Suction Roll Shells
When you buy a suction roll shell it really comes down to this: you want to know that you have selected the roll shell material for your machine from an experienced manufacturer that will reliably produce it to your specifications.
Worldwide, Sandusky International’s suction roll shells are found in the most advanced paper machines…designed for the most exacting performance in the harshest, most heavily loaded environments.
Sandusky International has more suction roll shell specific manufacturing and metallurgical experience than any other company in the world. For you this means that every suction roll shell we produce benefits from over a century of knowledge and experience. This knowledge and experience results in expertly crafted centrifugally cast suction roll shells that are precisely machined and drilled. Our suction roll shell materials were designed specifically for the paper machine operating environment and we can help you choose the right material for your application. From our time-tested Sandusky 1N Bronze for milder environments to the unmatched performance of our patented Sandusky Alloy 86 for the harshest, most highly loaded environments
Selecting the Correct Roll Shell Material
Suction roll shells look deceptively simple...large, bronze or stainless steel cylinders drilled with holes. But, it is only on the surface that they appear the same.
There is a significant difference among suction roll shell alloys. When properly selected, the material will withstand the white water chemistry and temperature, felt cleaning chemicals, machine speed, roll load and cyclic stresses of operation.
Selection of the optimum suction shell material for your application should be based on five specific factors:
Of these the single best predictor of suction roll shell performance for a loaded application is Critical crack growth resistance (the maximum size crack that can be tolerated without self-propagation leading to a rapid shell failure). Critical crack growth resistance relies on corrosion resistance, corrosion-fatigue resistance and low tensile residual stress.
The white water of a paper machine can be very aggressive and a suction roll shell is expected to operate for many years in this environment. As the use of bleaching agents, whiteners, brighteners and cleaning agents has increased so has the potential for suction roll shell corrosion via chemical attack. That is why it is important that a suction roll shell’s metallurgy has a high level of corrosion resistance.
The cyclic loaded roll shells in a paper machine are also subject to corrosion-fatigue (the tendency of the metal to fracture or crack from the combined action of the corrosive environment and repeated cyclic stressing). When a suction roll shell is nipped, it is subjected to applied stresses in addition to any residual stresses that are already present within the shell from its manufacturing process. These stresses are greatest at the inside diameter of the shell and most cracks will begin in this location. Applied stress (from the repeated cyclic stressing) and the residual stress (from the manufacturing process) are cumulative, so the higher the combined total stress, the more the suction roll shell is adversely affected with regard to its corrosion-fatigue resistance.
Applied stress cannot be avoided. Nip load, vacuum, and felt or wire tension all generate applied stress. Applied stress, alone, can eventually cause the failure of the suction roll shell especially in the presence of a corrosive environment (corrosion-fatigue). Simply, the higher the applied stress, the lower the number of operating cycles to failure.
However, residual stress can be avoided. Residual stress is mainly produced by differences in cooling rates through the shell during the heat process of manufacturing. A fast cooling rate produces more residual stress than a slower cooling rate. The speed of the cooling rate is determined by the metallurgy of the suction roll shell material.
Sandusky’s patented Alloy 86, DSA06 and Alloy EPV have the lowest residual stresses of any duplex stainless steel for suction roll shells. This low residual stress is generated via a proprietary, highly controlled, slow heat treatment process that is made possible due to its unique suction roll shell specific metallurgy. The combination of the very low residual stress and very high corrosion resistance gives these Sandusky Alloys the best Critical Crack Growth Resistance. A resistance that is up to eleven times greater than competitive materials.
Suction Roll Shells