Abrasive sanding belt grinding is a special form of abrasive belt grinding tool, with the help of tension mechanism to make it tensioned, and the driving wheel to make it move at high speed, and under a certain pressure, the abrasive belt and the workpiece surface contact to achieve the entire process of grinding processing.
Broadly speaking, belt grinding and grinding wheel grinding are also the cumulative effect of high-speed moving "micro-edge cutting tools" - the formation of micro cutting particles, so the grinding mechanism is roughly the same. However, because of the different composition characteristics and use mode of abrasive belt itself, abrasive belt grinding is different from grinding wheel grinding in both grinding mechanism and comprehensive grinding performance.
Performance:
1) Grinding wheel is rigid contact grinding
The abrasive sanding belt grinding is elastic contact grinding, and even in the case of inelastic steel contact wheels, because the substrate and binder that make up the abrasive belt have a certain degree of elasticity, not to mention the use of elastic rubber as the contact wheel in most cases.
Because of this, in addition to the grinding wheel with the same sliding, ploughing and cutting effects, there is also the abrasive extrusion on the workpiece surface, and the plastic deformation, the change of the cold layer and the surface tear and the thermoplastic flow caused by the friction of the contact point temperature increase. Therefore, from this point of view, belt grinding has multiple functions of grinding, grinding and polishing. This is also why the abrasive belt grinding surface quality is good.
On the other hand, due to the elastic grinding characteristics of the sand belt, the length of the contact between the sand belt and the workpiece in the grinding area is larger than that of the grinding wheel, and the number of abrasive particles participating in the grinding is large, and the load on a single abrasive particle is small and uniform, and the abrasive particle damage is small. The wear ratio of the entire abrasive belt (the ratio of the amount of grinding material removed to the abrasive grain consumption of the abrasive belt is called the grinding ratio, and the reciprocal of the grinding ratio is called the wear ratio) is much smaller than that of the grinding wheel.
2) The distribution of grinding grains on the grinding surface of the grinding wheel is disorganized
It is very irregular, in the actual grinding, the abrasive particles are cut with a large negative front Angle, a small back Angle or even a negative back Angle, and the cutting conditions are very bad. The abrasive belt is different, the abrasive belt is specially made, the geometry of the abrasive particle is often in the shape of a delta body, and is mostly made by a series of advanced processes such as electrostatic sand planting. The size and distribution of the abrasive particle are uniform, and the contour is good, and the sharp edge is outwards in the form of planting on the surface of the sand belt substrate, exposing more parts of the adhesive layer. Therefore, the abrasive belt is sharper than the abrasive wheel, the cutting conditions are better, the material deformation is small during grinding, the cutting rate is high, the grinding force and the resulting grinding heat are small, and the grinding temperature is low.
3) The grinding wheel is filled with binder
There is very little room. The chest-containing space between the abrasive sanding belt particles is generally at least 10 times larger than the grinding wheel, and the abrasive grain equiheight is good, so the effective cutting area of the abrasive belt particles is large, the cutting ability is stronger than the grinding wheel, and the abrasive chips can be directly taken away at any time, rarely remaining on the surface of the abrasive belt causing blockage, without increasing friction and heating, and the grinding zone temperature is low.
4) Perimeter of the sand belt
From the design point of view, it can far exceed the circumference of the grinding wheel, which makes the abrasive belt not only have a good heat dissipation strip during grinding, but also through the suspended part of the abrasive belt (that is, the part that is not in contact with the contact wheel, tensioning wheel, grinding plate, etc.) during operation, the abrasive stick on the abrasive belt can be naturally shaken off, further reducing the phenomenon of abrasive particles being filled. This reduces friction heat, which is also a reason for the low grinding temperature of the belt.
It can be seen that the processing mechanism of abrasive belt grinding is a more complex form that is the same as and different from abrasive belt grinding, which is the theoretical basis and fundamental starting point for analyzing and understanding the mechanism of abrasive belt grinding.
Belt grinding is accomplished by a large number of vertically oriented abrasive cutting edges arranged on the surface of the belt. Each abrasive particle can be regarded as a micro tool, so studying the grinding process of these single abrasive particles is the basis of studying the whole abrasive belt grinding.
