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45 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What is the function of a grinding machine |
The removal of metal, by a wheel made of small abrasive particles bonded together |
The removal of metal, perf |
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4 advantages of grinding |
- one cutting tool required. - can machine hard components. - high level of surface finish. - close tolerance work can be carried out with accuracy |
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6 factors influencing wheel selection |
- Arc of contact - finish required - material to be ground - amount of material to be removed - use of coolant - operation carried out |
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One thing to be aware of with the Arc of contact |
The greater the arc of contact the more heat is generated. To minimise this use a wheel with a more open structure |
Heat |
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5 types of abrasive |
Aluminium oxide Silicon carbide Diamond Cubic boron nitride Seeded gel |
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2 facts about diamond wheels |
- the only natural occurring abrasive - used to grind non ferrous materials |
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3 things to concider when selecting grit of a wheel |
- material being ground (fine grit for hard material, coarse for soft) - finish required (fine for good finish, coarse for rough) - Arc of contact |
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What is the "grade" of a grinding wheel and how is it measured |
- The hardness of the bond that holds the grit - A very soft, to Z very hard |
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What is the "bond" of a wheel |
The glue that holds the wheel together |
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6 types of bond |
- vitrified - rubber - resinoid - shellac - silicate - magnisite |
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What is the "structure" of a wheel |
- Refers to the grit spacing of the wheel. E.g close structure are dense |
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How is the structure designated |
0-3 close spacing, 4-6 medium, 7-12 open |
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5 things to note when ordering a wheel |
Diameter of wheel Wheel thickness Shape of wheel Bore diameter Wheel markings (composition) |
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6 markings on a wheel and the order 38A/60/K/5/V/BE |
38A - Abbrasive 60 - Grit size K - Grade 5 - Structure V - Bond BE - Manafacturers symbol |
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2 checks before mounting a wheel |
- Condition of wheel (check for damage) - Max RPM. |
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How to perform a ring test |
Suspend the wheel by string run through the spindle hole, lightly tap with a peice of wood. Good, will ring. Bad will dull thud |
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What do you do with the wheel if you find a dropped or cracked |
Tell your NCO, it needs to be destroyed and disposed of |
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Before fitting a grinding wheel what must you check |
That the blotters are in good condition |
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2 things to note about the flanges on a wheel |
- At least 1/3 the diameter of the wheel - the same size or it will cause un even preasure on the wheel |
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10 steps to mounting a grinding wheel |
- mount wheel to hub - balance - mount to spindle and tighten - fit guards - run wheel - true the wheel - rebalance - remount - adjust guards - true and dress for use |
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When starting the wheel for the first time what should you do |
Stand to the side |
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3 reasons a wheel may become unbalanced |
- Coolant pooling in wheel - Slipping between flanges - Loose balance weights |
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3 main grinding wheel faults |
- Loading - Glazing - Dressing |
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5 causes of a loaded wheel |
- Grade of wheel to hard for material being cut - grain structure of wheel to close - Grit to fine - dirty coolant - insufficient wheel dressing |
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4 fixs to loading |
Increase work head speed so wheel acts softer. Running the wheel slower. Dressing the wheel more coarsely. Increase traverse rate. |
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6 causes of glazing |
Grade to hard. Wheel speed to high. Work speed to slow. Cut too light. Not enough coolant. Blunt diamond when dressing wheel. |
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4 ways to fix glazing |
Increase work speed. Decrease wheel speed. Use a softer grade wheel. Re dress the wheel. |
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How can you make a wheel act softer |
Increasing the work speed but keeping all other movements constant |
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How to make the wheel act harder |
Slow the work speed |
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Rule of thumb for better surface finish |
Slower work speed = better finish |
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Define dressing and truing |
Dressing is done on the face of the wheel to improve its cutting action.
Truing changes the shape of the wheel. |
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3 things when dressing a wheel with a diamond bit |
The diamond should have a drag angel of 10-15 degrees. Must be on or below the centre line of the wheel. Make sure it is attached securely. |
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5 reasons for poor dressing |
Blunt diamond Poorly supported diamond Erractic traverse rate Infrequint dressing No coolant while dressing |
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6 factors when storing wheels |
Handled carefully. Stored in a dry place. Avoid extreme temperatures. Store out of direct sunlight. Thin wheels should be stored flat. No wheel on wheel contact (seperate with cardboard).
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What should never be done with a grinding wheel |
Exceed max RPM |
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Cutting speed calculations |
RPM = CS x 12 Pi x Diameter
CS = Pi x Dia x RPM 12 |
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13 operations for safe use of a grinding machine |
Select the correct wheel for the job. Ring test the wheel. Never exceed max rpm of wheel. Never enlarge the spindle hole or force wheel onto spindle. Use one clean blotter for each side of the wheel. Use matching recessed flanges 1/3 of the wheel. Only tighten spindle nut so it holds the wheel firmly. Adjust wheel guards and allow wheel to spin for 1 min before using. Dress wheel often. Carefully make contact with work peice. Never force the grinding action so the motor slows down or work peice becomes hot. If using coolant allow the wheel to spin out for 5 mins. Store the wheel safely if removed from machine. |
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What is used to reduce heat in a cutting disk |
Notching the wheel |
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What are cutting disks made of |
Resinoid |
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What materials are CBN (cubic boron nitride) used on and why |
Hardened ferrous materials and wear resistant super alloys. Reduced heating of the work and harder grains (stays sharper for longer) |
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How to know if a wheel is Ally oxide |
E.g. 32A, 19A The A stands for ally oxide |
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How to tell if a wheel is silicon carbide |
The letter will be a C. E.g. 39C |
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9 steps to balancing a grinding wheel |
Mount on balancing mandrel. Place on balancing unit. Let wheel roll until it stops. The heavy point is now at the bottom, mark top with chalk. Fit weights and move to the 10 and 2 ocklock position. Let the wheel roll again to see if its balanced. Move the weights the necessary direction equal distance. The wheel is balanced if it remains static. Place on the machine, true the wheel then re balance. |
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One major draw back of centreless grinding |
The possibility of lobbing (out of round but will measure the same across any point of the diameter.) |
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4 causes of lobbing |
Original job being out of round. The blade being flat topped. Centres being on the same height. To much grinding pressure. |
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