Patent Application
20080128936
The field of the present invention is in plastic injection molding machines.
Sprue Bars are generally known in the prior art and are used to convey molten plastic from the nozzle of the injection machine to the hot runners that feed a plurality of mold cavities for making plastic parts. A mold typically comprises two mold plates: a core plate and a cavity plate. The mold cavity and core plates are brought together into a closed position for injection of molten plastic and then separated into an opened position for removal of the finished part. Opening and closing the mold plates is achieved between two platens, one of which is typically stationary and the other of which is typically moved by mechanical, electrical or hydraulic actuators.
When the mold is closed, a sprue bar must engage either the mold cavity itself or more typically the hot runner which is used in many molds to distribute the molten plastic to the mold cavities. At its opposing end, the sprue bar must engage the nozzle of the injection machine. The injection machine introduces molten plastic into the channel of the sprue bar, under enough pressure to force the plastic into the mold cavities. Both ends of the sprue bar must adequately seal with their corresponding components in order to prevent leakage of the molten plastic. Even in the simplest configurations, the sprue bar is maintained in channels provided for it through other parts, including at least a platen and a mold plate.
Stack molds are frequently used in order to reduce production time. Stack molds include multiple molds so that multiple parts may be made in each injection cycle. In many configurations the stack is arranged along the axis the mold plates travel when the mold opens and closes. In such configurations some sprue bars may be maintained in and travel through channels provided for them in more than two other mold components. In some stack molds, sprue bars must extend through not only a stationary platen and a mold plate for the mold they serve, but also through the mold plates of a different mold in the stack. Examples of stack molds may be found in U.S. Pat. Nos. 5,522,720 and 5,578,333.
The proper alignment of the ends of the sprue bars with the injection nozzles is critical. Because sprue bars can extend outside the mold by half their length or more, their ability to align precisely with the injection unit nozzle may be adversely affected by only small variances in the mold. Molten plastic flashing or “drool” may cause the movement of one or more sprue bars out of its ideal alignment. Misalignment may become problematic by causing the sprue bar to lose its proper seal with its injection nozzle. Through repeated cycles of use, misaligned sprue bars may also cause undesirable early or accelerated wear or deformation of injection nozzles or the sprue bars themselves, necessitating replacement expense and interruptions in production.
Certain guide bushings or sleeves for alignment and guiding may be found in the prior art. For example, in U.S. Pat. No. 5,910,327 to Schad and assigned to Husky Injection Molding Systems Ltd., sleeves and guide bushings are used within the confines of the mold frame. A problem with maintaining proper sprue bar alignment position with such guide bushings or sleeves is that these components are internal to the molds. Accordingly, any adjustments to the sprue bar alignment components to compensate for misalignment requires a halt in production and a certain amount of disassembly of the mold components in order to reach and then properly adjust guide elements. Accordingly, it would be advantageous to have an alignment position mechanism external to the mold itself, that is, a device that does not require any disassembly of the mold to adjust.
Moreover, molders are reluctant to accept non-external modifications to their molding machines for the purpose of providing better sprue bar alignment because it is costly, time consuming and since they may have many machines which need to run the same mold. Each machine would need to be individually tailored to precisely interact with each mold having sprue bars, to achieve mold-machine flexibility. Furthermore, since molds having sprue bars may be configured with a different number and size of sprue bars, dedicated alignment devices for each mold would become unmanageable.
Other prior art alignment devices have been disclosed, as for example the alignment device of U.S. Pat. No. 6,241,507 V1 to Kuo which discloses a device for initial alignment of an injection nozzle and sprue bar. Disadvantageously, it does not provide for any maintenance of proper alignment through production cycles.
There is a need in the art for a sprue bar position alignment device and for such a device that may be adjusted externally to the moving mold components. There is a continuing need for durability and economy in construction and operation of these components.
