Technology for manufacturing bias buffing wheels has existed for more than half a century. Over time structural variations of this buff have been developed; some methods more costly than others. Regardless, material still represents a significant portion of this buff's cost and functionality. Depending on its dimensions and fabric, material can represent between 30 and 85 pct of a buff's total cost. To understand this more fully, it is important to be familiar with the manufacturing process.
A bias buff can be made from a number of fabrics. See Table I below for the most common materials. A roll of fabric, whether treated or untreated, is bias cut into strips. The ends of the strips are sewn together into a continuous roll. The resulting roll is trimmed to the proper length and width for the next process.
At the "Iris" machine, biased material is wrapped around a large round drum (also called a mandrel, hub or core). The drum size depends upon the desired dimensions and amount of cloth in the buff. Circularly converging steel blades force the fabric into a steel clinch ring in the drum's center channel.
TABLE I -- Bias Buff Fabrics (partial list)
|Material||Thread Count *||Yarn Size **||Uses|
|Cotton Muslin||60||60||20/1||20/1||General purpose cut and color|
|68||72||20/1||20/1||Medium thread count alternative to 60 × 60 and 86 × 80|
|86||80||20/1||30/1||Heavy thread count, longer wear, cut and color|
|Domet Flannel||40||42||20/1||10/1||Very soft, coloring|
* Thread Count is the number of threads lengthwise and crosswise per square inch. These counts (warp and fill) are often added together to get the number of "pics" or threads; i.e. 60 × 60 = 120 "pics" per inch. ** Yarn size refers to the yarn count system. In the yarn count system, the yarn count number is inversely proportional to weight. This system, therefore, is indirect. A 50-count spun yarn has twice the weight (thickness) of a 100-count spun yarn. Thus, 20/1 means that 1 yarn has a count number of 20. Note: The cotton muslin products listed above are untreated and unbleached. Domet Flannel is napped on both sides and is available bleached and unbleached.
* Thread Count is the number of threads lengthwise and crosswise per square inch. These counts (warp and fill) are often added together to get the number of "pics" or threads; i.e. 60 × 60 = 120 "pics" per inch.
** Yarn size refers to the yarn count system. In the yarn count system, the yarn count number is inversely proportional to weight. This system, therefore, is indirect. A 50-count spun yarn has twice the weight (thickness) of a 100-count spun yarn. Thus, 20/1 means that 1 yarn has a count number of 20.
Note: The cotton muslin products listed above are untreated and unbleached. Domet Flannel is napped on both sides and is available bleached and unbleached.
The Iris is named for the motion of the blades. This motion is similar to a camera shutter. As the inside diameter or aperture of the blades decreases, the material around the drum is folded in half and evenly pushed into the center channel. The teeth of the clinch ring are pressed into the fabric. The resulting buff has a pleated or "puckered" face.
By using biased muslin in this configuration, all thread ends are exposed to the buffing surface at a 45 degree angle forming a "V". Each thread runs from the periphery of the buff through the clinch ring and back out to the periphery on the other side. This enhances the structural integrity of the wheel while also minimizing fraying and raveling.
The pleats allow airflow through the buff, which cools it and the part surface. The pleats also stiffen the wheel, enhancing cutting capabilities. Additionally, pleating engenders greater compound adherence. The amount of pleating in a buff is dependent upon the yardage in each ply of cloth. Ply refers to the number of fabric layers in the buff's face. Since the Iris's blades fold the material in half, eight layers of drum wrapped fabric are needed to make a 16-ply buff. The more material in the buff, the greater the pleating. A buff's density, pleating number, pack and class number denote the amount of pleating or cloth per ply. Assume you are wrapping material around an Iris machine's drum in order to make a 16-inch outside diameter, seven-inch inside diameter, 16-ply buff. If an 18-inch drum is used, the density of the buff is two (18-inch drum size minus 16-inch outside diameter equals two). If a 20-inch drum is used, the density or pack is four.
By using a larger drum, more biased material is added to each ply of the buff. In the above example, a No. 4 density buff would have more than six linear inches of biased material per drum revolution than a No. 2 density buff. (20 x 3.1416 [p, Pi] = 62.83 linear inches; 18 x 3.1416 = 56.55 linear inches; 62.83 - 56.55 = 6.28 linear inches more material.) In total, this No. 4 density buff has 11 pct more material than the same size No. 2 density buff. The corresponding price differential should also be between nine and 11 pct. Depending on the application, the increased production life of the No. 4 buff may make it worth the added expense. Conversely, buying a buff with more density than required is an obvious waste of money. Thus, matching the right density to the application is critical.
To measure the density of an existing buff, cut one strip of cloth from the buff's first ply or layer. Make sure to cut one complete revolution around the clinch ring. It does not matter how wide the strip is. Next, lay the strip out flat and measure its length. Divide the strip length by 3.1416 (p). The resulting number should estimate the drum size used to manufacture the buff. Subtract the buff's original outside diameter from this estimated drum size to derive the density; i.e., No. 2, No. 4, No. 6. By calculating the density and performing some time studies with various alternatives, you can determine which density or combination of densities maximize productivity.
Because of increasing cost-reduction pressures in automatic and semi-automatic operations, there has been a tendency to equate increased efficiency with a lower buff price rather than a lower cost per finished part. Some companies are experimenting with smaller wheel diameters or fewer plies of fabric per buff in order to reduce costs. Unfortunately, many find that instead of reducing costs they spend more on the overall buffing operation due to more frequent buff changeovers, reduced finishing capabilities that cause longer dwell times and more rework.
