Abstract:
An apparatus and process for injecting molten plastic material includes a nozzle assembly through which plastic material flows and including a nozzle body with a heater affixed thereto. A mold cavity plate is positioned adjacent the nozzle body and is separable from the nozzle body so that separation of the mold cavity plate from the nozzle body exposes the nozzle body and permits removal of the nozzle body and the heater.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an apparatus and process for injection molding plastic material and particularly a nozzle assembly used in a hot runner assembly system and through which plastic material flows. 
     Typical hot runner nozzle assemblies include a nozzle body that has a heater in heat exchange relationship with respect thereto. It is generally necessary to disassemble the mold in order to replace or repair the heaters. This represents a time consuming and expensive procedure. Fast and easy serviceability are highly desirable in these systems. 
     The present invention provides an improved system and process which permits the convenient removal and replacement or repair of the nozzle body and heater without disassembly of the mold. 
     U.S. Pat. No. 5,374,182 to Gessner shows a nozzle assembly with a heater clamped to the exterior of the nozzle housing and providing a means for replacing the heater. The mold plate is latched over in the molding machine, thereby permitting exposure of the heater and providing access for its removal from the nozzle body. 
     U.S. Pat. No. 4,768,945 to Schmidt shows a nozzle assembly having a heater embedded into the nozzle body. It is well known that during the operation of the injection mold the nozzle heater may burn out. However, in order to replace the heater by removing the nozzle body so that a new heater can be installed, the mold must be disassembled so that the entire nozzle assembly can be removed. This is a time consuming and costly process which severely impacts the productivity of the mold. 
     U.S. Pat. No. 3,553,788 to Putkowski uses a hot runner nozzle assembly with a nozzle body that has a sliding fit connection to the hot runner manifold and the gate pad. The housing has an external heater clamped to its exterior. The sliding fit is designed to accommodate thermal expansion of the nozzle body as it is heated. The design relies on the sliding fit not leaking plastic when subjected to high plastic injection pressure inside the melt channel. However, replacement of the heater without dismantling the mold is difficult because the heater wiring is routed via the air space surrounding the hot runner manifold and is not accessible by removal of the cavity plate. Furthermore, sliding fit style hot runners tend to leak plastic when pressurized. 
     U.S. Pat. No. 4,095,931 shows a hot runner nozzle assembly with a heated nozzle assembly wherein both an outer sheath and an inner sleeve can be removed by unthreading them from the nozzle header and thereby exposing the heater. However, the wiring to the heater is routed through the nozzle header making it difficult to replace the heater without the expense and inconvenience of dismantling more of the nozzle assembly. 
     U.S. Pat. No. 3,295,169 to Moslo shows a heated machine nozzle with heaters clamped externally to a threaded, removable outer nozzle sleeve. There is no teaching of how this nozzle could be incorporated in a mold structure. In addition, these heaters do not transfer heat as efficiently as an integral heating element. Also, positioning of the heater in tight spaces can be a problem as they tend to be bulky. 
     U.S. Pat. No. 4,303,169 shows a nozzle tip portion which is screwed onto a heated body. An insulating bushing centrally locates the nozzle in the mold plate. However, in order to remove the heated portion, or even the nozzle tip, the mold plate must be disassembled from the hot runner. 
     Accordingly, it is a principal object of the present invention to provide an improved apparatus and method including a nozzle assembly with a nozzle body and heating means wherein the nozzle body and heating means may be simply, conveniently and expeditiously removed for replacement or repair of the heating means. 
     Further objects and advantages of the present invention will appear hereinbelow. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the foregoing objects and advantages are readily obtained. 
