Mold gate insert with a thermal barrier

This application claims the benefit of U.S. Provisional Application No. 60/371,711, filed on Apr. 12, 2002.

The present invention relates generally to an injection molding apparatus, and in particular to mold gate insert for providing a thermal barrier between a mold gate and a nozzle tip.

In an injection molding apparatus, a manifold receives a pressurized melt stream of a moldable material from a machine nozzle. The manifold distributes the melt stream to a plurality of hot runner nozzles. Melt is injected from each nozzle through a mold gate and into a mold cavity where the melt is cooled to its “freezing” temperature, and then ejected from the mold cavity. The cycle is repeated so that multiple molded products may be produced.

The number of molded products that are output over a set time period is limited by the cycle time of the injection molding apparatus. The cycle time is determined by several factors, including the physical and chemical attributes of the resin, the size of the molded product, and the time required for the product to cool in the mold before it is ejected.

Reducing the cooling time of the molded product will reduce the overall cycle time. However, undesirable physical defects often result from attempts to reduce the cooling time, particularly in products, such as preforms, made from polyethylene teraphthalate (PET). The most common of these undesirable characteristics are gate defects that occur in that portion of the preform in the vicinity of the gate. These common defects include crystalline halos and plugs, gate voids, internal dimples, scarred gates, and sticky or stringy gates. Many variables affect the quality of the gate area in a finished preform. Processing parameters, such as mold gate timing, nozzle tip temperature, and the flow rate of cooling fluid can all be adjusted to improve preform quality. However, insufficiently rapid heat transfer at the gate area remains one of the most persistent difficulties to overcome, and a continuing obstacle to greatly improved cycle times.

In a hot runner injection molding system with valve gating, the mold gate area is typically not cooled sufficiently. The mold gate is typically a tapered hole that is formed in a gate insert. A valve pin engages the mold gate to close the gate and prevent melt from flowing into the mold cavity. Because the mold gate is located between the high temperature nozzle tip and the mold cavity, heat is often undesirably transferred through the gate insert to the mold cavity. At the same time, the mold cavity quickly cycles between a high temperature when the gate is open to a low temperature sufficient to freeze the resin when the mold has been filled and the gate closed. The valve pin itself also transfers heat to the mold gate when the mold gate is closed. In order to lower the cycle time of the injection molding apparatus, it is desirable to thermally isolate the mold cavity from the nozzle tip.

Several prior art references disclose thermal shielding at the nozzle tip to limit cooling of the hot runner nozzle tip in the vicinity of the mold gate area.

U.S. Pat. No. 6,220,850 discloses a mold gate insert that is formed of two pieces. A first portion of the insert forms a gate land and is made of an insulating material to thermally shield the nozzle. The second portion of the insert forms a section of the mold cavity and is made of a highly thermally conductive material. During the cooling phase of the injection cycle, the second portion provides rapid dissipation of heat to cool the mold cavity, while the first portion creates a thermal barrier to shield the nozzle tip from the cooling of the second portion.

U.S. Pat. No. 5,879,727 discloses a thermal insulating element provided between a nozzle tip and a mold insert. The thermal insulating element limits the heat loss from the nozzle tip to the gate insert.

U.S. Pat. No. 5,554,395 discloses a seal that is provided between a bushing, which delivers a melt stream to a mold cavity, and a mold, which houses the mold cavity. The seal closes off the gap between the bushing and the mold and limits the conduction of heat therebetween.

Some of the disadvantages of prior art tip insulation include insufficient thermal sealing of the nozzle tip in cases where the mold insert form part of the mold cavity. In additional, prior art insulating devices are often complex to manufacture, particularly when more than one material is used.

It is therefore an object of the present invention to provide a mold gate insert having a thermal barrier, which obviates or mitigates the above disadvantages.

According to an aspect of the present invention there is provided an injection molding apparatus comprising:

a manifold having a manifold channel for receiving a melt stream of moldable material under pressure; a nozzle having a nozzle tip and a nozzle channel, the nozzle channel being in communication with the manifold channel for receiving the melt stream from the manifold channel; a seal coupled to the nozzle tip, the seal having an outer surface; a mold gate insert surrounding the nozzle tip, the mold gate insert including a mold gate to allow melt to travel from the nozzle channel into a mold cavity; a flange extending from an inner surface of the mold gate insert, a surface of the flange being in abutment with an outer surface of the seal; a groove provided in the mold gate insert, the groove being located adjacent the flange; and wherein the groove decreases the amount of heat that is transferred to the mold gate insert through the flange.

