GB2151328A - Tiedown chain - Google Patents

Abstract

A tiedown chain (50) adapted for attachment to a known chain tensioning and securing device (10) has non-reversible links (51) made longitudinally non-uniform by the provision of annular rib-like protrusions (57) to prevent inadvertent reversed insertion of the chain in the anchoring device. <IMAGE>

Description

SPECIFICATION Tiedown chain This invention relates to tie down chain.

U.S. Patent 2,903,767 discloses a chain tensioning and tiedown device which has come into widespread military use in fastening tiedown chains for diverse applications including securing loads such as airplanes and helicopters on the deck of an aircraft carrier. The device includes a pivotally mounted chain block defining an entrance path to receive a tensioned portion of the chain secured to the load. The block also defines an exit path from which the slack or free end of the chain emerges.

The securing device is designed to withstand heavy loading from a properly installed tensioned chain, but is less strong if the chain is inadvertently reversed during installation.

That is, the structural strength of the overall tiedown system is compromised if the tensioned chain is incorrectly fed into the exit path of the chain block, and the slack free end emerges through the entrance path. Although tiedown devices of this type are placarded with a warning to avoid reverse installation of the chain, the incorrect reverse insertion can be and sometimes is made.

This invention provides an oriented chain comprising a plurality of non-reversible unsymmetrical elongated links; each link between the chain-end links being interlocked with two adjacent links and having spacedapart ends and a pair of legs joining the ends, each such link having first and second portions on opposite sides of a theoretical plane normal to the link length and bisecting the link, the first and second portions having outwardly facing surface which are dissimilar in shape; the links being configured to be non-reversible whereby the links extending between the end links are maintained in a predetermined orientation with the first portions extending toward a first chain end, and the second portions extending toward a second chain end when the chain is extended.

Thus, this invention is directed to what can be characterised as a "one way" chain having links between the end links which are nonreversible, and wherein the links are formed by two portions which are unsymmetrical and not mirror images of each other. These features are readily visualised in terms of a conventional chain link having a racetrack or oval shape.

Non-reversibility in a link of this type is most easily provided by making the lateral internal spacing of the link legs smaller than double the cross-sectional diameter of the typically round metal stock forming the link.

Links having this geometry cannot be reversed because there is insufficient clearance space for the end portions of the adjoining links to exchange positions. Non-reversibility can also be provided by other link shapes (such as a wasp-waist link), by a lateral bar extending across the link, or by a protrusion which narrows the opening of the link.

In a chain with non-reversible links, it is possible to assign a directional sense to the links and the chain. One end of the chain can be designated as the load end, and the opposite end as the slack end when the chain is anchored to a tiedown device between its ends. Typically, the load end is identified by the addition of a hook or other attachment fitting. A first end portion of each non-reversible link always faces the load end, and a second end portion of the link always faces the slack end.

The non-reversible links are further formed to be unsymmetrical or anisotropic to the extent that the link end portions are of different shape when viewed from a generally central part of the link. For example, the second end portions (facing the slack chain end) can be laterally enlarged (or enlarged in a direction normal to the main plane of the link) with respect to the corresponding dimension of the first end portions. Alternatively, one or more protrusions can be formed on the second end portions of the links.

When used in combination with the previously described chain tiedown device, the unsymmetrical non-reversible links can be engaged with the device only in a correct orientation with the tensioned load end extending from the device entrance path, and the slack chain end emerging from the exit path. Incorrect reverse installation of the chain is prevented because the link second ends cannot be seated in the device exit path, and latching of the device cannot be completed. No modification of the device itself is required to achieve this significant safety feature.

