IES80449B2 - Injection screw - Google Patents

Abstract

An injection screw (10) has a head end (101); a tail end (102) and a thread (103) which travels the length thereof. The screw (10) has three sections viz a feed section (105); a compression section (106); and a metering section (107). In a preferred embodiment, a plurality of pins (50) project radially from the surface of the screw (10) in the metering section. Most preferably, a second set of a plurality of pins (51) projects radially from the screw (10) also in the metering section. When in use for the production of plastics material, the pins (50,51) prevent the passage of unplasticised material and enhance the mixing characteristics and homogenicity of the resulting material.

Description

This invention relates to an injection screw. Injection screws are employed in the production of plastics materials. A known injection screw is shown in Fig. A of the drawings.

In Fig. A, the screw 100 has a head end 101 and a tail end 102. Helically and integrally mounted on the surface of the screw 100 is a thread 103 which travels the length of the screw 100. At the head end 101 and located downstream of the thread 103 is check valve 104. At the tail end 102 there is a drive shaft engaging device or profile 124.

With reference to Fig. C of the drawings, there is shown an enlarged view of part of the screw 100.

The overall diameter X of the screw 100 is the distance between the notional lines 120; the root diameter Y of the screw 100 is the distance between the notional line 121. The distance between the line 120 and the line 121 is known as the depth of flight Z. The space between the line 120 and the line 121 is known as a flight 122. Varying the root diameter Y while keeping the overall diameter X constant will result in a variation of the volume of the flight 122.

The cross-sectional diameter of the root diameter Y varies along its length in three distinct stages. Thus, for a screw 100 being a length of approximately 1600 mm, a feed section 105 is provided between lines A-B; a compression section 106 is provided between lines B-C; and a metering section 107 is provided between lines C-D. The length of the sections are approximately 500 mm; 650 mm; and 400 mm. ,c With reference to Figure B, it will be observed that there are three cross-sectional views of the screw 100 taken along the lines B,C & D of Fig. A of the drawings. It will be observed that the cross-sectional view BI is along the line B; the cross-sectional view Cl is along the line C; and the cross-sectional view DI is along the line D. In the case of BI, the diameter Y is less than the diameter Y of B2 which in turn is less than the diameter Y of B3. Thus, it will be observed, as in Figure B, that the volume of the flight 115 in section A is greater than the volume of the flight 116 of section B which in turn is greater than the volume of the flight 117 of section C.

The combination of the screw 100 and a cylinder (not shown) enables plastics material to be fed in at the tail end 102 and, by virtue of the rotation of the screw 100 (by well-known means), the material is pushed towards the head end 101. En-route, the material is compressed in the compression section 106 and is metered for ejection at the head end 101 when passing through the metering section 107.

A problem arises in that there may be insufficient mixing of the material during its passage through the cylinder 100. Thus, if material of different colours is being fed, colour streaking is observed in the resulting product which is undesirable.

It is an object of the present invention to overcome this problem.

The invention, therefore, provides an injection screw comprising a body portion having a head end and a tail end; a helically disposed thread integrally mounted on the body portion extending from the tail end to the head end and wherein there is radially disposed on the body portion a means having openings therein through which openings material which is being moved from the tail end to the head end must pass through when the screw is in rotation in a cylinder.

Preferably, two such means are provided in spaced apart relationship relative to each other.

The invention will be understood in greater detail from the following description of a preferred embodiment thereof given by way of example only and with reference to the accompanying drawings in which: Fig. 1 is a side view of an injection screw according to the invention; Fig. 2 is a perspective view of the injection screw of Fig. 1 of the drawings; Fig. 3 is a cross-sectional view of the injection screw taken along the lines B-B of Fig. 1 of the drawings; Fig. 4 is a cross-sectional view of the injection screw taken along the lines C-C of Fig. 1 of the drawings; Fig. 5 is a cross-sectional view of the injection screw taken along the lines D-D of Fig. l of the drawings; Fig. 6 is a cross-sectional view of the injection screw, taken along the lines E-E of Fig. 1 of the drawings; and Fig. 7 is a cross-sectional view of the injection screw taken along the lines F-F of Fig. 1 of the drawings.

Referring now to the drawings and in particular to Figures 1-7, there is shown an injection screw 10 having a head end 101 and a tail end 102. Compared with the injection screw 100 of Fig. A of the drawings, the injection screw 10 does not have a check valve 104 but, if desired, a check valve 104 may be included.

The other characteristics of the screw 10 are the same as that described with reference to the screw 100. Thus, the description of the screw 100 (and associated reference numerals) is applicable to the screw 10. How the screw 10 differs from the screw 100 may be described as follows.

With particular reference to Figures 1 and 6 of the drawings, there is provided a first set of a plurality of pins 50 which project radially from the surface of the screw 10 each of which pins 50 is attached to or integral with the screw 10. Each pin 50 is approximately 10mm in diameter and of 200mm centres. The length of each pin 50 will be the same as Z (Figure C). As will be observed from Fig. 1 of the drawings, the pins 50 are located in the metering section 107.

In use, the pins 50 create extra sheer forces; the plastics melt thereby increasing the mixing characteristics, and also inhibiting the passage of unplasticised material.

To further enhance this effect, a second set of a plurality of pins 51 which are similar in construction to the pins 50 but which, as will be observed from Fig. 1 of the drawings are located in the compression section 106. The pins 51 also have a diameter of apporoximately 10mm being located at 20mm centres radially the surface of the screw 10.

When two sets of pins 50, 51 are present, the set of pins 51 is primarily present to prevent the passage of unplasticised material while providing mixing characteristics to the melt. The set of pins 50 primarily serve to provide further mixing characteristic to the melt.

It has been found that the provision of the set of pins 50 and more preferably for two sets of pins 50, 51 provide enhanced mixing characteristics and homogeniety to the resulting material than heretofore and this provides a more aesthetic as well as a technically better resulting product.

It will be appreciated that the pins 50, 51 may be replaced by any other suitable device which would impede the flow of material as it travels towards the end 101.

The invention is not limited by or to the specific embodiments described which can undergo considerable variation without departing from the scope of the invention.

Claims (5)

CLAIMS :

1. An injection screw comprising a body portion having a head end and a tail end; a helically disposed thread integrally mounted on the body portion extending from the tail end to the head end and wherein there is radially disposed on the body portion a means having openings therein through which openings material which is being moved from the tail end to the head end must pass through when the screw is in rotation in a cylinder and further wherein two such means are preferably provided in spaced apart relationship relative to each other.

2. A screw as claimed in Claim 1 or Claim 2 having a feed section located between the tail end and a first notional line located between the tail end and the head end the thread therein having a flight volume fv x ; a metering section located between the head end and a second notional line located between the head end and the tail end the thread therein having a flight volume fv 3 ; and a compression section between the first notional line and the second notional line the thread therein having a flight volume fv 2 ; and wherein ίν χ >ίν 2 >ίν 3 .

3. A screw as claimed in Claim 1 or Claim 2 wherein the means comprises a plurality of pins which project radially from the surface of the body portion and preferably each pin has a diameter of about 10mm and preferably of about 200mm centres. i*

4. A screw as claimed in Claim 2 or Claim 3 5. Wherein the means is located in the metering section. Έ

5. An injection screw substantially as hereinbefore described with reference to and as illustrated in Figures 1-7 of the accompanying 10 drawings.