PLASTIC INJECTION MOULDING SYSTEM WITH MULTIPLE TIP TORPEDO HEATER

Abstract: A plastic injection molding system has a plurality of multiple tip torpedo heaters (30) which each have a casing with a pair of opposed tips (3l a , 3l b ) disposed in respective sprue passageways (25 a , 25 b ) in a mold. An unsheathed electrical heating element (39 a , 39 b ) is disposed in an internal bore (36) of the casing (32) at each tip and heat transmitting material (60) is compacted in the bore in surrounding relation to the heating element for electrically insulating each heating element from the casing (32) and filing all air voids between the casing and heating element to effect direct heat transfer to the casing. Electrical leads (6l a , 6l b ) couple the plurality of heating elements to a power source to permit independent temperature control of the individual heating elements and the exposed surfaces of the respective casing tips over which fluid plastic material is directed.

Description: The present invention relates to plastic injection molding equipment in accordance with the pre-characterising portion of claim 1. In plastic injection molding equipment it generally is necessary that each passageway in the mold through which fluid plastic passes during its travel to a mold cavity be heated to a predetermined substantially uniform temperature in order to enable the proper material flow. For this purpose, it is common to utilize sprue torpedo heaters, runner torpedo heaters and the like in each passageway. In injection molding equipment in which there is provided a plurality of mold cavities for simultaneous molding of a plurality of parts, it usually is necessary that the sprue passageways to each cavity be heated in such manner. As a result, the number of mold cavities that can be included in the equipment can be limited by space considerations. Plastic injection molding equipment in accordance with the pre-characterising portion of claim 1 is known from CH-A-625 461. It is an object of the present invention to provide a relatively compact and more efficiently operable plastic injection molding system. According to our invention, in a plastic injection molding equipment in accordance with the pre-characterising portion of claim 1, the casing has a cylindrical outer exposed surface which together with said bore define an unobstructed annular fluid plastic flow passageway about each said tip and a portion of the casing adjacent said tip and substantially along the entire length of said casing through which fluid plastic material is directed at an elevated temperature, said electrical heating means comprising a core with a resistance wire disposed thereon and heat transmitting material surrounding the wire and core said heat transmitting material being compacted in said bore about the resistance wire and core for filling all air voids therebetween and for effecting efficient direct heat transfer outwardly through said casing for heating fluid plastic material directed through said flow passageway to a desired temperature, and temperature controlling means for controlling the temperature of said heating means and thus the temperature of said tips and fluid plastic material directed through said passageway and over said tips. One embodiment of our invention is illustrated in the accompanying drawings in which: FIG. 1 is a section of a plastic injection mold embodying the present invention; FIG. 2 is an enlarged fragmentary section of the mold shown in FIG. 1 taken in the plane of line 2-2; FIG. 3 is an enlarged longitudinal section of one of the multiple tip torpedo heaters utilized in the illustrated mold; FIG. 4 is an enlarged fragmentary section taken in the plane of line 4-4 in FIG. 3; FIG. 5 is a fragmentary section taken in the plane of line 5-5 in FIG. 4; FIG. 6 is a transverse section of the mounting arrangement and lead outlet for the torpedo heater shown in FIG. 3, taken in the plane of line 6-6; FIG. 7 is a transverse section taken in the plane of line 7-7 in FIG. 6; FIG. 8 is a diagrammatic illustration of the electrical winding and lead pin arrangement of the illustrated torpedo heater; FIG. 9 is a partially diagrammatic section of a plastic injection mold arrangement according to any alternative embodiment of the invention; FIG. 10 is an enlarged longitudinal section of the multiple tip torpedo heater utilized in the mold arrangement of FIG. 9; and FIG. 11 is a diagrammatic illustration of the electrical winding and lead pin arrangement of the torpedo heater shown in FIGS. 9 and 10. Referring to FIGS. 1 and 2 of the drawings, there is shown an illustrative plastic injection molding system 10 embodying the present invention. The system 10 includes a mold 11 and conventional plastic injection means, including a nozzle 12, for injecting fluid plastic material into the