WO2000032979A1 - Lubrication arrangement through deposition of solid lubricant film - Google Patents

Abstract

Arrangement for the deposition of a film of solid lubricant between a first surface and a second surface, in particular of metal, which are coupled to each other and moving in relation to each other so as to give rise to friction therebetween, comprising a strip (19) of support material inserted in an appropriate recess (21) of said first surface and impregnated with solid lubricant. Said strip of support material is impregnated solely with said solid lubricant, is accomodated substantially in an appropriate recess provided in said first surface and submitted to elastic pressure (20) against said second surface, and is not submitted to any other mechanical stress.

Description

LUBRICATION ARRANGEMENT THROUGH DEPOSITION OF SOLID

LUBRICANT FILM

DESCRIPTION

The present invention refers to an arrangement adapted to deposit a film of solid lubricant on to an element having a cylindrical or flat surface and used to transmit a rotaiy or translational motion with respect to support or working means that are coupled with the outei surface of said element; the latter may be for instance constituted by a plunger or piston, a propellei or drive shaft, a guide column, a saddle or slide of a machine tool.

The reasons and the advantages behind the fact that a lubrication with solid substances is preferred over a process using liquid substances in certain circumstances are generally well-known to those skilled m the art and, since this subject mattei does not fall within the scope of the present invention, they shall not be dealt with any further here.

Although leference will be made in the following description, for obvious reasons of greater simplicity thereof, to a drive shaft having a rotaiy motion and supported by two separate supports, it should be appieciated that the present invention has to be understood as applying to any element with a cylindrical surface on which a film of solid lubricant must be deposited

The treatment of such cylindrical surfaces with solid lubricant is generally known to be substantially based on the integration of two means having peculiar characteristics the fiist such means is constituted by the actual type of the solid lubricant itself, such a type of lubricant is in fact determined on the basis of the particular requirements of the lubricatung operation that has to be carried out, and its selection is made among the large number of widely differing solid lubricants existing on the maiket with generally known properties and characteristics

To a meiely indicative puipose, a few of the most common solid lubricants may be cited here giaphite, molybdenum disulphide, boion nitrate, carbon fluoride, Teflon, mica, special waxes, polyolefins, paraffins, carbon fibres and the like

The second such means is constituted by the support of said solid lubricants which owmg to them quite often having just a poor consistence, low resistance to lemoval and low tenacity, must theiefore be supported by high-strength elements which they aie associated to, and which, for reasons of greater simplicity, will be genei ally I efei I ed to as 'base heremaftei

Even such bases aie geneially known to be available in a wide ranging choice of types theieof Fiequently used aie in particulai bases compiismg mainly synthetic lesins of vanous composition oi even polyui ethane

Such an association is typically obtained by lmpiegnating the most appropnate base with the selected solid lubiicatmg substances so as to obtain a means that is capable of depositing a layei of solid lubiicant, having the desned chaiacteiishcs and pioperties on to a suiface that is driven to establish a fiictional contact with

Moie particulaily when a cylmdiical element, such as a dnve shaft, a stem, a piston a guide column and the like must be coupled to a means such as a bush, a nng acting as a bearing oi the like, a sealing πng, oi the like, said means coupled to the cylindrical element needs to be lubiicated

When the lubiicant being used is a solid lubiicant, then it is a common piactice foi a gasket oi lining to be aiianged le interposed between said means and said cylmdiical element to both act as a support and at the same time form a lubiicatmg base and possibly act also as an actual sealing means and peiform some further function as may be lequiied by the application Such a ciicumstance, while leading to clearly apparent simplifications at a construchon and manufacturing level, gives anyway use to a number of practical drawbacks as far as the lubrication of the portion of cylindrical surface coupled to said bush or rmg-like means is concerned

One of said many drawbacks denves from the fact that the amount of solid lubricating substance that can be impregnated m the base must be such as to ensure adequate characteristics of mechanical strength and, as a lesult, its porosity must be limited so that, conclusively, the amount of solid lubricant impiegnated m the base is limited accoidingly

A second kind of diawback is originated by the fact that said means bemg interposed m the above cited mannei must be limited m its thickness smce its unavoidable weaidown would otherwise cause a cleaiance to foim between the cylindrical surface and the bush oi ling-like means due to them becoming seiiously uncoupled, le sepaiated fiom each othei , with easily imaginable, unacceptable consequences

The limited extent of such a thickness of said interposed means furthei restricts the amount of solid lubiicant that can be impiegnated m the base, theieby furthei woisemng the umfoimity capacity continuity and dmation of deposition of solid lubiicant

Moieovei , the weaung out and, as a lesult, the I eduction m the thickness of said interposed means usually allows it owing to the motion and the unavoidable vibiations of the moving cyl diical element contained theiein, to oscillate against said interposed means

This usually occunmg ciicumstance causes said means, which, as mentioned eailier in this descnption is m all cases foimed by a base of synthetic oi anyway low-stiength substances, to become oval in its shape Eventually, aftei a certain penod of opei tion, the suiface of contact between said means and said cylindrical O 00/32979 PCT/EP99/08 __,-

surface that moves in relation to the latter, reduces itself from a cylindrical surface, or anyway a fully extended surface, to a surface that is limited around two preferential points of contact and friction, as anyone skilled in the art has been able to regularly experience.

