 2. The molten material passes through between a valve seat 2a and a back facing valve 1a of the backflow preventive ring 1 by the arrangement, and flows from a first molten material flow path B into respective channels 4c between the front end face 1b and the ring step face 4d of the screw head main body 4a and the material is stored in a front chamber A. Then the screw main body 3 is moved forward in the injection process to backflow the molten material, and the backflow preventive ring 1 is moved backward, and the back facing valve 1a is stuck close with the valve seat 2a to shut off the first molten material flow path B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backflow prevention device for an injection molding machine, and more particularly, to minimizing the backflow rate of molten material injected into a mold during injection molding of an injection molding machine. Therefore, the present invention relates to a backflow prevention device that enables precision molding.

[0002]

2. Description of the Related Art A conventional backflow prevention device of this type is disclosed in, for example, Japanese Unexamined Patent Publication No. 50-142664. This backflow prevention ring is designed to measure the injection amount when the molten material such as resin with low viscosity is injected until the backflow prevention ring is pushed back and closes the gap with the valve seat. Has the function of preventing the inaccuracy. For this reason, an annular valve seat, a cylindrical pusher and a screw head body are sequentially provided at the tip of the screw, and a backflow prevention ring having an inner diameter larger than the outer diameter of the pusher is externally fitted to the pusher. In a backflow prevention device that forms a molten material flow path between the backflow prevention ring and the push metal, at least one of the outer surface and the inner surface between the outer surface of the push metal and the inner surface of the backflow prevention ring. A resistance portion having a protruding portion is provided on one side.

[0003]

However, in such a conventional backflow prevention device for an injection molding machine, the resistance portion protruding into the molten material flow path is provided between the inner surface of the backflow prevention ring and the pusher. However, since it has a structure in which a relatively small gap cannot be changed, the flow resistance to forward and reverse flows through this gap is the same, which promotes flow during metering and reverse flow during injection. It is difficult to be compatible with prevention. In addition, repeated use of the backflow prevention device causes wear on the protrusions, and the backflow rate gradually increases, resulting in a decrease in precision of the molded product.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional technical problems.
In the configuration of the invention, the contacted portion 2 is provided on the front side of the screw body 3.
a, a shaft portion 2b, and a screw head body 4a, and a backflow prevention ring 1 having an inner diameter larger than the outer diameter of the shaft portion 2b is externally fitted to the shaft portion 2b, and the backflow prevention ring 1 and the shaft portion 2
In the backflow prevention device of the injection molding machine, the first molten material flow path B is formed between the backflow prevention ring b and the backflow prevention ring 1 so that the contact portion 1a of the backflow prevention ring 1 contacts the contacted portion 2a to prevent the backward movement. At the same time, the large diameter portion 2c is formed on the front side of the screw body 3, and the short tubular portion 1c is formed at the rear end portion of the backflow prevention ring 1, so that the large diameter portion 2c and the short tubular portion 1c are When the backflow prevention ring 1 moves forward, the second molten material flow path C is formed at a predetermined distance in the central axis direction, and when the backflow prevention ring 1 moves backward, it loosely fits into the second molten material. This is a backflow prevention device for an injection molding machine, which is characterized by substantially blocking the flow path C.
In the configuration of the invention of claim 2, the contacted portion 2a on the screw body 3 side forms a conical surface, and the contact portion 1a of the backflow prevention ring 1
Forms a conical surface that matches the contacted portion 2a. The backflow prevention device for an injection molding machine according to claim 1, wherein

[0005]

Operation: During the plasticizing process, the screw body 3 rotates,
The screw body 3 while heating, melting and kneading the molten material
It is transferred by thrust to the front end of. The molten material around the screw body 3 is pushed out of the backflow prevention ring 1 to cause the short tube portion 1c.
A second molten material flow path C is formed between the rear end and the front end of the large diameter portion 2c on the screw body 3 side. Second molten material flow path C
Is shortly formed between the rear end of the short tubular portion 1c and the front end of the large diameter portion 2c, so that pressure drop is unlikely to occur. As a result, the molten material transferred in the screw body 3 has the second molten material flow path C and the contacted portion 2a and the contact portion 1 of the backflow prevention ring 1.
It flows into the first molten material flow path B through the annular flow path between a and a and gradually accumulates in the front chamber on the front side of the screw head 4. In such a plasticizing process, the screw body 3
Gradually recedes. When a predetermined amount of the molten material has accumulated in the front chamber, the rotation and the backward movement of the screw body 3 are stopped, and the plasticizing / metering step of the molten material is completed.

