This invention relates to chain flail apparatus and, more particularly, to chain flail apparatus in which lengths of chain are attached at one end to the periphery of a rotatable drum or shaft such as in apparatus for de¬ barking felled trees or logs. The felled trees or logs are guided axially past the rotating drum to be contacted by the flail chains which act to strip away the bark.

Chain of conventional form having links formed with circular cross-section crowns and limbs is utilised in such chain flail apparatus. Such conventional chain is considered to have little or no lateral stiffness and limited torsional stiffness even when in tension.

By the present invention there is provided chain flail apparatus including lengths of chain attached at one end to a rotatable drum or shaft wherein the chain is fabricated with chain links of a form enhancing the lateral and torsional stiffness of the chain lengths compared with the lateral and torsional stiffness of conventional form chain links formed with circular cross-section crowns and limbs.

Preferably, the chain flail apparatus is provided with chain lengths composed of links having limbs and crowns of generally oval cross-section having a greater dimension in a direction perpendicular to a plane axial of the link than in a direction in that plane.

Chain formed with links having crowns and limbs of a non-circular cross-section is disclosed in GB-A-2 200 428, which, in turn makes reference to earlier forms of such chain in other patent specifications. However, this earlier disclosure is concerned with chain utilised in conjunction with chain conveyor installations and is directed toward a chain having a greater tension strength

directed toward a chain having a greater tension strength for a given link size. By the nature of the disclosures the dynamics of flail chains are not within the scope of the earlier disclosures.

The invention will now be described, by way of example, with reference to the accompanying drawings in which Figures l to 8 are portions of flail chain lengths indicating alternative configurations of chain links. Cross-sectional views of the links are shown superimposed on the links.

In a flail chain apparatus for de-barking felled trees or logs, chain lengths, approximately seven to nine links long are secured at intervals along and around a rotatable drum. Bolts extending over the length of the drum spaced at equi-angular intervals of 45° or 60° around the drum are secured at intervals through lugs mounted on the periphery of the drum and carry end links of the chain lengths. The drum and chains are contained within the body of the apparatus which includes a surrounding safety hood and guide rollers which are used to guide the logs past the rotating drum.

As shown in Figure 1, the chain length is composed of links 2 having crowns 4 and limbs 6. The crowns and limbs are of approximately constant, generally oval, cross- section, formed as a pair of semi-circles 8 linked by short, straight-line tangents 10. The dimension 12 between the two semi-circles approximates to the dimension 14 between the inner faces of the limbs 6. Typically a clearance of about one millimetre to one and a half millimetres is provided between the abutting faces with, for example, dimension 12 being twenty millimetres and dimension 14 being twenty three millimetres. The effect of making the limbs and crowns of generally oval cross-section and having limited clearance is to increase

the lateral and torsional stiffness of the chain length so that there is less freedom of movement of the chain links compared with chain of conventional form. It will be appreciated that when the flail chain is rotated by rotating the central drum at a relatively high speed the resulting centrifugal force puts the chain lengths in tension thereby urging adjoining crown portions into close contact to form a relatively rigid seating and further increases the stiffening effect. This tension is increased when the flail chain contacts the log by virtue of the pull on the chain in contact with the log thereby increasing the force urging adjoining crown portions into close contact and rigidfying the connections between the links. The enhanced stiffness of the chain and the flatter approach of the chain to the log have the effect of imposing a greater traction on the log surface by the chain, thereby enhancing removal of bark and any residual small branches or twigs from the log to achieve an improved performance of the chain flail apparatus as compared with apparatus utilising conventional, circular cross-section crowns and links, chain lengths since adjoining links of such chain are relatively free to pivot the one in relation to the other. It is anticipated that this will lead to a longer chain life compared to the life of chain lengths of conventional form.

A suitable material for the links is a carbon- manganese- boron steel. Alternatively, either case hardened mild steel or alloy steel links may be used.

It will be appreciated that other configurations of links may be utilised to achieve enhancement of the lateral and torsional stiffness of the chain by forming the links with dimensions such that rotation of adjoining links is curtailed or restricted.

Figure 2 shows an arrangement in which the contour of

the periphery of the cross-section of the links 16 corresponds to the curvature of the interior of the crowns 18 of the links, thereby producing contact between adjacent face portions of adjoining links. By virtue of the friction forces arising between the contacting faces when the chain length is in tension relative movement between adjoining links is restricted.

Figure 3 shows an arrangement in which the links have an oval cross-section of the crown portions 20 similar to that of Figure 2 but with round cross-section limbs 22, thereby reducing the mass of the link for a given length of link and reducing the inertia of the links when being revolved as flails.

Figure 4 shows an arrangement in which the links have an oval cross-section in crown portions 24 and a circular cross-section in limb portions 26. The oval cross-section has side portions of greater radius of curvature than the radius of curvature of the interior of the crown portions 24 such that a small gap 28 is formed between the interlocking crown portions thereby reducing the area of contact between the faces of adjoining links compared with the arrangement of Figure 3 whilst achieving a greater contact area than in a conventional link arrangement, further varying the dynamic inertia characteristics of the chain length.

Figure 5 shows an arrangement in which the links have an oval cross-section in crown portions 30 and a square cross-section in limb portions 32. The oval cross-section has side portions of a radius of curvature corresponding to the radius of curvature of the interior of the crown portion 30. Such links have a higher mass and dynamic inertia than a conventional link and have a different inertia characteristic from the chain lengths described above.

Figure 6 shows an arrangement in which the links have an oval cross-section in crown portions 34 and square cross-section in the limbs 36. The oval cross-section of the crown portions 34 has side portions of a greater radius of curvature than the radius of curvature of the interior of the crown portion 34 such that a small gap 38 is formed intermediate the interlocking crown portions thereby reducing the area of contact between the faces of adjoining links compared with the arrangement of Figure 5 whilst achieving a greater contact area than in a conventional link arrangement, further varying the dynamic inertia characteristics of the chain length.

Figure 7 shows an arrangement utilising a composite chain composed of alternate links 40, 42 respectively having circular cross-sections and oval cross-sections.

The radius of curvature of the side portions of the oval cross-section links 42 is greater than the radius of curvature of the interior of crown portions 44 of the circular cross-section links 40 such that a small gap 46 is formed intermediate the interlocking crown portions. As with the previously described arrangements the dynamic inertia characterisitics of lengths of such chain are different from those of chain lengths of conventional link form.

Figure 8 shows an arrangement utilising a composite chain composed of alternate links 48, 50 respectively having circular cross-sections and oval cross-sections. The radius of curvature of the side portions of the oval cross-section links 50 corresponds to the radius of curvature of the interior of the crowns 52 of the links 48 thereby increasing the area of contact between the faces of adjoining links compared with the arrangement of Figure 7, further varying the dynamic inertia characteristics of the chain lengths.

It will be appreciated that other configurations of the links giving rise to a chain having an enhanced lateral or torsional stiffness are possible and may be selected to give rise to dynamic inertia characteristics appropriate to an envisaged mode of utilisation.

It will also be appreciated that, if desired, different configurations of chain links may be utilised over the length of the chain lengths, giving a varying lateral and torsional stiffness and dynamic inertia characteristics over the chain lengths.

It further will be appreciated that chain having enhanced lateral and torsional stiffness may be used in flail chain apparatus having uses other than de-barking and that the invention includes chain for use in chain flail apparatus.