CNCL NO S/S

INTRODUCTION

The purpose of this Defence Standard is to provide designers and users with advice on the application of flame sprayed coatings, principally for wearing surfaces. It includes cleaning, preparation of surfaces, design considerations, metals and non-metals to be applied, quality control, inspection, and testing.

It is not intended to apply to aerospace parts and equipment.

This Defence Standard is divided into three parts:

Part 1, Unfused metal coatings

Part 2, Fused metal coatings

Part 3, Ceramic and cermet coatings.

Part 3 - Ceramic and cermet coatings - deals with the use and application of such coatings to engineering components to provide a variety of specific surface properties. The properties provided include:

Resistance to wear, galling, and abrasion at ambient and elevated temperatures.

Heat and electrical insulation.

Resistance to corrosion, oxidation, and erosion.

Resistance to 'wetting' by molten metals.

These coatings are used either to build up or repair components showing rapid destructive attack in service, or to provide specific desired service characteristics to new components by incorporating such coatings in the initial design, and applying them during the manufacture of new engineering components.

This Standard amplifies the recommendations given in BS 4495.

By way of example, the following are typical applications:

(1) Pump plungers and rotating pump seal rings and shafts are sprayed for wear and corrosion resistance with alumina, alumina/titania, or chromic oxide.

(2) Pump sleeves, mechanical seals and valve seats running in contact with 18/8 austenitic steel mating faces are sprayed with chromic oxide or alumina/titania ceramics t o overcome 'pick-up' and 'galling'. Air bearing housings are similarly treated.

(3) Sprayed ceramic coatings are applied to seal areas of ash crush rollers to prevent erosion.

(4) Diesel engine piston heads, rocket nose cones, and exhausts are coated with alumina or zirconia for thermal insulation.

(5) Sprayed ceramics are used to repair insulator pots, to insulate shafts of power tools, and to insulate induction heating coils.

(6) Alumina coatings are applied to 'wet' surfaces of diesel engine cylinder liners to withstand cavitation erosion.

(7) Thermocouple sheaths, heat treatment jigs and fixtures, and annealing and normalizing furnace rolls are coated with alumina, magnesium silicate, and zirconia for oxidation resistance.

(8) Ceramic coatings are used on soldering and brazing jigs and fixtures to prevent metal adhesion problems; and as linings to crucibles and molten metal launders to minimize molten metal attack.

This Standard must not be taken as approval to apply any flame sprayed coating to a component without the written consent of the purchaser or owner. This written consent may be in the form of a contract or order, or may be in the form of written permission from the Design/Approval Authority concerned.

If this Standard should be found unsuitable for a particular requirement the Director of Standardization shall be informed of the circumstances.