When Wichita Clutch sought a rolling diaphragm for a new actuator option
on its ModEvo pneumatic tension control brake, most suppliers were only
able to provide standard products that did not meet with the performance
requirements - until it met up with Ceetak, that is. The ModEvo brake is
used in printing and converting applications where it is used to control
the tension of paper or film webs. While the unit needs to develop
considerable braking forces, it must also have the sensitivity to cope
with web changes of varying thickness.
The rolling diaphragm option is more able to provide this sensitivity
than conventional piston designs, but Wichita needed something better
than conventional 'top hat' rolling diaphragms, which, in order to meet
the specification, were too large for this application. The seal had to
be compact enough to fit the actuator design, be able to operate at
temperatures as high as 200oC, provide a wide ranging stroke capability
and respond quickly and accurately to pressure changes.
Using its custom engineering service, Ceetak was able develop a diaphragm
that incorporates an internal bead, thereby optimising space for
increased stroke capacity. The unit is manufactured from a fluorosilicone
material and features nomex reinforcement for additional strength and
temperature resistance.