Aug. 06, 2024
Abrasive grains are available in a wide range of grit sizes and bonding agents. Determining which wheel is right for the job requires considering seven key factors: &#;
MetalsKingdom are exported all over the world and different industries with quality first. Our belief is to provide our customers with more and better high value-added products. Let's create a better future together.
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.
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 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:
For more Refacing Machineinformation, please contact us. We will provide professional answers.
Surface Speed (SFPM) = (π × Diameter (inch) × RPM) / 12
Surface Speed (m/s) = (π × Diameter (mm) × RPM) /
Wheel speed determines what bond type is best for the required speed, or if a special high-speed bond might be required.
As a general rule:
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.
If coolant is used:
If no coolant is used:
The horsepower of the grinding machine can play a role in determining the grade of the bond or the hardness of the wheel.
Due to how many factors are involved in determining the starting specification for a grinding wheel, there will be situations when factors point in opposite directions. In such cases, look at where the majority of the factors are pointing, or place precedence on the most important factors for the application. For simple comparison, review the chart below:
When deciding on a wheel specification for a particular operation, it is important to consider all factors. In the event that the factors conflict, the user may need to choose a key factor to determine the final specification.
Dave Goetz, Corporate Application Engineer, Norton | Saint-Gobain Abrasives
Many of us have used grinding wheels as part of our regular, daily work functions, but most of us don&#;t know why we use the wheel we do, or even if the wheel we are using the right one for the job.
There are many different types of abrasive grains, available in a whole range of grit sizes and held together by different bonding agents. How do we know which to use?
It's simpler than we might think. A grinding operation is a system, and as a whole, there are many parts to consider. One key component is the wheel. To determine where to start, consider the seven operational factors.
By taking each of these seven factors into consideration, it is possible to narrow the field down to a smaller list of options to start with for any grinding operation.
The first thing to consider when selecting a grinding wheel specification is what are we grinding? What is the material, and how hard is it? Is it easy to grind or difficult? By reviewing these elements, we can select the correct abrasive type, the grain&#;s attributes, the appropriate grit size, and bond type.
Knowing the properties of the material we are working with helps us select the proper abrasive grain and its attributes. By convention, we use aluminum oxide grains for grinding ferrous metals and silicon carbide for non-metals and non-ferrous metals. Ceramic and superabrasive grains can be used on either but generally under specific circumstances where the material being ground requires these types of grains or when we are looking to optimize process performance.
Once we know which grain type to start with, we can look at the material grindability. If the material is easy to grind, we will want to use a tough/durable grain. Since the material is easy to grind, the grain shouldn&#;t break down too soon or too easily, so the whole grain can be used to maximize wheel life. For materials that are hard to grind, we will want to use a mild/friable grain, which fractures more easily, stays sharper, and actually grinds the material.
For easy to grind materials, we would want a coarser grit. This is because the grain can easily penetrate the material, make and remove chips. Using a larger or coarser grit maximizes the stock removal, reducing cycle time.
Another aspect of the wheel we can dial in on based on the material being ground is the grade or hardness of the bond. If the material is considered easy to grind, we can use a harder grade, which ensures that the wheel doesn&#;t release the grain before it is consumed. Knowing that we want to use the abrasive grain for as long as we can, we want the bond to hold that grain in the wheel for as long as possible.
If the material is difficult or hard to grind and we use a blocky, tough, and durable grain, we run the risk of simply dulling the grain and opening the door to finish issues, such as burning, because the grain will rub and not grind.
The material being ground also helps us determine the grit size. For hard to grind materials, we would recommend a finer grit size because a smaller particle will penetrate hard materials and form a chip easier than a larger blockier one. Difficult or hard to grind materials are abusive to the abrasive grain and can cause them to blunt or dull. Since we need more sharp points to penetrate the material, we want to ensure the grains are being released before they become too dull and cause metallurgical damage. With hard materials, a softer grade should be used so that the material is constantly being exposed to sharp grains. The grade needs to be soft enough to release the dulled grains and keep exposing new sharper grains to the work.
Here we consider how much or how heavy the grinding pressure will be in the grind zone. The higher the grinding pressure or force per grain, the more severe the operation. It is operations like these where today&#;s ceramic and superabrasive grains do well. Much like the material we are grinding, severity of operation helps us determine the attributes of the abrasive grain.
If you are looking for more details, kindly visit Bevel Pipe For Welding.
If you are interested in sending in a Guest Blogger Submission,welcome to write for us!
All Comments ( 0 )