Next, in the injection process, the screw body 3
When is moved forward, the molten material accumulated in the front chamber is injected into the mold and tries to flow backward through the first molten material flow path B toward the rear part of the screw head 4. At this time, the pressure from the screw head body 4a side acts on the front end surface of the backflow prevention ring 1. As a result, the backflow prevention ring 1 moves backward, the rear end of the short tubular portion 1c is loosely fitted to the front end of the large diameter portion 2c, and the second molten material flow passage C is substantially cut off. In this way, when the short tubular portion 1c is loosely fitted into the large diameter portion 2c and the second molten material flow path C is substantially blocked, the contact portion 1a of the backflow prevention ring 1 is still in contact with the contacted portion 2a. Is not in contact with.

Thus, as compared with the state in which the second molten material flow path C is opened, a pressure difference before and after the backflow prevention ring 1 due to the forward movement of the screw body 3 becomes relatively large, and thereafter, The pressure increase in the front chamber due to the forward movement of the screw 3 can be quickly obtained with respect to the pressure on the screw body 3 side. As a result, the seating of the contact portion 1a of the backflow prevention ring 1 on the contacted portion 2a is promoted, and the backflow of the molten material is reliably prevented. Therefore, even when the molten material is a low-melting-point alloy, glass, or other material having a low viscosity, a large relative force for pushing back the backflow prevention ring 1 can be secured, and as a result, the backflow prevention ring 1 retracts quickly. Therefore, inaccurate weighing is prevented.

That is, the short cylinder portion 1c is provided so as to be fitted onto the large diameter portion 2c, and the rear end portion of the short cylinder portion 1c is slightly loosely fitted to the front end portion of the large diameter portion 2c at the beginning of the injection process. By substantially blocking the molten material flow path C by
The second molten material flow path C of the molten material is sharply narrowed in the initial stage of the loose fitting, and the pressure difference before and after the backflow prevention ring 1 is quickly obtained. Then, due to the rapid increase in this pressure difference, the time required until the contact between the contact portion 1a and the contacted portion 2a is shortened, and the contact portion 1a and the contacted portion 2a are strengthened. In close contact. As a result, the flow of the molten material from the front chamber toward the screw body 3 is blocked early and surely, and the inaccurate measurement of the molten material is well prevented.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 show an embodiment of the present invention.
In the drawing, reference numeral 5 indicates a heating cylinder, a nozzle (not shown) is attached to the front end (left end in the drawing) of the heating cylinder 5, and a heater for heating (not shown) is provided on the outer periphery of the heating cylinder 5. It is installed. Inside the heating cylinder 5, the screw main body 3 and the screw head 4 are incorporated so as to be movable back and forth and rotatable.
The screw head 4 has a rear end portion of the support portion 4b having a small diameter screwed to the front end portion of the screw body 3.

A push metal 2 is fitted on the outer periphery of the front portion of the support portion 4b of the screw head 4, and the push metal 2 is sandwiched between the annular step surface 4d of the screw head body 4a and the front end surface of the screw body 3. I'm wearing it. This screw head 4 and pusher 2
Thus, the screw head member 13 fixed to the screw body 3 is integrally formed. The outer peripheral edge of the rear end portion of the screw head body 4a is notched at predetermined intervals in the circumferential direction to form a groove portion 4c. The pusher 2 has a cylindrical shape, and a front side forms a cylindrical shaft portion 2b, and a conical surface-shaped abutted portion that gradually increases in diameter toward the rear is formed on the outer periphery of the rear end portion of the shaft portion 2b. A certain valve seat 2a is connected and formed, and is located at the rear end of the pusher 2 to form a large diameter portion 2c connected to the large diameter end of the valve seat 2a. Thus, on the front side of the screw body 3, the annular valve seat 2a, the shaft portion 2b, and the screw head body 4a are sequentially provided. The rear end portion of the pusher 2 is formed with a conical surface portion 2d that gradually reduces its diameter toward the rear and is connected to the front end portion of the screw body 3.

