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Title:
LOW-PRESSURE MOLDING SYSTEM
Document Type and Number:
WIPO Patent Application WO/2021/159122
Kind Code:
A4
Abstract:
The present invention relates to extrusion molding machines and methods of producing extrusion molded parts and, more particularly, to extrusion molding machines that adjust operating parameters of the extrusion molding machine during an extrusion molding run to account for changes in material properties and pressures of the extrusion material and methods of accounting for changes in extrusion molding material properties during an extrusion molding run and/or compounding of materials.

Inventors:
GRAM JES (US)
Application Number:
PCT/US2021/017256
Publication Date:
November 25, 2021
Filing Date:
February 09, 2021
Export Citation:
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Assignee:
GRAM JES TOUGAARD (US)
International Classes:
B29C45/77; B29C45/00
Attorney, Agent or Firm:
CHALFIE, Edward, J. (US)
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Claims:
AMENDED CLAIMS received by the International Bureau on 02 September 2021 (02.09.2021)

1 . A method of plastic molding at a substantially constant, relatively low pressure, comprising:

(a) using a rotating screw to introduce a molten thermoplastic material into an at least one mold cavity of a molding apparatus, for extrusion molding at a low, substantially constant melt pressures; and,

(b) while maintaining the melt pressure substantially constant at less than 6000 psi, wherein: the thermoplastic material has a melt flow index of about 0.1 g/10 min to about 500 g/10 min.

2. The method of claim 1 , wherein the molding apparatus comprises a means for building back pressure, such as a breaker plate or a pressure relief valve in a manifold having heated runners in fluid communication with the at least one mold cavity, wherein the melt pressure of the molten thermoplastic material is maintained substantially constant while the molten thermoplastic material is transported from an entry point through the back pressure building means to the heated runners.

3. The method of claim 1 , wherein the filling of the molten thermoplastic material into the at last one mold cavity includes applying a pressure to the molten thermoplastic material, and wherein maintaining the constant melt pressure includes monitoring the melt pressure of the molten thermoplastic material upon entering into the at least one mold cavity and the melt pressure of the molten thermoplastic material during filling of the at least one mold cavity, and adjusting the pressure applied to the molten thermoplastic material entering into the at least one mold cavity to maintain said constant melt pressure.

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4. The method of claim 1 , wherein the molding apparatus includes a pressure relief valve disposed between a breaker plate and the at least one mold cavity, the pressure relief valve having a predetermined set point at the substantially constant melt pressure and maintaining the substantially constant melt pressure on molten thermoplastic material through the pressure relief valve at a melt pressure higher than the predetermined set point, the pressure relief valve reducing the melt pressure of the thermoplastic material as it passes through the pressure relief valve and enter into the at least one mold cavity to maintain said constant melt pressure.

5. The method of claim 1 , wherein the molding apparatus automatically adjusting an extrusion molding process to compensate for variations in the flowability and/or temperature variations of a molten plastic material, the method including: providing an extrusion molding machine with at least one mold cavity; providing a molding controller, which includes a pressure control output that is configured to generate a control signal, which, at least partially determines an extrusion molding pressure and/or temperature for the extrusion molding process of the extrusion molding machine; measuring a first control signal generated from the pressure control output and/or temperature output at a first time in an extrusion molding cycle; measuring a second control signal generated from the pressure control output and/or temperature output at a second time in the same extrusion molding cycle, subsequent to the first time; comparing the first control signal generated from the pressure control output and/or temperature output and the second control signal generated from the pressure control output and/or temperature output to obtain a comparison result; and determining a third control signal for the pressure control output and/or temperature output, based at least in part on the comparison result, at a third time that is subsequent to the second time.

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9. The method of claim 5, wherein the comparison result is a flow factor (FF) that is used as a soft sensor melt viscosity input by the controller.

10. The method of claim 9, wherein the FF is determined by the formula:

FF=(CS1-CS2)/T; where CS1 is the first control signal;

CS2 is the second control signal; and T is the time difference between CS1 and CS2.

11 . The method of claim 10, wherein the third control signal is proportional to the flow factor.

12. The method of claim 10, wherein T is between 0.1 milliseconds and 10 milliseconds.

13. The method of claim 5, wherein the comparison result is used as a basis for a viscosity change index (VCI) that is used as a soft sensor melt viscosity input to by the controller.

14. The method of claim 13, wherein the VCI is determined by the following formula:

VCI=(CS1-CS2)/S where CS1 is a first control signal;

CS2 is a second control signal; and

S is the position difference for the melt moving machine component.

17. The method of claim 5, wherein the comparing of the first control signal and the second control signal includes comparing the first control signal and the second control signal to optimal control signals based on an optimal pressure curve, the method including: measuring a first control signal generated from a pressure control output of the controller at a first time in an extrusion molding cycle using a control signal measurement device;

76 measuring a second control signal generated from the pressure control output of the controller at a second time in the same extrusion molding cycle, subsequent to the first time using the control signal measurement device; comparing the first control signal generated from the pressure control output of the controller and the second control signal generated from the pressure control output of the controller to obtain a comparison result; and determining a third control signal for the pressure control output, based at least in part on the comparison result, at a third time that is subsequent to the second time.

18. The method of claim 5, wherein the providing of the extrusion molding machine includes providing a rotating screw melt moving machine component; and further including: measuring a first position of the melt moving machine component at the first time; measuring a second position of the melt moving machine component at the second time; determining a position difference between the first position and the second position; and wherein the comparing includes comparing the first control signal and the second control signal, based, at least in part, on the position difference, to obtain the comparison result.

21 . The method of claim 1 further including having a constant low-pressure extrusion in an injection molding machine given the constant low-pressure molding allowing a traditional injection unit to have much larger and more homogenous plasticizing output extruding the plastic into the at least one mold cavity.

22. The method of claim 21 further including having a constant low-pressure extrusion in an injection molding machine wherein the breaker plate and/or pressure valve is being built in to a manifold being bolted on to the mold in the machine and/or being part of such mold built into a hot runner manifold.

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23. The method of claim 21 , further including combining extruding plasticized material into the at least one cavity with injecting the plasticized material into said at least one cavity, thereby increasing the material that can be introduced into the at least one cavity in the machine and applying a constant low-pressure extrusion of the material using a space in front of the screw to hold a cushion of melted plasticized material while the mold opens and closes during a holding pressure phase of the molding process.

24. A method of plastic molding at a substantially constant, relatively low pressure, comprising:

(a) filling a molten thermoplastic material into an at least one mold cavity of a molding apparatus, having a hot runner system using a low and constant plastic pressure, and reduces pressure loss within the mold as it fills; and,

(b) while filling the at least one mold cavity with the molten thermoplastic material, maintaining the melt pressure substantially constant at less than 6000 psi,

25. The method of claim 24, wherein the method includes filling of an unbalanced manifold, with the manifold feeding heated runners in fluid communication with the at least one mold cavity.

26. The method of claim 24 further including a hot runner system having at least one cold runner portion in a mold component that is reheated during every molding cycle before injection of the next portion of molten plastic material.

27. The method of claim 26 further including reheating the at least one cold runner portion using conductive heating.