Plate heater for a manifold of an injection molding apparatus

An injection molding apparatus includes a manifold having a manifold channel for receiving a melt stream of moldable material and delivering the melt stream to a mold cavity through a nozzle channel of a nozzle and a mold gate. A heater is coupled to the manifold. The heater includes a heater plate that is formed by an extrusion process and at least one channel for receiving a heating element.

FIELD OF THE INVENTION

The present invention relates generally to an injection molding apparatus and, in particular to a plate heater for a manifold.

BACKGROUND OF THE INVENTION

As is well known in the art, a typical multi-cavity hot runner injection molding system includes a heated manifold for conveying a pressurized melt stream from an inlet to a plurality of outlets. A heated nozzle communicates with each outlet to deliver the melt to a respective mold cavity through a mold gate. Manifolds have various configurations depending on the number and arrangement of the mold cavities.

Different heating arrangements are known for heating manifolds. A common arrangement is an electrical heating element that is received in a groove in a manifold outer surface, as described in U.S. Pat. No. 4,688,622 to Gellert, which issued Aug. 25, 1987. Other arrangements include cartridge heaters that are cast into the manifold as described in U.S. Pat. No. 4,439,915 to Gellert, which issued Apr. 3, 1984, and plate heaters with cast-in heaters that are secured along the surface of the manifold, as described in U.S. Pat. No. 5,007,821 to Schmidt, which issued Apr. 16, 1991. Manufacture and assembly of each of these heating arrangements requires machining of the manifold, the heater or both, which can be both costly and time consuming.

For certain large molded parts that require melt delivered from large heated manifolds, the melt stream is heated by either multiple smaller heater plates attached to the manifold or heater elements pressed within grooves machined into the manifold surface. Each of these solutions has its benefits and limitations.

Heater plates provide more consistent heat distribution than a heater element in contact with the manifold surface. Further, heater plates may include more than one heater element allowing for redundancy. However, heater plates are typically made by investment casting methods, which does not accommodate the manufacture of larger plates due to warpage and bending that occurs as the plates get longer. Therefore, multiple shorter plates, i.e., plates typically less than 170 mm, are utilized for larger manifold applications, which require more control zones to operate. Further, heater elements of current heater plates are cast within the heater plate and cannot be replaced once they fail, so that the entire heater plate must be replaced upon failure of the heater elements therein.

Alternatively, heater elements that are pressed-in machined grooves on the surface of a manifold may be removed for replacement, although machining such grooves is time consuming and expensive. In addition, redundancy is provided for by machining a corresponding groove in an opposing surface of the manifold and pressing a secondary heater element into the second groove, adding to the time and cost associated with this production method.

Accordingly, what is needed is a manifold heater arrangement that provides the improved heat distribution and redundancy of a heater plate and provides for replacement of failed heater elements and fewer control zones. In addition, a heater plate that may be efficiently constructed, particularly at longer sizes, is desired.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention there is provided an injection molding apparatus including a heated manifold with a melt channel for transferring molten material from an injection molding machine to one or more hot runner nozzles which in turn inject the molten material to one of more cooled mold cavities to form a plastic part. One or more heaters are connected to the manifold in a configuration to provide heat to maintain the temperature of the molten material throughout the entire length of the melt channels in the manifold. The plate heater includes a heater plate body and at least two heating elements. A surface of the heater plate body has at least two channels therein and each heating element is received within a respective channel. At least one end cap is provided for commonly fixing terminal ends of at least two of the heating elements relative to the heater plate body.

Another embodiment of the present invention includes a method of manufacturing a plate heater for a hot runner manifold. The method includes providing an extruded bar like blank having at least two straight longitudinal grooves therein; planning a flat contact face of the blank; machining the grooves to fine forming straight longitudinal channels in the blank to gain a heater plate body; inserting longitudinal heating elements into the longitudinal channels in the heater plate body.

Further advantageous embodiments are defined in the dependent claims.

DETAILED DESCRIPTION OF THE INVENTION

Referring now toFIG. 1, an injection molding apparatus10is generally shown. Injection molding apparatus10includes a manifold12having a manifold melt channel14. Manifold melt channel14extends from an inlet16to manifold outlets18. Inlet16of manifold melt channel14receives a melt stream of moldable material from a machine nozzle (not shown) through a sprue bushing20and delivers the melt to hot runner nozzles22, which are in fluid communication with respective manifold outlets18. Although a pair of hot runner nozzles22is shown inFIG. 1, it will be appreciated that a typical injection molding apparatus may include only one or a plurality of hot runner nozzles for receiving melt from respective manifold outlets.