From the microscopic point of view, the abrasive particles on the surface of the sanding belt are as follows: the tip of a knife is circular, and the edge Angle is obtuse or blunt
Round cutting tool. The radius of the arc is from a few microns to tens of microns, and the size is related to the material and particle size of the abrasive particle. Due to this geometric characteristics of abrasive particles, when grinding, the cutting depth is small (chip thickness is thin), generally about 0.005 ~ 0.05mm. Therefore, the vast majority of abrasive cutting edges are used to cut the workpiece under the condition of large negative front Angle. This is the same as the cutting process of the machine tool, the workpiece material is deformed into chips under the extrusion and friction of the abrasive cutting edge, and the processing surface is formed. The elastic contact characteristic of abrasive belt makes the cutting process of abrasive cutting edge roughly divided into four stages: extrusion, sliding, ploughing and cutting. At first, the abrasive particles squeeze into the workpiece, because the cutting depth is less than the radius of the abrasive blade tip, forming a large negative front Angle, the workpiece surface only elastic deformation. With the increase of cutting depth, the pressure of abrasive particles on the workpiece surface gradually increases, and the workpiece surface begins to transition from elastic deformation to plastic deformation. The abrasive particles continue to squeeze, the friction intensifies, the thermal stress increases sharply, and the grooves are ploughed out on the surface of the workpiece, and the metal slips and protrudes on both sides of the grooves. The plastic deformation of workpiece material is increasing. As the cutting depth continued to increase, the pushed metal layer slipped significantly. When the pushing pressure exceeds the strength of the workpiece material, the chip flows out of the front tool surface and cuts away from the workpiece surface. The proportion of the four stages of the abrasive cutting process in the entire grinding process is also different.
Surface formation principle of abrasive belt grinding
Grinding process is the process of abrasive cutting edge cutting metal, it is the same as machine tool cutting, grinding metal also experienced elastic deformation, plastic deformation, cutting formation and other processes, and there are a lot of grinding force and grinding heat generation. Due to the different shape and distribution of abrasive particles in grinding process, the actual effective abrasive particles on the surface of abrasive belt are less than the total number of abrasive particles. Therefore, at the same time, the size of the extrusion, sliding, ploughing and cutting action of the abrasive particles on the metal is different, and the results are different. Even different parts of the same abrasive particle and the same part play different roles in different processing times. It can be seen that the grinding of sand belt is very complicated. In particular, the negative front Angle cutting process of the abrasive cutting edge, the cutting conditions are very poor, the intense extrusion at each stage makes the grinding surface produce serious plastic deformation, and a large number of plastic deformation of the metal is not a chip outflow, but still retained on the machined surface, so the hardening phenomenon of the machined surface is serious, and the residual stress is large. Due to the high speed movement of the abrasive particle and the blunt cutting edge of the abrasive particle, it will cause greater friction and elastic and plastic deformation in the grinding zone, and there will be greater heat generation during the grinding process, resulting in the rise of the surface temperature of the workpiece in the grinding zone, which will cause changes in the surface layer of the workpiece. Especially when the abrasive wear of the belt is serious, the grinding friction is intensified, and a large amount of grinding heat is generated, which causes the surface temperature of the workpiece to rise sharply, resulting in organizational changes in the surface metal (such as burns, cracks, thermal stress, etc.). This is one reason why the use of abrasive belt grinding can sometimes still burn the surface of the workpiece.
So, in summary,
The mechanism of belt grinding can be summarized as follows:
Because of the uniform distribution of abrasive particles on the surface of the abrasive belt, good contour, exposed sharp edge and sharp cutting edge, the cutting conditions are better than that of the grinding wheel, so that the grinding particles have large plowing and cutting effects during the grinding process of the abrasive belt, so the material removal rate is high and the efficiency is high.
After nearly 30 years of development, abrasive belt grinding has become a relatively complete and self-forming new processing technology. Because of its high processing efficiency, wide application range, strong adaptability, low cost of use, safe and convenient operation and so on, it is favored by users. In foreign countries, abrasive belt grinding technology has made great progress, its processing objects and application fields are becoming more and more extensive, it can process almost all engineering materials, from general daily life appliances to large-scale aerospace equipment can not be applied, and has become an important means to obtain significant economic benefits. As a processing technology, it has been paid more and more attention and developed rapidly because it has the following important characteristics:
Abrasive belt grinding is a kind of elastic grinding, is a kind of grinding, grinding, polishing a variety of composite processing technology.