Specific embodiments of this invention will now be described by way of example, and not by way of limitation, with reference to the accompanying drawings, in which: Figure 1 is a pictorial view of a chain tensioning and tiedown device; Figure 2 is a pictorial view of a chain block used in the tiedown device; Figure 3 is a reduced-scale side elevation of the device; Figure 4 is an enlarged view of the upper end of Fig. 3, showing the device partly broken away with an improperly installed conventional tiedown chain; Figure 5 is a view similar to Fig. 4, but showing a chain of this invention properly installed in the device; Figure 6 is a view similar to Fig. 5, but showing how the chain of this invention prevents inadvertent reverse installation; Figure 7 is an elevation, partly in section, of a tie down chain according to the invention;; Figure 8 is an elevation, partly in section, of a chain according to the invention with another style of links; Figure 9 is an elevation, partly in section, of a third link style of chain according to the invention; and Figure 10 is an elevation, partly in section, of a fourth link style of chain according to the invention.

With reference to the accompanying drawings, the chain tensioning and securing device briefly described above is fully disclosed in U.S. Patent 2,903,767 which is incorporated herein by reference. For convenience, however, a short description of the main structure is appropriate in this specification.

Referring to Figs. 1 and 2, a chain tiedown and tensioning device 10 as shown in the aforementioned patent has a frame formed by spaced-apart side plates 11 and 1 2. A chain block 1 3 (shown in greater detail in Fig. 2) is pivotally supported between the side plates by trunnions 14. Block 13 has a chain entrance path defined by a slot 1 5 which is open at its forward end and extends vertically through the block, giving the block a somewhat Ushaped appearance when viewed from the top. An upper surface 1 7 of the block is concavely dished around the top of the slot, to provide clearance for the first chain link above the block, and opposed legs 1 8 of the block define the sidewalls of the slot.

A chain exit path of the block is defined by a pocket 20 which extends laterally into each leg 1 8 on opposite sides of slots 1 5. The upper forward portions of the legs form lips 21 which overhang the front of the pocket. As suggested by the chain links shown in phantom line in Fig. 5, the pocket is dimensioned to receive a portion of a roughly horizontal link having a major plane generally parallel to the axis of trunnions 1 4. Slot 1 5 is configured to receive a portion of a tensioned vertical link having a major plane generally perpendicular to the trunnion axis.

A shoulder 26 at the lower forward end of each leg 1 8 provides rotation stops for the block, and another shoulder 27 at the upper rear part of the block provides a stop for rotation in the opposite direction. A bar 28 (Figs. 1, 3, and 4 to 6) is secured between frame side plates 11 and 1 2 to abut shoulder 27 for limiting block rotation in one direction when the device is unlatched, and bar 28 also limits rotation in the opposite direction when the device is either latched or unlatched by abutting the rear surfaces of legs 1 8.

A primary latch for the chain block is provided by a pair of spaced-apart cam plates 30 pivotally mounted on a shaft 31 secured to and extending between side plates 11 and 1 2. A primary latch handle 32 has a pair of upwardly extending legs 33 with elongated slots (not shown) receiving shaft 31, thereby rotatably supporting the handle on the shaft, and also permitting limited linear movement of the handle with respect to the shaft. An elongated slot 35 in the lower end of each cam plate 30 receives the platelike surface of handle 32 to couple the handle and cam plates, and to accommodate the linear movement of the handle.

A pawl or secondary latch 38 is rotatably and centrally positioned on shaft 31 between legs 33 of the primary latch handle. Latch 38 has an enlarged head 39 providing a thumbgrip surface, and also forming a rotation stop when the head abuts the front surfaces of legs 33. A spring (not shown) urges the head against these front leg surfaces, and also urges the primary latch handle linearly downwardly away from shaft 31. In this extended position, the lower end of the primary latch handle is captured in a pair of detent-like depressions 41 in side plates 11 and 1 2 when the primary latch is closed as shown in Figs. 1 and 3.

An elongated and centrally slotted shank 43 extends between and downwardly away from side plates 11 and 1 2 to a lower end 44 adapted for connection to a hook 44a (Fig. 3) which secures the device to a supporting surface such as the deck of an aircraft carrier or the floor of a cargo airplane. Teeth 45 on opposite edges of the shank mate with inter nal teeth (not shown) on the inside of an adjusting wheel 46. Rotation of the wheel enables movement of the shank with respect to the device frame to adjust the overall length of the device for removing slack from an attached tiedown chain.

