1 Introduction
Abrasive belt grinding is a new process for grinding and polishing the surface of a workpiece with a corresponding contact method and a belt that moves at a high speed according to the shape of the workpiece. With the progress and development of automobiles, building materials, decoration industry, mold industry and Other light industries, the surface machining quality, productivity and labor environment of metal and non-metal materials, especially difficult-to-process materials such as plastics, leather, rubber, stainless steel, ceramics, etc. More and more high requirements have been put forward, and it has been difficult to meet these requirements with conventional conventional cutting methods. In the past 50 or 60 years, abrasive belt grinding as a new process has played an increasingly important role in these processing areas. Belt grinding machines are mainly used as coarse grinding, deburring, large margin grinding, fine grinding, fine grinding, decorative polishing, centerless grinding and forming grinding. In modern industry, abrasive belt grinding technology is regarded as a very important processing method with its unique processing characteristics. Some foreign experts have commented on belt grinders as "future giants".
2 Belt grinding principle
The main methods for grinding belts are: free belt tensioning method, rotating belt method with contact wheel and contact plate method. The most commonly used is a rotating belt method with a contact wheel. As shown in Figure 1:
figure 1
The abrasive belt is placed on the outer surface of the transmission wheel and the contact wheel, and the belt is tensioned and moved at a high speed. According to the workpiece shape and machining requirements, the workpiece is ground or polished by the corresponding contact method and proper grinding parameters.
The basic components of belt grinding are:
(1) Spindle transmission. There is a single speed or variable speed drive with greater flexibility, sometimes with a reversible motor to change the direction of motion of the belt. The belt speed is 10 to 50 m/min, usually 16 to 30 m/min, and the power of the main transmission is 0.3 to 0.7 kW per 10 mm wide belt.
(2) Abrasive belt tensioner. The proper tension of the belt during grinding and guiding plays an important role in the belt grinding process, which affects the cutting performance of the belt and the surface roughness of the machined parts. When the belt tension is increased, the amount of metal removal can be increased, but at the same time, the surface roughness value and the consumption of the abrasive cover layer are also increased. Tests have shown that the belt tension is in the range of 6 to 8 N/mm, and the maximum amount of metal can be cut in each stroke during counter grinding. Tensioning mechanisms come in various forms, ranging from simple mechanical or spring methods to pneumatic and hydraulic tensioning devices for wide belts and heavy-load grinding machines. At the same time, in order to obtain maximum productivity, the belt replacement time must be minimized, and the operator can usually change the belt within 1 minute.
(3) Belt guide. When the belt is working, the idler or tensioner should be adjustable so that the belt is positioned and centered. Depending on the width of the belt, the device can be either manual or automatic. When the belt width is greater than 200mm, an automatic guide device is usually used to automatically align the belt between the contact wheel and the tensioner.
(4) Contact wheel. The contact wheel supports the abrasive belt at the grinding point, the body of which is made of aluminum or steel, and the wheel is covered with an elastic ring (thickness of 3 to 15 mm) made of rubber, fiber, felt or other materials. According to needs, various density rubber wheels can be made, and the surface of the wheel can be made into a staggered slotted type or a smooth type. Various rubber compounds are used as the cover for the contact wheel to meet certain grinding needs. These compounds include: neoprene, vinyl, silicone rubber, chlorosulfated polyethylene synthetic rubber.
(5) If a plate (steel, hard alloy or cast iron plate) is installed behind the belt to replace the contact wheel, the edging, quadrilateral, face, plane and finish grinding operations can be completed to ensure the flatness or straightness of the part. Sex.
There are also vacuum systems.
3 Belt grinding features
Belts and fragile tools have the following features compared to tools such as single-edged turning, milling, and grinding of wheels.
(1) High processing efficiency. The advanced “electrostatic sand-planting method†is adopted in the selected needle-like sand grains, so that the sand grains evenly stand upright on the substrate, and the front edge of the sand grains is upward, and the orientation is neatly arranged, the contours are good, the clearance of the chips is large, the contact surface is small, and the interface is small The cutting performance. Using this multi-blade and multi-blade cutting tool for grinding, the cutting rate of steel has reached 200-600 mm3/min per mm wide belt.
