GB2144184A - Sealing assembly of the kind equipped with at least one deformable lip particularly for bearings - Google Patents

Abstract

A one-piece seal (10) intended to be interposed between two relatively rotatable members (2,3) comprises a radially inner element (15) which is relatively soft and deformable and is provided with a sealing lip (18) which sealingly co-operates with the inner member (3). The seal also comprises a radially outer element (14) which is relatively hard and rigid, and is anchored in a slot (13) in the outer member (2). The two elements (14,15) are formed integrally without a break in continuity, and are formed, respectively, from two different blends of elastomeric substances and additives of inert minerals. The two blends mentioned above are moulded to the required configurations of the respective elements (14,15) and are co-vulcanized to form the one-piece seal. There may be a small clearance between the lip and the co-operating inner member. The inner element may comprise two lips (Fig. 3). <IMAGE>

Description

SPECIFICATION Sealing assembly of the kind equipped with at least one deformable lip, particularly for bearings The present invention concerns a sealing assembly of the kind equipped with at least one deformable lip, suitable for being interposed between two relatively movable components in order to close off from the external environment a cavity between the two above mentioned relatively movable components. The present invention concerns a sealing assembly for the protection of revolving bodies of a rolling bearing in a particular way.

It is well known that, for the protection of revolving bearings, numerous types of sealing assemblies may be used, the purpose of which is to prevent the escape of the lubricant contained inside the bearing as well as impeding the entry into the bearing of external or outdoor polluting agents like water and dust. Such assemblies mainly include a stiff element, made of plastics material or metal, and a deformable element, which is generally made of elastomeric material, stuck to the rigid material and provided with at least one deformable lip arranged to exert a sealing action on the outer surface of the inner bearing ring. If the lip inteferes with the inner ring it exerts on the same a sliding sealing action whilst, in case of non-interference, it defines an annular space of reduced dimensions between itself and the inner ring, so that a labyrinth seal is obtained.Some one-piece sealing elements are also known including a stiff plastic or metal washer. Such elements, being completely rigid, involve a substantial clearance relative to the inner ring and are therefore of little use, because they involve a sealing action only with respect to the smallest microscopic particles, which is completely unsatisfactory.

The sealing assemblies described hereinbefore, formed by different elements stuck together, possess a drawback, viz. they require different working steps i.e. careful preparation of the two elements, application of the sticking material, assembly and sticking) and, in the case of a metallic element, they involve a substantial weight and risk oxidation of the metallic part and/or of detachment from the latter of microscopic particles, which can damage the revolving tracks of the revolving bodies.

It is an object of the present invention to provide a sealing assembly of the kind described above, but without the above mentioned drawbacks. In particular it is desired to obtain a sealing assembly made enbloc, possessing, at the same time, properties of softness for the sealing lip and of stiffness in general.

This object is achieved, according to the present invention, by means of a sealing assembly which is suitable for interposition between two relatively movable members in order to close towards the outside a cavity between the relatively movable members in order to prevent the entry into said cavity of polluting agents, said sealing assembly including at least one relatively deformable lip facing the first of the relatively movable members, in order to exert a sealing action on that member, and a relatively rigid element suitable for integral assembly onto the other relatively movable member, characterised by the fact that said lip is a portion of a relatively soft and deformable element integral with said relatively rigid element, the latter, and the relatively soft element, being formed from a first and a second compound made of elastimeric substances and loaded with inert materials, said compounds or blends being vulcanized or similarly bonded together.

In order that the present invention may be more readily understood, two embodiments thereof will now be described with reference to the accompanying drawings, in which: Figure 1 is a fragmentary axial section through a rotatable bearing equipped with sealing assemblies according to a first embodiment of the present invention; Figure 2 is an axial section of an enlarged scale, of one of the sealing assemblies shown in Figure 1; and Figure 3 is an axial section, similar to Figure 2, of a second embodiment of sealing assembly.

