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Coating compound keeps its head under the hood.

In developing its Monomet cylinder head gasket, STE of Wilhelmshaven, Germany, used a powder coating compound of Victrex PEEK polymer and PTFE (polytetrafluoroethylene) to prevent micro abrasion, contact corrosion, and "welding" of the cylinder head to the cylinder block. In this critical role, reports Victrex, the highly durable PEEK/PTFE coating "allows the gasket to last longer, seal better, and [undergo repeated reinstallation] without any significant effect on cylinder head performance."

The Monomet gasket is a one-piece solid steel stamping with a tightly controlled thickness profile. The coating, which is applied in a secondary step, must meet a range of temperature, wear, and chemical resistance requirements. For example, says Victrex, the cylinder head gasket is subjected to temperatures that can vary between -40[degrees]F and 480[degrees]F and 250[degrees]C and 250[degrees]C). The critical requirement of simultaneously sealing the engine coolant, engine oil, and combustion gases presents an extreme challenge to the sealing material.

In addition, Victrex says, because of the distortion of the cylinder head, the gasket is subjected to compression forces as high as 29,000 psi (200 N/[mm.sup.2]). Moreover, the head gasket must absorb all the cylinder head movement, which results from constant temperature and pressure changes, while maintaining a seal with the least possible amount of friction.

To apply the PEEK polymer and PTFE compound to the gasket, Victrex explains, STE uses the Multislide coating process. One of its most difficult challenges was to ensure a permanent adhesion of the coating to the metal gasket. By using a special bonding agent, says STE, it "perfected the coating technology so that only a 20[micro]m [less than 0.00079 inch (0.8 mil)] coating is needed to pass 2000 hours of hot water testing at 248[degrees]F (120[degrees]C) and 900 hours of thermal shock testing." In addition, the company says, the coated gasket has proven itself in OEM testing and nearly three years of vehicle testing.

Victrex USA Inc., 3 Caledon Court, Suite A, Greenville, SC 29615; (800) VICTREX or (864) 672-7335; fax (864) 672-7328;

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Title Annotation:Plastics Applications
Comment:Coating compound keeps its head under the hood.(Plastics Applications)
Author:Molinaro, Hope
Publication:Plastics Engineering
Article Type:Brief Article
Geographic Code:1USA
Date:Sep 1, 2003
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