The entire surface of the grinding wheel is covered with a large amount of solid particles. Simply put, this is the grit of the grinding wheel. These particles are usually distributed evenly over the entire area of ββthe circle. Before proceeding with the selection of a circle for processing material, it is necessary to understand this characteristic.
Grinding wheels
To begin the analysis, you need to understand what constitutes a circle. It is a cutting abrasive tool. It is worth saying that there are circles that are used for manual processing, as well as for working on machines. Naturally, the granularity of grinding wheels in professional devices is selected as accurately as possible to ensure the possibility of the most efficient processing.
There are quite a few criteria by which circles are divided into several categories, but most importantly, these are abrasive materials and bonding elements. The following circles are used for this parameter:
- silicon carbide grains;
- elbor;
- electrocorundum;
- artificial or natural diamond.
It is important to understand here that it is the granularity of the grinding wheel that determines its main functional purpose. It is abrasive material that cuts off the microscopic layer of material. For its ligament, there are a variety of substances that can be both artificial and natural. Another feature of grinding wheels is the presence of a porous structure, which ensures the roughness of the coating.
Grit Overview
The choice of grain size of the grinding wheel depends on what requirements are imposed on the cleanliness of the processed surface. In order not to make a mistake, each circle has a special designation (marking).
If you know the labeling, then choose a suitable circle, in principle, is not difficult. It is very important to know that the grain size of grinding wheels for metal and wood coatings is significantly different, and therefore you need to pay attention to this fact when choosing a tool. If after work or during work on the surface of the circle notches, cracks and other defects appear, then an error was made at the stage of choosing the grain size of the working tool. How to determine this parameter correctly? It is necessary to rely on the following two factors: the required purity of processing, as well as the mode of operation, which plays an important role.
Currently, tools with such grit as 60, 100 and 120 are most often purchased.
Circle selection and recommendations
If it is necessary to perform flat grinding, which is actually carried out by the end face of the circle, then the grain size should be from 16 to 36. Round peeling grinding is performed using a wheel with a grain size of 24-36. The grit of the grinding abrasive wheel for round finish grinding should be from 60 to 100. There is such an operation, which is called the finishing of the multi-blade tool, which is carried out in a circle with grit 170-220. Finishing grinding is carried out with a circle characteristic from 180 to 320. There is a procedure called thread grinding. The essence of the process is clear from the name, and to perform the operation, a grain size of the circle from 100 to 280 is required.
There is an easier way to determine grit. Semi-finishing or finishing processing of the material requires the presence of fine fractions of grains. Roughing, on the contrary, is carried out with grains of a large fraction.
Marking
The described tool has a lot of parameters, which are usually indicated in its name. The grain marking of grinding wheels is not indicated separately; it is always included in the full marking of the wheel.
- The type of circle is always indicated first.
- The second important parameter is the dimensions of the device.
- Next, the type of abrasive material that was used to create the coating of the circle is indicated.
- Immediately after this, the designation of the grain size of the grinding wheel is indicated.
- The labeling always refers to the hardness of the material.
- Relationship structure.
- Type of ligament.
- Maximum working circle speed.
- Accuracy class.
- Class of imbalance.
The listed 10 points include both marking the graininess of the grinding wheel, and an indication of other parameters.
Distribution of circles into groups by grain size
There are several groups of tools that differ in grain size. The group of large fixtures includes those tools for which the marking is 320 b, 250 b, 200 b, 160 b, 125 b and several others. The next group is the middle one, which includes such designations as 50 k, b, 40 k, b, 32 k, b, etc. The small group of grain size includes brands such as 12 k, b, 10 k, b, 8 to, b and 3 to, b. The last group includes circles with the designations 5, 4, 3, as well as M63, M50, M40, M28.
Grain application
When choosing a suitable grain size, it is important to know that a different degree of this parameter affects the amount of material removed. For example, the high graininess of the flap grinding wheels will allow you to successfully process even large metal pipes. And if we talk about wood processing, you will have to purchase a circle with much less abrasive material.
A different degree of this characteristic is necessary in order to be able to carry out preliminary operations when peeling with a large cutting depth is required. Circles with a different degree are well suited for wiping operations, and a separate group is required for working with copper, brass and aluminum.