According to another aspect of the present invention there is provided an injection molding apparatus comprising:

a manifold having a manifold channel for receiving a melt stream of moldable material under pressure; a nozzle having a nozzle tip and a nozzle channel, the nozzle channel being in communication with the manifold channel for receiving the melt stream from the manifold channel; a seal coupled to the nozzle tip, the seal having an outer surface; a mold gate insert surrounding the nozzle tip, the mold gate insert including an inner surface for abutting the outer surface of the seal and a groove that is spaced from the inner surface; a mold gate provided in the mold gate insert to allow melt to flow from the nozzle channel into a mold cavity; and

wherein the groove decreases the amount of heat that is transferred to the mold gate insert through the flange.

According to another aspect of the present invention there is provided an injection molding apparatus comprising:

a manifold having a manifold channel for receiving a melt stream of moldable material under pressure; an injection nozzle having a nozzle body and a nozzle tip, the nozzle tip being surrounded by a nozzle seal, the injection nozzle having a nozzle channel for receiving a melt stream of moldable material from the manifold channel; a mold gate insert having a first portion and a second portion, the second portion being nested in the first portion and spaced from a mold gate to align the nozzle seal within the mold gate insert, the second portion being comprised of a thermally insulating material; a mold gate provided in the mold gate insert to allow melt to flow from the nozzle channel into a mold cavity; and wherein the second portion provides insulation between the first portion of the mold gate and the nozzle seal.

According to yet another aspect of the present invention there is provided a mold gate insert comprising:

a mold gate insert body comprised of a material having a high thermal conductivity; a mold gate provided in the mold gate insert body for allowing a melt stream to flow into a mold cavity; and

a thermal insulation element nested in the mold gate insert body, the thermal insulation element for abutting a nozzle seal of a nozzle to align the nozzle with the mold gate.

According to another aspect of the present invention there is provided an injection molding apparatus comprising:

a manifold having a manifold channel for receiving a melt stream of moldable material under pressure; an injection nozzle having a nozzle body and a nozzle tip, the nozzle tip being surrounded by a nozzle seal, the injection nozzle having a nozzle channel for receiving a melt stream of moldable material from the manifold channel; a mold gate insert having a thermal insulation element nested in a mold gate insert body, the mold gate insert having a nozzle seal alignment surface for abutting an outer surface of the nozzle seal; a mold gate provided in the mold gate insert to allow melt to flow from the nozzle channel into a mold cavity;

wherein the thermal insulation element provides insulation between the mold gate insert body and the nozzle seal.

The present invention provides an advantage in that the thermal insulation element reduces the amount of heat transferred from the nozzle to the mold gate insert. The present invention provides a further advantage in that the seal is aligned within the mold gate insert.

Embodiments of the present invention will now be described more fully with reference to the accompanying drawings in which:

FIG. 1 is a side sectional view of an injection molding apparatus of the present invention;

FIG. 2 is a side sectional view of portions of an injection molding apparatus of the present invention;

FIG. 3 is an enlarged view of portions of FIG. 2 ;

FIG. 4 is a side sectional view of a mold gate insert of the present invention;

FIG. 5 is a side sectional view of a further embodiment of an injection molding apparatus of the present invention;

FIG. 6 is an enlarged view of portions of FIG. 5 ;

FIG. 7 is a further embodiment of a mold gate insert of the present invention;

FIG. 8 is a side sectional view of two further embodiments of a mold gate insert of the present invention;

FIG. 9 is a side sectional view of a further embodiment of a mold gate insert of the present invention;

FIG. 10 is a side sectional view of yet a further embodiment of a mold gate insert of the present invention;

FIG. 11 is an enlarged view of the mold gate insert of FIG. 10 ;

FIG. 12 is side sectional view of still a further embodiment of a mold gate insert of the present invention; and

FIGS. 13(i) and (ii) are both side sectional views of a nozzle with a mold gate insert of the present invention.

Referring to FIGS. 1 and 2 , portions of a hot runner injection molding apparatus are generally shown at 10 . The injection molding apparatus 10 comprises a manifold 12 having a manifold melt channel 14 for receiving a melt stream of moldable material under pressure from a manifold bushing 16 . Manifold 12 is positioned between a back plate (not shown) and a mold plate 33 , such that manifold bushing 16 extends through the back plate and is in communication with a machine nozzle of an injection molding machine (not shown). Nozzle bores 19 are formed within mold plate 33 and a mold cavity plate 31 for receiving a respective hot runner nozzle 18 .

