Fosforikerros

Fosforikerros, or phosphating, refers to a chemical conversion coating formed on metal surfaces, most commonly on steel, by converting the surface into a layer of metal phosphate. The coating is created by immersion or spraying the metal in an acidic bath containing phosphate ions and metal ions (such as zinc or iron). The resulting layer is typically a crystalline, porous phosphate film that improves paint adhesion and provides a basic level of corrosion resistance.

There are two main types of fosforikerros: zinc phosphate and iron phosphate. Zinc phosphate coatings are often used as a pretreatment for automotive body parts, appliances, and other steel components to enhance adhesion and to improve corrosion resistance after painting. Iron phosphate coatings are generally thinner and yield a darker, gray-to-black appearance; they are used to improve paint adhesion and provide some wear resistance, particularly on smaller parts and fasteners.

The phosphating process is usually preceded by cleaning and degreasing and followed by rinsing and a sealing or passivation step to enhance corrosion resistance. The resulting layer is not a stand-alone protective coating; its primary purpose is to act as an adhesion-promoting and corrosion-inhibiting base for subsequent coatings, such as primers or powder coatings.

Advantages of fosforikerros include improved paint adhesion, increased corrosion resistance after coating, and the ability to reduce primer thickness. Limitations include that the coating itself offers limited long-term protection without subsequent coatings, and the process involves handling chemicals and waste streams that require proper environmental controls and treatment.

Applications span automotive manufacturing, construction equipment, metal furniture, and various steel components requiring reliable paint adhesion and initial corrosion protection.