(2) High quality of machined surface. When the abrasive belt is ground, there is little friction and heat at the contact surface, and the abrasive grain heat dissipation time interval is long, which can effectively reduce the deformation and burn of the workpiece. Therefore, the machining accuracy is high, the dimensional accuracy can reach ±0.002 mm, and the flatness can reach 0.001 mm. In addition, the abrasive belt is a flexible contact during grinding, and has multiple functions such as grinding, grinding and polishing. In addition, the vibration of the grinding system is small, and the grinding speed is stable so that the surface processing quality has a small roughness value and residual stress. The condition is good, the roughness of the workpiece can reach Ra0.4 ~ 0.1μm, and the surface has a uniform roughness. However, because the belt cannot be trimmed, the precision of the belt grinding is slightly lower than that of the grinding wheel.
(3) Process flexibility and adaptability. Abrasive belt grinding can be conveniently used for plane, cylindrical, internal circular grinding, complex special-shaped surface machining, roughing grinding with cutting allowance less than 20mm, deburring and pre-machining for coated parts, polishing surfaces, elimination Slab surface defects, sharpening and grinding of cutting tools, elimination of bulges at welds, manual labor in place of pliers work. In addition to a variety of general-purpose and special equipment, designing a belt grinding head can be easily installed on conventional off-the-shelf equipment such as lathes, planers and milling machines, which can not only greatly expand the functions of these machine tools, but also solve difficult-to-machine parts such as Ultra-long, super-large shafts, flat parts, irregular surfaces, and other precision machining.
(4) The sand is highly elastic, so the entire system has high vibration resistance.
(5) The size of the abrasive belt can be large, suitable for large-area and high-efficiency machining, and the equipment is simple, the operation is safe, and the use and maintenance are convenient. It takes less time to replace the abrasive belt and train the machine operator.
(6) Belt growth during processing, shape and size cannot reach high accuracy, sharp protrusions on machined parts and fine grinding with fine-grained abrasives, belts are less stable, and in most cases Abrasive belts cannot be corrected, so the service life is short.
4 Belt Grinding Machine Design
According to the requirements of a certain factory, grinding belts were used on the inner wall of the reaction tank of the plant in order to remove the surface defects such as oxide scale on the inner wall of the part and facilitate the enamel of the inner wall. The part has a large size, originally used grinding wheel grinding process, processing noise, cuttings flying everywhere, the working environment is very poor. The machine design mainly has the following three parts (see Figure 2):
figure 2
(1) Drive design The drive design of this machine is relatively simple and mainly consists of three parts:
1 The main movement of the belt. The motor drives the abrasive belt mechanism directly, due to the large diameter of the reaction tank. The axial length is longer, so the shaft at the front end of the motor is cantilevered. The rigidity of the welded base structure is better, especially the internal stress caused by welding.
2 Feeding movement of the belt. The feed motion of the belt drives the entire belt mechanism along the reaction tank in the axial direction through a trolley mechanism composed of a screw nut mechanism. In order to allow the belt mechanism to return quickly at the end of processing, the machine is equipped with a fast motor, and the fast motor and the feed motor are connected via an overrunning clutch.
3 Feed movement of the workpiece. Due to the large workpiece, the separate motor is set to drive the reaction tank to rotate through pulleys and gears.
(2) The main mechanism design 1 belt tensioning device. This mechanism is mainly used to adjust the relative position of the contact wheel and the workpiece through the screw and the spring, and to maintain the tension of the tensioning wheel.
2 contact wheel design. Since the part is large in size and used for roughing, a harder rubber contact wheel is used. The diameter of the contact wheel is 250mm. A wider groove pattern and a narrow working surface are used on the surface of the contact wheel to increase the pressure. , Improve cutting efficiency and belt life, according to the characteristics of the parts, groove groove spacing is taken as 10mm.
(3) The main technical parameters are: belt speed 20 to 30m/s, belt length 2500 to 3150mm, width 200mm, belt motor power 7.5kW.
5 Concluding remarks
As a new technology, abrasive belt grinding has been applied in various types of abrasive belt machines in the world. Domestically, it is still in the stage of promotion and application. Its superiority has been gradually recognized by people. If this new technology is further promoted and applied, it will certainly have a greater impact on China's manufacturing industry, and it will also play an important role in reducing the cost, improving the efficiency, and improving the precision of product processing for the current sluggish SMEs.
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