Technical field of the invention

This invention relates to a washer for guiding two reci- procally movable members relative to each other, said washer consisting of a body of plastics material with a circumferentia portion adapted to seat in one of said members and a central portion, confined by said circumferential portion, adapted to bear against the other member. A washer of this general type, serving to facilitate sliding, is previously known by US 3 445 143.

Background and prior art of the invention

In a number of various technical fields guiding problems may arise in connection with reciprocal displacement of two machine members relative to each other. As an example of such a technical field cranes may be mentioned, more specifically such cranes with an extendible jib composed of two or more sections telescopically movable relative to each other. These are usuall in the form of box profiles or girders which have the same cross-sectional shape, although of different sizes so that one girder can be inserted in the next, and soon. In practice the cross-sectional shape of the girders may be rectangular or, pre ferably, hexagonal, the girders in the latter case including upper and lower V-shaped or angled pairs of flanges between which vertical side flanges extend. Such crane jib girders should be capable of being displaced relative to each other not only with a minimum of friction but also with a minimum of play between the members. In other words the girders should, when th jib is extended or shortened, be capable of moving as linearly as possible relative to each other without rattling. The girder of previously known cranes are provided with special wear plate of nylon or similar material having a low coefficient of fric¬ tion. More specifically, at least one nylon plate or a pair of nylon plates have, as a minimum, been fixed by gluing at the to of and externally on the rear end of each interior box girder, as well as at least one plate or a pair of plates at the bottom and internally of the front end of each external box girder. Thanks to the low coefficient of friction of the nylon material these wear plates certainly facilitate the sliding between the

girders, but they do not provide any positive lateral guidance. With girders of hexagonal cross-section there is per se a cer¬ tain lateral guiding of the girders, inasmuch as the nylon pla¬ tes in this case are arranged in pairs on the angled flanges, but this lateral guiding may at best be maintained only as long as the plates are fresh and unworn. A particular problem is the fact that the box girders in practical production seldom or never can be manufactured with absolute accuracy, i.e. with absolute nominal measures along the entire girder length. The hexagonal type of girder is usually manufactured by bending a metal plate about five lines and welding the free edges after bringing them together. During such manufacture the size tole¬ rance in different axial sections may vary by as much as up to about 2 mm. This means that the lateral play between the inside of each external girder and the outside of an internal girder may amount to several millimetres. As long as the crane jib is used in a loaded condition this play does not cause any great problems, since the front and rear pairs of nylon plates are, in this condition, capable of also guiding the girders laterally. But as soon as the crane becomes unloaded the girders may lose all positive lateral guidance, allowing them to move rather freely in relation to each other and give rise to a rattling noise which is now and then very annoying.

By US 3 719 403 it is previously known to provide telesco ping box girders of a crane jib with resilient slide or wear plates instead of the fixed nylon plates attached by gluing. These resilient plates are each constituted by a square metal plate, one side of which is intended to bear against either the outside of an internal box girder or the inside of an external box girder, and the opposite side of which bears against a spring mounted in a retainer. In one embodiment said spring is a Belleville-spring and in another alternative embodiment the spring consists of a leaf spring bent to a special shape. Though these spring plates solve the problem of the uneven wearing that usually comes up in connection with fixed wear plates, these plates act in the same manner as the fixed nylon plates in so far as they are located on the upper side and the under side of each internal box girder without giving any lateral guidance whatsoever, i.e. between the side flanges of the girders. In comparison with the nylon plates this solution of the problem is

expensive to realize in practical production, since it not only calls for a plate as well as a spring but also a special retai¬ ner for the spring.

Objects and features of the invention

The present invention aims to overcome the above mentione disadvantages and provide a simple and inexpensive solution of the problem with deficient guiding of two box girders or member whose relative movement gives rise to rattles. Therefore, a pri- mary object of the invention is to provide a washer serving as guiding element, which is simple and cheap to produce and which easily lends itself to being fitted as a complement to existing slide or wear plates in crane jibs of the type described. It should secure an efficient lateral guidance of the various box girders or profiles of the jib, even when those are manufacture with low dimensional accuracy. In a broader aspect the washer should furthermore be capable of being used for the same purpos on other reciprocally movable members than box girders of a crane jib. Irrespective of the field of application, the washer should furthermore be capable of guiding the members relative t each other independently of varying clearance therebetween and at the same time the washer should not give rise to significant frictional resistance. In other words the washer should be capable of sliding easily and without substantial friction alon the member against which it bears.

According to the invention at least the primary object thereof is achieved by means of the features defined in the cha racterizing part of claim 1. Preferred embodiments of the inven tion are furthermore defined in the dependent claims.

Further elucidation of the prior art

US 3 445 143 disloses a puck-like washer made of plastic material, such as nylon, which in addition to a circumferential portion has a central portion confined therein, said central portion being arranged to bear with low friction against one of two reciprocally movable members. In this case the central por¬ tion of the washer is, however, comparatively thin and arranged to bear against a fixed support in the form of a head of a bolt The plastic washer is, together with the bolt head, inserted in a guide rail of C-shaped cross section, the primary task of the

washer being to reduce the friction between the bolt head and the rail. The central portion of the washer has, however, no scope to yield in the space between the bolt head and the rail, and therefore it would never be capable of accomodating to varying clearance.

FR 2 307 175 discloses a washer-like construction having an annular, yielding flange between a central portion and a cir¬ cumferential portion. This washer is, however, included in a shock absorber and its purpose is not to provide guidance bet- ween two members being displacable or movable by translation in relation to each other. What is more, this washer has no central core portion at all in as much as an aperture is recessed in the centre thereof .

