Apparatus for web caliper control

Apparatus in combination with a plural-roll calender for adjusting the thickness of a web passing through the calender comprising:

• separate header and source means for hot and cold fluids, and means for maintaining said fluids under uniform pressure and at predetermined respective hot and cold temperatures in respective header means;
• a plurality of nozzle means in communication with the header means and spaced along a roll of the calender and oriented toward said roll to direct a mixture of said fluids against longitudinally spaced portions of the roll;
• and
• separate valve means associated with each of the nozzle means for proportioning the flow of fluids from the headers for passage through the nozzles, each of the valve means including means which are movable, in unison, for increasing, by a certain amount, the volume of fluid flowing from one of the headers to an associated nozzle means while simultaneously decreasing, by the same amount, the volume of fluid flowing from the other of said headers to said associated nozzle means, so that the volume of fluid flowing from said nozzle means remains constant as the temperature of the fluid is varied.