Each hot runner nozzle22is received in an opening32in a mold plate34. A collar28surrounds the nozzle22. The collar28abuts a step36, which is provided in opening32to maintain a nozzle head26of the hot runner nozzle22in abutment with an outlet surface40of manifold12. A nozzle tip30is received in a downstream end of hot runner nozzle22and may be threaded thereto. A nozzle melt channel24extends through hot runner nozzle22and nozzle tip30. Nozzle melt channel24is in communication with manifold outlet18to receive melt from manifold channel14. Hot runner nozzle22is heated by a heater54and further includes a thermocouple56.

A mold cavity50is provided between mold plate34and a mold core52. Mold cavity50receives melt from nozzle melt channel24through a mold gate48. Cooling channels58extend through mold plate34to cool mold cavity50.

Manifold12is maintained in position relative to mold plate34by a locating ring46. Spacers44are provided between an inlet surface38of manifold12and a back plate42. Referring also toFIG. 2, manifold12is heated by heaters60, which are coupled to the outlet surface40and side surfaces62of the manifold12.

As shown inFIGS. 3-5, each plate heater60includes a heater plate body64having flange portions76and base portions78that define a pair of channels66therebetween. Each channel66extends within a respective side surface69of heater plate64. Although heater plate body64is shown having a pair of channels66, the heater plate body64may be adapted to alternatively include one channel66or a plurality of channels66.

The heater plate body64is formed by an extrusion process, as described below, from a material that is more thermally conductive than the manifold12, which is typically made from tool steel such as H13, P20 or SS420, for example. Suitable thermally conductive materials for heater plate body64include aluminum, aluminum alloys, copper and copper alloys, such as brass and bronze. Alternatively, another suitable material may be used.

Channels66of heater plate body64are shaped and sized to receive and secure heating elements (not shown) therein. As illustrated inFIG. 5, a cross-section of channel66may be described as key-shaped or bulb-shaped having a narrowed neck portion71and an enlarged cavity portion67. In one embodiment, neck portion71is narrower than a heating element to be seated in cavity portion67, wherein cavity portion67is sized to securely receive the heating element. Flange portions76, which form the upper surface of channels66, and base portions78, which form the lower surface of channels66, include heating element retaining holes74for receiving fasteners (not shown) that force a mating surface80of flange portion76toward a surface82of base portion78to impart a clamping force on the heating element. The clamping force increases the amount of contact, and therefore heat transfer, between the heating element and the heater plate body64.

The plate heater60further includes relief holes68, which are located at regular intervals along the length of the heater plate body64. The relief holes68are provided to receive mechanical items, including fasteners (not shown), for coupling the plate heater60to the manifold12. A thermocouple aperture70extends through heater plate body64and receives a thermocouple (not shown). Connectors72, which allow the heating elements to communicate with a power source (not shown), are coupled to the free ends of each of the heating elements. The heating elements may be powered independently, in parallel or in series. By powering the heating elements independently or in parallel, a fail-safe, redundant arrangement is provided in which one plate heater will continue to provide heat even if the other heating element fails. In an embodiment where independent control of each heating element is provided, an additional control zone and thermocouple are utilized. However in accordance with the present invention, regardless of how the plate heater is operated, the heating element(s) may be accessed for replacement simply by removing the fasteners from retaining holes74and exposing/removing the heating element from channel66.

In operation, melt is injected from the machine nozzle into manifold channel14of manifold12through sprue bushing20. Nozzle melt channels24of nozzles22receive melt from manifold outlets18and deliver the melt to mold cavities50through mold gates48. Plate heaters60provide heat to the manifold12so that the melt flowing through the manifold channel14is maintained at a desired temperature. Once the mold cavities50have been filled with melt, the melt is cooled and the molded parts are ejected from injection molding apparatus10.

Production of the heater plate body64will now be described. A billet of a selected material in a raw form is pushed through a die incorporating the profile shown inFIG. 5A, to produce a heater plate having the cross-section shown inFIG. 5. The die profile includes a linear portion65′, which corresponds to a contact surface65on the heater plate body64, and at least one extended portion66′, which corresponds to channel66of the heater plate64. The heater plate body64is manufactured using an extrusion process, which includes cold-working the initial extruded form. The cold-working of the extruded plate makes it harder and stiffer than its cast counterpart, allowing for improved performance with less warpage and bending. As such, a longer extruded heater plate body that is flatter and straighter than a plate produced by a casting process, for example, is achieved.

