Key Factors in Choosing a Grinding Wheel
The first thing to consider when selecting a grinding wheel specification is the workpiece material type and hardness. Is the material easy or difficult to grind? The relative ease of grinding is a major predictor of the appropriate abrasive type, grain attribute, grit size and bond type for the application.
By convention, aluminum oxide grains are used for grinding ferrous metals, and silicon carbide grains for non-metals and non-ferrous metals. Ceramic and superabrasive grains are compatible with all three types of materials, but are typically meant for specific circumstances where aluminum oxide and silicon carbide perform poorly.
With the grain type is established, material grindability determines many of the other necessary attributes for the grinding wheel. If the material is easy to grind, use a tough, durable grain. Since the material is easy to grind, grains shouldn’t break down too soon or too easily, so the whole grain can be used to maximize wheel life. A coarser grit is best for these materials, as the grains can easily penetrate the material and maximize stock removal. A harder grade (that is, a harder bond between the grains and the wheel) also corresponds to easier grinding, as the bond will prevent the wheel from releasing the grains before they are consumed.
For hard-to-grind materials, reverse these recommendations. Mild, friable grades perform better on these materials, as they fracture more easily and stay sharper. Finer grit sizes improve the ability of the particles to penetrate hard materials and form chips. Because the grits will dull and cause metallurgical damage such as burning if held for too long, soft grades are necessary to release dulled grains and expose the material to sharper ones.
Users should also consider the grinding pressure, or force per grain. The higher the pressure, the more severe the operation, and the better ceramic and superabrasive grains are likely to perform. The severity of the operation also helps determine the attributes of the abrasive grain.
Tough, durable grains are able to tolerate higher levels of pressure and not break down prematurely. Coarser grits also assist the grains in holding up to grinding pressure. There may be times where distributing the pressure over more cutting points is best, but even that situation requires balance to prevent the pressure from turning the finer grains into dust. Heavy pressure also requires harder grades so grains can stay on the wheel long enough to perform the required grinding work.
In contrast, mild, friable grains perform better in light-pressure operations, since durable grains will only rub and dull. Finer grit sizes ensure that the grains can still fracture properly and self-sharpen, and softer grades release dulling grains before they begin to rub and burn the material undergoing grinding.
The unique specifications of different grinding wheels determine their optimal applications. However, factors like coolant use and the horsepower of the grinding machine can alter these optimal applications. All images courtesy of Norton | Saint-Gobain Abrasives.
Required Form and Finish Accuracy
Grinding wheels achieved their ubiquity due to their speed, form repeatability and ability to achieve desired finishes. When selecting a wheel, it is important to determine whether the application requires Rapid stock removal or a fine finish. Equally important is whether the part will be simple and flat, or if there is a form to hold.
The required surface finish, dimensional tolerances, form holding requirements and stock removal rates factor into the appropriate grit size, grade and bond type.
For low-Ra finishes or close geometric tolerances, finer grits are helpful because they provide more points of contact between the work and wheel. This helps with precision finishes, which have a shallower scratch pattern and a lower micro-inch finish. Finer grains also aid in achieving and holding small-radius and complex forms. Coarser grits, by contrast, improve stock removal rates. Finding the optimal balance in grit size will decrease cutting cycle times.
Close geometric accuracy and form holding requires a harder grade. Harder grades enable the wheel to hold its profile longer and ensure the grains are held long enough to achieve the desired results.
This next recommendation may seem contradictory, but softer bonds are optimal for both finer finishes and higher stock removal. A wheel with a softer bond will easily release dull grains and keep newer, sharper grains in contact with the material. Sharper grains increase stock removal and improve finish by preventing dull abrasives from rubbing and burning the part during stock removal operations. Although the actual finish and stock removal rates from this operation are primarily dependent on grit size, keeping sharp grains in the grind zone benefits both.
