Hot runner manifold system

A manifold system (50) comprising a main manifold (56) with a plurality of arms (64), a plurality of sub-manifolds (52) spaced from the main manifold (56) and communicating with the main manifold (56) through a plurality of melt transfer bushings (68) disposed between the main manifold (56) and the sub-manifolds (52). The melt transfer bushings (68) may include static mixers (140) to homogenize the melt. An air plate (70) is disposed between a backing plate (58) preferably housing the main manifold (56) and a manifold plate (54) preferably housing the sub-manifolds (52). The air plate (70) has a plurality of air channels (74) that communicate with valve gate nozzle actuators (90), which are received in actuator cavities (72) in the air plate (70). The air plate (70) is bolted to the manifold plate (54), and the backing plate (58) is bolted to the air plate (70) with bolting patterns not constrained by location of the main manifold (56) or sub-manifolds (52). The manifold system (50), as shown in FIG. 5, has better thermal and geometric balance, closer nozzle spacing, and better bolting for less plate bowing.

TECHNICAL FIELD

The present invention relates, generally, to injection molding equipment. More particularly, the invention relates to hot runner manifold systems used for injection molding. The invention has particular utility in large cavitation systems.

BACKGROUND OF THE INVENTION

The state of the art includes various arrangements for hot runner manifold systems to transfer molten material, typically plastic resin, from an injection molding machine to a mold. Hot runner manifold systems are well known and typically include a manifold plate, a manifold housed in the manifold plate, and a backing plate that supports the manifold and manifold plate. The manifold system routes molten material from a central sprue, which connects to an injection unit on an injection molding machine, to a plurality of nozzles which inject the molten material into cavities in the mold. The manifold system divides the flow of the molten material into several branches as it flows from the central sprue to the nozzles. It is desirable that flow of molten material through the manifold system be balanced so that material arriving at each nozzle has approximately the same temperature and pressure to produce uniform parts in each mold cavity. Toward that end, manifold systems are preferably designed so that each branch provides substantially the same size and length of flow path for the molten material. With uniform flow paths at each branch, temperature and pressure differences between branches should be minimized. However, for molds with a high number of cavities, such uniform flow paths are not always possible due to location limitations on the manifold.

Referring toFIGS. 1 and 2, a prior art manifold system using two plates is shown with portions of the plates and main manifold cut away to reveal internal detail. For injection molding systems with many cavities in the mold, a manifold assembly10has a plurality of sub-manifolds12arranged in manifold plate14and fed by a main manifold16mounted in backing plate18. Sprue20connects to the main manifold16at a central location. Main manifold16has a melt channel22with branches to each arm24of main manifold16and connecting to an inlet of each sub-manifold12. Each sub-manifold12has its own melt channel network that communicates the molten material from main manifold16to nozzles (not shown) connected to each sub-manifold12. In the example illustrated, each sub-manifold12accommodates twenty-four nozzles. Typically, valve-gate type nozzles are used with such a system, and have pneumatic valve actuators at the upper end of the nozzle that actuate valve stems in the nozzle. The valve stems extend through apertures26in the sub-manifolds12and the actuators are housed in actuator cavities28formed in backing plate18.

Such prior art manifold systems have significant limitations and shortcomings. Specifically, since the main manifold16and actuator cavities28are both in backing plate18, and the main manifold16cannot pass through actuator cavities28, the transverse spacing of actuator cavities28, and hence the nozzles, can be greater than desired. That leads to the mold being larger than optimum, and flow length of the molten material being increased.

Air lines30are routed to each actuator through the backing plate18. The location of the air lines is constrained by the location of the manifold16. Also since the location of the arms24of main manifold16is constrained by the location of actuator cavities28, flow of molten material to portions of sub-manifolds12is not optimum. In the example illustrated, arm24aconducts molten material through melt channel22to branches32aand32bto two sub-manifolds12aand12bat portions34aand34blocated at the periphery of sub-manifolds12aand12b. Material then flows to a central location in the sub-manifolds and subsequently through multiple channels to the nozzles. Such a flow path increases the likelihood of the molten material having less uniform temperature and pressure throughout the sub-manifolds12, which can lead to unbalance in the system.

