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Charter Steel, a steel rod mill was experiencing several problems by employing a subcontractor to grind their large carbide forming rolls. The mill produces variously configured rolls in sizes up to 14 inches in diameter and 5 inches in width. Having these rolls ground outside of their facility was very costly and complicated due to the frequent changes in the part's pass configuration. Also, grinding the various rolls off-site created difficulties in monitoring part quality and making timely deliveries.
Recognizing the need for bringing the grinding process in-house, Charter turned to Weldon Machine Tool of York, Pennsylvania for help. Weldon's experience with steel mill applications, along with their ability to meet Charter's grinding needs, as proven during a live demonstration, led to the installation of a Weldon 1632 CNC cylindrical grinder in the Saukville mill.
Charter's 1632 grinder is equipped with a GE Fanuc control, rotary diamond dresser for dressing diamond grinding wheels, variable speed wheel drive, total enclosure, carbide specific coolant filtration system and a special variable-based programming system. This options package provides Charter with the flexibility to generate a wide variety of pass shapes on their carbide rolls. As part size and pass configurations change, the operator inputs the appropriate values into the part program. This simple process allows modifications for various configurations to be made quickly and easily by an operator, even those with little CNC experience.
Two grinding operations are typically performed on these carbide rolls. The first is a topping operation (an OD operation) using a straight-faced 14-inch diamond OD grinding wheel. The second operation is form grinding the pass configuration. At Charter, this is accomplished by using a plated diamond grinding wheel with a formed radius. Both plunge and contour grinding operations are used to finish grind the desired configuration. The most efficient way to remove stock is by plunge grinding. However, contour grinding provides the flexibility to generate multiple shapes while using the same wheel. According to Nick Currie, Plant Manager at Charter, they are able to grind 75 different pass configurations by utilizing five shaped radius forming grinding wheels. The cost savings from maintaining such a relatively low wheel inventory has proven to be an additional benefit to the mill.
Size, roundness, concentricity and straightness tolerance requirements are under 0.001 inch with a surface finish of 16 to 32 microinches. A typical re-grinding operation removes 0.025 inch to 0.050 inch of stock from the roll. On a new roll, stock removal can go up to 0.270 inch.
The flexibility and contouring capability provided by Weldon's 1632 CNC grinder has proven to be ideal for grinding multiple pass configurations on a wide variety of carbide rolls. By eliminating the need for an outside con-tractor, Charter Steel has significantly reduced costs and attained greater control over finished part quality.