IE53705B1 - Chain link for safety chain - Google Patents

Abstract

A link for a safety chain for example to secure a bicycle against theft, is made from a material having a rectilinear cross-section (F) e.g. in the form of a trapezium having longer and shorter sides (5,4) respectively at the inner and outer peripheries of the link. Alternatively the cross-section may be square or rectangular. Where the ends of the material used to form a link are welded together, a bead (6) is formed of angled section to keep a cutting tool away from the weld. The length of the opening in each link is less than 3 times the width (B) of the cross-section. There is strong resistance against cutting by shears, and against insertion of a lever.

Description

The invention relates to a chain link for safety chains.

Safety chain is generally to be understood to mean any device which is used as security against theft for example in order to connect a bicycle, moped or a light motor cycle to a fixed structure, to fasten a boat to a ring mounted on a jetty, or in order to fix the adjacent bars of a gate to each other, etc. Open-link chains which have links with a round, generally circular cross-section are usually used for this purpose.

In order to prevent unauthorised removal of the item fastened by the chain, the chain must be capable of resisting the cutting action of common metal shears or small shears generally known as bolt cutters or other similar implements, since a potential thief is not or at least not generally in 1.5 a position to have costly and heavy apparatus such as oxygen cylinders and the like with him. In addition it should also not be possible to attack the links of safety chains with metal saws or files.

For these reasons the links of conventional safety chains are - 3 at present subjected to surface heat treatment of the most varied type in order to improve as far as possible the resistance to repeated cutting or to the use of files or the like. However, as regards the action of suitable shears or the like, no entirely satisfactory results have been achieved until now.

With this as a starting point, the invention is directed to the provision of a link for safety chains which is particularly resistant to cutting strain caused by conventional, commercially-avai1able shears.

According to the invention a chain has links made from a length of material with rectilinear cross-section, each link being formed to define a generally rectangular opening, the length of the opening in each chain link being less than or equal to three times the width of the cross-section of the material.

According to a second aspect of the invention a chain having links made from a length of material with a rectilinear crosssection is used to secure an article against theft. That section of material makes the chain difficult to force.

In a preferred embodiment of the chain link the cross section is constructed in the form of an equal-sided trapezium in which the two parallel sides are arranged parallel to the longitudinal plane of symmetry of the chain link which is at right angle to the plane determined by the chain link itself, - 4 and the smaller of the two parallel sides of the trapezium faces outwards.

In conventional chain links with their round cross-sections there is practically point contact between the cross-section and the blades of the shears as is shown in FIGURE 1 of the drawings; the pressure exerted by the blades can cause such severe strain that a crack is easily produced in the surface of the chain link and the material yields immediately below the surface. This initial fracture is transmitted in successive waves to the centre of the cross-section as is shown in FIGURE 2, and the waves extend along the surfaces S which expand increasingly until they lead to a final fracture of the chain link.

When welding the ends of a length of material to form a chain link it has not proved possible always to maintain the material strength at the join. The join is thus the preferred point for attack and also the join is generally at the centre of a long side of the chain link.

In a chain link according to the invention with such a join a particularly advantageous embodiment consists of providing a bead which extends over the upper, inner and lower surface of the relevant long side and at right angles thereto in the region of the weld point and which (viewed in the longitudinal direction of the bead) has a cross-section with lateral surfaces converging steeply towards the tip of the bead.

This prevents a cutting implement being used at the weld point - 5 on the chain link since the steep slope of the side walls of the bead causes the implement to slide off laterally into the region in which the cross-sections are made from the original material. The cross-section of the bead is preferably constructed substantially in the form of a triangle or a pyramid and it is also preferred for the lateral surfaces of the bead to enclose an acute angle; in this way the lateral deflection effect for a cutting implement is particularly effective, although the angle should not be too acute in order to ensure that it causes a marked lateral deflection of the cutting implement. It is also advantageous of the bead to be made from material coming out of the cross-sectional profile at the weld point, and this can be achieved by constructing the bead during the welding process from the material coming out of the normal cross-sectional profile.

