CRATEX GRINDING WHEELS
What is Grinding?
Grinding (or abrasive cutting) is a machining operation that results in light cuts made by different abrasives. The tools used the most for grinding is a grinding wheel.
Grinding wheel is an abrasive cutting tool used to grind down, polish or cut different material, like metal or glass. It is composed of an abrasive compound, so it uses thousands of small abrasive grains distributed across the wheel and held together by a certain bonding material to wear away the surface. Each abrasive grain acts like a small cutting tool that passes over the workpiece and leaves a smooth surface. Dull abrasive grains break away from the bonding material, so the process of grinding sharpens the wheel. That way new sharp points are exposed, and a new cycle starts.
Grinding is used as a finishing process, and different grit sizes are responsible for finer or rougher grinding passes. The wheel you will use depends on the metalwork in question. Choosing the right wheel is essential, because if the chosen wheel is wrong for your project, you’ll end up losing time and money.
Chapter 1 of this article will present different grinding wheels and their basic applications, which should help choose the right tool for the job.
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Choosing The Right Grinding Wheel
CRATEX Abrasive Cutting & Grinding Products
Dressing of Grinding Wheels
How Grinding Wheels Are Made
Choosing the Right Grinding Wheel
Grinding wheels consist of two main components: the abrasive (cutting) grains and the bonding material that holds the grains together. The size of the grains and their spacing, the type of the bonding material and the abrasive used will determine the structure of the grinding wheel.
Types of Abrasives
Different abrasive types have different properties when it comes to impact resistance, strength, hardness and fracture toughness. Two types of abrasives can be used for making grinding wheels: natural and manufactured (almost entirely replaced natural materials). The abrasives consist of several chemical and mineral ingredients and the formula varies depending on the hardness of the material the wheel is intended to grind, polish or cut. There are two types of abrasive grains used to make grinding wheels. However, there are different formulas that are used even within these two categories. For example, a different formula will be used for wheels that are designed for hard steel and those designed for soft steel.
- Conventional abrasives – aluminum oxide (A), silicon carbide (S), Ceramic (C)
- Super-abrasives - diamond (D, MD, SD), cubic boron nitride (CBN)
Aluminum-oxide based abrasives used most often. They are used for metalwork–grinding most steels and other ferrous materials (alloy steel, high-speed steel, carbon-steel, annealed malleable and wrought iron, bronzes and other similar metals). The color and toughness of aluminum-oxide grinding wheels are influenced by the level of purity, and the abrasives used the most are 95% pure. There are various types of aluminum-oxide abrasives and their application varies depending on the grinding jobs. For example, nearly pure white wheels are the toughest, hard wearing and used for grinding heat-sensitive and high-strength steels.
Silicon-carbide based abrasives are used for cutting gray and chilled iron, cement, stone, and other non-ferrous materials (copper, brass, soft bronze, aluminum, magnesium) and nonmetallic (ceramics, gemstones, rubber), because they are harder and more brittle than aluminum-oxide wheels. However, although silicon-carbide abrasives are very sharp, they break down quickly and therefore not effective when it comes to high-pressure grinding. They work best under light pressure and are an excellent choice for putting on a smooth finish.
Ceramic grits are aluminum-oxide grits with microstructure much smaller than the conventional aluminum-oxide with a high level of purity. Its grains are sharp microcrystalline grains that cut aggressively when a light to moderate pressure is applied. Thanks to its fast cutting abilities and its strength and hardness, ceramic abrasives are used for precision grinding on titanium, stainless steel and high-nickel alloys. However, these abrasives are particularly heat-sensitive, so it is necessary to pay attention that the engineered process is executed in the correct manner.
Zirconia-alumina based abrasives are made from a different ratio of zirconium-oxide and aluminum-oxide and are in fact a type of ceramic abrasives. They are durable abrasives quite resistant to heat, used for rough grinding and cut-off operations on different steels and steel alloys.
Natural diamonds can be used for grinding very hard materials (like granite, stone, cemented carbides, marble), but have almost completely been squeezed out of the market by synthetic diamond wheels, due to the low cost of the latter. Manufactured diamonds are used for grinding aluminum oxide cutting tools, very hard steels and cemented carbide.