mold. The mold 11 comprises a frame or base 14 for supporting a plurality of mold cavity members 15 a , 15 b and core inserts 16 a , 16 b which together define respective part cavities 18 a , 18 b in a conventional manner. As will be understood by one skilled in the art, the core inserts 16 a , 16 b each are moveable relative to the respective cavity member 15 a , 15 b to permit removal of a formed part, and an injector pin 19 (only one which is shown) is provided in each core insert to facilitate such part removal. For communicating fluid plastic from the injection nozzle 12 to the cavities 18 a , 18 b , the mold frame or base 14 is formed with a sprue passageway 20 in communication with the nozzle 12, and in this instance, feeds a plurality of transversely directed runner passageways 21, in this case four in number. For heating the fluid plastic material in the sprue passageway 20, a torpedo heater 22 of a known type is provided, and for heating the material in the runner passageways 21, a respective conventional runner torpedo heater 24 is provided. In accordance with one aspect of the invention, each runner passageway feeds a plurality of sprue passageways and mold cavity gates which are heated by a single torpedo heater in a manner that permits a more compact and economical mold design for efficient simultaneous molding of a plurality of parts. To this end, in the illustrated embodiment, each runner passageway 21 feeds fluid plastic material to a pair of sprue passageways 25 a , 25 b and mold cavity gates 26 a , 26 b which are heated by a respective unitary torpedo heater 30. Since the fluid plastic flow from each runner passageway 21 and associated unitary torpedo heater 30 are identical, only one will be described in detail. In keeping with the invention, each torpedo heater 30 has a multiplicity of ends or tips 31 a , 31 b , in this case two in number, which each are adapted for heating plastic material flowing through a respective sprue passageway 25 a , 25 b and gate 26 a , 26 b for a respective mold part cavity 18 a , 18 b . The illustrated torpedo heater 30, as best shown in FIG. 3, has a cylindrical metal casing 32 with one end or tip 31 a having an integrally formed tapered configuration disposed in concentric relation to a tapered entry 34 a (FIG. 2) from the sprue passageway 25 a to the gate 26 a . The opposite end or tip 31 b of the torpedo heater 30 is a separate member of similar tapered configuration affixed to the otherwise open end of the casing 32. In accordance with a further feature of the invention, the multiple tipped torpedo heater 30 is adapted for independent, selectively controlled heating of plastic material flowing through each sprue passageway 25 a , 25 b and gate 26 a , 26 b for enhancing the balanced flow of plastic to the plurality of part cavities 18 a , 18 b . To this end, the illustrated torpedo heater casing 32 is formed with an elongated bore 36 and contains a plurality of selectively controllable heating elements 38 a , 38 b , in this case two in number, adapted for selectively heating the molten plastic material in the respective sprue passageways or zones 25 a , 25 b . The heating element 38 a comprises a resistance wire 39 a wound on a ceramic core 40 a that is disposed in one end of the casing bore 36 and has a diameter less than the diameter of the bore. The heating element 38 b in this instance, for reasons which will become apparent, includes a pair of cores 40 b , 40 b ′ disposed in the opposite end of the casing bore 36, with each core having a respective wound resistance wire 39 b , 39 b ′. The cores 40 a , 40 b , 40 b ′ each are interposed between a relatively thin frangible spacers. In this instance, the core 40 a is interposed between an end spacer 42 and a central spacer 44, the core 40 b ′ is interposed between the central spacer 44 and an intermediate spacer 45, and the core 40 b is disposed between an intermediate spacer 46 and an end spacer 48. The heating elements 38 a , 38 b each are adapted for independent connection to an electrical source to permit their selective energization. For this purpose, the heating element 38 a has a pair of lead pins or wires 50 a , 51 a . One end of the resistance wire 39 a is connected to the lead pin 50 a adjacent one end of the core 40 a and the other end of the resistance wire 39 a is connected to the lead pin 51 a adjacent the opposite end of the core 40 a , as illustrated in FIG. 8. The heating element 38 b similarly has a pair of lead pins 50 b , 51 b which in this case extend through the cores 40 b , 40 b ′ and the spacers therebetween. One end of the resistance wire 39 b is connected to the lead pin 50 b at a point adjacent one end of the core 40 b and the opposite end of the wound resistance wire 39 b is connected to the lead pin 51 b at the opposite end of the core 