Part requirements also determine the bond type. Vitrified wheels perform best for close tolerances and form holding, while organic and resin bonds are best for reflective and other fine finishes. Organic bonds, unlike vitrified bonds, have a little give to them. Some of the grinding forces go into the bond, reducing the chip size. Another benefit for fine finish grinding is the way organic bonds break down from the heat of the grind. They tend to hold grains a little longer, allowing them to run and dull. Planned plowing and sliding interactions that take place under these circumstances improve upon the initial scratch pattern formed during stock removal to generate a finer finish.
Area of Contact
Area of contact is partly related to severity of operation in that it considers the area of contact between the work and the wheel. When a wheel is applied to the work, the force applied is distributed over all the cutting points in the grind zone. The larger the area of contact, the lower the force per grain. Conversely, the smaller the area, the higher the force per grain.
Operations with a small area of contact should use tough, durable grains that will not fracture too early or suffer premature wear under higher force per grain. Ceramic or superabrasive grains may even be necessary in these operations. Finer grit sizes are optimal for small areas of contact, because in addition to providing more abrasive points at the area of contact, the relative pressure or grinding forces will be split among many grains. The high forces of operations with smaller areas of contact also call for harder-grade wheels, as these will hold their shape against premature wheel wear.
When the area of contact increases and becomes larger, such for a Blanchard segment, milder grains are more appropriate. Due to the increased number of grains in contact with the work in the grind zone, the force per grain is lower and the grains will fracture and self-sharpen more easily. Coarse grits spread the pressure into fewer grains to ensure they will continue to penetrate the work. As the risk of burning from dulled grains is higher in these operations, softer wheels grades should be used so grains release before doing damage to the part.
Operations’ wheel surface speeds can narrow down the bond type and wheel grade necessary to complete them. To calculate surface speed, use these equations:
Surface Speed (SFPM) = (π × Diameter (inch) × RPM) / 12
Surface Speed (m/s) = (π × Diameter (mm) × RPM) / 60000
Wheel speed determines what bond type is best for the required speed, or if a special high-speed bond might be required.
- Surface speeds of 8,500 SFPM (43 m/s) and below are compatible with both vitrified and organic bonds, although most common vitrified wheels are designed for 6,500 SFPM (33 m/s) and below.
- For surface speeds over 8,500 SFPM (43 m/s), an organic bond should be used for safety reasons. As a note, some newer vitrified bonds can run at speeds over 8,500 SFPM (43 m/s), but these typically require a special rating.
Wheels will also act differently based on their speed. For every 1,000 SFPM (5.08 m/s) the surface speed changes, the wheel will act one grade harder or softer. Slower wheel speeds equal softer performance, as the higher force per abrasive particle causes the grains and bond to break down quicker. Faster wheel speeds lead to harder performance, with the lower force per abrasive particle making the grains and bond act more durable.
Coolant has opposite effects on wheels with vitrified and organic bonds. Its presence makes vitrified wheels act softer, while organic wheels act harder.
Coolant in a grinding system affects vitrified and organic (resin) bonded wheels differently, and plans for its use must be considered when determining the wheel’s grade or hardness.
Andor Surface Grinding Wheel
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Grinding Techniques (Pty) Ltd, manufactures and supplies a wide range of abrasive products to the global market. Our product range includes: Reinforced Cutting Grinding Wheels, Bonded Abrasives, Tungsten Carbide Burrs, Coated Abrasives, Diamond wheels and Diamond Saws.
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Choosing The Right Grinding Wheel
The grinding wheel is a cutting tool. It’s an abrasive cutting tool.
In a grinding wheel, the abrasive performs the same function as the teeth in a saw. But unlike a saw, which has teeth only on its edge, the grinding wheel has abrasive grains distributed throughout the wheel. Thousands of these hard, tough grains move against the workpiece to cut away tiny chips of material.
Abrasive suppliers offer a wide array of products for a variety of grinding applications in metalworking. Choosing the wrong product can cost the shop time and money. This article presents some of the fundamentals of selecting the best grinding wheel for the job.
