Cooling. Section K of The Grinding Doc s Book of Grinding THE GRINDING DOC S BOOK OF GRINDING. by The Grinding Doc K :529 K :530

Size: px

Start display at page:

Download "Cooling. Section K of The Grinding Doc s Book of Grinding THE GRINDING DOC S BOOK OF GRINDING. by The Grinding Doc K :529 K :530"

Julian Dennis
5 years ago
Views:

THE GRINDING DOC S BOOK OF GRINDING The following slides are the property of Jeffrey Badger, Ph.D. They may not be used or copied, either in electronic or printed form, without the author s written permission.

1 THE GRINDING DOC S BOOK OF GRINDING The following slides are the property of Jeffrey Badger, Ph.D. They may not be used or copied, either in electronic or printed form, without the author s written permission. All pages of The Book of Grinding are printed in color. If the slides are not printed in color, they have been copied illegally. The Grinding Doc name and logo are trademarked items. Jeffrey A. Badger, Ph.D. The Grinding Doc Expert in grinding Independent Consultant Austin, Texas USA (+1) JB@TheGrindingDoc.com K :529 c K :530 Section K of The Grinding Doc s Book of Grinding Cooling

How the Coolant System is Often Designed K :531 Good work guys.

get this thing shipped out of here this afternoon.

2 How the Coolant System is Often Designed K :531 Good work guys. You ve spent the last two years designing and building this excellent, one-million dollar machine. Now let s throw on old some copper tubes for a cooling system and get this thing shipped out of here this afternoon. Conclusion: In many cases, you ll need to learn about cooling and develop your system yourself. Lego Nozzles K :532 Yikes!!

3 K :533 Conclusion: You may have to figure it out yourself and redesign your own cooling system. Purpose of the coolant Cooling is over-rated! It s lubrication that counts!!

4 What s the Purpose of the Coolant? K : To Lubricate at the Grit/Workpiece Interface Less friction, less heat generation Reduce Wheel Wear Improve Surface Finish 2. To Cool the Workpiece Both During Grinding and After the Fact 3.To Flush Away the Chips and Prevent Loading of the Wheel This is the most important. 4.To Provide a Barrier Between the Grit and the Workpiece to Retard Chemical Reactions Between Them First, A Few Basic Equations on Grinding Temperatures K :536 Simple Stuff Jaeger s moving heat source model. Equations from Changsheng Guo, Ph.D. Thesis, Investigation of Fluid Flow and Heat Transfer in Grinding, Univ. Mass, 1993.

5 The hot-spot K :537 Where things get hot! K :538 Concept: The Hot Spot Where all the action is

K :539 And right near the surface it can get to over 1000 2000 C F The Hot Spot 600 C 500 C 400 C 300 C 200 C 100 C From Werner, Younis & Schlingensiepen, 1980, Creep feed an effective

Proceedings 8 th North American Metalworking Research Conference, Society of Manufacturing Engineers, USA, 312-319.

6 K :539 And right near the surface it can get to over C F The Hot Spot 600 C 500 C 400 C 300 C 200 C 100 C From Werner, Younis & Schlingensiepen, 1980, Creep feed an effective method to reduce work surface temperatures in high-efficiency grinding processes. Proceedings 8 th North American Metalworking Research Conference, Society of Manufacturing Engineers, USA, K :540 And right near the surface it can get to over C F The Hot Spot 900 F 750 F 600 F 400 F 200 F From Werner, Younis & Schlingensiepen, 1980, Creep feed an effective method to reduce work surface temperatures in high-efficiency grinding processes. Proceedings 8 th North American Metalworking Research Conference, Society of Manufacturing Engineers, USA,

7 K :541 The air-barrier Get s way too much publicity. The Impenetrable Air Barrier K :542 The Hot Spot V wheel = 60 m/s = sfpm And right near the surface it can get to over 1000 C in the pore: V air = 60 m/s = sfpm At the surface: V air = 60 m/s = sfpm 1 mm () from surface: V air = 30 m/s = 6000 sfpm

