JPH0911295A - Cylinder unit for injection molding machine - Google Patents

Abstract

PURPOSE: To stabilize the injecting amount by rapidly and effectively closing a backflow preventing ring. CONSTITUTION: The spacer 28 fixed between a screw body 27 and a screw head 29 is formed of a magnet. At the time of metering, the resin pressure overcomes the force for drawing a backflow preventing ring 41 of the spacer 29, and the spacer 28 is separated from the ring 41. Resin flows to the end side in a cylinder body 21 through the gap 44 between both. At the time of injecting, when the screw 26 is advanced, the ring 41 is collided with the spacer 28 by the negative pressure at the rear side in the body 21 and the magnetic force of the spacer 28. Thus, the backflow of the resin is prevented. Accordingly since the spacer 28 is formed of the magnet, the ring 41 is rapidly and effectively closed when the metering is transferred to the injection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylinder device of an injection molding machine for measuring a molding material and injecting it into a mold, and more particularly to a structure for preventing backflow of the molding material.

[0002]

2. Description of the Related Art FIGS. 4 and 5 show the tip of a heating cylinder device of an in-line screw type injection molding machine. In the figure, 1 is a cylinder body and 2 is a screw. This screw 2 is a screw body 3
The screw head 4 is fixed to the tip of the screw main body 3 and the screw head 4
A spacer 5 is sandwiched between and fixed. Further, a backflow prevention ring 7 is installed on the outer peripheral side of the screw head 4 so as to hold a gap 6 and to be movable in a predetermined range in the axial direction. The backflow prevention ring 7 is slidably fitted to the inner circumference of the cylinder body 1. Further, in the conventional cylinder device, the spacer 5 and the backflow prevention ring 7
All were made of steel with a weak coercive force.

At the time of molding, in an injection molding machine, a predetermined amount of a molding material, that is, a thermoplastic resin, is plasticized and stored at the tip end side in the cylinder body 1, and a metering step is accumulated at the tip end side in the cylinder body 1. And an injection step of injecting the thermoplastic resin into the mold.

In the measuring step, the thermoplastic resin supplied into the cylinder body 1 is melted and plasticized by external heating and kneading by rotation of the screw 2. With this plasticization, the resin is sent forward (to the left in the drawing) by the rotation of the screw 2. At this time, since resin pressure is applied to the backflow prevention ring 7 from the rear, the backflow prevention ring 7 advances relative to the screw head 4 as shown in FIG. A gap 8 is formed between the end surface 5 and the end surface 5. The resin passes from the space 9 on the outer peripheral side of the screw body 3 in the cylinder body 1 through the gap 8 between the backflow prevention ring 7 and the spacer 5 and the gap 6 between the backflow prevention ring 7 and the screw head 4. , Is sent to the space 10 in front of the screw 2 in the cylinder body 1. Along with that, the screw 2 retracts due to the resin pressure. In addition,
Even during the measuring process, an appropriate back pressure is applied to the screw 2 by a hydraulic cylinder (not shown) or the like.

When the measuring process is completed, the injection process is started.
In this injection step, the screw 2 is moved forward by driving the hydraulic cylinder or the like, and the resin in the space 10 on the front side in the cylinder body 1 is injected from the nozzle 11 at the tip of the cylinder body 1. At this time, the cylinder body 1
By making the space 9 on the rear side of the inside negative pressure compared to the space 10 on the front side, the backflow prevention ring 7 is retracted relative to the screw head 4 as shown in FIG. The end surface of the prevention ring 7 and the end surface of the spacer 5 abut.
As a result, the space 9 on the rear side and the space 10 on the front side in the cylinder body 1 are blocked from each other, and the resin in the space 10 on the front side is prevented from flowing back to the space 9 on the rear side. .

[0006]

However, in the cylinder device of the conventional injection molding machine, when the process shifts from the measuring process to the injection process, the backflow prevention ring 7 is retracted with respect to the screw head 4 only by the resin pressure. Therefore, this backward movement tends to be delayed. If the backward movement of the backflow prevention ring 7 is delayed, in the initial stage of the injection process, through the gap 8 that is not completely closed between the backflow prevention ring 7 and the spacer 5, the inside of the space 10 on the front side in the cylinder body 1 will be described. Resin flows back into the space 9 on the rear side,
There is a problem that the injection amount becomes unstable. If the injection quantity becomes unstable, molding failure will occur.