A further preferred embodiment of the chain link according to the invention consists of selecting the length of the opening in the chain link so that it is less than (or at the most equal to) 3 times the width of the cross-section of the side of the chain link; this construction means that the available space is such that the largest lever that can be introduced into the chain link opening has a cross-section which is less than the cross-section of the side of the chain link itself; as a result the lever is more likely to break than the chain. If a bead is also present the space is largely filled by the projecting bead and only the tip of a cutting implement can be used since further projection of the cutting implement would be impeded by the next link - 6 in the chain which is at right angles to the link in question.

In order to make a cut here the cutting implement must be used at an angle; anyone using a cutting implement would then be forced to incline the longitudinal axis of the blade relative to the axis of the cross-section of the link, and as a result would have to cut through not a cross-section running at right angles to the axis of the edge but, depending upon the angle of inclination, a much larger crosssection. This effect can be particularly advantageously en10 hanced by a further preferred embodiment in which the width of the bead cross-section in the base region of the bead is greater than the greatest possible distance (viewed in the longitudinal direction of the chain link) between two chain links passed through the opening of the chain link with the same cross-section. This results in drastic lateral deflection of a cutting implement.

Thus, the chain link according to the invention provides a high degree of security against undesirable cutting or forcing of the chain links.

The invention may be carried into practice in various ways, and certain embodiments will now be described by way of example with reference to the accompanying drawings, in which: FIGURE 1 shows a conventional chain link for a safety chain ( in section) with a cutting implement applied to it; — 7 — FIGURE 2 shows the principal strain over the cross-section of the chain link according to Figure 1 at both points of contact with the cutting implement; Figure 3 shows a chain link according to the invention (cut) 5 with a cutting implement applied to it; Figure 4 shows the principal strain in the chain link according to the Figure 3 when a cutting implement is applied; Figure 5 shows a perspective view of a section of a safety chain consisting of chain links according to the invention; Figure 6 shows a lateral view of the view according to Figure 5 in which the two lateral chain links are cut in the central longitudinal plane; Figure 7 shows a view of two interengaging chain links according to the invention with a bead with a cutting implement attacking one of them; Figure 8 shows a side view of the view according to Figure 7 in which the chain link to which the cutting implement is applied is cut in the central plane of the bead; Figure 9 shows a perspective view of a section of a safety chain made from chain links with a bead according to the invention, and - 8 Figure 10 shows a side view of the view according to Figure 9 in which one chain link is cut in the vertical central plane in the longitudinal direction.

In the view according to Figure 1 a chain link 1 of conventional type, i.e. with a circular cross-section F, is shown in section between the blades of a cutting implement 2 such as a bolt cutter or metal shears. Because of the almost punctiform contact between the cutting lines of the cutting implement 2 and the surface of the chain link 1, when the cutting implement 2 is closed, a very high specific pressure is produced which results in a path of line of force S inside the cross-section of the chain link 1 below the points of contact between the cutting implement 2 and the chain link 1 in a manner which is shown schematically in FIGURE 2 by the path of lines of force S (concentration of lines of force).

By contrast FIGURE 3 shows a chain link 1 according to the invention ( also having a cutting implement 2 applied to it), but here the cross-section of the chain link 1 is constructed in the form of an equal-sided trapezium as can be seen immediately from FIGURE 3. Here the cutting implement 2 is no longer applied in a quasi-punctiform manner but along the whole side edges of the trapezium i.e. along the line of contact 3, so that the force exerted by the cutting implement 2 is distributed over a much greater contact surface than in the construction according to FIGURE 1. As a result, it is much more difficult to cause the first crack in the - 9 outer surface of the chain link 1 and cause the subsequent yielding of the underlying layers. As in FIGURE 2, in FIGURE 4, the path of lines of force S for the cross-section shape shown in FIGURE 3 is shown inside the cross-section F of the chain link 1, and it is clearly visible that the distribution of strain is much more even and less concentrated there.

