Sealing rings for mechanical seals


 About 50 years ago, usage of a mechanical seal as a construction element was restricts- ed to only a few fields of application.

Nowadays the mechanical seal can be regarded as the main high–quality sealing element in use

 for the sealing of rotary shafts.

This rapid development of the mechanical seal as a machine element has only been possable  through the continuous development of seal designs and through the systematic development of new and improved sealing ring materials.

 This also includes the further development of carbon- graphite materials by TISTAM, which has made it possible t   match increasingly severe operating conditions and thus the stricter requirements imposed on sealing ring materials.

In the development of new and improved grades of car- bon for sealing rings not only the required

material proper – ties, but also the question of cost had to be taken into account, particularly for sealing rings in low- priced mass produced seals.

carbon/graphite and electro-graphite grades, carbon/graphite and electro graphite grades with various synthetic resin and metal impregnations to high strength electro graphite grades with special impregnations to improve the oxidation resistance or the dry running capacity.

 The properties of synthetic resin- bonded carbon grades have been improved considerably compared to synthetic resin molding compounds containing carbon.

These grades are particularly suitable for the pressing-to-size of rings, even in fairly complicate-

Ed designs, for mass-produced seals.

In addition, a range of carbon/graphite grades with the above mentioned impreg-nations are available which are also suitable for the pres-sing-to-size or partially ores-sing-to-size for mass-produced seals.

Mechanical seals are mainly used for sealing between liquids and gases.

It should be noted that, with carbon seal rings, even liquids with low hydrodynamic lubricating capacity provide sufficient lubricating effect.

The sealing of gases and the dry running that arises from this is possible at low sliding speeds with carbon sealing rings e.g. in agitator seals, provided that the wear rate is sufficiently low.

 For the sealing of gases at high running speeds the use of carbon seal rings in so – called gas seals is also common, provided that the design of the seal ensures that contact between the sliding

During normal running, the gas pressure ensures contact-free operation of the sliding surfaces.

Sealing between gases is carried out otherwise with double-acting mechanical seals and a sealing liquid, the sealing as a lubricant for the sliding faces and for the dissipation of the frictional heat.  


1       - Grade selection

It must be said that it is impossible to cover all service conditions with one carbon/graphite material.

2-    Application limits

Running speed:                 70 m/sec max.

Pressure difference:          160 bar max.

Sliding pressure:               10-200 N/cm2

                                          Generally<50 N/cm2

Product of pressure

And speed:                        pxv max = 1250 N/cm2 x m/sec

3-   Pressure tightness of carbon sealing rings

Sliding rings made of redensified or impregnated carbon/graphite material are impervious to liquids and gas.

the pressure tightness of sliding ging is inspected by means of a hydraulic pressure test, from the inside of the ring with water, or under water using nitrogen.

Large series are inspected on a statistical basis.

Usual test pressures:  3, 5 or 10 bar

For special applications test pressures up to 20 bar are possible.

The same applies to ores-in and shrink-in fist.

Here, the following criteria are important

Here it is important to maintain tight dimensional tolerances particularly shape tolerances such as concentricity and conicity of both the bore and outside diameter.

Press in fits:   H7/s6

Shrink in fits: H7/x6 – x7    H7/z6 – z7 

Because of the changes in shape that occur during shrinking in, the flatness of the sliding surfaces

can only be achieved by refashioning after shrinking in.

Due to the lower shrinking stress at working temperature, compared to room temperature, the sliding surface is no longer as flat over its whole width at working temperature as it is at room temperature,

Resulting in a certain leakage until the running in of the sliding surfaces.   

4-   Installation of carbon sealing rings  

Usually, carbon sliding rings are installed in a push-fit seating over O-rings and in rubber

Or plastic sleeves, ant rotation locking being provided for in each case.

Adhesive bonding is customary for installation in metal holders or metal bellows.

The adhesive must be suited to the chemical and thermal require-ments. 

Special attention must be given to the pressure tight-ness of the joint. 


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