Abrasives Flashcards by Albert Falgui

5 types of abrasives

-emery (aka conundrum)
- silicon carbide
-aluminum oxide
- diamond
- CBN or cubic boron nitride

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__ is the best known of the natural abrasives and has been for many centuries in the form of loose grains, coated abrasives and eventually grinding wheels. Largely replaced by synthetic abrasives

Emery

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__is made of silicon sand and petroleum coke. Very hard and sharp abrasive grain. Black is for machining low strength materials such as cast, non metallic materials. Green is used for sharpening cemented carbide cutting tools

Silicon carbide

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__ is the most common abrasive. Used for cutting steel and other ferrous alloys having high tensile strength. Found on most bench grinders for sharpening drills, lathe tools etc

Aluminum oxide

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Aluminum oxide is white or light Grey im appearance. White is the used when precision is most important. Grey is better suited for roughing. T or f

True

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Zirconia alumina is a mixture of zirconium dioxide and aluminum oxide. The abrasive grain breaks down and expose new sharp cutting edges more readily that straight aluminum oxide. Very useful for applications requiring high MRR and cool cutting action. T or f

True

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Nothing is harder than __. Used for grinding wheels for finishing carbide or ceramic cutting tools or saws for granite or concrete. Typically ised for non ferrous and non metallic materials

Diamond

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__ is a synthetic abrasive second im hardness only to diamond. Most useful for grinding hard and tough alloy steels or steels having 50rc or more. Used for grinding space age and high cobalt alloys that are difficult to grind

Cubic boron nitride CBN

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Hardness of the 4 types of abrasives

Diamond - 7000
CBN - 4700
Silicon carbide - 2480
Aluminum oxide- 2100

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What does ANSI stand for

American national standards institute

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Designation for aluminum oxide and silicon carbide wheels consists of 5 standard elements. Ano GinaGawa Sayo Boy

-abrasive (A or C)

-grain size (numbers coarse to fine 10-600)

-grade (alphabet letters soft to med to hard)

-structure (dense to open 1 to 16)

-bond type (letter)

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Type of abrasive first element in designation letter. 2 letters

A - aluminum oxide
C - silicon carbide

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2nd element in designation. What are the grain size. Machinist typically use fine and medium grade

Very fine- 220,240,280,320,400,600

Fine- 70,80,90,100,120,150,180

Medium- 30,36,46,54,60

Coarse- 14,16,20,24

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3rd element inndesignation. The grade or hardness of the wheel is a measure of the stralength of the bond between the grains. It consists of which letters

The whole alphabet. Starting from soft to medium to hard

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Hard wheels retain their size and shape longer than soft wheels. Making hard wheels better suited for form or precision grinding. Soft wheels have much freer cutting action. T or f

True

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The __ (4th designation) of a wheel refers to the size of the open spaces between grains. If voids are large, the wheel is “open:, if small, the wheel is “dense” or “close”

Structure

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The structure of a wheel is specified by the 4th element designation which consists of a number 1-6 (1 having highest density) t or f

True

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The BOND type(5th designation) is identified by letters

Vitrified - V -6300 to 6500sfpm
Resinoid- B -9500 sfpm
Resinoid reinforced- BF- 16000 sfpm
Rubber - R- 16000sfpm
Rubber reinforced - RF- 16000sfpm
Shellac- E 16000sfpm
Silicate- S - 5500sfpm
Metal- M

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The designation for diamond wheels is similar to aluminum oxide and silicon carbide with these ff difference

7 instead of 5
type of abrasive are different letters
4th element for concentration of abrasives
-7th element identifies the depth of the abrasive layer

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Abrasive types for diamond wheels

Natural- D
Manufactured- SD or MD
Coated- CD
Armored copper- ASDC
Armored nickel - ASD

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The 4th designation for a diamond wheels refers to concentration of abrasive. What are the numbers