An external sprue bar position alignment device is comprised of a mounting bracket and a sprue bar alignment frame that is attached to the mounting bracket. The sprue bar alignment frame and mounting bracket define a channel configured to receive a sprue bar upon a mold closing. The sprue bar alignment frame and the mounting bracket are disposed to maintain alignment of an end of the sprue bar with an injection nozzle. The device includes an adjustment device, said adjustment device providing movement of at least one of the mounting bracket or the sprue bar position alignment frame relative to a path of the sprue bar such that at least one of the mounting block or the sprue bar alignment frame may bias the sprue bar in a selected direction upon the molding closing.
In one embodiment, the adjustable sprue bar position alignment device is operatively mounted between a mold platen face and an injection unit. One or more sprue bars may be received in the apertures of the sprue bar frame(s) in the device. The sprue bar position alignment device provides support for the sprue bars and aligns the sprue bars with the injection unit. In one embodiment, the sprue bar position alignment device is adjustable such that the sprue bar(s) may be moved in both the X and Y directions. An adjustable frame mechanism may be removable to accommodate multiple and/or various sprue bar configuration(s). Replaceable wear pads to decrease wear on the sprue bar are disposed within the aperture of the frame.
The device is adjustable to account for any misalignment as a result of sprue bar sagging or worn guide pads. The guide mechanism and wear components are serviceable without having to remove mold plates. The sprue bar position alignment device may be mounted using fasteners in existing tapped holes in order to retrofit existing molds without additional manufacturing. The framework is readily installed on a variety of machine platen configurations, using existing mounting locations in many cases.
The device may advantageously maintain an alignment of the sprue bar from a position between the mold and the injection unit, allowing for better durability and wear life of components.
The sprue bar position alignment device is adjustable for precision alignment with any injection unit nozzle. Adjustments may be made externally to the mold, that is, without disassembling the mold components.
It provides a framework for readily attaching a multitude of adjustable alignment fixtures, designed specifically for a particular sprue bar configuration.
The sprue bars slide on wear pads held in place by the position alignment frames. The sprue bar may also disengage the alignment device during mold opening. As the mold closes the sprue bar(s) engage and slide on the wear pad until the sprue bar engages the injection unit nozzle. The pads can be re-adjusted to account for their wear or minor changes in position of the mold frame or injection unit.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
a is an isometric view of a stationary platen with the sprue bar position alignment device in place; and
b is a close up of a stationary platen with the sprue bar position alignment device in place.
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
Referring now to the drawings wherein like reference numbers refer to like elements,
A stack mold 10 is positioned between a stationary platen 12 and a moving platen 14 of an injection molding machine 26. The moving platen 14 is typically moved by a mechanical, electric or hydraulic ram (not shown). Between the platens 12, 14 of the depicted embodiment are four sets of core and cavity plates 16A, 18A; 18B, 16B; 16C, 18C; 18D, 16D (shown from left to right), wherein each pair of plates mate with one another to define a hollow cavity corresponding to the shape of the plastic part being made and into which the molten plastic is injected. Hence, there are four core plates 16A, 16B, 16C, 16D and four cavity plates 18A, 18B, 18C, 18D, which are arranged in pairs as previously specified from left to right. These core and cavity plates 16A, 18A; 18B, 16B; 16C, 18C; 18D, 16D are fed molten plastic via hot runner plates 20 and 22. Hot runner plates are generally known in the industry. The hot runner plates 20, 22 have flow channels that carry molten plastic received from the sprue bars 24, 28, respectively, and distribute the molten plastic to the mold cavities at a plurality of preconfigured gates. In the depicted four level stack mold, the first hot runner plate 20 delivers molten plastic received from the first sprue bar 24 to the first core/cavity plate pair 16A, 18A located to the left of the hot runner assembly 20 and to the second cavity/core pair 18B, 16B located to the right of hot runner assembly 20 as is shown in
Each of the sprue bars 24, 28 has a first end 30, 32 that must mate and adequately seal with a first injection machine nozzle 34 and a second injection machine nozzle 36, respectively, which delivers the molten plastic to the sprue bars 24, 28 under pressure from the injection machine 26, after the stack mold 10 is fully closed. The closure of the stack mold 10 typically takes a fraction of a second. The entire molding cycle may take several seconds.
