INJECTION MOLDING SYSTEM WITH NOZZLE IN TANDEM

Abstract: This invention relates to an injection molding system having two heated nozzles mounted in tandem. The rearward nozzle (12) is considerably longer than the forward nozzle (10) and has a melt bore (90) which is considerably larger in diameter than the melt bore (44) of the forward nozzle. The smaller forward nozzle (10) has a backplate (74) secured to its rear end (48) with a thin flanged portion (76) which extends outwardly and rearwardly into bearing contact against a rearward mold core (16) to secure the forward nozzle (10) in position in a well (22) in a forward mold core (14). The rear face (84) of the backplate (74) has a seat (82) extending around the melt bore (80) to receive a cylindrical forward portion (106) of a gate insert (100) mounted on the forward end (96) of the rearward nozzle (12). Thus thermal expansion of the larger rearward nozzle (12) is taken up by the forward portion (106) of the gate insert (100) sliding in the seat (82). The smaller forward nozzle (10) has a portion (56) of the electrical heating element (52) extending into a forwardly extending nose portion (24) which provides sensitive temperature control in the gate (34) area.

Description: This invention relates generally to injection molding and more particularly to a hot tip gated, sprue gated or edge gated injection molding system comprising at least one nozzle to transfer pressurized melt into a mold cavity. The use of an elongated nozzle having an integral electrical heater for hot tip gating is well known in the art. Examples are shown in Gellert's US patent numbers 4,238,671 which issued December 9, 1980 and 4,557,685 which issued December 10, 1985. More recent examples are shown in Gellert's Canadian patents CA 1,267,514 and CA 1,261,573. While these earlier systems are completely satisfactory for many applications, in some situations where it is desirable to have a relatively lengthy melt bore leading to the cavity, misalignment at the gate due to thermal expansion and contraction has been found to be a problem. Furthermore when molding thin walled parts with a relatively short cycle time, sensitive temperature control in the gate area is critical. Also, if a single nozzle is used with a long small diameter melt bore, due to rapid flow drops of melt pressure and shear stress become unacceptably high. According to the present invention the above objective is acquired by means of an injection molding system comprising at least one nozzle for injecting pressurized melt into a mold cavity, a forward first elongate heated nozzle adjacent to a gate leading to the cavity and rearward second elongate heated nozzle mounted aligned in tandem with said first forward nozzle and a seat structure in between both nozzles providing for sufficient relative axial movement therebetween to provide for thermal expansion or contraction of the rearward nozzle wherein a continuous straight melt passage extends from the rearwards second nozzle to the forward first nozzle. According to a preferred embodiment of the present invention a hot tip gated injection molding system is provided comprising; a forward first elongate heated nozzle seated in a well in a forward mold core with a rear end and a forward end adjacent a gate extending from the well to a cavity, the first nozzle having a melt bore extending from an inlet at the rear end to a space surrounding the forward end leading to the gate, a backplate with a rear face having a seat therein concentrically aligned with a melt bore extending through the backplate, the backplate being mounted on the rear end of the first nozzle with the bore extending in axial alignment with the inlet to the first nozzle, the backplate having a portion which extends rearwardly into bearing contact with an upper mold core to hold the backplate and the first nozzle securely in place, a rearward second elongated heated nozzle which is substantially longer than the first nozzle seated in a well in a rearward mold core with a rear end, a forward end, and a central melt bore extending therethrough from an inlet at the rear end to the forward end, the bore being in axial alignment with the bore through the backplate and the inlet to the melt bore through the first nozzle, the