GB2261920A - A method of making a seal - Google Patents

Abstract

A grooved seal is formed by pressing a groove former (6) into an end face (5) of a seal blank and causing relative motion between the blank and the former (6). The former (6) takes the form of a rotatably mounted wheel held in a holder (8) which is caused to rotate by the relative motion. The groove (10) is thus formed by a crushing action which imparts a fine surface texture on the groove (10).

Description

A METHOD OF MAKING A SEAL This invention relates to a method of making a seal, in particular, a grooved seal.

Grooved seals are often used to form a seal about rotating shafts of machines. The grooves give an hydrodynamic effect which drives lubricant away from the seal. In the past these grooves have been machined into the seal material using a sharp cutting tool. However, the resultant grooves have had a coarse surface texture which retains a film of lubricant in the groove. Eventually, the retained oil burns onto the surface and the groove becomes choked and ineffective.

For some glass filled seal materials, the cutting tool is blunted after cutting grooves in a modest number of elements. If a blunt tool is used to cut further grooves, tearing and chipping can occur in the seal material producing a poor quality groove leading to premature failure.

Even whilst the tool is sharp, burring can occur requiring a further operation to be carried out to remove the burs.

It is an object of the invention to provide a method for forming a groove in a seal with a finer surface texture.

Accordingly the invention provides a method of making a grooved seal comprising the steps of providing a seal blank, providing a rotatably mounted groove former, pressing the former and seal blank into contact and causing relative motion of the former and seal blank to form a groove in the blank, the relative motion causing a rotational movement of the former.

By using a rotatably mounted groove former, the groove is formed by a crushing action in the material as opposed to a cutting action. The groove texture is, as a result, smoother and tearing and chipping is less likely to occur.

Preferably, the groove former is a wheel rotatably mounted in a holder.

The groove former will comprise a hard material of a cross section matching that of the required groove and, preferably, will comprise a tungsten carbide metal alloy.

A specific embodiment of the invention will now be described, by way of example only, with reference to the drawing in which: Figures 1 to 4 show a method of making a seal in accordance with the invention; and Figure 5 shows, in plan view, a seal groove forming tool in accordance with the invention.

With reference to Figure 1, a cylindrical rod 1 formed of polytetrafluoroethylene, PTFE, filled with 5% glass and 5% MoS2 is removably mounted in a lathe chuck 2. The outside diameter and inside diameter of the rod has been formed in a previous lathing operation well known to those skilled in the art. The lathe chuck 2 rotates the cylindrical rod 1 about central longitudinal axis 3.

As the chuck 2 rotates, a groove forming tool 4 is brought into contact with a planar annular end face 5 of the rod 1 and then pressed axially into the material. Progressively, the tool 4 is moved radially inwards, towards the axis 3 from distance X to distance Y from the axis 3.

As the tool 4 approaches Y, the pressure is gradually removed to form a helical groove centred on axis 3 with a gradual groove run out, that is to say, the depth of the groove gradually decreases as it approaches V.

As shown in Figure 2, the tool 4 comprises a tungsten carbide rolling wheel 6 rotatably mounted about an axle 7 in a wheel holder 8. The wheel 6 has a tapering edge 9 to form the desired crosssection of groove 10, as more clearly shown in Figure 3.

The seal is completed by a parting operation in which a cutting tool 11 is brought radially inwards, starting from a point the desired thickness Z of the finished seal from the end face 5, towards the axis 3 as shown in Figure 4. To form the next seal the cut end face of the remaining stock is machined flat and true and the previously described operations repeated.

A preferred form of seal groove forming tool is shown in Figure 5 and it comprises a holder 12 having a selectively rotatable carriage 13 mounted by a stud 14 at one end. The carriage 13 is retained by the stud in a generally circular recess 15 in the holder 12. Rotatably mounted in the carriage 13 are four tungsten carbide wheels 16, 17, 18 and 19. When wheel 16 has worn, the carriage 13 is rotated clockwise until unused wheel 17 is in position for use. Likewise, wheel 17 may be replaced by wheel 18 and wheel 18 by wheel 19.

In a test of two seals 896-008-7280-00 formed according to the invention, the seals were used to seal a shaft running at 6,000 r.p.m. at 1200C.

The lubricant used was B.P. UF7 which after 400 hours did not leak past the seal. No signs of burnt oil were found on the seals after completion of the test.

A further test was carried out to examine whether or not the groove would recover from the crushing action of the former.

A completed seal was placed in an air oven at 2000C for a period of 24 hours. Examination of the seal showed that material recovery had been minimal.

Claims (5)

1. A method of making a grooved seal comprising the steps of providing a seal blank, providing a rotatably mounted groove former, pressing the former and seal blank into contact and causing relative motion of the former and seal blank to form a groove in the blank, the relative motion causing a rotational movement of the former.

2. A method substantially as hereinbefore described with reference to the drawings.

3. A seal groove forming tool comprising a rotatably mounted groove former to, in use, be pressed into a surface of a seal blank relative motion of the tool and blank causing rotational movement of the former.

4. A tool as claimed in claim 2, wherein the groove former comprises a tungsten carbide wheel.

5. A seal groove forming tool substantially as hereinbefore described with reference to the drawings.