Cubic boron nitride is sharp, cool and extremely hard abrasive (2.5 times harder than aluminum oxide and almost as hard as diamond). It is used for grinding super-hard, high-speed steels, hardened cast irons, stainless and die steels. Metal-coated abrasives are used for general-purpose grinding, and uncoated abrasives are used in vitrified bond and electroplated metal systems.
Size of abrasive grains found in a grinding wheel can range from 6 to 10, which is the coarsest, to even 1000, which is the finest. It matches the number of openings in the screen the grains pass through, e.g. the higher the number, the smaller the opening. Grain size influences stock removal rate, surface finish and wheel chip clearance - the larger the grain, the faster the cutting, but the poorer the surface finish. The finer the grain, the more suitable for fine, precision finish work.
For example, the coarse size is used when surface finish is not that important, like snagging operations in foundries and steel mills; the medium size is used when there’s a need to get a certain control over the surface finish, like high-stock removal operations; fine sizes grains are used for fine-finish and for operations that require small-diameter grinding; and extra-fine grit sizes are used for lapping and polishing operations.
Bond Strength & Wheel Structure
Wheels also differ based on the tightness of the bond that holds the abrasive and the grain spacing. The hardness or the grade of the bonding material ranges from A-H which would be classified as ‘soft’, I-P as ‘moderately hard’ to Q-Z which is ‘hard’. Wheel grade will determine the wheel speed, grinding depth, maximum and minimum feed rates, coolant flow, etc. Soft-bonded wheels are quick to release the grains, so the wheel wears out fast. When it comes to hard-bonded wheels, dull grains cause glazing, so the grains wear out fast, so the cutting edges are lost quickly.
As for the grain spacing, it ranges from 1, which would be the densest, to 17 which would be the least dense. Wheels with less grain density are open-structure wheels, they cut more freely, have a greater effect on the finish and can cut deeper and wider with less coolant.
Types of Bond
The wheels are also differentiated by the bond or the substance that holds the wheel together with varying degrees of strength. Hard-grade bond is a bond that spans between each abrasive grain and provides an extremely strong hold, while soft-grade bonds span little, so a small force is required to cause the release of the grains.
The bond influences the effectiveness of the cutting operation, and the type you will use depends on the wheel operating speed, the precision required, grinding material and the grinding operation. For example, the wheels with hard-grade bonds are used on high-power machines and jobs with small contact areas. Wheels with soft-grade bonds are used for fast stock removal, for hard materials and jobs with large contact areas.
Standard types of grinding wheel bonds are:
- Vitrified (glass-based) – this type of bond is used most often - in 75% of all grinding wheels. The wheels with vitrified bond are rigid and strong even at elevated temperatures. Although they are unaffected by oils, acids and water, they have a rather poor shock resistance and can be broken down by the grinding pressure, which limits their application. They’re mostly used to 6,500 SFM;
- Resinoid (resin-based) – this type holds the second place as far as the popularity goes and it’s the kind of a bond that softens under the grinding heat. The resin-based wheels are primarily used in rough cut-off, rapid stock removal operations, as well as those where better finishes are required - all at speeds up to 16,500 SFM;
- Silicate (silicate-based) – silicate bonded abrasives are used when there must be minimal heat generated by grinding at a speed that is limited below 4,500 SFM.
- Shellac (shellac-based) – wheels with shellac bond are not used for heavy-duty grinding, but for producing smooth finishes on parts like crankpins, rolls, camshafts and cutlery;
- Rubber (natural or synthetic rubber-based) wheels are quite strong and therefore primarily used as thin cut-off wheels when burr and burn must be kept to a minimum, or driving wheels on centerless grinders, or to achieve extremely fine, smooth and high-quality finishes;
- Metal (various alloys) – these are primarily used for bonding diamond abrasives, in operations such as electrolytic grinding.
Sizes & Types of Grinding Wheels
The diameter of a grinding wheel can range from just 1" to 20", they can go from just 0.035" to up to 1/2" thick. The smallest wheels are used for different operations like auto body work while the largest ones can cut through railway tracks and thick metal constructions.
