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Piston of an earth mover These pistons used to fail by fatigue cracks. Deep rolling of 3 spots of the components made them fatigue resistant: The right angular fillet with radius R=4 between piston and rod, the undercut at the friction welded joint and the thread undercut are deep rolled in one setting with a selection of firmly installed tools on a CNC lathe. Threads 
Cyclic load changes under tension/compression, bending or torsion of threads generate considerable notch effect at the threat roods. A high tensile stress concentration is built up in the surface layer of the threat root area. These stresses are much higher than the calculated average stress. Therefore, fatigue cracks always start at the threat rood. This happens for instance on tie bars on all injection machines, hydraulic pistons, oil- and gas field drilling equipment and on threaded press spindles. All these components are increasingly deep rolled with ECOROLL® thread deep rolling tools EF90. 
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Small fillets with radius R > 0,2/<4 mm are deep rolled with mechanical deep rolling tools EF45. They are used as plunge in tools. cial bolt for a race car become fatigue resistant by deep rolling with EF45. The same tool is applied for fillets on gear shafts, on winches and rollers for steel mills or rotary presses. Bend shafts  Bend shafts and downhole motors for oil- and gas drilling and mud pumps are build according to the Moineau principle. The bend shafts connect rotor and drive shaft. Cyclic torsion and bending stresses fatigue the material. Bends hafts from 6 to 60 mm diameter and length up to 800 mm made of quenched and tempered high strength steel or titanium are deep rolled with ECOROLL® tools. "ballpoint" tools HG6 (figure 13) and HG13 achieve fatigue strength increase of 30 to 50 % in spite of the already optimal design and optimized metallurgical structure of the material. Geometrical and metallurgical optimization do not exclude deep rolling. Only the combination of all three methods leads to the best solution. Only this combination guarantees the full utilization of material properties and are the key to economical solutions and downsizing of components and products. |
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