40 b . The opposed ends of the resistance wire 39 b ′ are similarly connected to the lead pins 50 b , 51 b adjacent opposite ends of the core 40 b ′ such that the resistance wires 39 b , 39 b ′ are electrically connected in parallel across the lead pins 50 b , 51 b . To facilitate manufacture, the cores 40 a and 40 b ′ both are formed with four lead pin apertures, and the lead pins 50 b , 51 b , like the lead pins 50 a , 51 a extend through the core 40 a and into the end spacer 42, even through the lead pins 50 b , 51 b are not coupled to the resistance wires of the core 40 a . The lead pins 50 a , 51 a in the illustrated embodiment need only extend from the end spacer 42 into the space 55 defined between the intermediate spacers 45, 46. Alternatively, the core 40 a , like the core 40 b , need only be formed with two apertures for the respective lead pins 50 a , 51 a of that heating element, and the lead pins 50 b , 51 b can be made of shorter length so as to extend only between the spacers 48 and 44. At the location of the spacing 55, the torpedo casing 32 is formed with an aperture 56 to permit exiting of the leads from the pins 50 a , 51 a , and 50 b , 51 b for connection to an electrical source, as will become apparent. It will be appreciated that while in the illustrated embodiment the electrical resistance wires for the heating element 38 b are shown connected electrically in parallel, alternatively, the resistance wires could be connected in series. Moreover, while the illustrated torpedo heater has a pair of heating elements 38 a , 38 b , depending upon the length of the heater, alternatively greater numbers of axially aligned and independently controlled heating elements could be utilized so as to permit selective heat control at zones intermediate the opposed ends of the torpedo heater. To compensate for irregular heat drains or losses along the length of the torpedo heater 30, and thus provide a more uniform heat profile for heating fluid plastic directed through the sprue passageways 25 a , 25 b , the electrical windings 39 a , 39 b , 39 b ′, are shaded or concentrated at selected locations. In the illustrated embodiment, the windings 39 a and 39 b both are shaded, as illustrated in FIGS. 3 and 8, adjacent their respective tips 31 a , 31 b . In addition, the winding 39 b and 39 b ′ are shaded adjacent the spacing 55 to compensate for additional heat losses at such location. During manufacture of the torpedo heater 30, heat transmitting material 60, such as magnesium oxide powder or similar material, is deposited in the space between the cores 40 a , 40 b , 40 b ′ and the casing bore 36. The assembly preferably is vibrated to pack the magnesium oxide powder tightly within the casing to fill all air voids within the assembly. Means, such as an adhesive, may be provided for temporarily retaining the intermediate spacers 45, 46 in position so as to tightly retain the magnesium oxide powder within the casing. The assembly of the casing 32 and heating elements 38 a , 38 b is then swaged so as to reduce the diameter of the casing bore 36 and compress the packed magnesium oxide powder within the bore. This provides an effective heat transfer contact between the heating elements and the casing for enhancing efficient and uniform heat transfer to the casing. Following swaging, the adhesive or other means utilized for temporarily retaining the spacers 45, 46 within the casing may be removed, with the spacers 45, 46 being fixedly retained in mounted position by the resulting tight friction force. For coupling the pairs of lead pins 50 a , 51 a and 50 b , 51 b for the respective heating elements 38 a , 38 b to an electrical source, appropriate pairs of lead wires 61 a and 61 b are connected thereto. To independently control the temperature of the heating elements 38 a , 38 b , a respective thermocouple probe 62 a , 62 b is provided for each heating element. In the illustrated embodiment, a hypo tube 64 a , 64 b for each heating element is disposed adjacent the perimeter of the bore 36 of the casing and embedded in the magnesium oxide powder 60, and the respective thermocouple probes 62 a , 62 b for each heating element is housed within the hypo tubes 64 a , 64 b and extend to a predetermined point in the flow path for sensing the temperature at such point. It will be understood by one skilled in the art that power to the respective heating element may thereby be selectively controlled in a known manner. In keeping with the invention, means are provided for permitting the exit of the leads 61 a , 6l b from the torpedo heater and for supporting the torpedo heater intermediate its ends in concentric relation in the sprue passageways 25 a , 25 b so as to permit fluid plastic to be directed onto the torpedo heater at a generally central location, with the material then flowing