Tuesday, September 24, 2013

Advanced Scotch Yoke Design Increases Service Life

ROTEX recently replaced some old "orange" scotch yoke actuators with the DRS series. The customer is a major international producer and marketer of food and agricultural products.  The "orange" actuators were experiencing high wear and had to be rotated out and serviced every few months. After the ROTEX DRS actors were installed, at last count, they had 125,000 cycles without any internal corrosion or degradation.

Let's examine the design improvements that allow this superior performance:
  • Pneumatic cylinders are lined with hard chrome plating. Smooth to eliminate wear of piston seals, the surface is very hard, for long life.
  • Springs are lifetime lubricated and epoxy coated.
  • Inside the pneumatic module, dual oversized tie rods are protected from external corrosion. Where the tie rods pass through the piston head, ROTEX has improved the design by providing a slide bearing, where most designs don’t. This bearing is important to help maintain alignment and assure smooth operation.
  • Inside the frame module, the yoke is supported by life time lubricated bearings. Needle roller bearings ensure the most efficient torque transmission. The piston shaft is supported on each side of the frame module by solid bearings that ensure proper alignment and smooth operation.
  • Each piston shaft of the ROTEX DRS is equipped with two Flexijoints. These specially designed joints compensate for movement and changes in alignment to reduce internal stresses and increase output torque. The thrust transmitted through the Flexijoints ensures no side thrust on the cylinder walls and bearings.
  • Piston seal is ROTEX 3X design. Flexibility of the sealing material reduces friction, prevents leakage, and extends actuator life. The 3X shaped seal is wear compensating, and the unique shape of the seal retains the grease for longer periods. The piston is guided by a PTFE thrust bearing, which helps keep the piston centered, and seal wear to a minimum.
  • The tie rod seal is also of the ROTEX 3X design. Old fashioned O-rings are replaced by these flexible, low friction, resilient seals to reduce the failure rate of tie rod seals. Also reduces the wear and tear to the tie rods themselves.
  • ROTEX has also replaced the standard O-ring of the shaft seal. In this position, we provide a proven V-seal design. This self-energized, wear compensating seal guarantees low hysteresis and minimum friction. Like the X seal of the piston and tie rod seals, the inherent shape of the V-seal helps keep the grease where it needs to be.

In 13 months, the ROTEX DRS went 125000 cycles without internal corrosion nor significant wear.

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