The present invention relates to link chain made up of interconnecting links of opposed U-form

The above type of link chain is well known and generally has double curvature surfaces for transferring load from link to link. This link chain most commonly has its links manufactured from uniform (e.g. round) bar by bending the bar into opposed U-form and welding the adjacent ends of the bent bar to form a substantially elliptical link. A central strut known as a "stud" is often provided at the minor diameter of the ellipse to strengthen the link. The links of these prior ar chains therefore have a substantially circular limb cross section; and these prior art chains are generally deployed around pocketed driving wheels (wildcats) and curved surfaces such as ships stems and hawsepipe knuckles despite high bending stresses arising in particular links when in a pocketed driving or idling wheel and when a link of the chain is supported at a centrally located fulcrum when the chain is stretched* taut around a curved surface of relatively large radius and under substantial load.

In a pocketed wheel, each alternate link is supported at its shoulders while lying flat in a pocket and load is applied to it by the next link pivoting freely on it in a groove in the wheel at right angles to the bottom of the pocket. This produces an appreciable eccentricity between load application and support and gives rise to a large bending moment which induces very high bending stresses in the

pocketed link. The uniform round bar of the link does not provide the best shape^orientation^and position of sections to minimise and bear these induced bending stresses. Further, when a stud-link chain is stretched taut round a curved surface the links automatically tilt to an inclination of about 45 degrees to the surface since this is the condition of minimum potential energy with the axis of the chain at the smallest possible separation from the surface. In this attitude, due to the oval shape of each link, the links are supported obliquely at centrally located contact or fulcrum points adjacent the studs and so experience very high bending stresses which often damage the links. The most serious damage possibility occurs when a link is pressed edge-on in contact with the curved surface just prior to tilting into the 45 degree minimum energy attitude.

It is an object of the present invention _^ to obviate or mitigate the above disadvantages.

According to one aspect of the present invention a chain comprises integral links having opposed C- shaped ends connected by joining limb portions, the links being constructed such that the external profile of each link is of waisted or scalloped form at said joining limb portions when viewed from at least one viewpoint at right angles to the longitudinal axis of the link and at an angle to the plane of the link in the range 40 degrees to 90 degrees. Preferably the waisted part of the link has a

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viewed width not greater than 95% of the maximum viewed width of the link, and in a preferred example the waisted part has a viewed width reduction of at least 12% relative to the maximum viewed width of the link. The link preferably has a central stud.

According to another aspect of the present invention a chain comprises links having opposed C- shaped ends connected by joining limb portions, the section modulus about an axis perpendicular to the plane of the link of a cross- section of a shoulder located at each side of a central crown portion of each C-shaped end being greater than the corresponding section modulus of a cross-section of said central portion and also greater than the corresponding section modulus of a cross-section of a joining limb portion.

Preferably the depth of the above cross-sections measured in the plane of the link is greater, at each shoulder than at the crown and at the joining limb portions.

Preferably the above cross-sections at the crown and shoulder comprise opposed arcuate parts the radius of curvature of one of said arcuate parts being substantially greater than the radius of curvature of the other part.

Preferably the central stud is rectangular in section with a minimum dimension of stud cross-section in the plane of the link.

According to yet a further aspect of the present invention a chain comprises integral links

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having opposed C-shaped ends connected by joining limb portions, the links being constructed such that the join¬ ing limb portions are of waisted or scalloped form so that when links are supported on the peripheral surface of a cylinder having a radius greater than h of the chain pitch with the plane of one of said supported links normal to the axis of the cylinder or oblique thereto, said one link is substantially supported at two spaced points.

Preferably the radius of the cylinder is greater than h of the chain pitch.

An embodiment of the present invention will now be described by way of example with reference to the accomp¬ anying drawings in which:-

Fig. 1 shows a side view of a link of a chain accord- ing to the present invention;

Fig. 2 shows a sectional plan view of the link of Fig. 1 through section -A;

Fig. 3 shows a section of the link through section K-K of Fig. 1; Figs. 4 to 9 show sections of the link through sections C-C, D-D, E-E, G-G, H-H and M-M respectively in Fig. 1;

Figs. 10 and 11 show operational modes of a chain made up of the links of Figs. 1 to 9 and Fig. 12 shows by way of comparison operation of a prior art link chain; Fig. 13 shows in sectional end view the chain of Fig. 1 obliquely supported on a cylindrical surface; and

Figs. 14 and 15 show a side elevation and a sectional end view (through section K-K) of a modified link accord¬ ing to the present invention.

Referring to the drawings and especially to Fig. 1,chain-cable includes a series of interlinked stud links 1 each of which is symmetrical relative to a mid-transverse axisYY of the link , each link 1 comprising C-form ends 2 joined by limb portions 3 with a central stud 4 at the limb portions 2 there is thus provided a pair of spaced apertures 5 through which adjacent links pass. Each C-form end 2 includes a crown portion 6 and shoulder portions 7 adjacent the crown portion.

