WO2002060671A1

WO2002060671A1 - Injection nozzle

Info

Publication number: WO2002060671A1
Application number: PCT/CA2002/000110
Authority: WO
Inventors: Rudolf Allan Schrempf
Original assignee: Decoma International Inc.
Priority date: 2001-01-31
Filing date: 2002-01-30
Publication date: 2002-08-08

Abstract

An injection nozzle (10) has an accumulation chamber (16) communicating with an injection chamber (18) with a valve (32) regulating a flow of a composite melt therebetween. The accumulation chamber (16) has an inlet for receiving the composite melt and a first drive (30) regulating a volume of the accumulation chamber. The injection chamber (18) has a second drive (38) regulating a volume of the injection chamber and for driving the composite melt to flow through an outlet at a relatively high pressure. The melt is continuously fed into the accumulation chamber (16). The valve (32) is movable between an open position wherein the first drive urges the composite melt to fill the injection chamber (18) thereby moving the second drive (38) to expand the volume of the injection chamber (18), and a closed position wherein the continuously fed composite melt fills the accumulation chamber (16) thereby moving the first drive (30) to expand the volume of the accumulation chamber (16) and wherein the second drive (38) drives the composite melt through the outlet (40).

Description

INJECTION NOZZLE Field of Invention

This invention relates to an injection nozzle for injecting a thermoplastic material having long fibre reinforcement into a mold.

Background of Invention

Injection molded parts can be reinforced using fibres such as glass or carbon. In the final product, the fibres increase the strength characteristics. Generally, the fibres are added to the thermoplastic material and formed into pellets which are added to the feed hopper of the injection apparatus. The injection apparatus has a barrel having a compounding screw. The barrel is heated in order to heat the pellets of thermoplastic material above its melting point and homogenize the melt. The compounding screw forces the melt out of the barrel through a nozzle into a header of a mold. The header directs the melt into the mold cavity. The injection apparatus of the prior art has a tendency to break the fibres as the melt moves down the compounding screw. Further, the compounding screw is stopped and started during injection cycles of the mold, which induces stresses in the melt and increase likelihood of fibre breakage. The improved strength characteristics of the final product depends upon the length of the fibres. Thus, it is desirable to minimize the breakage of the fibres during injection.

Proposals have been made to melt the thermoplastic prior to the addition of the fibres. In United States Patent no. 5,165,941, a process is described in which a relatively large pellet is formed containing long glass fibres. The melted thermoplastic resin is introduced into the compounding extruder at a point downstream of the inlet point for the reinforcing fibers, so that the fibers are mechanically worked and heated before coming into contact with heated, molten thermoplastic resin. This pellet is then compression molded to form the final product.

Although this process preserves the length of the fibres in the final product, the process is relatively slow, thereby limiting mold cycle time.

Summary of Invention

The disadvantages of the prior art may be overcome by providing an injection nozzle which transfers the fibre melt to the mold with a minimum of fibre breakage. It is desirable to provide an injection nozzle which enables the compounding screw to continuously operate during injection cycles.

According to one aspect of the invention, there is provided an injection nozzle having an accumulation chamber receiving melt from a compounding screw. The accumulation chamber has a first drive for regulating the volume of the accumulation chamber. The accumulation chamber communicates with an injection chamber. A valve regulates the flow of melt between the accumulation chamber and the injection chamber. The injection chamber communicates with an exit port. The injection chamber has a second drive for driving at a relatively high pressure. The compounding screw continuously feeds melt to the accumulation chamber. Melt will feed from the accumulation chamber to fill the injection chamber. Once the injection chamber is filled, the valve is closed and the second drive is energized to eject the melt from the injection chamber through the exit port. While the valve is closed, the compounding screw continues to feed melt to the accumulation chamber. The first drive retracts in response to an increasing volume of melt in the accumulation chamber. Once the second drive has completed the ejection stroke, the valve opens whereupon the melt from the accumulation chamber will flow into the injection chamber. The second drive retracts in response to increasing volume of melt in the injection chamber. The first drive is energized to urge melt in the accumulation chamber towards the injection chamber without driving the melt back into the compounding screw.

