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mLine 178:
Line 178: − <blockquote>Abrasive grains are selected according to the mesh of a sieve through which they are sorted. For example, grain number 40 indicates that the abrasive grain passes through a sieve having approximately 40 meshes to the linear inch. A grinding wheel is designated coarse, medium, or fine according to the size of the individual abrasive grains making up the wheel. The softer and more ductile the material, the coarser the grain size. The larger the amount of stock to be removed, the coarser the grain size. The finer the finish desired, the finer the grain size.</blockquote>+ − − Line 217:
Line 215: + + Line 222:
Line 222: − <blockquote>Most wheels are graded according to hardness by a letter system. Most manufacturers of grinding abrasive wheels use a letter code ranging from A (very soft) to Z (very hard). Vitrified and silicate bonds usually range from very soft to very hard, shellac and resinoid bonds usually range from very soft to hard, and rubber bonds are limited to the medium to hard range.</blockquote>+ − − <blockquote>The grade of hardness should be selected as carefully as the grain size. A grinding abrasive wheel that is too soft will wear away too rapidly, the abrasive grain will be discarded from the wheel before its useful life is realized. On the other hand, if the wheel is too hard for the job, the abrasive particles will become dull because the bond will not release the abrasive grain, and the wheel’s efficiency will be impaired.</blockquote> − − <blockquote>The harder the material, the softer the wheel. The smaller the arc of contact, the harder the grade should be. The arc of contact is the arc, measured along the periphery of the wheel, that is in contact with the work at any instance. It follows that the larger the grinding wheel, the greater the arc of contact and, therefore, a softer wheel can be used. The higher the work speed with relation to the wheel speed, the milder the grinding action and the harder the grade should be.</blockquote> − − Line 261:
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Line 296: − <blockquote>Most grinding wheels are made of silicon carbide or aluminum oxide, both of which are artificial (manufactured) abrasives. Silicon carbide is extremely hard but brittle. Aluminum oxide is slightly softer but is tougher than silicon carbide. It dulls more quickly, but it does not fracture easily therefore it is better suited for grinding materials of relatively high tensile strength. The tensile strength of material to be ground is the main factor in the selection of the abrasive to be used.</blockquote>+ − − Line 320:
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Boyer Schultz 6-12 Surface Grinder (view source)
Revision as of 18:10, 11 August 2018
, 18:10, 11 August 2018→Auth/use notes: table floats
==== Grain size/grit ====
==== Grain size/grit ====
{|class="wikitable floatright"
{|class="wikitable"
! Grit class
! Grit class
! Coarser
! Coarser
| 180
| 180
|}
|}
<blockquote>Abrasive grains are selected according to the mesh of a sieve through which they are sorted. For example, grain number 40 indicates that the abrasive grain passes through a sieve having approximately 40 meshes to the linear inch. A grinding wheel is designated coarse, medium, or fine according to the size of the individual abrasive grains making up the wheel. The softer and more ductile the material, the coarser the grain size. The larger the amount of stock to be removed, the coarser the grain size. The finer the finish desired, the finer the grain size.</blockquote>
==== Hardness grade ====
==== Hardness grade ====
<blockquote>The grade of a grinding wheel designates the hardness of the bonded material. A soft wheel is one on which the cutting particles break away rapidly while a hard wheel is one on which the bond successfully opposes this breaking away of the abrasive grain.</blockquote>
<blockquote>The grade of a grinding wheel designates the hardness of the bonded material. A soft wheel is one on which the cutting particles break away rapidly while a hard wheel is one on which the bond successfully opposes this breaking away of the abrasive grain.</blockquote>
{|class="wikitable floatright"
{|class="wikitable"
! Grade class
! Grade class
! Softer
! Softer
| T
| T
|}
|}
<blockquote>Most wheels are graded according to hardness by a letter system. Most manufacturers of grinding abrasive wheels use a letter code ranging from A (very soft) to Z (very hard). Vitrified and silicate bonds usually range from very soft to very hard, shellac and resinoid bonds usually range from very soft to hard, and rubber bonds are limited to the medium to hard range.</blockquote>
<blockquote>The grade of hardness should be selected as carefully as the grain size. A grinding abrasive wheel that is too soft will wear away too rapidly, the abrasive grain will be discarded from the wheel before its useful life is realized. On the other hand, if the wheel is too hard for the job, the abrasive particles will become dull because the bond will not release the abrasive grain, and the wheel’s efficiency will be impaired.</blockquote>
<blockquote>The harder the material, the softer the wheel. The smaller the arc of contact, the harder the grade should be. The arc of contact is the arc, measured along the periphery of the wheel, that is in contact with the work at any instance. It follows that the larger the grinding wheel, the greater the arc of contact and, therefore, a softer wheel can be used. The higher the work speed with relation to the wheel speed, the milder the grinding action and the harder the grade should be.</blockquote>
==== Bonding material ====
==== Bonding material ====
==== Abrasive material ====
==== Abrasive material ====
{|class="wikitable floatright"
{|class="wikitable"
|+ Appropriate abrasives per work material
|+ Appropriate abrasives per work material
! Silicon carbide
! Silicon carbide
* Hard bronzes
* Hard bronzes
|}
|}
<blockquote>Most grinding wheels are made of silicon carbide or aluminum oxide, both of which are artificial (manufactured) abrasives. Silicon carbide is extremely hard but brittle. Aluminum oxide is slightly softer but is tougher than silicon carbide. It dulls more quickly, but it does not fracture easily therefore it is better suited for grinding materials of relatively high tensile strength. The tensile strength of material to be ground is the main factor in the selection of the abrasive to be used.</blockquote>
{|class="wikitable"
{|class="wikitable"