Method of manufacturing of a mechanical face seal

Details Method of manufacturing of a mechanical face seal Method of manufacturing of a mechanical face seal

1999-04-29

2001-03-13

Jenkins, Daniel J. (Department: 1742)

Powder metallurgy processes

Powder metallurgy processes with heating or sintering

Making composite or hollow article

C419S018000, C075S240000

Reexamination Certificate

active

06200524

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of powder metallurgy and more particularly to manufacturing of mechanical face seals from cemented carbides.
Such face seals usually are configured as disc shaped substrate made of an iron based alloy and provided with a ring like annular insert made of a wear resistant material. For the sake of brevity these seals will be further referred to as seals provided with working ring and the seals which are fully made of cemented carbide will be further referred to as solid carbide seals.
The ring insert is disposed within a corresponding groove previously cut in the seal substrate and is firmly adhered thereto. By virtue of high wear-resistance such face seals are widely used in various industrial fields and in particular in chemical industry for sealing shafts of mechanical rotary/centrifugal pumps. It should be understood however that the present invention is not limited strictly to manufacturing of mechanical face seals for pumps. The present method can be employed for manufacturing of face seals suitable for exploitation in any other heavy duty, abusive application where high abrasive resistance in combination with good mechanical properties is required. Among these applications can be mentioned seals for submersible electric motors for oil production from wells, seals for electric drills for oil well drilling, seals for turbo generators and compressors etc.
BACKGROUND OF THE INVENTION
Mechanical face seals provided with annular working ring made of cemented carbide are known and their advantages in comparison with mechanical solid carbide seals are explained for example in U.S. Pat. No. 4,280,841 assigned to Nippon Tungsten Co.
In this patent is described manufacturing of mechanical seal provided with a cemented carbide hardened layer or ring which is firmly bound to the seal substrate. According to one of the embodiments disclosed in this patent powder of tungsten carbide mixed with an addition of 6.5 percent of Co is placed within a groove formed in stainless steel substrate and is compressed therein to produce a green compact. The compact is then presintered by heating in vacuum to obtain carbide layer with the thickness 1.3 mm. Then a paste which is a mixture of Ni—P alloy is coated or sprayed onto the presintered compact and finally the presintered carbide compact is heated in a non-oxidizing atmosphere to obtain cemented carbide hardened layer strongly bonded with the substrate by virtue of diffusion-bonding effect.
The disadvantage of this method lies in the fact that use of low melting Ni—P alloy does not allow obtaining cemented carbide working ring with sufficient hardness. The function of Ni—P contained in the upper layer is merely to infiltrate into the bulk of the tungsten carbide and to provide for soldering with the substrate. The reported hardness in the '841 patent of the working ring lies between H
v
720-850 which is almost two times less than that of the solid carbide. Despite it is stated in the patent that the above hardness showed improved wear resistance one can assume that it might be still insufficient for many heavy duty applications. Moreover, due to relatively low hardness one can expect that mechanical end seal rings manufactured by this method have high coefficient of friction and are prone to seizure at relatively low loads.
The further disadvantage of the known method is associated with the fact that the thickness of the obtained working ring is limited to only 1.3 mm which shortens the service life of a seal provided with such a ring.
In GB1290980 is disclosed method of obtaining a wear-resistant surface on a steel part. This method comprises coating of at least the bottom of the groove made in the part by a copper layer, placing thereon a layer of powdered tungsten carbide, pressing this layer within the groove, superimposing an upper layer of copper powder on the layer of tungsten carbide, pressing the copper layer and then heating the whole part in a neutral atmosphere which is sufficient to melt the copper. The copper residing in the upper layer melts, impregnates the bulk of tungsten carbide portion and binds thereof, while the copper layer placed on the bottom of the groove provides reliable soldering of the bulk tungsten carbide portion to the substrate.
Unfortunately since copper is very prone to corrosion in presence of many industrial gases and liquids, especially H
2
S, organic acids, sulfuric acid, ammonia, sodium hydroxide, distilled water or natural gas the face seals manufactured by the above method are not suitable for use in those industrial applications where such gases or liquids might be expected.
Furthermore, the necessity in coating the groove walls by the copper layer renders this method technologically complicated.
In RU2021078 is described method of production of wear-resistant layer on working end surface of a face seal. This method involves filling circular groove made in a steel based substrate by a powdered tungsten carbide, pressing thereof within the groove, placing on the green compact of a layer of powdered Cu—P alloy, pressing this layer and then heating the substrate in vacuum until the upper layer melts and impregnates the tungsten carbide portion. It is mentioned that Cu—P effects reliable soldering between the substrate and tungsten carbide and thus eliminates the necessity in preliminary coating the groove by a copper layer.
Unfortunately since this method also utilizes copper it is inevitably associated with the same disadvantage, i.e. the seals manufactured according to this method are insufficiently chemically resistant in the presence of industrial or natural fluids.
In conclusion it should be emphasized that despite the fact that different methods for manufacturing of mechanical end seals employing working cemented carbide ring have been devised there is still a need for a new method ensuring producing of such face seals with improved performances comparable with the seals made of solid carbide, but being cheaper than solid carbide face seals.
OBJECT OF THE INVENTION
The object of the present invention is to provide a new and improved method for manufacturing of mechanical end seals enabling sufficiently reduce or overcome the above mentioned drawbacks of the known in the art methods.
In particular the main object of the present invention is to provide a new and improved method of manufacturing of mechanical face seals having improved hardness comparable with that of the solid carbide.
The further object of the present invention is to provide a new and simple method of manufacturing of mechanical end seals having improved friction properties and wear resistance by virtue of low coefficient of friction and high resistance to seizure.
The third object of the present invention is to provide new method of manufacturing of mechanical seals ensuring high strength of the working ring and reliable adhesion thereof to the substrate.
Still further object of the invention is to provide a new and improved method of manufacturing of mechanical face seals with improved chemical resistance by virtue of eliminating copper in their composition.
The above and other objects and advantages of the present invention can be achieved in accordance with the following combination of its essential features, referring to different embodiments thereof.
According to one of the preferred embodiments the present method is suitable for manufacturing of mechanical face seals, said seals configured as an iron based alloy substrate provided with annular groove. The groove is filled with a wear resistant material comprising at least one refractory metal carbide and a binder. The method comprises the following main sequence of steps:
filling the annular groove formed in the substrate with a powdered mixture of refractory metal carbide and the binder,
applying first external pressure onto said powdered mixture so as to produce a compacted bulk portion thereof, said compacted bulk portion being disposed within the annular groove,
placing a powder of the binder onto the

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