GB1573360A - Seals for shafts - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO SEALS FOR SHAFTS (71) We, PAULSTRA, a body corporate organised under the laws of France, of 61, Avenue Marius-Aufan, 92305 Levallois-Perret, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to seals formed of elastomer for rotary shafts, and of the type having ribs on a surface of the sealing rim adjacent to the edge intended to come into contact with the shaft when present.

These ribs are intended to exercise a hydrodynamic effect increasing the efficiency of the seal that is to say driving back the liquid or lubricant or dust which would tend to pass from one to the other or two environments which surround them, when the lubricant should in principle remain in one of these two environments.

Numerous rib shapes have been devised, particularly ribs inclined either in one direction or in two directions, this last solution having the advantage of ensuring that the liquid is kept in place independently of the direction of rotation. A herring-bone shape has particularly been provided for. Ribs of triangular or undulating shape have also been proposed.

It has been observed that these ribs often have the drawback of encouraging the intake, under the sealing rim, of dust or fluids which pass into the interstices between the shaft and the sealing rims, at the place where the ribs end.

According to this invention, we provide a seal formed of elastomer for a rotary shaft, with at least two series of generally curved ribs on a surface of the sealing rim adjacent to the edge intended to come into contact with the shaft when present, the first series comprising successive curves which are concave towards the contact edge of the rim and end on or near this edge, and have a radial height which increases away from the contact edge, and the second series comprising successive curves of relatively reversed concavity, and which are offset angularly with respect to the curves of the first series, and have a radial height which increases towards their ends.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing, in which: Figure 1 is a partial axial section of a seal or ring for a rotary arbor or shaft and embodying the invention; Figure 2 illustrates diagrammatically in expanded view the characteristic elements of the rim of the seal; and Figures 3 to 5 illustrate respectively sectional details taken on the lines III-III, IV-IV and V-V respectively of Figure 2.

The illustrated seal of elastomer for a rotary arbor is located at the end of a skirt 1 fixed to a support 2, and has a rim 3 generally subject to the effect of a spring 4. One annular surface 5 of the seal adjacent to the contact edge 6 of the rim (generally being outside the environment I to be sealed off) is provided with ribs.

With respect to the general structure of this seal, it is arranged in the usual way, but, with respect, more especially, to the said ribs, they are arranged in such a way that they comprise at least two series occurring one behind the other in relation to the contact edge 6, namely: -a first series, formed by a sequence of circular arcs such as 7, distributed around the axis A-A of the seal (for example in the illustrated embodiment, six in number), these arcs having their ends preferably in common, located at 8 on or near the contact edge 6 and consequently being concave towards the contact edge, and -a second series of circular arcs 9 of similar or different shape to those of the first, but of reverse concavity, that is to say, in the present instance, facing towards the environment II opposite the environment I to be sealed off.This second series is offset in relation to the first, around the axis A-A of the seal.

It can be seen from the drawing that the above-mentioned arcs are assumed to be of symmetrical shape in relation to a radial plane sectioning them at their top. However, provision could be made for an asymmetrical shape, as shown in dashed lines at 7, on Figure 2, particularly in the case of seals intended for arbors provided for turning in opposite directions, but at different working speeds.

The angular offset is assumed to be half the angle occupied by an arc around the axis, that is to say, 30 in the case of six arcs of 60 (solution given solely by way of example), but an asymmetrical offset is also possible.

It is not essential either to provide a symmetrical shape in transverse section for these ribs. An assymetrical shape has been shown in Figure 5 in dots at 91.

In any case, it is desirable to arrange matters so that, as illustrated, the depth of the ribs, or their radial height, always increases as it bears away from the edge 6, that is to say, in order to take into consideration the degree to which the base surface 5 widens out from the arbor to be sealed, thus diverging from the surface of the latter.

That means that: -in the case of the arcs 7, the height of the ribs as seen in the sections of Figures 3 to 5, will increase from the contact edge 6, where the said height can be zero, and -in the case of the arcs 9, this height will, on the contrary, increase from the top of the arcs to their base at 10.