Further, the backflow prevention ring 1 having an inner diameter larger than the outer diameter of the shaft portion 2b of the push metal 2 is slidably fitted on the shaft portion 2b of the push metal 2 with respect to the inner peripheral surface of the heating cylinder 5. The first molten material flow path B is provided between the backflow prevention ring 1 and the shaft portion 2b.
Is formed. The backflow prevention ring 1 has a tubular shape, and has a front end face 1b, an annular recess 1d in which the outer periphery of the front end is cut out in an annular shape,
The rearward facing valve portion 1a, which is an abutting portion of the inner peripheral surface, and the short tubular portion 1c, which extends rearward from the outer peripheral portion and has a relatively large-diameter cylindrical inner surface, includes the front end surface 1b and the rearward facing valve portion 1a. The length in the central axis direction between the small-diameter end portion and the small-diameter end portion is shorter than that of the shaft portion 2b, and the movable portion can be moved back and forth in the heating cylinder 5 with respect to the pusher 2. The backward valve portion 1 a of the check ring 1 has a conical surface shape that fits the valve seat 2 a of the pusher 2. Also, the short tube portion 1
The inner peripheral surface of c can be fitted onto the large diameter portion 2c of the pusher 2.
Therefore, during the injection process, the backflow prevention ring 1 retracts in the direction of the central axis, and the short tubular portion 1c loosely fits in the large diameter portion 2c.
The molten material flow path C is substantially blocked, and subsequently the backward valve portion 1
The first molten material flow path B is blocked by the contact of a with the valve seat 2a.

During the measuring step, the backflow prevention ring 1 advances in the direction of the central axis as shown in FIG. 2, and the front end surface 1b of the backflow prevention ring 1 abuts on the annular step surface 4d of the screw head body 4a. The short cylinder portion 1c is the large diameter portion 2c of the pusher 2.
The second molten material flow passage C is opened, and the first molten material flow passage B is connected to the second molten material flow passage C by being separated by a predetermined distance in the central axis direction. With the front end surface 1b of the backflow prevention ring 1 in contact with the annular step surface 4d of the screw head body 4a, the first molten material flow path B passes through the groove portion 4c and the outer peripheral portion of the screw head body 4a, and then the screw head body 4a. Connect to the front chamber A on the front side of the. Here, the first molten material flow path B
The molten material flowing through the second molten material flow path C is a plastic having a particularly low melt viscosity and a melt index MI value of 30 or more, aluminum, magnesium, zinc,
It is a low-melting metal such as tin or lead bismuth or an alloy thereof, or a low-viscosity material such as low-melting glass.

Next, the operation of the above embodiment will be described. During the plasticizing step, the screw body 3 in the heating cylinder 5 is rotated by a rotating mechanism (not shown), and the molten material is heated, melted, and kneaded, and is transferred to the front end portion of the screw body 3 by thrust. As shown in FIG. 2, the molten material between the heating cylinder 5 and the screw body 3 pushes out the backflow prevention ring 1 so that the front end face 1b of the backflow prevention ring 1 has the screw head body 4a.
Abutting against the annular step surface 4d of the short cylinder portion 1c and the pusher 2
The second molten material flow path C is formed between the large diameter portion 2c and the front end of the large diameter portion 2c. That is, since the pressure P1 generated by the propulsive flow due to the rotation of the screw 3 is higher than the pressure P2 of the molten material in the front chamber A, the molten material is sent to the front chamber A while pushing the backflow prevention ring 1. However, since the second molten material flow path C is formed with a short flow path length between the rear end of the short tubular portion 1c and the front end of the large diameter portion 2c of the pusher 2, pressure drop is unlikely to occur.