It will again be appreciated that such a further element is unavoidably the cause of a still more limited lubrication ability and uniformity.

Since the generality of the professional applications require that lubrication be assured in a continuative manner for long periods of time without any need arising for maintenance or replacement interventions, such a constraint sets a serious limitation in the use of bases impregnated with solid lubricant with the currently existing techniques.

To the puipose of eliminating these drawbacks, it is a known practice to use special manufacturing expedients in making said means for inteiposition. One of such expedients is shown for example in Figure 1 illustrating a solution proposed by VOEST-ALPΓNE, in which a hollow cylindrical element of the bush bearing type incorporates, in a multiplicity of portions of its outer surface, a respective number of pellets of solid lubricant elements.

Such a solution, while effective in acceptably solving the problem connected with the ability of maintaining the mechanical coupling accuracy, nevertheless retains, and may even aggravate, the limit of the scanty amount of lubricant that can be deposited and, therefore, the short duration of the period of effective lubrication before maintenance/replacement.

A different solution, illustrated in Figure 2, shows how a bush is formed by a ring 5 performing a mechanical support or centering function and integral with a second coaxial ring 6 having an elongated cylindrical shape. Such a second ring is provided, in correspondence of its inner surface, with a plurality of small rings 7 in relief, which are so separated from each other as to enable the hollow space existing between conhguous ungs to form annular cavities, these cavities are filled with respective rings 8 with bases containing solid lubricants

As the inner surface is set m motion and keeps moving with lespect to said rings 5 and 6, the solid lubiicant lmpiegnating the inner rings 8 is given off, thereby bung about the desired lubrication of the assembly

Such a solution, howevei , has a drawback in that, even if a considerable number of lubricating rmgs 8 are actually provided, these aie only used in the presence of a wearing down of the small imgs 7 so that the lattei by becoming shortei , enable an effective fπction to take place between the lubiicatmg imgs 8 and the mnei shaft 9 Piactically, a satisfactoiy lubncation can only be assured at the cost of a senous decay in the coupling accuiacy oi , conveisely, if such coupling accuracy must be anyway be assuied, it is the effectiveness of the lubncation ovei piolonged penods that is jeopardized

In particulai, as far as interposition means aie concerned which have substantially a sealing function, such as for instance heimetically sealing gaskets, along with a secondary lubncation function, the need furthei anses to consider that the need foi both such lequiiements to be met induces to come to a compromise in the pioperties of the selected matenals which unavoidably leads to a woisenmg in the specific sealing and stiength pioperties of the means

It would theiefoie be desnable, and is actually a mam puipose of the piesent invention to provide an aiiangement adapted to enable a film of solid lubricant to be leleased between two mutually coupled piefeiably metal suifaces, of which one is m motion lelative to said aiiangement, which does away with the afoie cited drawbacks is easy to manufactuie and apply and is capable of being produced economically with leadily available techniques and matenals

Accoidmg to the piesent invention, the above cited aim is leached, along with fuithei featuies of the invention m an aiiangement adapted to deposit a film of solid lubiicant as lecited m the appended claims A preferred, although not exclusive embodiment is described in detail below by way of non-limiting example with reference to the accompanying drawmgs, m which

- Figure 3 is a perspective view of a portion cross-sectioned by a plane passmg through the axis of a bushing for axial movements, compnsmg an arrangement according to the piesent invention,

- Figures 4A and 4B aie views of two annular stnps of support matenal accoidmg to the piesent invention closed with different coupling profiles of the matching edges theieof,

- Figuie 5 is a view of a type of elastic ring for compiessing the strip shown lllusti ated m the above cited Figui es ,

- Figuie 6 is a peispective view of a complete ling comprising the strip and the elastic nng of the pieceding Figuies 4 and 5,

- Figuie 7 is a longitudinal ci oss-sectional view of a penumatic cylinder piovided with complete imgs foi depositing solid lubiicant on to the stem and the walls of the chambei ,

- Figuie 8 is a view of an elastic coil-shaped element,

- Figuie 9 is a peispective, partially see-thiough view of a guide column or bushing foi lotaiy motions, piovided with an aiiangement accoid g to the piesent invention asd well as of an elastic lement of the type shown in Figure 8,

