When brass, bronze and nickel silver extrusions are utilized for architectural applications, straightness and flatness of the extrudant are as important a consideration as alloy selection, color, cross-sectional dimension tolerances and finish. In fact, for many architectural requirements, straightness is the most critical criteria in the fabrication and assembly of the finished product. Form, fit and function of an architectural component may be more dependant on straightness and flatness than any other single criteria. Here we will cover various methods for straightening bronze and nickel silver extrusions, including stretcher-straightening, roll straightening, hand straightening and press straightening.
Stretcher-straightening is a process where both ends of the extrudant are clamped and hydraulically stretched beyond its elastic limit. This process removes buckles, ripples, wavy edges, twist and edgewise curvature. Typically, the extrudant is stretched between 2 and 6 inches and, in the process, corrects dimensional variation between the front and back of the extrusion.
Roll Straightening, when used for architectural shapes, improves straightness by passing the extrudant lengthwise through a machine with rolls set up to repeatedly flex the product in two planes at right angles. Multiple set-ups and passes may be required to address all surfaces and features.
Hand Straightening further improves straightness by bending or twisting the extrudant by hand using adjustable supports and hand tools designed for the product.
Press Straightening is used on larger, or thicker profiles using hydraulically activated presses.
Typical tolerances for architectural shapes in brass, bronze and nickel silver are ¼ inch in 6 feet. Flatness is .007” per inch of width and twist is a maximum deviation from square of plus or minus one degree.
Please share this post with others who are interested in straightening bronze and nickel silver extrusions. You can also view our previous post on design considerations for bronze extrusions. We welcome you to share your experiences on straightening bronze and nickel silver in the comment box below – what tips or tricks can you share based on the methods explained above?