Miller Magazine Issue: 129 September 2020

71 ARTICLE MILLER / September 2020 al inspection, where the experienced miller uses a dome to inspect the condition of the rollers. A second possibi- lity is the analysis of the products in the laboratory. This mainly involves determining the particle sizes, moisture loss and/or ash content of the intermediate and end pro- ducts. Finally, monitoring energy consumption and yield can provide indications of roll wear. The most accura- te way to determine roll wear is to measure the surface condition. Servıce statıon or "on sıte"? The service stations operated by a number of globally active suppliers of milling systems are equipped for such measurements of the surface condition of the grinding rolls. However, this means that the rolls must be remo- ved, replaced by replacement rolls and transported to the service station for inspection and any necessary machi- ning. The whole procedure is very time-consuming and expensive. The ideal solution is to measure "on site". However, for reliable measurements in the mill, good spatial, hygienic and bright conditions must be available. For the mea- surement itself, the various suppliers present different measuring equipment. There are two basic types of equ- ipment. One works optically, the other measures tactilely, i.e. "touching". Optıcal or tactıle? Optical measurements are performed with no physical contact, typically with light or laser. In principle, the ref- lection of the light/laser by the surface and thus its con- dition is measured. The surfaces must be very clean and there must be no disturbing light sources. At best, even anti-reflection pastes must be applied. In tactile, i.e. con- tact measurement, a standardized diamond tip is pulled over the surface to determine the surface condition. Tactile devices are "all-rounders". In the case of smo- oth rollers, the surface is scanned by a diamond sty- lus and the Ra-value (roughness value) is determined. With corrugated rolls, the contours are measured with a needle stylus. Optical measurement offers advanta- ges where the surfaces are very sensitive. These can be mirrored or polished surfaces. Soft materials can also be measured better without contact. Advantages of tactıle measurement The advantages of tactile measurement are main- ly in its simplicity. The application is not complicated: Simply place the stylus, start measurement and read the result. For measurement, either so-called diamont stylus or needle stylus are used. They measure accor- ding to different principles. With diamont stylus, a skid is pulled over the workpiece, which usually surroun- ds the probe tip at the side. The recorded signal thus has the surface of the skid in the immediate vicinity of the probe tip as a reference. Macroscopic waviness or angular deviations of the surface are largely suppres- sed. The recorded signal describes the microprofile. In contrast to this, with the free stylus, only the probe tip is in contact with the workpiece, so that all geometric fea- tures of the test piece, such as waviness or angle errors to the reference plane, are represented in the measurement signal. The rollDetect system The Swiss company Diavite in cooperation with Büh- ler has developed a portable tactile device for measuring the surface condition of smooth and corrugated rolls. The rollDetect system has been in use for several years and has proven itself worldwide. It is used in Bühler servi- ce stations and also by Bühler specialists on the road for periodically checking the surface roughness of grinding rolls in flour milling, feed milling, and brewing industries. It consists of a scanning device that can be freely posi- tioned on the rollers and an evaluation unit. The values determined are with great accuracy by means of 15,000 measurements over a 15 mm measuring path. Smooth rollers are measured using a diamont stylus, while cor- rugated rollers are measured by a needle stylus, showing the effective surface structure of the examined roller. The values are then directly evaluated in a special evaluation device. The initial result of the evaluation, the tecReport, shows the current condition of the roll graphically as a deviation from the target condition and, in a traffic li- ght system, evaluates the condition of the roll as "gre- en = ok", "orange = to be observed", or "red = critical". A further function of the software creates the so-called ecoReport for each individual roller, which interprets the data determined, and taking into account all factors of economy, determines the optimum time for the inspecti- on of the roller - not too early and not too late, but just at exactly the right moment. Graphics to explain the two different stylus used for rolls. Diamont stylus for smooth rollers and needle stylus for corrugated rollers.