In one embodiment, a single extruded heater plate body may be later cut to produce a plurality of custom length heater plate bodies64. Accordingly, following extrusion, heater plate body64is cut to a desired length, which is determined by the surface40,62of the manifold12to which the plate heater60is to be coupled. Also following extrusion, contact surface65of the heater plate body64may be machined by a machining process such as milling or grinding, for example, in order to smooth out any imperfections resulting from the extrusion process. Machining of the contact surface65maximizes the amount of contact between the contact surface65and the surfaces40,62of the manifold12and therefore optimizes heat transfer therebetween. Relief holes68and thermocouple holes70are also machined into the heater plate body64. Following machining, the heating elements are positioned in the channels66and the fasteners are installed to clamp the heating elements in position. Once assembled, the plate heater60is coupled to the manifold12and the heating elements are linked to the power source.

The heating elements are removable from the channel66by unscrewing the fasteners to release the clamping pressure on the heating elements. The manner in which the heating elements are secured allows them to be replaced by an operator in the event that one or both of the heating elements needs to be repaired or replaced. As such, the entire plate heater60does not need to be scrapped and replaced when one or more heating elements fail, which provides a cost savings.

The plate heater60further provides some flexibility in that channels66accommodate heating elements having different diameters. In applications where heating elements having smaller diameters are installed, it may be desirable to fill any gaps between the heating element and the channel66with a thermally conductive paste. The thermally conductive paste does not affect the removal of the heating elements90from the channels66and breaks away when the heating elements are removed.

Referring toFIG. 6, an injection molding apparatus10aincludes a manifold12ahaving a plate heater60a, which is similar to plate heater60ofFIGS. 1-5. The plate heater60ais coupled to a front surface84of the manifold12a. As shown, the plate heater60ais the only primary source of heat for the manifold12a. In another embodiment, the plate heater60amay be provided in combination with additional plate heaters on the outlet and side surfaces40aand62aof the manifold12a, as shown inFIG. 1. The plate heater60amay alternatively be provided in combination with a heater located on inlet surface38a, adjacent to sprue bushing20a. The plate heater60amay also be paired with another manifold heating method known in the art, such as an embedded heating element, a cartridge heater or a film heater, for example. Operation of plate heater60ais similar to operation of plate heater60of the previous embodiment and therefore will not be described further here.

FIG. 7shows another embodiment of a plate heater60bfor heating a manifold. Plate heater60bis similar to the heaters60,60aof the previous embodiments; however, plate heater60bincludes a central aperture86, which extends through plate heater64b. The central aperture86is provided in order to allow a melt transporting, manifold supporting or manifold locating component to pass therethrough. The type of component is determined by the location of the plate heater60bon the manifold. For example, if the plate heater60bis located on an inlet surface of the manifold, a sprue bushing may extend through the central aperture86, whereas if the plate heater60bis located on an outlet surface of the manifold, a nozzle may extend through the central aperture86. Incorporating the central aperture86into the plate heater60bincreases the number of different locations at which the plate heater60bmay be coupled to the manifold.

Referring toFIGS. 8-10, another embodiment of a plate heater60cfor a manifold is shown. Plate heater60cincludes a heater plate body64chaving channels66cprovided in an upper surface88thereof. Heating elements90are fully received within channels66c. Similar to channels66of the embodiment ofFIG. 5, channels66care key-shaped to include a narrowed portion71cand an enlarged portion67c, as shown inFIG. 10. Accordingly, heating elements90sit below heater plate upper surface88in contact with substantially the entire surface of enlarged portion67cto provide for optimal heat transfer therebetween. As shown, a longitudinal length of each heating element90is generally arranged in a U-shape and includes an elbow92at one end and terminal ends94at an opposite end. The terminal ends94of each heating element90communicate with a power source (not shown) through a connector (not shown). Suitable materials for heater plate body64care the same as have been previously described with respect to plate heater64ofFIGS. 1-5. In addition, the number and arrangement of the heating elements90and channels66cdepends on the amount of heat required for a particular application and is not limited to the embodiment shown inFIGS. 8-10.