8 Air Velocity by The Grinding Doc K : m/s (49,250 SFPM) 0.25 bar 200 m/s 0.2 bar 150 m/s 100 m/s 50 m/s Air velocity in mm s Air pressure in bar 63DXNC Okamoto high speed grinder. B400 wheel 0.15 bar 0.1 bar 0.05 bar Air Pressure 0 m/s 0 bar -2 mm 0 mm 2 mm 4 mm 6 mm 8 mm 10 mm Radial Distance from the Wheel Face From Application of a Coherent Jet Coolant System in Creep-Feed Grinding of Inconel 718, MS Thesis, Joachim Steffen, Dalhousie University, taken from Coolant Shoe Development for High Efficiency Grinding, by Ramesh, Yeo, Zhong and Sim, Journ. Of Materials Processing Technology, 2001, V. 114, K :544 The Salmon 1 Ping Pong Ball Analogy If you really want to see how impenetrable the air barrier is, get a pingpong ball and take it over to your bench grinder. Now, drop that ping-pong ball onto the spinning grinding wheel. It ll fly off. Retrieve the ping-pong ball and look at it. You ll see scratch marks. ` If a ping-pong ball dropped lightly onto the wheel can penetrate the air barrier, high-density high-velocity coolant certainly can. 1. Stuart Salmon: Modern Grinding Process Technology, 1992.

9 The Train Analogy K :545 Here s one more. I m fine. The air barrier protected me. Next time you re at the train station and a train is cruising by your platform at 100 mph (160 km/hour), throw your body at the moving train. If you are deflected to safety by an air barrier, then it exists. K :546 So what s your point? Answer: Clyde The Cooler knows. The air barrier bets too much publicity.

10 K :547 We need the coolant speed to be the same as the wheel speed, so it will slide in between the pores in the grinding wheel and be carried to the hot-spot. 600 C 500 C 400 C 300 C 200 C 100 C From Werner, Younis & Schlingensiepen, 1980, Creep feed an effective method to reduce work surface temperatures in high-efficiency grinding processes. Proceedings 8 th North American Metalworking Research Conference, Society of Manufacturing Engineers, USA, K :548 We need the coolant speed to be the same as the wheel speed, so it will slide in between the pores in the grinding wheel and be carried to the hot-spot. 600 C 500 C 400 C 300 C 200 C 100 C From Werner, Younis & Schlingensiepen, 1980, Creep feed an effective method to reduce work surface temperatures in high-efficiency grinding processes. Proceedings 8 th North American Metalworking Research Conference, Society of Manufacturing Engineers, USA,

11 K :549 V coolant = V wheel 90% of the battle in cooling. Webster s Rule*: K :550 V coolant = V wheel Velocity of the coolant in m/s (or sfpm) must be the same as the Velocity of the wheel in m/s (or sfpm) V coolant = V wheel Never mind flowrates, tis velocity that matters! Not RPM, but sfpm or m/s * Named after world cooling guru John Webster.

12 Webster s Rule*: K :551 V coolant = V wheel A typical wheel speed: 60 m/s = sfpm = 130 mph = 220 km/hr 60 m/s =12000 sfpm = 130 mph = 220 km/hr Pressure is Relative to Velocity K :552 By Bernoulli s Equation Bernoulli s Equation = constant p r v2 + gh = constant p = 1 2 r v 2 Just call me Bernie pressure required (bar) = 1 2 r (velocity in m/s) =1.0 for water 0.9 for oil p=pressure ρ= density g=gravity constant h=height (assuming constant h, the gh terms disappear) Daniel Bernoulli

