JPH04327068A - Mechanical seal - Google Patents

Abstract

PURPOSE:To provide a mechanical seal capable of effectively preenting a blister as sealing a highly viscous oil even under the condition easy to cause such a phenomenon. CONSTITUTION:Of two sealed end surfaces relatively sliding and rotating, one is formed from a carbon material, and the other is formed from a cemmented carbide material in which boron nitride is uniformly disperesed and blended.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanical seal in which two sealing end faces are slidably rotated relative to each other.

0002

[Prior Art] In this type of mechanical seal,
In view of sealability and durability, one sealed end surface is generally made of a carbon material, and the other sealed end surface is made of a cemented carbide material such as tungsten carbide.

0003

[Problems to be Solved by the Invention] However, in recent years, as the field of use of mechanical seals has expanded, mechanical seals have been used for sealing high viscosity oil, etc., such as in pumps used in the petrochemical field, and for sealing high loads (PV). T) Since the usage conditions tend to be severe, such as sealing under conditions, the above-mentioned conventional mechanical seals are often unable to meet the requirements.

That is, when sealing high viscosity oil, high heat is generated due to increased sliding resistance between the sealed end faces, and this generated heat causes the carbon sealed end faces to shorten for a short time. The carbon may be partially raised, and the raised part may be destroyed and the carbon may be released.
Alternatively, even if the carbon does not come off, cracks may occur in the raised portion (hereinafter, such a phenomenon will be collectively referred to as "blister"). When blisters occur on the carbon sealed end faces, a large amount of leakage occurs between the sealed end faces, making it impossible to perform the desired sealing function.

[0005] Conventionally, attempts have been made to use mesoface-based carbon as a countermeasure against such blisters, but these have not been able to effectively prevent blisters and are less self-lubricating than ordinary carbon. Coupled with the fact that it is inferior in performance and expensive, it is difficult to say that it is an effective measure against blister.

The present invention has been made in view of the above problems, and can effectively prevent the occurrence of blisters even under conditions where blistering is likely to occur, such as when sealing high viscosity oil, and can provide a long-term service life. The object of the present invention is to provide a mechanical seal that can exhibit a good sealing function over a long period of time.

[0007]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the mechanical seal of the present invention has two sealed end surfaces that rotate in sliding contact with each other, one of which is made of carbon material and the other made of boron nitride. It is proposed to be constructed of dispersed and blended cemented carbide materials.

[0008] Sealed end face made of cemented carbide material blended with boron nitride (hereinafter referred to as "BN blended sealed end face")
can be obtained, for example, by adding an appropriate amount of boron nitride to tungsten carbide powder, uniformly dispersing and mixing it, press-molding it into a predetermined shape, and then sintering it. The amount of boron nitride added is generally 5
It is preferable to set the content to 25% by volume. Note that as the cemented carbide, titanium carbide and other cermets can be appropriately selected in addition to tungsten carbide.

[0009]

[Operation] On the BN compound sealed end surface, boron nitride is scattered in the form of independent fine pores, so even when sealing high viscosity oil, these pores act as a kind of oil pocket. This results in good lubrication between the sealed end faces and enhanced cooling. As a result, heat generation between the sealed end faces is suppressed as much as possible, and blisters generated thermally on the carbon sealed end faces are effectively prevented, ensuring good sealing performance over a long period of time. Ru.

By the way, under the same finishing conditions as the conventional sealed end material made of tungsten carbide, BN
The surface roughness of the compound sealing end face is 0.08 to 0.35μRa due to the presence of the above-mentioned pores, and maintaining the surface roughness within this range promotes the above-mentioned lubrication and cooling effects to ensure a good seal. It is extremely important to perform its functions. That is, if the surface roughness is less than 0.08 μRa, the lubrication and cooling effects between the sealed end faces will not be sufficiently performed, and if it exceeds 0.35 μRa, the sealing action due to sliding contact between the sealed end faces will not be maintained. This will result in a large amount of leakage. In the components of the BN compounded sealed end surface, boron nitride is uniformly dispersed in the cemented carbide structure in the above-mentioned form. Even when it is fitted into the end surface by sliding contact, the pores that function as oil pockets do not disappear, and the surface roughness can be maintained within the above range.