forward end of the rearward nozzle having a forwardly projecting portion which is received in the seat in the rear face of the backplate to allow sliding axial movement therebetween to provide for thermal expansion and contraction of the rearward nozzle. Preferred other embodiments of the present invention are laid down in the further subclaims. Further objects and advantages of the invention will appear from the following description, taken together with the accompanying drawing. Figure 1 is a sectional view of a portion of an injection molding system showing two elongated heated nozzles mounted in tandem according to a preferred embodiment of the invention. Reference is made to Figure 1 which shows one application of a preferred embodiment of the invention. In this case, a forward nozzle 10 and a rearward nozzle 12 are mounted in tandem in a forward mold core 14 and a rearward mold core 16 to provide a system to fill a cavity 18 to form a plastic top attached to the surrounding sidewalls 20 of a container. Of course, in other applications of the system, the forward and rearward mold cores 14,16 can be replaced by forward and rearward mold plates, but the concept remains the same. As can be seen, the forward nozzle 10 is seated in a well 22 in the forward mold core 14, and in this embodiment has a nose portion 24 with a tapered outer surface 26 which leads to a pointed tip 28. This nozzle 10 is described in detail in the applicant's Canadian patent 1 261 573. It has a circumferential insulation flange 30 which sits on a circumferential shoulder 32 to locate it in the well 22 with the pointed tip 28 adjacent a gate 34 leading to the cavity 18 with an insulative airspace 36 between it and the surrounding forward mold core 14 which is cooled by cooling water flowing through cooling conduits 38. The forward nozzle 10 is also located in the well 22 by a sealing and locating flange 40 which extends circumferentially adjacent the nose portion 24. As described in detail in Gellert's Canadian patent application serial number 549,519 filed October 16, 1987 entitled "Injection Molding Nozzle with Resilient Sealing and Locating Flange", said flange accurately locates the pointed tip 28 in central axial alignment with the gate 34 and prevents leakage of pressurized melt from the space 42 surrounding the nose portion 24. The forward nozzle 10 has a melt bore 44 which extends centrally from an inlet 46 at the rear end 48 of the nozzle 10 to a diagonal portion 50 which connects to the tapered surface 26 of the nose portion 24. The forward nozzle 10 is heated by an electric heating element 52 which is integrally brazed in as described in Gellert's Canadian patent application serial number 549, 517 entitled "Method of Manufacture of Injection Molding Nozzle Having Grounded Heating Element Brazed into Pointed Tip" filed October 16, 1987. The heating element 52 has a helical portion 54 which extends around the melt bore 44 and a longitudinal portion 56 which extends centrally in the nose portion 24. In this embodiment, the heating element 52 is suitable for low voltage such as 24 volts and has a single resistance wire which is grounded at the forward end 58 by being brazed in a nickel alloy adjacent an air-hard tool steel insert portion 60 which forms the pointed tip 28. The heating element 52 has a rear end 62 which extends radially outward through a collar portion 64 of the nozzle and is connected to a threaded stud 66. The larger diameter stud 66 is surrounded by ceramic insulation 68 inside a cylindrical sleeve 70 to form a cold terminal 72, as described in detail in the applicant's Canadian patent application serial number 549,520 filed October 16, 1987 entitled "Method of Manufacture of Injection Molding Nozzle Electrical Terminal." The cold terminal 72 receives a lead from an external power supply from which current flowing through to the ground at the forward end 58 heats the nozzle 10 and particularly the pointed tip 28 to a predetermined temperature. Of course, for certain applications, the longitudinal portion 56 of the heating element 52 extending through the nose portion 24 can have part with a multiple thickness of additional heat if required, as described in the applicant's Canadian patent application serial number 