Лако-красочные материалы — производство

This is the main process used to produce the ubiquitous 2 piece beer and beverage cans which can be made out of either tinplate or aluminium. As the name implies, a metal slug is drawn from a coil and ironed to produce, in a single piece, the bottom and side of the

A mechanical punching operation is used; in this the metal is first drawn into a shallow cup, then punched through a series of draw rings to form the familiar shaped beer/beverage can. After this stage, the can is thoroughly washed to remove all tooling lubricants and it is sometimes chemically or heat treated and dried to present a clean surface for the coating operation. The external coatings and inks are applied onto the can first, then the internal lacquer is spray applied. In between each coat the can is stoved in high speed, high temperature ovens.

As with the sheet fed process the DWI can is coated with a base coat using a mandrel rollercoating (5-10mg/m), decorated with an ink and then possibly overlacquered. The internal lacquer is spray-applied. What is different from sheet fed lines, is the speed at which the operation is performed. Modem 2 piece can production lines are capable of producing in excess of 1,800 cans per minute! With such speeds, residence times in the curing oven of 10 minutes are simply not practical. The ovens operate at much higher temperature (250-300°C), and cure requirements of the coatings are quoted in peak metal temperatures (pmt), which must be achieved in order to reach a satisfactory stage of cure. Typical stoving schedules may be between 6"-60" at a pmt of 160-200°C. Steel cans require different conditions to aluminium ones.

The internal coating is applied last by airless spray from static spray guns with an 80 millisecond burst of spray onto the inside of the spinning can. The can is then stoved, typically at 190-200°C for 60 seconds to 2 minutes peak metal temperature, upright in a flat bed conveyor oven. The tinplate can usually receives two coats of lacquer (wet on dry, i. e., each coat is stoved in turn), in contrast to the aluminium can which receives one coat of lacquer.

After coating, the can undergoes a further forming stage called necking, which reduces the diameter of the top, allowing a smaller diameter lid to be uses to seal the can after filling. This reduces the cost of the can by reducing the amount of metal required for the end, the most expensive grade of aluminium.

It should be noted that there are different types of necking processes. Furthermore, steel cans cannot be necked as easily as aluminium ones. For aluminium cans necking is always after all of the coatings (internal and external) have been applied, because the coatings act as lubricants for the process. Steel cans may be necked before the application of the internal lacquer. The tinplate acts as a lubricant both during the ironing and necking processes. Post lacquering can avoid any potential damage to the protective internal lacquer during the necking process. Different can making companies have alternative necking process and process protocols, there are in essence three main types; spin spin, die and spin die. Spin spin is the most demanding of the three.