Casting

The first step in the process is the melting of aluminum scrap and primary aluminum.  Temperatures in the 100,000- to 160,000-pound-capacity melting furnaces range from 1,350 to 1,450 degrees Fahrenheit.

Other metals are added to the aluminum to create alloys for specific end products. For example, manganese is added to make an alloy that is strong, corrosion resistant and easy to form. Zinc or copper adds strength to the alloys produced for demanding high-tech applications in aircraft and aerospace manufacturing.

After the alloy mixtures reach a precisely controlled chemistry, consistency, and temperature, the metal is introduced to a filtration process before it is cast into rolling ingot form. This filtration process uses the latest technology to remove impurities and foreign particles as small as 20 microns in size.

Then, state-of-the-art flow control is used to deliver molten aluminum to stationary ingot molds, where it is solidified, using heat transfer fundamentals, into rolling ingots up to 30 inches thick, 68 inches wide, 237 inches long, and weighing as much as 20,000 pounds.

Scalping/Soaking

The surface of a rolling ingot may contain oxides from its exposure to the atmosphere.  These impurities are detrimental to the finished aluminum product. So, prior to the first rolling operation, the ingots are processed through a machining station, where this outside skin is mechanically shaved off. This process, called ‘scalping,’ results in a smooth, blemish-free surface.

After scalping, the ingots enter large furnaces, called ‘soaking pits,’ where they are heated to temperatures as high as 1,100 degrees Fahrenheit. Computerized controls provide precise temperature control to assure uniform metallurgical properties in the finished product.

Hot Rolling

Next, the ingots are lifted by overhead cranes onto the hot line. Depending on the thickness desired, they may be processed through one, two, or three hot rolling mills. Kaiser’s computerized statistical process control (SPC) monitors the metal as it is processed and provides constant feedback of data, allowing the system to improve upon its own performance to attain maximum gauge uniformity.

In the first hot line process, the 132-inch mill reduces each ingot to a thickness between three and eight inches, depending on the product. Driven by two 5,000-horsepower reversing motors, the mill rolls the ingot back and forth reducing the metal into longer thinner slabs as the rolls are set tighter and tighter.

The second rolling mill on the hot line uses the same back-and-forth process. This mill further reduces the ingot to thicknesses not exceeding two inches.

The first of its kind in the world, Kaiser’s 6-high, 80-inch, 5-stand finish hot mill reduces the slab from the previous mills to a thickness ranging from .09 to 0.3 inches, and hundreds of feet long in a single continuous pass.  The metal exits the 80-inch mill at speeds of up to 1,200 feet per minute and is either rolled into coils up to 60 inches in diameter, or sent to a shear where it is cut into pieces of light-gauge plate.

Annealing

After hot rolling, some of the metal must be reheated (annealed) to soften the alloy and permit further reduction in thickness. Here the metal is heated at varying temperatures and cycle times depending on the alloy and end use.  Partial annealing is often used in the fabrication process to relieve internal stresses that build up during rolling and also to achieve desired metallurgical properties.

Cold Rolling

Coils are brought to the 2-stand cold mill after annealing, or in some cases directly from the hot line, for further rolling to even thinner gauges. The 2-stand cold mill is primarily designed to produce light-gauge heat-treatable products. Computer controls hold gauge variation to within plus or minus .002 inches or one-tenth the thickness of a human hair.

Finishing

After cold rolling, the aluminum may be heat-treated, stretched to maximize flatness and relieve tension, stenciled, slit, or sheared to various widths, lengths, or shapes depending on customer needs and requirements.

Coil slitters cut coil sheet to customers’ requirements and rewind to narrower width coils to specified inside and outside diameters.

Finishing & Heat Treat Products

A recent major expansion has increased Trentwood’s heat-treat capacity to better serve the global aerospace and general engineering markets. The hard alloy class of aluminum products gains strength through the heat-treating process. The metal is heated in horizontal or vertical furnaces to temperatures ranging from 850 to 970 degrees Fahrenheit for varying lengths of time depending on alloy and gauge. Heat-treating is followed by ‘quenching,’ a closely controlled, rapid cooling of the metal with water. Quenching locks the alloying elements into the dispersed pattern achieved during the heat-treat process.

Saws and shears cut plate and sheet products to required widths and lengths to meet specific customer requirements.

Inspection

Through out the entire manufacturing process, metallurgical characteristics and surface conditions are inspected. Chemical, physical, ultrasonic, and laser tests are used to verify the surface quality, tensile and yield strengths, and formability that Kaiser builds into its metal. In all, eight or more tests may be performed on a single order.

Shipping

Finished products are packaged and loaded for shipment by rail or truck. Special packaging assures protection during shipment.