Abrasives — Grits and Grains
Grinding wheels and other bonded abrasives have two major components: the abrasive grains that do the actual cutting and the bond that holds the grains together and supports them while they cut. The percentages of grain and bond and their spacing in the wheel determine the wheel’s structure.
The particular abrasive used in a wheel is chosen based on the way it will interact with the work material. The ideal abrasive has the ability to stay sharp with minimal point dulling. When dulling begins, the abrasive fractures, creating new cutting points.
Each abrasive type is unique with distinct properties for hardness, strength, fracture toughness and resistance to impact.
Aluminum oxide is the most common abrasive used in grinding wheels. It is usually the abrasive chosen for grinding carbon steel, alloy steel, high speed steel, annealed malleable iron, wrought iron as well as bronzes and similar metals. There are many different types of aluminum oxide abrasives, each specially made and blended for particular types of grinding jobs. Each abrasive type carries its own designation, usually a combination of a letter and a number. These designations vary by manufacturer.
Zirconia alumina is another family of abrasives, each one made from a different percentage of aluminum oxide and zirconium oxide. The combination results in a tough, durable abrasive that works well in rough grinding applications, such as cut-off operations, on a broad range of steels and steel alloys. As with aluminum oxide, there are several different types of zirconia alumina from which to choose.
Silicon carbide is an abrasive used for grinding gray iron, chilled iron, brass, soft bronze and aluminum, as well as stone, rubber and other nonferrous materials.
Ceramic aluminum oxide is another major development in abrasives. This is a high-purity grain manufactured in a gel sintering process. The result is an abrasive with the ability to fracture at a controlled rate at the submicron level, constantly creating thousands of new cutting points. This abrasive is exceptionally hard and strong. It is primarily used for precision grinding in demanding applications on steels and alloys that are the most difficult to grind. The abrasive is normally blended in various percentages with other abrasives to optimize its performance for different applications and materials.
Once the grain is known, the next question relates to grit size. Every grinding wheel has a number designating this characteristic. Grit size is the size of individual abrasive grains in the wheel. It corresponds to the number of openings per linear inch in the final screen size used to size the grain. In other words, higher numbers translate to smaller openings in the screen the grains pass through. Lower numbers (such as 10, 16 or 24) denote a wheel with coarse grain. The coarser the grain, the larger the size of the material removed. Coarse grains are used for Rapid stock removal where finish is not important. Higher numbers (such as 70, 100 and 180) are fine grit wheels. They are suitable for imparting fine finishes, for small areas of contact and for use with hard, brittle materials.
To allow the abrasive in the wheel to cut efficiently, the wheel must contain the proper bond. The bond is the material that holds the abrasive grains together so they can cut effectively. The bond must also wear away as the abrasive grains wear and are expelled so new, sharp grains are exposed.
There are three principal types of bonds used in conventional grinding wheels. Each type is capable of giving distinct characteristics to the grinding action of the wheel. The type of bond selected depends on such factors as the wheel operating speed, the type of grinding operation, the precision required and the material to be ground.
Most grinding wheels are made with vitrified bonds, which consist of a mixture of carefully selected clays. At the high temperatures produced in the kilns where grinding wheels are made, the clays and the abrasive grain fuse into a molten glass condition. During cooling, the glass forms a span that attaches each grain to its neighbor and supports the grains while they grind.
Grinding wheels made with vitrified bonds are very rigid, strong and porous. They remove stock material at high rates and grind to precise requirements. They are not affected by water, acid, oils or variations in temperature.
Vitrified bonds are very hard, but at the same time, they are brittle like glass. These bonds are broken down by the pressure of grinding.
Some bonds are made of organic substances. These bonds soften under the heat of grinding. The most common organic bond type is the resinoid bond, which is made from synthetic resin. Wheels with resinoid bonds are good choices for applications that require Rapid stock removal, as well as those where better finishes are needed. They are designed to operate at higher speeds, and they are often used for wheels in fabrication shops, foundries, billet shops and for saw sharpening and gumming.