The external sprue bar position alignment device 40 of the present invention is depicted in its mounting on the stationary platen 12. As schematically depicted, a first channel 42 and a second channel 44 are defined by components of the external sprue bar position alignment device 40 and act to maintain each of the sprue bars 24, 28 along a desired path that advantageously brings the first ends 30 and 32 of each of the sprue bars 24, 26 into adequate sealing contact with the machine nozzles 34 and 36, respectively. In alternative embodiments, the number of channels may be one or more depending on the number of sprue bars used. Therefore, it is envisioned that the external sprue bar position alignment device 40 may be used with one or more sprue bars.
As can be seen in
In the depicted embodiment the sprue bar position alignment frames 60 and 62 are attached to the mounting bracket. Each sprue bar position alignment frame has a channel 42 and 44 dimensioned to slidingly engage a sprue bar 90 in close cooperation.
As best seen in
As best seen in
Further adjustment may be provided by adjusting devices mounted on adjustment bars 100 and 110. These are fixedly attached to the mounting bracket and include a transverse through hole in which is fitted an adjusting screw 102 and 112. The adjusting screw may be threaded directly to the adjusting bar or made to smoothly engage the through hole and be threaded with a lock nut, 104 and 114 disposed as depicted, either between the adjusting bar and the frame 100, 60 or outside the adjusting bar 110. Against the fixed position of the adjusting bar 100 or 110, the adjustment screw may be used to bias the adjustment frame in a user selected amount in the preconfigured direction in which the adjustment screws are disposed, which is vertical in the depicted embodiment.
Also depicted in
As best seen in cutaway side view
As can be seen in
In operation, a cycle begins with an open mold. The sprue bar ends 30 and 32 are disengaged from the sprue bar position alignment device. They may also be disengaged from the stationary platen, depending upon the mold configuration at hand. As the mold closes, the sprue bars advance through the stationary platen in channels provided for them. Next the sprue bars engage the sprue bar position alignment device where the sprue bar end bushings at each of ends 30 and 32 enter the apertures of channels 42 and 44 in the sprue bar position alignment device. The beveled apertures and wear pads urge each sprue bar towards its intended, pre-configured path and the channels 42 and 44 maintain the sprue bar there. In the depicted embodiment, it is the mounting bracket and not the frames that the sprue bars first engage, although a reverse configuration is equally within the scope of the present invention. As the mold closes, the sprue bars advance through the channels 42 and 44 in the position alignment device and are thereby guided and maintained in their proper alignment for advantageous mating and sealing with the injection machine nozzles. Advantageous position is maintained by the close, sliding cooperation of the sides of the sprue bar with at least the wear pads 120, and also as needed with the sides 82, 84 and 88 of channels 42 and 44. Upon full closure of the mold, the molten plastic is injected, the plastic parts form, and the mold then opens to release the parts. This cycle repeats.
Through a number of cycles of use, the paths of the sprue bars between the stationary platen and the injection machine nozzles may vary from the ideal. In the short term, this may occur through a change in the material being injected, through molten plastic drool or through other variables inherent in the manufacturing process. In the longer term, sprue bar paths may diverge from the ideal because of component wear over time. In either case, an operator may accommodate for these divergences and use the sprue bar position alignment device of the present invention to bias the sprue bars back towards their advantageous ideal path. This may be done in a first direction by loosening the sprue bar position alignment mounting bracket and moving the device as a whole. An adjustment in another direction may also be made by loosening a frame on the mounting bracket and moving it relative to the mounting bracket. This may be further achieved by rotating the adjustment screws. Adjustments may be combined. Adjustments may be kept in place by tightening bolts or lock screws. Adjustments may be made to accommodate the dimensions of replacement wear pads, which may change over time. All adjustments are externally accessible. That is, the sprue bar path may be adjusted without any disassembly of the mold.
As various modifications could be made to the exemplary embodiments, as described above with reference to the corresponding illustrations, without departing from the scope of the invention, it is intended that all matter contained in the foregoing description and shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.