- Figuie 10 is a perspective, partially ci oss-sectional view of the guide column of Figure 9, - Figure 11 is a cross-sectional view (along the B-B line of Figure 10) of the guide column illustrated in the preceding Figures, as provided with a lubncation arrangement according to the piesent invention,

5 - Figures 12 and 13 are a perspective view and a cross-sectional view (along the A-A fine of Figure 12), respectively, of a linear guide provided with lubncation pads according to the piesent invention

The basic consideration which the present invention is grounded on is as 10 follows since each type of mteiposition means having to meet the requirement of performing at least two distinct tasks (eg sealing and self-lubncation) must be made using substances oi matenals capable of ensuring an acceptable compromise, it clearly ensues that, foi this veiy leason, a single mteiposition means will nevei be capable of ensuring the best lubrication chaiactenstics that 15 would theoieticaUy be achievable if the lubiicatmg substance is used alone, le without any othei substance used in combination therewith m view of performing also the lemain ng function oi task

Theiefoie, the pioposed solution is based on pioviding a lubncation means that 20 is adapted to solely peifoim such a lubncation task and no furthei functions, wheiem said possibly needed furthei functions must be coped with through the use of appiopnate diffeient means

This option is cleaily contiaiy to the geneial technical tiend of concentrating a 25 highei numbei of diffeient functions and tasks into a single element so that it is actuaUy moving m an opposite diiection with lespect to the geneiaUy accepted technical piejudice

With lefeience to Figuies 3 to 6, these can be noticed to lUustiate an outer body

30 40 provided with a cylindrical inner surface 41 m which theie are provided a pluiality of annulai lecesses 42 extending coaxiaUy with the axis of said cylmdiical surface Figuies 4A and 4B lllustiate diffeient foims of lealization of thejoming edges of a lubiicatmg strip, wheieas the nng 45 is an elastic nng having the task of retaining and compiessmg inwards the respective strip around which it is mounted

Figure 6 filustrates said strip and said rmg m their mounted state, le ready to be inserted m one of the surfaces to be lubricated, Figure 3 filustrates one of such surfaces m which said annular lecesses 42 accomodate said stnp-elastic nng assemblies

With refeience to Figure 7, this can be noticed to lUustrate a stem 11 and l elated piston 1 , which move with a rectilinear translational motion, are wrapped by lespective ships 13, 16 including of a base and a solid lubiicant of a general type that impregnates said base

Said ships aie in turn accomodated in lespective annulai lecesses 25, 24 piovided inside two lespective full oi solid bodies 27, 28 which m the considered case constitute, in an integral construction, the cylinder body and the piston, lespectively

It cleaily appeals that, in these cases, theie is no anomalous oi eccentnc stress piessmg the stemm and the piston against the lespective strips of solid lubiicant, which theiefoie act against said stem and said piston owing to the action of the lespective elastic elements 15 and 14 theieby ensuring a continuous and uniform lubncation on aU cylmncal surfaces that aie coveied by said lespective strips sliding by

The close analogy with the application lUustiated m Figure 3 should be noticed heie, since a deposition of a film of solif lubiicant is in both cases bi ought about between two mutuaUy coupled oi matching cylmdiical surfaces, le an inner and an outei one, performing a lelative motion, le moving with respect to each othei, and theiefoie m a I elation of friction with lespect to each other In the case of the piston 12, howevei , the lecess intended to accomodate the strip is provided in the inner body le in the piston itself, wheieas as fai as the stem is concerned, the lespective lecess is piovided m the mnei surface of the solid body 17 provided aiound such a stem With reference to Figures 8, 9, 10 and 11 , the contents of which has been explained earlier in this description, these can be noticed to ulustrate an arrangement for depositing a film of solid lubncant for use in those cases m which the cylmdncal surface to be lubricated, belonging to a shaft 22, moves with a rotary motion, or a motion with a rotaiy component, with respect to the guide column 18.

In this case, the particular feature constituted by the rotary motion between an inner shaft and the guide column 18, or an equivalent support element as far as the lubncation requirements are concerned, implies the circumstance that, in order to lubricate aU surfaces being m a relation of mutual friction, it becomes advantageous for the arrangement according to the present mvention, le both the lubncating stnp 19 and the elastic element 20, along with the recess 21 provided in the inner surface of said guide column, aie coil-shaped as lUustrated by way of example m the cited Figures

From the given examples the advantageous charactei of the piesent invention appears m its full evidence m particulai' when also a sealing gasket must be interposed between said surfaces. In this case, in fact, prior-art practices, according to which it is said sealing gasket that is impregnated also with lubncant in view of assigning the sealing gasket also the task of lubricating the fnctionmg surfaces, are overturned As a mattei of fact, according to the piesent mvention the fnctionmg surfaces are lubncated independently by an anangement according to the invention, so that it is actuaUy such surfaces that lubricate the sealing gasket which can in this mannei be designed and made m an optimum mannei since it is no longer subject to the constraint of having to be self-lubricating