Figure 1 shows a rotatable bearing (for example a ball bearing) including an outer ring 2, an inner ring 3 co-axial with ring 2, and a plurality of revolving bodies, i.e. caged balls 4, rolling along associated tracks 5 and 6 cut in the inner surface 7 of the outer ring 2 and the outer surface 8 of the inner ring 3. Between the outer ring 2 and the inner ring 3 there is an interspace or annular chamber 9 housing the balls 4. The chamber 9 is closed off from the external environment by sealing assemblies 10 located at opposite axial ends 11 and 12 of the bearing 1.

Each sealing assembly 10 is assembled in an inwardly opening annular slot or housing 13 cut in the outer ring 2, the sealing assembly extending towards the surface B of the inner ring 3 with which it co-operates to close the chamber 9 in a fluid-tight manner, in order to prevent entry into the latter of polluting external elements like water and dust, and to impede the escape of lubricant contained in the chamber 9.

With reference to Figure 2, each sealing assembly 10 has an essentially annular shape and comprises two annular elements or portions 14 and 15, forming a single piece and made of elastomeric material based on two blends having different characteristics, pressed and vulcanized or equivalently bonded together by means of a process of co-vulcanization already known as such through application to other fields, different from that of seals, in particular for making sleeves and other elements ("Bigum", "Silent Block"). This process consists essentially in preparing two compounds or blends comprising a blend of elastomeric substances in appropriate proportions (usually synthetic resins) with the addition of inert materials (carbon, oxides and/or silicates).Such blends or compounds are then introduced into a die for moulding the finished product, which is subsequently vulcanized in said die or in another one, in order to obtain the required properties and to pro duce a chemical welding or bonding, without solution or interruption of continuity between the portions having the different blends.

The radially outermost annular element or portion 14 is essentially flat and formed by a first blend based on nitrilic rubber having such a formula that the above mentioned element 14 becomes relatively hard and rigid, with at the same time a high degree of resiliency, higher than that of steel. Such unusuai mechanical properties in an element made of elastomeric material, are obtained thanks to vulcanization which is carried out in a way that is traditional and well known, by using as vulcanizing substances vinylic radicals and peroxides instead of traditional substances based on sulphur and elements of the sulphur group.

Such vulcanized or vulcanizing substances are introduced directly into a blend based on nitrilic rubber or based on other elastomeric synthetic elements with appropriate mineral additives (carbon, oxides and/or silicates), so that, upon preparing said blend, they all form an integrant part of the recipe. The compounds used are of a known and traditional type and differ from the known ones only by the fact that, after the vulcanization, they appear essentially free from sulphur and from elements of its group. The quantities of vulcanizing substances to be introduced into the blend are calculated in a known and traditional way through stoichiometric calculations, so as to saturate essentially all the unsaturated bonds (double bonds) during the vulcanization, which bonds are present in the elastomeric substances contained in the blend or compound.As is known, the saturation of all the double bonds of an elastomer involves the obtention of a hard and rigid substance like ebonite (substance obtained from the complete vulcanization of natural rubber including sulphur). By using as vulcanizing substances vinylic radicals and peroxides (i.e. in conditions to saturate the double bonds of the polymeric chains of the elastomers of the blend or compound by creating chemical bridges connecting the different chains in order to obtain tridimensional molecules), one obtains the same known harding effect, completed by a high resilience of the product after vulcanization, without any risk of depolymerizing the elastomeric resins of the compound with consequent cracks in the product.

Furthermore, the element 14 has a radially external end 16 which can be coupled with the associated seat or housing 13 of the outer ring 2 in order to shrink onto it the sealing assembly 10, and is able to undergo an elastic deformation in order to enable the introduction of the sealing assembly 10 into the bearing 1, inside the seat or housing 13.

The annular element or portion 15, which is the radially innermost one, is essentially flat and formed by a second blend of the same elastomer of the compound forming portion 14, with an entirely known traditional composition containing sulphur as a vulcanizing substance (or an element of the sulphur group or a compound able to yield sulphur). Also, the second compound contains a certain quantity of mineral additives, smaller than that of the first one, and formed mostly by carbon.

