There’s good reason our customers are so pleased with our HIGHSL flat panels– they really stay flat. We thought we’d give you all the technical details that results in this superior product that’s more homogenous and stable than other leveled sheet and plate.
Here’s how we do it: In order to eliminate material spring back, the strip of steel must be “stress equalized” by elongating the material’s entire cross section, top to bottom, and side to side, past its yield point to erase its previous memory. The coil strip is first processed on the Bradbury roller levelers, which eliminate cross bow and coil set and completely prepare it for the stretcher leveler. The coil strip is then stretched and subsequently cut-to-length to a specific sheet or blank size. An in-line stretcher leveler consists of a pair of entry and exit frames. These frames are adjustable relative to the desired part or stretch length. When required, each frame grips the material across its width. Large hydraulic cylinders connect these two frames.
When pressurized, these cylinders push the frames away from one another. The pressure exerted by the cylinders exceed the collective yield of the material and the coil strip is subsequently stretched in the direction of travel. The line’s feeding system pulls the material through the leveler incrementally. Between each feed cycle, while the material is stopped to be sheared, a portion of the strip is stretched. In addition to the material being sufficiently elongated lengthwise to exceed the yield point in all the material, top to bottom, and edge to edge, by virtue of the process, portions of the strip are stretched more than others at the same time. In effect, the material’s entire cross section is stretched to a common length or distance; that length being sufficient to both dimensionally and stress equalize the material at the same time. No subsequent processing is required.
The end result is material that is more homogenous and consequently more stable than other forms of leveling. While stretcher leveling is one of the oldest and most effective types of leveling ever developed, there is a limited understanding as to how the process works. Why this does not equate to overworking the material Typically there are concerns that the process works the material significantly more than with other types of leveling. Consequently, similar to the temper mill, if the material is over worked, this will change the properties of the material. However, while a temper mill may elongate the strip 1% or 2%, a stretcher leveler accomplishes its work with typically only 0.3% to 0.5% elongation. Relative to the percentage of elongation required to do its job, the Stretcher has very little impact on the metallurgical properties of the material. The stretcher leveler performs more overall work due to the fact the entire thickness of material is elongated. However, no specific portion of the strip is worked more than with any other leveling process.
There you have it, the ‘HIGHSL’ process. As always, don’t hesitate to ask a question or provide a comment. Or give us a call any time to discuss this process and/or your interests further.