Physical coupling, typically through the use of bolts, between the backing plate18and the manifold plate14stabilizes the layered structure by restricting bowing during the injection cycle. Plate bowing arises as a consequence of the injection pressure and pressure from spring-loaded seals at interfaces between the sub-manifolds12and nozzles and also between the sub-manifolds12and the arms24of the main manifold16. If the plates bow, leakage can occur at those interfaces. Pillars36are provided in manifold plate14where possible, and numerous bolt holes38are provided through backing plate18to facilitate such bolting. However, bolts cannot be put through the melt channel22of manifold16, so to make the bolt spacing adjacent the manifold16as tight as possible, the arms24of manifold16are made as narrow as possible. To maintain structural integrity of such narrow portions, the manifold16may have to be hardened or be made from a stronger material than is desirable.

SUMMARY OF THE INVENTION

The present invention provides an manifold system for an injection molding system comprising a main manifold with at least one arm, at least one sub-manifold spaced from the main manifold, and a plurality of melt transfer bushings between the main manifold and each sub-manifold. The main manifold has a main melt channel branching to each arm with an outlet at each branch. Each sub-manifold has an inlet and a plurality of secondary melt channels in communication with the inlet. Each melt transfer bushing is disposed between one of the sub-manifolds and one of the arms of the main manifold, and provides communication between the outlet of one of the arms of the main manifold and the inlet of one of the sub-manifolds. An air plate is disposed between the main manifold and the at least one sub-manifold, and between a backing plate, that preferably houses the main manifold, and a manifold plate, that preferably houses the at least one sub-manifold. The air plate has a plurality of actuator cavities for receiving actuators for nozzles. The air plate also has a plurality of air channels therein which communicate with the actuator cavities for conducting fluid, in use, to the actuators. The air plate also preferably has a plurality of cooling channels for conducting cooling fluid, in use, to cool the air plate.

The air plate preferably has a plurality of air plate bolt holes, which receive bolts to secure the air plate to the manifold plate. A plurality of the air plate bolt holes may be disposed directly beneath the main manifold. The backing plate has a plurality of backing plate bolt holes which receive bolts to secure the backing plate to air plate. A plurality of the backing plate bolt holes are disposed directly above sub-manifolds.

Each melt transfer bushing has a melt channel therein and preferably a static mixer is disposed in the melt channel to homogenize the molten material at the entrance to each sub-manifold. Preferably each melt transfer bushing has a heating device, such as an electric heater or at least one heat pipe which transfers heat from the main manifold and a sub-manifold to the melt transfer bushing.

Preferably, a plurality of valve gate nozzles are connected to each sub-manifold, each nozzle has a melt channel in communication with a secondary melt channel in a sub-manifold, and each nozzle has a valve gate actuator disposed in one of the actuator cavities in the air plate. Each sub-manifold has a plurality of manifold bushings aligning with the nozzles and providing the communication between the melt channel in the nozzles and the secondary melt channels in the sub-manifold. Each manifold bushing has a flat sealing surface, and each nozzle preferably has a non-flat sealing surface adjacent the flat sealing surface of the manifold bushing, which reduces the force required to adequately seal the sealing surfaces. Preferably the non-flat sealing surface is a raised conical surface around a melt channel of the nozzle angled less than one degree from planar.

Similarly, the main manifold preferably has a flat sealing surface, and the melt transfer bushing preferably has a non flat sealing surface adjacent the flat sealing surface.

The invention provides the opportunity for flow paths in such manifolds to be routed where needed without regard to nozzle location. The invention also provides the opportunity for a mixer to be inserted at each melt transfer bushing between manifolds to thereby enhance mixing of resin being conducted therethrough and balancing of the system.