The present invention is intended to solve such a problem, and when switching from the measuring process to the injection process,
An object of the present invention is to provide a cylinder device of an injection molding machine in which a backflow prevention ring can be promptly and reliably closed to stabilize the injection amount.

[0008]

In order to achieve the above object, the present invention provides a cylinder main body having a nozzle at its tip, and a cylinder main body rotatably and axially movable. The screw is housed in a screw body, a screw body, a screw head fixed to the tip of the screw body, a spacer fixed between the screw body and the screw head, and an outer peripheral side of the screw head. And a backflow prevention ring slidably fitted in the inner circumference of the cylinder body while holding a gap between them, and the end surface of the backflow prevention ring and the end surface of the spacer. By abutting, the space on the outer peripheral side of the screw body and the space in front of the screw in the cylinder body In the cylinder device of the injection molding machine, wherein the backflow prevention ring and the spacer are separated from each other by separating the end surface of the backflow prevention ring and the end surface of the spacer, the backflow prevention ring is made of a magnetic material, and the spacer Is composed of a magnet.

According to a second aspect of the invention, in the cylinder device of the injection molding machine according to the first aspect of the invention, the spacer is
It consists of Alnico.

[0010]

In the cylinder device of the injection molding machine according to the first aspect of the invention, at the time of measurement, the molding material is sent to the tip side, that is, the front side in the cylinder body by the rotation of the screw, and the screw moves backward. At this time, due to the pressure applied by the molding material to the backflow prevention ring, the backflow prevention ring moves forward with respect to the screw head against the force of the spacer made of a magnet pulling the backflow prevention ring made of a magnetic material, and the backflow prevention ring moves. The end face separates from the end face of the spacer. And, the gap between the end faces of these backflow prevention ring and spacer,
The molding material is sent from the space on the outer peripheral side of the screw body in the cylinder body to the space in front of the screw through the gap between the backflow prevention ring and the screw head. At the time of injection after the measurement, the screw advances, so that the molding material in the space in the cylinder body in front of the screw is injected from the nozzle. When switching from metering to injection, the space on the outer peripheral side of the screw body becomes negative pressure compared to the space in front of the screw in the cylinder body, causing the backflow prevention ring to retract with respect to the screw head, causing backflow. The end face of the prevention ring hits the end face of the spacer to block the space in front of the screw in the cylinder body from the space on the outer periphery of the screw body, but the spacer made of a magnet prevents backflow. By attracting the ring, the backflow prevention ring hits the spacer quickly and reliably. This reliably prevents the molding material from flowing backward from the space in front of the screw in the cylinder body to the space on the outer peripheral side of the screw body during injection.

Further, in the cylinder device of the injection molding machine according to the second aspect of the present invention, Alnico is used as the material of the spacer made of a magnet because heat resistance and an appropriate magnetic force can be obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a cylinder device of an injection molding machine according to the present invention will be described below with reference to FIGS. The cylinder device of the present embodiment is a heating cylinder device of an inline screw type injection molding machine used for injection molding of thermoplastic resin. Reference numeral 21 is a cylinder body having a substantially cylindrical shape. A heater 22 for heating is provided on the outer periphery of the cylinder body 21, and a nozzle 23 connected to a molding die is provided at a tip portion (left portion in the drawing). It is provided in. Then, in the cylinder body 21, the screw 26
Is rotatably housed and movably in the axial direction (left-right direction in the drawing). Although not shown, the screw 26 is rotationally driven by rotational driving means such as a motor and is axially driven by pressurizing driving means such as a hydraulic cylinder.

The screw 26 is the screw body.
A spacer 28 and a screw head 29 are fixed to the tip of 27. The screw head 29 is tapered on the tip side and has a plurality of recessed grooves 31 penetrating in the axial direction in the outer peripheral portion. Further, a small diameter portion 33 is formed at the rear portion of the screw head 29 (the right portion in the drawing) via a rearward facing step surface 32. A threaded portion 35 is formed so as to project through the 34. Then, the screw portion 35 penetrates through the substantially cylindrical spacer 28,
It is screwed into a screw hole 36 formed at the tip of 27. As a result, the spacer 28 is sandwiched and fixed between the tip surface of the screw body 27 and the step surface 34 of the screw head 29, and the screw head 29 is fixed to the screw body 27. The spacer 28 has a substantially cylindrical shape as described above, but its outer diameter is smaller than the inner diameter of the cylinder body 21.

