Patent Application
20050225000
1. Field of the Invention
The present invention relates generally to an injection molding apparatus, and in particular to an injection molding apparatus having a nozzle with a controlled heat distribution along the nozzle channel.
2. Background of the Invention
Hot runner nozzles often have an uneven distribution of heat along the length of the melt channel when operating in an injection molding apparatus. The nozzles are generally housed in an opening in a mold plate between a manifold and a mold cavity. The mold plate is typically cold, particularly near the manifold and the mold cavity. As a result, a nozzle head portion, and the area around a nozzle tip, tend to lose more heat through direct contact with the mold than the nozzle mid-section, which does not contact any part of the mold plate. The uneven distribution of heat along the nozzle causes the temperature of the melt flowing through the nozzle to vary as it travels toward the mold cavity. Any variation in melt temperature can adversely affect the quality of the molded products and is therefore undesirable.
A further disadvantage of an uneven temperature distribution along the length of the nozzle is that the nozzle is subjected to high stress due to the continuous cycling between higher and lower temperatures. This can result in a shorter nozzle life.
With the increased use of plastic materials that are more sensitive to fluctuations in temperature, the melt must be maintained within more accurate and controllable temperature ranges. If the temperature rises too high, to compensate for the heat loss through the contact with the mold, degradation of the melt will result; and if the temperature drops too low, the melt will clog in the system and produce an unacceptable product. Both extremes can necessitate the injection molding apparatus being shut down for a clean-out, which can be a very costly procedure due to the loss of production time.
There is therefore a need to provide a hot runner nozzle having a generally uniform temperature distribution along the length thereof.
In accordance with one aspect of the present invention, there is provided an injection molding apparatus comprising a manifold, having a manifold channel and an outlet, and a nozzle coupled to the outlet of the manifold. The nozzle has a first nozzle body, a second nozzle body, and a thermal barrier disposed between the first nozzle body and the second nozzle body. The first nozzle body, second nozzle body and the thermal barrier typically define a melt channel through the nozzle. The first nozzle body is heated by a first heater and the second nozzle body is heated by a second heater. There is further provided a first means for connecting the thermal barrier to the first nozzle body, and a second means for connecting the second nozzle body to the thermal barrier. The thermal barrier may take the form of a sleeve, or may alternatively take the form of a cylindrical nozzle body segment. The thermal barrier may also include a flange extending outwardly between the first nozzle body and the second nozzle body. With such a configuration, the flange is typically sandwiched between the downstream end surface of the first nozzle body and the upstream end surface of the second nozzle body. The first means for connecting the thermal barrier to the first nozzle body may be by a threaded engagement. The second means for connecting the second nozzle body to the thermal barrier may be by a threaded engagement. In one embodiment, an air gap is provided between the first nozzle body and an upstream surface of the flange and/or between the second nozzle body and a downstream surface of the flange. In an alternative embodiment, the thermal barrier does not include the flange, and an air gap is provided between the downstream end surface of the first nozzle body and the upstream end surface of the second nozzle body. The thermal barrier is typically formed of a material that has a thermal conductivity less than the thermal conductivity of the first nozzle body and the thermal conductivity of the second nozzle body. In an embodiment, the thermal barrier is formed of either ceramic or titanium.
In accordance with another aspect of the present invention, the first means for connecting the thermal barrier to the first nozzle body may be by a threaded engagement, a press-fit engagement, a brazing engagement, or any other means known in the art. The second means for connecting the second nozzle body to the thermal barrier may be by a threaded engagement, a press-fit engagement, a brazing engagement, or any other means known in the art. The first nozzle body, the second nozzle body and the thermal barrier thus form modular components to the nozzle body, and can be assembled and disassembled with ease. The nozzle may further include a sleeve heater located over the first and the second nozzle bodies. Alternatively, the nozzle may include a partially embedded heater located on the outer surface of the first and second nozzle bodies. In another alternative embodiment, the nozzle may include a first heater in contact with the first nozzle body and a second heater in contact with the second nozzle body.
