2016年2月3日星期三

Grinding wheels

Grinding wheels are made of natural or synthetic abrasive minerals bonded together in a matrix to form a wheel. While such tools may be familiar to those with home workshops, the general public may not be aware of them because most have been developed and used by the manufacturing industry. In this sector, grinding wheels have been important for more than 150 years.
For manufacturers, grinding wheels provide an efficient way to shape and finish metals and other materials. Abrasives are often the only way to create parts with precision dimensions and high-quality surface finishes. Today, grinding wheels appear in nearly every manufacturing company in the United States, where they are used to cut steel and masonry block; to sharpen knives, drill bits, and many other tools; or to clean and prepare surfaces for painting or plating. More specifically, the precision of automobile camshafts and jet engine rotors rests upon the use of grinding wheels. Quality bearings could not be produced without them, and new materials such as ceramic or material composites would be impossible without grinding wheels to shape and finish parts.
Sandstone, an organic abrasive made of quartz grains held together in a natural cement, was probably the earliest abrasive; it was used to smooth and sharpen the flint on axes. By the early nineteenth century, emery (a natural mineral containing iron and corundum) was used to cut and shape metals. However, emery's variable quality and problems with importing it from Indiaprior to its discovery in the United States prompted efforts to find a more reliable abrasive mineral.