Thus, the present invention provides an improved manifold and plate assembly, which overcomes the limitations and shortcomings of the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring toFIGS. 3-5, an example of the preferred embodiment of a manifold assembly of the present invention is illustrated and generally indicated by the reference numeral50. The hot runner manifold system50has a plurality of sub-manifolds52that are preferably arranged and housed in manifold plate54and are fed by a main manifold56preferably housed in backing plate58. As with the prior art manifolds, a sprue60connects to the main manifold56at a central location, and main manifold56has a main melt channel62that branches into arms64of main manifold56. Arms64may branch in several different directions, such as is illustrated, or a manifold may have only two arms aligned and extending opposite from each other and from sprue60to make a linear manifold. The manifold may also have only one arm, which in that case, functions to offset the flow in one direction only. Each arm has an outlet63of a branch of the main melt channel62that is in communication with the inlet65of one of the sub-manifolds52. The backing plate58is spaced from the manifold plate54, so that main manifold56is spaced from the sub-manifolds52, and at each arm64of main manifold56a melt transfer bushing68connects the outlet63of the main melt channel62to the inlet65of a sub-manifold52. Each sub-manifold52has a plurality of secondary melt channels104in communication with inlet65and nozzles92connected to sub-manifold52. Each sub-manifold52has apertures66through which valve stems for valve-gated nozzles pass.

Between the manifold plate54and the backing plate58is an air plate70that has a plurality of actuator cavities72for nozzle actuators90as well as a plurality of air channels74that conduct actuating fluid, such as air, to the actuators90. The terms air plate and air channel are used only as labels and are not intended to limit the invention to the use of air. Other gaseous or liquid fluids can be used with the air plate to actuator the actuators90. The actuator cavities72align with the apertures66in sub-manifolds.52. Because the actuator cavities72for the actuators90and air channels74are not in the same plane as the main manifold56, the main manifold56can take an optimum path to the sub-manifolds52. Flow through the sub-manifolds52can be better balanced by introducing the molten material centrally rather than at one end of the sub-manifold52, and the overall spacing of the actuator cavities72, and hence the nozzles, can be closer, thereby reducing the overall size of the manifold and mold compared to the prior art.

Air plate70preferably has cooling channels84that, in use, conduct cooling fluid, such as water, through air plate70, preferably proximate to actuator cavities72so that air plate70is sufficiently cool to prevent seal degradation for actuators90in actuator cavities72. Cooling of air plate70also enhances thermal isolation between main manifold56and sub-manifolds52, which minimizes thermal variation in sub-manifold52and improves the material flow balance in the system. Cooling channels84are aligned with and communicate with cooling ports86in air plate70, which are aligned with and communicate with cooling ports88in manifold plate54and cooling ports116in backing plate58.

Cooling ports116may be arranged to align with and communicate with cooling ports118in a platen119of an injection molding machine in which manifold system50can be installed. Preferably o-rings121, or similar types of seals, are used to provide sealing between adjacent plate faces at interfaces of cooling ports86,88and116. Such arrangement of cooling lines and ports in the plates54,58, and70eliminate the need for any cooling fluid hoses to be attached directly to the manifold system50. Cooling fluid is received directly from the platen, to which cooling fluid hoses are attached. This reduces the time necessary to remove manifold system50from the injection molding machine since there are no hoses or hose fittings to disconnect from the manifold system50.

Bolting together of the plates54,58and70is also improved with the present invention. Air plate70can be bolted to manifold plate54as desired with little concern for location of main manifold56since bolts76extend only between the air plate70and manifold plate54. A plurality of air plate bolt holes78in air plate70provide for such bolting, with air plate bolt holes78running under main manifold56as needed to best counteract forces tending to separate the plates. The backing plate58can then be bolted to air plate70with little concern for the position of sub-manifolds52, since bolts80extend only between backing plate58and air plate70. Backing plate bolt holes82can be located very close to where separation forces occur near ends of manifold arms64, and directly over a sub-manifold52. The better plate bolting of the present invention provides less likelihood of plate bowing, and thereby less likelihood of resin linkage at interfaces between components.