Nozzles 18 are coupled to respective outlets 20 of the manifold 12 and are positioned within nozzle bores 19 such that an insulative air space 41 is provided between nozzles 18 and nozzle bore 19 . A nozzle channel 22 extends through each nozzle 18 for receiving the melt stream of moldable material from the manifold 12 . Each nozzle 18 includes a nozzle body 29 and a nozzle tip 30 . Manifold heaters 39 and nozzle heaters 38 heat the manifold 12 and nozzles 18 respectively in order to maintain the melt stream at a high temperature. A mold gate 26 is provided in a mold gate insert 24 , which generally surrounds the tip 30 of each nozzle 18 . The mold gates 26 are openable to allow delivery of the melt stream to respective mold cavities 32 that are respectively formed between mold cavity plate 31 and movable mold cores 35 . A valve pin 34 extends through the length of each nozzle 18 and is movable by a valve piston 36 to open and close the mold gate 26 .

Cooling channels 40 are provided within mold cavity plate 31 adjacent the mold gate inserts 24 and the mold cavities 32 in order to facilitate cooling of the melt in the mold cavities 32 . The mold gate insert 24 is typically comprised of a highly thermally conductive material such as copper, for example. The high thermal conductivity of the mold gate insert 24 allows the mold gate 26 to be cooled rapidly so as to freeze the melt in the mold gate area. This minimizes the occurrence of drooling from the nozzle 18 . An insulation chamber 42 between mold gate insert 24 and nozzle 18 minimizes the heat transfer between the mold gate insert 24 and the nozzle 18 . The insulation chamber 42 is typically filled with air.

A seal 28 is provided between the nozzle 18 and mold gate insert 24 . The seal 28 is comprised of a thermally insulating material, such as steel or titanium, for example. The seal 28 restricts the back flow of melt so that the melt does not enter the insulation chamber 42 . In addition, the seal 28 acts to minimize the heat transfer between the mold gate insert 24 and the nozzle tip 30 .

As shown in FIGS. 2 and 3 , the lower end of the seal 28 abuts a mating surface 56 of a flange 46 , which projects from an inner wall 48 of the mold gate insert 24 . The flange 46 locates the seal 28 in the mold gate insert 24 so that the nozzle 18 is properly aligned with the mold gate 26 . A bubble area 60 is located between the seal 28 , mold gate 26 and the nozzle tip 30 . The bubble 60 is filled with melt, which becomes solid when the mold gate 26 is frozen. A water cooling cavity 52 surrounds the mold gate insert 24 to facilitate freezing thereof. Seals 54 are employed to prevent water from escaping from the cavity 52 . The nozzle assembly of FIGS. 2 and 3 further includes a thermocouple 50 .

FIG. 4 is an enlarged view of the mold gate insert 24 . A groove 44 is formed in the inner wall 48 of the mold gate insert 24 and is located adjacent the flange 46 . The groove 44 is continuous and generally concentric with an axis 45 of the mold gate 24 . The groove 44 extends the insulation chamber 42 so the thickness of the mold gate 24 between the inner wall 48 of the insulation chamber 42 and the outer wall of the mold gate insert 24 is reduced.

It will be appreciated that the groove 44 may be offset from the axis of the mold gate 26 and in addition, the groove 44 is not restricted to following a circular path. In an alternative embodiment, the groove 44 comprises a series of segments that are spaced in a generally circular path in the inner wall 48 of the mold gate insert 24 . In a further alternative embodiment, the groove 44 comprises a series of holes that are spaced along a path in the inner wall 48 . In a still further alternative embodiment, the path of the groove 44 zig zags.

During the cooling stage of the injection molding cycle, water flows through cavity 52 to cool the mold gate insert 24 and the cooling channels 40 cool the mold cavity 32 . The mold gate 26 and the melt located in the bubble area 60 freezes.

To reduce cycle time, it is desirable to freeze and subsequently heat the melt in the mold gate 26 as quickly as possible. The insulation chamber 42 reduces the heat transfer between the mold gate insert 24 , which is cooled, and the nozzle 18 , which is heated. The groove 44 reduces the amount of heat that is transferred directly from the seal 28 , which is in contact with the nozzle 18 , to the mold gate insert 24 . The flange 46 acts as a heat transfer fin providing increased surface area to dissipate the heat more efficiently.

Referring to FIGS. 5 and 6 , a further embodiment of the present invention is shown. A nozzle 18 a is a torpedo-type hot runner nozzle, which uses a thermal gating mechanism. A nozzle tip 30 a of the nozzle 18 a extends into a mold gate 26 a of a mold gate insert 24 a . Once the mold cavity (not shown) has been filled with melt, the melt in the mold gate 26 a is frozen in order to block the mold gate 26 a and thus prevent drooling from the nozzle 18 a . The mold gate insert 24 a has been previously described in relation to FIGS. 2 , 3 and 4 and provides the same thermal insulating advantages as has been previously described.