A last example of embodiment of the piesent invention is lUustrated m Figures 12 and 13 showing a lineai guide 30 with pads 32 impiegnated with solid lubricant and acting against the contact surfaces of a slide 31 sliding on said guide 30

In this particular case, which is assimilable to the case of a guide column and an mnei shaft moving with a lectilmeai and axial motion, said lubricating pads or strips 32 are plane and ananged so as to be able to mteicept most of the friction surface between the slide 31 and the related guide 30, and they may be inserted eithei in appropriate recesses provided m the guide, as lUustrated m the Figures, or m the slide itself.

5 Also m this case said strips must be fitted so as to be pressmg against the opposite membei , with respect to which they are inserted, by means of appropriate elastic elements 33 having such a shape as to be able to generate a pressure against the respective stnps m a direction which is normal to their outer plane surface; similarly to the previously considered cases, these elastic elements 10 33 are accomodated m appropriate recesses or cavities 34 provided behmd the lespective lubricating strips.

With legard to the elastic elements having such a function of pressmg said lubiicatmg strips against one of the two surfaces moving m relation to each other,

15 they may be constituted by any appropnate device or arrangement known m the art, that foi this reason shaU not be lUustrated here. It has however been found expenmentaUy that such elastic elements turn out to be particularly advantageous and effective when they are made out of layers of elastic material, such as for instance pads or mats made of appropriate elastomeπc compounds, smce they are 0 capable of ensuring a continuous pi essure evenly distributed against said stnp.

Furthei moie, the piesence of said lubricating strips having the sole purpose of depositing a film of solid lubncant, and not bemg therefore required to meet any other mechanical oi fuinctional lequirements, enables said strips to be made to a 5 rathei large thickness (which is on the other hand impossible to obtain m the case of lubricating strips that have to also meet other requirements, le. perform other tasks, accoidmg to pnor-art techniques) It has m fact been found expenmentaUy that lubrication stnps according to the present invention can be made to thicknesses in excess of 1 millimeter, without any drawback whatsoever from a 0 functional pomt of view Such a peculiarity aUows of course for the impregnation amount of solid lubricant and, as a lesult, the duration, consistency and uniformity of the lubricating effect to be increased accoidmgly. As far as the substance to be used as a lubricant is concerned, aU currently avaUable sofid lubricants adapted to impregnate the support base can be used, with particular reference to materials comprising polyurethanes and elastomers.

Claims

1. Arrangement for the deposition of a film of solid lubricant between a first surface and a second surface, in particulai" of metal, which are coupled to each other and moving with a translational or rotaiy motion, or a combination of said two motions, in relation to each other so as to give rise to friction therebetween, comprising at least a strip (13, 16, 19, 43, 44) of support material in an appropriate recess (21, 34, 42) of said first surface, said support material performing in particulai' as a binder and being impregnated with a substance having the properties of a solid lubricant adapted to be deposited by removal and cohesion against said second surface, characterized in that said strip of support material is:

- impregnated with or containing solely said solid lubricating substance,

- accomodated in said first surface and submitted to elastic pressure against said second surface, - is not submitted to any other mechanical stress, with the exception of said elastic pressure, with respect to said second surface performing a relative motion with respect thereto.

2. Arrangement according to claim 1 , characterized in that: - said first and second surfaces are coaxial cylindrical surfaces,

- said strip (13, 16, 43, 44) is in the shape of a closed loop arranged on a same plane that is orthogonal to the axis of said coaxial cylindrical surfaces,

- said first and second coaxial cylindrical surfaces are put in a translational motion along said same axis.

3. Arrangement according to claim 1, characterized in that:

- said first and second surfaces are coaxial cylindrical surfaces,

- said coaxial cylindrical surfaces are put in a mutuaUy rotary motion about the common axis thereof,

- said strip containing solid lubricant is in the shape of a cofi (19) winding around said second cylindrical surface.

4. Arrangement according to claim 1, characterized in that said first and second surfaces are at least partiaUy matching plane surfaces belonging to bodies

(30, 31) that are put in a relative rectilinear motion.

5. Arrangement according to any of the preceding claims, characterized in that between said strip and said recess (21 , 34, 42) there is arranged an elastic element (14, 15, 45, 20, 33) adapted to compress said strip against said second surface.

6. Arrangement according to any of the preceding claims, characterized in that the action exerted by said strip of support material against said second surface solely depends on the elastic pressure of the respective elastic element.

7. Arrangement according to any of the preceding claims, characterized in that said strip has a thickness in excess of 1.0 mm.

8. Arrangement according to any of the preceding claims, characterized in that said strip comprises polyurethane and/or elastomers.