There are also different types of grinding wheels, such as:
- Straight wheels, which are the most common style of wheels used for cylindrical, centerless and surface grinding operations, and are found on bench or pedestal grinders; they’re used for creating slightly concave surface;
- Cylinder or wheel rings, which are used in vertical or horizontal spindle grinders and have no center mounting support; they’re used for creating flat surfaces by using the end face of the wheel;
- Tapered wheels, which typically used for operations, like grinding thread and gear teeth; it’s basically a straight wheel that tapers towards wheel center, but it can accept higher lateral loads;
- Straight cup wheels, which are used for producing additional radial grinding surface;
- Dish cup wheels, which are used primarily in cutter grinding and jig grinding;
- Saucer wheels, typically used for grinding milling cutters and twist drills;
- Diamond wheels, used for grinding extremely hard materials (like carbide cutting tips, concrete, gemstones, etc.);
- Small mounted wheels, which are mounted on a steel mandrel, typically of hand tool; they come at all kinds of variations (different grains, bonds, etc.) and are therefore used for various operations, typically different off-hand and precision grinding jobs;
- Cut-off wheels, which are normally used on angle grinders for quick removal or trimming; they’re thin and usually have radial fibers as reinforcement.
Conclusion: The Perfect Wheel Is…?
We showed you different grinding wheel properties, all you need to do now is to put the correct ones together and get a perfect grinding wheel for your needs!
In case you are working on a hard material, you’ll probably want to use a softer grade and a fine-grit wheel, as hard materials resist the drilling of the abrasive grains into the surface, which dulls them quite quickly. The combination of a finer grit and a softer grade would be perfect, as the grains will dull, break away and leave new, sharp cutting points. In case you are working on softer materials, wheels with a coarse grit and harder grade would be the correct way to go.
Stock-removal speed is another factor to consider, so in case you need a wheel with rapid stock removal, you should choose coarser grits. The penetration level is greater, and they leave heavier cuts. Wheels with finer grits cut faster, so they are a perfect option for material that is hard to penetrate.
The abrasive material used in the making of the wheels, as well as the bond material, are one of the first things to consider. Different abrasive types are intended to be used on different materials – like we mentioned earlier in the article, aluminum oxide or zirconia-alumina should be used on steels and steel alloys, while silicon carbide is a suitable option for non-metallics, non-ferrous metals and cast iron. As for the different types of bonds, vitrified bonds have fast cutting abilities, rubber, resin or shellac bonds are used in case you wish to remove a smaller amount of stock or in case you want to achieve finer finishes.
Wheel speed is also an important factor to consider as different wheels can be used at different speeds. For example, vitrified wheels are used at speeds up to 6,500 SFPM, while organic-bond wheels can be used on speeds between 6,500 and 9,500 SFPM.
You should also think about the contact area between the grinding wheel and workpiece. In case you are dealing with a large area of contact, you should probably use a softer grade and coarser grit wheel. Finer grit and harder grade wheels are more suitable for a smaller area of grinding contact.
There are also wheels that are designed to bear a lot of pressure that created when the wheel and the workpiece are pressed together, plus, grinding machine horsepower should not be overlooked neither. A useful guideline would be: if the horsepower is smaller than the diameter of the grinding wheel, then a softer-grade wheel should be used, and harder-grade wheel should be used in opposite situations.
CRATEX Abrasive Cutting & Grinding Products
In this chapter will talk about various CRATEX grinding wheels, including the Spedecut cut-off and grinding wheels, and MX abrasives. The products presented are available for online purchase, but in case there is a need for non-standard size, shape or composition, contact us here and we’ll do our best to meet all your special requirement
1. CRATEX Rubber Abrasive Wheels
CRATEX grinding wheels are rubber-bonded, premium-quality silicon carbide abrasives of maximum endurance. They are produced in two types of bonds: standard and hard bond. The standard bond has a unique cushioning action, it provides smooth and soft cut without digging into the surface of the workpiece. It is ideal for smoothing and polishing metallic or non-metallic surfaces. It resists smearing or clogging and provides a perfect finish without losing dimensional tolerance and control. Hard-bond wheels have higher cutting power than the standard-bond wheels and are perfect for removing burrs on hard metals, like stainless steel. They can also be used for light metal removal. Hard bond (HB) is not available in kits and minimum quantities are required.
All grinding wheels come in four grits: Coarse (green), Medium (dark brown), fine (reddish brown) and Extra Fine (grey green). The grit depends on the metal and desired finishing action.
CRATEX large straight-edge wheels are perfect for removing rust, heat marks, tarnish, scratches, corrosion and excess solder.
CRATEX small grinding wheels have either a tapered or straight edge. Tapered or shaped wheels are extremely versatile which makes them ideal for fine operations on small and delicate parts. Straight wheels can be mounted on conventional portable motor tools. They are used on operations that require control of metal removal.
