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How Sandpaper is Made
I recently was fortunate to be able to take a tour of the Ali Industries abrasives factory in Fairborn, Ohio, where they manufacture their Gator Finishing line of sandpaper products. As a part of my tour, I was able to learn all of the steps that Ali uses to make everything from basic garnet sandpaper for hand sanding, to random orbit sanding disks, sanding belts for belt sanders and more. Ironically, most of these abrasive products are manufactured using the same (or very similar processes).
The... first step to making any sandpaper product is to print the backer on the back of the paper. On sheets of sandpaper, this is where the grit and type of paper is noted. As can be seen in the image above, this is done on very large rolls of paper (roughly four-feet wide), even though the printing may eventually be covered by a backing such as a hook-and-loop attachment for power sanders.
An interesting side note: In 1994, Ali Industries began building a huge sandpaper manufacturing machine (that they affectionately call "The Maker"). Printing the backing is the initial step performed by The Maker. The first paper that came off of this manufacturing line was a batch of 320-grit garnet sandpaper in 1997. A number of the upcoming steps will show parts of The Maker.Continue to 2 of 10 below.
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Adding the Grit to be Applied
The grit to be applied to the sandpaper is poured from bags (that are purchased from outside sources) into a hopper.
There are various types of grit used in different types of sandpaper. For instance, many hand sandpapers are made using garnet or aluminum oxide, while many abrasive papers used for power sanders are manufactured using black zirconium (which is basically the same material that cubic zirconium faux-diamonds are made from).
Surprisingly, this sand grit in the hopper feels far smoother... than it does on the sandpaper. The above picture is of some 120-grit abrasive, but it literally feels almost silky in the raw form.Continue to 3 of 10 below.
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Applying Resin to the Sandpaper
In order to add the grit to the paper, a resin must first be applied to the paper. The printed paper is fed through a vat containing the chosen resin in the image above.
There are a few different resins that are used in the manufacturing of sandpaper, but the two main types are urea resins, used for hand sandpapers, and phenolic resins for power sanding. Phenolic resins hold up much better to the heat generated by power sanding.Continue to 4 of 10 below.
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Adding the Grit to the Sandpaper
With the resin applied, the paper is ready for the grit to be applied. This is probably the most interesting and critical step of how sandpaper is made. One might expect that the grit is simply sprinkled evenly onto the paper, but in actuality, it is a bit more high tech.
The grit is sprinkled onto a conveyor belt that is electrostatically-charged, which in turn gives the grit a static charge. As the conveyor moves along, the resin-coated paper is brought down across a roller about two inches... above the conveyor. Because of the difference in the static charges, the grit literally leaps upward onto the resin-coated paper. More impressively, because the heaviest part of each uniquely-shaped grain carries a stronger charge, the thickest part of each grain is embedded into the resin, leaving the sharpest edge of each grain exposed.Continue to 5 of 10 below.
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Drying the ResinAfter the grit is applied to the paper, the entire roll is run through a huge oven. The long strip of paper is literally draped over a series of arms (see the image above) that will slowly carry the freshly-created sandpaper through a long oven. The temperature in this oven is closely monitored, and the draped paper is taken down one side of the oven, then back up the opposite side. The entire drying process takes less than an hour to dry the resin and bond the grit to the paper.Continue to 6 of 10 below.
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Adding a Second Coat of ResinAfter the sandpaper has dried in the oven, a second coat of resin is applied and then dried.Why, you might ask?By adding a second coat of resin to the paper, the grit is coated with resin, which will give it much longer life when in use than would occur without the second coat of resin.Continue to 7 of 10 below.
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Flexing the SandpaperOnce the sandpaper has had a second coat of resin applied and dried, the entire roll is next run through a machine called a flexer (see the image above). This is basically a series of rollers designed to loosen up the resins a bit without removing the grit from the paper. The result is a much more pliable sandpaper.Continue to 8 of 10 below.
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Applying the Backing
After flexing the sandpaper, the final manufacturing step before cutting and packaging is to apply any required backer to the sandpaper. For instance, many random orbit sanders utilize a hook-and-loop fastening system. It is during this step that the fabric backing for the hook-and-loop fastener would be applied to the sandpaper.Continue to 9 of 10 below.
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Printing the PackagingContinue to 10 of 10 below.
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Cutting and Packaging
The final step in how sandpaper is made is cutting and packaging.
Once the finished four-foot wide roll of sandpaper is completed, it is delivered to a cutting machine where the end product is cut and packaged. In the picture above, random orbit sanding disks are cut and packaged. The cutting machine will actually accommodate a number of rolls at one time, making packaging easier. For instance, if a finished package contains five random orbit disks of varying grits, the cutting machine operator... would install five rolls of the required grits onto the machine, and the five sheets would roll off into the machine stacked on top of one another to be cut all at once. This makes it easy for the operator to simply remove stacks of five disks at a time, as seen above.
In the case of other products, such as belt sander belts, there are additional steps to be taken. However, for most products that don't require additional manufacturing, the process is similar. Add the prescribed number of rolls to the cutter, run through the cutter and remove stacks from the back side, placing them into finished packages and into boxes for shipment.