GB2097316A - Filtered injection nozzles - Google Patents

Abstract

An injection moulding nozzle comprises a body 10 having a filter chamber 12 and a filter insert 18 defining a plurality of valleys 20 divided by ridges 22. Alternate valleys are open at the inlet end but blocked at the outlet end by an end wall 46 of a nozzle lead 38 while the other adjacent valleys are blocked at the inlet end at 30 and open at the outlet end into slots 58 in the end wall 46. The ridges are dimensioned to present a small longitudinal gap between each ridge and the well of the chamber 12 so that injection fluid can flow through the gap which is small enough to filter out solid particles. The head 38 is rotatable to open those valleys whose outlets are normally blocked to allow purging of filtered material from the nozzle. <IMAGE>

Description

SPECIFICATION improved injection moulding filter This invention relates to the design of an injection nozzle for a plastic injection moulding machine. In particular, it relates to an improved filter system for such nozzle.

Injection moulding of plastic articles involves the pressurized injection of molten or otherwise fluid plastics into a mould under pressure. The moulding operation often involves passing the plastic material through small openings or orifices and into small cracks and channels. Consequently, it is generally necessary to filter the fluid plastic in order to prevent foreign objects such as pieces of metal or unmelted bits of plastic from entering the moulding system where it would plug the machinery or impair the quality of the moulded article. Conventional filters which use a form of wire mesh or perforated metal present problems, in that they quickly become clogged and require frequent cleaning or replacement. They also establish considerable flow resistance. The replacement or cleaning is difficult and timeconsuming and often expensive.While the cleaning and replacement is going on, the machine is generally F It down and out of operation, thus interruc. Ing its productive capacity. Even more important is the fact that once the machine reaches stabilized conditions in the production process, a shut down usually interrupts the conditions of temperature, pressure and other perimeters and it is often difficult to start up the machine and get the process working smoothly and properly again.

It is therefore the object of this invention to provide an improved nozzle design in which a filtering mechanism is provided which is effective, efficient, will not clog easily or quickly, and is quick and easy to clean.

These and other objects are achieved by the present invention in which These and other objects and advantages are sought to be achieved by an improved injection moulding filter nozzle comprising a body having filter chamber comprising an inlet and an outlet end and a filter insert receivable within the chamber, which insert comprises a plurality of longitudinally extending valleys which are defined and separated by longitudinally extending ridges between them. Every second valley is dammed at the inlet end to prevent the inflow of injection fluids and every valley adjacent thereto is open at the inlet end. The ridges are dimensioned to define a narrow gap between the peaks thereof and the filter chamber wall and outlet means communicate with the outlet end of the dammed valleys.A nozzle head having a rear wall across the outlet end of the valleys blocking them except for slots communicating with the outlet end of the dammed valleys so that injection fluid enters one valley and spills over the ridges through the defined gap into the adjacent valleys and flows out through the nozzle head. The nozzle head is rotatable to orient the communicating slots opposite the end dammed valleys to enable them to be purged of accumulated matter. Thus, the gap between the peak of the ridge and the inner wall of the filter chamber forms a defined opening through which oversized particles may not flow as the fluid passes from one valley to the other.

When the nozzle is rotated a small amount of fluid pressed through the filter will force any accumulated matter out through the nozzle to purge it and by returning the nozzle to the operating position the filter is ready to function again in a matter of seconds.

The invention may be more clearly understood by the following description of preferred embodiments with reference to the accompanying drawings in which: Figure 1 is an exploded view of the elements of the filter nozzle in accordance with the present invention; Figure 2 is a rear perspective view of a portion of the nozzle head as seen in Figure 1; Figure 3 is a longitudinal cross-sectional view showing the assembled filter nozzle and illustrating the flow of fluid therethrough; Figure 4 is a cross-sectional view of the assembled filter nozzle in Figure 3; and Figure 5 illustrates the combination of the nozzle head of Figure 2 with the rest of the nozzle and its function therewith.

