Manufacturer Builds on Spindle Success

Tag: Ceramic Housing

If it isn’t broke, why fix it? That is Bryant Grinder Co.’s attitude toward the design of its grinding machine wheelhead spindles. The company has worked with that outlook since 1936.

However, changes in product material and developments in abrasive technology over the past 10 to 20 years are making more demands and presenting more opportunities on processing equipment and their subsystems.

With that said, Bryant had found that the design of its existing wheelhead spindles was presenting a manufacturing problem.

The spindle’s design was one that required that they be processed on machine tools unique to that purpose or there would be a strong possibility of extreme tolerance stack up.

This stack-up of tolerances could be overcome, but at a cost the current market could not absorb. The flip side of this was that some of the current design tolerances were not substantiating the quality of the rolling element employed to generate the composite accuracy and stiffness of the wheelhead itself.

As the company’s spindle division reviewed these problems and the current potential process developments at its disposal, the company decided to redesign its spindles, building on the success of the existing product.

The results can be seen in Bryant’s new Generation II spindle.

During the design of the Generation II spindle, the Bryant spindle division generated a list of objectives. The objectives included increasing torque and horsepower, improving lubrication of the rolling elements and the cooling of bearings and electrical components, and reducing specific tolerances that could compromise accuracy. In addition, the company aimed to design for manufacturing to eliminate any additional costs associated with higher precision and to enable the use of “smart” technologies that would enhance predictability and process capability of the wheelhead.

For better lubrication, Generation II spindles use air/ oil lube, and each bearing has its own dedicated injector to ensure proper lube to both bearings in a tandem bearing design. This makes for a cooler running bearing and offers an opportunity to increase preload for a stiffer, smoother-running spindle.

To ensure that the bearings and electrical components are cooled, Generation II spindles map the coolant flow back and forth over the bearing housings. That provides for a more efficient transfer of heat. A special construction of coolant channels also puts the coolant closer to the bearing for even better heat transfer from the bearing.

Previously, water jackets in the front bearing and the stator housing offered little in the way of mapped circulation. In the case of the front spindle bearing housing, the coolant was restricted by the location of the coolant outlet.Rear bearings on the Generation II spindles have the same type of heat transfer as their front bearings. Bryant said that arrangement is a first, even for its own spindles. The coolant is piped directly into the rear bearing housing with the same circulating philosophy as the front – the coolant comes from the same source, but the front and rear bearing housings are cooled separately.

Stator housings now are encased in brass housings that have helical grooves cut into them to channel coolant evenly over the entire stator surface. The company said those coolant channels remove heat generated from electrical power more effectively.

In testing, Generation II spindles ran at 60,000 rpm to 90,000 rpm for four hours, and head temperatures increased between 2 degrees and 4 degrees F. over ambient on the outer cases. The company said that the exhaust water from the spindle was too hot to touch, demonstrating the effectiveness of heat transfer.

Improved internal heat transfer allows Generation II spindles to run 20 degrees to 40 degrees F. cooler than previous spindles, which is important considering the spindles are available in operating speeds ranging from 6,000 rpm to 160,000 rpm.

During the design phase of Bryant’s spindle enhancement, the company discovered that many of the critical spindle components had tolerances substantially larger than the bearings used to support them. That was primarily due to the fact that the original bearing class used – and available – did not have the level of precision offered by ABEC 9 bearings.

In effect, the spindle component accuracies were compromising the inherent accuracies and longevity of the purchased bearing. All highfrequency Generation II spindles now use ABEC 9 hybrid ceramic bearings.

Tightening spindle tolerances usually involves increased manufacturing costs. However, Bryant followed development with a critical examination of all of its components to see where redesign would remove costs. Using the “error budgeting” concept, the company made changes in its more-demanding components and was able to redesign a considerable number of parts to reduce costs in tolerance stack-up.

For instance, the cartridge housing contained multiple bores on each end that required multiple operations to complete.

The new design created a single bore, all ground from the same end to eliminate the concentricity problem. Bryant also consolidated multiple-part components into single-part ones, standardized its designs and made its manufacturing processes more efficient.