How to Correctly Tension The Screen
Is your frequency of screen breakage higher than usual? Is screening efficiency unusually low? These problems may result because the screen is improperly tensioned.
When tensioning the screen under ambient temperature conditions, use your two fingers to push down on the center plate, and then turn the nuts until you can't turn them any further. Then, using a wrench, turn the tension nut another 180 degrees. That's it; tighten the lock nut and it's done. Over tightening the nuts causes the screen wires to stretch-sometimes to the breaking point.
Also, with too little screen tautness, wires may be allowed to flex, leading to repeated bending until the wire breaks due to fatigue. You can tell fatigue has occurred when the wire's broken ends are rounded and dark.
By taking a few seconds to ensure you tension the screen correctly, you save time and money. Simply use your hand to ensure the screen is tensioned uniformly.
Under elevated or varying temperature conditions, use a spring type screen tension assembly. Place the gasket and centerplate over the center-post. Place the cup washer, spring and inverted cup washer over the center-post, and thread the nut on the post to compress the spring until the screen is taut. Lock the second nut on the first, using wrenches on both.
When handling high capacity feeds and oversize capacity, you may wish to use a reverse tension assembly which gives mechanical support at the center of the screen as well as increases the rate of radial movement of the oversize product. To install a reverse tension assembly (see schematic above), use the following procedures:
- Thread the reverse tension sleeve, flanged-end down, on the center-post until the flange is below the top flange of the spacing frame.
- Place the centerplate and then the gasket on the sleeve. If it's a spring type sleeve, place the spring on the sleeve before adding the centerplate and gasket.
- Fit an A-gasket to the outside rim of the screen.
- Place the screen mesh uppermost on the spacing frame, carefully ensuring that the mesh does not snag on the center-post.
- Place the next spacing frame over the screen rim so that the lip of the frame is in contact with the A-gasket around the entire rim. Replace the clamp ring, ensuring that it is engaging the flanges uniformly.
- Raise the reverse tie-down until the screen is tensioned uniformly. Lock the jam nut on the reverse tie-down using wrenches on both.
Screen Tips - Volume 6, Number 2 Summer 1991