The abrasive belt has a stronger cutting ability than the abrasive wheel, so its grinding efficiency is very high. The high efficiency of abrasive belt grinding is reflected in its high cutting rate, grinding ratio (the ratio of the weight of the workpiece to the weight of the abrasive wear) and the power utilization of the machine tool. At present, the steel removal rate of the known belt grinding has reached 700mm3/mm·s, even more than turning or milling. The grinding ratio of the belt is much higher than that of the grinding wheel, up to 300:1, or even 400:1, while the grinding wheel is only 30:1. The power utilization rate of abrasive belt grinding machine, as far as the early development of abrasive belt grinding has reached 80%, ahead of other machine tools, and now it is as high as 96%, compared with only 52% of abrasive grinding machine, milling machine 57%, lathe 65%, so abrasive belt grinding is still a good energy-saving processing technology.
Abrasive belt grinding workpiece surface quality is high. In addition to its multiple roles of grinding, grinding and polishing, this is because:
Compared with grinding wheel grinding, abrasive belt grinding is called "cold grinding", that is, the grinding temperature is low, and the workpiece surface is not easy to burn and other phenomena.
The abrasive belt grinding system has low vibration and good stability.
Due to the light weight of the sand belt itself, the balance state of the grinding process structure system is easy to control, and all the rotating parts (such as the contact wheel, the drive wheel, the tension wheel, etc.) wear is minimal, and there will be no dynamic imbalance factors like the grinding wheel.
In addition, the elastic grinding effect of the sand belt can greatly reduce or absorb the vibration and shock generated during grinding.
The grinding speed is stable, and the belt driving wheel will not be the same as the grinding wheel, the smaller the diameter, the slower the speed.
The high surface quality of abrasive belt grinding workpiece is mainly manifested in small surface roughness value, good residual stress state, and no micro-cracks or metallographic structure changes on the surface.
From the surface roughness point of view, the abrasive belt grinding has reached Ra0.01mm, to achieve the effect of mirror grinding, and for the roughness value of Ra0.1mm or more, it is very easy to achieve.
The residual stress on the surface of abrasive belt grinding workpiece is mostly compressive stress, and its value is generally -60~-5Kg/mm², while the grinding wheel is mostly tensile stress, so abrasive belt grinding is very conducive to strengthening the surface of the workpiece and improving the fatigue strength of the workpiece.
Abrasive belt grinding accuracy is high. Due to the improvement of the quality of sand belt production and the production level of sand belt grinding machine, sand belt grinding has already entered the ranks of precision and ultra-precision processing, and the highest accuracy has reached less than 0.1mm.
Belt grinding cost is low. This is mainly reflected in:
Abrasive sanding belt grinding equipment is simple. Compared with the grinding wheel grinder, the abrasive belt grinder is much simpler, mainly because the abrasive belt weight is light, the grinding force is small, the vibration is small during the grinding process, and the rigidity and strength requirements of the machine tool are much lower than that of the grinding wheel grinder.
Abrasive sanding belt grinding is easy to operate and less auxiliary time. Whether it is manual or motorized belt grinding, the operation is very simple. From the replacement of the adjustment sand to the clamping of the workpiece being machined, it can all be done in a very short time.
The abrasive belt grinding ratio is large, the machine power utilization rate is high, and the cutting efficiency is high.
This results in reduced tool and energy costs for removing the same weight or volume of material, and a shorter footprint.
Belt grinding is very safe, low noise and dust, and easy to control, good environmental benefits.
Because the sand belt itself is very light, even if it breaks, there is no danger of injury. Belt grinding is not as serious as the grinding wheel, especially when dry grinding, the grinding chips are mainly the material of the workpiece being processed, and it is easy to recover and control the dust. Because the rubber contact wheel is used, the abrasive belt grinding will not form a rigid impact on the workpiece as the grinding wheel, so the processing noise is very small, usually <70dB. It can be seen that from the point of view of environmental protection, belt grinding is also worth promoting.
The abrasive sanding belt grinding process is flexible and adaptable. This is manifested in:
Belt grinding can be easily used for grinding plane, inner, outer circle and complex surface. Design a abrasive belt grinding head device as a functional component can be installed in the lathe after driving grinding, can also be installed in the planer used, but also can be designed into a variety of special grinding machines. Using this characteristic of abrasive belt grinding can easily solve some difficult parts, such as ultra-long, ultra-large shaft and plane parts precision machining.
