One of the defining features of the patented brush assembly used in a United Equipment Accessories slip ring is the riveted joint between the arm and the brush. In the early years this was not really considered a “critical fit” joint. The whole of the assembly was allowed to flex and find its own position on the conductor ring. The fact that it could follow a wide range of movement is what led to its success and separated it from the competition in the rough environment of construction equipment.
For six decades this riveted joint has been made using fairly standard impact type riveting presses. Although relatively consistent, there are a number of factors that can affect the final fit and clearance of the joint. The tolerances of each part of the entire assembly can become additive. As nearly all of the industry has become much more involved with high speed data communications circuits over the past few years, the performance of the brush assemblies has become ever more important. The fit of this riveted joint for use with high speed data is now at a critical level. The current presses could no longer meet the level of precision required for this joint. Research was done to find a suitable method to create this pivoting joint, but every option was extremely costly and much slower than the current process.
The basic mechanism and frame of the impact riveters was proven solid and reliable, but the stack up of the parts varied, causing the fit issues. A decision was made to approach the project as an upgrade to the current technology. Precise rivet tension control is not new to the assembly industry, and there are many ways to go about solving the problems, many of them quite complex. After careful consideration, a decision was made to design a pressure controlled system around the current impact press frame and mechanism. The current rivet feed system, anvils and punches were retained. The original fulcrum lever remained. The motor and flywheel, with its trip clutch and cam, were removed and replaced with a pneumatic cylinder with precise pressure and speed control, as well as all the necessary safety control equipment and circuitry.
A local custom engineering/manufacturing shop, Golden Hour Enterprises, made the modifications and manufactured the required component, as well as performed the initial functional testing. The new system is somewhat slower in cycle time, but much more consistent with the fit. The other advantage is that for the impact type presses, rivet length changeover required trial and error adjustment each time to get a satisfactory setting. The new system only requires a slight, noncritical anvil height adjustment and a known pressure setting.
Since this is built on the common platform currently used for the majority of our brush assembly, when the production level of high speed data brushes requires it, the other presses can be modified in the same way, spreading the design cost across the multiple units.
(Top left: original flywheel; remaining three pictures: modified pressure controlled press)
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