When reference is made to a cross-section F, of the chain links, this refers to the cross-sectional shape which is obtained when one individual side of a chain link 1 is cut through when the cutting plane lies at right angles to the longitudinal axis (central axis) of the link shape formed by the chain link. This cross-section is referred to as cross-section F and this cross-sectional shape is present along the entire periphery of the chain link. The crosssection thus indicates the cross-sectional shape of the length of starting material from which the chain link was produced.

A section of a safety chain in which chain links 2 according to the invention interengage is shown in perspective view in FIGURE 5. The cross-section F of these links 1 is in the form of an equal-sided trapezium, as can be s6en from the cut link on the left in the sectional view in FIGURE 5.

The parallel surfaces 4 and 5 of the trapezium (cf. FIGURE 4) are so arranged that the inner peripheral surface formed by the chain link and the other peripheral surface are parallel to each other and to the central longitudinal plane P which - 10 is at right angles to the central plane Q-Q determined by the chain link (FIGURE 6). As can be seen from FIGURES 3,5, and 6, when a cross-section of an equal-sided trapezium is used the longer of the parallel sides namely the side 5 (FIGURE 4) is used to form the inner peripheral surface of the chain link and the shorter of the parallel sides, namely the side 4 (cf. FIGURE 4) is used to form the outer peripheral surface; this ensures that the upper and lower surface of the chain link formed by the inclined sides of the trapezium cross-section enclose between them an angle the apex of which lies outside the surface enclosed by the chain link, so that the aligned inclination of commercially available cutting implements is taken into account and, as FIGURE 3 shows very well, an almost linear application of the cutters of such cutting implements 2 can be achieved when attempting to cut such chain links. Square crosssections F also provide a very good resistance against such cutting implements, although the trapezium shape gives even better results in many cases. In this way cutting of the chain is practically impossible. It has been shown that for cross-sections F of circular and trapezium shape to fracture the necessary cutting forces lie in a ratio of up to 1 : 10. The links 1 which are used with such crosssection are then produced with a relatively small length and width, as can be seen from the drawings, in order to pre vent the introduction and turning of the cutting blades towards the edges of the cross-section F. As is again shown in FIGURE 6, the position of the parallel sides 4 and 5 of the trapezium shaped cross-section F is chosen so -11that they come to lie parallel to the plane of symmetry P-P which extends in the longitudinal direction of the chain link and is aligned at right angles to the central plane Q-Q formed by the chain link itself.

If chain links with a square cross-section F or with a rectangular cross-section F are used, then two parallel sides are aligned in the longitudinal direction parallel to the plane of symmetry P described in greater detail in Figure 6, like the sides 4 and 5 in Figure 6, whilst the other two parallel sides lie at right angles thereto.

Figures 7 to 10 show chain links 1 according to the invention which are constructed with a square cross-section F. The welded seam which is produced during welding of the chain links is arranged (viewed in the longitudinal direction of the chain link 1) approximately in the centre of one side (at right angles to the longitudinal axis thereof). As can be seen particuarly well in Figure 7 or Figure 9 or also in Figure 10, an additional shaping of the chain link can be provided at this weld point on this long side: care is taken during welding of the chain link 1 to see that during the welding process a bead 6 is formed from material coming out of the normal cross-sectional profile, runs at right angles to the longitudinal direction of the side in question on the surface thereof and extends at least over the upper, inner and lower surface of the relevant side of the chain link. In all cases care will be paid to ensuring a smooth surface on the outside of the chain link so that 537 0 5 - 12 when the chain is used there is no undesirable projection to cause a risk of injury in handling the chain. This arrangement of the bead 6 is shown particularly clearly in the view according to Figure 8 which shows the extent of the bead over the upper, inner and lower surface of the relevant cross-section. The bead 6 is shaped in such a way that its cross-section (viewed in the longitudinal direction of the bead) has lateral surfaces which converge upwards at an angle to the tip of the bead and a cross10 section of the bead 6 in the form of triangle or a pyramid recommends itself as particularly advantageous (cf. Figures 9 or 10).

