The present disclosure generally relates to an extruder element. More particularly the disclosure relates to an extruder element for an extruder used for the manufacture of fibre reinforced thermoplastics.

BACKGROUND

Fibre reinforced thermoplastics are used for various types of applications such as automobile parts including bumpers, side panels and dashboards and for office automation equipment. Fibre reinforced thermoplastics are best suited for designs that demands weight saving, precise engineering, finite tolerance and simplification of parts in both production and operation. Molded fibre reinforced thermoplastic products are cheaper, faster and easier to manufacture than cast aluminum or steel products with similar tolerance and material strength. One of the factors that determines the strength and elasticity of a fibre reinforced thermoplastic is the length of the fibres present in the final product. It is observed that when longer fibres are used to reinforce thermoplastic, the mechanical strength and elasticity of the thermoplastic increases.

Various methods are known for the manufacture of fibre reinforced thermoplastics. In one method chopped fibres are added to melted plastic in an extruder. The chopped fibres may be added prior to or after the addition of the melted plastic in the extruder. This has a disadvantage as the fibres and the melted plastic do not mix uniformly when they meet, but form zones of fibre concentration and plastic concentration, that must then be blended downstream by mixing means in order to achieve uniform mixing and impregnation of the fibres. As excessive mixing is required down stream it causes breakage and damage to the fibres.

Another method involves feeding a continuous roving of fibre into the plastic melt in an extruder. In such systems the fibres are rapidly pinched off or cut off between the screw flights and the barrel wall at the point of entry. These fibres form entanglements, which are not completely impregnated, and are therefore very difficult to break up and mix with the remaining plastic melt. Such systems therefore require intensive and/or so long mixing and kneading or shearing zone. The result of this is that a very high proportion of very short fibres or fines are produced in the final product.

Both the methods described above require the use of mixing or kneading extruder elements in the fibre entry zone and in the fibre mixing or impregnation zone (the zone downstream to the fibre entry zone) in the extruder. Such mixing or kneading elements mix compounds primarily through a folding mechanism.

This folding mechanism results in the breakage of the fibres resulting in shorter fibres in the product. Moreover, the fibres produced have an uneven length due to the folding mechanism of these mixing or kneading elements.

Therefore there is a need for an extruder element that would allow for efficient mixing of the fibre with the plastic melt without causing breakage of fibres. The extruder elements should be such that they would allow for the production of fibre reinforced thermoplastic compositions in which long fibres make up as large a population as possible and the smallest or short fibres make up as small a proportion as possible of the product. Moreover, the extruder elements should be such that a substantial portion of the fibres in the product have a specific distribution of fibre length.

SUMMARY

The invention relates to an element for an extruder. The element has an outer surface in the form of a helical wave with a plurality of grooves formed on the crest of the helical wave. The element may be used in an extruder for processing long fibre reinforced thermoplastics.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

The accompanying drawings illustrate the preferred embodiments of the invention and together with the following detailed description serve to explain the principles of the invention.

Figure 1 illustrates on isometric perspective view of an extruder element in accordance with an embodiment.

Figure 2 illustrates a front view of the extruder element of figure 1.

Figure 3 illustrates a left hand side view of the extruder element of figure 2.

Figure 4 illustrates a right hand side view of the extruder element of figure 2.

Figure 5 illustrates a top view of an extruder element illustrated in figure 1.

Figure 6 is a pictorial representative of the extruder element in accordance with an embodiment

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

An element for an extruder shaft is disclosed. The element has an outer surface in the shape of a helical wave. A plurality of grooves are present along the outer surface of the element, the grooves are present along the crest of the helical wave.
With reference to figures 1 and 6, an extruder element for an extruder shaft in accordance with an embodiment is illustrated. The extruder element (10) comprises of a grooved axial bore (18) in which spines of the drive shaft are engaged. The element (10) has an outer surface (12) in the form of a helical wave extending between the first end (14) and second end (16) of the element.

An outer wave surface refers to an outer surface such that the flight depth of the element varies between a maximum and a minimum value to form wave crests periodically along the element. Flight depth refers to the depth of the channel or the distance from the edge of the flight to the core of the element. The flight depth is equal to one half the ratio of element outer diameter (D) to element root diameter. In accordance with an aspect the ratio of the element outer diameter (D) to element root diameter is in the range of 1.25 to 1.95.

The outer surface (12) in the shape of a helical wave refers to an outer wave surface forming periodic crests in a direction both along and perpendicular to the element axis, as depicted in figures 1 and 5. The crests formed along the element axis and crests formed perpendicular to the element axis are connected by the continuous outer surface of the helical wave profile such that a continuous helical crest (20) is formed along the outer surface of the element. The continuous helical crest (20) does not form a land on the outer surface.

A plurality of grooves (22) are present along the continuous helical crest (20) of the element (10). The grooves (22) may be present in a continuous manner on the crest of the helical wave on the outer surface (12). Alternatively the grooves (22) may be distributed in a pre-determined pattern.

In accordance with an embodiment, the grooves (22) are substantially perpendicular to the continuous crest axis, the continuous crest axis being the helical axis passing through the highest point of the continuous helical crest (20).
In accordance with an embodiment, the grooves (22) are substantially parallel to each other.

