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PHOSPHATE PRE-TREATMENT

Phosphate pre-treatment is the most commonly overlooked step in preparation for coating. It is also the most important.

The generic term "phosphating" is a process where an acid attacks the metal of the work piece and re-deposits a material that is a combination of the metal substrate (and other metals - like zinc) along with phosphate. This process creates a surface that is tightly adherent to the base metal, has more surface area, provides improved corrosion inhibition, and helps the powder coating stick better. It provides a good coating base so the finished part has increased useable life.

BENEFITS OF PHOSPHATE PRE-TREATMENT

  • Better Cleaning
  • Better Coating Adhesion
  • Rust Inhibitive Coating
  • Leaves Consistent Profile
  • Self pH Neutralizing System
  • Minimal Waste Created

TYPES OF PHOSPHATE

Iron Phosphate

Iron phosphate is the most frequently used pretreatment for powder coating. It can be used with almost any substrate. Zinc Phosphate may also be used as a pretreatment choice. However, this process is more costly to operate, uses heavy metals, and can produce considerable sludge, neither of which are environmentally friendly. For this reason, ICS has opted not to use zinc phosphate pretreatment.

PROCESS

conversion coating

In addition to the number of process stages, the factors that will affect the weight of an iron phosphate coating are time, temperature, concentration, acid consumed (pH), the condition of the substrate and the spray pressure. Time in Process - The more time that the chemistry has to work, the more work it will do. The process must be long enough to allow the chemistry to form to a uniform coating on the surface. Temperature of the Solution - Soils become more reactive in a heated solution and the chemicals become more aggressive. Concentration - A higher concentration of chemical will provide more total acid, more accelerators and it can provide more coating weight.

BARRIER PROTECTION

Phosphate Crystal Barrier

To understand how coatings fail one must first understand what makes organic coatings work. In broad terms, they work because they have good adhesive and cohesive strength and integrity, resist weathering and chemical deterioration, and impede the permeability of harmful corrosive agents. The fact that coatings are a relatively thin film separating two reactive materials indicates the vital importance of the complete coating system. The coating must be a completely continuous film and bonded well to the pretreated metal substrate in order to fulfill its function. Any imperfections in the barrier become a focal point for the development of corrosion and a breakdown of the protective structure.

CORROSION BASICS

Corrosion

When the organic finish (powder coating), is breached through to the ferrous metal substrate, moisture, air, minerals, and surface contaminants, such as pollution, combine to create electrolytes which allow electrical current to flow by the movement and discharge of ions. Moisture (electrolytes) will immediately penetrate any breach in the coating surface. As the coating is lifted by the growth of corrosion, a greater amount of moisture is trapped beneath the coating barrier and will prolong the electrolysis process, accelerating corrosion.

WHY PHOSPHATE

Iron Phosphare protection

The Iron Phosphate conversion coating method is by far the most common method of pre-treatment for powder application. The process is economical and effective for a host of product application both indoor and outdoor use. ICS completes this process on ALL material that comes through our shop, except where a special purpose powder formula specifically recommends no phosphate pre-treatment, such as with high-temperature powders.

BARRIER SYSTEMS

Duplex coating system

A coating System is the use of several layers in combination to achieve improved performance when special environments demand improved protection. The application of an approved primer layer, usually an epoxy, above the phosphate layer and beneath the final finish offers superior protection against water penetration. This method is particularly effective on products that have sharp edges and on architectural projects where the metals can not be easily removed and transported for re coating or maintenance.

From Start to Finish
  • Spray Wash system

    Feemont machine

  • Phosphate Spray wash

    Washing

  • Oven drying after Phosphate

    Drying

  • Washed and dried ready for coating application

    Ready for Coating