b'\x1b\x1a\x19 \x1f\x18\x1d\x17\x16Ask the Grinding DocHOW TO AVOID EMBEDDED PARTICLESD ear Doc: When grinding nickelAl 2 O 3 .Theoretically,atougher,the guys who sell filtration systems alloys, I occasionally get tinyor less friable, grit is less prone to swear that poor coolant filtration aluminum-oxide particles embed- break into small pieces and embedis the source of the problem. Im not ded in the workpiece. Its infrequentitself in the workpiece. convinced thats the cause, but the but unacceptable. What can I do? Third, consider putting a flush- theory holds water. If Al 2 O 3parti-The Doc replies: Youre ventur- ing nozzle at the exit point whencles come out of a nozzle and enter ing into uncharted territory. Thisgrindingand at the exit point ofthe grinding zone, they can embed is a problem I hear about occa- the dresser if youre performing CDthemselves into the workpiece.sionally, but Ive never seen a good to prevent swarf and busted-outFifth, one could argue that simply solution or good studyhaving better cooling in that explains itjust athe main arc of cut would lot of half-baked theories.help flush away particles. Since its infrequent, de- Aim coolant at the wheel/termining whether pro- workpiece interface, and cess changes had an ef- havethewheelveloc-fectcantakemonths.ity equal to the coolant Having said that, heresvelocity.what I tell my customers. Sixth, a gentler grind, First, look at the pos- especially during finish-sible causes. After dia- ing, will decrease the risk mond dressing, the tipsof fracturing the grit or oftheAl 2 O 3 gritsarebusting it out of the bond somewhatfragileandand getting crushed in crumbly. Immediatelythe arc of cut.upon first contact withFinally, a harder-grade the workpiece, the wheelJ. Badgerwheelcouldhelpby loses 3 to 10 m (0.0001"This is an electron microscope photo of embedded Al 2 O 3particles withkeepingentiregrits a diagram showing scraper nozzles.to 0.0004") off the radiusfrom breaking out of the as the tips of the grits break off.grit particles from traveling with thebond material and getting crushed This loss matters because you dontwheel and returning to the grindingin the arc of cut. On the other hand, want to finish or spark out with azone, as shown in the image. Unlikea softer-grade wheel could help freshly dressed wheel. Otherwise,a cleaning nozzle, which needs toby allowing the entire grit to break you run the risk of these crumblingbe over 50 bar (725 psi), the flushingout instead of fracturing into small grit tips embedding in the work- nozzle doesnt have to be super- pieces and becoming embedded. I piece. You want to leave at least 10high pressure. Just match the wheellean toward a harder gradeand mm 2(0.016 in. 2 ), which is the depthspeed, with the direction of the noz- a tougher grit.of grind times the length of grind, ofzle scraping away the swarf as itImperfect as it is, thats my ex-material for finish grinding.comes off the wheel. pert opinion. Let me know what This crumbly clean-up period isFourth, some peopleusuallyhappens.CTEespecially relevant if youre per-forming continuous dress. Here,about the author you dont want to use CD during fin-ishing or sparking out as the wheelJeffrey Badger, Ph.D., is an independent grinding will be crumbling off tiny pieces atconsultant. His three-day High Intensity Grinding Course the end of grinda bad idea. will be held April 6-8 in Spring eld, Massachusetts. For Second,examinethetypeofmore information, visit www.TheGrindingDoc.com.18MARCH 2020 GrindingDoc.indd 18 2/14/20 11:09 AM'