2. CRATEX MX Abrasives
MX products are made of premium brown aluminum-oxide. They are cotton-backed laminate-bond abrasives are much more aggressive and firmer than CRATEX rubber bond products. The difference between the two abrasives is that MX bond holds abrasive grains until they are won while abrasive grains get pushed back into the rubber material during use and they fall out as the rubber gets worn away.
The unique construction of MX abrasives gives them an amazing ability to grind, deburr and finish in one operation, because they contain characteristics of three types of abrasives: resinoid, vitrified and rubber-bonded. They do an amazing job with edge breaking, cleaning welds and blending machine lines, and can reduce finishing steps by half.
MX abrasives are available in two different bonds - latex and resin. Latex bonds are typically used for light deburring, blending, and finishing and they come in two grades – soft bond (for general purpose) and medium bond (medium-aggressive). Resin-bonded abrasives are used for light to medium stock removal and they also come in two grades – hard bond (aggressive) and extra bond (very aggressive).
There are grinders for round parts and grinders for flat surfaces. Those for round parts include machines like cylindrical and centerless grinders, and those for flat surfaces are called surface grinders. There are also form grinders (they move the workpiece and the wheel or just the wheel along different axes to grind precisely contoured surfaces) and tool & cutter grinders (for production and sharpening of cutting tools).
Various machines can be used for abrasive cutting such as bench grinders, industrial grinding machines, different hand power tools (such as die grinders or angle grinders) or grindstones.
Grindstones are round sharpening stones typically made from sandstone, mounted on grindstone machines that have speed-control pedals.
Angle or side grinder is used both for abrasive cutting and polishing. The angles grinders are powered by either an electric motor, compressed air or petrol engine. They are made with an adjustable guard for safety and additional side-handle for operations that require the usage of both hands.
There are a wide variety of side grinders on the market, so you’ll be able to find the perfect one for the project you’re working on. One of the main things to consider is the motor strength and the disc size, and the rule is – the greater the power, the bigger the disc. Common angle grinder discs are 4", 4.5", 5", 6", 7", 9" and 12".
Other specifications that could make a lot of difference are the power source, rpm and the size of the mandrel. Depending on the power source, angle grinders can be pneumatic, which have much smaller discs and are generally used for easier, more precise work, and electric, which are used for heavy-duty jobs. Although small electric and large pneumatic grinders do exist, smaller electric grinders have a tougher time maintaining adequate power, whereas pneumatic grinders can be both small and light, but equally powerful.
Depending on the operation, different kinds of discs can be used on these grinders, such as diamond-blade cut-off discs, abrasive grinding wheels, grinding stones, sanding discs, polishing pads and wire brush wheels.
Die grinders and rotary tools and can be used for grinding (with bonded abrasive stones called mounted points/stones or grinding points), but sanding (with coated abrasives like mounted sand paper drums), honing (with fine-grit mounted points), polishing or buffing (with cloth or fiber drums and polishing compound), lapping (with mounted lap and lapping compound) and machining (with drill bits, end mills or burrs) as well, and there is no conceptual difference between the two tools. However, over time their names started to refer more to two same tools used for two different operations: die grinder refer more to the pneumatic, heavy-duty tools, while rotary tools refer more the electric tools used for lighter tasks.
CRATEX Rotary Hand-piece CTX-800 is a precision air tool with different speed options. It has a high torque and construction made from rugged stainless-steel which makes it extremely light and perfect for all kinds of precision grinding, polishing and finishing operations. The tool has a collet that can be changed easily and that can take 1/8'' and 3/32'' diameter shanks and mandrels.
Bench grinders are most commonly seen in residential basements and garages and are standard equipment in machine shops. The name tells us a lot about the way the tool is being used – it is a bench-top type grinder that can be used for different operations depending on the type of wheels that are mounted.
Dressing of Grinding Wheels
Normally, grinding wheels are self-sharpening tools, but only to a certain extent. Occasional dressing (trimming) or trueing is required for optimal use. Dressing is cleaning operation. To dress a wheel means to remove the top layer in the purpose of exposing the fresh, sharp grains and returning the wheel to its original state. Truing achieves a concentric geometry between the periphery of the wheel and the spindle on which the wheel is mounted.
