factors affecting selection of grinding

  

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factors affecting selection of grinding 

Ans.: Selection of Grinding Wheels Wheels.

The proper selection of grinding wheels is Very Important for obtaining better finish and at the same time having more life of the wheel. In order to meet all these requirements, the various factors that influence the selection of grinding wheels

must be considered.

Wheel selection is also depend on type of material to be ground and the type of grinding operation. The important factors that need to be considered while selection of a grinding wheel are as follows:

• 1. Material to be ground and its hardness.

       Material to be ground and its hardness: The type of material to be ground determines the selection of abrasives, its grit size and grade. Aluminium oxide abrasives are ideal for grinding hard or high tensile materials such as alloy steel, high speed steel, annealed malleable iron and other ferrous metals. Silicon Carbide abrasives are excellent for grinding or cutting law tensile strength materials such as cast Iron, bronze, aluminium, copper and other nonmetallic materials. While choosing the grit size, the hardness of the material is a major determining factor. While finer grit wheels are required for hard and brittle materials, coarser grit wheels are ideal for soft and ductile materials. Material hardness also dictates the choice of wheel grades. For optimum performance, harder grade wheels are recommended for soft and easily penetrated materials while softer grades are ideal for hard materials

• 2. Stock removal and surface finish.

Stock removal and surface finish: The amount of stock removal and the degree of surface finish required also depends on the abrasive size and the type of bond. When an operation demands high stock removal rates, as in fettling, coarse grit wheels are used. Whereas, fine grit wheels are ideally suited to achieve extremely close surface tolerances and fine geometrical finish. Resinold, rubber or shellac bonded wheels are usually recommended for operations that require fine finishes.

• 3. The grinding process-wet or dry. 

Grinding Process Wet or Dry: The grade of the wheel is influenced by whether the operation is wet or dry. During dry grinding with vitrified wheels, in order to minimize the heat generated, soft grade wheels should be used. These can be at least one or two grades softer than the ones chosen for wet grinding operations. In wet grinding applications, where coolants reduce the heat, harder grade wheels can be used.

• 4. Peripheral speed of the wheel.

Peripheral Speed of the Wheel: The speed at which the grinding edge of the wheel passes the work surface is called the 'Peripheral Speed" of the wheel. This is a very important factor in grinding wheel selection. The maximum operating speed for standard vitrified wheels can be up to 60 m/s. This is indicated on the blotter or on the face of the wheel. Organically bonded wheels (resinoid, rubber or shellac) are used for most applications where the required speed rate is up to 48 m/s. Higher speeds for reinforced products can go up to 100 mps. Reducing the wheel speed reduces the wheel hardness.

• 5. The area of grinding contact-large or small.

 Area of Grinding Contact Large or Small: The area of grinding contact influences the selection of wheel grade and grit size. As far as wheel grade is concerned, it is normal practice to use soft grade wheels where the area of grinding contact is large and harder grade wheels where the area of grinding contact is small. In surface grinding, for instance, where the area of grinding is large, coarser grit, open structure wheels are recommended. Conversely, fine grit, closer structure wheels are ideal for use in narrower and close precision areas of contact, as in cylindrical grinding operations.

• 6. The grinding application.

The grinding application: Severity of a grinding operation can be due to various factors such as, the pressure of shock loads, heavy in feeds, high work speeds and traverse rates and intermittent grinding contact. Hence, for wheel selection, the grinding operation influences the choice of abrasive type. grade and even type of bond. The greater the severity of the grinding operation, the harder the grade of wheel required and tougher the abrasive that should be used. For example, for severe grinding operations, like snagging, a tough abrasive like A or ZA is required. Medium and soft grade wheels are ideally suited for precision grinding jobs.

• 7. Condition of the grinding machine. 

Condition of the Grinding Machine: Many grinding faults can be traced to poor machine conditions. These can vary from loose bearings, uneven or improperly spliced belts, belt slippage, worn gears, wrong alignment of machine. inadequate foundation or general machine vibration. It is very important that all grinding machines must be installed or fixed on flat and strong foundations.

• 8. The type of grinding machine used.

The Type of Grinding Machine used: A very important factor in a grinding wheel selection, is the type of the grinding machine. The type of wheel and grinding operation defines the type of machine to be used