As a result, the molten material transferred in the screw body 3 passes through the annular flow passage between the valve seat 2a and the backward valve portion 1a of the check ring 1 from the second molten material flow passage C to the first passage. 1 molten material flow path B, then flows into each groove portion 4c opened between the front end surface 1b of the backflow prevention ring 1 and the annular step surface 4d of the screw head body 4a, and the front chamber A on the front side of the screw head 4 It gradually accumulates inside. At that time, the first and second
The molten material that sequentially passes through the molten material flow paths C and B has excellent fluidity and therefore flows smoothly.

In such a plasticizing step, the screw main body 3 is forcibly retracted in accordance with the amount of the molten material in the front chamber A to maintain P1> P2. Thus, when a predetermined amount of molten material has accumulated in the front chamber A, the rotation and retreat movement of the screw main body 3 are stopped by operating the limit switch, etc., and the plasticizing and measuring process of the molten material is completed. To do. When the molten material is stored in the front chamber A by a predetermined amount, the pressure due to the propulsive flow is not generated and P1 = P
At 2, the flow of molten material stops.

Next, in the injection process, when the screw main body 3 is advanced by the action of a hydraulic cylinder or the like mounted on the rear part, the molten material accumulated in the front chamber A is injected from the nozzle into the mold. At the same time, it tries to backflow around the backflow prevention ring 1, mainly through the first molten material flow path B in the inner peripheral portion toward the rear part of the screw head 4.

In such a case, generally, the backflow prevention ring 1 is rapidly retracted under the pressure of the molten material, the backward valve portion 1a is brought into close contact with the valve seat 2a, and the first molten material flow passage B is blocked. , Backflow of molten material is prevented. However,
When the molten material is a low-melting-point alloy, glass, or other material having a low viscosity, the relative force for pushing back the backflow prevention ring 1 is small, and the backflow prevention ring 1 is delayed in retreat and the weighing tends to be inaccurate. .

Thus, when the molten material in the first molten material flow path B flows backward, the pressure P2 from the screw head body 4a side causes the outer periphery of the screw head body 4a and the respective groove portions 4c as shown in FIG. Front end surface 1b of the backflow prevention ring 1
And acts on the annular recess 1d. As a result, the backflow prevention ring 1 moves backward, the rear end of the short tubular portion 1c is loosely fitted to the front end of the large diameter portion 2c of the pusher 2, and the second molten material flow passage C is substantially cut off. In this way, when the short tubular portion 1c is loosely fitted in the large diameter portion 2c and the second molten material flow passage C is substantially blocked, the backward valve portion 1a of the check ring 1 still has the valve seat 2a.
Is not in contact with. Thus, as compared with the state in which the second molten material flow path C is opened, a large difference occurs between the pressures P2 and P1 before and after the backflow prevention ring 1 due to the forward movement of the screw body 3, and the screw thereafter. An increase in the pressure P2 in the front chamber A due to the forward movement of 3 is quickly obtained with respect to the pressure P1 on the screw body 3 side. As a result, seating of the backward valve portion 1a of the check ring 1 on the valve seat 2a is promoted,
As shown in FIG. 4, backflow of molten material is reliably prevented.

Pressure P2 before and after the backflow prevention ring 1
P1 is P1> P2 immediately before the end of plasticization, but becomes P1 <P2 when the screw 3 advances in the injection process. If it takes a long time to change from the P1 = P2 state to the P1 <P2 state, a large amount of molten material will flow backward. Low viscosity, melt index MI value of 30
In the case of a molten material such as plastic or metal that exceeds the above range, this time, that is, the time required for the backward valve portion 1a of the check ring 1 to adhere to the valve seat 2a tends to be long, and therefore, in general, , The reverse flow rate increases.