On the outer peripheral side of the screw head 29, a backflow prevention ring 41 having a substantially cylindrical shape is incorporated so as to be movable within a predetermined range in the front-rear direction which is the axial direction. A plurality of convex portions 42 formed forwardly on the tip surface of the backflow prevention ring 41 are slidably engaged with the rear portions of the concave grooves 31 of the screw head 29, respectively. The backflow prevention ring 41 is prevented from rotating. Further, the backflow prevention ring 41 defines a forward limit with respect to the screw head 29 by hitting the step surface 32 of the front end face thereof, and a backward limit of contact with the front end face of the spacer 28 by the rear end face. It has become so. A gap 43 is formed between the inner circumference of the backflow prevention ring 41 and the outer circumference of the screw head 29, including the convex portion 42 and the concave groove 31. On the other hand, the backflow prevention ring 41
The outer diameter of is substantially equal to the inner diameter of the cylinder body 21, and the backflow prevention ring 41 is slidably fitted on the inner circumference of the cylinder body 21.

The spacer 28 is made of a heat-resistant permanent magnet, and the material thereof is Alnico which is an aluminum-nickel-cobalt-iron alloy. On the other hand, the backflow prevention ring 41 is made of a magnetic material such as machine tool steel. The magnetic force of the spacer 28 is
The backflow prevention ring 41 is set to such a degree that the opening / closing operation described later can be smoothly performed by the pressure of the resin.

Next, the operation of the above configuration will be described. At the time of molding, in the injection molding machine, the cylinder body is made by plasticizing a predetermined amount of molding material, thermoplastic resin.
Weighing process to collect on the tip side in 21 and this cylinder body
An injection step of injecting the thermoplastic resin accumulated on the front end side in 21 into the mold is performed.

In the measuring step, the thermoplastic resin supplied into the cylinder body 21 is melted and plasticized by heating by the heater 22 and kneading by rotation of the screw 26. With this plasticization, the resin is sent forward by the rotation of the screw 26. At this time, the resin pressure is applied to the backflow prevention ring 41 from the rear side, and this resin pressure exceeds the force of the spacer 28 made of a magnet to pull the backflow prevention ring 41. Therefore, as shown in FIG. The prevention ring 41 advances relative to the screw head 29,
The back end face of the backflow prevention ring 41 is separated from the front end face of the spacer 28, and a gap 44 is formed therebetween. A space portion (rear space portion) 46 on the outer peripheral side of the screw body 27 in the cylinder body 21 communicates with a space portion (front space portion) 47 in front of the screw 26 through the gap 44. Then, as shown by the arrow in FIG. 1, the resin has a gap between the backflow preventing ring 41 and the spacer 28 from the space 46 on the rear side.
It is sent to the space 47 on the front side through 44 and the gap 43 between the backflow prevention ring 41 and the screw head 29. Along with that, the screw 26 retracts due to the resin pressure. Even during the weighing process, the screw 26 is driven by the pressure driving means.
A proper back pressure is applied to the front.

When the measuring process is completed, the injection process is started.
In this injection step, the screw 26 is moved forward by the driving of the pressure driving means, and the resin in the space 47 on the front side in the cylinder body 21 is injected from the nozzle 23 into the mold. At the time of shifting from the measuring process to the injection process, the space 46 on the rear side in the cylinder body 21 has a negative pressure compared to the space 47 on the front side, so that the backflow prevention ring 41 is screwed as shown in FIG. The rear end surface of the backflow prevention ring 41 and the front end surface of the spacer 28 come into contact with each other by retreating relative to the head 29. As a result, the space 46 on the rear side and the space 47 on the front side in the cylinder body 21 are blocked from each other, and the resin in the space 46 on the front side is prevented from flowing back to the space 47 on the rear side. . Moreover,
As described above, if the space 46 on the rear side in the cylinder body 21 is negatively pressured by shifting from the measuring process to the injection process, the spacer 28 made of a magnet attracts the backflow preventing ring 41 made of a magnetic material to cause this backflow. The prevention ring 41 hits the spacer 28 quickly and surely, and even after that, this state is surely maintained. This surely prevents the backflow of the resin during the injection process.