In accordance with an aspect, the grooves (22) are placed equidistant from each other. Alternatively the distance between grooves (22) may be varied. The grooves (22) may also be placed such that at least two grooves (22) are grouped together. A plurality of such groups may be present along the continuous helical crest (20). In the embodiment illustrated the grooves (22) are placed equidistant from each other.

In accordance with an embodiment, grooved area is less than 50% of the total outer surface area of the element.

In accordance with an embodiment, grooves (22) may extend to a flight depth of not more than 30 percent of the total flight.

With reference to figure 2, a front view of the extruder element (10) is illustrated, wherein the element is shown to form a wave pattern along the element axis. The distance between two successive crests of the wave is a factor of the outer diameter [D] of the element. The distance between two successive crests of the wave is also known as the pitch of the helical wave.

In accordance with an aspect, the distance between two successive crests or the pitch of the helical wave may vary from being half the outer diameter [0.5D] to twenty times the outer diameter [20 D], depending on the nature of the application. For processes involving the treatment of long fibres, the pitch or the distance between two successive crests is preferably at least one and a half times the outer diameter [1.5 D]. In the embodiment illustrated, the pitch or the distance between two successive crests is twice the outer diameter of the element [2D].

Figures 3 and 4 illustrate the left hand and right hand side views of the element (10) in accordance with an embodiment. In the embodiment illustrated the wave completes a cycle, and the two end points (14, 16) represent the start and completion of a wave along the element axis. However, the element (10) may be formed where a wave cycle is not completed between the two end points of the element (10), which would also depend on the distance between two successive crests forming the wave and the length of the element (10).

In accordance with an aspect, the axial length of the element (10) is in the range of 1.25 to 1.95 times the outer diameter of the element (10).

Figure 5 illustrates a top view of the element of figure I. As may be seen in the top view, a wave surface is formed in a direction perpendicular to the element axis. In the embodiment illustrated, one crest of the wave is formed on the element (10) in a direction perpendicular to the axis of the element, between two crests formed along the element axis. The outer surface (12) of the element (10) is a continuous surface including the crests formed both along and perpendicular to the element axis and thereby forming the continuous helical wave on the outer surface (12).

The element (10) may be used in an extruder for processing of long fibre reinforced thermoplastic.

Specific embodiments are described below:

An element (10) for an extruder, wherein the element (10) has an outer surface (12) in the form of a helical wave with a plurality of grooves(22) formed on the crest of the helical wave.

Such element(s) for an extruder wherein the grooves (22) are continuous.

Such element(s) for an extruder wherein the grooves (22) are substantially perpendicular to the helical wave on the outer surface (12).

Such element(s) for an extruder wherein the grooves (12) are substantially parallel to each other.

Such element(s) for an extruder wherein the grooves (22) are equidistant from each other.

Such element(s) for an extruder wherein two or more grooves (22) are arranged in a group.

Such element(s) for an extruder wherein the grooved area is less than 50 per cent of the total outer surface.

Such element(s) for an extruder wherein the depth of the groove (22) is not more than 30 percent of the total height of the crest of the helical wave.

Such element(s) for an extruder wherein the pitch of the helical wave is in the range of 0.5 to 20 times the outer diameter of the element.

Such element(s) for an extruder wherein the axial length of the element (10) is in the range of 0.5 to 6 times the outer diameter of the element.

Such element(s) for an extruder wherein ratio of element outer diameter to element root diameter ranges froml.25 to 1.95.

Such element(s) for an extruder used in an extruder for processing long fibre reinforced thermoplastics.

INDUSTRIAL APPLICABILITY

The element as disclosed is useful in an extruder and serves to disrupt a wave that is generated in the material that is being processed by the extruder. In particular, such elements having grooves allows the length of the fibres to be cut to a desired length to obtain a reinforced plastic having a specific distribution of fibre lengths.

The element as disclosed allows for a conventional extruder to be used for the incorporating fibres in a thermoplastics which retaining the desired fibre length.

We claim:

1. An element for an extruder, wherein the element has an outer surface in the form of a helical wave with a plurality of grooves formed on the crest of the helical wave.

2. An element for an extruder as claimed in claim 1, wherein the grooves are continuous.

3. An element for an extruder as claimed in any preceding claim, wherein the grooves are substantially perpendicular to the helical wave on the outer surface.

4. An element for an extruder as claimed in any preceding claim, wherein the grooves are substantially parallel to each other.

5. An element for an extruder as claimed in any preceding claim, wherein the grooves are equidistant from each other.

6. An element for an extruder as claimed in claim 1 or 2, wherein two or more grooves are arranged in a group.

7. An element for an extruder as claimed in any preceding claim, wherein the grooved area is less than 50 per cent of the total outer surface.

8. An element for an extruder as claimed in claim 1, wherein the depth of the groove is not more than 30 percent of the total height of the crest of the helical wave.

9. An element for an extruder as claimed in any preceding claim, wherein the pitch of the helical wave is in the range of 0.5 to 20 times the outer diameter of the element.

10. An element for an extruder as claimed in any preceding claim, wherein the axial length of the element is in the range of 0.5 to 6 times the outer diameter of the element.

11. An element for an extruder as claimed in claim l, wherein ratio of element outer diameter to element root diameter ranges from 1.25 to 1.95.

12. An element for an extruder as claimed in any preceding claim used in an extruder for processing long fibre reinforced thermoplastics.

13. An element for an extruder substantially as herein described with reference to and as illustrated by the accompanying figures.