Chain – staple – and horseshoe making – Chains – Links
Patent
1997-07-22
1999-02-23
Jones, David
Chain, staple, and horseshoe making
Chains
Links
F16G 1502
Patent
active
058732322
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with improvements in flanged joint joining links for chain which include means for preloading the flanged joint to prolong the fatigue life of the joining links.
Preloaded flanged joint joining links are known from the applicant's European Patent Specification No. 0034599 which discloses a link-shaped assemblage of members including two opposed U-shaped parts with end flanges and two opposed coupling shells with pockets for receiving pairs of end flanges. Inclined surfaces on the flanges are held in abutment when the flanges are placed partially aligned in the pockets of the coupling shells. When the coupling shells are drawn together by means of screws, the flanges are forced to slide into alignment along their inclined surfaces and along load transfer surfaces between flanges and coupling shells so that the widths of the flange pairs increase and stretch the pockets thereby establishing compressive preloading in the flanges and tensile preloading in the coupling shells.
This preloaded joining link has three disadvantages. First, high costs are incurred for the very precise fine-tolerance milling required to minimise the combined tolerance errors in flanges and pockets which can result in unacceptable uncertainty in the width excess between aligned flange pairs and pockets of the same order as that necessary to stretch the pockets and produce the desired preload. Second, relative movement as the preloading becomes high between flanges and coupling shells during sliding alignment of the flanges to stretch the coupling shell pockets tends to cause galling damage (pick up of material from one surface by the other due to adhesion when sliding under heavy loads) to the relatively small area load transfer surfaces between flanges and coupling shells. Third, a lack of interchangability of component parts between links arises from the necessity, despite the precise milling, to finalise the width of each abutting flange pair by grinding the inclined surface on each flange following accurate measurement of the widths actually achieved in the corresponding pair of pockets in order to minimise variance in preload stress between abutting coupling shells. The first mentioned disadvantage has prevented wide-spread adoption of the preloaded link even through it provides a needed technical solution for premature failure due to fatigue of chain joining links in the offshore industry.
It is an object of the present invention to provide an improved preloaded joining link which obviates the above disadvantages.
According to the present invention a chain joining link comprises a link-shaped assemblage providing opposed U-shaped portions for retaining adjoining chain sections, the assemblage including a plurality of assemblable parts to enable the joining link to be fitted to the adjacent chain sections, at least one of the parts being provided with flange means while another of the parts is provided with recess means to receive the flange means during assembly of the link, the width of the recess means being greater than the corresponding width of the flange means, and wedge means including a wedge for insertion into the recess means following insertion of the flange means to take up the difference between the widths at a first insertion position of the wedge from which forced further insertion of the wedge through a predetermined distance to a second insertion position stretches the recess means without relative movement occurring between flange means and recess means to establish a correspondingly predetermined compressive preload in the flange means and a correspondingly predetermined tensile preload in the material surrounding the recess means.
Preferably the wedge includes a portion which protrudes from the recess when the wedge is located in the second insertion position. Preferably the protruding portion has an inclined surface arranged to co-operate with a wedge-shaped tool slidable transversely through the link between stops on the tool to move the wedge forcibly through a predetermi
REFERENCES:
patent: 2537405 (1951-01-01), Gilbert
patent: 3139720 (1964-07-01), Robbins
BruPat Limited
Jones David
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