TAPPI TIP0402-10

This TIP is to provide means of evaluating suction roll shells used in fourdrinier and press sections of a paper machine. The suction roll manufacturers use methods of varying complexity for sizing the shell during the design stages. The method presented here is comparatively simple, and it enables a paper mill engineer to compare shells of various designs and manufacture.The calculation determines a number of safety factors which indicate relationship between the material properties and the working stress at inside and outside surfaces of a shell in axial and tangential directions.In general, the larger the safety factor, the stronger the shell. This, however, is true only if shells of the same material are evaluated. At present, fatigue strength of shell materials is not necessarily determined by the same methods: size and shape of test sample, speed of testing, and environment may vary from one manufacturer to another. Level and distribution of residual stresses left in the shell casting, forging, or fabrication also may vary. Allowances should be made for these variables when the shells of different manufacture and material are evaluated.Results of this method of evaluation agree within 15% with calculating methods of various shell manufacturers.

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