563,981 filed April 13, 1988 entitled "Injection Molding Nozzle Having Multiple Thickness Heating Element and Method of Manufacture." A steel backplate 74 is located against the rear end 48 of the forward nozzle 10 and has a relatively thin flanged portion 76 which extends outwardly and rearwardly across an insulative air space 78 and bears against the rearward mold core 16. Thus, as described in detail in Gellert's Canadian patent application serial number 557,681 filed January 29, 1988 entitled "Improved Mounting for Injection Molding Nozzle", the flanged portion 76 of the backplate 74 bearing against the rearward mold core 16 holds the backplate and the forward nozzle 10 in place without extensive heat loss to the mold core. The backplate 74 has a central melt bore 80 extending therethrough which is equal in diameter to and axially aligned with the inlet 46 to the melt bore 44 through the forward nozzle 10. The backplate 74 also has a cylindrical seat 82 in its rear face 84 which is concentrically aligned with the central melt bore 80. The rearward nozzle 12 is similarly seated in a well 86 in the rearward mold core 16 with an insulative air space 88 between them. However, the rearward nozzle 12 is normally several times longer than the forward nozzle 10 and has a central melt bore 90 which is considerably large in diameter than the melt bore 80 through the backplate 74 and the melt bore 44 through the forward nozzle 10. As can be seen, the central melt bore 90 extends from an inlet 92 at the rear end 94 to the forward end 96 in axial alignment with the bore 80 through the backplate 74 and the inlet 46 to the melt bore 44 through the forward nozzle 10. In this embodiment, the bore 90 has a threaded mouth 98 at the forward end 96 which receives a removable gate insert 100. The gate insert 100 is similar to those shown in the applicant's Canadian patent application serial numbers 529,897 filed February 17, 1987, and Gellert's Canadian patent application serial number 532,677 filed March 20, 1987 and 549,516 filed October 16, 1987. A gate insert having a separate electrical heating element is shown in Gellert's Canadian patent application serial number 559,000 filed February 16, 1988 entitled "Injection Molding Heated Gate Insert and Method". The gate insert 100 is made of steel with an intermediate portion 102 between a threaded cylindrical rear portion 104 and a cylindrical forward portion 106. The cylindrical forward portion 106 is made to fit in the cylindrical seat 82 in the rear face 84 of the backplate 74. The intermediate portion 102 has a hexagonal surface 108 which can be engaged by a wrench to tighten it into place. The gate insert 100 has a central melt bore 110 which extends therethrough in axial alignment between the melt bore 90 of the rearward nozzle 12 and the melt bore 80 through the backplate 74. As can be seen, the melt bore 110 through the gate insert 100 is tapered to smoothly reduce the melt bore diameter from that of the rearward nozzle 12 to that of the forward nozzle 10. While the rearward nozzle 12 is shown with the removable gate insert 100, it can merely have a cylindrical projecting portion in place of the gate insert 100, similar to that shown in Gellert's U.S. patent number 4,579,520 which issued April 1, 1986. Alternatively, a hollow nozzle seal can be used to extend between the forward end 96 of the rearward nozzle 12 and the seat 82 in the rear face 84 of the backplate 74. The nozzle seal has a rear portion which is seated in the forward end 96 of the nozzle 12 and a forward nose portion which is received in the seat 82 similar to that shown in Gellert's U.S. patent number 4,286,941 which issued September 1, 1980. In any event, the rearward nozzle 12 is located in the well 86 in the rearward mold core 16 by an insulation flange 112 seated on a circumferential shoulder 114 in a position wherein the forward end 96 of the gate insert 100 (or equivalent in an alternate arrangement) slides in the seat 82 in the rear face 84 of the backplate 74. The rearward nozzle 12 also has an integral electrical heating element 116 and can be made, for instance, by the methods disclosed in Gellert's U.S. patent number 4,403,405 which issued September 13, 1983 or Gellert's Canadian patent application serial