Developers

The purpose of a developer is to effectively pull the penetrant back out of a defect to allow it to be seen by an inspector. The action of pulling it back to the surface also allows the penetrant to spread along the surface around the defect, thus magnifying the strength of the indication.

With UV fluorescent penetrants, the developer particles both reflect and refract the UV light, which makes the indications brighter.

With visible penetrants, the developer, in addition to pulling the penetrant back to the surface, creates a white background to create an ideal contrast between the indication and the surrounding surface.

Under AMS 2644, there are five primary classifications of developer, namely:

  • Form a – dry powder developer
  • Form b – water soluble developer
  • Form c – water suspendible developer
  • Form d – nonaqueous solvent based developer for fluorescent penetrants
  • Form e – nonaqueous solvent based developer for visible penetrants

Dry powder developers

Dry powder developers (ZP-4D) are generally considered to be easy to use and inexpensive. They can be applied using the following techniques:

  • Dipping
  • Powder spray applicator – for example, powder spray bulb dispenser
  • Powder storm cabinet
  • Electrostatic spray gun

Water suspendible developer

With a water suspendible developer like ZP-5B, the developer particles are suspended in water. It is important to keep the developer suspension stirred or agitated to prevent the particles from settling out of the suspension. After application of the developer, you will need to dry the parts to remove excess water. Water suspendible developers can be applied using the following techniques:

  • Immersion dip
  • Flow on

Water soluble developers

With a water soluble developer (ZP-14A), the developer particles are dissolved within a water carrier. After application, a film of developer  will form on the surface of the part during the drying stage. As with water suspendible developers, water soluble developers can be applied using the following techniques:

  • Immersion dip
  • Flow on

Non-aqueous developers

Non-aqueous developers are solvent based, where the developer is suspended in a solvent based carrier. Being solvent based, there is no need for heat drying as the solvent evaporates quickly from the part.

In general, these products are supplied and used as aerosols for convenience and ease of use. If used in bulk, they will need to be applied using a spray gun, with care being taken to keep the developer stirred/agitated.