Another type of organic bond is rubber. Wheels made with rubber bonds offer a smooth grinding action. Rubber bonds are often found in wheels used where a high quality of finish is required, such as ball bearing and roller bearing races. They are also frequently used for cut-off wheels where burr and burn must be held to a minimum.
The strength of a bond is designated in the grade of the grinding wheel. The bond is said to have a hard grade if the spans between each abrasive grain are very strong and retain the grains well against the grinding forces tending to pry them loose. A wheel is said to have a soft grade if only a small force is needed to release the grains. It is the relative amount of bond in the wheel that determines its grade or hardness.
Hard-grade wheels are used for longer wheel life, for jobs on high-horsepower machines and for jobs with small or narrow areas of contact. Soft grade wheels are used for Rapid stock removal, for jobs with large areas of contact, and for hard materials such as tool steels and carbides.
The wheel itself comes in a variety of shapes. The product typically pictured when one thinks of a grinding wheel is the straight wheel. The grinding face— the part of the wheel that addresses the work — is on the periphery of a straight wheel. A common variation of the straight wheel design is the recessed wheel, so called because the center of the wheel is recessed to allow it to fit on a machine spindle flange assembly.
On some wheels, the cutting face is on the side of the wheel. These wheels are usually named for their distinctive shapes, as in cylinder wheels, cup wheels and dish wheels. Sometimes bonded abrasive sections of various shapes are assembled to form a continuous or intermittent side grinding wheel. These products are called segments. Wheels with cutting faces on their sides are often used to grind the teeth of cutting tools and other hard-to-reach surfaces.
Mounted wheels are small grinding wheels with special shapes, such as cones or plugs, that are permanently mounted on a steel mandrel. They are used for a variety of off-hand and precision internal grinding jobs.
Grinding wheels are generally labeled with a maximum safe operating speed. Don’t exceed this speed limit. The safest course is not even to mount a given wheel on any grinder fast enough to exceed this limit.
These diamond metal bond wheels offer superior performance in round tool grinding.
Tying It All Together
A number of factors must be considered in order to select the best grinding wheel for the job at hand. The first consideration is the material to be ground. This determines the kind of abrasive you will need in the wheel. For example, aluminum oxide or zirconia alumina should be used for grinding steels and steel alloys. For grinding cast iron, nonferrous metals and non-=metallic materials, select a silicon carbide abrasive.
Hard, brittle materials generally require a wheel with a fine grit size and a softer grade. Hard materials resist the penetration of abrasive grains and cause them to dull quickly. Therefore, the combination of finer grit and softer grade lets abrasive grains break away as they become dull, exposing fresh, sharp cutting points. On the other hand, wheels with the coarse grit and hard grade should be chosen for materials that are soft, ductile and easily penetrated.
The amount of stock to be removed is also a consideration. Coarser grits give Rapid stock removal since they are capable of greater penetration and heavier cuts. However, if the work material is hard to penetrate, a slightly finer grit wheel will cut faster since there are more cutting points to do the work.
Wheels with vitrified bonds provide fast cutting. Resin, rubber or shellac bonds should be chosen if a smaller amount of stock is to be removed, or if the finish requirements are higher.
Another factor that affects the choice of wheel bond is the wheel speed in operation. Usually vitrified wheels are used at speeds less than 6,500 surface feet per minute. At higher speeds, the vitrified bond may break. Organic bond wheels are generally the choice between 6,500 and 9,500 surface feet per minute. Working at higher speeds usually requires specially designed wheels for high speed grinding.
In any case, do not exceed the safe operating speed shown on the wheel or its blotter. This might be specified in either rpm or sfm.
The next factor to consider is the area of grinding contact between the wheel and the workpiece. For a broad area of contact, use a wheel with coarser grit and softer grade. This ensures a free, cool cutting action under the heavier load imposed by the size of the surface to be ground. Smaller areas of grinding contact require wheels with finer grits and harder grades to withstand the greater unit pressure.