In the embodiment illustrated inFIG. 5, air plate70is shown as a relatively thin plate while manifold plate54and backing plate58both are thicker with pockets that house the sub-manifolds52and main manifold56respectively. Alternatively, the air plate70could be thicker and incorporate the pockets to house the main manifold56and/or the sub-manifolds. Such an arrangement allows manifold plate54and/or backing plate58to be substantially thinner plates, either bolting to air plate70.

Referring toFIGS. 5 and 6, sub-manifolds52are constructed and arranged such that a plurality of nozzles92connect to them in a manner well-known in the art. Any nozzle configuration and any nozzle attachment method known in the art can be used with sub-manifold52. For example, in the embodiment illustrated, nozzle92is spring-loaded against a manifold bushing94by spring96. Nozzle92preferably has a non-flat sealing surface98adjacent the flat sealing surface100of manifold bushing94, which reduces the force required to adequately seal the sealing surfaces because of reduced contact area. Preferably the non-flat sealing surface98is a raised conical surface around melt channel108in nozzle92that is angled less than one degree from planar as described in U.S. patent application Ser. No. 09/575,353, hereby incorporated herein by reference. A similar sealing interface is preferably provided between end102of melt transfer bushing68and main manifold56.

In the embodiment illustrated, manifold bushing94communicates with a melt channel104in sub-manifold52and directs molten material to nozzle92through a manifold bushing melt-channel106that is aligned with the axial melt channel108in nozzle92. A sealing interface112occurs between valve stem110and manifold bushing valve stem guide channel123to prevent resin linkage along valve stem110to actuator90.

Another example of a nozzle/manifold assembly is illustrated inFIG. 7, where nozzle120has a melt channel122with a non-axial portion124that engages a manifold bushing126which communicates with melt channel104. A sealing interface114occurs between valve stem128and a valve stem guide channel125in nozzle120to prevent resin linkage along valve stem128to actuator90.

FIGS. 6 and 7also illustrate different embodiments for actuator90. In the embodiment illustrated inFIG. 6, actuator90is housed in a separate cylinder130, which is installed in actuator cavity72formed in the bottom of air plate70. Cylinder130seals between the base132of actuator cavity72and a backup pad134disposed between sub-manifold52and air plate70. Such sealing of a cylinder in an actuator cavity with a backup pad is described in U.S. Pat. No. 6,343,925 assigned to the same assignee as the present invention and hereby incorporated herein by reference. In the embodiment illustrated inFIG. 7, actuator cavity72is formed in the top of air plate70and is itself the cylinder for actuator90. A separate seal plate136is optionally provided to seal actuator cavity72, or backing plate58itself could seal actuator cavity72. This requires each actuator cavity to be a cylinder of sufficient quality to allow proper operation of actuator90, but it does not require any seal that is dependent on the loads generated by installation of components below the air plate70.

Referring toFIG. 8, another advantage of the hot runner manifold system50of the present invention is that since the main manifold56is spaced from the sub-manifolds52, the melt transfer bushings68are sufficiently long to allow installation of a static mixer140in the flow channel148of each melt transfer bushing. The static mixer140homogenizes the molten material at the entrance to each sub-manifold52, thereby providing a more balanced flow of the molten material. Static mixers suitable for such application are well known. The invention is not limited to the use of any particular static mixer. An example of one suitable mixer, as illustrated, is described in U.S. Pat. No. 6,382,528 assigned to the same assignee as the present invention and hereby incorporated herein by reference. Mixer140has a spiral groove142around a central shaft144with an increasing space between the shaft144and the lands146adjacent the groove142. Flow of the molten material through the mixer140is transitioned from spiral flow to axial flow and homogenized in the process. Another example of a static mixer suitable for use in melt transfer bushing68is a stack of static mixing elements as described in U.S. Pat. No. 6,394,644, herein incorporated by reference.