Coarse grain of the circle is most often required when grinding is carried out by the end face of the circle. In addition, they are also used when internal grinding is necessary. Most often, such devices are used on machines that are characterized by increased rigidity and processing power.
Circles with medium and fine grit are used for operations such as:
- grinding of hard metal alloys;
- treatment of hardened steels;
- surface finish;
- sharpening other tools.
Medium-grained and fine-grained circles are also used if very high accuracy is required from the work. Currently, this characteristic must comply with GOST R 52381-2005. This GOST of graininess of grinding wheels replaced the previous document with the number 3647.
Difference of designations in accordance with GOST
It is worth saying that the marking should be known from both documents, since it still remained on many old samples. In accordance with GOST 3647-80, the graininess of a circle is indicated in units that are 10 ΞΌm, for example, 20 = 200 ΞΌm. If the composition contains micropowder, the letter M is added to the micron. As for the new sample, the grain size of the circle is indicated by the letter F with a number.
Suppose, according to the old standard, the grain size of a circle is indicated by the number 200, which on average is 2500-2000 microns. According to the new GOST, the same circle will be designated as F8 or F10. The approximate size of the first circle is 2460 microns, and the second - 2085 microns.
Tool types
As it has already become clear, the cleanliness of the surface that will be ground depends on the granularity of the abrasive material . However, it is worth saying that there are also different grains in their shape. They can be presented in the form of splices or small crystalline fragments with an arbitrary shape. There are high-quality grinding wheels, in which not only a good indicator of grain size, but also the grain itself is presented in the form of a full crystal. If we talk about the parameter of the grain itself for the grinding wheel, then it is worth highlighting three main parameters: thickness, width and length of the grain.
However, it is immediately worth noting here that specialists in this field most often use width as the main and only characteristic. Depending on the size of the grain, it will depend on how much material the wheel can remove in one pass, and therefore the overall performance of the grinding wheel.
If we talk about deciphering the labeling of the material, then it is quite simple. The essence of grain marking is as follows: the numerical indicator of the characteristic is indicated in the prefix. The higher the indicated number, the higher the quality of the grinding material.
Diamond tools
The most expensive and high-quality grinding wheels are diamond. These devices have such a concept as the concentration of the diamond layer, which is expressed in the number of diamonds per cubic millimeter of powder of the abrasive layer. This parameter is considered one of the main, as it affects the efficiency and economy. It is worth saying that this concentration directly depends on the grain size of diamond grinding wheels. In other words, the higher the granularity index, and the harder the material to be processed, the more precisely the amount of diamond crystals in the abrasive layer will increase.
To date, several groups of diamond wheels are produced . They can have a 150-, 100-, 75-, 50- and 25 percent diamond concentration. At present, the presence of 4.39 carats is considered a 100% concentration. One carat is equal to 0.2 g contained in 1 cubic centimeter.
Grit for diamond wheels
Granularity for diamond grinding wheels is the size of the diamond grains themselves in the abrasive layer or intergrowths of crystals. The three main indicators are the same three indicators as for ordinary grains, but here, too, only the width is taken into account. The grain size for diamond wheels is selected based on what kind of roughness should be in the end, on the type of material and on the size of the allowance.
It was previously said that with a decrease in the size of the grains, the quality of grinding increases. This is true, however, fine grain is not always preferred. The fact is that the use of such tools leads to their strong salting, and the treated coating can be cauterized during grinding. If we talk about productivity, then small grains also negatively affect this parameter.
Today, there are four main categories into which diamond grinding wheels are divided, depending on their grain size. Fine grain 100/80, medium 125/100, coarse 160/125, larger grains 200/165.
Fine grit wheels are used to fine-tune other tools, for example, knife blades, cutters or other devices. The middle group is well suited to maximize the sharpness of any cutting surface, and larger circles are already used directly to remove the top layer.
Circles for wood
As a material for processing wood, sandpaper is considered the most suitable. However, circles may well have both polymer and metal brushes. In addition, you can use traditional tools with grains. If it is necessary to carry out a large peeling of wood, then a grain size of 40 to 60 will be required, for an average cleaning, the index increases by 20 and ranges from 60 to 80. The finest grain size is from 100 to 120 and is used for surface finishing.
In addition, as in the case of metal, you need to correctly select the grain size of the grinding wheel for wood, depending on which operation will be performed.