As described above, according to the configuration of the above-described embodiment, the spacer 28 is made of a magnet, so that the backflow prevention ring 41 can be promptly and reliably closed at the time of shifting from the measuring step to the injecting step. Therefore, the injection amount is stabilized and molding defects can be prevented.

Further, since Alnico is used as the material of the magnet forming the spacer 28, the heat resistance of the spacer 28 can be sufficiently ensured. That is, the molten thermoplastic resin can sufficiently withstand the heat of about several hundreds of degrees Celsius. At the same time, an appropriate magnetic force can be obtained, and smooth operation of the backflow prevention ring 41 can be ensured. The magnetic force should be strong so that the backflow prevention ring 41 can be quickly and surely applied to the spacer 28 during the injection process, but it is strong enough not to separate the backflow prevention ring 41 from the spacer 28 by the resin pressure during the pressure holding process. Must not be A material other than Alnico can be used as the material of the magnet that forms the spacer 28 as long as it is a heat-resistant material that can obtain a magnetic force that satisfies these conditions.

Further, it is conceivable to use a magnet for the backflow prevention ring. However, if the backflow prevention ring is a magnet, the backflow prevention ring is attached to the screw head or the cylinder body made of a magnetic material, so that the backflow prevention ring is smooth. Movement may be disturbed. Therefore, it is preferable to use the spacer 28 fixed between the screw body 27 and the screw head 29 as a magnet as in the above embodiment.

Besides, the present invention can be variously modified. For example, although the thermoplastic resin is taken as an example of the molding material in the above-mentioned embodiments, the present invention can be applied to the injection molding of a thermosetting resin or another molding material.

[0023]

According to the invention of claim 1, the end surface of the backflow prevention ring movably incorporated on the outer peripheral side of the cylinder head and the end surface of the spacer fixed to the tip of the cylinder body are brought into contact with each other. , Blocking the space on the outer peripheral side of the screw body and the space in front of the screw in the cylinder body, and by separating the end surface of the backflow prevention ring and the end surface of the spacer, the both space portions are communicated with each other. In the cylinder device of the injection molding machine, the backflow prevention ring is made of a magnetic material and the spacer is made of a magnet. As a result, the injection quantity can be stabilized, and therefore molding defects can be prevented.

Further, according to the second aspect of the present invention, since the spacer is made of alnico, it is possible to ensure sufficient heat resistance of the spacer and to obtain a proper magnetic force, so that the smooth operation of the backflow prevention ring is ensured. it can.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a cylinder device of an injection molding machine of the present invention, showing a time of weighing.

FIG. 2 is a sectional view of the same as above, showing the state during injection.

FIG. 3 is an exploded perspective view of the same.

FIG. 4 is a cross-sectional view showing an example of a cylinder device of a conventional injection molding machine, showing a measuring time.

FIG. 5 is a cross-sectional view of the same as above, showing at the time of injection.

[Explanation of symbols]

21 Cylinder body 23 Nozzle 26 Screw 27 Screw body 28 Spacer 29 Screw head 41 Backflow prevention ring 43 Gap between the backflow prevention ring and screw head 46 Space in the cylinder body on the outer peripheral side of the screw body 47 Than the screw in the cylinder body Space in front

Claims (2)

[Claims] 1. A cylinder body having a nozzle at its tip, and a screw housed in the cylinder body so as to be rotatable and axially movable. The screw includes a screw body and the screw body. A screw head fixed to the tip of the screw head, a spacer fixed between the screw body and the screw head, and is installed movably in the axial direction while maintaining a gap on the outer peripheral side of the screw head and the cylinder body. It has a backflow prevention ring slidably fitted to the inner circumference, and by abutting the end surface of this backflow prevention ring and the end surface of the spacer, the space on the outer peripheral side of the screw body in the cylinder body and the screw The front end of the backflow prevention ring and the end of the spacer In a cylinder device of an injection molding machine that separates the two surfaces from each other by separating them from each other, the backflow prevention ring is made of a magnetic material, and the spacer is made of a magnet. Cylinder device of molding machine. 2. The cylinder device of an injection molding machine according to claim 1, wherein the spacer is made of alnico.