Melt transfer bushing68preferably has a heating device150so that there is little temperature loss in the molten material as it flows through melt transfer bushing68. The heating device150preferably is an electric heater, but heating device150may be at least one heat pipe that draws heat from main manifold56and sub-manifold52to sufficiently heat melt transfer bushing68. Alternatively, melt transfer bushing68could be constructed of a material sufficiently thermally conductive to not require any heating device150. Melt transfer bushing68may itself function as a heat pipe drawing sufficient heat from main manifold56and sub-manifold52.

Melt transfer bushing68is preferably fastened to sub-manifold52, such as by bolts152(only one of which is shown for clarity) which provide sufficient compressive force between the melt transfer bushing68and sub-manifold52to seal the interface154between melt channel148in melt transfer bushing68and melt channel104in sub-manifold52. To seal the interface156between melt channel148in melt transfer bushing68and melt channel62in main manifold56, force is exerted by a spring device158acting between main manifold56and backing plate58and preferably aligned with melt channel148. The main manifold56preferably has a flat sealing surface160, and the melt transfer bushing68preferably has a non-flat sealing surface162adjacent the flat sealing surface160. Preferably the non-flat sealing surface162is a raised conical surface around the melt channel148of the melt transfer bushing68, and is angled less than one degree from planar, as previously described. Of course, sealing between the melt transfer bushing68and main manifold56could be achieved using alternative techniques readily appreciated by one skilled in the art.

With melt transfer bushing68fixed to sub-manifold52by bolts152, relative lateral motion between sub-manifold52and main manifold56due to thermal expansion differences occurs at interface156. Because of the high frictional load at interface156from spring device158, rather than melt transfer bushing68sliding relative to main manifold56at interface156, melt transfer bushing68may bend during such movement allowing interface156to leak. A centering feature159, such as a ring, acts between melt transfer bushing68and air plate70to facilitate sliding of melt transfer bushing68relative to main manifold56at interface156when there is relative lateral motion between sub-manifold52and main manifold56. Centering feature159keeps melt transfer bushing properly located in air plate70and minimizes risk of leaking at interface156by minimizing likelihood of melt transfer bushing bending. Alternatively, melt transfer bushing could be made substantially stiff to sufficiently resist bending on its own, but such a design would be more massive, requiring more heat.

The present invention advantageously provides an improved hot runner manifold system with less likelihood of plate bowing and its associated leakage, better thermal and geometric balance, and closer nozzle spacing all due primarily to the main manifold being spaced from the sub-manifolds. The additional space also allows for insertion of an air plate that provides all the air for valve gate actuators as well as cooling fluid to better thermally isolate the main manifold from the sub-manifolds and to simplify installation and removal of the manifold system from an injection molding machine. There is also room for static mixers in melt transfer bushings between the main manifold and sub-manifolds to improve melt homogeneity. The invention provides the opportunity for flow paths in such manifolds to be routed where needed without regard to nozzle location. The invention also provides the opportunity for a mixer to be inserted at each melt transfer bushing between manifolds to thereby enhance mixing of resin being conducted therethrough and balancing of the system.

It will, of course, be understood that the above description has been given by way of example only and that modifications in detail may be made within the scope of the present invention. For example, it will be appreciated by one skilled in the art that more than two levels of manifolds may be supported by the invention. Sub-manifolds52may be grouped, for example, in groups of four, with each group fed by an “X” shaped manifold. Two, four, or more of those X-shaped manifolds with their sub-manifolds may be grouped and fed by another manifold. Such layering of manifolds can continue for as much space as the platen spacing of the molding machine allows.

It will also be appreciated by one skilled in the art that a manifold system of the present invention can be used with hot-tip type nozzles instead of valve gate type nozzles. With no valve gate to actuate, the air plate has no actuator cavities and no air channels, but can have cooling channels. The benefits of separating the main manifold from the sub-manifolds when used with hot-tip type nozzles are improved thermal isolation between the main manifold and sub-manifolds, which can be enhanced by cooling the air plate, and the ability to install static mixers in the melt transfer bushings to homogenize the melt and better balance the system.