Choosing the Correct Backing for Your Sandpaper & Abrasive Products

Whether paper, cloth or film, the backing used for coated abrasive products must be smooth enough for a uniform adhesive coating, strong enough to withstand grinding pressures and flexible enough to conform to contours if that is necessary to your application.

Paper: The paper backings used for coated abrasives are highly specialized technical papers made to very exact specifications for abrasive use, thereby assuring certain essential physical properties such as finish, strength, adhesion, flexibility and weight.

Paper weights are determined by the number of pounds in a papermaker's ream of 480 sheets that are 24" x 36" in size. The standard paper weights used in coated abrasives are shown below and are indicated by a letter code which appears immediately after the grit size on the finished product backing. Briefly stated, the lighter the backing, the greater the degree of flexibility and the heavier the backing, the greater resistance to tearing.

• A-weight (40 lbs) -Light and flexible. A weight is primarily used for sheet products used on hand sanding operations in grits 80 and finer.
• C-weight (70 lbs) -Stronger and less flexible than A weight. This backing is chosen for hand sanding and for use on small, portable power sanders. Used for intermediate sanding in grits 36 through 80.
• D-weight (90 lbs) -Stronger and less flexible than C weight. This backing is also used for hand sanding and small, portable power sanders on coarse and intermediate grits 24-80.
• E-weight (130 lbs) -Stronger and less flexible than D-weight, this backing is primarily used on roll, belt and disc applications where high resistance to tearing is needed.
• F-weight (165 lbs) -The strongest, least flexible paper backing utilized. Used primarily for heavy-duty sanding discs, sheet goods and sanding belts used in the floor sanding market and paper wide belts used in woodworking applications.
  

Cloth: Cloth backings are more durable than paper, offer greater resistance to tearing, and tolerate continual bending and flexing during use. The cloth used for abrasive backings are manufactured in the traditional way most cloth is processed--by interlacing threads running at 90' angles with each other. The friction at the numerous points of intersection hold the fabric together. Cloth used for abrasive backings often requires desizing, shrinking, drying, stretching, filling and calendering in order to produce the desired strength, flexibility and coating surface.

The standard cloth weights used in coated abrasives are also indicated by a letter code which appears immediately after the grit size on the finished product backing.

• J-weight (Jeans) -The lightest and most flexible cloth backing, this backing is used where finish and uniformity of surface are more important than stock removal. Most often seen on abrasive shop/utility rolls, cloth sheets and sanding belts. Ideal for finishing, blending and where considerable flexibility and conformity are required, such as contour work on curved surfaces.
• X-weight (Drills) -Stronger and stiffer than J-weight, this backing is used on a multitude of abrasive products from coarse grit stock removal through fine grit finishing and polishing. Consistent productivity, good finishes and long product life are characteristics of abrasive products made on an x-weight backing such as sanding belts and cloth sanding discs.
• Y-weight (Heavy Duty) -The strongest cloth backing utilized, this backing is used on coarse grit products designed for extreme pressure and heavy stock removal operations. Used most often in heavy duty, long life premium abrasive belt materials.

Polyester Film: Polyester based film backings offer special properties that lend themselves to specialized sanding applications. Film backed abrasives offer thicknesses having ultra tight tolerances...which is important for the electronics, fiber optics and surgical instrument/medical applications. The benefits of a film backed abrasive product is now also being realized in the automotive and solid surface markets.

Sanding Wood

Wood surfaces are not only sanded to make the surface smooth! Although that is the most important reason, there is another factor to take into consideration: wettability.

This concept is easily demonstrated with The Water Drop Test. The photo to the right shows the differences in wettability on a piece of yellow birch. The two arrows are pointing to the inactive and activated surfaces.

The test has three drops of water placed on the surface at the same time. The drops were then photographed after 30 seconds. The water on the left was dropped on an unsanded wood surface and as you can see, it has kept its large contact angle with the wood surface. The surface under the middle drop was sanded with two passes of 220 grit sandpaper and you can easily see that the wettability is much improved. The last drop has almost completely soaked into the surface. Why? This section of the wood was treated to five passes of the 220 grit sandpaper.

So, why is this important? Because it reminds us that when sanding the surface of wood you are not only making the surface smoother. You are also reactivating the wood. Both time and heat cause extractives like tannins, oils & resins from within the wood to rise to the surface. Think about how this may affect your finish on the wood. Bottom line: All wood should be sanded no greater than 24 hours before it is finished and sealed.

Properly sanded surfaces result in beautiful finished products. You will save time and money by reducing the amount of finish needed--one would have to use only a fraction of the coating or stain on an activated surface! And even better is that by allowing the stain to wick out evenly you achieve a much more uniform color and finish.

Source: WoodworkingNetwork.com
For more information on sanding wood or any other surfaces, please give Abrasive Resource a call at 800-814-7358 or check us out online at AbrasiveResource.com

Wood Sanding for a "Green" Finish

If you're hopping on board the "Green Finishing" train, you need to consider how to move from solvent-based coatings into water-based finishing. The average final sanding grit for solvent-based finishes ranges between 150-220 grit. When using water-based finishes, the final sanding grit usually runs between 220-280 grit. Moving to a higher abrasive grit for water-based finishes allows for a higher polish of the wood to reduce fiber raise and minimize stain blotching of the wood.

