GB2240592A - Hydrodynamic shaft seals - Google Patents

Abstract

A hydrodynamic shaft seal is formed by through moulding a base section (3) of elastomeric material through holes (5) in a PTFE lining section (4). When the seal is located about a shaft relative rotation of the seal results, because of the differing coefficients of friction of the liner section (4) and the base section (3), in a hydrodynamic pumping action. <IMAGE>

Description

HYDRODYNANIC SHAFT SEALS This invention relates to hydrodynamic shaft seals, and in particular, a hydrodynamic shaft seal for use as a rotary shaft seal.

In accordance with the present invention a hydrodynamic shaft seal comprises: - a base section of elastomeric material; and - a lining section of a second material having a lower edge adjacent to, or in contact with, the shaft wher In sealing contact therewith; wherein the base section and lining section ar- moulded with respect to each other so that for least a part of the circumference of the shaft seal the base section extends below the lower edge of the lining section, and over this portion is in contract with the lower edge of the lining an provides the seal with a smooth, and flus, sealing surface which Incorporates a hydrodynamic pumping means.

The difference in texture i.e. adhesion and frictional properties, between the materials of the base section and lining section means that the rotation of the shaft induces a hydrodynamic pumping action.

When the shaft seal is assembled about a shaft, the seal is stretched, particularly in the vicinity of the sealing contact area, in order to achieve the required design/sealing configuration with respect to the shaft. The stretching of the shaft seal causes essentially symmetric distortion and curving, in the axial direction, of the shaft seal sealing surface, this distortion, and curving of the shaft seal 111 be greater n the lining section of the shaft seal than n tne base section.

Further, this distortion anc curving causes the base section of the shaft seal to project beond the face of the lining section of the shaft seal in the area of the lower edge of the lining section.

The actual sealing contact between, or in close proximity to, the shaft and the above mentioned projection causes the hydrodynamic pumping action on relative rotary motion between the two. This hydrodynamic pumping action will be additionally enhanced by the change in frictional dra exerted on an oil film as the film passes from a low friction surface, for example PTFE, to a relatively higher frictional drag surface, for example the base elastomeric material of the base section.

The lower edge of the lining section in the finished hydrodynamic shaft seal is, preferably, shaped so as to provide the shaft sea with desired hydrodynamic pumping action/means upon relative rotation of a shaft in which it is in sealing contact.

The shaft seal made in accordance with the present invention is preferably formed so that in operation the lower edge of the lInIng section is either in contact with the shaft, or in close proximity thereto. In this way the most efficient pumping action is achieved for the particular shape of the lower edge of the lining section.

Preferably, the second material i.e. that of the lining section is polytetrafluoroethelyne (PTFE).

In certain circumstances it is beneficial to provide the shaft seal with an enhanced sealing contact with the shaft. In these circumstances the seal, preferably, also Includes a garter spring. The garter spring may be arranged so that It acts agaInst the base section and thereby indirectly against the lining section in order to enhance the sealing contact.

A hydrodynamic shaft seal made in accordance the present inventIon can be ncorporate in, for example, standard rotary shaft seals, high pressure rotary shaft seals, or unitised rotary shaft seals. These shaft seal constructions may be manufactured so that they incorporate any of the known additional aids, for example, dust lips, protective arrangements.

Normally, with the above type of shaft seal a stiffening ring is provided. Therefore, preferably the shaft seal incorporates a stiffening ring of metal or suitable plastic material.

In a particular type of shaft seal arrangement the shaft seal further comprises a unitising member which is placed around the shaft. This type of arrangement provIdes a unitised shaft seal with all the known advantages such an arrangement provides.

The invent on also Includes G method of manufacturing a shaft seal in accordance with the present invention, which method comprises: - preshaping and forming the lining section: - positioning the lining section In a mould; - injection moulding the base section so that the base section material adheres to the lining section and forms the hydrodynamic pumping means; and - trimming or cutting the base section and/ or the lining section.

