TPT September 2007

T ube M ills: R olling & F orming M ethods

Developments for cold stretched reduced tubing

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Instead of switching rafts, roll passes are ‘engaged’ or ‘disengaged’ quickly to compensate for the various diameters

Formtek Metal Forming Inc, USA, has developed a new concept within the carbon steel, small diameter tubing markets, specifically aimed at the cold stretched reduced tubing market. Under the Yoder brand name, the cold stretched reduced process assists tube producers in manufacturing tubing that is usually used in the automotive fuel line, appliance refrigerator, and other small diameter markets. The new process specifically targets tubing that is too small for high frequency induction welding (where impeders are too small for this range). Producers of this tubing need the speed that high frequency or square wave welding can offer to meet production requirements. Cold stretched tube reducing mills are not new, as the Yoder Company has pioneered them for many decades. Using this technology, a mother tube diameter of sufficient size is used for high frequency induction or square wave welding. The tube diameter is cold reduced down to sizes as small as 3 / 16 " (4.76mm). Wall thicknesses are approximately 0.026" to 0.028" (0.66 to 0.71m) during the creation of the mother tube. The size can typically be slightly increased or decreased. Since acquiring Yoder in 2001, Formtek has added new innovations to its product family and one of these was to change the cold reducing process. As mentioned, a mother tube is reduced to tubing of smaller

diameters by multiple rolls stands that cold work the tube pass-by-pass. When a different diameter is required, roll passes in the reducing section are rearranged with certain sizes requiring the addition or subtraction of working passes. Even though the passes are rafted or sub-plated, a few (or sometimes several) hours would be required for a changeover. Formtek has introduced a new method so that only the final ‘finishing pass’ is changed without affecting the other reducing pass arrangements. Instead of switching rafts, roll passes are ‘engaged’ or ‘disengaged’ quickly to compensate for the various diameters. The company’s extensive knowledge of roll tooling design and manufacturing was an important factor in the success of this process change. The finishing pass is changed so that final, proper sizing is applied to produce tubing within a diameter tolerance of ±0.003" (0.08mm). Changeover times are reduced by 50 per cent so that producers are quickly up and running on the next diameter. Even lower changeover times are possible if multiple finishing passes are used, which essentially ‘dedicates’ the tooling to the pass. Formtek Metal Forming has already implemented this concept to a major tier 1 automotive supplier with great success and has recently received a second order from an international producer. This process has also been expanded so that the tubing manufacturer can produce tubing in the

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cold stretch reducing process. This is in addition to tubing in the conventional mill process up to 1" (25.4 mm) diameters. By rafting the mother tube forming sections, rafting the reducing section and adding a cutoff, tube producers have the ultimate flexibility in offering reduced tubing or conventional tubing in a diameter range from 3 / 16 " to 1" (4.76 to 25.4mm). This is a minimum to maximum diameter range of over 1:5 when most other tube mills are only capable of offering 1:4. This can be accomplished at speeds of up to 600ft/min (180m/min) for the smallest diameter. This processing technology has been applied to larger diameter products as well. Formtek has secured orders for a reducing section to cold reduce stainless steel pipe at Ø 1.875" (47.6mm) down to Ø 1.720" (43.7mm) without changing a single roll. Formtek Metal Forming Inc – USA Fax : +1 216 831 7948 Email : sales@formtekcleveland.com Website : www.formtekgroup.com

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S eptember /O ctober 2007