[0011] In addition to the above-mentioned points, the BN-containing sealed end surface has various properties that are effective in increasing the reliability of the mechanical seal under severe usage conditions. For example, since boron nitride is a self-lubricating substance as is well known, B is made of cemented carbide material in which boron nitride is uniformly dispersed.
The N-blended sealed end face has extremely superior self-lubricating properties compared to a sealed end face made of a normal cemented carbide material. In addition, boron nitride, like cemented carbide such as tungsten carbide, has excellent wear resistance and corrosion resistance, so adding boron nitride will not impair the properties of the cemented carbide itself. do not have. Furthermore, since boron nitride is dispersed in the structure of the cemented carbide, thermal cracking is prevented in the dispersed pores, and the heat cracking resistance is significantly improved. Furthermore, stress is relaxed in the dispersed boron nitride portions, improving toughness and thermal shock resistance. Furthermore, since boron nitride, a solid lubricant, is dispersed in cemented carbide, there is no risk of the lubricant leaking out and degrading the properties of the sealing material itself, as would be the case when an oil-containing material is used. There is no.

0012

[Example] As an example, we will introduce a mechanical seal that can be installed on a rotating shaft with a shaft diameter of 40 mm, and the sealing end surface material is a combination of ordinary carbon and tungsten carbide in which boron nitride is evenly dispersed. ■ was produced. In addition, as a comparative example, a mechanical seal ■ has the same structure as the mechanical seal ■ above, but the sealing end surface material is a combination of ordinary carbon and tungsten carbide without boron nitride, and a mechanical seal ■ that uses mesoface carbon and boron nitride. Mechanical seals ■ consisting of combinations with unblended tungsten carbide were manufactured.

[0013] Each of the mechanical seals ■■■ was assembled on the rotating shaft, and the mechanical seals were repeatedly turned on and off at 30 minute intervals under the following conditions.

Sealing fluid: C heavy oil Fluid pressure: 7Kgf/cm2 Fluid temperature: 30°C (temperature when operation is stopped) Rotation speed: 3
600r. p. m.

[0015] As a result, in the mechanical seal (■) of the comparative example, the fluid temperature rose to 90°C during operation, and after the number of starts and stops was 2 (2 hours), blistering occurred and a large amount of leakage occurred. . In addition, with mechanical seal ■, the fluid temperature rises to 90°C during operation, and the number of starts and stops is 15 (15
Blistering occurred at the time (time) and a large amount of leakage occurred.

On the other hand, in the mechanical seal (2) of the example,
It was confirmed that the fluid temperature rose only up to 80°C during operation, and even after 160 starts and stops (160 hours), no large leakage occurred and no blisters were generated. Finally, a blister occurred after the number of starts and stops was 164 (164 hours).

[0017] From these experimental results, it has been found that by using a combination of cemented carbide containing carbon and boron nitride as the sealing end surface material, it is possible to effectively prevent the occurrence of blisters even under the above-mentioned severe conditions. It is understood that it is possible to exhibit a good sealing function over a long period of time.

[0018] As the constituent material of the carbon sealed end surface, ordinary carbon is sufficient as described above, but it is of course possible to use mesophase carbon if necessary. Further, the mechanical seal according to the present invention can be suitably used even under conditions where the sealing fluid is not a high viscosity fluid such as the above-mentioned heavy oil C. That is, B
The presence of pores on the N-blended sealed end surface promotes the lubrication and cooling effects, and can effectively prevent blisters on the carbon sealed end surface.

[0019]

[Effects of the Invention] As is clear from the above explanation, according to the present invention, even under severe conditions such as when sealing high viscosity oil, the lubrication effect and cooling effect between sealed end faces is promoted. Therefore, it is possible to effectively prevent blisters on the carbon sealed end face, and to exhibit a good sealing function over a long period of time.

Claims (1)

[Claims] 1. A mechanical seal comprising two sealing end faces that rotate in sliding contact with each other, one of which is made of a carbon material and the other is made of a cemented carbide material in which boron nitride is dispersed.