Diamond blades are tensioned by the manufacturer to run true at the recommended rpm, which is stamped on the blade. Tensioning is designed to keep blades from distorting at high speeds. The blade is manufactured in the form of a dish that will straighten when the blade is rotated at optimum speed. The dishing is small, about 0.0005 inch per inch of diameter. The tensioning can be accomplished by a mechanical roller tensioning machine or a hammersmith. This process is especially critical for blades of larger diameter (more than 24 inches).
If the design speed is not achieved, the blade will tend to wander as cutting begins. When a blade is said to be out of tension, the amount of dish is not correct. Such a blade wobbles while out of the cut, and it wanders when placed in the cut. An out-of-tension blade cannot be made to cut a straight line.
MACHINE DRIVE POWER
Another factor to consider when optimizing the cost-effectiveness of any diamond blade is the amount of power available to a blade. This also has an effect upon tool performance. Operating a machine with less power than is required can result in blades that will polish or glaze over, resulting in slow cutting speeds.
Machine power requirements for typical concrete cutting machines are:
Application Power requirements: Flat saws 8 to 100 hp and Wall saws 10 to 35 hp
To provide the proper cutting tool, a saw blade manufacturer must know the maximum horsepower of the machine. Generally, but not always, blades with soft bond segments will break down faster if used with high horsepower equipment. On the other hand, blades with hard bond segments cut better when used on high horsepower equipment.
Diamond cutting tools require that pressure be applied for maximum performance. Sufficient pressure must be applied to maintain sharp cutting crystals. If too little pressure is applied, the diamond crystals are likely to become dull and polished. Conversely, too much pressure can also damage the diamond-cutting tool.
MATERIAL TO BE CUT
Knowing as much as possible about the concrete can be of enormous benefit to the cutting operator and the tool manufacturer. To recommend a blade, a manufacturer must know the type of aggregate to be cut and if rebar will be present. Limestone or coral aggregates are relatively soft and abrasive, providing little problem for the diamond blade to cut. Concrete with river gravel or quartzite aggregate is of medium difficulty to cut. Flint or granite aggregate generally is considered among the most difficult to cut.
Aggregate size also can affect the cutting performance of a diamond blade. Concrete aggregates often range from 1/2 inch to 2 inches. Concrete made with 2-inch flint aggregate will be extremely difficult to cut, but concrete with 1/2-inch flint aggregate may be cut more easily. This is because there is more coarse aggregate per unit volume of concrete than when a larger, maximum-size aggregate is used.
The type of aggregate has a pronounced effect on blade wear, and hence life. Hard aggregates shorten blade life and slow the cutting rate so cutting concrete with a hard aggregate will cost much more than cutting concrete with a soft aggregate. Cutting concrete made with hard aggregates also requires more power. If there is not enough power, bit speed or blade speed should be reduced.