If a cutting implement 2 is used to break such a chain link, as shown in Figure 7, then the cutting surfaces of this cutting implement are deflected by the side walls of the bead 6 in such a way that cutting at the welding point itself is not possible. Since the weld point is a particularly favourable region for undesirable cutting, the arrangement of the bead 6 ensures that the cutting implement 2 slides off laterally into the region in which the cross-section is made from the original material which has been heat treated on its surface. Furthermore if the chain link only has a short width of opening (approximately 3 x L - cf. Figure 10), then because of the space filled by the projecting bead 6 this means that only the tip of the blades of the bolt cutter can be placed on the cross-section to be cut (cf. the view according to Figures 7 or 8) because otherwise they would be severely impeded by the next chain link lying - 13 adjacent thereto at right angles. If anyone attempted to apply the cutting implement 2 to the chain link 1 not with the tip but over a greater cutting line, then they would be forced to hold the axis of the cutting implement 2 inclined relative to the axis of the cross-section F, and this would result in a cutting cross-section which no longer ran at right angles to the axis of the edge but a much greater cross-section would have to be cut through depending upon the chosen angle of inclination, and this is also a hindrance (cf. Figure 10). There is also the additional advantage that even a lever which might be introduced in order to break the chain link 1 can only have a rectangular __2 cross-section of the surface s . , which is a limiting condition in that such a lever is more likely to break than the chain 1. If the width of the bead crosssection in the base region of the bead 6 is chosen so that it is greater than the greatest possible distance t (Figure 10) (viewed in the longitudinal direction of the chain link) between two chain links passed through the opening of the chain link 1 with the same cross-section F, these being pushed apart until they come to rest on the closed chain link, then it is particularly reliably ensured that a cutting implement 2 is so drastically deflected by the bead 6 that it is reliably impeded by the side of the adjacent link. The ' distance of the tip of the bead on the inside of the link from the opposite side is indicated by s as can be seen in Figure 10.

The bead arrangement according to the invention provides an - 14 increased resistance to undesirable cutting and it also reduces the likelihood of breaking such a chain link by the introduction of a lever. The chain link can be made from any suitable material, but preferably from drawn steel extrusions or wires.

Claims (13)

Cl aims

1. A chain having links made from a length of material, with a rectilinear cross-section, each link being formed to define a generally rectangular opening, in which the length of the 5 opening in each chain link is less than, or equal to, three times the width of the cross-section of the material.

2. A chain as claimed in Claim 1, in which the cross-section has two parallel sides which are parallel to the plane of symmetry of the chain link which is at right angles to the 10 length of the link and at right angles to the plane of the link itself.

3. A chain as claimed in Claim 1 or Claim 2, in which the cross-section is in the form of a symmetrical trapezium.

4. A chain as claimed in Claim 3 in which the shorter of the 15 two parallel sides of the trapezium is on the outer periphery, and the longer side is on the inner periphery, of the chain link.

5. A chain as claimed in any of Claims 1-4 in which in the links the ends of the material are welded in the centre of 20 the length of one long side, and in the region of the weld, a bead is provided which extends over the upper, inner and lower surface of the side of the link and has a crosssection with lateral surfaces converging at an angle towards the tip of the bead. - 16

6. A chain as claimed in Claim 5 in which the cross-section of the bead is generally triangular or pyramid-shaped.

7. A chain as claimed in Claim 6 in which the sides of the bead meet in an acute angle. 5

8. A chain as claimed in any of Claims 5-7 in which the bead is made from material derived from the cross-sectional profile of the material at the weld.

9. A chain as claimed in any of Claims 5-8 in which the width of the cross-section of the bead in the base region of the bead 10. Is greater than the greatest possible distance viewed in the longitudinal direction of the chain link, between the two adjacent chain links.

10. A chain constructed substantially as herein specifically described with reference to Figures 5 and 6, or 7-10 of the 15 accompanying drawings.

11. A link for a chain as claimed in any preceding claim.

12. A chain having links made from a length of material with a rectilinear cross-section used to secure an article against theft. 20

13. A chain used as claimed in Claim 12 the chain being as claimed in any of Claims 1-10.