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Surface treatments

  • Surface treatments are applied to castings for engineering, aesthetic and economic reasons. The surfaces of industrial castings may be treated to provide improved surface-related properties such as wear, fatigue and corrosion resistance. In castings used in consumer products, improved appearance is also an important objective of surface treatments.

  • In many cases, surface treatment permits a casting to meet mutually exclusive design objectives. For example, the application of an abrasion-resistant coating will enable a casting to be both wear resistant, a surface property, and impact resistant, a bulk property. However, regardless of the engineering and aesthetic objectives, the main reason for using surface-treated castings is that they offer the most cost-effective means of meeting these objectives.

  • Surface treatments commonly applied to castings include: thermal and mechanical hardening treatments: the application of fused coatings to reduce friction and improve wear and corrosion resistance; the use of hot dipped metal coatings to improve appearance and corrosion resistance: the electrodeposition of metal coatings to increase corrosion and wear resistance and improve appearance and the application of diffusion coatings to increase resistance to wear, oxidation, and corrosion.

  • Thermal surface hardening is a common and highly cost-effective method of improving the wear and fatigue resistance of castings. Thermal hardening involves the rapid heating of the surface layer of a casting to produce a high carbon austenite which, upon removal of the heat source, is cooled sufficiently rapidly, either by self-quenching or the application of a quenching medium, to produce a martensitic structure. In addition to significantly increasing hardness, the formation of martensite creates compressive stresses in the surface layer, impeding the formation and propagation of cracks. Although slightly softer than hardened steel, the combination of a martensitic matrix and graphite nodules in surface hardened can produce superior resistance to sliding wear. Flame, induction, and laser hardening are the most common methods used to thermally surface harden castings.

    Anodizing - The Optimum Finish for Architectural Aluminum

    Anodizing is an electrochemical process, unique to aluminum, that increases the thickness of a passive, naturally occurring, protective aluminum oxide film.
    It is the only finish that satisfies each of the factors that must be considered when selecting a high performance architectural aluminum finish.

  • Anodizing is a reacted, not an applied finish that is integrated with the underlying aluminum for total bonding and unmatched adhesion.
  • It is non-selective process and protects all exposed and unexposed surfaces. An anodized finish is a uniformly thick, ceramic-like, transparent coating that does not hide defects or potential problems.
  • It is sapphire hard and provides superior resistance to abrasion and scratching. Scars and wear from fabrication, handling, installation, graffiti, and frequent usage are virtually non-existent.
  • Harder, smoother surfaces mean less friction, easier movement, and extended hardware and weather-strip life in operating components.
  • Anodized surfaces, like other adjacent or surrounding materials, are unaffected by acidic cleaning solutions or misplaced mortar when properly protected or timely and thoroughly rinsed.

    Electroplated Hard Industrial Chrome
  • Typically, wear occurs when hard particles are present between two surfaces sliding against each other with intended motion. These hard particles can be either foreign particles from the environment or metal debris from one or both mating surfaces. The predominant historical coating to protect against this type of wear is hard industrial chrome. Electroplated hard industrial chrome can be applied in various thickness ranges from 0.0001" up to approximately 0.020" without degradation of the wear properties.

    Hard industrial chrome is a porous coating which contains microscopic fissures due to the way in which chrome is applied to the base metal. While chrome of 0.005" -0.010" thick will provide optimum protection against wear, over time, a corrosive environment will break down the chrome before its typical wear life has been realized. It does this by attacking the base metal under the chrome and the subsequent rust causes a break in the adhesion of the chrome.

    The way to combat this is to apply a thin layer, less than 0.001" up to 0.002" thick, of Nickel before applying the chrome. This layer will provide the corrosion resistance needed to allow the chrome to realize its full wear resistant life.

    Whether we apply Chrome, or Nickel-Chrome, we can achieve a wide range of surface finishes to meet customer needs. Typical polish finishes range from 1-2 RMS up to 32 RMS. Typical matte finishes (blasted or nodular) can range from 30 RMS up to 200 RMS. Lower RMS provides higher friction between the roller and the material passing over it.

Hot dip galvanizing is a self inspecting process that relies heavily on proper design to achieve a quality result. The major difference between hot dip galvanizing and paint coatings is that hot dip galvanized coatings can only be applied to perfectly prepared surfaces.

Hot dip galvanizing provides the highest quality corrosion protection for steel. Understanding the fundamentals of the galvanizing process and important design factors for steel products to be galvanized will help you to get the best protection for steel products. This section describes the galvanizing process and important design factors. More Information is available in the Industrial Galvanizers "Design for Galvanizing Manual" which can be downloaded.

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