13 Or, in More Practical Terms K :553 For Water-Based Coolants: pressure required in bar = (velocity in m/s) 2 or 200 exit velocity in m/s = 200 x pressure in bar For Oils: pressure required in bar = (velocity in m/s) 2 or 220 Meters? Isn t that a musical term? exit velocity in m/s = 220 x pressure in bar A 60 m/s wheel speed needs (60) 2 /220 = 16 bar for oil Or, in Real Units K :554 For Water-Based Coolants: pressure required in psi = or (velocity in sfpm) 2 (velocity in m/s) ,000 exit velocity in sfpm = x pressure in psi For Oils: pressure required in psi = or (velocity in sfpm) 2 588,000 Long live the Empire exit velocity in sfpm = 588,000 x pressure in psi A sfpm wheel speed needs (12000) 2 /588,000 = 245 psi for oil

14 Coolant Pressure by The Grinding Doc K :555 0 sfpm 4000 sfpm 8000 sfpm sfpm sfpm sfpm 50 bar 750 psi Water-based 40 bar 600 psi Oil 30 bar 450 psi 20 bar 300 psi 10 bar 150 psi 0 bar 0 psi 0 m/s 20 m/s 40 m/s 60 m/s 80 m/s 100 m/s Coolant Exit Velocity The 80% Rule: V coolant = 0.8 X V wheel K :556 80% is good enough.

15 % coolant utilization (of maximum), or Coolant flowrate / Pore volume by The Grinding Doc Q: Do we really need the coolant velocity to be exactly the same as the wheel velocity? K :557 A: The Liverpudlians* found that 80% was enough, i.e., if the coolant velocity was 80% of the wheel velocity that was just as good as having the coolant velocity equal to the wheel velocity. The graph on the next page illustrates this. They found that the best you could do was to fill the volume of the pores to 50% of their full capacity, and that once you got to 80% there wasn t any additional benefit. 1. Optimization of fluid application in grinding. Mike Morgan et. al. CIRP 57/2008, p % K :558 50% 40% 30% 20% 10% Optimum zone: Coolant velocity is 80% to 100% of wheel velocity. 0% 0% 20% 40% 60% 80% 100% 120% 140% 160% 180% 1. Optimization of fluid application in grinding. Mike Morgan et. al. CIRP 57/2008, p V coolant /v wheel

16 The Ol Bucket-&-Stopwatch Technique K :559 Can get messy but you re not an accountant, you re a grinder! Or, If You Don t Have a Pressure Gauge K :560 The ol Bucket-&-Stopwatch Technique: 1) Fill up a bucket 2) Measure how long it took to fill up the bucket 3) Calculate the flowrate in liters/minute or gallons per minute 4) Measure the orifice area 5) Calculate the velocity

The Ol bucket-&-stopwatch technique K :561 Flowrate in liters/minute = Flowrate in GPM = bucket size in liters time to fill bucket in seconds x 60 bucket

Exit Velocity in sfpm = x 19.25 total orifice area in inches 2 The Ol Bucket-&-Stopwatch Technique can get messy.

17 The Ol bucket-&-stopwatch technique K :561 Flowrate in liters/minute = Flowrate in GPM = bucket size in liters time to fill bucket in seconds x 60 bucket size in gallons time to fill bucket in seconds x 60 Exit Velocity in m/s = flow rate in liters/min total orifice area in mm 2 x flow rate in GPM Exit Velocity in sfpm = x total orifice area in inches 2 The Ol Bucket-&-Stopwatch Technique can get messy. If your nozzle exit velocity is high, then the situation on the left may not work due to excessive splashing. The solution is to direct the coolant into a large hose, as show on the right. K :562

Calculating Outlet Area K :563 Circular nozzle nozzle

nozzle area in square mm = nozzle height in mm X nozzle

18 Calculating Outlet Area K :563 Circular nozzle nozzle area in square mm = nozzle area in square inches = 3.14 X (nozzle diameter in mm) X (nozzle diameter in inches) 2 4 Rectangular nozzle nozzle area in square mm = nozzle height in mm X nozzle width in mm nozzle area in square inches = nozzle height in inches X nozzle width in inches

ANCA > How to run a Grinding Test

ANCA > How to run a Grinding Test How to run a Grinding Test Often, the full potential of grinding wheels is not completely utilised. This may be due to a lack of systematic approach. The following describes