Patent Application
20050069604
This invention pertains generally to hot runner components for an injection molding apparatus, and more particularly, to a heater for such a hot runner component.
Hot runner systems are used in injection molding machines for feeding a fluid plastic material or melt stream that is maintained at an elevated temperature to a mold cavity. One component of a hot runner system is a hot runner bushing or nozzle. A hot runner bushing or nozzle generally consists of a body defining a central passageway for conveying the fluid plastic material to a mold cavity through a gate.
To maintain the fluid plastic material at an elevated temperature, a hot runner bushing also includes an electric heater that generally consists of a resistance wire that is helically wound around the central passageway. This resistance wire can be wound directly on the nozzle or bushing body or be incorporated into a separate sleeve that can be positioned over the body. In either case, the resistance wire is encased in an outer shell with an electrically insulative powder, such as magnesium oxide, interposed in surrounding relation about the resistance wire. To ensure efficient thermal conductivity, the nozzle or bushing body and heater are swaged so as to compact the powder and thereby fill all the voids around the resistance wire.
Unfortunately, conventional hot runner bushing heaters are labor intensive to manufacture. Moreover, manufacturing these heaters requires multiple steps including winding the resistance wire, filling the heater with the electrically insulative powder and swaging the heater. As a result, conventional hot runner bushing heaters are time-consuming and expensive to manufacture. Another problem with conventional hot runner bushing heaters is that they have a relatively large cross-sectional area. This makes them difficult to use with relative small hot runner components. Additionally, the relatively large size of the heaters makes them more susceptible to condensation and moisture.
The invention provides a hot runner component for heating and directing fluid material of a melt stream to a mold cavity. The hot runner component includes a body having a fluid passageway therein for conveying the melt stream and a heater for heating the melt stream as the melt stream passes through the fluid passageway of the body. The heater includes a core arranged in surrounding relation to the fluid passageway of the body, a thermally-sprayed dielectric substrate layer on the core and a thermally-sprayed electrical resistance element layer overlying the dielectric substrate layer. The resistance element layer forms a discrete pattern. The heater further includes a thermally sprayed dielectric overlay layer that overlies a substantial portion of the resistance element layer.
In an alternative embodiment, the invention provides a method for making a hot runner component for heating and directing fluid material of a melt stream. The inventive method includes the step of thermally spraying a dielectric powder material onto an outer surface of a heater core to form a dielectric substrate layer. An electric resistance powder material is thermally sprayed onto the dielectric substrate layer to form an electric resistance element layer with the electric resistance element layer being formed in a discrete pattern. A dielectric powder material is thermally sprayed over a substantial portion of the resistance element layer to form an dielectric overlay layer. The heater core is then arranged in surrounding relation to a fluid passageway extending through a hot runner component body.
Referring now more particularly to
In the illustrated embodiment, the hot runner bushing 10 consists of a cylindrical body 12 having a central flow passageway 14 extending longitudinally through the body 12 for conveying the pressurized melt stream. The hot runner bushing 10 includes an annular flange or head 16 at the inlet or upstream end 18 of the bushing 10 (see, e.g.,
For heating the melt stream during its travel through the flow passageway 14 of the bushing body 12, the hot runner bushing 10 includes a heater 24. According to one important aspect of the present invention, one or more components of the heater 24 are thermally sprayed (e.g., flame sprayed or plasma sprayed). Using thermally sprayed components allows the heater 24 to be manufactured in an easier and more cost effective manner as compared to conventional hot runner bushing heaters. Specifically, conventional hot runner bushing heaters require multiple labor-intensive steps to manufacture. In contrast, the use of thermally sprayed components eliminates, for example, the need for swaging as well as manual addition of cement for wire management. The use of thermally sprayed components also enables the heater 24 to have a relatively thin profile as compared to bulky conventional heaters. The reduced profile of the heater 24 makes it less susceptible to condensation and moisture and makes it easier to use with relatively small hot runner components.
Thermal spraying is a well-known process and, as such, is not described in detail herein. Generally, in a thermal spraying process a powdered material is fed in a carrier gas to a flame spray gun or torch (either arc plasma or gas). The flame spray gun heats the powdered material and the hot powder fuses together and to the substrate to which it is being applied forming a thin coating or layer. The application of the components of the heater of an exemplary embodiment of the present invention is shown diagrammatically in
The thermally sprayed components of the heater 24 are applied onto a preformed core 26 (see
A dielectric substrate layer 28 (see
For producing heat, a thermally sprayed resistance element layer 30 is applied over or on top of the dielectric substrate layer 28 (see
The resistance element layer 30 can be formed into the desired pattern in at least two different ways. First, the resistance element powder can be flame sprayed over the entire dielectric substrate layer 28. The desired pattern can then be formed by removing the unwanted areas of the resistance element layer 30 such as by micro sandblasting. The removal process can be facilitated through the use of a mask that covers the portions of the resistance element layer 30 needed for the final pattern. Alternatively, a mask with openings in the form of the desired pattern can be used when the resistance element powder is flame sprayed onto the heater 24. When the mask is removed, the resistance element layer 30 will be in the desired pattern. As will be appreciated, the present invention is not limited to any particular method for forming the resistance element layer 30 into the desired pattern.
To ensure efficient thermal conductivity, a thermally sprayed dielectric overlay layer 32 is provided over the resistance element layer 30. To form the dielectric overlay layer 32 (shown partially cutaway to expose the resistance element layer in
For connecting the resistance element layer 30 to an electrical power source, the heater 24 has leads 36 extending radially through an upper end of the outer shell 34 as shown in
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
| Number | Date | Country | |
|---|---|---|---|
| 60480554 | Jun 2003 | US |
