Prepping A Car for Finishing

Body Shop Business published a great article about car refinishing a few years back. The mindset that car refinishing is easy seems to be spreading throughout the industry. But there are no shortcuts to perfect paint jobs, and thorough prep work is essential to a lasting, quality repair.

No Scuff ’n Shoot Here
by Nathan Tarr

Clean, Clean, Clean
Many times I’ve observed a refinish tech pull a job into the paint shop, pull out a DA and go to town on the car. And I cringe every time I see it. Why? Because they’ve violated what I consider the golden rule of prep work: Always work with a clean surface.

There are many contaminants on a car’s existing finish, and every paint company makes several types of cleaners to get these contaminants off. The first thing all refinish techs should do to any car they work on is spray it down with their chosen paint company’s waterborne cleaner. Wipe off the cleaner using clean towels, making sure you’re actually cleaning the panel and not just smearing around the gunk. These waterborne cleaners are designed to rid the panel of nasty stuff like bird droppings, bug guts and grubby body tech fingerprints.

You’ll also want to use some solvent-based cleaner on the panel and clean it again. When you just start sanding on an unclean surface, you’re just grinding all that wax and gunk into the paint, which will ultimately result in a repair that just doesn’t last.

R-E-S-P-E-C-T
Technicians generally don’t have to deal with customers, so we usually don’t have a personal connection with the cars we’re working on. As a result, it’s pretty easy to become thoughtless with other people’s property. But as professionals, we all need to treat these cars in a professional way. Before you go slopping up a customer’s interior, close the windows and cover up any openings that allow dust and sanding goop to go where it doesn’t belong. It’s also a good habit to protect the panels next to the ones you’re sanding with masking tape instead of relying on your extreme skill with sandpaper. The extra time you spend protecting the customer’s car will be nothing compared to the time it’ll take you to fix an extra panel you damaged after zoning out.

Inspect the Damage
The car is clean and protected, but you’re still not ready to get on with this “scuff and shoot” just yet. Now is a good time to check over the body technician’s work. I make sure the repair looks right and is finished in the appropriate grit. Most primers are made to fill 180 grit scratches, so an 80 grit repair is unacceptable in my mind. Yes, my primer will fill the coarser grits, but only for the time being. In most shops, it isn’t standard operating procedure to take care of primer shrinkage three months after the car is delivered to the customer. Now is the time to give the body tech a second chance to finish his repair…

To read the complete article, please visit Body ShopBusiness.com

Why do some woodworking shops use Silicon Carbide paper wide belts?

We’ve been supplying sanding belts to the woodworking industry for 29 years now and the “traditional” belt recommended for wood sanding has always been an aluminum oxide, open coat belt.  It is the most common, all-purpose woodworking abrasive, and for good reason. It is the only abrasive mineral that fragments under the heat and pressure generated by sanding wood. This characteristic is called friability and is highly desirable. As you sand, aluminum oxide renews its cutting edges constantly, staying sharp and cutting much longer than other minerals. Aluminum oxide is also a relatively tough abrasive, which means that its edges won't dull much before they fragment. Its friability and toughness make aluminum oxide the longest lasting and the most economical mineral for wood sanding applications.

But sometimes life or price isn’t the determining factor.  In recent years, higher end woodworking plants have started to incorporate Silicon Carbide paper-backed belts into their wide belt finishing line. Why, you ask? Well, here are some of the properties of a silicon carbide paper belt that are beneficial to woodworking:

1. Different types of abrasive minerals will stain differently. The same grit belts of Silicon Carbide will stain differently than Aluminum Oxide, with a lighter color gradient than when sanded with the traditional Aluminum Oxide belts.
   
2. Silicon Carbide is sharper than Aluminum Oxide, and is effective at removing the “hairs” that is the result of the wood fibers being bent instead of cleanly cut by an Aluminum Oxide belt. These fibers then “stand up” after staining and contribute to a blotchy finish.  Common practice is now to belt sand with Aluminum Oxide in your coarser grits, and then switch to Silicon Carbide for your finer grits to eliminate any fuzziness that was created by sanding with the AO belts.
3. Paper backed belts have a flatter substrate, so the grain height is much more exact over the whole surface than cloth backed belts.  All of the grit starts and ends at the same height—you don’t have the potential for variation like you do when some of the grain sits on top of the cloth threads versus in between the cross-hatched woven cloth threads.
4. Finally, paper belts run cooler—they dissipate the heat more effectively than cloth belts. And less
   heat=less glazing of the mineral as it wears down & higher quality cutting, which contributes to a finer finish.

