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With growing demand of plastics in our live producers of extruders start to develop stronger drive units for the screws in order to rise the rotation (rpm) and output. The higher rpm create much more stress on the elements placed on the shaft with different gearings so that these at least cracked because they were through hardened and very “brittle”. A material with highest abrasion and corrosion resistance on the outside and high toughness on the inside was needed.
The solution was to HIP powder metallurgical steel on a soft conventional steel bar. With this solution it is possible to choose to highest wear resistance and hardness for the screw element because the inner gear section stays soft and tough even after heat treatment. In order to this there is an additional advantage in machining because the inner section could easily be machined after heat treatment and possible dimension changes.