Next, consider the severity of the grinding action. This is defined as the pressure under which the grinding wheel and the workpiece are brought and held together. Some abrasives have been designed to withstand severe grinding conditions when grinding steel and steel alloys.
Grinding machine horsepower must also be considered. In general, harder grade wheels should be used on machines with higher horsepower. If horsepower is less than wheel diameter, a softer grade wheel should be used. If horsepower is greater than wheel diameter, choose a harder grade wheel.
Care And Feeding
Grinding wheels must be handled, mounted and used with the right amount of precaution and protection.
They should always be stored so they are protected from banging and gouging. The storage room should not be subjected to extreme variations in temperature and humidity because these can damage the bonds in some wheels.
Immediately after unpacking, all new wheels should be closely inspected to be sure they have not been damaged in transit. All used wheels returned to the storage room should also be inspected.
Wheels should be handled carefully to avoid dropping and bumping, since this may lead to damage or cracks. Wheels should be carried to the job, not rolled. If the wheel is too heavy to be carried safely by hand, use a hand truck, wagon or forklift truck with cushioning provided to avoid damage.
Before mounting a vitrified wheel, ring test it as explained in the American National Standards Institute’s B7.1 Safety Code for the Use, Care and Protection of Grinding Wheels. The ring test is designed to detect any cracks in a wheel. Never use a cracked wheel.
A wise precaution is to be sure the spindle rpm of the machine you’re using doesn’t exceed the maximum safe speed of the grinding wheel.
Always use a wheel with a center hole size that fits snugly yet freely on the spindle without forcing it. Never attempt to alter the center hole. Use a matched pair of clean, recessed flanges at least one-third the diameter of the wheel. Flange bearing surfaces must be flat and free of any burrs or dirt buildup.
Tighten the spindle nut only enough to hold the wheel firmly without over-tightening. If mounting a directional wheel, look for the arrow marked on the wheel itself and be sure it points in the direction of spindle rotation.
Always make sure that all wheel and machine guards are in place, and that all covers are tightly closed before operating the machine. After the wheel is securely mounted and the guards are in place, turn on the machine, step back out of the way and let it run for at least one minute at operating speed before starting to grind.
Grind only on the face of a straight wheel. Grind only on the side of a cylinder, cup or segment wheel. Make grinding contact gently, without bumping or gouging. Never force grinding so that the motor slows noticeably or the work gets hot. The machine ampmeter can be a good indicator of correct performance.
If a wheel breaks during use, make a careful inspection of the machine to be sure that protective hoods and guards have not been damaged. Also, check the flanges, spindle and mounting nuts to be sure they are not bent, sprung or otherwise damaged.
The grinding wheel is one component in an engineered system consisting of wheel, machine tool, work material and operational factors. Each factor affects all the others. Accordingly, the shop that wants to optimize grinding performance will choose the grinding wheel best suited to all of these other components of the process.
About the author: Joe Sullivan was a senior product manager for Norton Company, Worcester, Massachusetts.
What Are Superabrasives?
Superabrasives make up a special category of bonded abrasives designed for grinding the hardest, most challenging work materials.
Because carbides, high speed steels, PCD, PCBN, ceramics and some other materials used to make cutting tools can be nearly as hard as conventional abrasives, the job of sharpening them falls to a special class of abrasives-diamond and the CBN, the superabrasives.
These materials offer extreme hardness, but they are more expensive than conventional abrasives (silicon carbide and aluminum oxide). Therefore, superabrasive grinding wheels have a different construction than conventional abrasive wheels. Where a conventional abrasive product is made up of abrasive all the way through, superabrasive wheels have abrasive on the cutting edge of the wheel that is bonded to a core material, which forms the shape of the wheel and contributes to the grinding action.
Superabrasive wheels are supplied in the same standard grit range as conventional wheels (typically 46 through 2,000 grit). Like other types of wheels, they can be made in a range of grades and concentrations (the amount of diamond in the bond) to fit the operation.