Basically, it comes down to finish. Silicon Carbide belts may not last quite as long, and they usually cost more than Aluminum Oxide belts—but they are the preferred wide belt for final finishes in a lot of professional cabinet shops and furniture manufacturers!

Interested in ordering sanding belts?. Just give us a call at 800-814-7358 or contact us through our website.

Are you interested in grinding welds with a flap disc?

Overlap flap discs grind like a depressed center wheel and blend like a fiber disc all in one operation, reducing production time and lowering costs.

Premium closed coat blue Zirconia abrasive flap discs are the best all-around overlap disc capable of fast cutting, long life and superior finish. Backing is made from non-flexible consumable fiberglass.Choose from either standard density or the thicker, high density Xtreme disc. Use in place of a grinding wheel or fiber disc on a right angle grinder for stock removal, grinding and blending of welds, castings and other metal finishing.

Choose from Type 27 flat discs that are designed for finishing on flat surfaces and used at up to a 15 degree angle or the Type 29 conical discs, which are to be used at a 15 - 25 degree angle and are the best choice for speed and maximum stock removal.

Please go to the Overlap discs on our website and find the size that works for your grinder.

Please watch this great you tube video by Kevin Caron on how to use these flap discs . . .

You can "Reclaim" your used Resin Fiber Discs

Are you tired of paying $2.00 and $3.00 for a 7" x 7/8" zirconia or ceramic fiber disc and only using the outside inch or two in your shop? It’s such a waste of money…

Don’t you wish there was an easy way to cut them down so you could “reuse” the disc on a smaller 4-1/2” or 5” grinder? Less waste and better for the environment…

Now there is a way! Abrasive Resource will laser cut your used fiber discs into smaller sizes and ship them back to you so you can reclaim them for another grinding cycle…

          ~  Most heavy grinding occurs on the outside periphery of a 7 x 7/8 resin fiber disc.

          ~  After this “first” use, discs can be boxed up and sent to Abrasive Resource to be laser 
              resized with Laser Blade technology to 4-1/2” x 7/8” or 5” x 7/8” grinding discs.

          ~  Your reclaimed discs are shipped back to your plant within 2 weeks—freight paid.

          ~  Cost is based on order volume and starts at $.50 a disc with a 1000 piece minimum 
              order.

 For more details or a custom quote, give us a call at 800-814-7358.

Eliminating chatter marks when wide belt sanding wood

Chatter marks are the most common sanding defect and problem when widebelt sanding wood and can come from different sources. Common causes and solutions are:

• If the marks are uniformly spread across the board, the rollers being out of balance can cause the problem, or the bearings may be worn. The rollers may have become “oval” or the pad, where fitted, may have become stuck.

• Another cause can be vibration caused by poor machine mounting or loose foundation plates. The spacing between the chatter marks will indicate whether it is the contact roller or a defective abrasive belt.

• Splice marks are similar to chatter marks but are caused by a poor belt splice. There is a difference between the frequency of marks caused by a splice and chatter marks from a roller. To see if the marks are from the drum or the splice, sand two workpieces, one at a fast conveyor speed, and the other at a slow conveyor speed. Compare the marks; if the marks are similar it is chatter from the drum. If the spacing of the marks is different, the abrasive belt splice causes them.

• Make sure your contact roller has the proper rubber hardness (durometer) for your application. Experts recommend a durometer of 60 for most sanding applications. Harder contact rollers will take off more material but they are also less forgiving increasing the likelihood of unwanted marks.

• Use a platen for finish sanding. The platen will sand less per pass and also spreads the sanding over a larger surface area because it is actually wider than the contact roller. Running your material through a couple of times during the finishing process with the platen activated should give you a nice smooth finish.

• Slow it down – Running your conveyor belt slower will allow more time for abrasive sanding to remove the chatter marks.

• Other actions to cure chatter include: Use an abrasive belt with a butt splice; replace the contact drum bearings; replace the drive motor bearings; tighten the drive belts; replace or dress the contact drum; balance the contact drum; check the conveyor bed drive coupler/drive belt; and relieve tension from the abrasive belt when it is not in use to avoid flat spots on drums.

To read the original blog post, please check out the Woodworking Network.

For sanding belts from Abrasive Resource, please check out the Sanding Belts on our website.

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
aaaaaaaaaaaaaaaaaindustrial abrasive.
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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.