In shaft seals which include a stiffening ring, the method of manufacturing a shaft seal in accordance with the present invention comprises: - preshaping and forming the lining section and the stIffenIng ring; - positioning the lining section and the stiffening ring in a mould; - injection moulding the base section so that the base section material ad@eres to the lining section and forms the hydrodynamic pumping means; and - trimming or cutting the base section and/ or the lining section.

The general basis of the method of manufacture of a shaft seal in accordance with the present invention is that generally known in the industry, and therefore no specific detail thereto is required in appreciating the present invention.

The use of preformed PTFE lining section is, preferred, where the axial length, i.e. length of the shaft seal in the direction of the shaft's axis of rotation is relatively long. ThIs enables any creasing or folding during te manufacturing operation to be eliminated.

In a preferred method of manufacturing a hydrodynamic shaft seal the base section is through moulded through crifices in the lining section to provide a sm@oth and flus@ surface, and is then trimmed or cut through the orifices to provide the necessary shaping to the lower edge of the lining section.

Alternatively, the lining section may be preshaped and the base section moulded so that it extends below the lower edge of the lInIng section.

The invention will now be illustrated by way of description of an example shown in the accompanying drawings, in which: Figure 1 shows a cross-section view of a shaft seal made in accordance with the present invention; Figure 2 shows a cross-section view of an alternative shaft seal made in accordance with the present invention; Figure 3 shows a cross-section view o a second alternative shaft seal made in accordance with the present invention.

Now referring to Figure 1 of the drawings, a first embodiment of a hydrodynamic shaft seal i made in accordance with the present invention comprises: - a stiffening ring 2; - a base elastomeric section 3; - a PTFE lining section 4 having cut outs 5, in the lower edge thereof; and - a garter spring 6.

The stiffening ring 2 may be made from metal or suitable plastics material, and is of a generally L-shaped configuration having a first arm 7 and a second arm 8. The first arm 7 Is provided with a chamfered section 9, to aid the mounting of the scan about a shaft in a suitable body. The second arrr 8 is attached to the base elastomeric section at an end 10 thereof.

The PTFE lining section 4 is of generally conal shape, and has a passage 11 passing therethrough.

At the narrow end of the PTFE lining section 4 the lining section 4 ant the base elastomeric section 3 are trimmed to provide a trimmed surface T.

In use a rotating shaft (not shown may be passes through the passage 11, so that a surface 12 of the shaft seal can provide a sealing contact therewith.

The cut outs 5 in the PTFE lining section 4 are shaped like open trapeziums so as to provide the seal with a hydrodynamic pumping means 13.

The base elastomeric section 3 is formed so that it is bonded to the end 10 of the second arm 8 of the stiffening ring 2 and the garter spring 6 and is bonded to the PTFE lining section 4, so that the seal is held together as a single unitary member.

The garter spring E is assembled and positioned so that it acts against the base elastomeric section 3, and thereby the PTFE lining section 4, so as to enhance the sealing contact between the surface 12 of the PTFE lining section 4 and a shaft which extends through the passage 11.

The shaft seal is manufactured using the following steps: - preshaping and forming the stiffening ring 2 and the PTFE lining section 4, so that it has tooth like projections 4a; - preparing, placing and appropriately positioning the stiffening ring 2, the PTFE lining section 4 in a mould; - Injection moulding the base elastomeric section 3; and - trimming the seal member along the cut line.

In the moulding of the base elastomeric section 3, the elastomeric material Is causes to adhere to the end 10 of the second arm 8 of the stiffening ring 2, as weli as being bonded to the P-FE lining section 4.

Further, the base elastomer extends around the PvFE lining section 4, so that it forms â smooth and flush surface with the surface 12 of the PTFE lining section 4.

In use the shaft seal 1 is placed about a shaft so that the shaft extends through the passage 11 and the surface 12 is in contact with the surface of the shaft so that the edge of the PTFE lining section is in contact or alternatively in close proximity with the shaft. Therefore, as the shaft rotates the difference in the surface adhesion/friction qualities between the PTFE, and the base elastomer causes a pumping action to be induced.