There are four types of bond used in superabrasive wheels. Resinoid bond wheels are exceptionally fast and cool cutting. They are well-suited to sharpening multi-tooth cutters and reamers, and for all precision grinding operations. Resin is the “workhorse” bond, most commonly used and most forgiving. Vitrified bond wheels combine fast cutting with a resistance to wear. They are often used in high-volume production operations. Metal bond wheels are used for grinding and cutting nonmetallic materials, such as stone, reinforced plastics and semiconductor materials that cannot be machined by other cutting tools. Single-layer plated wheels are used when the operation requires both fast stock removal and the generation of a complex form.
GUIDE TO GRINDING WHEELS
What is a grinding wheel? Grinding wheels contain abrasive grains and layers of fiberglass bonded into a wheel shape by another substance. The abrasive grains act as grinding tools, removing material from a workpiece to shape and refine it. Grinding wheels are useful in many grinding and machining operations.
Several types of grinding wheels are available, so when a facility is choosing a wheel, it’s essential to consider the specifications of contrasting styles and how well they can handle different environments and operational challenges. In this guide to grinding wheels, we discuss a few grinding wheel types, as well as their materials, design and benefits for specific applications.
TYPES OF GRINDING WHEELS
Grinding wheels — along with other more portable grinding products like cones and plugs — come in various styles. Selecting the right type of wheel for a given application allows users to get demanding metal fabrication jobs done quickly and accurately.
There are three main types of grinding wheels, where various numbers differentiate between wheels with specific properties and uses — type 1 snagging wheels, type 27 grinding wheels and type 28 grinding wheels.
A type 1 snagging wheel has a straight profile and a relatively small diameter of about 2 to 4 inches. Its size makes it ideal for use on high-speed die grinders for grinding off excess metal. Weiler Abrasives’ type 1 snagging wheels incorporate aluminum oxide grains for a long life grinding and a consistent cut-rate.
Type 27 is by far the most common abrasive grinding wheel. Type 27 grinding wheels differ from other wheels in that they have a flat profile with a depressed center. A depressed center allows for clearance when the operator must work at a constrained angle.
Using a wheel with a depressed center allows for a range of grinding angles, typically from 0 to 45 degrees. However, the optimal angles for working with type 27 grinding wheels range from 25 to 30 degrees. The steeper the grinding angle, the more aggressive the cut will be.
Working at shallow angles with these wheels requires some consideration of potential ramifications. Grinding at shallow angles can prolong the wheel’s lifespan, but it also often compromises the cut-rate. On harder materials, shallow grinding angles may also increase unwanted vibration and chatter.
Type 28 grinding wheels, also known as saucer wheels, have similarly depressed centers and are optimized for low grinding angles. They differ from type 27 wheels in that their concave or saucer-shaped design allows for better access to the workpiece — especially in tighter areas, such as corners, fillets and overhangs — and increased aggression at smaller working angles. They can work at angles between 0 and 30 degrees but typically work best for use with grinding angles from 0 to 15 degrees.
The materials in each grinding wheel break down into a few main components — the grains, the bond and the fiberglass that reinforces the wheels to give them strength and stability for use in demanding applications. The grit of the wheel is also an essential element that helps determine performance.
GRAINS AND GRAIN BLENDS
The abrasive grains provide the essential functionality of a grinding wheel because they remove material from the workpiece. A few commonly used grinding wheel abrasives are ceramic alumina, zirconia alumina, aluminum oxide, white aluminum oxide, aluminum oxide and silicon carbide. Grains can be blended together to achieve different performance characteristics as well.
- Ceramic alumina: These grains offer the benefit of self-sharpening and micro-fracturing crystals. They are relatively cool when in use, and they provide the longest operating life under moderate to high pressure. They grind at lower temperatures and generate less friction — one main benefit of these qualities is that they minimize heat discoloration on the workpiece. Ceramic alumina is ideal for hard-to-grind metals such as armored steel, titanium, hard nickel alloys, Inconel tool steel and stainless steel.