Grinding wheel dressing can be done by different tools, such as:
- Dressing sticks, which are abrasive sticks usually made from the same materials, only with a strong bonding agent. They’re mostly used for dressing smaller conventional wheels (e.g. saucer and cup-shaped). The grinding stick is held against the wheel surface, which caused excess bond removal;
- Star dressers, or mechanical dressers, are long hand tools with free-running discs or star-shaped cutters on one end. The dressing is performed by turning the grinding wheel off first and then applying the star dresser’s head with force on the grinding wheel that is slowing down; they’re mostly used for coarse conventional wheels;
- Diamond dressers are diamond tools with a short handle and either a broad surface with small embedded diamonds on one end or a single diamond brazed into the tip. The dresser is placed in a tool holder and held against the surface of the running wheel.
CRATEX offers four different square dressing blocks each available in four different grits that are perfect for dressing, truing and shaping different kinds of grinding wheels. The shape is quite easy to handle, and the structure makes it a long-lasting dresser that enables you to achieve optimum performance from all your wheels.
Best seller: Dressing stick 6'' x 1/2'' x ½''
How to Dress a Grinding Wheel
The procedure of dressing a grinding wheel would be as follows: the dresser is placed on a work-rest, up to 1/8'' away from the wheel face, under a slight angle (5-20 degrees). Light pressure should then be applied in a straight line across high points of the grinding wheel until a smooth and even surface is obtained. Important is to note you shouldn't run the wheel at full speed until all signs of imbalance are removed. After the wheel has been shaped, it can be run at full speed for a minute or longer, after which the work can be applied.
The manufacturers have a great responsibility to produce grinding wheels that are safe to use, but no matter how careful they are during the production, they have very little control over the products once they are shipped and delivered to the customer. The consumers are the ones who should make sure that the wheels are handled, stored, mounted and maintained properly. If not, their behavior can contribute to an unfortunate accident resulting in painful or debilitating injuries to both the operator or others present.
It is advisable that the storage room has a constant level of temperature and humidity since the variations ca damage the bonds in some wheels. The wheels should also be protected from banging and kept in a secured spot. To avoid bumping or dropping them, pay special attention to the way you handle them.
The Ring Test
Grinding wheels are breakable and can be extremely dangerous if used damaged. They can contain microscopic cracks in them which will cause them to explode at high speeds and send shrapnel flying across your workspace in all directions. It is essential to inspect every grinding wheel before you mount it and use it, regardless if it is a used one or it’s brand new that you took right out of the box. Remember – the wheel can seem to be in a perfect condition, but that might not be the case.
Since a cracked wheel can cause serious injury to the human body, and be lethal even, it is fortunate that there is a quick and simple way to test if your wheel is good to go or not. This is determined by a Ring test, and the name is self-explicatory, really: the grinding wheel is hanged on a screwdriver blade and suspended in the air. Next, you’ll visually divide the grinding wheel into 8 equal parts (best is to imagine pizza slices), you’ll take the second screwdriver by the blade, and you’ll tap 8 times, once in each slice with it’s handle. You’ll start at the top, then the bottom, left and right, following the cross shape, and then in remaining parts.
A high-pitched ring sound will tell you that the wheel is in perfect condition, and if you don’t hear it, but hear a dull thud, it means that the wheel has cracks in it.
Angle grinders produce sparks when grinding ferrous metals and shards when cutting other materials. In addition, there is a possibility the blades could break, so safety goggles or a full-face shield and protective clothing (work gloves, fire-retardant clothing) is a must when grinding. Otherwise, the risk of seriously injuring your face damaging your eyesight is great. Angle grinders should always be used with their guard and handle, and the workpiece should always be firmly secured in a vise. Hearing protection is also necessary, as the grinders are often very loud, especially when cutting. Since abrasive cutting generates a lot of dust, different kinds of masked can be used depending on the material you’re working on.
When working on a bench grinder, it is essential to note the maximum rpm ratings that are printed on the wheel label. The rpm of the grinder must be either equal or lower than the wheel’s rpm. An overspeeding grinding wheel is bound to explode, which can be lethal. Wheel guards are there to intercept the exploding fragments, so make sure you never use a bench grinder without the wheel guards.
How Are Grinding Wheels Made
#1 Grinding Wheel Evolution – From Sandstone to Superabrasives
Grinding operations, and therefore grinding wheels, have had an important place in the manufacturing industry for more than 150 years. The rapid industrialization that took over the world during the mid-19th and beginning of the 20th century transformed the society from an agrarian into an industrial one and caused the development of large spectrum of industries. The demand for all sorts of tools, including the grinding wheels was on the rise, so people constantly sought room for improvement.
