Traditional Synthetic Abrasives-A Modern History

 Silicon carbide was discovered by the American inventor Dr. Edward G. Acheson in 1891 while attempting to produce artificial diamonds from coke and silica sand.  Finding that these new crystals approximated the hardness of diamond and immediately realizing the significance of his discovery, Acheson applied for a U.S. patent. His early product initially was offered for the polishing of gems and sold at a price comparable with natural diamond dust. The new compound, which was obtainable from cheap raw materials and in good yields, soon became an important
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As an abrasive, Silicon Carbide is black in color and is the hardest and sharpest of the minerals used commonly in coated abrasives. It’s harder than Aluminum Oxide but considerably more friable—which means that it fractures readily, exposing new sharp edges. Silicon Carbide is most effective with non- ferrous metals such as brass, copper, bronze, magnesium, titanium and aluminum where fast, cool cutting is desirable.  Non-metallic applications include ceramic, stone, glass, plastic, leather and rubber.  Silicon Carbide is superior to any other abrasive in its ability to penetrate and cut faster under light pressure.
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Aluminum Oxide was introduced in 1900 by CT Jacobs.  It is produced from the raw mineral Bauxite where it is fused in electric arc furnaces at temperatures up to 2600’ C, which is a temperature 800’ C hotter than lava in a volcano! The AO ingots are cooled and then crushed with a roll crusher to produce a large volume of splintery, sharp and friable abrasive particles that break down easily to remain sharp and produce a minimum of heat buildup. The crushed AO is then sized into the various grits used in producing coated abrasive products.
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Aluminum Oxide remains the most popular abrasive used in sanding products, as it is considered the most “all purpose” abrasive.  It is a reddish-brown in color, extremely tough and its blocky shape facilitates the penetration of tough materials without excess fracturing or shedding. It is specified for applications on high tensile materials such as carbon steel and alloy steel as well as wood, composites and solid surface. 
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These traditional synthetic minerals used in abrasives offer many advantages over the traditional naturally occurring minerals. Synthetic minerals are consistent without unforeseen impurities. In addition, we have the technology to control the grain characteristics in a synthetic mineral.  Grains for coated abrasives are different than the grains used in grinding wheels. They are elongated to achieve the best bonding results and abrasive performance.

Aluminum Oxide is manufactured in two levels of abrasive grain surface density: closed coat and open coat. A closed coat product is one in which the abrasive grains completely cover the surface of the backing. The greater number of “abrading points” per square inch results in a larger amount of material being removed before the product becomes worn out. An open coat product is one in which the abrasive grains cover approximately 50% to 60% of the coat side of the backing. Open coat AO frequently cuts faster and provides a greater resistance to loading, which makes it an ideal choice for sanding on softwoods.

Sanding Belts & Grinding Metal

Abrasive Resource can have sanding belts made up for you in any width or length you may need for grinding or polishing metal. We show the more popular sizes in an aluminum oxide material on our Sanding Belts page, but we can custom fabricate any size, grit or abrasive material you require in just a day or two!

Offhand grinding on metal is the most traditional way to use sanding belts and covers all the methods of abrading metal where the operator holds the workpiece in their hand and presents it to the abrasive belt (as opposed to the piece being held in a fixture.)

This type of grinding is done on a Backstand Sander—also called a polishing jack or belt grinder. These machines vary considerably in horsepower, ranging from one to 75 HP. Typically, units with 7-1/2 to 15 HP provide a good working power for most applications at speeds between 3500 and 7000 sfpm. All grinding should be below the center line of the contact wheel and the workpiece should be brought up to the belt.

