DE102006031172A1 - Process to manufacture extruded plastic product by combined translatory and rotary motion of helical press - Google Patents

Abstract

In a plastic injection molding process with a helical press, the press effects a combined translatory and rotary motion. The press has a back-flow prevention ring (3). A plastic mass is released into the press inlet chamber under rotary action (6) and is then forced by into the tool chamber by translatory action (5). During the translatory action (5) the helix also rotates (6) to prevent back-flow towards the inlet. The helical speed of rotation is set such that the pressure (9) on the back-flow prevention ring (3) at the inlet is greater than that (8) from the helix, as measured by pressure sensors on each side of the ring. The helix speed of rotation is deduced from a mathematical model, such that no speed components are present towards the helical channel.

Description

The The invention relates to a method for operating an injection process by means of a plasticizing and injection screw, wherein the plasticizing and Injection screw is translational and rotationally movable and a backflow stop comprising a locking ring, wherein plasticized plastic mass is conveyed by rotary motion in a screw anteroom, wherein from the antechamber by a translational movement of Screw the plasticized plastic mass into the cavity of a Promoted tool becomes.

At the Injection occurs because of the axial screw movement, that material in the screw channel relative to the screw towards feeder is moved or flows back. This leads especially with larger dosing paths for longer dosing times, because the material displaced during injection is at the beginning of dosing first promoted back to the front must become.

task The invention is to provide a method in which the dosing shortened can be.

The solution the object is in connection with the preamble of the claim 1 characterized in that during the translational movement additionally a rotational movement accomplished is, with the additional rotatory movement is carried out such that a plasticized moving Plastic compound in the screw flights in the direction of the filling opening of the Cylinder is prevented. A backflow of the material during the Injection thus does not occur.

Training is provided, adjust the screw speed so that the one acting on the locking ring Pressure on the side of the worm anteroom is always higher as the pressure on the locking ring on the side of the helix. Consequently will be the pressing prevents the Sperringes.

A further training is that the determination of the present pressures takes place by means of pressure transducer in the antechamber and the screw flights. The screw speed can be so when injecting a mathematical Model are regulated, so no speed component occurs in the direction of the screw channel.

In The drawings schematically illustrate the method of the invention. It shows

1 the course of the screw retraction speed over the axial screw path (prior art),

2 a section through a snail tip, and

3 the velocity components of the melt around the screw

1 shows the time course of the screw retraction speed during dosing, here you can see that at the beginning of dosing, the screw speed is lower or even a drop in speed is present.

To prevent backflow of the material during injection, the screw must also rotate in this process phase. The rotational speed is coupled with the axial velocity so that no pressure build-up in the screw flights can take place, but only the backward drag flow is compensated. A pressure build-up in the flights due to the rotation must be avoided in order not to press the locking ring of the backflow preventer. If the pressure during injection in the screw flights is higher than in the antechamber, the locking ring does not close, as in 2 shown, and it flows melt back into the screw flights. 2 shows an example of a screw 1 with a snail tip 2 a locking ring 3 and a stop ring 4 , The axial movement 5 and the rotational movement 6 are indicated by the directional arrows, the force vectors illustrate the pushing force 8th and the closing force 9 , Is the pushing force 8th greater than the closing force 9 creates a leakage current 7 ,

Analogously, this also applies to other reverse flow barrier types such as the central ball backflow lock. The Sperring 3 In order to fulfill the desired sealing function of the non-return valve, the so-called stop ring must 4 abut and be pressed against this.

During injection, the cylinder moves at the speed ν _{Zy, α} relative to the screw. This velocity can be decomposed into a component in the channel direction, ν _{Zy, z} , and into a component transverse to the channel direction, ν _{Zy, x} . This division will be in 3 clarified. Usually, the screw does not rotate during the injection, so that the component leads to a volume flow in the screw threads, as a result of which melt flows back. If now the backflow of the melt should be avoided, then the screw must additionally perform a rotational movement. The cylinder therefore moves relative to the screw now in addition to the velocity component ν _{Zy , u} . This component must be large _enough to give a resulting velocity ν _{Zy, res} is perpendicular to the screw bridge. The connection between the injection speed and the necessary peripheral screw speed during injection is therefore: ν Zy, u = ν Zy, α · tanφ where φ is the helix pitch angle. The relationship between the screw speed n and the screw peripheral speed is ν zy . u = D · π · n where D is the screw diameter. For the control of the screw speed as a function of the axial injection speed so a mathematical model is applicable.

At the Injecting the melt in the metering zone thereby only in a vortex flow moves However, there is no backflow of melt. For the Following dosing the screw is now completely with Melt filled and therefore can immediately build up a pressure.

By the snail rotation during Injection also turns the helical passages of the intake zone into one higher Proportion filled with granules. This is the subsequent Dosing also reduces the risk of air being in the worm anteroom promoted becomes.

1

slug

2

screw tip

3

locking ring

4

stop ring

5

Axial movement of the screw 1

6

Rotational movement of the screw 1

7

leakage current

8th

impression force

9

closing force

10

flighting

φ

Screw pitch angle

V _{zy, a}

axial Speed of the cylinder

V * _{zy, x} , V * _{zy, z}

speed with pure axial movement

V _{zy, u}

circumferential speed

V _{zy, res}

resulting speed

Claims (4)

Method for operating an injection process by means of a plasticizing and injection screw, wherein the plasticizing and injection screw is translationally and rotationally movable and a return flow barrier with a locking ring ( 3 ), wherein plasticized plastic mass by means of rotational movement ( 6 ) is conveyed into a worm anteroom, wherein from the worm antechamber by a translational movement ( 5 ) of the screw the plasticized plastic mass is conveyed into the cavity of a tool, characterized in that the screw ( 1 ) during the translational movement ( 5 ) additionally a rotational movement ( 6 ), wherein the additional rotational movement ( 6 ) is performed such that a displacement of plasticized plastic mass in the screw threads in the direction of the filling opening of the cylinder is prevented. A method according to claim 1, characterized in that the screw speed is adjusted so that the on the locking ring ( 3 ) acting pressure ( 9 ) on the side of the worm anteroom is always higher than the pressure ( 8th ) on the locking ring ( 3 ) on the side of the screw flights. Method according to claim 2, characterized in that that the determination of the existing pressures by means of pressure transducer takes place in the antechamber and the screw flights. Method according to claim 1, characterized in that that the screw speed when injecting a mathematical Model is regulated, so no speed component in the direction of the screw channel occurs.