Penetrant testing: Energy saving in high volume processes
Doing penetrant testing of medium-sized series parts, such as in the automotive industry, the components are often transported through the testing process by carriers. In this way, a high output can be achieved. The single process steps are often done by means of immersion applications.
Water-based wet developers are often used here. To improve the operating life of the medium and to optimize the inspection results, depending on the manufacturer, temperatures of 50-70°C (120-160°F) are recommended for waterbased immersion baths. This temperature is usually achieved by electrical heating elements.
As part of the efforts to save energy in production processes, the question is currently being raised as to whether the operating temperature of wet developers can be lowered.
The following aspects must be taken into consideration here:
Bacterial contamination of waterbased mediums
The bacterial contamination of the developer can lead to impairment of the inspection result. Pathogenic germs, in turn, can pose a health risk to test personnel.
Temperatures above 50°C (120°F) ensure that the rate of germ growth is reduced to stopped.
Temperatures between 30 and 40°C (85-105°F), on the other hand, provide optimal conditions for exponential CFU development (colony forming units). Therefore, working with completely switched off rather than with reduced heating is recommended here.
Regular analysis of the CFU count can determine when the contamination of an aqueous medium exceeds a critical value. Foaming or the development of odors can also be the result of a high bacterial contamination. Companies with metal working and lubricant applications are likely to have sufficient in-house expertise in this area.
The process should generally be monitored by using reference block no. 2 according to ISO 3452-3 or other eligible specimen.
Influence on the inspection result
Heating the developer medium also leads to quicker drying on the test part surface. This reduces the effect of “bleeding” of the penetrant, which can lead to more contoured, sharper indications. Blurred indications caused by a longer drying time can be perceived by test personnel as more difficult to evaluate.
Saving energy in the penetrant testing process is possible. For this purpose, the heating of the waterbased wet developer should not be reduced, but switched off completely. In the event of critical development of the CFU count, odor development or impaired test results, the developer medium should be changed immediately. In this case, it is essential to choose a complete fresh preparation in order to ensure the best possible operating life.
Whether the energy saving compared to a possibly increased material consumption (wet developer concentrate) is still cost-effective needs to be evaluated separately.