Patent Application
20090142439
The present invention generally relates to the processing of resin material. More specifically, the present invention relates to the preparation of resin material prior to its use in an injection unit.
The injection molding process typically comprises preparing a resin material (typically a polymeric or sometimes metal material) in an injection unit of an injection unit for melting, injecting the now-melted material under pressure into a closed and clamped mold, solidifying the material in its molded shape, opening the mold and ejecting the part before beginning the next cycle. The molding material typically is supplied to the injection unit from a hopper in the form of pellets or powder. The injection unit transforms the solid material into a molten material (sometimes called a “melt”), typically using a feed screw, which is then injected into a hot runner or other molding system under pressure from the feed screw or a plunger unit. A shut off valve assembly is typically provided to stop and start the flow of molten material from the barrel to the molding system.
Some examples of known molding systems having such an injection unit are: (i) the HyPET™ Molding System, (ii) the Quadloc™ Molding System, (iii) the Hylectric™ Molding System, and (iv) the HyMet™ Molding System, all manufactured by Husky Injection Molding Systems, Inc.
The resin material often needs to be prepared before processing. This can including drying the resin material (such as with PET resin) or preheating the resin material. Preprocessing is usually done with equipment auxiliary to the molding system, requiring additional power consumption to run the auxiliary equipment. Efforts have been made to reduce the power consumed for resin pre-processing. For example, U.S. Pat. No. 4,573,897 to Piazzola (published Mar. 4, 1986) teaches a system for extruding, drawing, vacuum molding or processing, or the like hot processing of plastomers or elastomers, which can conveniently utilize the hot air from the cooling process of its heated component parts. The system makes use, to heat the extruder cylinder, of ventilated electric thermal units wherein ventilation is performed in closed circuit fashion. In particular, arrangements are made to convey the hot air from the cited electric thermal units, through specially provided ducting, to areas of the system where application of heat is required.
Japanese patent 56,144,141A2 (published Nov. 10, 1981) teaches a method wherein the exhaust port of a cylinder cover and the interior of a resin supplying hopper are communicated. Hot wind discharged from the exhaust port 15 is introduced into the resin supplying hopper 9 by a blower 17 through a communicating duct 16 and dries and preheats the resin in the resin supplying hopper 9. In this case, the heat capacity of the hot wind discharged from the exhaust port 15 is different in accordance with the revolving speed of a screw in the cylinder 8, however, a driving motor for the blower 17 is controlled at a revolving speed in accordance with the revolving speed of a driving motor for the screw and the blower induces the heat capacity of the hot wind which is suitable for the revolving number of the screw, therefore, the most suitable hot wind temperature may be obtained. When the temperature in the communicating duct 16 has become higher than a predetermined temperature, a temperature indicating and adjusting meter 20 adjusts a wind volume adjusting valve 21 in accordance with a signal from a thermometer 19 and the hot wind of a constant temperature is introduced into the resin supplying hopper 9 at all the times.
U.S. Pat. No. 6,755,640 to Bauer et al (published Jun. 29, 2004) teaches a plastics injection molding machine includes a heatable plasticizing cylinder having an inlet side for incoming plastic material and a machine drive, and an injection mold receiving the plastic material from the plasticizing cylinder for making an injection molded article. Acting between the machine drive and the inlet side of the plasticizing cylinder is a heat transport system for preheating the incoming plastic material with waste heat generated by the machine drive to thereby realize a recovery of energy. The heat transport system 24 includes a circulating pump 26, a first heat exchanger 28 in the area of attachment flange 22 at the upstream end of the plasticizing cylinder 10 for cooling the hydraulic screw drive 14, and a second heat exchanger 30 for cooling the central unit 20.
According to a first broad aspect of the present invention, there is provided a resin-processing machine operable to process resin material. The resin-processing machine comprises:
According to a second broad aspect of the invention, there is provided a heat exchanger assembly, operable to extract heat from a hydraulic circuit after having passed through an resin-processing machine, and wherein
According to a third broad aspect of the invention, there is provided a method for preheating a supply of resin material prior to its processing in a resin-processing machine, the method comprising:
A better understanding of the non-limiting embodiments of the present invention (including alternatives and/or variations thereof) may be obtained with reference to the detailed description of the non-limiting embodiments of the present invention along with the following drawings, in which
The drawings are not necessarily to scale and are sometimes illustrated by phantom lines, diagrammatic representations and fragmentary views. In certain instances, details that are not necessary for an understanding of the embodiments or that render other details difficult to perceive may have been omitted.
Referring now to
The mold unit 24 includes a hot runner 28 which distributes the molten resin material into a mold 30. The mold 30 may have a single cavity 32 or multiple cavities 32, and in the presently-illustrated embodiment, two cavities 32 are shown. The mold 30 includes a stationary mold portion 30a that is supported by a stationary platen 34. The mold 30 also includes a movable mold portion 30b that is supported by a movable platen 36 that is movable relative to the stationary platen 34. The movable platen 36 is connected to an actuator 38 and the actuator 38 is used to stroke or to move the movable platen 36. In the presently-illustrated embodiment, actuator 38 is a hydraulic actuator. Clamp locks 39 are provided to keep the two mold parts 30a and 30b together during injection. In the presently-illustrated embodiment, the clamp locks 39 are also hydraulically motivated.
