GB2078313A

GB2078313A - Floating seal assemblies

Info

Publication number: GB2078313A
Application number: GB8012345A
Authority: GB
Original assignee: Komatsu Ltd
Current assignee: Komatsu Ltd
Priority date: 1980-04-15
Filing date: 1980-04-15
Publication date: 1982-01-06
Also published as: GB2078313B

Abstract

A seal ring 12 comprises a base of anti-abrasion iron having a sealing portion 16 formed thereon by plasma spraying a cermet containing tungsten carbide and nickel. The coated layer of cermet is lapped to obtain a finished seal. The sealing portion is preferably shot blasted to remove grease before plasma spraying. <IMAGE>

Description

SPECIFICATION Floating Seal Assemblies The invention relates to floating seal assemblies suitable for the axles or reduction gearing of tracked construction vehicles such as bulldozers and excavators.

Such floating seal assemblies comprise a pair of annular seal rings held abutting against each other by a pair of "0" rings mounted thereon. The outer peripheral edges of the seal rings on the opposed surfaces are smooth and have central recesses, while their inner parts are tapered. The abutting smooth surfaces form a seal and prevent both the entry of sand and mud from the outside and the leakage of the lubricating oil. After an extended period of use, the sealing portions become worn, and the sealing contact is reduced. The sealing face pressure is increased and the wearing is accelerated.

Consequently, the sealing contact faces gradually move towards the inner tapered portions.

A seal ring according to the invention comprises a casting of anti-abrasion iron having a sealing portion formed thereon by plasma spraying a cermet containing tungsten carbide and nickel. The sealing portions which require this treatment are narrow.

The invention includes a method of producing such a seal ring which comprises plasma flame spraying as above and lapping the resulting layer to produce a finished seal.

The seal ring is preferably produced from a blank of special cast iron or steel having a high hardness (HRC 65-70) which contains as its main components the metals Fe, Cr, W, Mo, Ni, V and Mn.

It is advantageous to treat the sealing portion of the ring base by shot blasting to clean the sealing portion prior to plasma spraying. The thickness of the cermet coating is preferably from 0.07 mm to 0.15 mm, and more preferably from 0.09 mm to 0.12 mm.

Drawings Figure 1 is a cross-section of a floating seal assembly including a pair of seal rings according to the invention; Figure 2 is a cross-sectional view of seal rings wheren the outer sealing portion has worn out, the taper angle being exaggerated; Figure 3 is a schematical cross-section of a plasma spraying machine used in the method of the invention; and Figure 4 is a diagram showing a comparison in durability between seal rings produced by the method of the invention and those produced by a conventional method.

Referring to Figure 1, a well known floating seal assembly 10 comprises a pair of seal rings 12, 12 of anti-abrasion cast iron and a pair of elastomeric retaining members 14, 14 ("0" rings) mounted so as to permit one of the seal rings to rotate relative to the other and in sealing contact with each other. In Figure 2, first sealing portions 16, 16 of the seal rings 12 are worn out, and second sealing portions 18, 18 are in sealing contact. The thickness D of the layer requiring a high hardness can be obtained by the following formula.

D = t x sina where t is a width of seal rings in sealing contact, and a is an inclined or tapered angle formed by tapered portions 20, 20.

For example, the sealing contact width of a conventional seal ring having a diameter of 100 mm is from 1.0 mm to 2.00 mm, and the tapered angle a of the tapered portions 20, 20 is from one to two degrees. Therefore, if t is 2.0 mm and a is 2 degrees, D = 0.07 mm. In general, a high hardness is required only for the seal ring, about 0.1 mm thick from the sealing faces.

