Tapered stainless steel containers made to measure, for technology & industry

The surface finish has a decisive influence on the chemical and physical properties of stainless steels. In hygiene-sensitive sectors such as the pharmaceutical, cosmetics and food industries, technical terms such as EHDG or hygienic design are becoming increasingly important. The background to this is that operators want to avoid the carry-over of particles and the associated contamination of their batches as far as possible. One of the decisive factors here is the cleaning behavior of surfaces and the associated adhesion behavior of particles. 

BOLZ INTEC, a long-standing producer of containers and special constructions made of chrome-nickel steels, has asked itself precisely these questions and has investigated the properties of surfaces in several years of research work in cooperation with the University of Constance. In addition to the usual roughness profile of surfaces, which is currently used as the main feature when describing surface quality, attention was paid to other factors such as their final surface energy and examined in more detail.

The current state of the art is the assessment of surfaces using non-destructive testing, such as roughness depth measurement in conjunction with optical testing. However, in addition to these, there are other criteria that should not be ignored. Among other things, the way in which the surface is finished should be considered. It has been found that different grinding methods show different adhesion behavior in the final assessment of the surface, although the Ra value of both surfaces is the same. This means that the way in which the material is removed plays an important role here. As an experiment, the container was ground with an automated grinding process over a long period of time, in contrast to the usual manual grinding. This fine removal over a longer period of time resulted in less adhesion and therefore better cleaning. In the further course of the investigation, this was referred to as the final surface energy.

BOLZ INTEC has made use of the knowledge gained from the research cooperation with the University of Constance and developed a process in which the low and constant removal of the stainless steel surface is achieved semi-automatically over a long period of time. The process is called Optimized Grind Finishing or OGF process. The removal in the container is achieved with geometrically indeterminate grinding wheels that move inside the container. The major advantage of the OGF process is that, in addition to its outstanding quality, the surface is reproducible. The result is independent of undefined variables, such as the manual contact pressure during conventional grinding by an employee or the quality of the abrasives.

In the course of the investigations in cooperation with the University of Constance, BOLZ INTEC has further refined stainless steel surfaces refined using the OGF process and subjected them to an electropolishing process. In this process, the peaks in the surface structure are further removed, which, in addition to optical advantages, also brings chemical changes, such as improved corrosion protection through a reinforced passive layer. In the final assessment of the study, the improved cleaning behavior was demonstrated with the help of a test based on VDA19.1 (March 2015)/ISO16232 (December 2018). The OGF process drastically reduces residual dirt adhesion in containers and thus offers the operator the added value of significantly reducing the risk of contamination of two batches.