Gas-assisted mold surface heating system

A gas-assisted mold surface heating system is disclosed, which comprise: an air supply, for providing air with a flow rate larger than 300 L/min; a heater, for heating air to a temperature higher than 400° C.; a mold, configured with a mold cavity, an inlet and an outlet; and an air storage tank; wherein, the inlet is connected to the heater through a pipeline for allowing the air from the air supply to flow into the cavity after being heated by the heater and thus to be for heating up the surface of the mold cavity while the heated air is being enabled to flow out of the cavity through the outlet and into the air storage tank. With the aforesaid system, surface temperature of the mold cavity can be raised to a point higher than a glass transmission point in a short period of time.

FIELD OF THE INVENTION

The present invention relates to a mold heating system, and more particularly, to a gas-assisted mold surface heating system capable of heating a cavity surface of a mold by high temperature and high flow rate air.

BACKGROUND OF THE INVENTION

“With rapid advance of manufacturing technology, there are many methods being developed for molding plastics into required products, such as injection molding, blow molding, hot embossing molding, compression molding, draw molding, and so on. Among which, injection molding is the most common method of plastic part manufacturing which is used to create a large variety of products with different shapes and sizes, ranged from as simple as a cup to a very complex automotive dashboard, and also ranged from as small as a watch gear weighted only 0.01 gram to a very large bathing tub weighted more than 20 kilograms. Most importantly, they can create products with complex geometry that many other processes cannot, since it is advantageous in its ability of making complex plastic parts at high production rates and high tolerances of repeatability with high precision in dimension.”

In a plastic injection molding process, a plastic material is fed into a heated barrel, melted, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the mold cavity. Generally, the mold is only heated to a temperature that is lower than the glass transition point of the plastic material which is to be molded therein, so that the melted plastic is able to solidify to the configuration of the mold cavity as soon as it come into contact with the cavity surface.

In response to the smaller, thinner and lighter trend for the modern 3C products, a more advanced plastic injection molding process is in demand for satisfying the requirement of producing products configured with microstructures measured in hundreds of micrometers or even tens of micrometers, such as backlight panels, fiber optic connecters, etc., that can not be manufactured by conventional plastic injection molding as it is troubled by the molding conditions of flowability and plastic solidification while being used for manufacturing the aforesaid products configured with microstructures.

It is noted during the development of the present invention that the key for manufacturing the aforesaid products configured with microstructures by plastic injection molding relies on how to enable the mold surface temperature to change rapidly and dynamically. Moreover, it is important to keep the mold at a temperature higher than plastic's glass transition point during the procedure of filling the melted plastic into the mold, and then enable the mold temperature to drop rapidly for the purpose of reducing the total cycle time for plastic molding, by that the microstructures of high aspect ratio can be formed perfectly on the molded products with high precision.

Thus, the focal point of the present invention is how to heat up a mold in relatively short period of time and cool down the same thereafter as well.

SUMMARY OF THE INVENTION

In view of the disadvantages of prior art, the primary object of the present invention is to provide a gas-assisted mold surface heating system capable of guiding a heated air to flow directly to and through a cavity surface of a mold in high flow rate for heating the cavity surface to a temperature higher than a glass transition point in a short period of time.

To achieve the above object, the present invention provides a gas-assisted mold surface heating system, comprising: an air supply, for providing air with a flow rate larger than 300 L/min; a heater, for heating air from the air supply to a temperature higher than 400° C.; a mold, configured with a mold cavity, an inlet and an outlet; and an air storage tank, for storing air exhausted from the outlet; wherein, the inlet is connected to the heater through a pipeline for allowing the air from the air supply to flow into the mold cavity after being heated by the heater and thus to be for heating up the surface of the mold cavity while the heated air is being enabled to flow out of the cavity through the outlet and into the air storage tank. With the aforesaid system, surface temperature of the mold cavity can be raised to a point higher than a glass transmission point in a short period of time.

With the aforesaid system, surface temperature of the mold cavity can be raised to a point higher than a glass transmission point in a short period of time by the use of hot air with temperature higher than 400° C. and flowing with a flow rate larger than 300 L/min, so that the microstructures of high aspect ratio can be formed perfectly on the molded products with high precision.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

For your esteemed members of reviewing committee to further understand and recognize the fulfilled functions and structural characteristics of the invention, several exemplary embodiments cooperating with detailed description are presented as the follows.

