Brush maintenance and adjustment

The operation of the washout unit of any platemaking machine is a matter of routine. Keep the water level of the bath about a quarter of an inch above the brush, if too low plate surfaces will score. A cup of distilled white vinegar added to the bath will provide a bit of needed acidity and keep mineral deposits from accumulating. After filling the tank and the bristle tufts are saturated, rub them with the flat of your hand to reduce their stiffness.

A minimum amount of care will provide long life to the brush. Degradation to brushes is primarily the result of platen wear pressure due to incorrect brush adjustment, distortion of the tufts, and accumulation of photopolymer debris. Never reheat a saturated bath as debris will adhere to the heating element and harden to the brush unit as well as the inside walls and floor of the tank. Brushes are expensive to replace so daily maintenance pays off.

Empty the bath water at the end of each day to prevent mildew and corrosion. If removable, drain the brush while flushing the bath. Photopolymer residue can accumulate at the floor of the brush and eventually interfere with washout effectiveness by distorting bristle tuft pattern. Spray the tank clean with a high-pressure hose but take care not to spray the bristles or they will tangle and mat. Fill the tank with fresh water and flush again. Clean the sides and bottom with a damp rag. Afterwards, rub the bristles slightly with the flat of your hand to spring the tufts upright. Leave the washout unit open overnight to allow the brush to completely dry out. Some manufacturers suggest never allowing the brush to dry. Defer to your manual.

Replace brush when it begins to fail to completely clean the floor of the photopolymer plate. The incidence of this will increase sporadically but will get progressively worse. Though it is otherwise hard to discern, replacement is forthcoming when the surface of the brush begins to reveal patterns where tufts are no longer retaining their shape. If distorted tufts are partially clinging to photopolymer debris on the brush plate floor, this can be remedied with a paint brush cleaning comb or heavy duty de-tangle dog hair comb (better). Regular use will improve the efficiency of the brush and greatly extend its working life.

To reduce wear on the brush test its surface level to the platen. The least amount of pressure is the correct pressure. On a perfectly leveled machine, a dry platen lowered to the wet brush (with water level reduced below the brush) should just show the markings of the wet tufts. If it is dry or overly wet, adjustment is necessary. The brush is adjustable, generally, simply by turning adjusting screws fitted to the brush frame. Consult your owner’s manual for the correct adjustment for your machine.

Essentially, if the platen is completely wet, lower the brush until the tufts no longer mark (and re-adjust until they do), if completely dry, raise them until they just touch. Compensate in raising or lowering for corners that may remain wet or dry. Tufts should just mark the platen—if only two sides of the platen show markings (parallel either horizontally or vertically) or if only the center area; that is okay. To be safe, turn adjusting screws uniformly only a half-a-turn until correct. Do not overly compensate for corners that may be either dry or wet.

Note that if you are routinely processing significantly different thicknesses of plate material or use a detachable PVC carrier sheet, the brush should be adjusted to compensate. If this is the case, it will pay to work out a procedure involving shims that can be easily inserted and removed.