how to choose a grinding wheel? This article mainly writes the specifications and properties of the grinding wheel, how to choose the grinding wheel, how to store and transport the grinding wheel, etc.
Types and performance of grinding wheels
Grinding wheels are the most important type of abrasive tools in grinding. The grinding wheel is a porous body made by adding a binder to the abrasive, compacted, dried and roasted.
Due to the different abrasives, bonding agents and manufacturing processes, the characteristics of the grinding wheel vary greatly, so it has an important impact on the processing quality, productivity and economy of grinding.
The characteristics of the grinding wheel are mainly determined by factors such as abrasive, particle size, binder, hardness, structure, shape and size.
(2) Classification of grinding wheels
There are many types of grinding wheels.
According to the abrasive used, it can be divided into ordinary abrasive (corundum (Al2O3) and silicon carbide, etc.) grinding wheel and super-hard abrasive (diamond and cubic boron nitride) grinding wheel;
According to the shape of the grinding wheel, it can be divided into flat grinding wheel, bevel grinding wheel, cylindrical grinding wheel, cup grinding wheel, dish grinding wheel, etc .;
According to the bonding agent, it can be divided into ceramic grinding wheel, resin grinding wheel, rubber grinding wheel, metal grinding wheel and so on.
White corundum wheel
Brown corundum grinding wheel
Green silicon carbide grinding wheel
(3) The properties of the grinding wheel and how to choose a grinding wheel
The grinding wheel is a circular fixed abrasive with a through hole in the center made of abrasives and bonding agents.
The characteristics of the grinding wheel are determined by factors such as abrasive, particle size, hardness, binder, shape and size, which are now introduced as follows.
1. Abrasive and its selection
Abrasive is the main raw material for manufacturing grinding wheels, which is responsible for cutting work. Therefore, the abrasive must be sharp, with high hardness, good heat resistance and certain toughness. The names, codes, characteristics and uses of commonly used abrasives are shown in Table 1.
Table 1 Commonly used abrasives
|Oxide series||Brown corundum||A(GZ)||Contains 91 ~ 96% alumina. Brown, high hardness, good toughness, cheap price||Grinding carbon steel, alloy steel, malleable cast iron, hard bronze, etc.|
|White corundum||WA(GB)||Contains 97 ~ 99% alumina. White, higher hardness, lower toughness than brown corundum, good self-sharpness, less heat generation during grinding||Precision grinding hardened steel, high carbon steel, high speed steel and thin-walled parts|
|Carbide series||Black silicon carbide||C(TH)||Contains more than 95% silicon carbide. It is black or dark blue and shiny. Harder than white corundum, brittle and sharp, good thermal conductivity and electrical conductivity||Grinding cast iron. Brass, aluminum, refractory and non-metallic materials|
|Green silicon carbide||GC(TL)||Contains more than 97% silicon carbide. Green, higher hardness and brittleness than TH, good thermal conductivity and electrical conductivity||Grinding cemented carbide, optical glass, precious stones, jade, ceramics, honing engine cylinder liners, etc.|
|Super Hard Abrasive||Synthetic diamond||D(JR)||Colorless and transparent or light yellow, yellow green, black. High hardness, more brittle than natural diamond. The price is many times more expensive than other abrasives||Grinding high-hardness materials such as cemented carbide and precious stones|
|Cubic boron nitride||CBN(JLD)||Cubic crystal structure, hardness is slightly lower than diamond, higher strength, good thermal conductivity||Grinding, grinding, honing various hardened and toughened steel and high molybdenum, high alum, high cobalt steel, stainless steel|
2. Granularity and selection
Particle size refers to the size of abrasive particles. There are two types of particle size: abrasive grain and micro powder. The abrasive particles are classified by the screening method, and its particle size number is expressed by the number of holes within one inch of the screen.
For example, 60 # abrasive grains indicate that it can pass through a screen with 60 holes per inch, but cannot pass through a screen with 70 holes per inch.
The size of 120 # means that it can pass through a screen with 120 holes per inch.