In accordance with yet another aspect of the present invention, there is provided a nozzle for use in an injection molding apparatus. The nozzle is comprised of a heated nozzle body, having a first nozzle body segment and a second nozzle body segment, and a thermal barrier coupled to the nozzle body and disposed between the first nozzle body segment and the second nozzle body segment. The nozzle includes a nozzle body melt passage which traverses through the nozzle body, wherein the nozzle body melt passage is defined by the inner surface of the first nozzle body segment, the inner surface of the thermal barrier, and the inner surface of the second nozzle body. The nozzle body segments are preferably formed of a thermally conductive material. The thermal barrier is preferably formed of a material that is less thermally conductive than the material which forms the nozzle body segments. The nozzle may further include a first heater thermally coupled to the first nozzle body segment and a second heater thermally coupled to the second nozzle body segment. The term “thermally coupled” is defined by a thermal link between the heater and the nozzle body segment. In other words, the heater is positioned with respect to the nozzle body segment such that the heater provides heat to the nozzle body segment. Alternatively, the nozzle may include a heat source which takes the form of a sleeve heater surrounding at least a portion of the nozzle body.
In accordance with still another aspect of the present invention, there is provided an injection molding apparatus comprising a manifold having a melt channel therethrough, a nozzle in fluid communication with the melt channel of the manifold, a heat source thermally coupled to the nozzle, and a mold component having a gate and a mold cavity adapted to receive melt from the nozzle through the gate. The nozzle is formed of a nozzle body, having a first nozzle body segment and a second nozzle body segment, and a thermal barrier, or insulating member, coupled to the nozzle body and separating the first nozzle body segment from the second nozzle body segment. The nozzle body is preferably formed of a thermally conductive material. The insulating member is preferably formed of a material that is less thermally conductive than the material which forms the nozzle body. The heat source may take the form of a sleeve heater or a coil heater embedded into the nozzle body. The heat source may alternatively include a first heater thermally coupled to the first nozzle body segment and a second heater thermally coupled to the second nozzle body segment.
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.
Referring now to
Nozzle 118 is received in an opening 122 in a mold plate 124. Nozzle 118 includes a nozzle body 123 and a nozzle tip 125. A collar 140 abuts a shoulder 142 of opening 122 and a shoulder 143 of the nozzle body 123 to maintain a head portion 144 of the nozzle body 123 in abutment with the manifold 112. The nozzle 118 is heated by a heater 146 and further includes a thermocouple 148. In this embodiment, the heater 146 is embedded in the outer surface of the nozzle body 123.
Nozzle tip 125 is received in a downstream end of nozzle body 123. The nozzle tip 125 is coupled to the nozzle body 123 by a threaded connection 126 and therefore may be easily removed for repair or replacement. A nozzle melt channel 120 extends through nozzle body 123 and nozzle tip 125. The nozzle melt channel 120 is in communication with the manifold outlet 116 and receives melt from the manifold channel 114.
A mold cavity 128 is provided between a cavity mold plate 134 and a mold core 136. The mold cavity 128 receives melt from the nozzle melt channel 120 through a mold gate 130. The mold gate 130 is selectively opened by a valve pin 132, which is movable into and out of engagement with the mold gate 130 by an actuator (not shown). Cooling channels 138 extend through the cavity mold plate 134 to cool the mold cavity 128.
Referring to
A mold cavity 28 is provided between a cavity mold plate 34 and a mold core 36. The mold cavity 28 receives melt from the nozzle through a mold gate 30. The mold gate 30 is selectively opened by a valve pin 32, which is movable into and out of engagement with the mold gate 30 by an actuator (not shown). Cooling channels 38 extend through the cavity mold plate 34 to cool the mold cavity 28.