Optimum belt speed depends mostly upon the material you are grinding. Testing indicates that as the belt speed increases, so does the amount of metal being removed. However—as belt speed increases, the amount of heat generated also increases which may result in premature dulling of the abrasive grains (glazing) and/or heat damage to your workpiece.  The optimal speed range in sfpm for grinding belts is shown in this table:

Next you need to factor in grinding pressure. Pressure is an important part of the grinding process as it causes the abrasive grain on the belt to fracture and create a continuing supply of fresh, sharp cutting edges. An operator will generate this pressure against the contact wheel in a range of 20-50 psi. On an average offhand operation of moderate stock removal, a 70-75 durometer rubber contact wheel is the most useful. For more information on contact wheels, refer to our 2005 Sandpaper Blog post “Contact Wheels for Abrasive Belts”.

Finally, remember to check that the abrasive belt, idler assembly and contact wheel are enclosed within a sheet metal hood when using a backstand grinder. The hood must confine flying sparks and fumes as well as protect the operator from a belt breakage.

Abrasive Grinding

It’s January 2013 and the beginning of a new year is always a good time to think about learning something new or improving on what you already have, right? So for Abrasive Resource this means we are spreading our arms just a little wider this year. For the last sixteen years we have been your “go to” source for coated abrasives—sanding belts and sanding discs. Now we are welcoming some bonded abrasives into our product line, and I think you’ll like what you see!
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For years our customers have asked us for abrasive grinding wheels—whether you use them for auto body work, sharpening tools or metal fabrication. Now we have partnered with Camel Abrasives to offer you the most requested bonded abrasives line from over the years.  These abrasive grinding wheels are used on cut off saws, die grinders, angle grinders and bench grinders. 

Using Bonded Abrasives

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When using bonded abrasives, always follow these recommendations:

• Allow the wheel to attain full speed before it touches the workpiece.
• After installing a wheel, test run the tool for 60-90 seconds before touching the workpiece.
• Use gentle pressure when touching the wheel to the workpiece.
• Cut or grind with a smooth, even pace. Do not force the wheel…but do not proceed so slowly that burning occurs.
• Do not exceed cutting capacities as specified on the wheel by Camel Abrasives.
• Wear eye and ear protection, gloves, a long sleeve shirt and any other safety gear recommended by your tool’s manufacturer.
• Never use a dust collection attachment when cutting metal.
• Do not use cutting lubricants with cut-off wheels and only use them on grinding wheels if specifically endorsed by your tool’s manufacturer.

For more information on the types of abrasive grinding wheels Abrasive Resource is now carrying visit our abrasive grinding page at abrasiveresource.com.

Proper Sanding Belt Tension

How to Maintain Proper Sanding Belt Tension for Better Performance
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When consulting with customers, abrasives suppliers place a great deal of emphasis on choosing the best abrasive product for the job. To put that product to its best use, however, it’s just as important to select and set the correct machine parameters. One of the most overlooked aspects of wood sanding operations is maintaining proper tension on the coated abrasive belt once it is mounted on the sanding machine.

In basic terms, the amount of tension on the coated abrasive belt should be just enough to keep the belt from slipping on the drive wheel, and to keep the belt from tracking off the machine. Several methods can be used.

Some sanding machines have fixed belt tension. For example, portable sanders, such as the 3” x 24” machines, have fixed tension that is derived from a loaded spring. This tension is factory-set and is not readily adjustable.

However, most sanding machines have some type of adjustable tensioning device. These include use of weights, screw-type mechanisms, or pneumatic cylinders. On screw-adjusted tension devices, such as those found on edge sanders and some mould sanders, it’s often difficult to determine the proper amount of tensioning unless the operator is experienced with the machine. As a general rule, the belt should make five or more full rotations after the machine is turned off. If the belt comes to a stop very quickly, it’s likely that the tension is too high.

Pneumatic cylinder designs are the preferred type of adjustable device. They compensate for stretching of the abrasive belts, provide a range of delicate adjustment, and can be rapidly released and applied for quick belt changes. Using an air gauge installed on the sander can monitor pneumatic tension. Quite often, these gauges are not properly maintained, and will give incorrect readings. Air pressure gauges are relatively inexpensive, and should be replaced if broken.