For abrasives with a particle size of less than 40 μm (micron, 1 mm = 1000 microns), it is called fine powder. Micro powder is classified by micro measurement method, and its particle size number is expressed by the actual size of the abrasive (W). See Table 2 for the abrasive particle sizes of various particle numbers.
Table 2 Grinding wheel particle size table
|Granularity number||Particle size（um）||Granularity number||Particle size（um）||Granularity number||Particle size（um）|
The choice of abrasive particle size is mainly related to the roughness of the processed surface and productivity.
During rough grinding, the grinding allowance is large, and the required surface roughness value is large, so coarse abrasive particles should be used. Because the abrasive grains are thick, the pores are large, and the grinding depth is large, the grinding wheel is not easy to block and heat.
When fine grinding, the margin is small, and the roughness value is low, and finer abrasive particles can be selected.
In general, the finer the abrasive particles, the better the roughness of the grinding surface. The particle size is not the only factor that plays a decisive role. I have seen the mirror surface polished with 80K wheels. See Table 3 for the application of different granularity grinding wheels.
Table 3 Scope of use of different size grinding wheels
|Granularity number||Particle size range/μm||Scope of application||Granularity number||Particle size range/μm||Scope of application|
|12-36||2000-||Rough grinding, rough grinding, cutting billet, grinding burr||W40-20||40-28
|Precision grinding, super-precision grinding, thread grinding, honing|
|Rough grinding, semi-fine grinding, fine grinding||W14-10||14-10
|Fine grinding, fine grinding, super fine grinding, mirror grinding|
|Precision grinding, profile grinding, tool sharpening, honing||7-5||Super precision grinding, mirror grinding, making abrasives, etc.|
3. Binding agent and its selection
The role of the bonding agent is to bond the abrasive particles together so that the grinding wheel has the necessary shape and strength.
(1), ceramic binder (V): good chemical stability, heat resistance, corrosion resistance, and low cost, accounting for 90%, but it is brittle, not suitable for thin slices, and not suitable for high speed. The linear speed is generally 35m / s.
(2), resin binder (B): high strength and good elasticity, impact resistance, suitable for high-speed grinding or grooving and cutting work, but poor corrosion resistance and heat resistance (300 ℃), good self-sharpness.
Regarding self-sharpness: the grinding effect of the grinding wheel mainly depends on the sharp edges and corners exposed by the abrasive grains. During the grinding process, the sharp edges and corners will slowly wear off and become dull, weakening the grinding ability of the grinding wheel. At this time, the abrasive particles on the surface will fall off or break, forming a new grinding edge to achieve a sharp grinding effect, which is self-sharpening.
(3), rubber bond (R): high strength, good elasticity, impact resistance, suitable for polishing wheels, guide wheels and thin grinding wheels, but poor corrosion resistance and heat resistance (200 ℃), good self-sharpness.
(4) Metal bond (M): bronze, nickel, etc., high strength and toughness, good formability, but poor self-sharpness, suitable for diamond, cubic boron nitride grinding wheels.
Table 4 Binding agent code, performance and use
|Ceramic binder||V||Clay, feldspar talc.||(1) Resistant to water, acid, alkali and heat (2) Brittle and difficult to block (3) Cheap (4) Linear speed of 35M / S||Grinding of narrow grooves except cutting parts|
|Resin bond||B||Resin made of carbolic acid and formaldehyde||1) High strength and good elasticity 2) Poor heat and corrosion resistance 3) Storage time no more than one year||Grinding narrow grooves. Grinding wheel for cutting. Grinding wheels for polishing|
|Rubber binder||R||Elastomer||1) High strength and high elasticity 2) Good concession and vibration absorption 3) Not oil resistant||Narrow groove grinding surface|
|Rhododendron soil binder||Mg||1) Good self-sharpness 2) Low grinding heat||Grinding metal with large surface area and poor thermal conductivity|
4. Hardness and selection
The hardness of the grinding wheel refers to the difficulty of the abrasive particles on the surface of the grinding wheel falling off under the action of the grinding force. The hardness of the grinding wheel is soft, which means that the abrasive particles of the grinding wheel are easy to fall off, and the hardness of the grinding wheel is hard, which means that the abrasive particles are more difficult to fall off. (Important! The hardness of the grinding wheel does not refer to the hardness of the grinding wheel)
The hardness of the grinding wheel and the hardness of the abrasive are two different concepts. The same kind of abrasive can be made into different hardness grinding wheels, which mainly depends on the performance and quantity of the bonding agent and the manufacturing process of the grinding wheel. The obvious difference between grinding and cutting is that the grinding wheel has “self-sharpening”. Choosing the hardness of the grinding wheel is actually choosing the self-sharpening of the grinding wheel. Fall off.