The nozzle 18 includes three modular components: a first nozzle body segment 50, a second nozzle body segment 52, and a thermal barrier 54 which forms an intermediate nozzle body segment between the first nozzle body segment 50 and the second nozzle body segment 52. The first nozzle body segment 50 is downstream of the manifold 12 and the second nozzle body segment 52 is downstream of the first nozzle body segment 50. The first nozzle body segment 50 and the second nozzle body segment 52 are removably coupled to one another by the thermal barrier, or insulating member, 54. Together, the first nozzle body segment 50, the second nozzle body segment 52 and the thermal barrier 54 define a melt channel 56, which allows melt to flow from the manifold channel 14 to the mold cavity 28. The first and second nozzle body segments 50, 52 are typically comprised of a tool steel (e.g., H13); however, they may alternatively be comprised of any tool steel or any other material typically used in the injection molding art, as would be apparent to one skilled in the relevant art. In addition, the materials of the first nozzle body segment 50 and the second nozzle body segment 52 may be different from one another.
A nozzle tip 24 is coupled to the second nozzle body segment 52 at a downstream end thereof by a transfer seal 62. An outwardly extending flange 64 of the nozzle tip 24 is sandwiched between an upstream surface 66 of the transfer seal 62 and the second nozzle body segment 52. The transfer seal 62 includes a threaded outer wall 68 that mates with a threaded inner wall 70 of the second nozzle body segment 52 to maintain the nozzle tip 24 and transfer seal 62 in position relative to the second nozzle body segment 52.
The first nozzle body segment 50 is heated by a first heater 58 and the second nozzle body segment 52 is heated by a second heater 60. The first and second heaters 58, 60 are operable independently to allow the temperature of the first and second nozzle body segments 50, 52 to be independently controlled. In the embodiment shown, first and second heaters 58, 60 are embedded in first and second nozzle body segments 50, 52, respectively. In alternative embodiments, first and second heaters may be thermally coupled to first and second nozzle body segments in any manner known to the art. The term “thermally coupled” is defined by a thermal link between the heater and the nozzle body segment. In other words, the heater is positioned with respect to the nozzle body segment such that the heater provides heat to the nozzle body segment. First and second thermocouples 74 and 76 are coupled to the first and second nozzle body segments 50 and 52, respectively, to provide temperature measurements therefor.
The heaters 58, 60 are provided to maintain the melt at a generally constant temperature as it travels through the nozzle 18. Typically, the second heater 60 is set at a higher temperature than first heater 58 in order to compensate for the heat loss from the second nozzle body segment 52 to the cold cavity mold plate 34. The thermal barrier 54 substantially limits heat transfer between the first nozzle body segment 50 and the second nozzle body segment 52; thereby allowing for more efficient and accurate temperature control of each individual nozzle body segment 50, 52.
As shown in
The outwardly extending flange 94 is sized to extend radially to at least an outer diameter of the first and second nozzle body segments 50, 52. As such, the thermal barrier 54 completely separates the first nozzle body segment 50 from the second nozzle body segment 52. Typically, the nozzle body segments will have equal outer diameters. In the case of two nozzle body segments with different sized outer diameters, however, outwardly extending flange 94 is sized to extend radially to at least an outer diameter of the larger of the first and second nozzle body segments 50, 52.
A first air gap 96 is provided between an upstream surface 98 of the outwardly extending flange 94 and the first nozzle body segment 50. Similarly, a second air gap 100 is provided between a downstream surface 102 of the outwardly extending flange 94 and the second nozzle body segment 52. In another embodiment, the first and second air gaps 96, 100 are eliminated and the upstream and downstream surfaces of the thermal barrier 54 contact the first and second nozzle body segments 50, 52, respectively. The air gaps 96, 100 provide additional insulation between the first and second nozzle body segments 50, 52; however, the thermal barrier 54 alone provides sufficient insulation to limit heat from transferring between the first nozzle body segment 50 and the second nozzle body segment 52.
The thermal barrier 54 is comprised of a material that is less thermally conductive than the material of the first nozzle body segment 50 and second nozzle body segment 52. Suitable materials include titanium and ceramic, for example. Because it acts as an insulator, the thermal barrier 54 substantially limits heat transfer between the first nozzle body segment 50 and the second nozzle body segment 52.
In operation, melt is injected from the machine nozzle into the manifold channel 14. The manifold channel 14 distributes the melt to a plurality of nozzle melt channels, including melt channel 56 of nozzle 18. Melt is injected from the melt channel 56 into the mold cavity 28 through mold gate 30. The melt in the mold cavity 28 is then cooled and the mold cavity 28 is opened to release the molded parts.
