Author - Amit Gabani
Developer increases the brightness intensity of fluorescent penetrant indications and the contrast of visible-penetrant indications. Developer also provides a blotting action, which serves to draw penetrant from within a discontinuity to the part surface until the thickness of the surface film of penetrant exuded from the discontinuity is increased to levels above the threshold of visibility. Another developer function is spreading the penetrant on the surface, enlarging the appearance of the indication.
There are four types of developers: Dry powder, Water soluble, Water suspendible and Non Aquas (Solvent Suspendible)
- Form a - Dry Powder
- Form b - Water Soluble
- Form c - Water Suspendible
- Form d – Nonaqueous- Type 1 Fluorescent (Solvent Based)
- Form e – Nonaqueous - Type 2 Visible Dye (Solvent Based)
- Form f - Special Applications (used for permanent record keeping)
Dry powder developers are fluffy white powders that may be applied manually with powder spray bulbs or spray guns or by dipping and dragging parts in the dry powder developer. In automated penetrant systems, dry powder developers are applied in swirl cloud or dynamic cloud chambers. Dry powder developer is generally considered to be the least sensitive but it is inexpensive to use and easy to apply. When a dry developer is used, indications tend to stay bright and sharp since the penetrant has a limited amount of room to spread.
Water soluble developers consist of a powder dissolved in water and applied by dipping a part in the solution, flowing die solution over a part or spraying the solution onto the part. Drying is achieved by placing the wet but well drained part in a recirculating, warm air dryer with the temperature held between 70 and 75°F. If the parts are not dried quickly, the indications will be blurred and indistinct. Properly developed parts will have an even, pale white coating over the entire surface.
Water suspendible developers are similar to the water soluble type except that the powder, which is insoluble in water, remains in suspension until it precipitates onto the part as it is dried. Parts coated with a water suspendible developer must be forced dried just as parts coated with a water soluble developer are forced dried. The surface of a part coated with a water suspendible developer will have a slightly translucent white coating.
Nonaqueous developers suspend the developer in a volatile solvent and are typically applied with a spray gun. Nonaqueous developers are commonly distributed in aerosol spray cans for portability. This type of developer is the most sensitive form because the solvent action contributes to the absorption and adsorption mechanisms of the developer by entering the discontinuity and dissolving into the penetrant.