In the illustrated embodiment, referring first to Figure 1, the nozzle includes a body 10 which is generally elongated and cylindrical, having a cylindrical filter chamber 12 extending axially therethrough and having a circular cross-section of constant diameter coaxial with the body, and having an inlet end 14 and an outlet end 16.

A filter insert 18, which is generally elongated and cylindrical, is removably insertable in the filter chamber of the body coaxial therewith and extending generally from the inlet to the outlet end thereof.

The surface of the insert 18 comprises a series of longitudinally extending circumferentially spaced valleys such as 20 defined by and separated by a series of longitudinally extending ridges 22 projecting radially to form barriers between adjacent valleys. The valleys and ridges are formed on the cylindrical surface of a core 24 which has conical ends 26 and 28 respectively.

At the inlet end of the filter insert every second, or alternate, valley is blocked by a dam 30, while every other valley is in open communication with the inlet end of the body of the nozzle.

The inlet end of the insert has a convoluted or corrugated shape with reference to the plane of the ends of the valleys providing a series of raised parts 32 which match and engage a corresponding series of slots 34 in the periphery of the inlet portion of the body so as to provide rotational orientation to the insert when assembled.

The peaks of the ridges 35 at the outlet end and at the inlet end and top of the dams 30 are radially dimensioned to fit with close tolerance with the internal circumferential diameter of the filter chamber 12 so as to hold the insert centrally or coaxialiy in position within the body 10. However, the intermediate regions of the length of the ridges as at 36 are lowered somewhat to a smaller radius dimension so as to provide a gap of determined size between the external radius of the ridges and the internal radius of the filter chamber as can be seen in Figure 3. It is the dimension of this gap which determines the size of material which will pass through the filter.

A nozzle head 38 is adapted to attach to the outlet end of the body and filter chamber and provides a passage 40 therethrough terminating in the downstream direction at an outlet orifice 42.

The neck portion 44 of the nozzle head is received within the outlet 1 6 of the body 10 and the rear wall 46 abuts against the outlet ends of the ridges 22, as seen in Figure 3. The head is attached to the body and held against the insert by a collar 48 having a shoulder 50 which engages the ring 52 on the circumference of the nozzle head. The internal threads of the collar engage the external threads of the body and the collar can be tightened on by a wrench engaging the hexagonal portion 54.

As can be seen in Figure 2, the entry of the passage 40 at the rear wall 46 is conically tapered, as seen at 56, to match the conical end 26 of the insert and is further enlarged by a series of slots 58 at spaced intervals around the rear wall 46. These slots are located and positioned so as to communicate with the outlet end of every second or alternate valley in the insert as seen at the juncture 60 in Figure 3.

A pair of protuberances such as 62 are designed to engage the slots such as 64 in the ring of the nozzle head to limit the rotational movement of the head when assembled. In fact the notch is sufficiently wide to allow rotation of the nozzle head only enough for the slots 58 to move from one valley to the next adjacent valley of the insert 1 8, which insert is itself held against any rotational movement by the engagement of the slots 34.

Of course, rotational movement of the nozzle head would only be possible if the collar 48 is somewhat loosened and the nozzle head is itself provided with a hexagonal portion 66 to aid in its rotation by means of a wrench.

In operation, it will be understood that a nozzle of the type illustrated is used to communicate and convey molten or fluid plastic between a source such as the conduit 68 leading from a pressurized supply of ground and melted plastic and the entrance to the actual mould machinery in which the plastic is injected. The fluidized plastic is pumped through the nozzle at elevated temperature and very high pressure to ultimately be injected in quickburst into a mould. Under these conditions the nozzle of the present invention must serve also to filter the material being so conveyed to eliminate foreign objects.

To accomplish this the nozzle is attached to the supply, usually by threaded means, and is assembled with the insert in the filter chamber and engaging the slots 34 while the collar 48 securely holds the head 38 against the outlet end of the insert.