25,50,75,100

100% means that there are 75carats of diamond per cubic inch of conglomerate

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Shapes of grinding wheels

-straight grinding wheel
-tapered grinding wheel
-cylindrical grinding wheel
-straight cup grinding wheel
-flaring cup grinding wheel
-dish grinding wheel
-saucer grinding wheel
-recessed and relieved GW

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Straight grinding wheels are used for sirface and cylindrical grinding, tool, offhand grinding and snagging. T or f

True

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__grinding wheels have a taper of both sides and are used for __ type operations. They are mounted between tapered flanges as a safety measure to prevent pieces of the wheel from flying

Tapered and Snagging

Cylindrical grindingnwheels are used on horizontal and vertical spindle surface grinders, cutting takes place mainly on the __ of the wheel

Face

__ cup wheels are used for both surface grinding and tool cutter grinding. The edge maybe plain or beveled.

Straight

F__cup wheels are used almost exclusively on tool and cutter grinders. If bond is resinoid, the wheel may be used for snagging.

Flare

__ wheels are ised exclusively on tool and cutter grinders because their thin shape permits the wheel to fit between teeth of milling cutters and other narrow spaces

Dish

__ wheels are small grinding wheels of.variouz sizes and shapes for grinding in small and awkward places. Extensively ised for internal grinding and jig grinding

Mounted

Mounted wheels are held on steel shafts called __. Which are in turn held in a chuck or collet of any handheld power tool such as an air grinder

Mandrel

Variables to be considered when choosing a grinding wheel

-type of material being ground -amount of stock to be removed -surface finish -area of contact -with or without coolant -machine condition and HP -wheel speed

Abrasive type and material being grounded

Aluminum oxide- steel, hardened steel, HSS cutting tools Silicon carbide- cast iron, non ferrous metals, non metals, carbide (green) Diamond - carbide or ceramic cutting tools CBN- hardened steel, super alloys

If using coolant, use a wheel with OPEN structure to allow free flow of coolant. T or f

True

Softer wheels for machines with low HP. T or f

True

If using high spindle speed, use a softer wheel. T or f

True

For removing stock quickly

Grain- coarse grain Bond type- vitrified is stronger Structure- open Structure for chip clearance Grade- softer keeps wheel sharp

If surface finish is most important

Grains- fine Grade- hard produce better finish than soft Bond- resilient bonds like rubber or shellac Structure- closed leaves better surface finish than open

If using big area of contact

Structure- wheel should be open for clearance Grain- coarse Grade- soft

2 of the common grinding wheel problems

-glazing -loading

A wheel is said to be __ when thr face of the wheel takes on a shiny appearance. This means that the abrasives have become dull and are no longer cutting

Glazed

Softer materials like aluminum or brass tend to fill up the spaces between the abrasive grains called __ the wheel

__ grinding is a process whereby a revolving grinding wheel is ised as a cutting tool to produce a flat or irregular contour on a workpiece. It is passed under a grinding wheel at a controlled rate

Surface grinding

4 types of surface grinders

-horizontal w/ reciprocating table -horizontal w/ rotary table -vertical w/ reciprocating table -vertical w/ rotary table

This is the most common type of surface grinder and is often referred to as a toolroom grinders or simply a horizontal surface grinder

Horizontal w reciprocating table

This grinder leaves the wheel in constant contact with the workpiece and leaves a circular pattern finish which is desirable for metal to metal sealing of mating round parts

Horizontal w rotary table

This grindernusesna cylindrical or straight cup grinding wheel mounted on a vertical spindle. The wheel cuts on its face and rim, wheel head can be tilted a few degrees to increase pressure on the rim where the wheel contacts the workpiece

Vertical w reciprocating table

The grinding wheel is mounted on a vertical spindlenand cuts on its rim and face. The surface of the workpiece has a pattern of intersecting arcs. This grinder is ised for grinding large plates flat and parallel and is most efficient because of constant contact

Vertical w rotary table

Parts of a horizontal surface grinder

-column -wheel head -spindle housing -table -table controls -saddle -base

2 types of magnetic chucks are

-electromagnetic -permanent

An__ chuck uses electricity to produce the magnetic field necessary to hold the workpiece. Major drawback is ig power fails, the grinding wheel throws the workpiece off the table

Electromagnetic chuck

On a __ chuck, the bikding power is provided by a series of permanent magnets fastened in a silicon iron grid.