However, the short cylinder portion 1c is provided so as to be fitted onto the large diameter portion 2c of the pusher 2, and at the beginning of the injection process, the rear end portion of the short cylinder portion 1c has a large diameter portion 2c as shown in FIG.
If the molten material channel C is substantially blocked by slightly loosely fitting it to the front end of the second molten material channel C, the second molten material channel C sharply narrows at the beginning of the loose fitting, and the P1 <P2 state is You can get it quickly. Then, the pressure difference between P2 and P1 rapidly increases, so that the time required for the contact between the backward valve portion 1a and the valve seat 2a is shortened, and the backward valve portion 1a and the valve seat 2a are strongly adhered to each other. To do. As a result, the flow of the molten material from the front chamber A toward the screw main body 3 side is blocked early and surely, and the inaccurate measurement of the molten material is well prevented. In particular, low viscosity plastics, low melting point metals such as aluminium, magnesium, zinc, tin, lead bismuth or alloys thereof, low melting point glass, etc. can be properly prevented from backflow during injection molding, and stable precision molded products can be obtained. It becomes possible to mold it.

[0021]

As can be understood from the above description,
According to the backflow prevention device of the injection molding machine according to the present invention, when the molten material flows back through the molten material flow path in a state where the fluidity at the time of measurement is relatively large, the backflow with the large-diameter portion on the screw body side occurs. The short tube portion of the prevention ring is loosely fitted to rapidly reduce the flow passage area of the molten material flow passage, and it is possible to favorably prevent backflow of the molten material during the injection pressure holding step. As a result, it is possible to minimize the weight variation and the dimension variation of the molded product and perform the precision stable molding. In particular, the above effect is remarkable for injection molding of a low-viscosity material such as a plastic having a low melt viscosity and a melt index MI value of 30 or more, a low-melting metal or its alloy, a low-melting glass. In addition, by ensuring a long length of loose fitting between the large diameter part and the short tube part, wear due to repeated use of the backflow prevention device is reduced, and fluidity at the time of weighing is ensured while ensuring accuracy of the molded product. The decrease can be suppressed.

[Brief description of drawings]

FIG. 1 is a sectional view showing a backflow prevention device of an injection molding machine according to a first embodiment of the present invention.

FIG. 2 is an explanatory view of the same operation.

FIG. 3 is an explanatory view of the same operation.

FIG. 4 is a similar operation explanatory diagram.

[Explanation of Codes] 1: Backflow prevention ring, 1a: Rearward facing valve portion (contact portion), 1
b: front end face, 1c: short cylinder part, 2: push plate, 2a: valve seat,
2a: valve seat (contact portion), 2b: shaft portion, 2c: large diameter portion, 2
d: conical surface portion, 3: screw body, 4: screw head, 4a: screw head body, 4b: support portion, 4c:
Grooves, 4d: annular step surface, 5: heating cylinder, 13: screw head member, A: front chamber, B: first molten material channel, C: second molten material channel.

Claims (2)

[Claims] 1. A contacted portion (2a), a shaft portion (2b) and a screw head body (4) are provided on the front side of the screw body (3).
A backflow prevention ring (1) having a) and an inner diameter larger than the outer diameter of the shaft portion (2b) is externally fitted to the shaft portion (2b),
A first member is provided between the backflow prevention ring (1) and the shaft portion (2b).
The molten material flow path (B) is formed and the backflow prevention ring (1)
A backflow prevention device for an injection molding machine, in which a contact portion (1a) of the screw abuts against a contacted portion (2a) and a backward movement is prevented. Is formed, and the short tube portion (1
c) is formed, and the large diameter portion (2c) and the short tubular portion (1c) are formed.
When the backflow prevention ring (1) moves forward, when the backflow prevention ring (1) moves backward, it forms a second molten material flow path (C) with a predetermined distance in the central axis direction. A backflow prevention device for an injection molding machine, which is loosely fitted to substantially block the second molten material flow path (C). 2. A contacted portion (2) on the screw body (3) side
2. The injection molding machine according to claim 1, wherein a) forms a conical surface, and the contact portion (1a) of the backflow prevention ring (1) forms a conical surface that matches the contacted portion (2a). Backflow prevention device.