According to another aspect of the invention, there is provided an injection nozzle which is provided with an accumulation chamber communicating with an injection chamber with a valve regulating a flow of a composite melt therebetween. The accumulation chamber has an inlet for receiving the composite melt and a first drive regulating a volume of the accumulation chamber. The injection chamber has a second drive regulating a volume of the injection chamber and for driving the composite melt to flow through an outlet at a relatively high pressure. The melt is continuously fed into the accumulation chamber. The valve is movable between an open position wherein the first drive urges the composite melt to fill the injection chamber thereby moving the second drive to expand the volume of the injection chamber, and a closed position wherein the continuously fed composite melt fills the accumulation chamber thereby moving the first drive to expand the volume of the accumulation chamber and wherein the second drive drives the composite melt through the outlet.

Description of the Drawings Drawings which illustrate a preferred embodiment of the present invention in which,

Figure 1 is a schematic representation of the injection molding system incorporating the injection nozzle of the present invention; and

Figure 2 is a detailed sectional view of the injection nozzle of Figure 1.

Description of the Invention

Referring to Figure 1, an injection molding system is generally illustrated whereby plastic pellets 101 are fed from a hopper 112 into a barrel 14, where the pellets 101 are transported along the length of the barrel 14 through a reciprocating compounding screw 24. Barrel 14 is an elongated hollow cylinder in shape.

Compounding screw 24 is rotatably mounted within the barrel. Axial rotation of the screw 24 is achieved by a hydraulic motor 118. The pellets 101, preferably having reinforcing fibres, are heated while traversing the barrel 14 by heater bands 120. The pellets 101 melt to form a melt pool. The compounding screw 24 moves the composite melt to flow continuously from the outlet 26.

Referring to Figure 2, injection nozzle 10 of the present invention is illustrated in detail. The injection nozzle 10 has a housing 12 defining barrel 14, an accumulation chamber 16, an injection chamber 18, a valve housing 20 and an exit housing 22. Outlet 26 communicates with an inlet of accumulation chamber 16.

Accumulation chamber 16 has a first drive assembly comprising a piston 28 and a first drive 30. Piston 28 is slidably and sealingly mounted in the accumulation chamber 16 for controlling the volume thereof. Piston 28 reciprocates in a sealed fit against the inside wall of the accumulation chamber 16. A first drive 30 effects movement of the piston 28. Preferably, piston 28 reciprocates along a path generally perpendicular to the barrel 14.

Naive housing 20 extends between accumulation chamber 16 and injection chamber 18. Naive 32 is mounted in the valve housing 20 and controls flow of composite melt through transfer port 34. Transfer port 34 is the outlet of accumulation chamber and the inlet of injection chamber 18. Preferably, valve 32 is of a rotational type, operably engaging a drive to effect rotational motion in order to open and close flow between the accumulation chamber 16 and the injection chamber 18. However, it is apparent to those skilled in the art that any type of valve capable of opening and closing the flow of melt between the accumulation chamber 16 and injection chamber 18.

Injection chamber 18 has a second drive assembly comprising a piston 36 and a second drive 38. Piston 36 is slidably mounted in injection chamber 18 for controlling the volume thereof and ejecting a dosed shot of composite melt under relatively high pressure through outlet or exit port 40. Piston 36 reciprocates in a sealed fit against the inside wall of injection chamber 18. A second drive 38 effects movement of piston 36. Preferably, piston 36 reciprocates along a path substantially parallel to the barrel 14.

In the preferred embodiment, second drive 38 is hydraulic and first drive 30 is pneumatic.

As is well known in the art, the first and second drives 30, 38 and the valve 32 are commonly controlled for synchronized operation by a computerized controller 168, preferably the same controller that controls operation of the injection apparatus. The respective volumes of the accumulation chamber 16 and injection chamber 18 are selected to provide a desired amount of melt or dosed shot of melt into the manifold. The volumes and the timing of the valve are also selected so that the continuous flow of melt from the barrel 14 is not interrupted. Additionally, the faces of the pistons 28, 36 can be contoured to minimize stresses induced in the melt. In operation, the valve 32 will initially be open. Composite melt will flow through the outlet 26 into accumulation chamber 26. Piston 28 will be moved to minimized position, wherein the volume of accumulation chamber 16 is minimized. The composite melt will fill the minimized accumulation chamber and then flow through the transfer port 34 into the injection chamber 18. The second drive 38 will be in a de-energized state. The flow pressure of the composite melt created by the compounding screw 24 will cause the second piston 36 to retract, expanding the volume of the injection chamber 18. Alternatively, the second drive 38 can be actuated to retract from the minimized position to a storing position. Once the piston 36 has retracted to a desired volume, the valve 32 is closed. The second drive 38 is energized to drivingly move the piston 36 to eject the composite melt in the injection chamber 18 out the exit port 40 and into a manifold of a mold. At the completion of the injection stroke, the valve 32 opens.

