Cooling gizmo has issues: General Industry Coverage

Dear Doc: At a trade show, a company displayed a grinding wheel with slots, where coolant is poured into the center of the wheel and then ejected into the grinding zone. What’s your take on this design?

The Doc Replies: Here’s how this gizmo works: Coolant is poured at low velocity into a recess around the rim of the wheel, centrifugally accelerated by the wheel and ejected everywhere through slots around the wheel perimeter. And everywhere includes a small portion—around 2 percent on a good day—that’s the grinding zone. But this technology is nothing new, having been developed in the 1970s for creep-feed operations.

I’ve visited hundreds of grinding shops on five continents and have never seen one of these gizmos in actual production use. Maybe I’m just going to the wrong places. Or maybe they look pretty in a display case, but they’re not doing the hard work on the shop floor.

Why is that? There are several reasons. First, the spindle motor has to accelerate the coolant to the wheel speed, which requires a lot of power. Second, as previously noted, the coolant is ejected not just at the grinding zone, but along the entire wheel circumference. Third, the coolant is ejected from the slots, but not necessarily where it’s needed most, which is the unslotted regions where the abrasive meets the workpiece. Fourth, all that coolant flying out means that if there is any coolant coming from a main nozzle, it gets deflected. Fifth, the wheel is expensive. Sixth … well, let’s stop there.

Whenever a wheel salesman pitches me about some new grinding technology, my first question is always: Can you give me some hard science behind the technology and some verified data from case studies? The answer is usually vague, including references to high quality and state-of-the-art technology, with anecdotes about some company in some distant land that saw cycle times drop drastically. But I seldom get real, hard science.

Keep in mind we’re talking about a coolant gizmo, not just slots in the wheel. Slots alone, when used with a high-velocity main nozzle, can reduce grinding temperatures when creep-feed grinding.