The grinding wheel is an industrial consumable. As the use time increases, its wear will increase until it is unusable. Replace with a new grinding wheel. What do we need to do to extend the service life of the cutting wheel more during the use of the grinding wheel, and Guarantee its cutting efficiency?
These types of questions arose while testing a new wheel specification with one of our customers. The company was having issues keeping the wheel at a set dress frequency throughout the wheel’s life. We believe that a wheel should wear the same from new through stub and that other factors must be affecting wheel performance.
He customer disagreed and felt that what they were experiencing was due to how the wheel changes as it wears. “What we set for an initial dress rate and expect the wheel to do when it is new, cannot be the same near stub.” The customer said. “We need to adjust the dress rate at certain points during the wheel’s life based on its diameter and how it wears.”
They felt that we needed to change how we judged the wheel’s performance. That we cannot expect the dress frequency to be the same from start to finish. Therefore, they felt we should consider an average, not maximum (or initial). Dress frequency as a way to judge how well the wheel actually performs.
It is true that a cutting wheel gets smaller as it is applied, and as it does, the surface speed changes.
Wheel speed (sfpm) = 0.2618 x diameter (inches) x rpm
For every 1,000 sfpm drop in wheel surface speed, the effective grade of the wheel tends to shift one grade softer. Softer wheels are freer cutting, impart rougher finishes, provide higher stock-removal rates and wear quicker than harder wheels. Softer wheels also tend to break down easier and, therefore, need to be dressed more frequently.
In addition, wheel wear occurs mostly while dressing, and a softer wheel generally needs to be dressed more often to hold form, geometry or face profile, and will eventually find itself in what is commonly called a “vicious circle.”
This is especially true on older machines and manual grinders where the machine typically does not compensate for wear and the spindle speed is constant. Meaning the “softening” of the wheel will continue and increase, as the diameter approaches stub. However, if the grinder does compensate for wear and adjusts the spindle speed to maintain a constant surface speed. This softening is somewhat mitigated.
The performance or behavior of a wheel will change as it wears based on the surface speed changes previously mentioned. But these changes are offset to some degree when the wheel speed is compensated for by the controller on the machine. The customer’s machine compensated for spindle speed, so these speed changes should be considered negligible.
Although, our customer’s engineer did not completely disagree. He did suggest that even though the spindle speed is increasing to maintain a constant surface speed. Wheel performance will still deteriorate as it gets smaller. The thought is that performance will still change throughout use because the contact length changes. The contact length will keep getting shorter as the wheel diameter gets smaller, and wheels with a shorter contact length tend to act softer.