- Zirconia alumina: Zirconia alumina grains provide a fast cut and a long life on metal workpieces. They are self-sharpening and deliver Rapid, consistent grinding, especially on metals like steel and stainless steel. They also hold up well under high pressures and extreme temperatures.
- Zirconia alumina blended with ceramic alumina: If you like the performance of a zirconia alumina grinding wheel but are looking for an extra boost a blend with ceramic alumina will deliver faster cutting with less effort.
- White aluminum oxide: White aluminum oxide grinding wheels offer a relatively fast cut-rate and an extensive lifespan. They are ideal for grinding stainless steel and harder-grade steel.
- Aluminum oxide: An aluminum oxide grain is ideal for steel, iron and other metals. Although it is hard and durable and provides a sharp, fast initial cut, the grain dulls over time and lacks the cut-rate and potential longevity of some other grains. Aluminum oxide provides exceptional value and cost-effectiveness while still offering the excellent quality and consistent performance necessary in a grinding wheel.
- Silicon carbide: Silicon carbide is an extremely hard grain that is very sharp and fast cutting but friable, not as tough as other grains.
- Silicon carbide/aluminum oxide blend: A wheel made from a blend of silicon carbide and aluminum oxide provides ideal grinding for aluminum and other soft alloys. These grains offer extended life spans and fast, consistent cut rates on aluminum and other soft metals.
Grains also come in various sizes — the size of a grain refers to the size of the individual abrasive particles, similar to the grades for sandpaper particles.
The bond is the substance that causes the abrasive grains to adhere to the wheel. Bonds can consist of different materials. Common materials include shellac, resinoids, rubber and glass or glass-ceramic. At Weiler Abrasives, our portable grinding wheels contain resinoid bonds.
The bond on a grinding wheel may be either hard or soft. A harder bond extends the wheel’s lifespan, provided the user operates and maintains the wheel correctly. A softer bond, on the other hand, allows for smoother grinding and exposes new grains more quickly. Choosing the correct bond for a given application can help balance performance and longevity. The type of metal can also influence the bond that’s best for your application.
A grinding wheel’s bond sometimes contains iron, sulfur and chlorine, which can pose challenges if they adhere to the workpiece during grinding. Weiler Abrasives offers several wheels that minimize these elements. Our Tiger Ceramic, Aluminum, and INOX wheels are contaminant-free, containing less than 0.1% chlorine, sulfur and iron. They help prevent corrosion on stainless steel and aluminum workpieces.
The bond on a grinding wheel helps provide a consistent cut rate by exposing new grains over time. As older grains become worn, the grain particles fracture as they are designed to — thereby exposing new abrasive surfaces, leaving fresh abrasive particles exposed in their places. Ideally, the composition of the binding is such that under normal working conditions, wear and tear will remove worn abrasive particles and leave fresh ones in place, maintaining the wheel’s superior cut-rate and performance.
The abrasive particles bound to the wheel also have a characteristic known as grade. Grade refers to hardness, but not the hardness of the particles themselves — it refers instead to the strength of the bond holding the particles to the wheel. A wheel with a stronger bond typically has a longer life. A softer bond is designed to break down faster to maintain a consistent cut rate as new sharp grains take the place of worn ones. The letters N, R, S and T specify the hardness of a bond, with the letters that come later in the alphabet referring to harder bonds. As a general rule, a wheel with a softer bond will perform better on a hard metal, while a hard bond will perform better on a softer metal.
The fiberglass structure and design on a grinding wheel provides reinforcement, rigidity and superior grinding ability. All Weiler grinding wheels come with triple-reinforced fiberglass that gives additional support and strength for aggressive stock removal. Our Tiger brand of performance grinding wheels has the outer layout of fiberglass cut back to allow for aggressive grinding from the outset with no break-in period.
