Metallic structure control The metallic cylinders destined to the rubber lining must satisfy precise criteria of construction. Materials which can be used for construction of rolls are: carbon steel, alloyed steel, cast iron or aluminium. Stainless steels, such as AISI 304 or chromed steel can be used only in special cases. Parts to be lined must be welded, bolted connections can not be lined. Depending on the roll size, diameter and length, the metal construction must be especially strong in order to avoid, during machining of the lining (roughening and grinding), any vibration which can arise when holding the roll on the center holes only. The trunnions must have the center holes and, in case of used rolls, the center holes must be in good conditions. All the surfaces to be rubber lined must be free from any: blister, cracks, pitting and projections. The indications of the specification DIN 28053 must be always followed.