Permanent magnetic chuck

Magnetic chuck accessories

-adapter plate -magnetic chuck blocks -magnetic v blocks -magnetic sine chuck -Magna vise clamp -double sided tape -special fixtures

An __ plate improves the ability of a standard chuck to hold workpieces having thin cross sections

Adapter plate

__ support workpieces having odd shapes. These blocks do not have the same holding power and should only be used for light grinding

Magnetic chuck blocks

__ contain their own magnetic system to energize a 90deg groove base. Used to hold round, square and rectangular work pieces

Magnetic v blocks

A __ sets a workpiece to a precise angle for grinding. Used in the same way as a sine plate.

Magnetic sine plate

__ clamps holds workpieces that are non magnetic or that have small bearing surfaces. The clamps are placed on each side of the WP and when the magnet is turned on the comb like structures are pulled down and grips the wp

Magna vise clamps

__ tape is suitable for very light cuts on thin or non magnetic workpieces

Double sided tape

__ such as toolroom vises, angle plates and vacuum chucks are usednto hold irregular workpieces.

Special fixtures

3 types of grinding fluids when grinding

-soluble oil and water- used for light to moderate stock removal -chemical grinding fluids - moderate to heavy stock removal where high surface finish is required - straight grinding oil- offers best accuracy, surface finish and wheel life for very hard materials

3 Methods of delivering coolant

-flood cooling system -through the wheel cooling system -mist cooling system

Advantages of a horizontal grinder

-grinding a flat, edge, vertical/angular surface -form grinding -cutting off -creep grinding

If the surface placed on the magnet is a ground surface, prevent scratching it using a piece of paper under the workpiece. T or f

True

Crossfeed and depth for grinding

Crossfeed- .03 to .05 for roughing .02 to .005 for finishing Depth- .001 to .003 roughing .0005 to .001 finishing

Most accurate way to grind an edge is to clamp the wp to an angle plate. T or f

True

__ grinding is used for any surface that is not flat such as angles, radii or any irregular profiles. It involves dressing the wheel to the mirror image of the desired countour

Form grinding

Very complex profiles can be created by guiding a __ with a mechanical or hydraulic tracer attachment

Diamond dresser

__ is a process of imparting a contour to a wheel face using hardened steel or carbide roller

Crush dressing

Abrasive cutting off wheels can be used on hardened steel, ceramics, tubing, thin walled shapes or any material that would be damaged by normal grinding, t or f

True

__ grinding is capable of much higher metal removal rate than any other type of grinding. Sometimes more than 1in depth combined with low feedrate. Needs more hp and a heavy and rigid machine

Creep feed grinding

For creep feed grinding. Wheel must be open and soft grade. T or f

True

Surface grinding problems, causes and solutions

Burning/discoloration -wheel grade is too hard Burnished work Surface -wheel is glazed Chatter or wavy pattern -wheel out of balance, out, too hard or glazed

The purpose of a cylindrical grinder is to finish a shaft to precise size and shape. 2 main types of cylindrical grinder are

Center Centerless

Center type grinders are for custom one off work and are the type most used in machine shops. Centerless grinders are for production work. T or f

True

There are 2 types of center grinders, they are

Plain center grinder- primarily used for manufacturing Universal center grinder- more versatile since both wheel head and headstock can be swivelled to allow the grinding of tapers

A __ rest supports long, slender workpieces and keeps it from sprinijg away from the grinding wheel. It also helps lessen chatter

Center rest

Head stock and foot stock on a center grinder are like chuck and steady rest on a mill. T or f

True

Spindle speeds on an internal grinding operation have high rpm. 45000 or higher is not uncommon. T or f

True

The most common wheel dresser is an industrial __ dresser

Diamond

The most important aspect of grinding a parallel section on a cylindrical grinder is to align the upper table. If it is not aligned, wp will be tapered. t or f

