NL8104062A - METHOD FOR COATING MECHANICAL SEALS, AND FORMED PRODUCTS MANUFACTURED BY THIS METHOD - Google Patents

Description

** * VO 2275

Method for coating mechanical seals, as well as shaped articles manufactured according to this method.

The invention relates to a method for coating mechanical seals, more in particular a method for coating a sealing surface that rotates relative to a counter surface, in particular the sealing surfaces of pumps used in the petrochemical and wood processing industry .

Hitherto known methods of manufacturing the sliding surfaces of mechanical seals exist e.g. from "welding with stellite, plasma spraying with a ceramic material and by mechanically attaching a carbide ring to the contact surface. Stellite-welded sliding rings generally work reliably, but their useful life is often very short. On the other hand, ceramic coatings have a disadvantage that they are easily damaged Very often the damage already occurs upon application or when the rotating object starts to move, which causes the supply of extra frictional heat to the sliding surface.

When using a carbide ring mechanically attached to a contact face, damage often occurs to the carbide ring when the rotating object begins to move. Bit is a result of a jump in the thermal conductivity between the carbide ring and the sliding ring body, because a seal must be used between them. On the other hand, the seal is also often damaged and thus causes leakage. Attempts have also been made to coat the sliding surface of a mechanical seal by plasma spraying. This is stated in e.g. the publication "Plasma Technology Grundlagen und Anvendung",

Deutscher Verband für Schweisstechnik, 1970, pp. H8 - 151, as well as in U.S. Pat. Nos. 3,6 ^ 2,519 and 3-936,295. Sen 8104062 - 2 - Tungsten carbide-cobalt mixture, too. used according to the invention, is mentioned as a coating material.

It should be noted, however, that the prior art has encountered difficulties in obtaining good adhesion of the coating to the base and in achieving sufficient internal strength and thermal conductivity for the coating. This is the reason why methods other than plasma spraying, as described above, are still used in e.g. applications in the petrochemical industry.

However, it has been noted in connection with the invention that with the aid of the proper spraying technique, the correct mixture and the correct grain size, excellent results compared to those of the conventional technology can be achieved. It is also important that the material is not sintered after plasma spraying, as proposed in the aforementioned US patents. If the entire porosity of the coatings on e.g. the seals used in pumps for the petrochemical industry, is lifted by sintering, then the film of the pumped material, which forms on the surface, is broken and thus the coating also wears quickly.

The object of the invention is to avoid the annoying drawbacks of the prior art. In other words, the aim is to obtain a mechanically durable sliding surface that does not wear easily or is damaged.

The features of the invention are as follows: high energy plasma spraying is used, the spray mixture used contains 80-9 wt% tungsten carbide and 6-20 wt% cobalt, nickel or iron, and its grain size is 50-60 µm, and after the plasma spraying, the coating layer is allowed to cool without subsequently sintering it, so that a certain porosity remains in the layer.

The accompanying drawing is illustrative and is a cross-sectional view of a mechanical seal coated in accordance with the invention, in which the seal is indicated by the reference numeral 1 and the sliding ring by the reference numeral 2.

35 In practice, the coating is effected by coating the contact surface 8104062 * Γ * ζ · * - 3 - which is normally made of acid-resistant steel, by plasma spraying with energy-rich spray values and by using spray material consisting of a mixture of tungsten carbide and an iron group metal. The usual composition of the mixture is 80-9 wt.% Tungsten carbide and 6-20 wt.% Cobalt, nickel or iron. The grain size of the mixture is usually 5-60 µm. A layer thickness of less than even 0.2 mm can be used.

Examples 10 To conduct practical experiments, the sealing surfaces of a series of mechanical seals were coated by high energy plasma spraying with a spray mixture consisting of tungsten carbide. and . cobalt in a ratio of 83: 17 · The measured thickness of the coatings on the seals was 0.2 mm.

The seals produced in the manner described above were fitted in early January 1980 in four benzene pumps (GA 17215-17218) from an oil refinery. Until then, stellite-welded seals, which survived approximately 1-4 weeks of effective rotation time, were used in the aforementioned pumps.

20 The constant replacement of seals posed a significant financial burden to the factory due to the frequent downtime and also because personnel had to be wary of the replacement of the seals.

Since no maintenance service interruption had occurred by early February 1981, all of the aforementioned pumps were opened to check the condition of the seals. At that time, it was noted that all the seals were in excellent condition and, therefore, there was no need to replace the seals even at that time. By this time, the effective rotation time of each pump was over 5 months.

As can be seen from the above, the useful life of the seals manufactured according to the invention at that time was even 20 times longer than that of seals welded with stellite. When it is decided at some point in the future that the trial period is over and the seals are replaced, the increase in the stated useful life will be increased from 8104062 - t *.

j- * k V

«- k - self-evidently be even greater than 20-fold. In addition to the vast improvement in service life, which was unexpectedly observed, a seal made in accordance with the invention is also advantageous in that the thickness of the coating used, which is at most 0.5 mm, but usually about 0.2 mm, deviates from the API 610 standard. According to API 610, the thickness of the coating must be at least 0.76 mm, which means that normally almost four times more coating material is used than when the coating is done according to the invention. In other words, the improvement in the useful life is even more surprising when it is remembered that it is accomplished by using a coating thickness that should hardly have any useful life. When sealing surfaces of seals according to the invention, the contact surfaces of the sliding ring are machined as shown in the drawing. The machining of the contact surfaces has its own significance in terms of adhesion of the coating to the base and in terms of its useful life. A further advantage of the construction according to the drawing consists in that the formation of pores at the edges of the coating is reduced and that it is thus easier to machine the contact surfaces of the constructed objects later on.

8104062

Claims (3)

Method for coating a sealing surface which rotates with respect to a counter surface, in particular for coating the sealing surfaces of pumps used in the petrochemical and wood processing industry, characterized in that high-energy plasma spraying is used, the material used spray mixture contains 80 - 9b by weight tungsten carbide and 6 - 20% by weight cobalt, nickel or iron and its grain size is 5 - 60 µm, and the coating is allowed to cool without subsequent sintering after the plasma spraying, so that a certain amount of porosity in the coating persists. Method according to claim 1, characterized in that the sprayed coating has a thickness less than 1.2 mm, preferably less than about 0.2 mm. 3. Molded article manufactured in whole or in part according to the method according to any one of the preceding claims. 8104062