Method for operating an injection moulding machine

Patent metadata

Field	Value
Publication number	US-11052591-B2
Application number	US-201615737180-A
Country	US
Kind code	B2
Filing date	Jul 19, 2016
Priority date	Jul 20, 2015
Publication date	Jul 6, 2021
Grant date	Jul 6, 2021

Abstract

In a method for operating an injection moulding machine in the absence of a backflow barrier, plastic melt is injected by a plasticising device into a cavity in a screw antechamber of a plasticising screw adapted to rotate about a longitudinal axis and to move translationally by a drive unit during an injection phase and a holding-pressure phase. A rotational drive of the drive unit is controlled such that a speed of the plasticising screw causes overlay of a backflow of the plastic melt from the screw antechamber back into screw threads of the plasticising screw by an opposing delivery flow as a result of a rotation of the plasticising screw due to a translational injection movement of the plasticising screw. A differential flow is established from the backflow and the opposing delivery flow and influenced at least during the injection phase by influencing the speed of the plasticising screw.

First claim

The invention claimed is:

1. A method for operating an injection moulding machine, said method being executed in the absence of a backflow barrier and comprising:
injecting plastic melt by a plasticising device into a mould cavity from a screw antechamber of a plasticising screw by both rotating the plasticising screw about a longitudinal axis and moving the plasticising screw translationally both during an injection phase and during a holding-pressure phase;
controlling a rotational drive of a drive unit such that a rotation speed of the plasticising screw causes overlay of a backflow of the plastic melt from the screw antechamber back into screw threads of the plasticising screw caused by the translational injection movement of the plasticising screw is superimposed by an opposing delivery flow as a result of the rotation of the plasticising screw, thereby establishing a differential flow from the backflow and the opposing delivery flow;

and influencing the differential flow at least during the injection phase by influencing the speed of the plasticising screw.

2. The method of claim 1 , wherein the differential flow is MΔ>O, which is equivalent to the opposing delivery flow being greater than the backflow.

3. The method of claim 1 , wherein the differential flow is {dot over (m)} Δ =0, which is equivalent to the backflow being of same size as the opposing delivery flow.

4. The method of claim 1 , wherein the differential flow is MΔ<O, which is equivalent to the backflow being greater than the opposing delivery flow.

5. The method of claim 1 , further comprising determining and controlling the speed of the plasticizing screw in dependence of at least one melt parameter, or adaptively adjusting the speed during the injection phase and/or during the holding-pressure phase of a single cycle to at least one melt parameter.

6. The method of claim 5 , wherein the melt parameter is a parameter selected from the group consisting of a melt pressure of the plastic melt in the screw antechamber, a melt pressure of the plastic melt inside the mould cavity, a melt viscosity of the plastic melt, a melt temperature of the plastic melt, a plasticising torque, a torque of the plasticising screw during the injection and holding-pressure phase, and any combination thereof.

7. The method of claim 1 , wherein the backflow, the opposing delivery flow and the differential flow resulting therefrom are mass flows or volume flows of the plastic melt.

8. The method of claim 1 , further comprising influencing a translational stroke of the plasticising screw at least during the injection phase in dependence of an absolute size of the differential flow, such that
the translational stroke of the plasticising screw is lengthened in relation to a theoretical zero position, when the differential flow is {dot over (m)} Δ <0, or
the translational stroke of the plasticising screw is shortened in relation to a theoretical zero position, when the differential flow is {dot over (m)} Δ >0.

9. The method of claim 1 , configured for implementation throughout an entire injection phase and/or during an entire holding-pressure phase.

10. The method of claim 1 , further comprising varying the speed of the plasticising screw over the time to influence the differential flow, in particular to keep the differential flow constant during the injection phase and/or during the holding-pressure phase of one and the same injection moulding cycle.

