Metal clad carbon rings ( GAP SEAL )


 With one piece carbon/graphite phite sealing rings, a suffi-ciently tight seal gap over a wide temperature range can only be achieved by corre-spondingly tight assembly tolerances and thespecial  procedure of shrinking into a metal holder.

It is the lower coefficient of thermal expansion of carbon/graphite material compared to steel which necessitates its shrinking into a metal holder.

The meta clad ring are under shrinkage stress and expand in correspondence to the coefficient of thermal expansion of the metal holder material.

The shrink fits and the shrinking in temperatures have to be selected in accordance with the maximum

Service temperature.

Customary shrink fist and shrinking in temperatures:

H7/z8      350 - 400C

H7/za8     450 - 500

To be observed when shrinking into meta holders:

Because of dimensional changes during shrinking in:

-         subsequent machining of the ring bore

-         subsequent machining of thin walled steel holders (~ 0.2mm oversize for machining)

Wall thickness of the steel holder: 2-5 % of the outer diameter of the carbon ring, minimum 2mm.

In most gap seals, depending on the pressure drop (see design recommendations), several rings are arranged behind another in steel or cast iron chamber rings.

Due to the pressure drop the rings are pressed axially against the face of a chamber ring resulting in additional axial sealing.

The precondition is that the chamber face is well mechanical (Rt <=2 ) and as the metal clad x carbon rings are concerned, that the carbon ring protrudes axially from the metal holder.


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