In use, a conventional tiedown chain 48 is engaged in the chain block 1 3 of the device as shown in Fig. 3. The tensioned part of the chain extends upwardly from the device entrance path (slot 1 5) to a load such as an aircraft being secured to a carrier deck. The slack tag end of the chain emerges from the device exit path (pocket 20). The tension load of the chain is transferred by the generally vertical link in slot 1 5 to the generally horizontal link which is trapped in pocket 20 of the relatively massive chain block. Rotation of the latched chain block is blocked by the upper ends of cam plates 30 which abut shoulders 26, and by bar 28 which abuts the rear surfaces of chain-block legs 1 8.

The tension load is thus transferred from trapped and generally horizontal link to the chain block, through trunnions 14 to side plates 11 and 12, and from the side plates through shank 43 to the supporting deck or other surface. The rear end of the horizontal link is trapped by blind pocket 20, and this link cannot escape the chain block in the rearward direction. Any relatively light force which might tend to urge the horizontal link forwardly out of pocket 20 is resisted because the tip of secondary latch 38 abuts the lower end of the vertical link in slot 1 5 (Fig. 5), and thereby limits forward movement of the hori zontal link.The heavy tension load of the tiedown chain urges the horizontal link into (rather than forwardly away from) and against the rear wall of pocket 20, and the secondary latch can be lightly constructed as it normally serves as little more than a keeper (and a quick release) for a lightly loaded or slack tiedown chain.

As described in detail in U.S. Patent 2,903,767, the normal latched position of the device (with latch handle 32 seated in and retained by detents 41) locks the chain block against rotation. When the chain is to be released, the latch handle is moved upwardly to clear detents 41, and then rotated outwardly to move the tips of cam plates 30 out of abutting engagement with shoulders 26 of the chain block. This permits the chain block to rotate to a position where the chain slips out of the device. With a slack or lightly loaded chain, disengagement can also be achieved simply by rotating secondary latch 38 until the engaged links can be slipped out of the chain block.

Tiedown devices of the style of device 20 are ruggedly constructed, and have proven reliability in providing secure anchorage of heavy military aircraft in extreme conditions such as on the pitching deck of an aircraft carrier in heavy seas, or in a cargo aircraft in violently turbulent air. This reliability, however, depends on proper installation of the tiedown chain with the tensioned or load end of the chain extending from the chain-block entrance path, and the slack end extending from the exit path. In spite of personnel training and warning legends on the device itself, incorrect reverse installation has occurred, with a resulting compromise of the structural integrity of the device.

A properly installed chain (Figs. 3 and 5) transfers the chain load to trunnions 14 without imposing any signficant moment of force tending to rotate chain block 1 3 clockwise (as seen in Figs. 3 and 4 to 6) against the restraint of cam plates 30 bearing on shoulders 26. A small clockwise torque is intentionally provided to ensure that the chain block will automatically rotate to an open position (in which the chain is released without further manipulation) when latch handle 32 is opened. This light torque load, however, is easily withstood by cam plates 30 when the latch handle is closed, and any unusual side loads on the slack end of the chain are resisted by the tip of secondary latch 38.

Even without the secondary latch, a tensioned chain will be held captive in the chain block due to the inclination of pocket 20 (Fig. 5).

An improperly installed conventional chain 48 is shown in Fig. 4, with a slack end 48a emerging from slot 1 5 of chain block 13, and a tensioned end 48b extending from chainblock pocket 20. The line of action of the tension force is separated from the axis of trunnions 14 by a signficant lever arm, resulting in a heavy torque load (arrow 49 in Fig.

4) on the chain block. When the tiedown chain is very heavily loaded, this torque or moment may lead to distortion or failure of the chain block, cam plates 30, or secondary latch 38, leading to separation of the chain from the tiedown device.

Consideration has been given to modifying the structure of the tiedown device to solve this problem, but no acceptabie solution was achieved. It was then recognized by the present inventor that the problem could be corrected with a modified chain, and without requiring any modification of the numerous tiedown devices already in service. The solution is structurally effective, and is economi cally attractive in view of the relatively inexpensive and expandable nature of tiedown chains.