In the orientation illustrated in Figures 3 and 5, the protuberance 62 is in its extreme anticlockwise position and the slot 58 is located opposite the ends of those valleys which have dams 30 at their inlet end. The next adjacent valley, each respectively, are open at the inlet end but closed at the outlet ends by the rear wall 46 of the nozzle head where no similar slot exists.

Thus, the molten plastic flowing downstream in the conduit 68 enters the inlet end of the nozzle and flows into the inlet ends of the valleys which have no dam locking them. Thence it flows longitudinally along the valley until its flow is blocked by the rear wall 46 closing the end of the valley. This leaves the only possible outlet the gap between the peak of the ridges defining the valley and the internal circumference of the filter chamber. The plastic therefore spills over the top 36 of the ridges into the next adjacent valley which is the one blocked by the dam 30. Once they are in it can, under continued pressure, flow out through the outlet end into the slots 58 and through the passage 40 and out of the outlet orifice 42 into the mould.

Of course, the gap 70 of determined and limited dimension will not allow any foreign bodies of a larger size to pass through so that such material is filtered out of the stream and collects at 72 at the downstream of the first valley.

Because of the length of the insert and its valleys it will be some time before the filtered material 72 builds up along the length of the valley and eventually restricts the flow through the gaps in the filter chamber.

When the accumulation of filtered particles eventually begins to restrict the flow through the gaps, the nozzle can be briefly disengaged from the mould while the collar 48 is loosened, although not necessarily removed, and the nozzle head is rotated counter-clockwise as far as it can go until the other side of the notch 64 stops against the protuberance 62. In this position, with possibly the additional precaution of tightening the collar 48, a small amount of molten plastic is then pumped through the nozzle (but not into the mould). Because the head has been rotated, the slots 58 will be located opposite the ends of the valleys which were formerly blocked and where the filtered material has accumulated and will allow this material to pass through the slots and the passage 40 and out of the orifice 42. It will be understood that the orifice 42 is sufficiently large to allow passage of this material, most of which is fine enough that it is only blocked by the narrow gap 70 of the filter device.

Once the accumulated matter is purged from the nozzle, the collar can be loosened and the head rotated back to the operating or moulding position illustrated in Figure 5, the collar tightened and the nozzle reattached to the mould machinery so that production can resume. It will be appreciated that all of these steps require very little time or effort and the whole operation can be accomplished in the matter of a few seconds without wasting production time and without substantially interrupting the process so that the conditions of continuous output have to be reestablished.

Although some dimensions of the disclosed assembly must be made to careful tolerance, such as the dimensions of the peak 34 which must fit snugly in the circumferential diameter of the chamber, and the position of the rear wall 46 which must fit snugly against the ends of the ridges 22, these dimensions need not be a fluidtight seal so long as there is no gap large enough to permit the flow through of material intended to be filtered by the dimensions of the gap 70. Of course, the collar 48 will have to be sufficiently tight to prevent leakage of material out of the nozzle at that juncture.

Although the foregoing disclosure illustrates a preferred embodiment of the present invention with specific details not necessarily central to the principle of the invention, it will be realized that numerous modifications and variations might be employed without departing from the inventive concept herein.

Claims (4)

1. An injection moulding nozzle comprising: - a body having a filter chamber comprising an inlet end and an outlet end; - a filter insert receivable within said chamber; ~said insert comprising a plurality of longitudinally extending valleys; ~said valleys being defined by longitudinally extending ridges therebetween; ~at least one of said valleys being dammed at the inlet end thereof; ~at least one of said valleys adjacent said dammed valley being open at the inlet end thereof; ~said ridges being dimensioned to leave a defined gap between said ridges and said filter chamber wall; ~outlet passage means communicating with the outlet end of said dammed valley.

2. A nozzle head having a rear wall across the outlet end of said valleys; ~said end wall having slots therein communicating said passage way with said outlet end of said dammed valley.

3. Said nozzle being rotatable to orient said slots opposite said undammed valley to purge same.

4. An injection moulding nozzle substantially as herein described with reference to and as illustrated in the accompanying drawings.