Alternatively, the piston 36 can be retracted a selected amount immediately prior to the opening of the valve 32. The retraction of piston 36 relieves the pressure in the outlet of the nozzle and in the runners of the manifold enabling thermal gating.

The compounding screw 24 rotates continuously, moving composite melt into the accumulation chamber 16. After the valve 32 closes, the composite melt will fill the accumulation chamber 16 and then urge the piston 26 to move from the minimized position to increase volume of the accumulation chamber 16. Once the valve 32 is opened at the end of the pressure stroke of the piston 36, the first drive 30 is energized to move the piston 26 to the minimized volume position. The composite melt is thereby urged into the accumulation chamber 16 through the transfer port 34 and ultimately to the injection chamber 18.

The pressure generated by the first drive 30 must be less than the pressure generated by the compounding screw 24 in order to prevent the composite melt from flowing from the accumulation chamber 16 back into the barrel 14 through outlet 26. Preferably, the first drive 30 generates a pressure in the order of 10 bar whereas the pressure generated by the second drive 38 is in the order of 150 bar.

The above-described embodiment of the invention is intended to be an example of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention.

Claims

What is Claimed:

1. An injection nozzle comprising an accumulation chamber having an inlet for receiving a melt, an outlet, and a first drive assembly regulating a volume of the accumulation chamber, an injection chamber having an inlet communicating with outlet of the accumulation chamber, an outlet and a second drive assembly regulating a volume of the injection chamber and for driving the composite melt to flow through the outlet of the injection chamber at a relatively high pressure, and a valve positioned between the accumulation chamber and the injection chamber regulating a flow of melt therebetween.

2. An injection nozzle as claimed in claim 1 wherein said first drive assembly comprises a piston sealingly and slidingly engaging within said accumulation chamber and a first drive operably engaging said piston effecting movement thereof from a minimized volume position to an expanded volume position.

3. An injection nozzle as claimed in claim 2 wherein said second drive assembly comprises a piston sealingly and slidingly engaging within said injection chamber and a second drive operably engaging said piston effecting movement thereof from a minimized volume position to an expanded volume position.

4. An injection nozzle as claimed in claim 3 wherein said valve is synchronized to open and close with movement of said first drive assembly and said second drive assembly.

5. An injection nozzle as claimed in claim 4 wherein the first drive assembly moves from the expanded position to the minimized volume position and the second drive assembly moves from the minimized volume position to the expanded position when the valve is open and said first drive assembly moves from the minimized volume position to the expanded position and the second drive assembly moves from expanded volume position to the minimized volume position when the valve is closed.

6. An injection nozzle as claimed in claim 5 wherein said first drive assembly exerts a pressure on said melt sufficient to urge said melt to flow out said outlet without creating a backflow of said melt through said inlet of said accumulation chamber.

7. An injection nozzle as claimed in claim 6 wherein said first drive assembly generates a pressure on said melt of about 10 bar.

8. An injection nozzle as claimed in claim 7 wherein said second drive assembly generates a pressure on said melt of about 150 bar.

9. An injection nozzle as claimed in claim 8 wherein said first drive is pneumatic and said second drive is hydraulic.

10. A method of intermittently inj ecting a dosed shot of melt from a barrel of a continuous flow injection apparatus to a manifold, comprising the steps of: (i) providing an accumulation chamber having an initial minimized volume and filling said accumulation chamber with melt from said continuous flow of melt and thereafter establishing a flow of melt from the accumulation chamber to an injection chamber;

(ii) expanding a volume of said injection chamber, filling said injection chamber with melt;

(iii) closing communication between said accumulation chamber and said injection chamber discontinuing said flow of melt therebetween;

(iv) expanding a volume of said accumulation chamber for receiving said continuous flow of melt from said barrel and simultaneously reducing said volume of the injection chamber ejecting a dosed shot of melt into said manifold;

(v) opening communication between said accumulation chamber and said injection chamber re-establishing flow of melt therebetween; and

(vi) reducing said volume of said accumulation chamber to said minimized volume.

11. A method as claimed in claim 10 wherein steps (ii) to (vi) are repeated to deliver a series of dosed shots of melt to said manifold.

12. A method as claimed in claim 10 wherein said volume of said injection chamber is expanded prior to the opening step in an amount to relieve pressure of said melt in the manifold thermally gating said melt.

13. A method as claimed in claim 10 wherein step (vi) occurs at pressure sufficient to urge said melt to flow towards said injection chamber without backflowing said melt to said barrel.