Aquitherm™ - P(Tripass) (Peripherally drilled, Water or Oil Heated)
The peripherally drilled-type calender roll consists of a peripherally drilled chilled cast iron roll body and bolted-on flanged journals. Peripherally drilled fluid passages, approximately 2 inches below the outer surface of the roll and under the chilled zone, give this roll its name. The size of the central bore is based on roll diameter and application as well as residual stresses, operating temperatures, loading, weight, and deflection criteria.
The Aquitherm-P has the following operational characteristics:
- Water Heated
- Oil Heated
- Steam Heated
- Steam/Water Heated
The peripheral drilled fluid passages may be configured as Mono-Pass (one peripheral hole per pass), Duo-Pass (two adjacent peripheral holes per pass), Tri-Pass (three adjacent peripheral holes per pass in series), or Tri-Pass-II™ (three adjacent peripheral holes in parallel, the two outer holes flowing out and returning in the middle hole at twice the velocity). The patented Tri-Pass-II™ design has more efficient transfer of heat, which allows operation at higher thermal loads and temperatures. This also keeps the central bore empty, reducing overall weight.
With mono-flow rotary joints, the heating fluid enters one end of the roll, passes through the peripheral hole(s) and exits through the other end of the roll. With a duo-flow rotary joint (fluid entering and exiting the same end), the fluid enters one end of the roll, passes through the peripheral holes and exits through the same end of the roll as it entered.
The heating medium can be hot water (typically 250 degrees F. surface temperature) or hot oil (typically 400 degrees F. surface temperature). For high temperatures, special alloyed chilled cast iron is used, which has higher tensile strength and a fine-grained, more uniform chill that enhances heat transfer. This special alloy also inhibits corrosion.
Insulation is used to protect the bearings from excessive heat, and to reduce the oxbow effect at the paper web edges. On large diameter, long oil-heated calender rolls, temperature drop compensation inserts (T.D.C.), inserted in the peripheral fluid passages, increase the velocity of the oil passing through, contributing to the roll's thermal efficiency.