Referring to FIG. 7 , a further embodiment of a mold gate insert 24 b is shown. In this embodiment, a groove 44 b has a generally rectangular profile and is filled with an insulating material 62 such as a ceramic paste, for example. As shown, the groove 44 b is slightly larger than the groove 44 of the previous figures.

It will be appreciated by a person skilled in the art that a larger groove will provide increased insulation capability, however, the size of the groove is limited by the structural requirements of the mold gate insert 24 .

Further embodiments of a mold gate insert 24 c and 24 d are shown in FIG. 8 . Embodiment (i) includes a pocket 64 that has an open side 66 . The seal 28 c abuts the open side 66 of the pocket 64 to seal air inside. Alternatively, there may not be a complete seal formed between open side 66 and seal 28 so that melt may leak into the pocket 64 . The melt would also act as an insulator.

Embodiment (ii) of FIG. 8 includes a pocket 68 that is provided between an inner wall 48 c of the mold gate insert 24 d and a second insert portion 70 . The pocket 68 may be filled with air or, alternatively, a ceramic insulating material. The second insert portion 70 may be comprised of the same thermally conductive material as the mold gate insert 24 d or it may also be different. The second insert portion 70 may alternatively be made of a less thermally conductive material.

Referring to FIG. 9 , still a further embodiment of a mold gate insert 24 e is shown. In this embodiment, seal 28 e abuts a smaller portion of mating surface 56 e of flange 46 e so that melt may fill the space provided between the seal 28 e and the mating surface 56 e and act as an insulator.

A further embodiment of a mold gate insert 24 f is shown in FIG. 10 . A nozzle 18 f , which includes a nozzle body 29 f and a nozzle tip 30 f , extends through the mold gate insert 24 f to deliver melt through a mold gate 26 f and into a mold cavity (not shown). The mold gate 26 f is selectively openable by a valve pin 34 f that extends through the nozzle 18 f . A seal 28 f is provided between the nozzle tip 30 f and the mold gate insert 24 f . Other components of the injection molding apparatus are similar to those described in relation to FIGS. 1–3 .

The mold gate insert 24 f , which is shown in FIG. 11 , includes a thermal insulation element 74 that is nested within a mold gate insert body 72 . The thermal insulation element 74 includes an inner wall 56 f that abuts the seal 28 f . The thermal insulation element 74 is comprised of an insulating material, which has a lower thermal conductivity than the material of mold gate insert body 72 . The thermal insulation element 74 may be comprised of materials such as high temperature polymers such as high performance polyimide (such as VESPEL), PEEK, or titanium, for example.

The inner wall 56 f of the thermal insulation element 74 aligns the seal 28 f within the mold gate insert 24 f . This allows the nozzle 18 f to be aligned with the mold gate 26 f so that the valve pin 34 f may operate efficiently. The thermal insulation element 74 further serves to insulate the mold gate insert 24 f from the nozzle 18 f.

Referring now to FIG. 12 , a nozzle 18 g includes a nozzle body 29 g , a nozzle tip 30 g and a valve pin 34 g , which extends through the nozzle 18 g . The seal 28 , which has been shown in the previous figures, has been integrated into the nozzle tip 30 g . A mold gate insert 24 g includes a mold gate 26 g , which is aligned with the nozzle 18 g to allow melt to pass therethrough into a mold cavity (not shown). The mold gate insert 24 g is similar to the mold gate insert 24 f of FIGS. 10 and 11 and includes a mold gate insert body 72 g and a thermal insulation element 74 g . An inner wall 56 g of the mold gate insert 24 g abuts the nozzle tip 30 g to provide a seal therebetween.

It will be appreciated by a person skilled in the art that the mold gate inserts described herein may be used with any nozzle having a nozzle seal surrounding a tip thereof. FIG. 13 is divided into (i) and (ii) to show two different mold gate inserts surrounding a nozzle 18 h . FIG. 13 (i) shows the nozzle 18 h surrounded by a mold gate insert 24 h that is similar to the mold gate insert 24 f of FIGS. 10 and 11 . FIG. 13 (ii) shows the nozzle 18 h surrounded by a mold gate insert 24 hh , which is similar to the mold gate insert 24 shown in FIGS. 2–6 .

The nozzle 18 h includes an integral nozzle tip 30 h and nozzle seal 28 h . When assembled in an injection molding apparatus, an outer surface 76 of the nozzle 18 h abuts the inner wall 56 h , 56 hh of the mold gate inserts 24 h and 24 hh , respectively, to provide a seal therebetween. It will be appreciated by a person skilled in the art that the nozzle 18 h may be used with any of the mold gate insert embodiments that have been previously described.

The many features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention that fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.