The injection unit 22 includes an extrusion barrel 40 which defines a melt channel 42 for the resin material. Extrusion barrel 40 is adapted to receive an injection screw 44. A machine nozzle 46 connects extrusion barrel 40 to the hot runner 28 on mold unit 24. Resin material (typically thermoset or thermoplastic pellets) is stored, prior to its use, in a hopper 50 located above extrusion barrel 40.
Hopper 50 can include auxiliary desiccant or heating equipment (not shown) used to pre-process the resin prior to it being fed into melt channel 42. While hopper 50 is depicted as a single container, those of skill in the art will recognize that hopper 50 can include multiple containers designed for different stages of pre-processing.
The resin material is fed from hopper 50, through a feed throat 52 into melt channel 42. The rotational movement of screw 44 melts the resin prior to it exiting through nozzle 46. Heater bands 53 are provided along the length of extrusion barrel 40 to improve heating of the resin material. In addition to rotating, screw 44 is preferably operable to reciprocate back and forth to express the melted material out through nozzle 46 and pack the material within the mold 30. The rotational movement of screw 44 is provided by an actuator 54, which in the presently-illustrated embodiment is a hydraulic motor. Injection of the molten material is provided by translating screw 44 within extrusion barrel 40 via a piston coupled to screw 44. In the presently-illustrated embodiment, the piston is a hydraulically-actuated piston defined within actuator 54.
A hydraulic circuit 56 (indicated by the dotted lines in
As the hydraulic fluid moves through injection molding machine 20, it heats up and will require cooling prior to returning to tank 60 for maximal operating efficiency. A heat exchanger assembly 62 is provided to extract the excess heat from the hydraulic fluid in hydraulic circuit 56 prior to it returning to tank 60. In addition to cooling the hydraulic fluid for reuse, heat exchanger assembly 62 uses the waste heat to preheat the resin stored in hopper 50.
In a typical usage scenario, the hydraulic fluid stored in tank 60 would be at a temperature of approximately 50° C. after a short period of operation for injection molding machine 20. Upon passing through injection molding machine 20 and returning to tank 60, the hydraulic fluid would heat up to a temperature of approximately 60° C. (prior to passing through heat exchanger assembly 62).
In the presently-illustrated embodiment, heat exchanger assembly 62 includes a first heat exchanger 64, a blower 66, and a second heat exchanger 68.
The heated hydraulic fluid exits injection unit 22 and mold unit 24, and passes into the first heat exchanger 64, which in the presently-illustrated embodiment is an oil-to-air heat exchanger. In the presently-illustrated embodiment, the hydraulic fluid has just passed through the actuator 54, actuator 38 and clamp locks 39, and has reached its maximum temperature. Within the first heat exchanger 64, heat from the hydraulic circuit 56 is transferred to an adjacent air circuit 70. The blower 66 circulates the heated air in air circuit 70 through into hopper 50, where it heats up the stored supply of resin material. The air cools as it exits hopper 50, and is returned into the first heat exchanger 64.
After transferring waste heat to air circuit 70 in the first heat exchanger 64, the hydraulic circuit 56 passes through a second heat exchanger 68, which is preferably illustrated embodiment is an oil-to-water heat exchanger. Within the second heat exchanger 68, heat from the hydraulic circuit 56 is transferred to an adjacent water circuit 72. After this further treatment, the hydraulic fluid in hydraulic circuit 56 is at, or approaches its starting temperature, and is returned to tank 60.
The inventors have determined that the invention can provide significant energy savings. For example, PET plastic resin is often stored in outdoor silos, and normally can enter hopper 50 at an incoming temperature of 15° C. If the hydraulic fluid in hydraulic circuit 56 leaves injection unit 22 at a temperature of 60° C., first heat exchanger 64 can raise the temperature of the PET resin to approximately 50° C. (i.e., a gain of 35° C.), resulting in pre-processing energy savings.
Those of skill in the art will recognize that adaptations can be made to heat exchanger assembly 62. Referring now to
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Other variants of resin processing machines are within the scope of the invention. For example, an injection unit 22 could inject the molten resin material using a shooting pot rather than a translating screw (not shown). Alternatively, the resin-processing machine could have a co-injection design using both a translating screw and a shooting pot (not shown). Alternatively, the invention could be adapted for other resin-processing machine which lack a molding component, such as an extrusion machine adapted to manufacture plastic films.
The invention provides preheating of resin material using waste heat generated during the extrusion and/or molding process. The description of the non-limiting embodiments provides examples of the present invention, and these examples do not limit the scope of the present invention. It is understood that the scope of the present invention is limited by the claims. The concepts described above may be adapted for specific conditions and/or functions, and may be further extended to a variety of other applications that are within the scope of the present invention. Having thus described the non-limiting embodiments, it will be apparent that modifications and enhancements are possible without departing from the concepts as described. Therefore, what is to be protected by way of letters patent are limited only by the scope of the following claim
