A Method for Flatness Evaluation of Large Circular Rings

Flatness evaluation of granite and other surface plates in rectangular form is well established and standards are available. There are situations where the large flanges of some of the cylindrical shells have to be evaluated for flatness of the large flange, in the form of a circular ring. The flange is of three meters size. This needs a measurement and evaluation technique for its application. This paper details such an application. Since the measured data on the surface are on a polar form, it requires polar grid to obtain measurements. Depending on the width of the ring the measurements may be available on just one circle, i.e the mean circle of the ring or on different circles on the ring. Since the data is on a circle the relative height deviations must sum up to zero on each circle. This paper details a measurement and evaluation technique for this application and there are no standards for the same.