Now referring to Figure 2 of the drawings a second type of hydrodynamic shaft seal 1 is shown, this shaft seal 1 is essentially identical to that described above, and like numerals have bee useo to illustrate like components.

The only difference between the two forms of shaft seal resides in the fact that in the second form, tat of Figure 2, the ct outs 5, provided in the PTFE lining section are of alternative configuration to those shown in Figure 1.

The method of manufacture for these two forms of hydrodynamic shaft seal is essentially identical.

Now referring to Figures 3 of the drawings, a second alternative shaft seal is shown. In this case the shaft seal is identical in the final product to that shown and described with reference to Figure 1 of the drawings. Therefore, like numerals have been used to describe like components.

The differences between the two shaft seals, that of Figure 1 and that of Figure 3, resides in the method of manufacture therefore.

A shaft seal made in accordance wtth Figure 3 of the drawIngs is manufactured using the following steps: - preforming the PTFE lining section 4 and the stiffening ring. The PTFE lining section is formed with a number of trapezium shaped orifices in a bana therein; - positioning the PTFE lining section 4 Garter Spring 6 and the stiffening ring appropriately within the mould; - moulding the base section of the shaft seal so that it adheres to the stiffening ring, garter spring and the PTFE lining section 4. The base section once moulded will extend into the orifices in the PTFE lining section 4 so that it forms a smooth and flush surface with the surface of the PTFE lining section not in contact with the base section; an - trim-mIng the shaft seal along the cut line. The cut line passes through the orifices in the PTFE lining section 4.

In this way a shaft seal in accordance with the present invent ion is formed.

Claims (13)

1. A hydrodynamic shaft seal adapted for use with a shaft comprising a base section of elastomeric material; and a lining section of a second material having a lower edge adjacent to, or in contact with, the shaft when in sealing contact therewith; wherein the base section and lining section are moulded with respect to each other so that for at least a part of the circumference of the shaft seal the base section extends below the lower edge of the lining section, and over this portion is in contact with the lower edge of the lining to form a smooth, and flush, sealing surface which incorporates hydrodynamic pumping means.

2. A hydrodynamic shaft seal as claimed in claim 1 which the lower edge of the lining section is shaped to give a hydrodynamic pumping action upon relative rotation of the shaft.

3. A hydrodynamic shaft seal as claimed in claim 1 or 2 wherein the lower edge of the lining section is, in use, in contact with the shaft or in close proximity to the shaft.

4. A hydrodynamic shaft seal as claimed in claims 1, 2 or 3 wherein the lining section is formed of polytetrafluoroethelyne.

5. A hydrodynamic shaft seal as claimed in any preceding claim comprising a garter spring arranged to act against the base section to urge the lining section into sealing contact with the shaft.

6. A hydrodynamic shaft seal as claimed in any preceding claim comprising a stiffening ring to increase the rigidity of the seal.

7. A hydrodynamic shaft seal as claimed in any preceding claim wherein the hydrodynamic pump means is shaped as a trapezium.

8. A hydrodynamic shaft seal as hereinbefore described with reference to and as illustrated by figures 1, 2 or 3.

9. A method of making a hydrodynamic shaft seal comprising: preshaping and forming a lining section; positioning the lining section in a mould; and injection moulding a base section such that the base section material adheres to the lining section and forms hydrodynamic pumping means.

10. A method as claimed in claim 9 further comprising preshaping and forming a stiffening ring and positioning the stiffening ring in the mould prior to injection moulding the base section.

11. A method as claimed in claim 9 or 10 wherein the base section is through moulded orifices in the lining section to form hydrodynamic pumping means.

12. A method as claimed in claims 9, 10 or 11 further comprising trimming the base section and lining section after moulding to form a lower edge.

13. A method substantially as hereinbefore described with reference to and as illustrated by figures 1, 2 or 3 of the accompanying drawings.