Please refer toFIG. 1, which is a schematic diagram showing a gas-assisted mold surface heating system of the invention. The gas-assisted mold surface heating system shown inFIG. 1is adapted for heating a mold2in a plastic injection molding process, which comprises: an air supply11, a heater12, an air storage tank13and a pipeline14.

“The air supply11is capable of providing air with a flow rate larger than 300 L/min. Substantially, the air supply11is an air compressor that is preferably designed to provide air with a flow rate ranged between 300 L/min and 500 L/min. As shown inFIG. 1, the air supply11is sequentially connected to the heater12, the mold2, and the air storage tank13by the pipeline14. Moreover, for controlling the amount of the air flowing in the whole gas-assisted mold surface heating system, the system further configured a flow control valve15on the pipeline14at a position between the air supply11and the heater12.”

“The heater12is used for heating air from the air supply11to a temperature higher than 400° C. Substantially, the heater12is an electric heater with a preferred capacity capable of heating the air to a temperature between 400° C. and 600° C. In order to use the heated air efficiently, the heater12is disposed neighboring to the mold2.”

The air storage tank13is connected to the pipeline after the mold2since it is used for storing the hot air after it is used for heating the mold2. For improving energy efficiency, there is a recycle pipeline16being disposed in the heating system of the present embodiment in a manner that it is connected to the storage tank13by one end thereof while the other end of the recycle pipeline16is connected to the pipeline14at a position between the heater12and the air supply11. Moreover, in order to control the amount of air being recycled efficiently, there is a flow control valve15arranged in the mold heating system that is connected to the recycle pipeline16to be used for controlling the air flow of the recycled air.

The mold2, being adapted for a plastic injection machine3, is composed of at least two dies21,22capable of being integrated into a unity when clamping while forming a mold cavity23therein. The mold2is configured with at least an inlet24and at least an outlet25that are connected to the mold cavity23and are disposed respectively at two ends of the mold cavity23relating to its long axis. In this embodiment the inlet24and the outlet25are disposed on the same die of the mold2. As shown inFIG. 1, the inlet24is connected to the heater12through the pipeline14whereas the outlet25, being formed on the mold2at a position corresponding to the inlet24, is connected to the air storage tank13through the pipeline14, by that the hot air from the heater12can be fed into the mold cavity23through the inlet24and then can be exhausted out of the mold cavity23through the outlet25after heating the surface of the mold cavity23.

Since the air supply11of the invention is designed to provide air with a flow rate larger than 300 L/min that is to be heated by the heater12to a temperature higher than 400° C., there will be a large amount of high-temperature air flowing through the surface of the mold cavity23for heating the same to a designated temperature in a comparatively short period of time. In fact, the surface of the mold cavity can be heated to 120° C. in about 8 seconds, by which the microstructures of high aspect ratio can be formed perfectly on the consequent molded products with high precision.

Besides the aforesaid plastic injection machine, the mold2can be adapted for injection compression molding process. Generally, the injection compression molding process comprises the steps of: feeding, pressure-keeping, compressing, cooling, and so on. However, the gas-assisted mold surface heating system of the invention not only is used for heating the mold before the feeding step, but also is used for keeping the temperatures of the mold and the injected plastic during the pressure-keeping and the compressing steps, so that the microstructures of high aspect ratio can be formed perfectly on the consequent molded products with high precision.

Please refer toFIG. 2, which is a schematic view depicting how air is flowing and trapped in a mold cavity when there is a big difference between its sectional area and those of its inlet and outlet. As shown inFIG. 2, it is noted that when there is a big difference between the sectional area of the mold cavity23and those of its inlet24and outlet24, it is more than likely to have vortexes being formed at the corners next to the inlet24which causes a portion of the hot air flowing into the mold cavity23through the inlet24to be trapped at the corners and thus adversely affects the heating efficiency, and moreover, it is going to cause the flowing speed of the hot air to accelerate at the position between the joint of the outlet25and the mold cavity23so as to cause overheating thereat and consequently cause the surface of the mold cavity23to be heated unevenly.

Therefore, when there is a big difference between the sectional area of the mold cavity23and those of its inlet24aand outlet25a, the inlet24aand the outlet25ashould be tapered in a manner that the sectional area relating to ends of the inlet24and the outlet25aare connected to the mold cavity23is larger than those of their another ends in respective, as shown inFIG. 3. With the aforesaid tapering design, the speed of the hot air flowing through the mold cavity23is evenly distributed so that the surface of the mold cavity23can be heated evenly.