End caps96are provided at ends98and100of the heater60c. Each end cap96is coupled to the heater plate body64cby fasteners (not shown), which extend through apertures102. The end caps96are provided to distribute the heat from the exposed elbow92and terminal end94portions of the heating elements90. The plate heater60cfurther includes relief holes68c, which are drilled at regular intervals along the length of the extruded heater plate body64c. The relief holes68care provided to receive mechanical items including fasteners (not shown) for coupling the heater60cto the manifold.

As shown, the plate heater60cincludes multiple thermocouple apertures70cfor receiving thermocouples (not shown). Each thermocouple is dedicated to one control zone of the plate heater60c. Each control zone typically controls a maximum heater input of 15 amps. The number of control zones, and therefore thermocouples, is determined by the desired heat output for plate heater60c. Heating elements90may be powered independently, in parallel or in series. Powering the heating elements90independently or in parallel provides a fail-safe, redundant arrangement for the plate heater60c. In one embodiment, a parallel arrangement requires fewer control zones and therefore is less costly than independent control of each heating element90.

Operation of the plate heater60cis similar to operation of plate heaters60,60a,60bof the previously described embodiments, and therefore will not be described further here.

The plate heater60cis produced in a similar manner as has been previously described with respect to heater60ofFIGS. 1-5; however, the profile for the die of plate heater60cdiffers and is shown inFIG. 10A. The profile includes a linear portion65c′, which corresponds to contact surface65cof the heater plate body64cand extended portion66c′, which corresponds to channel66cof the heater plate body64c. Following extrusion, ends98,100of the heater plate body64care machined by a machining operation such as milling or grinding, for example, to accommodate the terminal ends94of the heating elements90. The heating elements90are then positioned in the channels66cand may be deformed to provide three-sided contact with its respective channel66c, by a technique such as rolling a tool under pressure over the heating elements90. In accordance with one embodiment of the present invention, the rolling or swagging operation flattens the top side of heating element90and maximizes the amount of contact between the remaining three-sides of heating element90and its respective channel66c, in order to optimize the heat transfer therebetween. Other techniques for deforming the heating elements90may alternatively be used.

The heating elements90are replaceable by an operator. This provides a cost savings, as the entire plate heater60does not need to be scrapped and replaced when one or more heating elements fail. In various embodiments of the present invention, deformation of the heating elements90in the channels66cmakes it possible for heating elements90having different diameters to be installed without significantly reducing the amount of contact between the heating element90and the channel66c. In embodiments where heating elements having smaller diameters are installed, it may be desirable to fill any gaps between the heating element90and the channel66cwith a thermally conductive paste. The thermally conductive paste does not affect the removal of the heating elements90from the channels66cand breaks away when the heating elements90are removed for repair or replacement.

It will be appreciated by a person skilled in the art that by deforming the heating elements90into the channels66c, no additional clamping plate is required so that the heating elements90are unenclosed.

Referring toFIGS. 11 and 12, another embodiment of a plate heater60dfor a manifold12dis shown. In this embodiment, a heater plate body64dincludes a pair of channels66dfor receiving heating elements90d. The channels66dare provided in a contact surface65dof the heater plate body64dso that upon assembly, the heater elements90dcontact an upper surface38dof the manifold12d. This arrangement allows for direct contact between the heating elements90dand the manifold12d, therefore providing efficient heat transfer therebetween. A thermally conductive paste may be included to fill any gaps and increase the amount of contact between the heating element90dand the both the channel66dand the manifold12d. Apertures104are provided for receiving fasteners (not shown) to fix the plate heater60dto the manifold12dand clamp the heating elements90dto the upper surface38d.

Although plate heater60dis shown coupled to the upper surface38dof the manifold, it will be appreciated that similar to the previous heater embodiments, the plate heater60dmay be coupled to any surface of the manifold12d. Further, one channel66dor a plurality of channels66dmay be provided depending on the amount of heat required for a particular application.

The heater plate body64dmay be formed by an extrusion process or a combination of extrusion and machining. The heater plate body64dis made of a suitable material such as those materials previously described with respect to plate heater60ofFIGS. 1-5.

