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WHY FLEXIBLE COUPLINGS GIVE SATISFACTION.

21st November 1922
Page 11
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Page 11, 21st November 1922 — WHY FLEXIBLE COUPLINGS GIVE SATISFACTION.
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A British Invention which has Won a World Market. How Fabric Disc Joints are Made. Points to be Considered.

VEW ARTICLES invented and Manu.

factored in this country -have received such universal appreciation and won so great a success as have the Hardy flexible Couplings patented and manufactured by E. J. Hardy and Co., Ltd., Queen 'Victoria Road, c;:ventry. The various types of flexible -discs made by them have beenProtected in most foreign countries, and the makers have granted sole licences to mantifacture them or to sell under these patents,in the United States, to the Thermoid Rubber Co., Trenton, N.J.; in Fiance to Etablissemeats Brampton, 218, Houleyard Lafayette, Calais ; in Germany and Northern Poland to Budge Bad; Koch stress() 32, Berlin, S.W. 68; and in Austria, Czecho-Slovakia, Jugo-Slavia, Ranmania and Southern Poland to Defies and Friedmann A.G., Mitterberggasse 11, Vienna.

The idea of the flexible disc joint is by no means new, and it is chiefly owing to the great improvements which they have made_ in it that the Hardy Co. have won their success.

Originally, and; in fact, even now, in certain instances, leather was almost exclusively used, but the difficulty with this material is that, it is almost impossible to guarantee that any two leather discs are of equal strength, or that even in a single disc the strength vaj.115be the same at one side as at the other; also leather is susceptible to climatic and other conditions, and frequently flexible leather discs were found to have cracked across, become stretched or torn. These couplings were also very deleteriously affected by oil or water, whieli-softene'd them and rendered them quite incapable of taking anything like their normal load.

The Hardy disc is made in several different types, known as the Hardy, the .Cartflex, the H.P.C„..and the Model.S. The type most generally employed is the first. In this the 'metho'd of lainination is equally to space the angle of the warp 'and weft threadS in each piece Of fabric used in its construction. As the-greatest strength of a piece of fabric Bea a/orig the lines of the thread, it must follow that by spacing the varieua layers evenly the same tensile strength will exist in every part.

The Canflex is somewhat similar in its construction, but combines the advantage of an elastic drive with the plain flexible drive given by the first type. It is built up of layers of fabric as with the model just described, but in each square of fabric the portion in which the weft threads are parallel to the lines of drive is removed and replaced bya sheet of rubber. The method of lamination is to space the fabric equally at an angle of 60 degrees, so that in the completed disc it will be found that between each pair of bolt holes there is nothing but rubber and fabric on the cross.

It is well known that fabric, if pulled on the cross, is flexible, and the disc can, therefore, give slightly under the drive. but the fabric is returned to its natural position, after the distorting force has been removed, by the layers of rubber.

In practice; when the clutch is-let in, the three driving arms and the clutch spider will begin to extend the tension segments of the disc and will continue to do so until the driving force exerted is counterbalanced by the elasticity of the segments, when the arms of the driving spider will begin to. revolve without' shock.

The H.P.C. disc—the name of which is xii abbreyiatien of " Hundred. per Ce-nt." Particularly interesting, as it is capable of Withstanding greater loads than the ordinary _type. . We have 'already pointed', out that the greatest tensile strength of woven material -lies along the lines of-. the threads of which' it is _woven. If, therefore, it is possible to arrange the material so that the threads are in a straight line between each pair of bolt ho es, the resulting disc is very much stronger than one built on the ordinary plan. The makers were, however, faced with the difficulty of praiding these threads between the Six points of Et hexagon representing the 'six bolt holes of each dise,-whereas fabric is only•woven• with the threads-at right, angles. ' However, they, overcame this difficulty by building 'up each lamination of three.specially shaped pieces of fabric, which,.if,plimed together and with the six bolt holes cut in the correct positions, give the desired result..

. The second layer of the disc is also composed of three seictitms of fabric Siinilar to those used in the first layer, but they are turned over before being placed in position and also staggered 60 degrees. This brings the three joints to a position parallel to the three on the first layer, but still within the dead or Compression part of the disc. This building up is continued' in a similar manner until sufficient layers have been obtained.

The Model S disc is designed to meet the 'diffieulty of providing great flexibility with smaller' diameter, and is particularly adapted for taking_ up the declutching action in -light vehicles. It is composed of strips of fabric in direct lines between the six -bolt holes; this means that. there will be twice the DIMher•of layers cf material at each hole as compared with the sections between' the holes. Between the central layers are inserted strips of material to fill these spaces, hut between the two or four outside layers on each side is left a. gap or gaps.

Experience has proVed that the discs are much more efficient. if steel plates are riveted on each side, surrounding the bolt holes. Dining a particular test, Et finished disc, complete with riveted steel. -plates. broke at a pull of 1,688 lb.. but without the plates it, broke at 930 lb.

The shape and size of the plates are of the greatest importance. If there is little or no angularity and no movement through declutching, they may, with advantage, be fairly large, and they should be designed so that each side radiates directly from the centre of the disc.

Where declutching action has to be 1i27 provided for a plate of a different shape must be used, and it is neeessary to have each side of each plate parallel to the edges of its neighbours, and, consequently, the plates usually have to be of triangular shape. In either ease, the corners and edges must be nicely rounded to prevent damage to the fabric disc by cutting.

If the joint is to be made up of two or more discs, these must be assembled with steel plates between them, the whole being riveted together, preferably in a jig consisting of a fiat steel plate into which are fixed six bolts representing the bolts from the three driving and three driven arms of the spiders, and each belt provided with a nut and washer for tightening the discs and plates together while riveting. In erecting such a joint, six plates are mounted on the first disc by means of the correct number of rivets; this disc is then placed on the jig with the rivets pointing upwards, six snore plates are then placed

in position on the rivets, and the second disc forced into position by means of a small tube and a hammer, and so on until the whole joint is assembled, after which the heads of the rivets can be formed by the use of the hammer. With the small diameter imposed by

the space usually available, it is not advisable to attempt a drive with an angle of more than seven degrees. Where little or no angularity has to be provided for, the company recommend one thick disc, but where considerable angularity is encountered it is advisable to couple up two or three discs, each a in. thick, into one joint. The advantage of the single disc is that a compression drive is provided iii what might be called the three dead segments, so that the actual tension on the three live segments is

reduced. •

In deciding upon the use of these joints it is necessary to consider whether there Is parallel or angular distortion, or both. With parallel distortion two joints are necessary,but if the distortion be only angular' one joint is sufficient.

Great care must be taken in riveting the plate as, if the rivet holes fall on the tangential line from the centre hola of the disc, the latter is thereby considerably weakened.

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Locations: Trenton, Vienna, Berlin, Brampton

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