     An apparatus for injection molding plastic material is provided in accordance with the present invention, which comprises: a nozzle assembly through which plastic material flows, said nozzle assembly including a removable nozzle body with a forward end portion, a rearward end portion and a nozzle channel therein through which said plastic material flows; heating means affixed to the nozzle body and generally embedded therein; a mold cavity plate adjacent said forward end portion and separable from the forward end portion; wherein separation of the mold cavity plate from the forward end portion of the nozzle body exposes the forward end portion and heating means and permits removal of the nozzle body and heating means from the nozzle assembly. A nozzle header is generally provided engaging the rearward end portion of the nozzle body, wherein the nozzle body is removable from the nozzle header. 
     In accordance with the process of the present invention, a nozzle assembly is provided through which plastic material flows, said nozzle assembly including a removable nozzle body with a forward end portion, a rearward end portion and a nozzle channel therein through which plastic material flows; affixing heating means to the nozzle body and generally embedding the heating means in the nozzle body; positioning a mold cavity plate adjacent the forward end portion of the nozzle body, wherein the mold cavity plate is separable from the forward end portion; separating the mold cavity plate from the forward end portion of the nozzle body to expose said forward end portion and said heating means and permit removal of the nozzle body and heating means from the nozzle assembly. 
     Further features of the present invention and advantages of the present invention will appear hereinbelow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more readily understandable from a consideration of the accompanying, illustrative drawings, wherein: 
     FIG. 1 is a sectional view through a nozzle assembly of the present invention; 
     FIG. 2 is a sectional view through a preferred embodiment of a nozzle assembly of the present invention; 
     FIG. 3 is a sectional view of an alternate embodiment of the nozzle assembly of the present invention; and 
     FIGS. 4A and 4B are sectional views of a further embodiment of the nozzle assembly of the present invention, with FIG. 4A showing the complete nozzle assembly and FIG. 4B showing the mold cavity plate removed. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows a nozzle assembly  10  of the present invention including a nozzle body  12  having a forward end portion  14  and a rearward end portion  16 . The rearward end portion includes threads  18  for threadably engaging corresponding threads  20  on nozzle header  22  to fix nozzle body  12  in place in the nozzle assembly. The nozzle body includes a heater  24  embedded therein with wiring thereto wired to be accessible when the forward end portion  14  of the nozzle body  12  is exposed as will be shown in subsequent embodiments. Nozzle tip  26  having a tip end  28  is threaded into the forward end portion of the nozzle body. FIG. 1 shows the nozzle header  22  spaced from the manifold plate  30  by spring means  32  and located by dowel  34  to prevent rotation of the header when the nozzle body is threaded into the header. Mold cavity plate  36  is positioned adjacent the forward end portion  14  of nozzle body  12 . Mold cavity plate  36  is separable from the forward end portion  14  of the nozzle body by any desired and convenient means, as by screw  38  or a plurality of such screws. The nozzle body also includes a nozzle channel  40  therein through which plastic material flows to a mold (not shown) from a manifold channel  42  in a hot runner manifold  44 , all in a conventional manner. 
     In accordance with the embodiment of FIG. 1, the nozzle body  12  fastens to nozzle header  22  and seals at the interface between the nozzle body and header. This permits one to make the header out of a hard and durable material suitable to withstand the sliding wear at the interface  46  between the manifold and header. Additionally, the header could be made of a material of low thermal conductivity, such as titanium, so that it will not transfer heat away from the nozzle or manifold to the adjoining manifold plate. The nozzle body may be made of a thermally conductive material, such as beryllium copper, carbide or any suitable tool steel. 
     Thus, in accordance with the embodiment of FIG. 1, the mold cavity plate  36  is separated from the forward end portion  14  of the nozzle body  12  as by disengaging screw  38 , when the mold is spaced from the nozzle assembly. This permits the easy and convenient removal of the nozzle body and heater from the nozzle assembly for repair or replacement of the heater. 