number 532,677 filed March 20, 1987 entitled "Injection Molding Nozzle and Method" The heating element 116 has a helical portion 118 which extends around the central melt bore 90 and a rear end 120 which extends radially outward to a pair of cold terminals 122 which receives electrical power from external leads (not shown). In this embodiment, the heating element 116 is of the double resistance wire type and suitable for relatively high voltage such as 115 volts or 240 volts. The rearward nozzle 12 is held securely in position by a backplate 124 having an outwardly and rearwardly flanged portion 126 which abuts against a collar 128 which is bolted to the mold. The backplate 124 is secured by bolts 130 to the rear end 94 of the rearward nozzle 12 and has a central melt bore 132 which receives pressurized melt from the nozzle 134 of a molding machine and conveys it to the inlet 92 of the rearward nozzle 12. Alternate structure can be provided to hold the rearward nozzle 12 in place in the well 86. While a single cavity system has been shown in this embodiment, of course a manifold can be used to distribute the melt in a multi-cavity system as well. In use, after the injection molding system has been assembled as shown and described above, electrical power is applied to the heating elements 52 and 116 to heat both nozzles 10 and 12 to a predetermined operating temperature. When the longer rearward nozzle 12 heats up, the forward portion 106 of the gate insert 100 slides in the seat 82 to narrow or eliminate the gap between them. As the rearward nozzle 12 is considerably longer than the forward nozzle 10 it will be appreciated that this takes up the thermal expansion of the rearward nozzle 12 in the seat 82 substantially reduces movement of the pointed tip 28 of the forward nozzle 10 due to thermal expansion and contraction which can otherwise result in the pointed tip 28 being out of position in the gate 34. Of course, if the pointed tip 28 is not accurately located relative to the gate 34, the gate will become too hot or too cold or heat distribution will be unequal and malfunction will quickly occur. The alignment of the forward and rearward nozzles 10,12 provides a continuous straight melt passage 138 from the nozzle 134 of the molding machine through the backplate 124, the rearward nozzle 12, the gate insert 100 and the backplate 74 to the forward nozzle 10. Pressurized melt is introduced from the molding machine nozzle 134 and flows through the melt passage 138 to the space 42 surrounding the nose portion 24 of the forward nozzle and from there through the gate 34 to fill the cavity 18. As described above the diameter of the melt bore 90 of the rearward nozzle 16 is considerably larger in diameter than the melt bore 44 of the forward nozzle 10. As the rearward nozzle is considerably longer, this substantially reduces pressure drop and shear stress, as the melt flow through the system The space 42 remains filled with melt, a portion of which solidifies adjacent the cooled forward mold core 14 and the sealing and locating flange 40, preventing it escaping into the insulative air space 36. After the cavity 34 is filled, injection pressure is held momentarily to pack and then released. After a short cooling period, the mold is opened to eject the container. After ejection, the mold is closed and injection pressure is reapplied to fill the cavity 34. This cycle is repeated continuously with a frequency dependent on the size and shape of the cavity and the type of material being molded. The small size of the forward nozzle 10 and the longitudinal portion 56 of the heating element 52 extending into the nose portion provide relatively sensitive temperature control in the gate area which is critical to superior performance with some materials. While the description of this system and its use have been given with respect to a preferred embodiment, it is not to be construed in a limiting sense. Variations and modifications will occur to those skilled in the art. For instance, while the smaller forward nozzle 10 is shown having a nose portion 24 with a pointed tip 28 for hot tip gating, it can have a configuration to provided edge gating or sprue gating. Reference is made to the appended claims for a definition of the invention.