Brief description of the attached drawing In the drawing: Fig 1 is a partially sectioned perspective view of a guide washer according to the invention, Fig 2 is a cross sectional view through the washer in an unloa- ded condition,

Fig 3 is a similar sectional view showing the same washer moun¬ ted on one of two members movable relative to each other, the washer being illustrated in a moderately loaded condi tion, Fig 4 is a corresponding sectional view showing the washer in a condition of maximum load in which the core portion of th washer is completely impressed, and Fig 5 is a sectional view corresponding to Fig 2, but having dimensional indicators.

Detailed description of a preferred embodiment of the invention In the drawing reference numeral 1 generally designates a guide washer according to the invention. This washer is mounted on one of two members 2, 3 reciprocally movable relative to eac other. One member 2 presents a circular, drilled hole or aper¬ ture 4 serving as a seat for the washer 1. The members 2, 3 , which are movable relative to each other in the direction of th double-arrow A, may be portions of metal plates or flanges included, for instance, in the box girders of a crane jib. The members in question may however have any shape and be included

in other constructions, such as telescopically extendable sup¬ port legs of vehicles provided with cranes . The physical shape of members 2, 3 and the field of application thereof is accor¬ dingly not critical for the inventive idea, provided that the members are reciprocally movable relative to each other in the manner indicated by the arrow A.

The washer 1 consists of a body form-pressed or moulded one piece of plastics material, the body including a cylindrica collar 5 and a flange 6 projecting radially outwardly therefrom Spanning the collar 5, at the flange end, a disc has a central, thick core portion 7 and an annular transition portion 8 inter¬ mediate the core portion and the collar. This disc or central portion has a generally frustroconical shape, with the core por tion 7 outwardly confined by a substantially circular plane sur face 9 which, at the circumferential circular edge thereof, develops into a conical surface 10 forming the external surface of the annular transition portion 8. The opposite surface 11, inside the core portion 7 and the annular portion 8, is substan tially plane and merges at its periphery into the collar 5 by a smoothly rounded transition surface 12. In practice the flange is preferably continuous around the entire periphery of the collar, and its external and internal surfaces 13, 13' are parallel. The thickness of the core portion 7 is advantageously at least twice the thickness of the flange 6. In a strain-free condition the core portion projects proud of the surface 13 of the flange 6 a distance which is at least equal to the thicknes of the flange. The outer diameter of the collar 5 should be about equal to the diameter of the seat-forming aperture 4 in the member 2. With reference to Fig 5, an actual size of a prototype washer made is indicated. The outer diameter D^ of the flange 6 is 45 mm and the outer diameter D2 of collar 5 is 30 mm. The inner diameter D3 of the collar is 24 mm, so that the wall thickness of the collar is 3 mm. The outer diameter D of the central disc of the washer is 26 mm. The cone angle α for the conical surface 8 can be within the range of 50 to 70° or sui¬ tably about 60°. The flange thickness t__ is 2 mm, and the depth of the collar 5 is 5 mm. The total thickness t2 of the body, i.e. the axial distance between the surface 9 and the annular inner edge surface 14 of the collar, is 10 mm, so that the

distance by which the core portion 7 projects outwardly from the outer surface 13 of the flange 6 is 3 mm. The radius of the internal transition surface 12 is 2 mm.

The washer described operates in the following manner. In a strain-free condition the washer is mounted in aperture 4. In practice the washer may be loosely mounted in the aperture, or possibly with a certain press-fit. Alternatively, it is also possible to attach the washer by means of a light glue joint, using a dab of glue or adhesive. In the next step members 2, 3 are brought into cooperation with each other. In the case of telescopically movably box girders or profiles of the type referred to above, one box girder is inserted in the other. Depending on the clearance existing between such box girders, the core portion 7 of the washer will at least slightly be im- pressed into the free space 15 within the collar 5, as illust¬ rated in fig 3, where the clearance between the members 2, 3 is designated 16. This clearance may vary quite considerably along the axial length of the members (i.e. in the direction of arrow A) depending on the actual tolerances in manufacture, although the clearance is always at least equal to the thickness of the flange 6. When the members 2, 3 are thereafter displaced reci¬ procally relative to each other in the direction of arrow A the core portion 7 of the washer will be impressed into the space 15 to a varying degree depending on the momentary actual clearance between said members. In other words the outside surface 9 of the core portion 7 will always be kept urged against member 3 while providing a resilient guiding of members 2, 3 relative to each other. In an extreme position in which the clearance 16 approaches the thickness of the flange 6 the core portion 7 of the washer will be completely impressed into space 15, as illustrated in fig 4.

As the plastics material of the washer 1, polyurethane ma advantageously be used.

The advantages of the invention are as follows. The simpl washer can be cheaply mass produced. It enables two reciprocall movable members of a machine or construction to be mutually gui¬ ded in a manner which accomodates to varying clearance. The washer can be mounted in a simple and safe manner merely by drilling a hole in the machine member in question. The material of the washer has a rather low coefficient of friction and so

the members will be movable relative to each other without sub¬ stantial frictional resistance. In addition the washer is easy to replace after wearing.

Conceivible modifications of the invention

Of course the invention is not limited merely to the emb diment described above and shown in the drawing. Thus, it is, for example, possible to have instead of the continous flange 6 a number of tabs spaced apart by gaps. In such a way material will be spared. Furthermore the geometrical shape of the core portion 7 the tapering transition portion 8 may differ. Natu¬ rally the specific dimensions given in connection with Fig 5 should be seen merely as examples.