The general principle of selecting the hardness of the grinding wheel is: when processing soft metals, in order to prevent the abrasive from falling off prematurely, the hard grinding wheel is used. When processing hard metals, in order to make the blunt abrasive particles fall off in time, thereby exposing new abrasive particles with sharp edges and corners (that is, self-sharpness), soft grinding wheels are used.
The former is because when grinding soft materials, the abrasive wear of the grinding wheel is very slow and does not need to be detached too early; the latter is because when grinding hard materials, the abrasive wear of the grinding wheel is faster and requires faster Update.
When fine grinding, in order to ensure the grinding accuracy and roughness, a slightly harder grinding wheel should be used. When the thermal conductivity of the workpiece material is poor, and it is easy to cause burns and cracks (such as grinding carbide, etc.), the selected grinding wheel should be softer.
Do you know how the hardness of the grinding wheel is tested in the factory? Don’t laugh at all: it’s a chisel.
Table 5 Grinding wheel hardness classification and code
|so soft||so soft||D．E．F．|
|medium soft||medium soft 1||K|
|medium soft 2||L|
|medium hard||medium hard 1||P|
|medium hard 2||Q|
|medium hard 3||R|
|so hard||so hard||Y|
Note: The “code” in the above table is the current new national standard code. The old national standard code is represented by the first letter of Chinese characters + digits, such as: medium hard 1 = ZY1, some grinding wheels are still using the old national code, As shown in the figure above, there is a “R3” on the grinding wheel, which is “soft 3”.
Table 6 Simple selection criteria for grinding wheel hardness
|soft||←————Grinding wheel hardnes————→||hard|
|Hard and crisp||←————Workpiece material————→||Soft and sticky|
|slow||←————Workpiece feed speed————→||fast|
|good||←————Material machining performance————→||bad|
5. Organization of grinding wheel
The organization of the grinding wheel is the proportional distribution of the amount of abrasive, bond and pore. Simply speaking, it is the distance between abrasive particles. The distance between abrasives is very difficult to measure, and the percentage of abrasive in the volume of the grinding wheel, that is, the abrasive rate, is used as the organization standard.
Depending on the organization, compact or loose grinding wheels with different densities can be made to suit different grinding conditions. The abrasive particles of the grinding wheel can be quickly broken after being blunt, so that the new blade is exposed to continue grinding.
The densely organized grinding wheel has fewer pores and the loosely organized grinding wheel has more pores. Although there are many blowholes, the bonding degree is weak, but there is a large cutting space, which can improve the cutting effect. Large pores and few holes are called coarse grinding wheels; small pores and many holes are called dense grinding wheels.
Simply put, the large-diameter grinding wheel is suitable for grinding soft and sticky materials, such as aluminum and copper; on the contrary, it is suitable for grinding hard and brittle materials.
6. The shape of the grinding wheel
The shape of the grinding wheel is roughly divided into five types, flat, hypotenuse (double hypotenuse, single hypotenuse), dish, bowl and cup.
Flat-shaped grinding wheels are the most widely used. They can grind flat surfaces, outer circles, slots, etc., and can be shaped into various shapes for grinding according to actual needs.
There is no need to talk too much about the bevel edge grinding wheel. Everyone understands that the carpenter usually uses a single bevel edge grinding wheel to grind the alloy saw blade.
Disc-shaped and bowl-shaped grinding wheels are usually used to grind various tools and cutting tools, such as drills and milling cutters.
The cup-shaped grinding wheel can be used for many purposes. For example, this type of grinding wheel is used on the machine of the grinding knife. In addition, the bowl-shaped grinding wheel can also be used for vertical grinding.