Referring to Fig. 7, a modified tiedown chain 50 according to the invention has a member or interconnected links 51. One end links 51 a is engaged with a conventional hook 52 which is selected for connection to a fitting on the aircraft or other load to be secured. The opposite end of the tiedown chain simply terminates in a final link 51, and the location of hook 52 thus designates the load or tensioned end of the chain.

Links 51 are generally of conventional oval or racetrack shape, with two exceptions. First, the cross-sectional diameter (dimension 53 in Fig. 7) of each link is chosen to be more than one-half the internal spacing (dimension 54 in Fig. 7) of link legs 55 which are joined by curved link ends 56. Second, protrusions 57 are formed on the link legs toward the end of the link which faces away from the tensioned end of the chain.

As discussed above, the relationship between the link cross-sectinal diameter and the link internal spacing gives the links the important property of nonreversibility. This property can be achieved in other ways (for example, by including in each link an internal protrusion or a central bar 59 shown in phantom in Fig. 7), but the aforesaid dimensional relationship is a simple and inexpensive way to accomplish the goal.

Protrusions 57 are dimensioned such that the link end bearing the protrusions cannot be inserted in pocket 20 of the chain block. As shown in Fig. 7, the protrusions are formed by annular ribs of weld metal on the links, with the outside diameter of the ribs being larger than the clearance space provided by pocket 20 in chain block. The protrusions need not, however, encircle the entire link, and a reliable alternative is to form only a laterally extending "bump" or external protrusion 62 on each leg of a link 63 as shown in Fig. 8. Protrusions 62 extend sideways from the link legs sufficiently to ensure interference with the sidewalls of pocket 20, and thereby to block reverse insertion of the link.

The chain-link protrusion can thus be formed to extend laterally outwardly in the direction of the plane of the flat link, or can also be formed to extend away from the link in a direction perpendicular to the plane of the link. Tiedown chain 64 shown in Fig. 9 has links 65 with protrusions 66 oriented in this latter manner, but care must be taken to ensure that the protrusions are limited in size to avoid interference with entry of the slack end of the link in slot 1 5 defining the entrance path into the chain block.

In either case, reverse insertion is blocked by interference of the protrusions with the walls defining pocket 20. Even a single protrusion can be used, but two protrusions are preferred to enable immediate visual identification of the link end facing the slack end of the chain.

Another alternative approach to the design of asymmetrical links 68 in a tiedown chain 69 is shown in Fig. 10. Rather than relying on a cross-sectional enlargement of the link legs as in links 51, 63, and 65, links 68 have legs of a constant cross-sectional shape, but asymmetry is achieved by enlarging the lateral internal spacing of link legs 70 at a slack chain end 71 as compared to the corresponding dimension at a load end 72 of the link.

This gives the link roughly the shape of a rounded-corner truncated triangle as shown in Fig. 10. End 71 is sized to be too large to fit into pocket 20, but smaller end 72 and the adjacent link-leg portions can be fully seated in the pocket. Nonreversibility of the link is maintained by keeping the lateral internal spacing of the link legs at slack end 71 less than double the cross-sectional dimension of the link.

Fig. 5 shows a tiedown chain 50 (of the style described above) as properly installed in chain block 1 3 of tiedown device 1 0. Vertical link 51b of the tensioned end of the chain is correctly fitted in slot 1 5 which is sufficiently wide to accommodate protrusions 57. A more nearly horizontal link 51c is seated in pocket 20 of the chain block, and protrusions 57 of this link do not interfere with full insertion of the link in the pocket.

Fig. 6 shows an attempt to install chain 50 in an improper reversed orientation in the tiedown device. Protrusions 57 on link 51c block insertion of this link in the chain-block pocket, preventing seating of the link and proper engagement of secondary latch 38 with vertical link 51b in slot 15. The operator is thus immediately warned of the incorrect chain orientation, and the chain is reversed for a correctly seated installation.

