High temperature, self lubricating, low friction materials and hard ceramic coatings for aerospace applications

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Low Friction Oxidation resistant Graphite and Ceramic

At Ceramisis our engineers have developed a range of low friction, oxidation resistant graphite and ceramic materials for use as bearings and seals in high temperature valve applications. This development has been predominantly for the aerospace industry, for bleed and butterfly valves, operating at up to 700°C in air.

The two main grades used for the above applications are our Boronised Graphite grade HTBG210 and our fine grained hot isostatically pressed Boron Nitride grade BN200. These grades offer the following advantages:

• Very low oxidation rates up to 600°C/900°C in air (HTBG210/BN200 respectively)

• Self lubricating

• Low friction (hot or cold)

• Good wear resistance

• Excellent thermal shock resistance

• High compressive strength

• Light weight

• Stable in damp or humid conditions

• Good electrical conductor/insulator (HTBG210/BN200 respectively)

• Good chemical stability

Boronised Graphite grade: HTBG210 applications.
The above properties make this material ideally suited to triple seals in hot air bleed valves, in aerospace applications. Triple seals made from HTBG210 very quickly polish the bore of the valve they are sealing, giving very low leakage rates. Once this initial polishing has taken place, very low wear rates were experienced, to the seal and the valve bore, during service. Leakage rates remained constant throughout the valve's service life, as the seal was hardly effected by oxidation or wear, and did not therefore deteriorate.

This material also has a major advantage over conventional high temperature phosphate impregnated graphite's, in that it is very stable in damp and humid conditions. Phosphate impregnated graphite's have been known to leach out the oxygen inhibiting phosphate, if the valve became wet due to condensation or high humidity. This leached phosphate could then cause the valve to seize.

Hot isostatically pressed Boron Nitride grade: BN200 applications.
This material has an extremely low friction coefficient and superb oxidation resistance, up to 900°C in air. It is ideally suited to bearing applications in hot air valves. It has a major advantage over metal bearings in that it exhibits low friction hot or cold enabling smaller actuators to be used. High temperature self lubricating metal bearings exhibit low friction when hot, but their friction increases dramatically when cold. This can give poor valve performance during start up, or necessitate a larger actuator to be used.

Specifications

Boronised Graphite grade: HTBG210

Density	g/cm3	1.85
Hardness	Shore D	60
Flexural Strength	MPa	70
Compressive Strength	MPa	120
Modulus of Elasticity	GPa	20
C.T.E.	10-6/°C	4.6
Max Operating Temp	In Air	600°C

Hot isostatically pressed Boron Nitride grade: BN200

Density	g/cm3	2.2
Flexural Strength	MPa	32
Compressive Strength	MPa	113
Young's Modulus	GPa	58
C.T.E.	10-6/°C	8.0
Thermal Conductivity @ 20°C	W/mK	49
Thermal Conductivity @ 800°C	W/mK	28
Max Operating Temp.	In Air	900°C

If you would like more information on the above products please contact us by E-mail, telephone or fax.

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