     The preferred embodiment of FIG. 2 shows a nozzle header  50  spaced from manifold plate  30  by annular insulating sleeve  52 . The nozzle body  12  is threaded through the nozzle header  50  so that the nozzle body seals directly against the manifold  44 , thereby eliminating the need for a second sealing surface as shown in FIG.  1 . The threaded connection between the nozzle body and header causes the header to push the nozzle body into sealing relationship with the manifold. FIG. 2 also shows a thermocouple  54  with its associated wiring  56  that may also be embedded in the nozzle body. Heater  24  also includes its associated heater wiring  58 . Thermocouple and heater wiring extend in channel or groove  60  which is machined in the manifold plate. To remove the nozzle body, the flexible heater and thermocouple wires can be bent up and out of the groove to allow rotation of the nozzle body without damage to the wires. Alternatively, the groove can be machined in the cavity plate (as shown in FIG. 2) so that the wiring is free to rotate as the nozzle body is unthreaded and is readily accessible upon removal or unlatching of mold cavity plate  36 , along with the easy accessibility of the nozzle body, heater and thermocouple. Wrench flat  62  or other suitable means is provided on the nozzle body for engagement with a suitable tool to permit tightening or loosening of the nozzle body&#39;s threaded engagement in the nozzle assembly. 
     During operation, the manifold  44  slides across its interface with the nozzle body  12  due to thermal expansion of the manifold. The nozzle header or insulating collar  50  locates the nozzle body in its desired position in the manifold plate  30  and maintains its centered position while the manifold slides across the nozzle body. The nozzle header also serves to push the nozzle body against the manifold to maintain plastic sealing forces at the interface between the nozzle body channel  40  and manifold channel  42 . The nozzle body can be assembled to the header before placing the nozzle into the manifold plate bore  64  or it can be assembled from the opposing side of the manifold plate  30 . Once the mold is in production if a heater fails on the nozzle body the mold cavity plate can be easily removed or spaced away from the nozzle body exposing the forward end portion  14  of the nozzle body. The nozzle body can then be easily disassembled from the nozzle assembly without having to disassemble the manifold and manifold plate. The advantageous integral heater and nozzle body can then be conveniently removed without additional disassembly of the hot runner system. 
     As shown in FIGS. 1 and 2, the nozzle tip  26  is constructed as a separate piece detachable from the nozzle body, which can be done in the construction of the present invention. This is done heretofore because the nozzle tip  26  is subject to wear and damage especially at nozzle tip end  28 . Threading the nozzle tip into the nozzle body enables replacement of the nozzle tip without replacing the nozzle body; however, this has the disadvantage of making the nozzle tip weaker than if it was an integral part of the nozzle body. In accordance with the present invention, the nozzle tip portion can be made stronger and easy to service if it is permanently fixed to the nozzle body, as for example shown in FIG. 2 as by brazing, or as shown in FIG. 3 by making the nozzle body  66  and nozzle tip  68  integral. Also, in accordance with the embodiment of FIG. 3, wiring channel  70  is located between mold cavity plate  36  and manifold plate  30  and is readily accessible upon removal or unlatching of the mold cavity plate. 
     FIG. 4A shows a one piece nozzle body and nozzle tip  72  as in FIG. 3, but including a slip on heater  74 . FIG. 4A shows mold cavity plate  36  fixed to manifold plate  30  by screw  38 , and FIG. 4B shows the mold cavity plate removed or unlatched for access to and removal of the nozzle body and heater. 
     Thus, in accordance with the present invention, a nozzle body is provided containing an integral heater that is detachable from the hot runner assembly system in an expeditious and convenient manner without requiring disassembly of the mold structure other than removal of the cavity plate or cavity inserts. In addition, the present invention provides a nozzle assembly containing a nozzle body centering component that remains assembled to the hot runner system when the nozzle body is removed, wherein the nozzle assembly sealing to the hot runner manifold provides a sliding and sealing action. Also, in accordance with the present invention, the nozzle body heater and thermocouple wiring is routed so that the nozzle body can be rotated for removal. In addition, the foregoing features and advantages are simply and conveniently obtained in a highly advantageous structure. 
     It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.