During the injection process, the melt is maintained at a generally uniform temperature by first and second heaters 58, 60 as it travels through the first nozzle body segment 50, the thermal barrier 54 and the second nozzle body segment 52. A schematic graph of the temperature distribution is generally shown in
It will be appreciated by a person skilled in the art that although the hot runner nozzle 18 is shown as being valve-gated, it may alternatively be thermal-gated. Further, a torpedo tip may be used in place of the nozzle tip shown in
The nozzle 518 is heated by a sleeve heater 558. The sleeve heater 558 is disposed about the outer surface of the nozzle 518 to thereby maintain the melt at a generally constant temperature as it travels through the melt channel 556.
Because it acts as an insulator, the thermal barrier 554 substantially limits heat transfer between the first nozzle body segment 550 and the second nozzle body segment 552; thereby allowing for more efficient and accurate temperature control of each individual nozzle body segments 550, 552. The thermal barrier 554 is comprised of a material that is less thermally conductive than the material of the first and second nozzle body segments 550, 552. Suitable materials include titanium and ceramic, for example.
The nozzle 618 is heated by a sleeve heater 658. The sleeve heater 658 is disposed about the outer surface of the nozzle 618 to thereby maintain the melt at a generally constant temperature as it travels through the melt channel 656. The sleeve heater 658 includes a cut-out 659 which produces a gap between the sleeve heater 658 and the nozzle 618. The length of the cut-out 659 corresponds approximately to the length and location of the thermal barrier 654, such that the sleeve heater 658 does not come in contact with the thermal barrier 654. The cut-out 659 may be used in order to better control the temperature gradient along the nozzle 618.
The nozzle 718 is heated by a heater 758. The heater 758 takes the form of a thermal coil embedded in the outer surface of the nozzle 718 to thereby maintain the melt at a generally constant temperature as it travels through the melt channel 756. The thermal coil of the heater 758 is wound around the nozzle 718 at varying pitch, so that the heater spiral has a tighter pitch at the ends of the nozzle 718, and a wider pitch about the area of the nozzle 718 comprising the thermal barrier 754.
In the embodiment shown in
The injection molding apparatus 810 further includes a nozzle tip 819 to direct melt into a mold cavity gate (not shown). Together, the first nozzle body segment 850, the thermal barrier, or intermediate nozzle body segment, 854, the second nozzle body segment 852, and the nozzle tip 819 define a melt channel 856. The melt channel 856 is in fluid communication with a manifold melt channel (not shown) upstream of the nozzle 818 and a mold cavity gate (not shown) downstream of the nozzle 818.
The first and second nozzle body segments 850, 852 are typically comprised of tool steel (e.g., H13); however, they may alternatively be comprised of any tool steel or any other thermally conductive material typically used in the injection molding art. In addition, the materials of the first nozzle body segment 850 and the second nozzle body segment 852 may be different from one another. As discussed in previous embodiments, the thermal barrier 854 is comprised of a material that is less thermally conductive than the material of the first and second nozzle body segments 850, 852. Suitable materials include titanium and ceramic, for example.
As shown, the first nozzle body segment 850 is heated by a heater 858, and the second nozzle body segment 852 is heated by a heater 859. The heaters 858, 859 are typically thermal coils embedded in the outer surface of the nozzle body segments 850, 852 to thereby maintain the melt at a generally constant temperature as it travels through the melt channel 856.
It shall be understood that the nozzles shown in
The many features and advantages of the invention are apparent from the detailed specification. It is intended by the appended claims to cover all 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 are intended to be covered by the claims.
This application claims the benefit of U.S. provisional patent application 60/559,976, filed Apr. 7, 2004, and 60/600,388, filed Aug. 11, 2004, which are hereby incorporated by reference in their entirety herein.
| Number | Date | Country | |
|---|---|---|---|
| 60559976 | Apr 2004 | US | |
| 60600388 | Aug 2004 | US |