The conventional round-bar stud link is usually designated by the nominal diameter D of the bar (e.g. 76mm) and the chain pitch is defined by the formula p = 4D. The present link 1 is not of round bar section but the chain pitch can be measured i.e. inside distance P between crowns aind for convenience the present link is designated as if it were a round p bar link from the formula, i.e. D = T- ^τ ^ ^e inks 1 can be made of alloy steel and the exemplary link is designated 76mm.

The cross section of the link 1 at the crown portion 6 approximates to an elliptic form (see Fig. 2) and has an arcuate outer surface O and an arcuate inner surface I joined to the outer surface O by side surfaces T, the outer surface O having a radius R_ greater than the radius R of the inner surface I. As can be seen from Figs. 4 and 5 the radius R increases substantially in the shoulder portions 7, but in the limb portions 3 the outer surfaces O have considerably scalloped sides 8, (see Figs. 3 and 9),

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the tangent to the scalloped sides 8 making an angle of approximately 43 to the plane of the link, i.e. the mid-longitudinal plane XY.

An important feature of the link 1 is that the outer surfaces O of the limb portions 3 are of a waisted form (see Fig. 1) in side view so that the width of the link at the mid section K-K (Fig. 3) is substantially less than the links maximum width

W_ which occurs at the section G-G (Fig. 7) . In this example, W—l = 0.85 but other ratios are possible e.g. the ratio may be as high as O.97 or as low as

O.75 for operating on cylindrical surfaces of radii 2OD to 1.5D. The benefits of this waisted construction will be appreciated from a consideration of Fig. 10 which shows the chain of Fig. 1 passing around a cylinder 11. Thus as can be seen, where the radius R of the cylinder 11 is 235.6mm (i.e. 3.ID) for the link 1 of designation 76mm the particular links whose outer surfaces engage with the surface of the cylinder 11 do so over the entire waisted portion of the outer surface. Where the cylinder 11 has a radius R V _** greater than 235.6mm (e.g. 267mm as shown dashed in

Fig. 10.) , links engaging the cylinder 11 do so sub¬ stantially solely at spaced points S., S_. Further, for 3.1 D < R * ^ O the position of either of S. or S„ lies between the sections H-H and G-G as indicated in Fig. 1. The bending moment arm V. defined by the distance from each point of contact S. , S to the plane XY of an adjacent link is less than the corresponding bending moment arm V of the

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prior art link shown in Fig. 12. By virtue of the above support arrangements bending moment effects due to the oblique tensile loading T on the link 1 are considerably reduced in the link, in comparison with single mid-point loading as was the case with previous chain cable, (round bar) as shown in Fig. 12. Where the radius R of the cylinder 11 is considerably less c then 235.6mm, the benefits with respect to bending moment reduction for the chain cable having 76mm designated links 1 according to the present invention are not so great, but it is established practice in the art where 76mm chain is used to utilize curvatures in chain handling appliances of a radius equal to or greater than 266mm and it is practical and feasible to restrict similarly the radius of curvature of hawsepipe knuckles and hull plating.

Additionally the scalloped sides 8 of the limb portions 3 permit the link to rotate about its longitudinal axis x - x while in contact with a cylindrical surface having a radius R ^- 3.1 D so that no point loading on a fulcrum will occur at the centre of the link. Also, the scalloping is sufficient to allow up to 4 splaying of the links beyond the 90 to each other when wrapped around and in contact with a cylindrical surface. It is a further feature of the link 1 that the shoulder portions 7 have a greater section depth, section area and section modulus than the crown portions 6. It can be seen in Figs. 4 - 6 that the shoulder sections illustrated in these figures have a greater depth and area than the central crown section AA of

Fig. 2 and the mid-transverse plane section KK of Fig. 3.

Referring to Fig. 1,section ratios (referred to section DD) are as follows:

SECTION AREA DEPTH SECTION MODULUS AA O.925 0.937 O.791

BB 0.938 0.944 O.861 CC 0.949 0.964 0.904 DD l.OOO l.OOO l.OOO EE O.993 O.991 0.984 FF O.933 O.952 O.879

GG O.849 0.914 0.749

LL O.747 0.73O 0.566

KK 0.741 0.724 O.556

76mm Round Bar O.945 1.206 1.133

The provision of a relatively high section modulus at section DD reduces bending stresses at the shoulders 7 where high stress concentration is known to be present in round-bar stud-link chains. Further, the progressive reduction of section modulus towards the crown encourages the crown portion 6 to 'wrap round' the crown of the next adjacent link under load both to limit the flexure and, hence, stresses in the crown 6 and to spread the load over the crown portion and so reduce the moment arm inducing bending stresses in the shoulders 7. The relatively low section moduli of the sections of the joining limbs 3 over the considerable distance between section GG and KK allow flexing to occur without unacceptably high stress concentration. The deepening of the sections at the

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shoulders 7 serves also to reduce the eccentricity betwee load application and support points in links lying fla in the pockets of driving and idling wheels and so reduc the high bending stresses induced by passage over suc wheels.

