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Adhering to sound advice

Connect, no. 130, May/June 2004, p.3

HVOF spraying system
HVOF spraying system

When a leading surfacing specialist found difficulty in executing bond strength trials on high velocity oxy-fuel (HVOF) coatings, it turned to TWI for a solution to its difficulties.

The company's coating adhesion tests had failed because it was unable to obtain an adhesive with sufficient bond strength to test the coatings to the exacting standards of ASTM C633-01.

As part of TWI's Joining Forces Yorkshire and Humber programme, Scarborough based Dowding and Mills contacted TWI to accept its offer of a Product and Process Review and Feasibility Study, free direct technical support.

The task the company faced corresponded closely to an area of expertise held by TWI's surfacing team. It involved applying a tungsten carbide cobalt chromium coating to mild steel test coupons using high velocity oxyfuel spraying. The ultimate objective of the work was to demonstrate that the coating would adhere to a substrate material used in fan manufacture.

So finding an adhesive with sufficient bond strength to test the coatings proved crucial. Without this vital element the joint fails between the adhesive and the coating. To test the coating properly the joint should fail between the coating and substrate.

TWI was able to provide the very high strength adhesive and, using its Instron 8500 test machine, successfully carry out the tests to the specification.

Before it consulted TWI, the client company was achieving adhesive strengths of about 8800psi. The minimum requirement for an HVOF coating is 9500psi. The strengths achieved by 10 tests following TWI's work averaged well over 10000psi.

TWI's help was available to Dowding and Mills under the Joining Forces Yorkshire and Humber technology transfer programme. The programme aims to boost growth, competitiveness and innovation in the region's small and medium sized companies.

For more information on the programme and how your company can benefit contact - TWI Technology Centre (Yorkshire) on 0114 269 9046.

For more information please email:


contactus@twi.co.uk