In the embodiments described above, the interference or blockage which prevents reverse insertion of the tiedown chain is between the device exit path defined by pocket 20 and an enlargement on the slack-chain end of the links. Conceptually, however, it is possible to provide the interference between the device entrance path and protrusions located at the load end of each link. This approach, however, requires a different geometry of the entrance and exit paths to ensure that a properly oriented link can be fully seated in the exit path, and the configurations already described are accordingly preferred as no modification of the existing tiedown devices is needed.

The end of the tensioned portion of the chain is unambiguously designated to the user by the presence of a hook for attachment to the load to be secured. The opposed end of the chain can be permanently secured to the tiedown device if desired, or can simply be a free slack end. In the latter case, the chain should be of sufficient length that the end link on the slack end (which is reversible because engaged by only one adjacent link) will not be coupled to the tiedown device.

Even this possible ambiguity can be eliminated in several ways. First, the slack-end link can have a central bar or other means as described above to prevent reversal. Second, the final link, even though reversible, can be made circular or some other enlarged shape which cannot be received regardless of orientation in the pocket of the chain block.

There has been described an improved tiedown chain which eliminates inadvertent and unsafe reverse installation of the chain in a widely used style of chain tiedown and tensioning device. No modification of the device is required, and only a simple and relatively inexpensive change in the shape of the chain links is required to achieve this important objective.

Claims (14)

1. An oriented chain comprising a plurality of non-reversible unsymmetrical elongated links; each link between the chain-end links being interlocked with two adjacent links and having spaced-apart ends and a pair of legs joining the ends, each such link havig first and second portions on opposite sides of a theoretical plane normal to the link length and bisecting the link, the first and second portions having outwardly facing surfaces which are dissimilar in shape; the links being configured to be non-reversible whereby the links extending between the end links are maintained in a predetermined orientation with the first portions extending toward a first chain end, and the second portions extending toward a second chain end when the chain is extended.

2. The chain defined in claim 1 wherein the legs of each link are laterally spaced apart by less than twice the minimum cross-sectional dimension of the link.

3. The chain defined in claim 1 wherein said shape dissimilarity is provided by a pro trusion on the second portion of the links.

4. The chain defined in claim 1 wherein said shape dissimilarity is provided by a pair of protrusions on the second portion of the links.

5. The chain defined in claim 4 wherein the protrusions are annular ribs.

6. The chain defined in claim 4 wherein the protrusions extend laterally from the links.

7. The chain defined in claim 4 wherein the protrusions extend from the links in a direction perpendicular to the main plane of the links.

8. The chain defined in claim 1 wherein material forming each link has a cross-sectional diameter more than one-half the width of the lateral internal opening of the link, and wherein each link second portion has a protrusion.

9. In combination with a chain tiedown device having chain entrance and exit paths for receiving tensioned and slack chain links respectively, the exit path being configured to receive only a part of the link therein seated, a chain comprising: a plurality of interlocked links, each link having first and second joined portions, the first portion including the link end facing the direction of a chain-tensioning load, and the second portion facing the direction of a slack end of the chain; the first link portion being configured to be insertable in seated engagement in the exit path of the chain tiedown device, and the second link portion being configured to be non-insertable inseated engagement in the exit path; and whereby the chain can be engaged in the device only if the slack links extend from the exit path, with improper reverse installation of the chain being blocked by the inability of the link second portions to be seated in the exit path.

1 0. The combination defined in claim 9, wherein the links are configured to be nonreversible with respect to the interlocked adjacent links.

11. The combination defined in claim 10 wherein non-reversibility is provided by configuring the links with central openings of insufficient size to enable the interlocked adjacent links to be interchanged in position.

12. The combination defined in claim 10 wherein each second link portion has at least one protrusion which prevents said second portion from being received in the exit path.

1 3. An oriented chain substantially as hereinbefore described with reference to, and as shown in, Fig. 7,8,9 or 10 of the accompanying drawings.

14. The combination of a chain tiedown device and a chain substantially as hereinbefore described with reference to, and as shown in, Figs. 5 and 7 or Figs. 5 and 8 or Figs. 5 and 9 or Figs. 5 and 10 of the accompanying drawings.