METHODS FOR COOLING MOLDS

Abstract

Methods are provided for cooling a plastic part that has been produced in a mold. Carbon dioxide is fed through a capillary tube from a carbon dioxide source to the mold thereby providing cooling of the plastic part and avoiding hot spots in the plastic part prior to removal from the mold. The capillary tube is a smaller capillary tube located concentrically inside a larger capillary tube. Alternatively, the smaller capillary tube may extend from the end of the larger capillary tube telescopically thereby increasing the length of the capillary but also reducing its diameter as it progresses along its length.

Claims

1. A method for cooling a mold used in production of plastic parts comprising feeding carbon dioxide to the mold through a capillary tube comprising a smaller capillary tube located concentrically inside a larger capillary tube.

2. The method as claimed in claim 1 wherein the mold is selected from the group consisting of an injection mold and a gas assist mold.

3. The method as claimed in claim 1 wherein the carbon dioxide is fed to the mold as a liquid at a pressure of 800 to 900 pounds per square inch.

4. The method as claimed in claim 1 wherein the plastic parts are selected from the group of thermoplastics consisting essentially of Polypropylene (PP), Acrylonitrile-butadiene-styrene (ABS), Polycarbonate (PC), mix of PC and ABS Polyamide (PA), Polyether ether ketone (PEEK), Polyethylene (PE), Polyethylene terephthalate (PET), and Polystyrene (PS).

5. The method as claimed in claim 1 wherein the smaller capillary tube is two or more smaller capillary tubes.

6. The method as claimed in claim 5 wherein five smaller capillary tubes are present in the larger capillary tube.

7. The method as claimed in claim 1 wherein the larger capillary tube has a diameter of 0.157 cm.

8. The method as claimed in claim 1 wherein the smaller capillary tube has a diameter of 0.081 cm.

9. The method as claimed in claim 1 wherein the larger capillary tube is fitted inside the mold.

10. The method as claimed in claim 1 wherein the smaller capillary tube extends from and end of the larger capillary tube.

11. A method for delivering carbon dioxide to a mold used in production of plastic parts comprising feeding carbon dioxide through a capillary tube comprising a smaller capillary tube located concentrically inside a larger capillary tube, wherein the smaller capillary tube extends telescopically from an end of the larger capillary tube.

12. The method as claimed in claim 11 wherein the mold is selected from the group consisting of an injection mold and a gas assist mold.

13. The method as claimed in claim 11 wherein the carbon dioxide is fed to the mold as a liquid at a pressure of 800 to 900 pounds per square inch.

14. The method as claimed in claim 11 wherein the plastic parts are selected from the group of thermoplastics consisting essentially of Polypropylene (PP), Acrylonitrile-butadiene-styrene (ABS), Polycarbonate (PC), mix of PC and ABS Polyamide (PA), Polyether ether ketone (PEEK), Polyethylene (PE), Polyethylene terephthalate (PET), and Polystyrene (PS).

15. The method as claimed in cairn 11 wherein the smaller capillary tube is two or more smaller capillary tubes.

16. The method as claimed in claim 15 wherein five smaller capillary tubes are present in the larger capillary tube.

17. The method as claimed in claim 11 wherein the larger capillary tube has a diameter of 0.157 cm.

18. The method as claimed in claim 11 wherein the smaller capillary tube has a diameter of 0.081 cm.

19. The method as claimed in claim 11 wherein the larger capillary tube is fitted inside the mold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a schematic cross section showing a larger capillary tube with three smaller capillary tubes present therein.

[0023] FIG. 2 is a schematic showing a smaller capillary tube extending from a larger capillary tube.

DETAILED DESCRIPTION OF THE INVENTION

[0024] In the method for cooling plastic parts according to the invention, liquid carbon dioxide is supplied at a pressure of 800 to 900 pounds per square inch (psi) to the capillaries. The supply of carbon dioxide may be from either liquid carbon dioxide cylinders with a siphon (dip) tube or from a bulk carbon dioxide tank depending upon the usage amounts. If the liquid carbon dioxide is from a bulk tank, a pressure boosting unit must be employed to increase the pressure to 800 to 900 psi. The liquid carbon dioxide will flow through stainless steel hoses to the cooling solenoid valves which are controlled by a 24V DC signal.

[0025] An advantage of the invention is in keeping the carbon dioxide in its liquid form from its source, whether cylinder, with siphon tube, Dewars, or full scale bulk tank to the delivery point. This is accomplished by keeping the cross section of the delivery system at its original cross section or reduced in size through its travel from the source of carbon dioxide to the end of the capillary tube. In the method of the present invention, up to five capillaries can be accommodated in a telescoping fashion from the carbon dioxide source to the mold. It is anticipated that a large number of capillaries can be so joined if the source volume is high enough.

[0026] To reach very remote or exceptionally small areas of the plastic part forming mold, a telescoping capillary was designed. This telescoping capillary comprises a combination of two capillary tubes, one located concentrically inside the other. For example, the first outer capillary tube has an outer diameter of 0.062 inches (0.157 cm) and an inner diameter of approximately 0.032 inches (0.081 cm). A second capillary tube having an outer diameter of 0.030 inches (0.076 cm) is brazed into place inside of the first capillary tube.

[0027] This design provides several advantages over using a single capillary. The tube in a tube design provides for strength of a larger capillary over most of the liquid carbon dioxide travel while providing the small diameter size to reach areas that a 0.062 inch capillary cannot thereby providing a robust delivery system. The large outer capillary size also provides adequate carbon dioxide volume for the majority of its travel and thereby minimizes the travel through the reduced diameter section of capillary.

[0028] Turning to the drawing figures, in FIG. 1 a cross section of a larger capillary tube 1 is depicted with smaller capillary tube 2 present therein. As noted the larger capillary tube 1 concentrically encloses the smaller capillary tubes 2, 3 and 4. The smaller capillary tube 2 will be connected to the larger capillary tube by appropriate connection means such as welding, soldering or other metal joining technique.

[0029] In FIG. 2, there is depicted the alternative embodiment whereby the smaller capillary tube extends from the end of the larger capillary tube, thereby providing the ability to feed liquid carbon dioxide to ever smaller locations. In this embodiment the larger capillary tube 3 will have the smaller capillary tube 4 telescopically extend from its end thereby lengthening the overall capillary tube length but also providing a smaller cross sectional diameter to allow the liquid carbon dioxide to flow to. The smaller capillary tube would be joined to the larger capillary tube by conventional means such as welding or soldering in the instance where stainless steel is employed as the capillary tube material.

[0030] In one embodiment of the invention, the system for providing cooling starts at a bulk tank typically with post tank pressurization or a cylinder with the carbon dioxide exiting the storage system at approximately 850 pounds per square inch (5.810.sup.6 Pascals). The exits are typically about 0.25 inches (0.63 cm) in diameter. The carbon dioxide travels via a carbon dioxide compliant hose to a solenoid. When the solenoid is activated, it allows the carbon dioxide to pass through the solenoid to a distribution manifold containing a plurality of distribution points.

[0031] The distribution points are where the capillaries are attached using a nut and ferrule or similar means. The capillary can be a single diameter for the length of the capillary. For smaller areas needing cooling, smaller capillaries can be located concentrically inside the larger capillary tube. The characterization of the system to provide cooling is that at every transition point namely bulk tank or cylinder to hose through the solenoid, and through the capillaries, the carbon dioxide stream remains the same diameter or reduces in diameter in order to keep the carbon dioxide in its liquid state until it has reached the final end point where it experiences its phase transition and the cooling required.

[0032] While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of the invention will be obvious to those skilled in the art. The appended claims in this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.