In addition, it is noted that the shape of the mold cavity as well as the positions of the inlet and outlet can all affect the heating of the mold cavity. In the embodiment of the present invention, the shape of the mold cavity23bis optimized by enabling the ratio between the lengths of its long axis L and short axis S to be larger than three when the inlet24band the outlet25bare disposed respectively at two ends of the mold cavity23brelating to its long axis, as shown inFIG. 4. With the aforesaid configuration, air can flow more smoothly in the mold cavity23bfor achieving a better heating efficiency.

On the other hand, when the inlet24cis disposed at an end of the mold cavity23crelating to its short axis S while the outlet25cis disposed at another end of the mold cavity23crelating to its short axis S away from the position corresponding to the extending of the inlet23b, the shape of the mold cavity23cis optimized by enabling the ratio between the lengths of its long axis L and short axis S to be smaller than three, as shown inFIG. 5. With the aforesaid configuration, hot air flowing into the mold cavity23ccan be utilized efficiently for heating the surface of the mold cavity23c. In addition, since the outlet25cis disposed at another end of the mold cavity23crelating to its short axis S away from the position corresponding to the extending of the inlet23bwhile extending along the long axis L, air can be enabled to flow more smoothly in the mold cavity23bfor achieving a better heating efficiency.

As known to those skilled in the art that the smaller the mass of the portion required to be heated, the better the heating efficiency will be. Therefore, the present invention provides two different molds being adapted for the gas-assisted mold surface heating system of the invention, as shown inFIG. 6AandFIG. 6B. InFIG. 6A, the mold4further has an insert41adisposed right next to the mold cavity43in manner that the insert41aand the mold4is separated by an heat insulation layer41bsandwiched therebetween. The insert41ais made of a material of high heat transfer coefficient, such as electroforming nickel-based alloys, and is formed with a thickness about 0.5 mm. The heat insulation layer41ba material of low heat transfer coefficient, such as ceramics, and cobalt oxide, and is formed with a thickness about 0.5 mm.

In this embodiment, since the insert41ais made of a material of high heat transfer coefficient of only about 0.5 mm in thickness and also since the inert41aand the mold4are separated only by the heat insulation layer41b, the hot air flowing into the mold cavity43is used for heating only the insert41awhose mass is comparatively much smaller than the whole mold cavity so that the mold heating system of the invention is able to heat the surface of the mold cavity to 140° C.˜165° C. in about 4˜8 seconds. Thus, the heating efficiency of the present embodiment is substantially better than the embodiment shown inFIG. 1.

InFIG. 6B, the mold4also has an insert41cdisposed right next to the mold cavity43in manner that the side of the insert41copposite to that facing toward the mold cavity43is in direct contact with the mold4. Similarly, the hot air flowing into the mold cavity43is used for heating only the insert41cso that the heating efficiency of the present embodiment is substantially better than the embodiment shown inFIG. 1.

In order to close the inlet and the outlet automatically when clamping, the present invention provides a mold adapted for the gas-assisted mold surface heating system of the invention, as shown inFIG. 7AandFIG. 7B. As shown inFIG. 7AandFIG. 7B, the mold5is composed of two dies51,52capable of being integrated into a unity when clamping; and the inlet54is formed at a specific location on the die52while forming a block511on another die51at a position thereof corresponding to the inlet54. Moreover, the die52is formed with a recess521at a position corresponding to the block511and the recess is designed to communicate with the inlet54. Thus, the aforesaid configuration can ensure air to flow without obstruction through the inlet54when not in clamping, as shown inFIG. 7A, and enabling the flow in the inlet54to be blocked by the block511when clamping.

In addition, the present invention further provides another mold adapted for the gas-assisted mold surface heating system of the invention, as shown inFIG. 8AandFIG. 8B. As shown inFIG. 8AandFIG. 8B, the mold6is composed of two dies61,62capable of being integrated into a unity when clamping; and the die62is formed with an extrusion portion621at a specific location thereof that will abut against the die61by the top thereof while clamping; and since the inlet64is formed inside the die62and is opened to the top of the extrusion portion621, air flowing through the inlet64is able to flow into the cavity when not clamping as the top of the extrusion portion621is not abutted against the die61, as shown inFIG. 8A; and air flowing through the inlet64is blocked from flowing into the cavity when clamping as the top of the extrusion portion621is abutted against the die61. It is noted that although the two aforesaid molds are configured differently, both can close the inlet automatically when clamping.