The carbon content of vulcanizing elements based on sulphur is calculated in such a way that only a part of the unsaturated bonds present in the elastomeric substances of the second compound is saturated. Thus element 15 appears relatively soft and deformable.

The sealing assembly 10 is therefore formed essentially as a single piece with two portions or elements 14 and 15 formed in turn by two different blends which are co-vulcanized, the blend of element 15 being a traditional soft and deformable blend, and the blend of element 14 being a blend of traditional basic composition with the aim of obtaining a relatively rigid element, without sulphur and elements of the sulphur group, but containing in spite peroxides and vinylic radicals as vulcanizing elements in such a quantity that all double bonds present are saturated.

The two blends are introduced into the same die for moulding, and are then co-vulcanized together and at the same time, thus activating the vulcanizing elements (sulphur, peroxides, vinylic radicals) present in the compounds, increasing the temperature of the die above that of the medium. A chemical type bond is obviously created between the two blends, so that a one-piece seal is obtained, without discontinuity.

With reference to Figure 2, element 15 is provided with an inner annular lip extending in an essentially radial direction towards the axis of the sealing assembly 10. The lip 18 is arranged to interfere with the surface 8 of the inner bearing ring 3, so that it can be resiliently deformed and exert on the latter a pre-established pressure causing a sliding seal between assembly 10 and ring 3.

In an embodiment which is not illustrated here, the lip 18 does not interfere with surface 8 because the inner diameter of the sealing assembly 10 appears slightly larger than the outer diameter of the ring 3, so that a slight annular clearance is present between lip 18 and ring 3, the breadth of which is established in advance. In this way, the lip 18 is able to co-operate with the surface 8 in order to determine said annular clearance, and to establish a labyrinth seal without any contact.

In Figure 3 is shown a sealing assembly 19 based on the kind of assembly 10 shown in Figures 1 and 2. The difference here consists only in the fact that the assembly 19 comprises an inner element 15a provided with two radial lips 18a for sealing purposes, whilst the outer element 14a is identical to that of the assembly 10. The features which are similar to or the same as those already described have been given the same numbers with the suffix a. Elements 14a and 15a are produced by using the same blends as used for the elements 14 and 15, which were previously described.

From the foregoing description, the advantages of the present invention appear to be obvious. It allows a sealing assembly to be made enbloc i.e.

in one piece, and consisting of elastomeric materials as a whole. This permits such an element to be produced quickly and economically by means of a single pressing step. It also allows the avoidance of complex and costly steps, like the applying of adhesive materials. Furthermore, this single piece seal appears to be formed by two portions having different physical properties, thanks to the use of blends having different compositions which are then vulcanized. It is thus possible to obtain, even in case of relatively thin seals, a sufficient stiffness of the bearing portion without diminishing the properties of softness of the sealing lip, or of the sealing lips if two or more are provided, which are therefore made in the traditional way.Further it is possible to avoid the use of metallic inserts, so that the sealing complex is considerably lighter, and possible damage to bearings due to oxidation of such inserts is to be avoided.

From the foregoing it will be clearly apparent that variants and modifications may be made without departing from the scope of the present invention. In particular it is possible to produce sealing assemblies having whatever shape is required, and with whatever number of sealing lips is required, which can all or in part co-operate with one of the relatively movable members either in the manner of a sliding seal or a labyrinth seal. Furthermore, the radially outermost end or edge portion 16 (or 16a) of the sealing assembly 10 (or 19) can be formed from the same blend as that of the lips 18 (or 18a) which is relatively soft. In this case the sealing assembly 10 (or 19) comprises three annular and mutually concentric portions, formed by covulcanized elastomeric blends, as described hereinbefore. There should, in particular, be a first radially innermost portion 15 (15a) provided with at least one lip 18 (18a) formed from a vulcanized traditionally made blend, an intermediate portion 14 (14a) formed from a relatively stiff blend due to the fact that it was vulcanized with vinylic radicals and peroxides instead of sulphur, and a radially outer portion 16 (16a) formed from a vulcanized blend in a traditional way, with sulphur. In this way a greater stability of the complex 10 (19) can be obtained in the seat 13 due to the greater adherence of the soft blend to the metal of the seat 13. Finally the sealing assembly embodying the invention can be applied to any relatively movable members, and not only to rotatable bearings.