opposite substantially equal distances along the torpedo heater to the respective part cavity 18 a , 18 b . To this end, the support means in the form of a collar 70 is provided which has an internal longitudinal aperture 71 substantially greater than the outer diameter of the torpedo heater casing 32 so as to permit the substantially uninterrupted flow of plastic along the torpedo. The collar 70 is disposed in off centered longitudinal relation to the torpedo heater 30, in this case on the left side of the heater, as viewed in FIG. 3. For concentrically supporting the torpedo within the ring, in this instance a pin 72 is welded in an aperture in the collar 70 and extends inwardly for engaging a topside of the torpedo heater, as viewed in FIG. 3. A bushing 74, also is welded in an aperture in the collar, extends inwardly for engaging and supporting an underside of the torpedo heater. The bushing 74 is formed with a central aperture 75 that communicates with the aperture 56 in the torpedo heater casing 32 to permit exiting of the leads 61 a and 61 b , as well as the leads from the thermocouples 62 a , 62 b . It will be understood that the bushing 74 may have a threaded outer end for receiving the threaded fitting of an appropriate convolute tubing through which the lead wires of the torpedo heater and thermocouples may be trained to the electrical source and control. In operation of the plastic injection molding system 10, molten plastic is directed from the nozzle 12 into the sprue passageway 20 (FIG. 2) for feeding the plurality of transversely directed runner passageways 21. Each runner passageway, in turn, feeds a plurality of sprue passageways 25 a , 25 b which can be selectively heated by the respective unitary torpedo heater 30. The flow of plastic in each sprue passageway 25 a , 25 b may be independently controlled for maintaining a balanced flow of material into the plurality of part cavities 18 a , 18 b for optimum and efficient operation of the mold. In the event adjustment in temperature in one sprue passageway is necessary, it may be accomplished without affecting the temperature or flow in the other sprue passageway. The off centered mounting of the support collar 70 for the torpedo heater further permits the introduction of the fluid plastic onto the torpedo heater at a generally central location so that the flows to the respective part cavities 18 a , 18 b are substantially the same length. Referring now to FIGS. 9-11, there is shown a plastic injection molding system 80 embodying an alternative form of the invention. The molding system 80 in this instance includes a multiple tip torpedo heater 81 disposed in the path of the flow stream to a mold cavity 82 so that the flow stream passes over the entire length of the heater 81 and is maintained at the desired, substantially uniform temperature during such travel. The molding system 80 includes a manifold plate 84 that may be externally heated in a conventional manner and is formed with a flow passageway 85. The flow passageway 85 communicates with the sprue inlet 86 of an annular head 88 that is interposed between the manifold plate 84 and a central manifold plate 89. A cavity plate 90 is disposed in adjacent relation to the manifold plate 89 and is formed with a gate 91 that communicates with the mold cavity 82 defined by the cavity plate 90 and a core insert 94. For heating the fluid plastic flow stream during its travel between the sprue inlet 86 and the gate 91 of the mold cavity 82, the multiple tip torpedo heater 81 is mounted with one tip disposed adjacent the sprue inlet 86 and the opposite tip disposed adjacent the mold cavity gate 91. The torpedo heater 81, as best shown in FIG. 10, has a cylindrical casing 95 with one end or tip 96 having an integrally formed tapered configuration disposed in concentric relation to a tapered entry from the sprue inlet 86. The opposite end or tip 98 of the torpedo heater 80 is a separate member of similar tapered configuration affixed to the otherwise open end of the casing 95 and disposed in concentric relation to a tapered entry to the gate 91. The heater casing 95 is formed with an elongated bore 99 and in this case contains heating elements 100 a , 100 b adjacent each tip for heating a respective half of the heater. The heating elements 100 a , 100 b each comprise a resistance wire 101 a , 101 b wound on a ceramic core 102 a , 102 b , which each are interposed between respective pairs of frangible spacers 104 a , 105 a and 104 b , 105 b . Heat transmitting material 106 a , 106 b , such as magnesium oxide powder, is tightly compacted in the space between the cores 102 a , 102 b and the casing bore 99 in the manner previously described. In keeping with a further aspect of the invention, the resistance wires 101 a , 101 b for the heating elements 100 a , 100 b