Stage 4 - Treatment The purpose of this stage is to treat the can to a coating of Zirconium which is a chemically applied to the aluminum in order to achieve a thin, electrically-conductive conversion coating that will provide corrosion resistance. The corrosion resistance is to prevent discoloration of the base when the decorated cans are passed through the ‘FILLERS’ retort sterilization process prior to filling the cans with the consumer liquids. There are some requirements that do not require the cans to be treated. The can maker will request that the washer is fitted with a treatment stage or not as determined by their customers requirements. The treatment stage is a heated process where a chemical cocktail containing Zirconium Phosphate is diluted and sprayed onto the cans to deposit a microscopically thin layer of Zirconium onto the can surfaces. Can Washing Stages 5 & 6 - Second Multiple Rinses It is important that all residual chemical salts are removed from the cans surfaces by passing the cans through a number of separate rinse stages where demineralized or Deionized water is sprayed onto the cans. The graph below indicates how the conductivity is likely to fall as the cans pass through the four rinsing processes.
Stage 7 - Mobility Enhancer (M.E.) As the throughput of the can making lines have increased and the cans travel at higher speeds have caused mechanical handling problems because the uncoated cans are prone to sticking together. The purpose of this stage is to spray a chemical known as a Mobility Enhancer (M.E.) onto the can external surfaces. M.E. reduces the surface tensions between the cans preventing them sticking together as they travel to the downstream to the lacquer and decoration processes. Can Drying The cans leave the Washer and presented to a Vacuum Transfer Unit which transfers the cans, using vacuum technology, to the can dryer. The cans are placed onto the dryer conveyor belt which transfers the cans into the Washer Dryer cavity. Hot air is blown onto the cans which elevates the temperature of the can and any moisture that is on the surface of the can. As the temperature of the can rises, the thermal energy, the water evaporates and is removed and discharged to atmosphere. The dried cans are conveyed past a quality control station where sample cans are removed and tested. If the quality of the bulk can pack is acceptable the cans proceed on a conveyor belt to the internal spray stage where the cans are internally sprayed with lacquer. Prior to being dried and then decorated. Recent Developments For many years deionized water has been used as the main source of water to finally rinse the cans prior to drying However, the De-Ionizing process is capital intensive and the operating costs are expensive Over the last few years the Reverse Osmosis (R O) process has been used to produce de-mineralized water to rinse the cans The R O process is proving to be a cost effective option The Stolle washers have developed innovative technology in conjunction with the can makers to provide significant water saving.
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FUNDAMETALS Newsletter
Q1 2023 [ 13 ]
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