Claims: An injection molding system comprising at least one nozzle for injecting pressurized melt into a mold cavity, characterized by a forward first elongate heated nozzle (10) adjacent to a gate (34) leading to the cavity (18) and rearward second elongate heated nozzle (12) mounted aligned in tandem with said first forward nozzle (10) and a seat structure (74) in between both nozzles (10, 12) providing for sufficient relative axial movement therebetween to provide for thermal expansion or contraction of the rearward nozzle (12) wherein a continuous straight melt passage (138) extends from the rearward second nozzle (12) to the forward first nozzle (10). An injection molding system as claimed in claim 1, characterized by (a) said forward first elongate heated nozzle (10) having a rear end (48) and a forward end seated in a well (22) in a forward mold core (14), said first nozzle (10) is disposed adjacent the gate (34) extending from the well (22) to the cavity (18), the first nozzle (10) having a first melt bore (44) extending from an inlet (46) at the rear end (48) to a space (42) surrounding the forward end leading to the gate (34), (b) a backplate (74) with a rear face (84) having a seat (82) therein, said seat (82) concentrically aligned with a second melt bore (80) extending through the backplate (74), the backplate (74) being mounted on the rear end (48) of the first nozzle (10) with the second melt bore (80) extending in axial alignment with the inlet (46) to the first nozzle (10), the backplate (74) having a portion (76) which extends rearwardly into baring contact with a rearward mold core (16), said rearward mold core (16) holding the backplate (74) and the first nozzle (10) securely in place, (c) said rearward second elongate heated nozzle (12) having a rear end (94), a forward end (96) and a central third melt bore (90), said second nozzle (12) heing substantially longer than the first nozzle (10) and heing seated in a well (86) in a rearward mold core (16) said central third melt bore (90) extending through said second nozzle (12) from an inlet (92) at the rear end (94) of said second nozzle (12) to the forward end (96) of said second nozzle (12), the third melt bore (90) being in axial alignment with the second melt bore (80) through the backplate (74) and the inlet (46) to the first melt bore (44) through the first nozzle (10), the forward end (96) of the rearward nozzle (12) having a forwardly projecting portion which is received in the seat (82) in the rear face (84) of the backplate (74) to allow sliding axial movement between said forwardly projecting portion and said seat (82) to provide for thermal expansion and contraction of the rearward nozzle (12). An injection molding system as claimed in claims 1 or 2, characterized in that the forward nozzle (10) has a nose portion (24) at the forward end with a portion (58) of an electrical heating element (52) integrally brazed into the nose portion (24). An injection molding system as claimed in claim 3, characterized in that the nose portion (24) extends to a pointed tip (28) which is adjacent to and in central axial alignment with the gate (34) to provide a hot tip gated system. An injection molding system as claimed in at least one of the preceding claims 2 to 4, characterized in that the forwardly projecting portion of the forward end (96) of the rearward nozzle (12) is provided by a gate insert (100), said gate insert (100) having a threaded cylindrical rear portion (104) which is screwed into the forward end (96) of the rearward nozzle (12), a cylindrical forward portion (106) which is received in the seat (82) in the rear face (84) of the backplate (74), and a central fourth melt bore (110) extending through said gate insert (100) in axial alignment between the third melt bore (90) through the rearward nozzle (12) and the second melt bore (80) through the backplate (74). An injection molding system as claimed in at least one of the preceding claims 2 to 4, characterized in that the forwardly projecting portion (106) of the forward end (96) of the rearward nozzle (12) is provided by a nozzle seal, said nozzle seal having a rear portion which is seated in the forward end (96) of the rearward nozzle (12), a forward nose portion which is received in the seat (82) in the rear face (84) of the backplate (74), and a central fourth melt bore (110) extending through said nozzle seal in axial alignment between the third melt bore (90) through the rearward nozzle (12) and the second melt bore (80) through the backplate (74). An injection molding system as claimed in at least one of the preceding claims 2 to 6, characterized in that the rearwardly extending portion of the backplate (74) is a thin flanged portion (76) which extends outwardly and rearwardly into bearing contact against the upper mold core (14). An injection molding system as claimed in at least one of the preceding claims 2 to 7, characterized in that the third melt bore (90) through the rearward nozzle (12) is larger in diameter than the first melt bore (44) through the forward nozzle (10). An injection molding system as claimed in at least one of the preceding claims 1 to 8, characterized in that the rearward nozzle (12) has a high voltage integral electrical heating element (116) and the forward nozzle (10) has a low voltage integral electrical heating element (52).

Inventors: MCENROE, MICHAEL C., SCHMIDT, HARALD HANS
Applicants: MOLD-MASTERS LIMITED
Application year: 1989
Main classification: B29C45
IPC codes: B29C45