Most wood sanding applications (such as mold sanding using narrow cloth belts) require a belt tension of approximately 40 psi. However, there are some special exceptions. For example, abrasive planing operations using coarse grits typically demand belt tension in the range of 70 to 90 psi.

Intermediate wide belt sanding (grits 60 to 220) normally uses a tension in the range of 60 to 75 psi for cloth belts. On these applications, tension for paper belts should be set at about 20 to 25 percent less than that for cloth belts. This is because cloth belts will stretch very slightly during use, while paper belts will not. In any case, the wide belt machine manufacturer should be consulted for specific recommendations regarding air tension settings. On drawer sanders, a specialized machine for sanding the inside lip of a drawer front where it joins the sides, it’s best to use the least amount of belt tension possible when installing a new belt. This means that you should be able to easily rotate the belt by hand with the machine turned off. After running the sander for 10 minutes, it may be necessary to slightly increase the tension as the belt stretches slightly.

Because the goal is to keep the belt from slipping, users sometimes err on the side of using too much belt tension. Several problems can result from excessive belt tension. They include:

• Premature bearing wear
• Excessive wear of the rubber contact drum
• Excessive wear of graphite covers on platens
• Excessive wear of mould blocks

Excessive belt tension changes the characteristics of a rubber contact drum; it makes a soft wheel act harder and decreases the effectiveness of the serrations. Excessive belt tension can also lead to belt failure. It can cause the belt joint to mark the work piece, and can cause tracking problems. But the leading problem caused by excessive belt tension is the generation of heat. One recent study showed that an increase in belt tension from 40 to 60 psi caused the sanding heat at the area of contact to jump by 100°F. Excessive heat often leads to premature loading of the belt and wear on flexible belts.

Consult with your abrasives supplier and machine manufacturer to ensure that you’re using the proper amount of belt tension. Maintained correctly, belt tensioning can maximize abrasive belt life, provide the best possible finish, and extend the life of the sanding machine components.

Please visit our website and check out our many sanding belts that are available to ship quickly.

**Original article can be found at the Woodworking Network.** 

Should you do an Abrasive Audit?

An abrasive audit is a detailed recording over a two week period of all the abrasives that are being used in your production, along with the details on how the abrasive is being used. Looking at the cost, usage and application of every abrasive product in your shop or plant can lead to productivity gains, improvement in processes, opportunities for supply consolidation and cost reduction.

We walked through this process a while back with a furniture manufacturer. After assessing their requirements over a few phone conversations and emails, we determined that our company could offer a significant savings to this furniture manufacturer in their abrasives purchases. We switched them to a new and improved abrasive belt material which reduced their pricing resulting in a savings of $59,142.00 for this customer in a one year period. In addition, our sanding belts lasted approximately 15% longer than the former supplier’s belts. Consequently, this customer was able to use approximately 294 fewer belts in the same time frame. Bottom line savings totaled 62% by switching to belts offered by Abrasive Resource.

Things important to know during an abrasive audit:

1. What are the abrasives currently being used for each part and what is its cost?
2. What is the number of pieces or parts you are able to finish per abrasive product?
3. What is the amount of each abrasive you buy in a year?
4. Are there bottleneck areas where the sanding operation is slowing things down?
5. Does one operator or operation consistently consume more abrasives than another?
6. Have there been changes in technology that might help improve productivity or cost?

If you would like to prepare for your own abrasive audit, gather past order information on the abrasives you purchase. You will want to make a list of all the products that you buy along with specifications and quantities. Your abrasive supplier will be happy to walk alongside you during this audit—giving suggestions, sending samples and providing quotations so that you can assess your particular situation and improve the grinding and finishing processes in your plant. If you have any questions, don’t hesitate to call us at Abrasive Resource. Abrasive products are all we do. And if you’re not makin’ dust, you’re eatin’ it!