The base materials, abrasives and binders of the sand belt have a large selection range, which can meet the needs of various uses. The grain size, length and width of the sand belt also have various specifications, and a variety of forms such as roll and ring are available.
For the same workpiece, abrasive belt grinding can be processed by a variety of different grinding methods and process structures.
Belt grinding has a wide range of applications
The superior grinding performance and flexible process characteristics of abrasive belt determine that it has an extremely wide range of applications, from daily life to industrial production of all walks of life, abrasive belt grinding in almost all fields. The variety of its application forms and the wide range are incomparable to any other processing methods. It is manifested in:
Belt grinding can grind almost any engineering material. In addition to the materials that the grinding wheel can process, it can also process non-ferrous metals such as copper, aluminum and non-metallic soft materials such as wood, leather and plastic. In particular, the "cold state" grinding effect of abrasive belt grinding makes it more unique in the processing of heat-resistant and difficult to grind materials.
Belt grinding can process various shapes of workpieces with high surface quality and accuracy requirements. Belt grinding can not only process the common flat, inner and outer round surface of the workpiece, but also with high efficiency to process the surface quality and precision requirements are high large or shaped parts. For example:
Polishing of large area plate.
The maximum width of the grinding wheel is only 1000mm, while the sand belt can be more than 2500mm. The widest known belt grinder has a sand bandwidth of 4900mm. The common processing width of sand belt grinding in actual use is 50~2000mm, and the processing thickness is 0.4~150mm. Its productivity is up to 1000m2/h. This kind of wide abrasive belt grinding can be widely used in steel plate, stainless steel plate, silicon steel sheet, aluminum plate, copper plate, particleboard, plywood, medium density fiberboard, leather, insulation board, ceramic board and aerospace equipment, ships and nuclear physics research equipment used in a variety of high precision and low roughness of the surface processing of large plates. The precision machining of the intermittent plane such as the cross-section of the engine gearbox can also be formed with a wide sand belt grinding, and can ensure better sealing than the traditional milling and planing surface.
Continuous polishing of metal strip or wire
Due to the development of wide abrasive belt grinding, the thin strip has the same grinding conditions in the entire width, so that the local force is not too large, resulting in stress deformation, so the surface of cold-tied steel strip, copper, aluminum strip and other alloy strip is suitable for continuous abrasive grinding with abrasive belt. The processing width is 600~2100mm, the processing thickness is 0.1~2.2mm, the surface roughness is 3.2~0.1mm, and the strip running speed is 3~80m/min. Planetary belt grinding provides a very effective and economical processing method for polishing rolled wire of stainless steel or other materials. The known wire polishing diameter is 0.8~20mm. The continuous running speed is 6~150m/min.
Inner and outer circular polishing of workpiece with large length-diameter ratio.
In modern industry, it is very convenient to use abrasive belt grinding to process the outer round surface of various large shaft workpieces and the inner round surface of tube workpieces with a large ratio of length to diameter. Generally, it can be achieved by adding a belt grinding device to a large standard equipment. For large batches, a special abrasive belt grinder can be used. Such as large generator rotor, roll, paper dryer and other workpieces of the outer circle and cylinder, oil pipelines, pressure vessels and other workpieces of the inner circle surface processing.
Polishing of complex shaped workpieces.
The forming and grinding of curved surface workpiece is difficult. However, all kinds of complex surfaces can be easily processed by using the flexibility of the sand belt. The inner corners with a radius of curvature of only 3mm can also be polished by the sand belt. Such as aircraft engine sheets, turbine blades, navigation blades, condenser lamp bowls, mirrors, tableware, handles, water heating appliances, etc., can be used for high efficiency and high quality polishing processing.
Abrasive sanding belt grinding equipment has various forms and varieties. It can be performed on a variety of general purpose belt grinding equipment. General sand belt grinding equipment small portable belt sander, universal belt sander, desktop belt sander; The large ones include outer round abrasive belt grinding machine, flat abrasive belt grinding machine, centerless abrasive belt grinding machine and inner round abrasive belt grinding machine. Special abrasive belt grinder camshaft abrasive belt copy grinding machine, industrial tank abrasive belt polishing machine, automobile tire end face abrasive belt polishing machine, motorcycle oil tank abrasive belt polishing machine, special stainless steel star basin hair machine.
