Backings

There are multitudes of different backings that can be used when making coated abrasives.  The most common types are paper, cloth, film, and fiber.  Paper and cloth can be rated on the following scale.

Thin, Flexible, and Less Durable	Awt Paper	Bwt Paper	Cwt Paper	Ewt Paper	Fwt PorC	Jwt Cloth	Twt Cloth	Xwt Cloth	Ywt Cloth	Thick, Stiff, and Durable

Film and fiber have unique characteristics that lend themselves to certain applications.  Abrasive film material is more durable than paper products and excels in finishing applications.  Film is completely smooth and offers a polishing surface that is consistent, not varying in thickness or containing voids.  This provides a better overall finish.

Fiber or vulcanized fiber is made by pressing layers of paper piles saturated with gelatinizing zinc chloride.  Once the material is pressed the zinc chloride is then leached out and the material is left to dry.  After the drying process is complete, resin and grains are added to the material which is then die-cut to produce discs.  Moisture is then reintroduced during the curing process to create the final product.  Fiber discs are ideal for weld removal and grinding large surfaces of ferrous materials.

Bond Types

Just as there is a diverse world of abrasive grains and backings, bonding types vary depending on the application, grain used, and substrate.  Coated abrasives have two adhesive layers which anchor and lock the mineral to the backing.  The make or base coat and the size coat, see Fig. 4C.  These bonding layers can be made from:

• Animal Hide Glue or Gluebond – First type of adhesive used.  This system is used for both make and size coats.  Not a waterproof bond.  Good for polishing.
• Urea Resin – Used as both make and size coat.  More durable than gluebond but still not waterproof.  Used in some sheet and shop roll production.
• Phenolic Resin – A synthetic adhesive used in both make and size coats.  Resistant to heat, pressure, and moisture.  Most widely used system today.

Flexibility of the Material

Once abrasive materials are made, depending on the backing, they can be flexed to add conformability.  This is a mechanical process employed after the material has been produced.  A good rule of thumb when looking at flexibility is to choose an abrasive material that is not more flexible than required to conform to the shape needed.  Flexing a material fractures the bonding layers, making the material more pliable.  The more the bonding layers that are broken, the more life is reduced.

• Single Flex – This provides little or no crosswise flexibility.  This is a single mechanical flex which creates flex lines at a 90º angle to the edge or running direction of the material.  Simply put, this is a one directional flex for pulleys and contact wheels.
• Double Flex – Two mechanical 45º flexes which makes the material moderately flexible in all directions.
• Triple Flex – Two 45º flexes combined with one 90º flex giving maximum pliability and softness.

	Life
Flexibility		Stiffness

Troubleshooting

Below are common abrasive challenges which can be overcome with the following corrective actions.

• Glazing – One of two things can be considered glazing.  One, the dulling of the abrasive tip.  This is most commonly seen when grinding ferrous materials.  Two, metal welding itself to the abrasive tips.  Usually caused by excessive heat being generated during the grinding operation.

Corrective action:  

• Look at the mineral.  It could be too hard or too fine.
• Increase the speed and/or pressure to breakdown the grain.
• The contact wheel could be too soft.
• If too much heat is being generated, look at using a product with a grinding aid.
  
  
  
• Loading – One of two things can be considered loading.  One, material packed in-between the abrasive grains.  This is most commonly seen when grinding non-ferrous materials.  Two, metal welding itself to the abrasive tips.  Usually caused by excessive heat being generated during the grinding operation.

Corrective action: 

• Look at reducing the grinding pressure or soften the contact wheel.
• Decrease the speed.
• If possible look at adding a coolant or increase the exhaust.
• An open-coat material might be another option.

• Stripping or chunking – This is when large abrasive particulate and bonding adhesive comes off of the material without having time to work or breakdown.

Corrective action: 

• The grain could be too soft.
• Reduce the amount of flexing the material has to overcome.
• Make sure the work piece is being utilized evenly.