There are many types of grinding wheels with handles (such as those used in electric grinders). The grinding wheels can be made into many shapes to meet different needs.
7. The size of the grinding wheel
The size of the grinding wheel is usually represented by a string
Examples of signs for grinding wheels:
SPA400 × 100 × 127A60L5B35
SPA —– shape code
400 —— Outer diameter D
100 —— thickness H
127 —- Aperture D
A ——— Abrasive
60 ——– Granularity
L ——— Hardness
5 ——— Organization number
B ——– Binder
35 ——- Maximum working linear speed m / s
Storage and transportation of grinding wheels
The strength of the grinding wheel is low and it is susceptible to factors such as temperature, humidity, vibration, collision, extrusion and storage time. It is of great significance to prevent the accident by properly storing and transporting the grinding wheel. To this end, the following should be done:
1. The grinding wheel should be stored on a dedicated storage rack.
2. The storage of grinding wheels should be reduced as much as possible to prevent cracks caused by impact and vibration. The grinding wheel is brittle, please don’t hit, fall and collide.
3. Be careful not to contact oil when storing rubber bond grinding wheels; do not contact alkali solution with resin bond grinding wheels. Ceramic abrasive tools should not be placed in a humid or frozen place, otherwise the abrasive strength and grinding force will be reduced.
The resin and rubber bond grinding wheel should be sandwiched between two smooth and flat metal plates during storage. The metal plate should be larger than the diameter of the grinding wheel. In addition, do not put it directly under damp and blower to prevent bending and deformation. The grinding wheel cannot be stored for a long time, and the resin and rubber will deteriorate after more than one year. At this time, it must be strictly inspected before use.
Rubber and resin bond thin grinding wheels should be prevented from deformation during storage.
4. The storage of the grinding wheel should be based on the manufacturer’s instructions. The expired grinding wheel cannot be used casually.
5. During the transportation of the grinding wheel, it can not be installed with metal objects and reduce vibration and impact.
6. Abrasive tools should be stored in a dry place, the room temperature is not less than 5 degrees Celsius; when the grinding wheels are stacked, the stacking height is generally not more than.
7. The grinding tools should be placed separately according to the specifications, and the storage place is marked with signs to avoid confusion and errors. The placement method should depend on the size of the grinding shape. Abrasive tools with larger diameter or thicker should be placed upright and slightly inclined, and thinner and smaller grinding wheels should be placed horizontally, but not too high, and a flat iron plate should be placed under each one to prevent deformation of the grinding wheel Or cracked.
Diamond grinding wheel
The reason why the diamond grinding wheel is taken out alone is because many people don’t know much about the diamond grinding wheel, and it is easy to enter the wrong area. Anyone who sees the word “diamond” will have only one idea, that is, “hard”.
At present, diamond is the material with the highest hardness in nature, so abrasive tools made of diamond have inherent advantages, especially when used in difficult-to-grind materials.
There is a table below, which shows the hardness indexes of various abrasives. This table is from a textbook of a university in Taiwan. From the table, it can be seen that the hardness comparison between the hardness of various materials is a bit similar to the Mohs scale Method, you can make a reference:
The diamond grinding wheel mainly uses diamond as the main abrasive, and then is formed by a bonding agent. The bonding agent is roughly divided into four types: metal, resin, ceramic and electroplating, which can be made into various shapes.
Diamond wheels can be used for grinding, polishing, grinding and cutting purposes. At the same time, it is used to grind high-hardness alloys and non-metallic materials. The high hardness of diamond, high compressive strength and good wear resistance make the diamond grinding wheel the most ideal tool for hard and brittle materials and cemented carbides during grinding. The diamond grinding wheel not only has high efficiency and high precision, but also the surface of the workpiece after grinding The roughness is good, the grinding wheel consumption is low, the service life is long, and at the same time, a large amount of dust will not be generated during grinding, and the working conditions are improved.
The use of diamond grinding wheels: It is used for hard and brittle materials with low iron content that are difficult to be processed by ordinary grinding wheels, such as cemented carbide, agate gemstone, semiconductor materials, glass, high-alumina ceramics, stone, etc.
