Coatings of engineering polymers like polyether ether ketone (PEEK) and liquid crystal polymer (LCP) can now be applied onto large surfaces by high velocity thermal spraying methods.
As PEEK and LCP are resistant to most chemicals, have a low moisture permeability and a high melting point (>300°C), they are attractive coating materials to protect large vessels in the petrochemical, brewing and other foodand drink processing industries. LCP has already been accredited for use in commercial food processing because of its chemical inertness.
High velocity thermal spray gun Thermal spraying of polymers comprises the propulsion of the coating material in powder form through a flame onto a locally preheated substrate. Using a high velocity thermal spray process, dense PEEK and LCP coatings have beenprepared at TWI with a porosity content of less than 2%. This was achieved without the post heating stage which is required with the more conventional application method of electrostatic spraying.
The coatings were mechanically bonded to the grit blasted substrate with a bond strength of 18MPa for the PEEK coating. PEEK and LCP coatings have been prepared at TWI in thicknesses of 50µ to 1mm and have shown low levels ofdegradation.
The range of polymer coatings produced by thermal spraying is not limited to PEEK or LCP. Polypropylene (PP) and polyethylene (PE) are commonly applied by this technique. Also, dense coatings of high performance thermoplastics likepolyphenylene sulfide (PPS) or nylon have been prepared. Thermal spraying is an attractive and more environmentally friendly way of applying thermal plastic coatings than painting as it prevents the use of volatile organic compounds(VOC). Composite and graded coatings, consisting of materials of different melting points, can also be prepared by thermal spraying.
For more information please contact Carole Reignier
carole.reignier@twi.co.uk