Buffing is a chemical and mechanical action. Regardless of the cloth used, cotton, sisal, wool, polyester/cotton blends, a buffing wheel acts primarily as a carrier of abrasive compound to the part's surface. Thus, for developments to be beneficial, they must enhance the buff's carrying capability or increase the time that compound can effectively be carried. A truly improved buff must cut and/or color faster for longer periods achieving the same or better (consistent) results for less money per finished piece. Therefore, arbitrarily reducing fabric content to lower costs may be self-defeating.
Thread count, fiber composition and stiffness affect the abrasive carrying capability of a fabric. Cotton muslins, as well as other fabrics, have alternating warp (lengthwise), fill (crosswise) and threads (yarns). Table I above delineates some of the characteristics of popular thread count materials.
Thread ends act like tiny brushes, particularly in the coloring operation. Therefore, the number and thickness of a fabric's threads help determine its function. For example, 80 by 80 muslin has finer (thinner) threads. It is often used for coloring but almost never for cutting. Some manufacturers are experimenting with higher thread count materials, such as 200 "pics" per inch (warp threads plus fill threads equals the number of pics) to further utilize the brushing capabilities of fiber ends.
Fiber composition is another critical factor. For example, polyester/cotton blends are being used more frequently in automatic mush buffing applications. These blends can reduce the amount of lint created in automatic operations as well as provide an excellent finish. Unfortunately, they cannot be used for higher surface speed applications because polyester has an inherently lower tolerance to frictional heat. Polyester can begin to melt causing a glazing effect. The buff will not hold compound properly. If the polyester hardens, it can leave fine scratches on a surface.
With regard to stiffness, fabric treatments alter the durability and abrasive carrying capability of traditional materials. However, these treatments are costly and the resultant buff's are normally more expensive than untreated counterparts. There are two treatment categories, mill and dip. Mill treatments are applied to the fabric by a contract textile finisher or bleachery prior to biasing. The material is then converted into a buff just like an untreated fabric. Mill treatments can be applied to a variety of thread count materials. However, 86 by 80, 68 by 72 and 60 by 60 cottons are the most common.
Mill treatments have a plethora of color varieties. Some are related to specific buff manufacturers. A few are standard throughout the finishing industry. Unifirm is a colorless starch treatment often used for cutting aluminum, steel and stainless steel. Yellow (sometimes called Maize) is another starch-based treatment used for cutting brass, bronze, copper and aluminum. There are also wax-based treatments that increase a fabric's compound retention and lubrication in addition to stiffness. These treatments come in many colors. They are also used for cutting applications with brass, bronze, copper and aluminum.
Dip treatments are applied to the material after it has been converted into a buff. A completed buff is immersed into a vat of chemical solution. One can differentiate a dip treatment from a mill treatment by examining the thread along the bias seam. If the seam is the same color as the buff material, it usually indicates that it was dipped. Stains on the clinch ring are indicative of this type treatment. Also, the coloring of the cloth tends to be less uniform. Although a variety of stiffness levels are available, dip treatments often feel firmer than mill treatments.
Buff manufacturers have created an entire color spectrum of dip treatments. However, they are usually classified as either water- or solvent-based. Solvent-based treatments build upon the prolonged life advantages offered by mill treatments. Cutting applications, particularly in automatic operations, are positively affected. Unfortunately, many of the most effective solvents are being phased out in compliance with environmental regulations. Therefore, water-based treatments have been and are continuing to be developed and refined.
One problem with water-based treatments is that they add difficult variables to the process. The fabric layers of a water-based-treated buff can adhere to one another, inhibiting airflow. Solvents evaporate more quickly, avoiding this problem. However, manufacturers are already overcoming these obstacles.
Recent developments include buffs with combinations of materials, such as a combination of 60 by 60 with 86 by 80 thread count muslins. Mixing certain materials in the proper proportions as dictated by the application allows manufacturers to specifically design a buff to match buffing requirements and other parameters.
Assume you want a buff with both good cut and color capabilities. Perhaps a combination buff with 86 by 80 Unifirm mill treatment and 86 by 80 untreated muslin would be a cost-effective product. A myriad of possible fabric combinations can be designed for each specific requirement. This trend towards specialization is again driven by cost-conscious automatic and semi-automatic operations. As with buff density, the objective is to customize the buff so that the optimal buff cost/performance benefit point is attained.
Improvements in material capabilities will continue. However, some may take place at the molecular level. Individual fibers are formed from tangled molecules. These fibers are spun into yarns. Rather than use chemical treatments, which tend to be random in nature, an ideal method for improving the fabric would be to reorganize the actual molecular structure so that the fabric has the specific characteristics desired. Imagine a material with enhanced strength and higher resistance to frictional heat. The feasibility of molecular nano-technology in textile fabrics is currently under review, and developments show great promise.
Nanotechnology combines the principles of chemistry, physics, mechanical engineering and computer science. It is essentially an activity where molecules are organized in controlled, specific reactions. Using specialized biological components as mechanical devices, an assembly system can be devised where a material's molecules are altered. Therefore, a textile fabric's characteristics can be custom designed at the molecular level inherently enhancing its capabilities. In the coming years, patented designer fabrics with specialized characteristics should change the mechanical finishing industry.
The author wishes to acknowledge the work of David R. Forrest in Molecular Nanotechnology