The maximum height h (Figure 3), of the ribs 7 can approximately equal the minimal height of the ribs 9 (accordingly at their top), while the maximal height H of these last will be considerably greater than h, but the above mentioned equality is not an essential requirement.

The base 10 of the arcs can be on the edge 11 at the other side of the surface 5 from the contact edge 6, but this is not essential and the edge 11 could especially be placed outside the field of the arcs 9, as represented in dots at 11, in Figure 2.

The two series of arcs 7 and 9 can overlap, as shown, that is to say that the annular areas, occupied respectively on the surface 5 by the said series, can overlap. But the two series could be further apart from each other.

A greater overlap could also be provided for, that is to say, arranging matters so that the arcs 7 and 9, instead of having an empty space between them, as shown at 12, Figure 2, come together until they almost touch, indeed partially penetrate one another (this not freing illustrated). Another variant would consist in giving the ribs 9 even in this area 12 (m-n Figure 2), where they approach the ribs 7, a greater height than the latter (also not illustrated).

The shapes of the ribs need not be circular arcs, but could be other generally curved shapes providing the necessary concavity.

By proceeding as has just been said, a general structure is therefore realised which, while ensuring the desired hydrodynamic effect by these sorts of rib, exercises a double barrier against the passage of dust and fluids, by the presence of two series of ribs occuring one behind the other (more than two series, being possible if need be).

It is probable - but in any case, practice will prove it - that this improvement of the sealing effect is due to the fact that the fluid or dust streams having succeeded in entering into the space between the two series of ribs, strike against the sides of the latter at the relatively low incidence a (Figure 2), which considerably reduces turbulence and promotes repulsion towards the environment I to be sealed off. Moreover, the double-ribbed profile allows reduction to the minimum of axial bulkiness of the frusto-conical surface of the rim.

In any case an efficient obstacle to the passage of dusts is realised, even after wear of the contact edge of the rim.

The arcs of the ribs can have a symmetrical shape in relation to a radial plane passing through their top or, on the contrary, an asymmetrical shape, particularly in cases where the shaft to be sealed is induced to rotate in either one of the two opposite directions, and at. different speeds.

The ribs can be realised by the usual methods, for example by moulding by means of moulds supplied with scorings corresponding to the ribs to be obtained.

Following from which, one thus has the possibility of constructing seals whose functioning is sufficiently evident from the above and which, in relation to those of the type in question already existing, offer numerous advantages, particularly: - that of ensuring a good sealing - that of efficiently resisting dust, and - that of fulfilling these conditions even after wear, since the barrier created by the series of above-mentioned ribs draws nearer to the arbor progressively with the wear on the rim.

WHAT WE CLAIM IS: 1. A seal formed of elastomer for a rotary shaft, with at least two series of generally-curved ribs on a surface of the sealing rim adjacent to the edge intended to come into contact with the shaft when present, the first series comprising successive curves which are concave towards the contact edge of the rim and end on or near this edge, and have a radial height which