11. The method of claim 1 , further comprising predefining the speed proportionally to a feed speed of the plasticising screw in a translational direction or proportionally to a melt pressure of the plastic melt, measured in particular in the screw antechamber or behind a screw shaft.

12. The method of claim 1 , further comprising:
pre-controlling the speed of the plasticizing screw at a start of the injection phase with a proportionality factor k 1 =f v in dependence of the feed speed in accordance with n scr =v inj *k 1 , wherein n scr is the speed, v inj is the feed speed, until the plasticising screw contacts the plastic melt, so that a melt pressure rises;
setting the speed with a proportionality factor k 2 =f p via a product n scr =p s *k 2 , when the product n scr =p s *k 2 is greater than a product n scr =v inj *k 1 , wherein p s is the melt pressure; and
setting the speed in the holding-pressure phase with a proportionality factor k 3 =f p_pck via a product n scr =k 3 *p s_pck , wherein p s_pck is the melt pressure in the holding-pressure phase.

13. The method of claim 1 , wherein the speed of the plasticizing screw during the injection phase and during the holding-pressure phase is predefined as an adjustable profile.

14. The method of claim 1 , further comprising generating during the holding-pressure phase a holding pressure of the plastic melt at least partially via the rotation of the plasticising screw.

15. The method of claim 1 , further comprising increasing the speed of the plasticizing screw for a predefined screw diameter for increasing an output factor and thus a shot weight.

16. The method of claim 1 , further comprising regulating or controlling the speed of the plasticising screw component-specifically for adjusting an optimal flow front speed of the plastic melt within the mould cavity.

17. The method of claim 1 , further comprising:
determining the speed of the plasticising screw at least during a part of the injection phase;
setting the speed of the plasticising screw proportionally to a melt pressure with the factor k 2 =f p in accordance with the equation:
n scr =f p *p s ,

wherein p s is the melt pressure and n scr is the speed of the plasticizing screw; and
measuring the melt pressure, with k 2 =f p being a proportionality factor determined in a process-specific manner.

18. The method of claim 1 , further comprising:
determining the speed of the plasticising screw at least during a part of the injection phase;
setting the speed proportionally to the feed speed with the factor k 1 =f v in accordance with the equation:
n scr =f v *v inj ,

wherein v inj is the feed speed and n scr is the speed of the plasticizing screw; and
measuring the feed speed or determining the feed speed from process data, with k 1 =f v being a proportionality factor determined in a process-specific manner.

19. The method of claim 1 , further comprising:
determining the speed of the plasticising screw at least during a part of the holding-pressure phase;
setting the speed proportionally to the melt pressure in the holding-pressure phase with the factor k 3 =f p_pck in accordance with the equation:
n scr =f p_pck *p s_pck ,

wherein p s_pck is the melt pressure in the holding-pressure phase and n scr is the speed of the plasticizing screw; and
measuring the melt pressure in the holding-pressure phase, with k 3 =f p_pck being a proportionality factor determined in a process-specific manner.

20. The method of claim 1 , further comprising:
determining and setting the speed of the plasticizing screw in the injection phase using the equation:
n scr =f v *v inj

wherein n scr is the speed of the plasticizing screw and v inj is the feed speed, when:
f v *v inj >f p *p s

wherein p s is the melt pressure; and/or
determining and setting the speed of the plasticizing screw in the injection phase using the equation:
n scr =f p *p s
when:
f v *v inj <f

Assignees

• Krauss Maffei Tech Gmbh

Inventors

• Schiffers Reinhard
• Kruppa Stefan
• Moser Stefan
• Busl Matthias
• Wortberg Johannes

Classifications

• B29C45/5092

  Intrusion moulding, i.e. the screw rotates during injection · CPC title

• B29C2945/7619

  barrel · CPC title

• B29C2945/76545

  Flow rate · CPC title

• B29C2945/76933

  The operating conditions are corrected immediately, during the same phase or cycle · CPC title

• B29C45/7646

  viscosity · CPC title