Another embodiment of the present invention is shown inFIGS. 13 and 13A. Plate heater60eincludes an extruded heater plate body64ehaving four channels66efor receiving four heating elements90ein an upper surface88ethereof. Although four channels and heating elements are shown, a fewer or greater number may be employed without departing from the scope of the present invention. Channels66eand heating elements90eextend the length of heater plate64ein parallel with each other. In contrast to the embodiment shown in cross-section inFIG. 10, channels66ehave a straight-walled, u-shaped cross-section sized slightly larger than heating element90ewith a channel depth that fully receives heating elements90etherein. Accordingly, an uppermost point of heating elements90esits at or below heater plate body upper surface88ein contact with the walls of channel66eto provide for optimal heat transfer therebetween. Heating element90emay be swaged, or otherwise pressed, into channel66eto make three-sided contact with heater plate body64e. In one embodiment, a top surface of heating element90emay be flattened during the swaging process. Heating elements90eare thus held in-place within channels66ewithout an additional cover or clamping arrangement so that they are easily replaced if one should fail.

In another embodiment shown inFIG. 13Bwhich is combinable with the embodiment ofFIG. 13), channels66emay have a groove portion71eand an undercut portion67ethat is a slightly enlarged area below groove71e, similar to narrowed portion71cand enlarged portion67cshown inFIG. 10. Heating elements90e, each of which has an outer diameter that is slightly larger than groove portion71ebut roughly equivalent to undercut portion67e, are then pressed through groove portions71eto sit within undercut portions67eof channel66e. In an embodiment, undercut portion67eis sized to fully receive and to maintain contact with heating element90efor maximum heat transfer therebetween. One method of making the embodiment ofFIG. 13B, includes forming an undersized version of channel66eduring the extrusion process that forms heater plate body64e, and then machining groove portion71eand undercut portion67eto a suitable geometry to accommodate heating element90eas previously described.

Each heating element90eincludes terminal ends94e(one of which is shown inFIG. 13A), and is connected in parallel to or wired independent of at least one other heating element90e. Thus, multiple heating elements90ewired in parallel or independently provide redundancy in operation for heater plate64e. Terminal ends94eare positioned between an upper and lower portion of a respective end cap110, which are attached at each end of heater plate64eby clamps112. As in previous embodiments, one or more heater60emay be attached to a top, side and/or bottom surface of the manifold depending on the application and heating needs. The end cap110comprises four inlets, each aligned with one of the channels66erespectively and receiving a terminal end94eof a heating element90e. The upper and lower portion of the end cap110each including a half of four inlet channels95efor receiving a straight portion of the terminal ends94e. The inlet channels95eintersecting a through channel96efor receiving bent end portions of the terminal ends94e. The through channel96ehaving two outlets97efrom which the connecting ends98eof the terminal ends94eproject. The upper and the lower portion of the end110each including a half of the through channel96e. The end cap110is made out of an electrically insulative material that can withstand molding temperatures, preferably a ceramic material.

The end cap110is shaped like an extension of the heater plate body64eand the height hcand the width wcof the end cap110are equal or smaller than the height hband the width wbof the heater plate body64e. Due to the fact that not only a straight portion, but also a bent portion of the terminal ends94eare positioned in the end cap110forces applied to the connecting ends98edo not influence the connection of the heating element90ein the channels66e. As with the embodiment shown inFIG. 9such an end cap110could also position not only terminal ends94e, but also the combination of terminal ends94eand a conventional bend (like elbow92inFIG. 9) or only such conventional bends. The two halves of the end cap110are identical and having respective connecting means to be fitted together.

With regard to the materials of the heater plate body64e, the arrangements of heating elements and their electrical connection etc. it is referred to the above embodiments. These features and techniques are also applicable here.

Another embodiment of the present invention is shown inFIG. 14-18. This embodiment is similar to the embodiment disclosed inFIG. 13-13B. Thus, only the differences are explained in the following. With regard to the remaining features and aspects it is therefore referred to the above.

This embodiment also includes end caps110on both ends of the plate heater60f. The height hcof the end cap110is smaller than the height hbof the heater plate body64f. Each end cap110is connected to the end of the heater plate body64fby using a U-shaped clamp112f. Whereas the side face of the end cap110including the inlets is pressed against the end face of the heater plate body64fthe three other side faces of the end cap110are held in the framelike structure of the U-shaped clamp112f. The clamp112fdoes not only have an overall U-shape, but also a U-shape cross-section. So that the end cap110can be inserted in this framelike structure provided by clamp112f. The legs of the U-shaped clamp112fare bolted to the heater plate body64f. The clamp112fdoes have side windows99fbeing in alignment with the outlets97fof the end cap110so that the connecting ends98fprojecting out of the windows99frespectively. The clamp112fis preferably made from a steel material.

End caps110as described with some of the above embodiments can be used with all of the heater designs disclosed.