Eight Steps to Avoid Trim Squirt Nozzle Buildup and Improve Sheet Edges
Minimizing wet end breaks due to poorly designed trim squirt systems will increase machine efficiency and productivity. This includes avoiding buildup on the trim squirt nozzles above the sheet. The following steps can help minimize buildups and improve sheet edge finishing.
The location of the trim system is a key factor in an effective system. The trim system should be fully accessible to the operator for safety, easier adjustment, and routine cleaning. Typical mounting options include flat box rails or the suction couch mount. An unsupported wire may require small vacuum boxes positioned under the wire at the nozzle.
- The nozzle and gooseneck pipe leading to the nozzle should have an anti-stick coating. In addition, the water temperature used in the trim squirt system should be above the stock temperature. This will avoid condensation on the outside of the pipe and minimize fiber buildup.
- The cut loose fibers may reattach between the sheet and the trim in cases with lump breakers or HV flat boxes resulting in poor sheet edges when the trim gets separated on the pick-up. A wider cut is required. One or two double-offset jets ensure a wider cut.
- One double-jet nozzle is better than two single-jet nozzles. Two nozzles in a row lead to buildup on the pipe and the nozzles on the second unit. However, if two nozzles in a row are necessary for the application, the two units should be kept close together to minimize this effect.
- Better jet quality, due to its laminarity, translates to minimal splash. Sapphire and ruby nozzles are the best option. The bowed pipe is the best for approach flow because it minimizes water turbulence as water is delivered to the nozzle thus maintaining jet laminarity.
- Correct nozzle geometry to the wire is important. Set proper MD and CD angles by using a strobe light. Angles will change depending on machine speed, paper grade, pressure, and fabric type.
- If fiber buildup is a problem on the nozzle and bowed pipe, create an air curtain or full cone water jet on the bowed pipe.
- Visually inspect the final product at the reel to make sure the edge is clean. Better sheet edge finishing minimizes cracks during drying and drags starch/ink onto the dryers (this applies to coated papers). Clean and precise sheet trimming is essential to operate a high-efficiency paper machine.
