The grinding wheel market is vast, but seven application factors can help users reduce the market to the grinding wheel they need.

Abrasive grains are available in a variety of particle sizes and binders. To determine which wheel is suitable for the job requires consideration of seven key factors:

The first thing to consider when selecting the size of the grinding wheel is the type and hardness of the workpiece material. Is the material easy to grind or hard to grind? The relative ease of grinding is the main predictor of the appropriate abrasive type, particle properties, abrasive particle size, and binder type to be applied.

Conventionally, alumina particles are used for grinding ferrous metals, and silicon carbide particles are used for grinding non-metal and non-ferrous metals. Ceramic and superabrasive particles are compatible with all three types of materials, but are usually used in specific situations where alumina and silicon carbide are not performing well.

With the determination of the particle type, the grindability of the material determines many other necessary attributes of the grinding wheel. If the material is easy to grind, use tough and durable particles. Since the material is easy to grind, grains should not be broken down too early or too easily, so whole grains can be used to maximize the life of the grinding wheel. Coarse gravel is best for these materials because the particles can easily penetrate the material and remove the material to the maximum. A harder grade (ie, a harder bond between the particles and the grinding wheel) also corresponds to easier grinding, because the bond prevents the grinding wheel from releasing the particles before they are consumed.

For materials that are difficult to grind, reverse these recommendations. Mild, fragile grades perform better on these materials because they break more easily and stay sharper. The finer particle size improves the ability of the particles to penetrate hard materials and form chips. Because abrasive particles can become dull and cause metallurgical damage, for example, if left for too long, a soft grade is required to release the dull particles and expose the material to sharper particles.

Users should also consider grinding pressure or force per grain. The higher the pressure and the stricter the operation, the better the performance of ceramic and superabrasive particles may be. The severity of the operation also helps to determine the properties of the abrasive particles.

Tough and durable grains can withstand higher pressure and will not decompose prematurely. Coarse abrasives also help the grain to withstand the grinding pressure. Sometimes it may be best to distribute the pressure over more cutting points, but even in this case it needs to be balanced to prevent the pressure from turning finer particles into dust. Heavy pressure also requires a harder grade, so the particles can stay on the grinding wheel long enough to perform the required grinding work.

In contrast, mild, fragile grains perform better in light pressing operations, because durable grains will only rub and darken. The finer grain size ensures that the abrasive particles can still fracture and self-sharpening properly, while the softer abrasive particles will release passivated abrasive particles before they start to rub and burn the material being ground.

The unique specifications of different grinding wheels determine their best application. However, factors such as the use of coolant and the horsepower of the grinder can change these optimal applications. All images courtesy of Norton | Saint-Gobain Abrasives.

Grinding wheels are ubiquitous because of their speed, shape repeatability, and ability to achieve the desired finish. When choosing a grinding wheel, it is important to determine whether the application requires fast cutting or finishing. Also important is whether the part is simple and flat, or whether there is a shape that can be fixed.

The required surface finish, dimensional tolerances, shape retention requirements, and cutting rate will affect the appropriate abrasive particle size, grade, and bond type.

For low Ra surface treatments or tight geometric tolerances, finer abrasives are helpful because they provide more contact points between the workpiece and the grinding wheel. This helps with precision finishes, with lighter scratch patterns and lower microinch finishes. The finer grains also help to achieve and maintain small radii and complex shapes. In contrast, coarser abrasives can increase the cutting rate. Finding the best balance of abrasive particle size will reduce the cutting cycle time.

Tight geometric accuracy and shape retention require harder grades. The harder grade allows the wheel to maintain its profile longer and ensures that the particles stay long enough to achieve the desired result.

The next suggestion seems contradictory, but a softer bond is best for finer surface treatments and higher cutting volumes. Combined with a softer grinding wheel, it is easy to release dim particles and bring newer, sharper particles into contact with the material. By preventing dull abrasives from rubbing and burning parts during cutting operations, sharper particles can increase the amount of cut and improve the finish. Although the actual finish and cutting rate of this operation mainly depend on the size of the abrasive grains, keeping sharp abrasive grains in the grinding zone is good for both.

Part requirements also determine the type of bonding. Ceramic grinding wheels perform best in terms of close tolerances and shape retention, while organic and resin adhesives are best for reflective and other fine finishes. Organic bonds, unlike vitrified bonds, have a little bit for them. Some grinding force will enter the joint, thereby reducing the chip size. Another benefit of fine grinding is that organic bonds will decompose due to the heat of grinding. They tend to keep the grains longer, making them run and dull. The planned plough and sliding interaction that occurs under these conditions improves the initial scratch pattern formed during the cutting process to produce a finer finish.

The contact area is partly related to the severity of the operation, because it takes into account the contact area between the workpiece and the wheel. When the grinding wheel is applied to the workpiece, the applied force will be distributed on all cutting points in the grinding zone. The larger the contact area, the lower the force of each particle. Conversely, the smaller the area, the higher the force per grain.

Small-area contact operations should use tough and durable particles that will not break or wear prematurely at higher force per particle. Ceramic or super abrasive particles may even be required in these operations. A finer particle size is best for small contact areas, because in addition to providing more abrasive points in the contact area, the relative pressure or grinding force will be dispersed among many particles. High operating forces with a smaller contact area also require harder wheels because they can maintain their shape and prevent premature wear of the wheels.

When the contact area increases and becomes larger, for example, for the Blanchard segment, it is more suitable to use milder grains. Since the number of crystal grains in contact with the workpiece in the grinding zone increases, the force of each crystal grain is lower, and the crystal grains are more likely to fracture and self-sharp. Coarse sand distributes the pressure into fewer particles to ensure that they continue to penetrate into the workpiece. Since the risk of burnt by passivated particles in these operations is higher, a softer wheel grade should be used to release the particles before damaging the part.

The surface speed of the operating wheels can reduce the type of bonding and wheel grade required to complete them. To calculate the surface velocity, use the following formula:

Surface speed (SFPM) = (π × diameter (inch) × RPM) / 12

Surface speed (m/s)=(π×diameter (mm)×RPM)/60000

The wheel speed determines which type of bonding is best for the required speed, or whether special high-speed bonding may be required.

The wheel will also take different actions based on its speed. For every 1,000 SFPM (5.08 m/s) change in surface speed, the effect of the wheel will harden or soften. The slower the wheel speed, the softer the performance, because the greater the force of each abrasive grain, the faster the abrasive grains and binders decompose. The faster the wheel speed, the stronger the performance, and the smaller the force of each abrasive grain, the more durable the action of abrasive grains and binders.

Coolant has the opposite effect on wheels with vitrification and organic combination. Its existence makes the ceramic wheel behave softer, while the organic wheel behaves harder.

The coolant in the grinding system has different effects on ceramic and organic (resin) bonded grinding wheels. When determining the grade or hardness of the grinding wheel, its use plan must be considered.

If no coolant is used:

The horsepower of the grinder can play a role in determining the bond grade or the hardness of the grinding wheel.

Since there are many factors involved in determining the initial specifications of the grinding wheel, there will be situations where the factors point in the opposite direction. In this case, please check the orientation of most factors, or prioritize the most important factors in the application. For a simple comparison, please check the chart below:

When deciding on a wheel size for a particular operation, it is important to consider all factors. If these factors conflict, the user may need to select a key factor to determine the final specification.

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