What to buy circles for a grinder: types and types, marking

Recommendation points

• Basic sizes and markings
• Turnover: maximum and golden mean
• Processed materials
• Used abrasives
• Binder and circle reinforcement
• Summary: signs of a quality product

We suggest you consider such a seemingly trivial question as the choice of cutting wheels for a grinder. We will tell you about the signs of a really high-quality product, explain the main reasons for the quick grinding of discs and help you navigate a wide range of them..

It is understood that this review will be of most interest to specialists who often use angle grinders during work and try to choose a cutting technique that is optimal in the ratio of speed / wear of consumables. To determine the manufacturer of the discs, you should try them repeatedly in action, and also save a couple of washed off leftovers for testing. Purely visually, disks can only be sorted by marriage, revealing cracks, large shells and other defects. To understand the fundamental differences in quality, several remnants of different discs will have to be broken..

Basic sizes and markings

Almost all wheels sold in Russia are manufactured in accordance with GOST 21963-2002, which contains technical production conditions, classification and marking scheme, as well as GOST R 52588-2006, which regulates requirements for the safety of abrasive materials. It is highly desirable to have a compliance stamp on the disc.

The first group of cut-off wheel designations is the index of the abrasive material: A – electrocorundum, C – silicon carbide. Along with the designation of the material, there can be a two-digit number, which increases with the quality of the grade of abrasive particles. The second group of symbols is the grain size of the circle. According to the standard, it should be at least 60, but the value can vary widely for a wide range of technological operations.

After the first two groups of designations, the indicators of the total hardness (soft, medium-hard, hard, extra hard, only 8 gradations) and the structure (density, fullness) of the disc are indicated through a space: from the densest – 1, to the most porous – 12. Note here that the hardness of the disk can be different under other external conditions: temperature, humidity, speed.

According to the accepted marking, cutting wheels are characterized by a binder (R – vulcanite, B – bakelite, V – ceramics) and the presence of reinforcement, which is marked with the letter F following the designation of the material. It should be noted that there are circles with a combined binder, in which case several letter indices are in front of the indicator of the presence of reinforcement. The marking ends with special indices: one of four classes of imbalance according to GOST 3060–86, a class of dimensional accuracy and / or an NM indicator – for non-metallic materials.

As for the basic dimensions, they are almost always indicated by a separate group of symbols such as Diameter x Fit x Thickness. The outer diameter of the discs used for the operation of angle grinders is 125 (115), 180 and 230 mm, the seat is usually 22, 23 mm. For side saws, a freer choice of diameter and size of the bore is allowed. The thickness is chosen according to the material and cutting technique, but keep in mind that the increase in the disk resource with increasing thickness is very insignificant..

Turnover: maximum and golden mean

Two basic safety requirements when working with angle grinders are not to remove the protective cover and not to exceed the permissible speed. If everything is clear with the first one, then what pitfalls are hidden when the rated speed of the circle and the power tool does not match?

Let’s start with the fact that, due to its strength and structure, the disc may simply not be able to withstand increased centrifugal loads. In addition, the concept of a leverage is also valid: at high revolutions, the load on the root of the disc increases as the square of the increment in the distance from the center and therefore discs that are not turned 230 mm on angle grinders under 125 mm always and guaranteed to break when trying to cut.

Other limitations arise from the temperature resistance of the abrasive and binder. Proper cutting requires efficient chip removal, which is not possible if the resin begins to melt and the disc edge loses porosity. Even a slight increase in speed can lead to a noticeable decrease in cutting efficiency, or the disc will simply begin to crumble.

Cutting at a speed less than the recommended speed is allowed according to safety standards, but the feed force must accordingly decrease. Cutting speed also drops noticeably, but there is a slight increase in resource. It is best to choose a disc that exactly matches the parameters of the tool: as you grind, the real value of the working speed and torque becomes lower than the maximum, and the disc is consumed more and more slowly.

Note: to convert revolutions to speed, you need to convert the speed to hertz (divided by 60), and then multiply by the circumference of the disk – diameter ?.

Processed materials

Abrasive discs can cut not only steel and cast iron, but also non-ferrous metals, stainless steel, as well as plastic, concrete, brick and stone. According to the general classification, cutting wheels are conventionally divided into metallic and non-metallic, but more detailed recommendations on the choice of grain size, structure and density, as a rule, are not given.

The general essence is as follows: the higher the hardness of the processed material, the more dense the structure of the circle should be, and the higher the viscosity, the more pores the binder should contain. The main cause of rapid wear is overheating of the edge caused by the adhesion of chip particles and their sintering. Because of this, the friction becomes very high and it becomes difficult to cool..

Used abrasives

With the grit size of the abrasive, the situation is less obvious. Many people know that the higher the speed and the softer the material to be cut, the larger the cutting tool you can choose. This is partly true for cut-off abrasive wheels: for steel, the grain size should not be less than 60, optimally – 80 or 100 grit. For aluminum or brass, it is allowed to use discs with grit from F20, for cutting stone – 36-50. For cutting plastic and wood parts, discs with the largest (F14, F16) grain are suitable.

Electrocorundum is considered the main abrasive material and is used for cutting non-ferrous metals and steels, including stainless ones. Silicon carbide is used in more specific types of discs for cutting stone, brick, and also in coarse grained discs. The microhardness of carbide is slightly higher, but it is inferior to electrocorundum in heat resistance. It should be remembered that abrasive materials differ significantly in properties from grade to grade..

Binder and circle reinforcement

According to their properties, vulcanite and bakelite differ little, except that the latter material is more tolerant to variable dynamic loads. In general, the strength characteristics of the disc depend not so much on the main binder as on the additives, additives and the production process..

The highest resource is possessed by circles with a dense and uniform, but fragile structure. In this case, the thinnest layer on the edge surface is evenly crumbled, exposing a fresh set of abrasive particles. The nature of grinding does not depend on grain size, since crumbling binder particles are usually several times larger than abrasive particles.

Wheels without reinforcement – as a rule, small-sized discs with a diameter of 115 or 125 mm, where compensation for the destructive effect of centrifugal force is not required. The same discs have the smallest thickness – about 1–1.25 mm. The thicker the disk, the more mesh layers it can have..

The most obvious way to assess the structure of a cut-off wheel is to break the worn out residue in half. If there is a web of cracks along the fracture line, the disc is of low quality. If a circle of normal hardness and density simply crumbles into sand, easily exposing the reinforcing mesh at the fracture line, this is also a sign of low-grade products. It is optimal if the disc gives a clear line at the fracture, while large scales and delamination do not form at the edges, and only fine dark sand pours out of the crack.

Summary: signs of a quality product

To cut quickly and save consumables, you should use discs with a balance class of no more than 2, without visible defects, with a clear and evenly applied label. Working speed, grain size and disc structure are selected exactly for the workpiece material and cutting technique.

In practice, cutting-off wheels made by LugaAbrasiv, as well as more expensive, but time-tested Bosh and Makita, have proven themselves well. HILTI can boast of high quality consumables with a reasonable cost, these disks have a very high working life.

Naturally, the use of expensive discs will not necessarily provide savings in the constantly repetitive routine cutting operations, but can provide a significant increase in the quality of surface treatment. Therefore, a series of tests is recommended. Cut the same steel shoulder straps, for example, angle steel, into thin plates and count the number of cuts. After making 20-30 cuts with each of the tested discs, measure their final radius, draw conclusions about the grinding speed. Please note that the wear rate in different parts of the disc may differ, the most important is the extreme part, because the cutting depth depends on it. Also remember that a properly selected disc is always better than an expensive brand that is not designed for individual tasks – there are no universal cutting wheels.