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. Moulded fibre reinforced thermoplastic products are cheaper, faster and easier to manufacture than cast aluminium 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.
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.

SUMMARY

The invention relates to an element for an extruder. The element has a continuous outer surface in the form of a helical wave.

The invention also relates to an element for an extruder, wherein the element has a continuous outer surface in the form of a helical wave having an axial length in the range of 0.5 to 6 times the outer diameter of the element (10), a helical pitch in the range of 0.5 to 20 times the outer diameter of the element (10) and the ratio of element outer diameter to element root diameter ranges from 1.25 to 1.95.
The element may be used in an extruder for processing of long fibre reinforced thermoplastic.

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 a continuous outer surface in the shape of a helical wave. A continuous surface as used herein refers to a smooth surface without any abrupt changes in profile and without the formation of a distinct land.

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 splines of the drive shaft are engaged. The element (10) has a continuous outer surface (12) in the form of a helical wave extending between the first end (14) and second end (16) of the element.

The 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 continuous outer surface 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.

With reference to figure 2, a front view of the extruder element (10) is illustrated, wherein the element (10) 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 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 of the invention. 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 1. 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 (10), between two crests formed along the element axis. The outer surface of the element is a continuous surface including the crests formed both along and perpendicular to the element axis and thereby forming the continuous helical wave outer surface.

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(l0) has a continuous outer surface (12) in the form of a 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 (10).

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

Such element(s) for an extruder wherein the ratio of element outer diameter to element root diameter ranges from 1.25 to 1.95.

An element for an extruder, wherein the element has a continuous outer surface in the form of a helical wave having an axial length in the range of 0.5 to 6 times the outer diameter of the element (10), a helical pitch in the range of 0.5 to 20 times the outer diameter of the element (10) and the ratio of element outer diameter to element root diameter ranges from 1.25 to 1.95.

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

INDUSTRIAL APPLICABILITY

The element as disclosed is useful in an extruder and serves to generate waves in the material being processed by the extruder. In particular, such elements having a continuous outer surface in the form of a helical wave serve to convey the material without adversely affecting the length of the fibre used for reinforcement.

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

We claim:

1. An element for an extruder, wherein the element has a continuous outer surface in the form of a helical wave.

2. An element for an extruder as claimed in claim 1, wherein the pitch of the helical wave is in the range of 0.5 to 20' times the outer diameter of the element.

3. An element for an extruder as claimed in claim 1 or 2, wherein the axial length of the element is in the range of 0.5 to 6 times the outer diameter of the element.

4. An element for an extruder as claimed in claim 1, wherein the ratio of element outer diameter to element root diameter ranges from 1.25 to 1.95.

5. An element for an extruder, wherein the element has a continuous outer surface in the form of a helical wave having an axial length in the range of 0.5 to 6 times the outer diameter of the element (10), a helical pitch in the range of 0.5 to 20 times the outer diameter of the element (10) and the ratio of element outer diameter to element root diameter ranges from 1.25 to 1.95.

6. An element for an extruder as claimed in any preceding claim used in an extruder for processing of long fibre reinforced thermoplastic.

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