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. reverse concavity, that is to say, in the present instance, facing towards the environment II opposite the environment I to be sealed off. This second series is offset in relation to the first, around the axis A-A of the seal. It can be seen from the drawing that the above-mentioned arcs are assumed to be of symmetrical shape in relation to a radial plane sectioning them at their top. However, provision could be made for an asymmetrical shape, as shown in dashed lines at 7, on Figure 2, particularly in the case of seals intended for arbors provided for turning in opposite directions, but at different working speeds. The angular offset is assumed to be half the angle occupied by an arc around the axis, that is to say, 30 in the case of six arcs of 60 (solution given solely by way of example), but an asymmetrical offset is also possible. It is not essential either to provide a symmetrical shape in transverse section for these ribs. An assymetrical shape has been shown in Figure 5 in dots at 91. In any case, it is desirable to arrange matters so that, as illustrated, the depth of the ribs, or their radial height, always increases as it bears away from the edge 6, that is to say, in order to take into consideration the degree to which the base surface 5 widens out from the arbor to be sealed, thus diverging from the surface of the latter. That means that: -in the case of the arcs 7, the height of the ribs as seen in the sections of Figures 3 to 5, will increase from the contact edge 6, where the said height can be zero, and -in the case of the arcs 9, this height will, on the contrary, increase from the top of the arcs to their base at 10. The maximum height h (Figure 3), of the ribs 7 can approximately equal the minimal height of the ribs 9 (accordingly at their top), while the maximal height H of these last will be considerably greater than h, but the above mentioned equality is not an essential requirement. The base 10 of the arcs can be on the edge 11 at the other side of the surface 5 from the contact edge 6, but this is not essential and the edge 11 could especially be placed outside the field of the arcs 9, as represented in dots at 11, in Figure 2. The two series of arcs 7 and 9 can overlap, as shown, that is to say that the annular areas, occupied respectively on the surface 5 by the said series, can overlap. But the two series could be further apart from each other. A greater overlap could also be provided for, that is to say, arranging matters so that the arcs 7 and 9, instead of having an empty space between them, as shown at 12, Figure 2, come together until they almost touch, indeed partially penetrate one another (this not freing illustrated). Another variant would consist in giving the ribs 9 even in this area 12 (m-n Figure 2), where they approach the ribs 7, a greater height than the latter (also not illustrated). The shapes of the ribs need not be circular arcs, but could be other generally curved shapes providing the necessary concavity. By proceeding as has just been said, a general structure is therefore realised which, while ensuring the desired hydrodynamic effect by these sorts of rib, exercises a double barrier against the passage of dust and fluids, by the presence of two series of ribs occuring one behind the other (more than two series, being possible if need be). It is probable - but in any case, practice will prove it - that this improvement of the sealing effect is due to the fact that the fluid or dust streams having succeeded in entering into the space between the two series of ribs, strike against the sides of the latter at the relatively low incidence a (Figure 2), which considerably reduces turbulence and promotes repulsion towards the environment I to be sealed off. Moreover, the double-ribbed profile allows reduction to the minimum of axial bulkiness of the frusto-conical surface of the rim. In any case an efficient obstacle to the passage of dusts is realised, even after wear of the contact edge of the rim. The arcs of the ribs can have a symmetrical shape in relation to a radial plane passing through their top or, on the contrary, an asymmetrical shape, particularly in cases where the shaft to be sealed is induced to rotate in either one of the two opposite directions, and at. different speeds. The ribs can be realised by the usual methods, for example by moulding by means of moulds supplied with scorings corresponding to the ribs to be obtained. Following from which, one thus has the possibility of constructing seals whose functioning is sufficiently evident from the above and which, in relation to those of the type in question already existing, offer numerous advantages, particularly: - that of ensuring a good sealing - that of efficiently resisting dust, and - that of fulfilling these conditions even after wear, since the barrier created by the series of above-mentioned ribs draws nearer to the arbor progressively with the wear on the rim. WHAT WE CLAIM IS:

1. A seal formed of elastomer for a rotary shaft, with at least two series of generally-curved ribs on a surface of the sealing rim adjacent to the edge intended to come into contact with the shaft when present, the first series comprising successive curves which are concave towards the contact edge of the rim and end on or near this edge, and have a radial height which

increases away from the contact edge, and the second series comprising successive curves of relatively reversed concavity, and which are offset angularly with respect to the curves of the first series, and have a radial height which increases towards their ends.

2. A seal according to claim 1, wherein the ribs are in the shape of asymmetrical curves.

3. A seal according to claim 1 or 2, wherein the curves of the second series end near that edge of the surface carrying the ribs which is remote from the contact edge.

4. A seal according to claim 2 or 3, wherein the maximum radial height of ribs of the first series is of the same order of size as the minimum radial height of the ribs of the second series.

5. A seal substantially as described hereinbefore with reference to the accompanying drawing. - - --