Grinding Journal - Fall 2007 - (Page 25)

Top Left: Although the Mägerle has a probe to measure part position and calculates offsets, craftsman Doug prefers to measure it and make adjustments himself. Top Right: Mägerle MGC with a triple flute C-profile wheel grinding solid core at 31 inches/minute at full depth of cut with a stock removal of 0.15 inches deep. the distance between tips, which helps him adjust the clearance. It’s also important to calculate the many radii in a given flute form, as each flute shape is different and therefore requires a different wheel shape to be ground properly. It’s worth noting that most regrind shops measure flute profiles with an optical comparator, which are highly operator dependent. (The operator tends to “measure” the nominal value.) Tiruna’s vision system is operator independent. Considering coating After grinding, Tiruna also recoats the roll with chrome, Hard Chrome, or tungsten carbide in thicknesses of 0.002 to 0.006 inches. The type and depth of coating affects the type of profile and the “depth” of the grind. Some customers rely on Tiruna’s experience in adding the right amount of coating based on the roll’s flute profile, while others specify a particular type and amount. In either case, Tiruna’s experience determines the proper flute profile based on the expected finish coating. Compensating for sag and other crowning achievements Because corrugating rolls operate as a set, the flutes must match from one twin to the other and the rolls must mesh along the whole length of the tool (again, perhaps a dozen feet or more). All rolls appear flat, and indeed, some are intended to be. But a flat roll will sag as it’s supported at each end. A typical sixteen inch diameter roll will generally have a 10-12 inch diameter hollow through the center, in part to limit the sag by lowering the weight. Yet Tiruna would probably still have to compensate for about 0.002 inches in negative crown to achieve the desired flat profile. Other rolls are designed to have a slight crown and if the shop who last serviced the roll didn’t hold it properly, that crown may not be centered. The user might have determined this by noting that the paper seemed to bind in an area despite equal pressure at each end. If not, Tiruna would have discovered such a problem by measuring the roll before grinding. At any rate, Tiruna would now have to account for this, Grinding Journal 25

Table of Contents Feed for the Digital Edition of Grinding Journal - Fall 2007

Grinding Journal - Fall 2007 Contents From Virginia: Apparently no credit crunch for machine tools Why measure cutting tools Other perspectives on CNC tool measuring Productive grinding of superalloys SUPER service grinding BIG rolls Problem Solver

Grinding Journal - Fall 2007

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