Z-High

In the conventional production of cold-rolled stainless steel, the production process typically comprises four steps: the metal is first annealed and pickled in a Hot Anneal & Pickle Line, then cold rolled on a single-stand reversing cold mill, and again annealed and pickled in a Cold Anneal &Pickle Line. If the final surface finish is specified as a bright finish (2B finish) versus a matte finish (2D finish), the strip is finally temper rolled on a skin pass mill with polished rolls.

Sometimes, it’s better to switch than fight. Take the case of the Coshocton plant of Cyclops’ Steel Div, which converted a vintage 4-Hi mil to a Sendzimir type by adding sets of cluster rolls in place of conventional work rolls.

by John W. Turley

At the beginning of 1985, the steel and non-ferrous industries found themselves in a bind — they were faced with low consumption, shrinking markets, higher costs, increased quality demands, and lower prices. This was not an enviable position, particularly as it followed three decades of relatively good prosperity.

The customer of the mid-1980s has had to accept smaller cars; higher interest rates, and greater costs for owning his home. He has experienced inflation a bigger food budget, higher taxes, and a spouse who has a second job and shares in decisions of how to make ends meet. What does that mean? It means that the customer is more choosy and more difficult to satisfy.

Sendzimir mills have traditionally been associated with the superior cold rolling of hard-to-roll materials such as stainless steel. What is not so readily apparent is that this concept is being profitably applied to hard aluminum alloys, such as those containing 3-5% magnesium. Moreover, a version of the Sendzimir Z-high mill has recently been optimized for aluminum rolling by incorporating slightly larger work rolls in order to allow for greater draft reductions inherent in the breaking down of aluminum.

In 2001, Jupiter Aluminum placed a contract with Sendzimir for a Z-High® mill. More commonly associated with steels, what is the Z-High® and what can it do for aluminum rollers? In 1943, the United States was fully engaged in World War II. Armament production was essential, and the steel company Armco, in Middletown, Ohio, had been asked to find a way to roll 3.5% oriented-grain silicon steel down to 0.002 inch for the production of small transformers that would make airborne radar possible. Armco’s engineers tried a number of different approaches, but nothing worked. Even the narrow 4-high mill with very small diameter sapphire rolls failed because the high lateral force caused the rolls to snap in the middle.

T. Sendzimir Inc.—originator of the cluster mill design—is modifying its existing Z-High® Mill to make it compatible with operating conditions within the continuous casting environment. Company officials believe the potential for this new design is “exciting.”

Armco Inc.’s Coshocton Operations as once again invested in Sendzimir equipment. The company has just modernized its first Z-High®, installed in 1981, to meet the design specifications of its second Z-High®, installed in 1997. “The new design incorporates computerized pass-line and side-support beam adjustment,” says Kerry Fender, General Supervisor, Cold Rolling, Armco Coshocton Operations. “This enables operations to make accurate adjustments assuring optimum strip quality for our customers.”…

The first cluster mills with small-diameter work rolls came on the market in the early 1930s. They were initially used to roll low-carbon steel and very special materials in narrow widths. It was only in 1950 that the industry fully recognized the suitability of the Sendzimir cluster mill for rolling stainless steel.

Mitsubishi Shindoh, a Japanese copper sheet and strip producer, has been operating since 2000 a 26 in (660 mm). wide Sendzimir Z-mill with a pre-stressed split housing supplied by Sendzimir Japan, Ltd. The mill includes Sendzimir’s patented Flexible Shaft Backing Assemblies for improved control of strip shape and is rolling copper and copper alloys.