Modern-day industries cannot imagine a world without grinding wheels anymore since they are used by nearly every manufacturing company for wide variety of operations ranging from cleaning to cutting steel and masonry blocks. But, long before superabrasives and CNC machines, there was sandstone. It is probably the earliest abrasive made of quartz mineral grains that were bonded with some natural cement and used to sharpen and polish flint axes.
Then, in the early 1800s, emery was introduced to United States and Europe from India, and so the time of emery grinding abrasives begins. Emery is a natural mineral that contains corundum and iron and was predominantly used to shape and cut metals. However, importation costs and issues and variable quality of the abrasive encouraged people to explore other options and to seek abrasives that are much cheaper and available than the imported material.
By the 1890s the search led to the development of synthetic silicon carbide and synthetic corundum which eventually led to the discovery of superabrasives that we know today as synthetic cubic boron nitride (CBN), synthetic diamond, seeded-gel aluminum oxide and so on.
At the same time the developers worked on improving the boding material in the grinding wheels as well, as the improved grains were not much without an equally powerful bond. The research led to the introduction of the rubber bond in the early 1940s and vitrified bond by the 1870s.
Like we’ve seen in Chapter 1 there are numerous types of abrasives used for making grinding wheels with all sorts of bonds today, and there is no doubt that the innovation won’t stop here.
#2 Sugar, Spice & Everything Nice – Grinding Wheel Mixture
Abrasive grains and the bonding material are the main but not the only components of the grinding wheel.Different additives are added as well, such as iron-oxide for wheels that cut and grind iron to enhance the metal cutting properties, or the mineral cryolite that lubricates the abrasives. Powdered and liquid resins are added to bond all these ingredients together.
Today, a computer program automatically scales and weighs various ingredients, and the process starts by adding powdered resin and additives into the mixer first. After about a minute the abrasives and liquid abrasives are added with care. After another five minutes of turning, the mixture reaches the consistency of a damp beach sand and is called “blend”. Last step in this phase is screening out globs and chunks, so that the mixture has a smooth and even texture.
#3 And Then There Was Wheel – The Molding
First, a machine places a reinforcement disc made of fiberglass at the base of the wheel, after which a device called a shuttle spreads the mixture or “blend” into a wheel shaped mold. The diameter and depth of the mold cavity corresponds to the dimensions of the model of the specific grinding wheel. Next, a galvanized steel ring designed to protect the shaft that spins the grinding wheel is placed in the center of the wheel.
Lastly, a pressure force press applying the pressure of up to 5000 pounds per square inch compacts the blend into its final shape and size (by the way, that’s the weight of about 30 cars in case you are wondering).
The mold is then removed from the press and the wheel carefully striped from it. Every single grinding wheel coming off the line is weighed to ensure it meets the design specifications.
#4 Today’s Special - Flambe Wheel
After they’re taken of the line, the wheels are placed into an oven with temperature that rises gradually from 70 to 400 degrees Fahrenheit over a period of 24 hours. Of course, the temperature can vary depending on the types of wheels and ovens (e.g. vitrified bonds are fired to temperatures between 1700-2300 degrees Fahrenheit). The firing process cures the resin and bonds all the ingredients together.
When the grinding wheels come out, they’re hard as a rock and are resistant to heat produced by the high-speed grinding and are resistant to cleaning solvents.
#5 And Voila! – A Grinding Wheel
After the wheels are taken out of the oven, they are transferred to the finishing area. The last steps concerting the shaping of the wheels are: reaming the arbor holes, making the wheel circumference concentric with the edges, adjusting the shape and thickness of the wheel or creating special contours if necessary and balancing large wheels to reduce vibration during grinding. The extent of the grinding wheel quality inspection will depend on the size and the use of the wheel. Typically, larger wheels (over 6 inches in diameter) are thoroughly inspected and tested as they can be extremely dangerous if they break. As for the other wheels, the manufacturer usually monitors the quality of the material used and the production process.
The last step of the production process is labeling. Labeling is conducted by automated machinery that transfers the wheels from a station to station. The information about the manufacturer is usually labeled on the front of the wheel and the safety warnings on the back. The wheels are then packed, shipped and delivered to your home address!