Assessing the Cleanability of Stainless Steel Surfaces – Development of a Testing Method for Starch and Protein Based Soils

To measure the cleanability of stainless steel surfaces under standardized conditions, a test stand was set up. Three stainless steel plates (size 200 x 100 mm) can be fixed to the test stand and sprayed with a water jet from a low-pressure nozzle for a period of several minutes. The plates were previously soiled with a starch or protein film with a pre-defined layer thickness and dried for several hours at 40°C / 50% RH. The progress of the cleaning is determined at set times by removing the plates and taking photographic pictures. When using starch-based soils a staining with a solution of iodine / potassium iodide (Lugol’s solution) is necessary. For proteinaceous soils an illumination with UV light is sufficient without staining. With the image processing program ImageJ, the area of the cleaned surface can be identified and quantified. Preliminary studies show that the method is suited better for starch-based soils than for protein films. A starch film has high adhesion to the stainless steel plate and is rinsed gradually from the surface. Protein films, however, form a strong cohesive soil layer which disintegrates in the region of the spray jet as plaques in an unpredictable way. This results in a high degree of variance of the values that were measured. Our findings indicate that for the test soils used, neither the alloy (AISI 304 L / 316 L) nor the roughness of the surface (0.8 / 0.2 microns) have a significant influence on the cleanability of stainless steel surfaces.