are electrically connected in series in order to permit the utilization of heavier gauge resistance wire for particular applications, and thus enhance the reliability and life of the heater. Such series connection of the heating element resistance wires 101 a , 101 b has been found to have particular advantage in relatively smaller size torpedo heaters which would otherwise require relatively fine gauge wire in order to achieve the desired resistive requirements, particularly when connected to a 240 volt electrical power source. To facilitate the series connection of the heating element resistance wires 101 a , 101 b , a lead pin 115 is provided which extends substantially the length of the casing bore 99 through the cores 104 a , l04 b of both heating elements. A second lead pin 116 a extends through the core 104 a of the heating element 100 a with one end thereof extending into a space 118 between the heating elements, and a third lead pin 116 b extends through the core 104 b of the other heating element 100 b with one end thereof similarly extending into the space 118 between the heating elements. As best illustrated in FIG. 11, the resistance wire 101 a for the heating element 100 a has one end connected to the lead pin 115 and its other end connected to the lead pin 116 a . The resistance wire 101 b for the heating element 100 b has one end connected to the lead pin 115 which is common to the heating element 100 a and its other end connected to the lead pin 116 b . The lead pins 116 a and 116 b in turn are connected to a power source through lead wires 119 a , 119 b , with the result that the current flows in series through the resistive wires 101 a , 101 b of the heating elements. A thermal couple probe 120 is provided for sensing the temperature at one of the tips to permit proper control of the operating temperature of the heating elements. The lead wires 119 a , 119 a and thermal couple 120 exit through an opening 121 in the casing 95 and centrally through a bushing 122 of a support collar 124 in a manner similar to that previously described, except that in this instance the opening 121 and bushing 122 are located at a central location along the length of the torpedo heater. It will be understood that the ends of the collar 124 are maintained in sealed relation between the annular head 88 and cavity plate 90 between which it is disposed. In operation of the mold system 80, the melt stream is directed over the entire length of the torpedo heater 81 between the sprue inlet 86 and mold cavity gate 91. By appropriately shading the windings of the heating elements 100 a , 100 b , as previously described, a substantially uniform heat profile may be generated along each heating element. Since the heating elements 100 a , 100 b in this case are substantially identical, as the melt stream passes over the length of the torpedo heater it may be maintained at the desired uniform temperature with a high degree of accuracy and efficiency. From the foregoing, it will be appreciated by one skilled in the art that the present invention provides a relatively compact and efficiently operable plastic injection molding system. The system further permits more efficient space utilization, by permitting single runner passageways to each communicate with plurality of sprue passageways, which in turn can be heated by multiple tip torpedo heaters. The multiple tip torpedo heater furthermore has a relatively compact and economical design which lends itself to easy and versatile installation and efficient operation.

Claims: A plastic injection molding system (10) comprising means (11) defining a generally cylindrical bore (25 a ) with tapered opposite ends (34 a ) communicating with respective relatively small diameter gates (26 a ) through which fluid plastic material is directed, means (11) defining a mold cavity (18 a ) in communication with at least one of said gates (26 a ), a torpedo heater means (30) comprising an elongated metal casing (32) having a tapered tip (31 a , 31 b ) at opposite ends thereof, supporting means (70) supporting said heater means (30) concentrically in said bore (25a) with said tips (31 a , 31 b ) each in closely adjacent relation to one of said gates (26 a , 26 b ), said casing (32) being formed with an internal bore (36) extending to a location adjacent each said tip (31 a , 31 b ), electrical heating means (38 a , 38 b ) disposed in said bore adjacent of each said tip (31 a , 31 b ), means (61 a , 61 b ) exiting said casing intermediate the ends thereof for electrically coupling said heating means (38 a , 38 b ) to a power source for enabling heating of said heating means (38 a , 38 b ), characterised in that said casing (32) has a cylindrical outer exposed surface which together with said bore (25 a ) define an unobstructed annular fluid plastic flow