Popular Woodworking 2009-10 № 178, страница 51

lightest and most flexible and "F" being the heaviest paper. Lighter paper is more flexible, but it also can tear more easily. Heavier paper can be more durable, but it can be stiff depending on the glue used and how the sandpaper is made.

The sandpaper at Ali Industries is "C" weight. Gary Carter, the senior director of sales, says C-weight paper is a premium weight that they've treated to get good performance when hand and power sanding.

The paper is in giant 55"-wide rolls and can vary in length from 180 to 500 meters. It begins unspooling on a large horizontal spindle and is pulled first into a large print-

ing press. There the grit number, the brand name and other information is printed on it - then it's baked with ultraviolet heat so it's instantly dry.

Glue, Grit Then Baking

From the ultraviolet heater, the paper gets its first coat of glue, which can be a phenolic resin (for sanding discs and belts) or a urea resin, for hand-sanding sheets. During our visit, the resin was a pure red and looked like the Plasti Dip stuff that some homeowners coat tool handles with.

The paper descends into the resin on a giant roller that dips the unprinted side into the bath and rolls it immediately upward. From there the flypaper-like stuff rolls into a little room where the magic trick occurs.

Roll it out. Here you can see the 55" rolls of paper as they are fed into a printer that inks the grit and brand on the backside of the paper.

A pot of glue. The red stuff in the tray is the resin. The glued paper travels up out of the tray and into the room where it gets its grit.

In a low-ceilinged room under the giant rolling machines the glued paper is brought down parallel to a conveyor belt - about 1" above the conveyor. On the belt is the loose grit, which could be anything from garnet to aluminum oxide.

At a certain point on the conveyor, the grit is statically charged and it leaps (yes, leaps) up and embeds itself in the resin on the paper above it.

Carter explains that the static charge does two things: One, it causes the stuff to jump in the air. Two, it makes the individual particles orient themselves so the blunt part of the grit becomes embedded in the resin and the sharp point is facing your work.

You can see the grit jumping up into the resin, which is a bit mesmerizing. Any excess grit (there isn't much) is captured at the end of the conveyor.

It's officially sandpaper now, but the resin is still wet so the roll of paper has to go into an oven to be baked. The oven looks a bit like a huge taffy puller. Giant mechanical arms loop the paper up and down like ribbon candy and move steadily through the warmed room to the end and back.

More Glue, More Baking

After the resin is somewhat cured, the paper is coated with another layer of resin, which improves the durability of the paper (only the cheapest sandpaper has one layer of resin). Then it's baked again and spooled back into

Jumping oxide! The stuff on the top rollers is the paper with the resin. The conveyor below it carries the grit. When the grit reaches a certain point it jumps up and embeds itself in the resin.

Enormous oven. The paper, grit and resin all come into the oven on arms that fold the stuff in undulating curves through the warmed rooms.

64 ■ Popular Woodworking October 2009