We have already seen that the availability of abrasives currently offered in the market for the operations of, among others, grinding, sanding, grinding, polishing, weld cleaning, burr removal, level, satin Y surface finishing it is extremely broad.
The procedure conventional For these operations it is carried out in multiple stages and consists of using coated abrasives, starting with a coarse grain for the chip removal (roughing) and continuing with a succession of increasingly finer grains that will make it possible to carry out the surface conditioning until finally achieving the finish wanted.
However, if we have already carried out the chip removal and we are missing everything else, it is useful to know that there is a type of abrasive that not only has the property of being less aggressive (contrary to the case of super abrasives or diamonds), but which is also capable of providing us with a much more uniform conditioning and finish in fewer stages, without damaging the workpiece or compromising critical tolerances obtained in previous machining or molding operations.
The abrasives that meet these characteristics are called nonwoven textile abrasivesIt is interesting to note that the advantages they offer are due to the design they present, which allows them to “adapt” perfectly to the surface of the piece. How do they do it? Let’s go by parts.
Structure and cutting action of nonwoven textile abrasives
Like coated abrasives, non-woven materials have a base of substratum (nylon fiber), a binder resin (phenolic or polyurethane) and the abrasive grain (silicon carbide or aluminum oxide). However, the structure that these materials form is different. While in coated abrasives said structure is flat, in nonwovens it is three-dimensional, since they are composed of a network of nylon fibers of variable density linked together by synthetic resins, on whose surface the abrasive grains are impregnated, as we see in the following figure.
East three-dimensional design produces a “cushion” material of open mesh which is extremely flexible, durable and, above all, easily adaptable to any surface, because as the product moves over the part, the open mesh compresses or expands, absorbing part of the force applied to the product -which would otherwise be would transfer to the piece- and allowing the grain to be constantly in contact with the entire surface of said piece. In addition, the uniform dispersion of the abrasive throughout the mesh provides a continuous supply of new grain as the old grain and fibers wear away during use.
This wear mechanism also translates into an advantage. In conventional products, once the grain of the coated abrasives wears away, it changes shape and produces a different scratch pattern on the part. Instead, nonwoven textile abrasives, by virtue of their three-dimensional structure, allow that once the grain wears the substrate to break and the grain is lost to expose a new grain and continue with the same scratch pattern, that is, it produces a much more uniform finish.
However, this is not the only advantage. The fiber and resin of the nonwoven products They are completely waterproof, so the product can be used both wet and dry. The open mesh allows the product to withstand the load and not generate heat during operation, as well as being washable, non-conductive, non-metallic, non-oxidizable and completely flexible.
While conventional bonded or coated abrasives are chosen for their grain size, the nonwoven textile abrasives are specified by grain designations and ranges. This means that when in nonwoven products it is spoken of grain, it refers to the amount of abrasive grain impregnated in the network of nylon fibers. The lower the number, the greater the amount of abrasive grains. If the grains are larger, the cut will be more aggressive and with a rougher finish. If they are smaller, a fine and smooth finish is obtained. Thus, we have the following grain categories in the nonwoven textile abrasives:
Thick (C): 50-80
Medium (M): 100-150
Fine (F): 180-220
Very delicate (VF): 240-360
Ultra thin (UF): 600
Microfine (SF): 1000-1200
Different products for different applications
The nonwoven abrasive products They are available in a number of variants: sheets, rolls, discs, belts and wheels (or grinding wheels), each with a specific application.
Leaves: They are generally 230 x 280 mm rectangles intended for use by hand or with orbital sanders. Available from coarse to microfine grained, they are a good alternative to steel wool for jobs ranging from automotive repair to craft.
The application of nonwoven abrasive sheets covers the aeronautical industry (for example, in the conditioning of titanium parts, such as turbine blades) and finishes in stainless steel products, brass accessories, zamac accessories, jewelry and in the preparation of surfaces for painting wood .
Rolls: If the sanding application covers larger areas, both by hand and by machine, the rolls are more suitable as they are simply cut as needed. They come in various widths, from 100 to 150 mm, and in lengths of 10 m.
Discs: Various designs are marketed and their diameter ranges from 1 to 8 inches. High speed grinders use discs with a hole in the center. Such a thick disc provides an effective means of removing surface contaminants such as rust, residue, corrosion, and weld spatter. These discs can be grouped with spacers to create a wide grinding wheel for burr removal.
Angle grinder discs are used for cleaning, burr removal, harmonizing and finishing, as well as rust and coating removal. Discs featuring a triangular profile combined with holes and backing pads provide a clear view of the cutting surface. This improved visibility allows better control of the process and also the holes in the disk disperse heat.
Bands: They are endless abrasive sections that contain seams at different angles. Those designed for portable, bench and stand sanders are suitable for cleaning, buffing and polishing. They work for both metal and wood.
Wheels: They are used in the jewelry and oil industries and in the manufacture of fittings and accessories, as they allow the removal of small cast iron surpluses, as well as polishing, conditioning, smoothing and polishing surfaces of different hardnesses, shapes and textures. The preferred materials are stainless steel and other metal surfaces.
Wheels are divided into three categories: flap, convolute, and unitized.
The flap wheels They are manufactured by assembling sheets of non-woven material around a central axis and are the best option when a perfect adaptation to the surface is essential or when a brushed finish is desired.
The convoluted type wheels, created by wrapping the non-woven material Around a central core and bonding the layers together, they are easily adapted to match preformed parts. They are used in a single direction of rotation and their applications include jewelery, fittings and bijouterie, among others.
The unitized wheels They are suitable for general cleaning and removal of burrs. They are built by compressing the layers of non-woven textile material and joining them together to form a grinding wheel. They are widely used in the aeronautical and metalworking industries and in the maintenance of equipment with special alloys, among many other uses.
Nonwovens versus common items
The following table shows a summary of some advantages offered by certain nonwoven products on the conventional elements used in the finishing of pieces.