Here, please note that it is “metal and non-metallic materials with low iron content”
The following are personal opinions:
1. About the binder and its use.
The diamond wheels of metal bond are generally made of bronze sintered diamond particles, which are mostly used for stone cutting and grinding. They have high bonding strength and long service life. They are suitable for heavy cutting operations.
The diamond grinding wheel with resin bond is more widely used, and it is very good for grinding cemented carbide. I used a new diamond grinding wheel to grind a dozen solid carbide (YG6x, hardness greater than YG8) seal cutters (8mm wide 8 pieces of 6 mm wide and 8 pieces of 6 mm wide). After grinding, it was found that the grinding wheel was almost not worn. It really did not even wear off the skin, and the efficiency was very high.
The production of diamond grinding wheels with ceramic bond is more troublesome, and there are few on the market, and we can’t use them, so I won’t go into details here.
Let’s talk about electroplating. The electroplated diamond grinding wheel is to plate the diamond particles on the substrate by electroplating. This kind of grinding wheel is really a good thing. I like this kind of grinding wheel very much.
The advantage of this type of grinding wheel is that the substrate can be processed into any shape, coated with a layer of diamond particles, and shaped for grinding. Diamond wheels are very hard, and you can’t repair them into any shape like dressing corundum wheels. At this time, the formed substrate is very important, and because there is only a layer of diamond on the surface, the cost is relatively low.
The disadvantage of electroplating is that it is easy to touch off the diamond particles coated on it. Most of the particles are hung up by the workpiece instead of being worn away. Fortunately, I have better conditions. After polishing, I can get it in the factory and plate it, which is very convenient.
I don’t dare to buy the “electroplated diamond whetstone” of a certain treasure. The glitter on it is mostly green silicon carbide particles. I don’t know how to make abrasive tools, but I asked the master in the factory. The master said that it is technically very difficult to electroplat diamond and silicon carbide on the steel plate at the same time. This shows that others are also using technology to make money, it is understandable.
2. About diamond grinding wheels
Many people like to use diamond wheels to grind planers, chisels, etc. They think diamond is very hard and the grinding efficiency is high, but this is actually not a good choice. Diamond is very hard, but it is not suitable for grinding iron-carbon alloys (steel).
At first, you will use diamond to grind, and you will feel that the “under meat” is very fast. The carbon in the diamond will react chemically with the carbon in the steel. As a result, the diamond will soon be worn away. In the factory, the diamond grinding wheel is repaired by using an iron block, and the diamond is worn away little by little. Therefore, it is not to say that diamonds cannot grind steel, because diamonds are too expensive.
3. The choice of sharpening
Ordinary whetstones are usually used for grinding steel tools used by hand. Silicon carbide or alumina are good. A softer whetstone may work best. This is the best way to “how fast and save”. I don’t need to sharpen the knife with natural stones, and finally I will sharpen it, and then run into a piece of impurities and fall apart, blindly delaying the effort.
Some people think that “natural magma” is easy to use. This is correct. This kind of stone is relatively soft, and it is worn away. It is equivalent to grinding away the blunt particles on the surface, and the sharp blade is exposed. The particles also play the role of grinding and polishing. I have n’t seen the “slurry” grinded down by the old shaving master ’s grindstone. I am wrapped up in a towel and hid it.
Don’t be superstitious about “natural Japanese magma”, it is often priced at hundreds or hundreds. Japan’s stones will not be better than those of the heavenly dynasty. The island nation estimates that there are more new volcanic rocks.
Also, those “natural agate whetstones” and “ruby whetstones” on a treasure are all sintered with corundum. Anyway, if I have such a large piece of beautiful gemstone, I would definitely not be willing to sell it as a whetstone.
There are three reasons why I do n’t use natural stone sharpeners: first, there may be impurities; second, it is not durable and wears too fast; third, there is not much granularity to choose from.
If conditions permit, the grinding knife can use boron nitride whetstone, pay attention to “boron nitride”, not “boron carbide”, this kind of abrasive has high hardness, very suitable for grinding metal materials, it can certainly “how fast” “Province” won’t account for it, but four accounts for three, and it’s enough