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FLEXO Magazine : June 2012
the containment blade, or an ink source that already has foam in it. Manufacturers have tried pressurizing the chamber, as well as adding cell packers or dual cavity zones to help alleviate this air pocket problem. Although these may be steps in the right direction, the results are inconclusive and often don’t provide a solution to the overall problem. Steps in chamber evolution with the best results are actu- ally reduced cavity sizes and very narrow blade gaps. Newer chamber geometries are more circular in shape, providing a smooth, laminar flow. The smaller cavity size limits the open space or dead zones inside the chamber. Fluid actually accelerates through the chamber, quickly taking the micro-foam out. This replenishment of clean, foam-free liquid through the chamber provides a much more efficient means of filling the anilox cells. The result is a consistent ink film, which allows printers to run at higher press speeds with reduced air entrapment and ghosting issues. Smaller cavity chambers may also be less forgiving than their bigger counterparts, as there is no extra space or buffer zone inside the cavity. This necessitates having more precise fluid control throughout the whole cycle with the chamber, pumps and valves. Integrating pumps and valves to the smaller chamber creates a practical solution for ink de- livery. It also results in much faster and more efficient wash- ups. Introducing on board viscosity and pH control helps take the whole pro- cess to a higher level. CHAMBER LOADING CONFIGS The loading system positions the chamber and blades into perfect alignment with the anilox roll. Overall, it is essential that the chamber be firmly held in place in a precise and con- sistent manner. If the operator can have a repeatable process that doesn’t require continual adjustments, the likelihood of success and consistency is much greater. Several techniques are used for chamber loading: • Mechanical Loading provides a rigid loading solution but requires an operator to routinely make adjustments to compensate for blade wear • Pneumatic Cylinders or Bladders are often used. Since the air is compressible, they are subject to position chang- es due to press vibration or pulsations from ink pumps • Air-Over-Oil loading systems are comprised of rolling diaphragm cylinders that are filled with oil. Compressed air and valves initiate the motion. Since the oil in the cylinders is not compressible, rigid positioning of the chamber can be achieved. As blades wear, the cham- ber can still slowly index inward to compensate without operator involvement BLADE CLAMPING Another function of the chamber is to firmly hold the con- tainment and doctoring blades in place. Many different sizes and materials of blades are used depending on the applica- tion. Blades are commonly made of steel, SST, plastic, or composite materials. The blades are consumable items that need to get replaced on a regular basis. The blade-clamping portion of the chamber needs to make provisions for an easy and quick swap out. Simple mechanical fasteners are often used and various quick-change designs are gaining popularity. A series of tool- less designs incorporate levers and cam-action clamps, while others utilize a powerful magnetic clamping action – between the chamber and the blade clamp – that captures the doctor blade (regardless of material type) between the two. END SEALS End Seals provide the sealing required where the blades touch the roll at each end of the chamber body. These also are consumable items and need to get changed on a regu- lar basis. Various material types are used, including foam, felt, rubber, and plastic. The seal’s biggest enemy is the heat and dryness caused by the friction of the seal running on the anilox roll face. Lubrication helps prolong their life as does cleanliness and good housekeeping skills when making ready. Often times spare chamber bodies (fitted with new blades and seals) are utilized to help speed changeovers. These can quickly get swapped into place to get the press up and running again while the worn components are changed out off line. CHAMBER MATERIALS The most common material that chambers are made from is aluminum. Its reasonable cost, weight and ease of machin- ing make it a practical choice for most applications. If corro- sion becomes an issue SST is often used. Inert materials or carbon fiber are also being used in the market. Even though their associated cost is higher, they offer a good solution in corrosive environments. INK & WASH UP Many levels of automation are available. They vary from a simple, stand-alone pump next to the press all the way up to a fully automatic, product lifecycle (PLC)-controlled system. Higher levels of automation typically add to the overall cost of 104 FLEXO june 2012 www.flexography.org