Softer species of wood will stain best when up to 280 grit sanding abrasives are used. Harder, tight grained species of wood may only need the 220 grit as a final sand. To be successful in water-based finishing, you need to rethink the process from start to finish. This surface preparation is your first step.

If you would like to try some sample sanding products in a finer grit for water-based finishing, please visit our website at www.abrasiveresource.com or give us a call at 800-814-7358!

Surface Speeds for Metal Finishing

The effect of surface speed when grinding and finishing metals is addressed in the "Metal Finishing Guidebook", published by Elsevier. They ask us to think of each individual abrasive particle on the abrasive belt as a single point cutting tool. The speed of the belt or number of times a minute each particle contacts the work in a given time frame, will determine the rate of removal and the working life of the individual particle. An increase in the surface speed will cause the pressure to be applied to many more particles in a given time frame and will reduce the penetration of a given particle into the workpiece. When this speed reaches beyond a critical point, rapid dulling of the abrasive grain takes place, the rate of cut decreases, and excess heat is generated.

To resharpen or restore the cutting capacity of the abrasive, added pressure must be exerted to cause fracture of the grain. This added pressure will generate added heat and soon, burning will result in removal of the belt. Conversely, as speeds are slowed, more pressure is exerted on each grain, causing the grain to resharpen with less heat generation. To understand this more fully, the Metal Finishing Guidebook refers us to the following table, where suggested speeds, abrasive, contact wheel, grit size, lubricant and operation have been compiled into a quick reference chart: Suggested Surface Speed and Abrasives for Various Metals.
If you have any questions regarding abrasive belts, please give Abrasive Resource a call at 800-814-7358 or visit us online at www.abrasiveresource.com.

Revive Your Furniture's Finish

If the finish on your furniture appears dull and dry, but is otherwise intact, you can revive it with a simple cleaning and a coat of wax.

Start by wiping the finish thoroughly with a clean rag dampened with naphtha. Naphtha is a fast drying solvent that is often used as a lubricant for rubbing out hardened shellac finishes and can improve an older shellac coating with a simple rub down. One of the most popular is VM&P Naphtha, which should be available at the big box home improvement stores as well as hardware stores and paint stores. This step removes any oil-soluble grime.

Then, switch to a detergent to remove water-soluble dirt. One squirt of Dawn
brand dishwashing liquid mixed into a pint of warm water. Use a slightly dampened cloth, not one that is dripping wet!

Next, lightly dry sand the finish with a 400 grit sandpaper and follow up with a 600 grit. The goal here is to remove only the very top layer of finish, but not to sand all the way through to the wood.

Wipe off the sanding dust with a rag dampened with the naphtha and then use a natural or dark-colored paste wax (depending on the color of your wood) to bring the luster back up.

"Buffing out a Finish"

Whether you are buffing out a car, a floor, some metal parts, a countertop or even the finish on a guitar...the verb "buff" derives from the obsolete English word buffe, from the French word for buffalo.

When buffalo were abundant in the 19th century, buffalo hide was used for polishing metal to a high gloss. Soon, any sort of soft leather used for polishing was coined as a "buff", which then inspired the verb "to buff".

Sandpaper Grits

Sandpaper grit size refers to the size of the particles of abrading materials embedded in the sandpaper. There are a number of different standards that have been established for grit size. These standards establish not only the average grit size, but also the allowable variation from the average. The two most common are the United States CAMI (Coated Abrasive Manufacturers Institute, now part of the Unified Abrasives Manufacturers' Association) and the European FEPA (Federation of European Producers of Abrasives) "P" grade. The FEPA system is the same as the ISO 6344 standard. An additional measuring system used in sandpaper grits is micron grade (generally used for very fine grits). Also, cheaper sandpapers sometimes are sold with nomenclature such as "Coarse", "Medium" and "Fine", but it is never clear to what standards these names refer.

FEPA Grading: The majority of coated abrasives manufactured today use the FEPA standard (Federation of European Producers of Abrasives), otherwise known in the industry as “P” grading. Abrasives in the P scale are graded to higher tolerances than CAMI graded abrasives.

CAMI Grading: This grading standard is used exclusively by US manufacturers of coated abrasives, and is overseen by the Coated Abrasive Manufacturer’s Institute and the American National Standards Institute (ANSI). The CAMI-scale tolerates a wider range of grain sizes within the definition of the grit.

Micron Grading: This refers to an abrasive particle’s actual diameter in micrometers, rather than the total number of abrasive grains that can pass through a linear inch in a screen or mesh (as the FEPA and CAMI grading system use). Micron grading has the tightest tolerances for grain size and in abrasives are typically used only in fine grits, when a stray scratch from an outsized grain would make a substantial difference to the finish.

If you have additional questions about sandpaper grits and how they compare to one another, please give Abrasive Resource a call at 800-814-7358 and be sure to download our grit comparsion chart at abrasiveresource.com

Abrasive Resource is your source for the finest abrasive products!