Patent Application
20070188562
The present invention relates generally to an injection molding apparatus and, in particular to a heater for a manifold.
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.
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 heater comprises an extruded profile heater plate with channels to accept heater elements. The extruded profile heater plate can be cut to any length and configured to fit any size or shape of manifold. A means to mount the extruded profile heater plate to the manifold is also provided.
Another embodiment of the present invention includes a method of manufacturing a heater for a hot runner manifold. The method includes extruding a heater plate including at least one channel from a raw form to a final form using an extruder die; cutting the heater plate to a length based on the configuration of the manifold; and pressing a heater element into the heater plate channel. The heater plate is then coupled to the manifold surface for providing heat thereto. In another embodiment, a contact surface of the heater plate is machined to maximize contact between the contact surface and a surface of the manifold.
Embodiments of the present invention will now be described more fully with reference to the accompanying drawings in which like reference numerals indicate similar structure. The drawings are not to scale.
Referring now to
Each hot runner nozzle 22 is received in an opening 32 in a mold plate 34. A collar 28 surrounds the nozzle 22. The collar 28 abuts a step 36, which is provided in opening 32 to maintain a nozzle head 26 of the hot runner nozzle 22 in abutment with an outlet surface 40 of manifold 12. A nozzle tip 30 is received in a downstream end of hot runner nozzle 22 and may be threaded thereto. A nozzle melt channel 24 extends through hot runner nozzle 22 and nozzle tip 30. Nozzle melt channel 24 is in communication with manifold outlet 18 to receive melt from manifold channel 14. Hot runner nozzle 22 is heated by a heater 54 and further includes a thermocouple 56.
A mold cavity 50 is provided between mold plate 34 and a mold core 52. Mold cavity 50 receives melt from nozzle melt channel 24 through a mold gate 48. Cooling channels 58 extend through mold plate 34 to cool mold cavity 50.
Manifold 12 is maintained in position relative to mold plate 34 by a locating ring 46. Spacers 44 are provided between an inlet surface 38 of manifold 12 and a back plate 42. Referring also to
As shown in
The heater plate 64 is formed by an extrusion process, as described below, from a material that is more thermally conductive than the manifold 12, which is typically made from tool steel such as H13, P20 or SS420, for example. Suitable thermally conductive materials for heater plate 64 include aluminum, aluminum alloys, copper and copper alloys, such as brass and bronze. Alternatively, another suitable material may be used.
Channels 66 of heater plate 64 are shaped and sized to receive and secure heating elements (not shown) therein. As illustrated in
The heater 60 further includes relief holes 68, which are located at regular intervals along the length of the heater plate 64. The relief holes 68 are provided to receive mechanical items, including fasteners (not shown), for coupling the heater 60 to the manifold 12. A thermocouple aperture 70 extends through heater plate 64 and receives a thermocouple (not shown). Connectors 72, 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 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 heater plate is operated, the heating element(s) may be accessed for replacement simply by removing the fasteners from retaining holes 74 and exposing/removing the heating element from channel 66.
In operation, melt is injected from the machine nozzle into manifold channel 14 of manifold 12 through sprue bushing 20. Nozzle melt channels 24 of nozzles 22 receive melt from manifold outlets 18 and deliver the melt to mold cavities 50 through mold gates 48. Heaters 60 provide heat to the manifold 12 so that the melt flowing through the manifold channel 14 is maintained at a desired temperature. Once the mold cavities 50 have been filled with melt, the melt is cooled and the molded parts are ejected from injection molding apparatus 10.
Production of the heater plate 64 will now be described. A billet of a selected material in a raw form is pushed through a die incorporating the profile shown in
In one embodiment, a single extruded heater plate may be later cut to produce a plurality of custom length heater plates 64. Accordingly, following extrusion, heater plate 64 is cut to a desired length, which is determined by the surface 40, 62 of the manifold 12 to which the heater 60 is to be coupled. Also following extrusion, contact surface 65 of the heater plate 64 may 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 surface 65 maximizes the amount of contact between the contact surface 65 and the surfaces 40, 62 of the manifold 12 and therefore optimizes heat transfer therebetween. Relief holes 68 and thermocouple holes 70 are also machined into the heater plate 64. Following machining, the heating elements are positioned in the channels 66 and the fasteners are installed to clamp the heating elements in position. Once assembled, the heater 60 is coupled to the manifold 12 and the heating elements are linked to the power source.
The heating elements are removable from the channel 66 by 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 heater 60 does not need to be scrapped and replaced when one or more heating elements fail, which provides a cost savings.
The heater 60 further provides some flexibility in that channels 66 accommodate 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 channel 66 with a thermally conductive paste. The thermally conductive paste does not affect the removal of the heating elements 90 from the channels 66 and breaks away when the heating elements are removed.
Referring to
Referring to
End caps 96 are provided at ends 98 and 100 of the heater 60c. Each end cap 96 is coupled to the heater plate 64c by fasteners (not shown), which extend through apertures 102. The end caps 96 are provided to distribute the heat from the exposed elbow 92 and terminal end 94 portions of the heating elements 90. The heater 60c further includes relief holes 68c, which are drilled at regular intervals along the length of the extruded heater plate 64c. The relief holes 68c are provided to receive mechanical items including fasteners (not shown) for coupling the heater 60c to the manifold.
As shown, the heater 60c includes multiple thermocouple apertures 70c for receiving thermocouples (not shown). Each thermocouple is dedicated to one control zone of the heater 60c. 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 heater 60c. Heating elements 90 may be powered independently, in parallel or in series. Powering the heating elements 90 independently or in parallel provides a fail-safe, redundant arrangement for the heater 60c. In one embodiment, a parallel arrangement requires fewer control zones and therefore is less costly than independent control of each heating element 90.
Operation of the heater 60c is similar to operation of heaters 60, 60a, 60b of the previously described embodiments, and therefore will not be described further here.
The heater 60c is produced in a similar manner as has been previously described with respect to heater 60 of
The heating elements 90 are replaceable by an operator. This provides a cost savings, as the entire heater 60 does 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 elements 90 in the channels 66c makes it possible for heating elements 90 having different diameters to be installed without significantly reducing the amount of contact between the heating element 90 and the channel 66c. In embodiments where heating elements having smaller diameters are installed, it may be desirable to fill any gaps between the heating element 90 and the channel 66c with a thermally conductive paste. The thermally conductive paste does not affect the removal of the heating elements 90 from the channels 66c and breaks away when the heating elements 90 are removed for repair or replacement.
It will be appreciated by a person skilled in the art that by deforming the heating elements 90 into the channels 66c, no additional clamping plate is required so that the heating elements 90 are unenclosed.
Referring to
Although heater 60d is shown coupled to the upper surface 38d of the manifold, it will be appreciated that similar to the previous heater embodiments, the heater 60d may be coupled to any surface of the manifold 12d. Further, one channel 66d or a plurality of channels 66d may be provided depending on the amount of heat required for a particular application.
The heater plate 64d may be formed by an extrusion process or a combination of extrusion and machining. The heater plate 64d is made of a suitable material such as those materials previously described with respect to heater 60 of
Another embodiment of the present invention is shown in
In another embodiment shown in
Each heating element 90e includes terminal ends 94e (one of which is shown in
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.
