This stage starts by loading furnaces Nº 1 and Nº 2 with 18 MT each of raw aluminum (alloy AA1070, purity 99,7%), which is supplied by world known aluminum producers. Once production cycle is established and the quality controller approves, following charges will be based on percentages of 60% in-plant scrap and 40% ingots (raw aluminum). Once furnaces are loaded temperature is brought up in order to melt the metal; The melt is subject to treatment using salts from which the chlorine has bee removed, in order to produce a melt that is as low as possible in hydrogen and oxides. Stirring, dead-melting and slag removal is done afterwards. In the meanwhile, the furnace exit spouts and troughs temperature is set to receive the melt when it is ready for casting. By hydraulically tilting means the furnaces are emptied in a uniformly controlled manner. To ensure a consistent metal quality with low oxide levels, the molten aluminum is degassed, refined and filtered before it enters the casting wheel. All atmospheric emissions from the furnaces are within the environmental regulations due to the fact that we use only 99.7% pure aluminum.
The melt is poured into the strip casting wheel, which rotates at a speed of up to 7 meters/min. A solid strip of 180 mm wide by 20 mm thick is formed between the grooved periphery of the strip casting wheel and the steel belt. The strip casting wheel is water cooled. The cast strip leaves the unit at a temperature of about 350 ºC in a horizontal direction without any transverse deviation. It is immediately hot rolled down by up to 55% by means of the Hot Roll Mill. Following this, it passes through a cooling bath before being cold rolled to its final thickness. Gauge control devices assure the strip thickness tolerance during the Cold Roll Milling process. The correctly sized coil is then coiled into 1800kgs coils. Each coil is properly identified with casting batch number, weight, and thickness. The finished coils are then stored to await stamping.
This stage counts with five high speed stamping presses, each one has a decoiler where a coil is mounted. The strip passes through a straightener into the press, and at the center base of it is located the die. This die has a series of punches that has the size of the diameter of the slug. The strip is lubricated while it is being punched. Cut slugs fall on a conveyor belt which takes them into rectangular baskets. Punched strips (scrap) are then cut in pieces and conveyored back to the foundry area to be compacted into 50lb bales before sent back to the furnace. In this process we get about 50% of slugs for each ton of punched strip. This of course might change according to the slug size. Each of our five presses cut about 18 MT of slugs per day in two shifts which represents 1,125 MT/month (based on 25 days).
Annealing (Thermal Treatment)
This stage counts with three tunnel type annealing furnaces, electrically heated. The aim of annealing is to produce a material with minimum strength, maximum ductility, soft temper and to burn the lubricant used during the stamping process. In order to obtain this, metal baskets with slugs are placed inside an annealing furnace and the temperature is raised to 520 ºC for a timed cycle of four hours, temperature and time necessary to occur annealing. With this we obtain a Brinell hardness of 17 to 19 HB. Total time of loading furnace, pre-heating, annealing and unloading is of eight hours, permitting two cycles per furnace per day obtaining 1000 tons of annealed slugs per month
The surface of the slugs is treated in order to obtain a rough texture. This is done by one of two methods: tumbling or shot-blasting. Tumbling, the first of the two methods, is done by placing the slugs inside of a mechanically operated gyratory drums. Slugs hit each other hence roughening the surface. Final customer needs this roughness in order to apply a lubricant necessary for cold extrusion. If slug has an inner hole, surface finish is done by a shot-blasting machine that uses aluminum shots to shoot the slug while they are rotating on a belt. The surface finish stage last between 12 and 15 minutes depending on slug size. This stage also makes sure no scrap is attached to the border of the slug. Once surface treatment stage is completed, slugs are transported on a conveyor belt to a hopper which will feed the next stage.
Selection and Packing
In this last stage slugs exit the hopper by means of a conveyor into 5 automatic packing lines. Slugs keep going on the conveyor until they fall inside a cardboard box which is filled until it reaches 25 Kg. Each box is properly weighted and identified. Once boxes are marked with customers information, they are placed on 1.00mts x 1.20mts wooden pallets, containing 40 boxes of 25 kgs each. Each pallet weights 1,000 kg which is protected with plastic wrap ideal for export purposes. Daily capacity of this stage is 40MT per day which enable us handle 1000 MT per month.