Chain – staple – and horseshoe making – Chains – Links
Patent
1981-04-30
1984-01-31
Husar, Francis S.
Chain, staple, and horseshoe making
Chains
Links
59 86, F16G 1306
Patent
active
044281870
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with joining shackles or links for chain and, in particular, joining shackles for stud-link marine anchor chain.
Dismantlable joining shackles are known for joining chain and probably the most common type of joining shackle presently in use is the Kenter shackle comprising two interlocking machined C-shaped parts held in engagement by an interlocking central stud and a long taper pin through all three parts. Dimensional limitations imposed on the joining shackle to permit it to be inserted through the apertures in common links of stud-link chain and be compatible with Ships' deck machinery so constrains the design of the interlocking parts that only small radii can be employed in stress reducing fillets at internal section discontinuities. In consequence, high stress concentrations occur inside the assembled shackle at these fillets. This leads to failure under cyclic loading at a total number of cycles much less than that which cause failure of the common links of stud-link chain.
Fatigue tests in sea water have shown that a Kenter joining shackle has only one-third of the cyclic load life of corresponding common links of stud-link chain. For this reason, offshore drilling vessels have had no alternative for more than 15 years but to use continuous lengths up to 5,000 feet of stud-link chain for each anchor to avoid the known high incidence of fatigue failures of joining shackles in service.
It is an object of the present invention to provide an improved joining shackle or link obviating or mitigating the above disadvantages.
According to the present invention a chain joining link comprises a link shaped assemblage including, at least one detachable member which when detached permits fitting of the assemblage to end links of successive chain sections and which when fitted provides a secure link between the chain sections, said assemblage including at least one member provided with flanged ends adapted for preloading and which when assembled provide the link ends, other members defining coupling means for joining said flanged ends so that the flanged ends are preloaded in compression and the coupling means are preloaded in tension.
Preferably two facing flanged link ends of the members are arranged to co-operate with recess means in at least one clamp member, and wedge means are provided on at least two members arranged to expand the clamp member or members and compress the flanges when the link is assembled so that the joint is preloaded.
In a preferred embodiment, the joining link includes two U-links providing two pairs of facing flanged ends and joined by said coupling means, and the clamp member comprises a pair of half shells, fastening means being provided to draw said half shells together so as to preload the flanged ends and the half shells.
Preferably the clamp member is provided with threaded fastener means to permit pressure to be developed via the wedge means on the flanged members.
Preferably the operating surfaces of the wedge means are in the form of inclined surfaces machined at less than 5.degree. and preferably less than 2.degree. relative to a plane transverse to the plane of the link.
Preferably the sliding inclined surfaces of the wedge means are coated with a low friction coating.
Preferably the low friction coating is plated zinc giving a coefficient of static friction value less than 0.05.
Preferably water ingress to the surfaces of the joining link is prevented by suitable application of a sealant.
Preferably the link ends of the U-links taper towards the flanged ends.
Preferably an aperture is provided at the symmetry plane of each half shell so that a substantially equal distribution of stress is present in the clamp member adjacent the recesses for the flanged ends.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:
FIG. 1 shows a side view of a joining link for a link chain, according to the present invention;
FIG. 2 shows a plan view, partly in section, of the joining l
Husar Francis S.
Jones David B.
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