Method for cooling thin cores in plastic molds

Abstract

A method for cooling a mold used in the production of plastic parts is described. A capillary feeds liquid carbon dioxide to a channel present in the mold typically used in making plastic parts having thin gaps or thin open sections in the plastic part. The channel will be approximately the same size as the inner diameter of the capillary but will increase in size either stepwise or progressively as it passes through the mold, particularly at the location where cooling is desired therefore providing more effective cooling to the mold and slides and lifters present therein.

Claims

1. A method for cooling slides and lifters present in a mold used in production of plastic parts, comprising: providing a mold to be cooled for producing plastic parts, the mold including slides and lifters in the mold; feeding liquid carbon dioxide through an inner diameter of a capillary connected to a channel present in the mold to be cooled, wherein the channel is of a same size as the inner diameter of the capillary at a position before the channel progresses into the mold; increasing the size of the channel to be larger than the inner diameter of the capillary at another position inside a slide or lifter where cooling is needed, dimensions of the channel at the another position becoming greater than the inner diameter of the capillary as the channel progresses from the another position; and expanding the liquid carbon dioxide to a gas beginning at the another position in the channel for the cooling to begin and continue along as the channel progresses in the mold.

2. The method as claimed in claim 1 wherein the increasing the size of the channel is progressive.

3. The method as claimed in claim 1 wherein the increasing the size of the channel is stepwise.

4. The method as claimed in claim 1 wherein more than one channel is present in the mold.

5. The method as claimed in claim 1 wherein the feeding of the liquid carbon dioxide is at a pressure of 800 to 1000 pounds per square inch.

6. The method as claimed in claim 1 wherein the increasing the size of the channel is at a ratio greater than 2 to 1 and less than 5 to 1 channel to capillary.

7. The method as claimed in claim 1 wherein the plastic parts are selected from the group consisting of thermoplastics parts, polypropylene with glass reinforcement, polypropylene without glass reinforcement, polyethylene with glass reinforcement, polyethylene without glass reinforcement, polyamides with glass reinforcement, polyamides without glass reinforcement, acryl-butadiene-styrene, polycarbonates, and mixtures thereof.

8. The method as claimed in claim 1 wherein the mold is selected from the group consisting of injection molds, gas assist injection molds, and foaming molds.

9. The method as claimed in claim 1 wherein the cooling further comprises reducing a temperature from when the plastic parts are in a melted state to a temperature when the mold can be removed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic representation of a lifter or slide present in a mold showing the positions of the capillaries in relation thereto.

(2) FIG. 2 is a schematic cross-sectional representation of the mold along line A-A in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(3) Liquid carbon dioxide is fed through capillaries to one or more channels that are present in a mold, such as a blade style manifold that is used in the production of thin gaps or thin open sections in plastic parts. The liquid carbon dioxide is fed through a capillary into the channel where the carbon dioxide will be delivered to the location within the mold where cooling is desired. The channel will have the same approximate dimensions as inner diameter of the capillary and it will progress into the mold. As this progression occurs, the channel will increase in dimensions to a size greater than the capillary. This is performed in a singular step or progressively as the channel progresses the mold. This increase in size will allow for the expansion of the liquid to a gas (phase transition) cooling to contact the particular location within a mold where cooling is desired. This can take place in small or thin cores as well as to provide cooling to slides and lifters.

(4) Thus, the present invention will reduce production cycle times and allow for cooling in molds that previously were not able to be cooled. The open circuit design allows for the liquid carbon dioxide to enter the gas phase and be dispersed rather than having a closed circuit with running cooling water.

(5) For example, 0.060 inch cores were employed in a mold and were able to reduce cycle times from over 22 seconds to below 15 seconds.

(6) Turning to the figures, FIG. 1 is a schematic representation of a mold showing the position of a lifter or alternatively a slide in relation to the capillary holes to the mold and the lifter or slide. A cross sectional line A passes through the mold and lifter or slide. A mold 10 contains a series of capillaries or holes 20. These capillaries or holes 20 will have the same size internal diameter as they pass from the mold 10 to the lifter or slide 50. As they pass through the mold 10 and into the lifter or slide 50 they will expand 30 in diameter as they progress through the lifter or slide 50 to provide cooling. The carbon dioxide that is fed through the capillary or holes 20 will expand when it encounters the expanded diameter holes 30 and provide the cooling. The expanded carbon dioxide will then pass through the mold 10 and be exhausted through lines 40.

(7) FIG. 2 is the cross sectional designation A from FIG. 1. The cross section shows a portion of the mold 60 and a lifter or slide 70. The expansion holes 80 are shown at the point where they have expanded to provide the necessary cooling to the lifter or slide. The expansion holes can be made using additive manufacturing to accommodate curved lifters or slides to provide conformal cooling.

(8) 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 invention.