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| Posted on 12/14/06 at 06:29 AM | |
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I'm exactly who you should question. Granted, too much pressure concentrated in one spot can damage the stencil. If you are in a hurry and put the pressure washer too close you can damage the stencil. This is why children are not allowed to drive race cars. If you are interested in using a pressure washer to speed up production I don't think that is such a good idea. Developing with a pressure washer can help to open small details. The fine mist of most pressure washers generates smaller drops of water than some garden style sprays. If you're satisfied with the details you get, you have no need for high pressure. Yesterday when I washed out a screen I used city water pressure for 95% because the stencil needs lots of water to dissolve the unexposed stencil. I could achieve the same effect using a dip tank and NO pressure. To finish, I used the pressure washer on some fine detail that was resisting me. Then, to test for wet strength, I blasted a corner of the stencil until it broke down. Since I tested to failure, I now know, how far I can push that material. If using a high pressure washer only means full blast at 3" from the stencil to you, try 3 feet away, then 2 feet and slowly get closer. Too close and you could damage your screen. Again, think race car. If your stencil is underexposed, high pressure could blast out the screen. When any emulsion is dried properly and exposed fully, there is no risk in developing with a pressure washer unless you get too close. Sacrifice a screen. Do a ten step exposure test and double your usual exposure. See if more exposure makes the stencil more durable at washout time. Check to see how much exposure it takes to close up fine lines. If fine lines close up and the whole stencil is still not competely hardened, your lamp may not have enough penetration power or your stencil might not crosslink fast enough to reproduce those fine lines. Lamp power, age and the UV range they output can also effect exposure. Everyone should ask thenselves "How am I measuring". Diazo, dual-cure and SBQ stencils are sensitive to a different range of UV light. 20 watt, 40 watt, 250 watt, 500 watt lamps are less expensive than 3K and 5K lamps, so you might have to use a faster SBQ stencil that is more sensitive to UV light to reproduce fine lines. ____________________ Richard Greaves, ASPT Ulano Corp. New York Technical Services 718-943-1338 direct | |
  
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