passageway about each said tip (31 a , 31 b ) and a portion of the casing (32) adjacent said tip (31 a , 31 b ) and substantially along the entire length of said casing (32) through which fluid plastic material is directed at an elevated temperature, said electrical heating means (38 a , 38 b ) comprising a core (40 a , 40 b ) with a resistance wire (39 a , 39 b ) disposed thereon and heat transmitting material surrounding the wire (39 a , 39 b ) and core (40 a , 40 b ), said heat transmitting material (60) being compacted in said bore (36) about the resistance wire (39 a , 39 b ) and core (40 a , 40 b ) for filling all air voids therebetween and for effecting efficient direct heat transfer outwardly through said casing (32) for heating fluid plastic material directed through said flow passageway to a desired temperature, and temperature controlling means (50 a , 51 a , 50 b , 51 b , 61 a , 61 b , 62 a , 62 b ) for controlling the temperature of said heating means (38 a , 38 b ) and thus the temperature of said tips (31 a , 31 b ) and fluid plastic material directed through said passageway and over said tips. The plastic injection molding system of claim 1 in which said electrical coupling means (61 a , 61 b ) and said temperature controlling means (50 a , 51 a , 50 b , 51 b , 61 a , 61 b , 62 a , 62 b ) is operable for independently controlling the temperature of each said heating element (38 a , 38 b ). The plastic injection molding system of claim 1 or claim 2 in which said electrical heating means (38 a , 39 b ) includes an individual electrical heating element (38 a , 38 b ) disposed in said bore (36) adjacent each said tip (31 a , 31 b ). The plastic injection molding system of claim 3 in which each said heating element (38 a , 38 b ) includes a respective elongated insulating core (40 a , 40 b ) and an associated resistance wire (39 a , 39 b ) assembled therein. The plastic injection molding system of claim 4 in which said electrical coupling means (61 a , 61 b ) includes a pair of lead pins (50 a , 50 b , 51 b ) extending through the core (40 a , 40 b ) of each heating element (38 a , 38 b ) with the resistance wire (39 a , 39 b ) of each heating element (38 a , 38 b ) being coupled between the lead pins (50 a , 51 a , and 50 b ) for the respective core (40 a , 40 b ), and said coupling means (61 a , 61 b ) connects pairs of said lead pins (50 a , 51 a , 50 b , 51 b ) for each heating element (38 a , 38 b ) to a power source. The plastic injection molding system of any of claims 4 or 5, wherein said temperature controlling means includes a thermocouple (62 a , 62 b ) associated with each heating element (38 a , 38 b ), each said thermocouple (62 a , 62 b ) extending into the casing bore (36) to a predetermined temperature sensing point. The plastic injection molding system of claim 5 in which one heating element (38 b ) comprises a pair of axially spaced insulating cores (40 b , 40 b ') which each have an associated resistance wire (39 b , 39 b '), said resistance wires (39 b , 39 b ') for said axially spaced cores (40 b , 40 b ') both being coupled between the lead pins (50 b , 51 b ) for each said one heating element (38 b ). The plastic injection molding system of claim 7 in which said casing (32) is formed with an aperture (56) adjacent the spacing between said axially spaced cores (40 b , 40 b '), the lead pins (50 a , 50 b 51 b ) for each heating element (38 a , 38 b ) extending to a location adjacent said casing aperture (56), and said electrical coupling means (61 a , 61 b ) extends through said casing aperture (56) for connecting said lead pins (50 a 50 b , 51 b ), to said power source. The plastic injection molding system of any of claims 4-8 in which the resistance wire (39 a , 39 b ) of at least one of the heating elements (38 a , 38 b ) is shaded at a predetermined location. The plastic injection molding system of claim 9 in which resistance wires (39 a , 39 b ) for the heating elements (38 a , 38 b ) are shaded at locations immediately adjacent the ends of each tip (31 a , 31 b ). The plastic injection molding system of any of claims 7-10 in which the resistance wires (39 b , 39 b ') for said axially spaced cores (40 b , 40 b ') are shaded at locations immediately adjacent the spacing between the cores (40 b , 40 b '). The plastic injection molding system of any preceding claim in which said supporting means comprises a collar (70) having an aperture (71) substantially greater than the diameter of said casing (32) for receiving said casing (32) while permitting fluid material flow between said casing (32) and collar (70), and retaining means (72), (74) for holding said casing (32) concentrically within said collar (70).

Inventors: LEVERENZ, DAVID
Applicants: FAST HEAT ELEMENT
Application year: 1987
Main classification: B29C45
IPC codes: B29C45, H05B3