True

On a center grinder if speed is set too high the grinding wheel acts as if it were too soft. Too slow, wp shows burn marks. T or f

True

Use cutting speed or sfm when calculating rpm for grinders. T or f

True

Rate of traverse travel for grinding should be 1/2 to 2/3 of wheel for roughing. 1/8 to 1/3 for finishing. T or f

True

Remember to use the large end of the taper for calculating cutting speeds

__ grinding uses the face of the wheel to grind an steep taper or irregular profile into the workpiece. The wheel head is fed straight in

Plunge grinding

When plunge grinding it is essential that you lock the table in place, especially when grinding near a shoulder. Feed the wheel head in carefully by hand. T or f

True

When doing internal grinding operations you should always consider deflection on the spindle. Use the biggest diameter and shortest length spindle. T or f

True

For internal grinding the diameter of the stone should be 2/3 to 3/4 to the diameter of the bore. Sfm for vitrified stone should be around 6500sfm. Always use a softer wheel, if not slow it down. T or f

True

One of the most common problems when internal grinding is the bell mouth shaped produced when the stone first enters the wp. This is caused by deflection. T or f

True

Planetary internal grinders are used where size, shape or weight is inappropriate to rotate the wp. Thr grinding wheels on these machines rotates in a circular or planetary movement

True

The purpose of __ is to restore the cutting qualities of the wheel by removing worn or loaded grains

Dressing

The purpose of __ is to ensure the wheel is round and concentric with the machines spindle axis and to shape the face of the wheel

Truing

3 tools used for dressing and truing wheels

Star wheel dressers Abrasive stick and wheels Diamond dressers

A __ dressers is a quick means of dressing and truing a wheel, although it is not an accurate means. It is exclusively used on off hand grinding machines and not precision grinding machines

Star wheel dresser

An __ is guided across the face of the wheel by hand and is typically used to shape wheels on tool and cutter grinders. Made of silicon carbide with hard bond

Abrasive sticks

A __ dresser is ised for surface, cylindrical and internal grinders and consists of either a single diamond point or cluster of small diamonds. Most precision grinders have a built in dresser with feeding mechanism

Diamond dresser

It is important not to overheat a diamond dresser or let the holder wear so much that the diamond falls out. T or f

True

If coolant is to be used when grinding, coolant is also used when dressing. T or f

True

Feed the diamond dresser between 3-7ipm. Rough depth .001-.002. Finish .0005 per pass

True

Diamond dresser should be off center of the wheel by 1/8 to 1/4. T or f

True

Do NOT use a diamond dresser on a diamond or CBN wheel. Use abrasive stocks. Diamond and cbn are considered superabrasives. T or f

True

4 steps to installing a grinding wheel

-inspect -mounting -balancing -truing and dressing - secondary truing and dressing

Some cracks are too fine to be seen during a visual inspection. Perform a __ to check for these cracks. Suspend the wheel and tap with a non metallic tool like a screwdriver handle. Wheel should emit a clear metallic sound. A dull thud means it is probably cracked

Ring test

Ring testing is not effective for diamond rings. T or f

True

There should be approximately. 005 clearance between the bore of a grinding wheel and adapter for grinding machines. Too tight = scrap. Too loose = install a sleeve. T or f

True

Flanges should be the same size as each other and not less that 1/3 of the diameter of the wheel. Make sure the flanges are clean. T or f

True

A __ is a circular piece of paper fitted between the grinding wheel and flanges. It provides a cushion between the wheel and flanges

True

Most wheels are balanced while they are at rest (static balancing) although some grinding machines are equipped to balance wheels that are spinning at operating speeds(dynamic balancing)

True

You shield store grinding wheels in a secure area that is dry and where temp doesnt change too much. Large wheels should be set on edge and small can be set flat on their side

True

Max safe operating speed for grinding wheels

(Rated surface speed x dia of wheel)÷ 4

Fpm for table speed or traverse Ipm for depth speed or wheel speed

True

Abrasives Flashcards

(116 cards)