Selection of Grinding Wheel

How To Specify a Grinding Wheel

To specify a grinding wheel requirement, it is important to follow the following steps: 

Standard Wheels: 

1. Specify the wheel size by quoting in mm the overall dimension of 

Diameter x Thickness x Bore 

The diameter and thickness can be specified in nominal dimension whereas the bore diameter should be indicated to the closest two decimal places. 

E.g. 400 x 53 x 127 mm 

2. Indicate the type and shape of the wheel face. 

3. Specify wheel grading. 

Customised Wheels: 

1. Specify the dimensions in the order of 

Diameter x Thickness x Bore 

2. Mention the type of wheel required. 

3. Indicate the recess size and depth for types 5 & 7 wheels (ROS & RBS) 

4. Indicate the shape of the wheel face, if it is applicable 

5. If the dimension has special tolerance of diameter, thickness or bore, this needs to be indicated. 

6. Specify wheel grading. 

7. A detailed drawing of the wheel to be provided. 

Grinding wheels can be manufactured in a wide range of standard shapes or customised to different application requirements. For ease of selection, refer to the list of Standard Grinding Wheel Shapes.

Wheel Selection

Available in standard sizes or customised to specific grinding applications, wheels are manufactured to suit the grinding needs of all customer requirements. Since there are as many types of wheels as there are grinding applications, correct wheel selection is of critical importance.

Factors affecting the Selection of a Grinding Wheel 

Wheel selection is dependent on the kind of material to be ground and the type of grinding operation. The eight important factors that need to be considered in the selection of a grinding wheel are: 

Material to be ground and its hardness:

The choice of abrasives, their grit size, and their grade are determined by the type of material to be ground. For grinding tough or highly tensile materials like alloy steel, high speed steel, annealed malleable iron, and other ferrous metals, aluminium oxide abrasives are best. 

Cast iron, bronze, aluminium, copper, and other non-metallic materials with low tensile strengths are suitable candidates for grinding or cutting using silicon carbide abrasives.

The choice of wheel grades is also determined by material hardness. Harder grade wheels are suggested for soft, readily penetrated materials for best performance, while softer grades work best for hard materials.

Stock removal and surface finish:

The size of the abrasive and the kind of bond also affect how much stock must be removed and how smooth a surface must be. Coarse grit wheels are utilised when an operation necessitates high stock removal rates, such as in fettling. Exquisite grit wheels, on the other hand, are the best choice for achieving exceptionally tight surface tolerances and fine geometric finish. 

For tasks requiring fine finishes, resinoid, rubber, or shellac bound wheels are typically advised.

The grinding process - wet or dry: 

Whether the operation is wet or dry affects the wheel's grade. Soft grade wheels should be used while dry grinding with vitrified wheels to reduce the amount of heat produced. These may be at least a grade or two softer than the ones selected for wet grinding operations. 

Harder grade wheels can be utilised in wet grinding operations where coolants lower the heat.

Peripheral speed of the wheel:

The "Peripheral Speed" of the wheel refers to the speed at which the grinding edge of the wheel crosses the work surface. This is a crucial consideration when choosing a grinding wheel. 

For typical vitrified wheels, the top working speed is 60 m/s. This is noted on the blotter or the wheel's face. Most applications requiring a speed of up to 48 m/s employ organically bonded wheels (made of resin, rubber, or shellac). For reinforced goods, higher speeds can reach 100 mph. Wheel toughness decreases as wheel speed decreases.

The area of grinding contact - large or small:

The choice of wheel grade and grit size is influenced by the area of grinding contact. When it comes to wheel grade, it is customary to utilise softer grade wheels where there is a larger area of grinding contact and harder grade wheels where there is a smaller area of grinding contact. 

For instance, coarse grit, open structure wheels are suggested for surface grinding when the grinding area is big. On the other hand, fine grit, closer structure wheels work best when used in smaller, more precise contact regions, such cylindrical grinding operations.

The grinding application:

The pressure of shock loads, heavy feeds, fast work speeds and traverse rates, and intermittent grinding contact can all contribute to how difficult a grinding process is. As a result, the grinding process affects the choice of abrasive type, grade, and even kind of bond when choosing a wheel. 

The harder the wheel grade needed and the rougher the abrasive that needs be utilised, the more severe the grinding process. For example, a harsh abrasive like A or ZA is needed for demanding grinding operations like snagging. Precision grinding operations are best suited for medium- and soft-grade wheels.

Condition of the grinding machine: 

Poor machine conditions are the cause of a lot of grinding errors. These can include faulty machine alignment, an insufficient foundation, loose bearings, unequal or incorrectly spliced belts, belt slippage, worn gears, and general machine vibration. It is crucial that all grinding machines be fastened or mounted on flat, sturdy foundations.

The type of grinding machine:

The type of grinding machine is a crucial consideration when choosing a grinding wheel. The kind of equipment you use depends on the wheel and grinding process. It is crucial to select the right wheel for the application and the machine.

a. Machine Power (Kw): 

Machine power is another crucial consideration. This has a significant impact on the stock removal rate. The speed of the grinding wheel and the cutting power will both decrease in proportionally if the motor power is insufficient. Increased heat and excessive pressure between the wheel and the workpiece may result from this. A wheel of a tougher grade can be employed for more effective functioning if the machine's power is high.

b. Machine Speed: 

It is important for the user to make sure that the maximum rpm listed on the wheel and the machine are compatible. The user must never go faster than the permitted speed restrictions. Wheels should have a locking device installed to prevent them from going faster than the declared maximum permitted speed on machines with variable rotational rates.