BACKGROUND OF THE INVENTION

During the production of plastic parts through molding operations, they are processed and ejected after they have cooled down to a certain temperature. The length of time that it takes for each part to cool accounts for the better part of the production cycle time. A cycle time that is too long will be detrimental to efficiency and profitability.

For small or thin cores, the problems are exacerbated. Typically channels are made in a two piece laminated core where the two pieces are welded together and water is run through the channel. Unfortunately, these small channels can clog in short order due to mineral content in the water, organic compound content or a combination of both. These cores are usually 0.060 inches (0.15 cm) thick at the end and may be as large as 0.090 inches (0.22 cm) with draft included. The water channels therefore are generally 0.030 inches (0.07 cm) or smaller in diameter. Carbon dioxide reduces the clogging as it is a cleaning agent keeping the small channels open.

A second issue with a two piece design is that there is risk in the weld failing between the two halves and leaking water into the mold. Lastly a closed circuit loop is needed to attach the closed cooling loop to a chiller and/or water tower to function properly.

Alternatively, another method is to blow cooled air on the cores between shots of resin. However, this only allows for cooling while the mold is open and not when it is needed most as during the resin injection, pack and hold phase of the plastics production process.

This also impacts on cooling water being used for lifters and slides. It is difficult to get the water into lifters and slides in injection molds due to their size or configuration. It is also difficult to get a spot mold cooling capillary into slides and lifters due to the motion involved in their operation. One means of addressing cooling for these operations is to place the capillaries into the mold ending adjacent to the slide or lifter requiring cooling. The hole or channels in the slides or lifters would be larger than the capillary thereby allowing for expansion of the carbon dioxide to provide cooling to the lifter or slide.

These shortcomings can be overcome with the methods of the present invention.

SUMMARY OF THE INVENTION

In one embodiment of the invention, there is disclosed a method for cooling a mold used in production of plastic parts comprising feeding liquid carbon dioxide through a capillary to a channel present in the mold wherein the channel increases in size to dimensions that are greater than the capillary as the channel progresses into the mold.

In another embodiment of the invention, there is disclosed a method for cooling slides and lifters present in a mold used in production of plastic parts comprising feeding liquid carbon dioxide to the slides and lifters through a capillary to a channel present in the mold wherein the channel increases in size to dimensions that are greater than the capillary as the channel progresses into the mold.

In these embodiments, the channel is the same size as the capillary before the increase in size.

The carbon dioxide liquid is fed through a capillary to a channel that is present in the mold to be cooled. The channel is the same size as the inner diameter capillary and this channel will increase in size to dimensions that are greater than those of the capillary as the channel progresses into the mold.

The increase in size typically is in a specific location in the mold where the operator desires for cooling to begin. The expansion of the liquid into its gas phase provides the cooling due to the phase transition of the liquid to a gas at the appropriate location. Keeping the channel size approximately the same as the inside diameter of the capillary allows for the operator of the mold to provide the liquid carbon dioxide to the area where the operator desires cooling to start. By expanding the channel at that location from the diameter of the capillary and then allowing the gas to exit through one or more channels carries the cooling effect along the path.

A single channel can be employed in the methods of the present invention but more than one channel may also be used to provide cooling.

The tolerances between the capillary and channel will be designed to limit expansion and direct the liquid carbon dioxide to the area where expansion to the gas phase and cooling are desired.

Typically the applications for cooling by the methods of the present invention are in areas where the capillary is too large to reach. The capillary is essentially being extended by using a hole in the mold which is the same size as the inside diameter of the capillary. The capillary thus connects with the desired channel or channels and allows for the expansion of the carbon dioxide liquid to gas thereby creating cooling at the spot where cooling is needed in the mold.

The plastics that are typically cooled by the methods of the present invention are thermoplastics.

The carbon dioxide will be fed from a liquid carbon dioxide source such as a cylinder or bulk container with the pressure of about 800 to 1000 pounds per square inch (psi) to provide for liquid that is relatively bubble free. Preferably, the pressure is about 900 psi. This liquid carbon dioxide stream will be fed to a solenoid that is controlled by an SMC (system management controller). This will ensure that the carbon dioxide liquid reaches the desired area of cooling as a liquid and expands at that location to a gas.

Typically, the channel that connects to the capillary will have approximately the same dimensions as the capillary. As the channel progresses further into the mold its size will increase to dimensions larger than the capillary. This increase can be either progressive or it can be in one step at a time. By progressive, it is meant that the size of the channel increases in a gradual manner. By one step at a time, it is meant that the channel will increase in size and remain that increased size further into the mold. The channel may then increase in size one or more times, each increase being for a length of channel into the mold until a next increase, if any is made to the channel. This increase will have a ratio that is greater than 2 to 1 and less than 5 to 1 channel to capillary ratio thereby providing for the expansion of the liquid carbon dioxide to gas.

The molds will produce plastic parts that are made from plastics selected from the group consisting of polypropylene with or without glass reinforcement, polyethylene with or without glass reinforcement, polyamides with or without glass reinforcement, acryl-butadiene-styrene, poly carbonates and mixtures thereof. Virtually any thermoplastic resin can be treated by the methods of the present invention.

The mold will typically be any type of mold for producing plastic parts. This can include standard injection molds, gas assist injection molds, foaming molds, etc. that are used in the production of thermoplastic plastic parts and pieces. Typically in injection molding, melted plastic is forced into a mold cavity. Once cooled, the molded article can be removed. The cooling therefore is the reduction in temperature from when the plastic is in a melted state in the mold to when the mold can be opened and the now solid plastic part or piece can be removed without risking the structural integrity of the plastic part or piece.