In Figure 3 the plasma spraying device comprises a soundproof dust-collector housing 22 made of steel plate and glass wool. The housing 22 has a bottom wall 24, and a plate 28 mounted on the bottom wall 24 so as to be horizontally rotatable by a motor 26. The plate 28 has an annular magnet 30 secured thereto so as to attract and carry a seal ring 12. A plasma gun 32 is carried so as to oscillate freely opposite the sealing face of the seal ring 12, and is connected through a linkage 34 to a motor 36. The arrangement is such that plasma spraying is effected by oscillating the plasma gun 32 over the sealing face of the seal ring 12 while it is being rotated.

A gas supply hose 38, a cooling water supply pipe 40 which serves also as an electrode, a cooiing water discharge pipe 42, a duct 44 connected to a dust collector, and a spraying material supply nozzle 46 are provided.

The gas supplied through the gas supply hose 38 contains nitrogen and hydrogen gas. These gases are heated by the plasma gun 32 to a high temperature, and are ionized in the plasma form so that the nozzle at the leading end of the plasma gun 32 injects plasma having a temperature of several thousand degrees Celsius. As a result, the spray powder supplied through the nozzle 46 is fuxed by the plasma and is sprayed on the sealing portion of the seal ring 12.

Example A pipe or flat plate shaped blank casting made of SS 41 steel (Japanese Industrial Standard) which is a low carbon steel was subjected to cold forging and machining to form a seal ring base of a predetermined shape having an outer diameter of 100 mm.

The sealing portion of the seal ring base thus obtained is subjected to shot blasting using blasting materials WA No. 20 to 24 to give the surface of the sealing portion a degree of roughness of about 30p.

After checking that the sealing portion is free from oily matter and rust, the seal ring base is put on the plate 28 (Figure 3) so as to be attracted by the magnet 30. The plasma spray machine used is a 7 M System of METCO Inc., and the spraying powder employed is 439 NS-2 METCO Inc. The powder 439 NS-2 is a cermet containing WC and Ni as its main components. The powder supply rate is 0.95 is 1.0 glsec, and plasma spraying is performed for ten seconds. The distance between the leading end of the plasma gun 32 and the seal ring base 12 is kept about 75 mm, and the seal ring base 12 is rotated at 930 rpm. During the plasma spraying, the plasma gun 32 makes a weaving motion, the amplitude of which is 4 mm and the frequency is 0.5 Hz. The thickness of the plasma sprayed coating is about 0.15 mm.The sealing portion coated by plasma spraying is lapped to obtain a finished seal ring product with a high-hardness coating of about 0.09 mm on the sealing portion thereof.

Figure 4 shows durability test results of a seal ring produced by the method of the invention and that produced by a conventional casting method under the same condition. The outside diameter and inside diameter of the seal rings are 100 mm and 80 mm, respectively. In this drawing, solid lines indicate seal rings produced by the method of the invention, whilst the region surrounded by dotted lines indicates seal rings produced by the conventional method. The durability of the seal rings produced by the method of the invention is superior to that of the seal rings produced by the conventional method. As the seal ring base according to the invention can be produced by subjecting a comparatively mild steel to cold forging and machining, the working is easy and the production cost low. As the sealing portion can be coated with a high-hardness material by plasma spraying, working can be effected in a short time and efficiently.

Claims

1. A seal ring for a floating seal assembly which comprises a casting of anti-abrasion iron having a sealing portion formed thereon by plasma spraying a cermet containing tungsten carbide and nickel.

2. A seal ring according to claim 1 in which the thickness of the cermet is from 0.07 mm to 0.15 mm.

3. A seal ring according to claim 1 in which the thickness of the cermet is from 0.09 mm to 0.12 mm.

4. A method of producing a seal ring according to any preceding claim in which the plasma spraying is followed by lapping the resulting layerto produce a finished seal.

5. A method according to claim 4 in which prior to plasma spraying the sealing portion is cleaned by shot blasting.

6. A floating seal assembly comprising a pair of seal rings according to any of claims 1 to 3 and a pair of elastomeric retaining members disposed to urge the pair of seal rings into sealing contact with each other at sealing portions thereof.

7. Afloating seal assembly as herein described with reference to the drawings.