The grit of a wheel is critical for supplying the right abrasion. Grit measurements generally range from coarse to fine. On Weiler Abrasives’ grinding wheels, the coarsest grit has a rating of about 24 and the finest grit — the grit on snagging wheels — has a rating of about 36. Selecting the right grit level for a particular application helps ensure sufficient grinding power. A course grit has a better removal rate, while a finer grit requires less pressure during application and allows for a better final finish on the workpiece.
SELECTING THE RIGHT SIZE GRINDING WHEEL
When selecting a grinding wheel, users should consider two primary factors — diameter and thickness. Both metrics affect the wheel’s usability and performance.
The choice of diameter for a grinding wheel generally depends on the available tool. The primary reason for fitting the grinding wheel diameter to the tool is safety — the operation of the tool should never exceed the RPM rating on the abrasive. Smaller power tools tend to operate at higher RPM than larger power tools, and the design of abrasives and brushes enables them to meet the same standards. Running a wheel with only an 8,500 RPM rating on a grinder that operates at 13,000 RPM could cause the abrasive to fail and injure the operator.
Choosing the correct diameter also enhances safety because it allows for the use of proper guards. Trying to fit a 6-inch abrasive on a 4.5-inch grinder necessitates removing the protective guards, and running the grinder without guards would increase the operator’s chance of injury if the abrasive failed.
Product life is an additional factor in the choice of grinding wheel diameter. Larger-diameter wheels last longer. Especially in applications where the operator must run the grinding wheel for a sustained period, using a larger-diameter wheel can improve productivity by reducing the number of times the operator must stop and replace the abrasive.
The configuration of the workspace and workpiece also influence the choice of diameter. For instance, an operator working in a cramped space or on a tricky area of the workpiece may choose a die grinder with a small 3-inch wheel for better access.
The thickness of a grinding wheel impacts its performance and wheel life. Our grinding wheels typically come with a quarter-inch thickness. This measurement gives our wheels a superior balance of precision, wheel life, and cut-rate when grinding.
Combination grinding and cutting wheels with 1/8-inch thickness are also available. These wheels allow for grinding and for making cuts that require a thinner wheel. The benefit of these thinner combo wheels is that they enable the operator to perform both 90-degree cuts and shallow-angled grinding without having to change the abrasive used on the wheel.
GRINDING WHEEL APPLICATIONS
Thus far, we’ve discussed how different wheel types and compositions can influence the performance of a grinding wheel. And we’ve explored how selecting particular wheel diameters and thicknesses can optimize grinding wheels for specialized applications.
Now let’s examine a few particular applications that require the use of grinding wheels and consider the optimal wheel specifications for each.
- Multipass welding work: For work on pipelines, pressure vessels, and other critical to quality welding operations, operators will likely want a wheel such as the Tiger Zirc pipeline grinding wheel. This wheel incorporates ceramic-infused zirconia alumina with a 1/8th-inch thickness for precision and control when grinding the weld bead in a bevel. This wheel offers diameters ranging from 4 1/2 to 9 inches.
- Mechanized pipe welding: For mechanized pipe welding, operators generally need thinner wheels that allow them to grind the bead without expanding or marring the bevel. The Tiger Mech wheel is an ideal solution, designed for grinding starts and stops on J and K bevels. This wheel incorporates ceramic-infused zirconia alumina and a thin 3/32-inch thickness that allows for precision and consistency. The 4 1/2-inch to 7-inch diameters allow for several grinder size options when notching mechanized pipe welds.
PARTNER WITH WEILER ABRASIVES FOR SUPERIOR GRINDING WHEELS
To see the benefits of high-quality surface conditioning solutions in your workplace, make Weiler Abrasives your trusted source for portable grinding wheels. We are here to help with all your grinding challenges by providing the expertise to help you select the best abrasive grinding wheel to meet your unique surface conditioning requirements.
We also set ourselves apart from our competitors with our Value Package, offering safety training for safe and proper wheel use and direct field support that helps you solve your operational challenges and get the most productivity and profit out of your grinding wheel.