The limb portions on either side of a common apertur 5 converge slightly towards the transverse mid-plane. The effect of this is that when the link is under tension " greatly reduced compression forces occur in the stud 4 This is in contrast to the conventional elliptical lin where the corresponding limb portions diverge with th result that very high compression forces occur in the stu when the link is under tension. By virtue of the greatl reduced compression force the stud 4 can be of considerabl reduced size, and this provides a saving in weight. Indee the above link 1 of the present invention can have a weigh reduction of approximately 20% over corresponding conven tional stud links (round bar) - the present 76mm link shoul weigh about 32 Kg compared to 40.5 Kg for the round ba link.

A particularly significant feature of the above chai cable using the links 1 is that it can fully replace corresponding conventional chain cable without the nee for alteration in the existing chain handling equipment. The chain cable with links 1 has the following fur ther features:

1. The thickened shoulders 7 are contoured to giv the same load transfer zones as conventional stud-lin chain and hence enable the link to fit conventional wildcat (cable lifters). Fig. 11 shows the chain cable of th present invention engaged in a wildcat 12 or cable lifter the dashed line shows a conventional chain cable link i the wildcat pocket 12A. The load transfer zones are marke W in Figs. 1 and 11. 2. Close toroidal fit-up is provided at the crow to give spread support between links.

3. The section modulus of centre sections KK fo bending transverse to the plane of the link exceeds tha of conventional round bar stud links ^" of equal pitch b

5-5%. 4. The width of the crown 6 of a C-end at sectio

AA is within 5% of the maximum separation between sid limbs of adjacent link.

5. Torsional flexibility of the present chain when tau for elastic deformation without permanent set, is - 3-5° ove each pitch length of the chain.

The links can be made by a casting operation, bu can also be made by forging for example using the technique described in UK patents 353 131; 730 811 and 822 241.

The above chain cable of the present invention fur ther avoids the following disadvantages of conventiona elliptic stud link chain:

(a) Round-bar elliptical stud-link chain has a uni form limb cross-sectional area which is not uniformly stres sed under load so giving rise to localised high stres concentrations, which shortens greatly the fatigue life and to unnecessarily high link weight which gives low spec ific strength.

(b) The relatively long stud at the minor diamet of the ellipse must be of thick section to carry the lar compressive loads of approximately 40 percent of cha tension resulting from the elliptical form of the lin and so makes the stud-link unnecessarily heavy.

(c) The very small contact areas between the lo transfer surfaces of adjacent links encourages rapid weari down of these load transfer surfaces.

Modifications are of course possible. For exampl the cross-sections of the link could be of some other fo than those shown. Indeed the present invention encompass a 'waisted' form link where the link has cross sectio of substantially circular form. In a modification, t

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inner surface of the crown has a flattened portion as show dashed in Fig. 2 to enforce load spreading between adjacen links despite manufacturing tolerances and, in particular to reduce bending moment within each link by splittin the resultant applied tensile load in two halves each space from the axis of the chain whereby the moments of eac said, half of the resultant applied tensile load about the neu¬ tral axis of adjacent highly stressed sections (for example sections DD, EE and FF) are substantially reduced and consequentially, the peak tensile stresses at such section are also substantially reduced. Typically the flattene portion shown dashed would be 20mm to 40mm wide for 76m chain.

Whereas Fig. 1 shows the chain link waisted as viewe at right angles to the plane of the link XY, it would b possible for the link to be arranged such that the waistin effect is present when the link is viewed at an angle i the range of 40" to 90° to the plane of the link, eve although the link is not so waisted when viewed at righ angles to the plane XY. ^' Figs. 14 and 15 show this alter native construction: when the link of Fig. 15 is viewe in the direction of arrow OV a waisting effect will b apparent by virtue of the diagonally disposed scallop 8. and 8_. When the link of Figs. 14 and 15 is supporte on a cylindrical surface of radius 3.1 D and with the plan of the link XY oblique to the axis of the cylinder, th link will be supported' in roughly the same manner as des cribed for the link shown in Fig. 10 and this will provid reductions in bending moment stress in comparison wit conventional round bar link. In particular when the cylin der radius is greater than 3.1 D, the link will have space two point contact on the cylindrical surface. The lin construction of Figs. 14, 15 will have definite benefit since the normal operational mode of a chain passing aroun a cylindrical non-pocketed fairlead is with the links ob lique to the fairlead axis (e.g. at 45°). For satisfactor

stressing characteristic of the modified link, the cross sectional area at the waisted part is maintained roughly equal to that of the link of Fig. 1 (for 76mm link): this results in the sides of the apertures 5 being of slightly diverging form as will be apparent in Fig. 14 whereby the stud 4 becomes subject to higher compressive loads.

Fig. 13 shown the chain of Fig. 1 supported on a cylindrical surface 11 having a radius of 3.1 D and at an oblique angle to the surface, i.e. the mid transverse axis Y-Y is oblique to the centre line (not shown) of the cylindrical surface 11: the scalloped portion 8 enables the supported chain link to "wrap round" the cylindrical surface. The chain of Figs. 14, 15 will be supported in a similar manner as in Fig. 13 when the chain links are arranged in oblique fashion as shown.

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