Claims (14)

1. A sealing assembly for interposition between two relatively movable members in order to close a cavity between the two members and hinder the entry of pollutants into said cavity, said sealing assembly comprising at least one relatively deformable lip facing one of the relatively movable members so as to sealingly co-operate therewith, and a relatively stiff element suitable to be assembled integrally with the other relatively movable members, wherein said lip is a part of a relatively soft and deformable element which is enbloc or formed in one piece with said relatively stiff element, the latter element, as well as the relatively soft and deformable element, being formed respectively from a first and a second blend including elastomeric substances and additives of inert materials, said blends having been vulcanized together.

2. A sealing assembly according to claim 1, wherein said first and second blends are based on a rubber, whilst a part of the unsaturated bonds present in said second blend has been saturated with elements of the sulphur group and the unsaturated bonds present in the elastomeric substances of said first blend have been essentially all saturated through vinylic radicals and peroxides.

3. A sealing assembly according to claim 1 or 2, wherein said inert materials comprise carbon, oxides and/or silicates, wherein said relatively rigid element is formed by vulcanized elastomeric substances without sulphur and sulphur group elements, and wherein said rubber is a nitrilic rubber.

4. A sealing assembly according to any preceding claim, which has an annular shape and comprises a first essentially flat and radially innermost annular element formed from said second blend, and a second essentially flat and radially outermost annular element formed from said first blend.

5. A sealing assembly according to claim 4, which is intended to be interposed between relatively movable members comprising an outer ring and an inner ring of a rotatable bearing, said second annular element possessing a relatively high degree of resilience, higher than that of steel, so as to be resiliently deformable in order to allow the introduction of said sealing assembly into a housing of said bearing.

6. A sealing assembly according to claim 4 or 5, wherein said relatively deformable lip has an annular shape extending in a predominantly radial direction, and is arranged to interfere with a surface of one of said relatively movable members, so as to be capable of undergoing a resilient deformation in order to exert a predetermined pressure upon said surface of said one of the members.

7. A sealing assembly according to claim 4 or 5, wherein said relatively deformable lip has an annular shape extending in a predominantly radial direction towards a surface of one of said relatively movable members and is co-operable with said surface to determine, between the latter and said one of the members, a clearance of a pre determined breadth in order to exert on said one of the members a labyrinth sealing action.

8. A sealing assembly according to any of claims 4 to 7, wherein said relatively soft and deformable annular element includes at least two annular lips extending towards said one of the members.

9. A sealing assembly according to any of claims 4 to 8, including a third element having an annular shape, positioned radially externally of the relatively stiff and relatively deformable annular elements, the third element being formed enbloc with the former elements, and being formed from said second blend.

10. A process for moulding a sealing assembly provided with a relatively soft and deformable element and a relatively rigid element integral with the relatively soft and deformable element, wherein two blends are prepared based on elastomers, the first containing vulcanizing substances formed by peroxides and vinylic radicals in such a quantity that effectively all double bonds contained therein can be saturated by the elastomeric substances of the first blend, and the second containing vulcanizing substances based on sulphur in such a quantity that it can saturate only a portion of the double bonds of the elastomeric substances of the second blend, disposing said first and second blends in a common die for carrying out moulding operations thereon and then co-vulcanizing them together, such vulcanized substances contained therein being in conditions to increase the temperature of the die above that of the surrounding medium.

11. A sealing assembly for interposition between two relatively movable members, substantially as hereinbefore describe with reference to Figures 1 and 2 of the accompanying drawings.

12. A sealing assembly for interposition between two relatively movable members, substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

13. A process for moulding a sealing assembly, substantially as hereinbefore described with reference to the accompanying drawings.

14. In combination, a pair of relatively movable concentric members, fitted with one or more seals as claimed in any of claims 1 to 9, 11 and 12, or with one or more seals moulded by the process as claimed in claim 10 or 13.