Use the following tips to control the variables most commonly encountered in garment screen printing.
1. Always allow the squeegee to rest for 12-24 hours before attempting to sharpen. Swelling from inks and solvents will soften the blade and can cause it to get chewed up during sharpening.
2. Use an appropriate grinding grit for the amount of material that is to be removed. In other words, select a coarse grit for removing a lot of material, and a fine grit to just polish the edge.
3. Remove as little material as possible at a time so as not to melt and distort the polyurethane squeegee, and to extend the useful life of the squeegee blade. Use multiple passes on grinder type sharpeners, using smooth slow motion with minimal pressure.
4. Make sure the squeegee edge is straight and that free height is even to the handle along the squeegee’s entire length.
5. Always sharpen new blades after they are inserted in a squeegee handle/holder. In most squeegee holders the blade becomes distorted from the clamping screws and uneven placement. The new blade must be sharpened to ensure the length is trued and parallel to the holder.
6. Implement a regular schedule and procedure for sharpening squeegees. Don’t wait until print problems stop production to address this critical maintenance issue. Also, maintain your squeegee sharpener according to manufacturer recommendations.
Repeated sharpening will slowly shorten what is called the free height of the blade. This refers to the dimension of the blade extending out of the holder. As the free height is reduced, it cannot flex as well and becomes stiffer to print with, regardless of durometer. A squeegee in this state will act like a harder (higher durometer) blade, making it more difficult to print with and changing ink deposit and print quality.
Inks, solvents, environmental conditions, and time will slowly harden the squeegee material, increasing its durometer and reducing its suppleness. The increase in stiffness will necessitate excessive squeegee pressure and will lead to poor print quality. Squeegee replacement should be scheduled on a regular basis and the cost factored into your operations. As a rule of thumb, polyurethane squeegee blades have a useful life of one year or less depending on their formulation, use, and maintenance.
Thoroughly cleaning your squeegees (and holders) immediately after printing will minimize ink contamination during printing. Having streaks of other colors show up in white ink during printing creates misprinted shirts and will cost valuable production time as you stop the press to deal with the problem. Having some squeegees designated for only white can help avoid this situation as well.
A buildup of ink from inadequate cleaning can also lead to squeegee marks and streaks from dried ink stuck to the squeegee’s edge or flaking and falling into the ink during printing. Do not allow squeegees to soak in any type of solvent for extended times. The polyurethane will swell and can permanently lose its resilience.
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