Creating a technology to coat the insulating material on the “cold” section of a cartridge-style electric heater for operation in aggressive environments

Introduction. Currently, fluorine polymers have become quite widespread in various industries. One of the fields of application of fluoroplastic coatings in the oil industry is their use as protective coatings to prevent the deposition of paraffin plugs on the walls of tubing and field pipelines. Fluoroplastic parts find promising application in machines and units of oil refining and petrochemical industries, where high corrosion resistance, sufficient strength and high tribotechnical properties are required. The complexity of the ubiquity of fluoroplastic coatings is its low adhesion to the metal surface. In this regard, fluoroplastic coatings are typically complex systems comprising directly fluoroplastic polymer, binders and functional fillers. Materials and methods. The study used metal plates made of titanium alloy VT6 and carbon steel St3 coated with an aqueous fluoroplastic suspension. Fluoroplastic polymer coatings have poor adhesive strength to the metal surface on which they are applied. Therefore, in order to ensure a high level of adhesion of the coating to the metal substrate, it is necessary to use complex methods of preliminary surface preparation. The coating was applied to the pre-prepared surface of the metal plates by air spraying using a spray gun and compressed air. The key parameters for the formation of the fluoroplastic film were drying and sintering modes. Adhesion was evaluated by the methods of “X-shaped” notch (State Standard 32702.2-2014) and tearing in a tensile machine on cylinders (State Standard 32299-2025). Results. Proposed method comprises application of intermediate primer layer from suspension containing chromium (III) oxide, phosphoric acid, water and fluoroplastic. The intermediate adhesive primer layer was applied by air spraying under the same conditions as the base fluoroplastic coating. This ensured that the proposed drying and sintering conditions met the base layer. The use of a primer made it possible to realize a gradient transition from the metal substrate to the fluoroplastic layer and significantly increase the adhesion properties. Conclusion. The results show a significant improvement in adhesion compared to the control samples without primer: the tensile strength value by the tear method is 2.56 N/mm2, and by the X-notch method - from 5 points to 1 point (traces of peeling or removal of the coating along the incisions). The method is easy to implement and promising for use in protective coatings.