GMT is among the leading manufacturers of belt grinding machine in India.
HEAVY-DUTY BELT GRINDING MACHINE
GMT Belt Grinding Machine achieves high production efficiency, quality finish and economy, which cannot be achieved by any other method of grinding or polishing. For example, by changing grit sizes, a machine may be converted from a heavy-duty grinder to a fine micro-polisher.
You can convert belt grinding machines to semi-automatic or fully automatic working. Furthermore, in most applications, belt grinding imposes less strain on the workpiece when compared to other forms of grinding. Cracking, burning, etc., do not occur during the process of belt grinding.
CLASSIFICATION OF BELT GRINDING MACHINES
An abrasive belt grinding machine is usually classified by the surface that forms the coated abrasive backing at the work area. This backing has an important effect on the material removal rate and the finish. The backing governs the choice of contact pressure, the angle of cut and the speed of operation.
All our machine models are similar in construction. A coated abrasive belt runs over two pulleys – one driving pulley one idler pulley. Finally, there is a provision to prevent the belt from ‘walking’ or ‘running’ off the pulleys.
Belt Grinding Machine may be classified according to the backing used as :
- Platen Grinding Machines
- Contact Wheel Grinding Machines
- Free Belt Grinding Machines
- Centreless Grinding Machines
In construction, all the machines are similar. A coated abrasive belt runs over two pulleys – one driving pulley and one idler pulley. There is (a) provision to maintain the belt under constant tension between the two pulleys. (b) a mechanism to prevent the belt from ‘walking’ or running oﬀ the pulleys.
1. PLATEN GRINDING MACHINES
The platen’s function is to shape the workpiece by exerting maximum pressure on the areas that do not conform to the conﬁguration on the platen. Most platens are ﬂat; they are also often shaped in the traverse direction to conform to the contour of the workpiece. The belt, working at high speed, is interposed between the workpiece and the platen ﬁxed to the machine. Platens are generally smooth faced but occasionally have grilled or serrated patterns to increase aggressiveness. The platen’s face, which is in contact with the abrasive and belt backing, must always be smooth to decrease friction and wear of the belt backing.
Therefore, for a given material removal rate, the horsepower required for platen machines is much higher than that of serrated wheel machines. One compromise solution that emerges is using a rubberized and serrated idler pulley for the heavy work and a platen for ﬁnishing work, both on the same machine. But, in general, machines are designed for light and medium-duty operations.
2. CONTACT WHEEL GRINDING MACHINES
In contact wheel grinding, a coated abrasive belt travels over a wheel, which applies opposing pressure to the workpiece. Generally, a motor drives the contact wheel directly. The position of the idler pulley is in tandem with the contact wheel to support the belt at the correct tension.
Rubberized Contact Wheels consist of solid rubber, tyres vulcanized to metallic hubs. Also, the hub is made of aluminium to decrease the weight of the rotating mass. Besides, a judicious choice of hardness, form and size of the wheel is necessary to ensure effective and economical operation.
The rubber’s hardness or density is directly related to the stock removal rate and the quality of the surface finish. For a given wheel diameter and grain size, the harder the wheel, the faster the cut and the coarser the finish. In fact, a substantial change in hardness can have the same effect as a jump in grain size.
Form or face, as applied to contact wheels, means the peripheral surface. Besides a plain metallic, rubber or serrated rubber face, plain metallic or soft rubber faces are best for very fine polishing or burnishing. They also ensure that the maximum belt area is in contact with the work and ensures the lowest grain pressure. Serrated wheels, however, offer very definite advantages and are in use more widely.
Serrations or slots are alternate lands and grooves across the face of the wheel. The ratio of the width of grooves to land, the depth of the groove and the shape of the land, together with the wheel’s hardness and diameter, play an important part in the cutting action of the coated abrasive. The effect of the groove is to decrease the contact area. Therefore, for a given infeed force, the serrated increases the unit pressure, causing the grain to be more aggressive, and the stock removal rate increases. Serrations also provide a means of controlling the breakdown of abrasive grains, thereby ensuring renewed sharp edges. A further advantage results from the coated abrasive’s flexing action ahead of the point of in-feed pressure. Finally, flexing of the belt results in good chip clearance and prevents chips from wedging between adjacent grains.
Similarly, like grinding wheels, contact wheels have maximum safe operating speeds. Tests have shown that a surface speed of 3000 meters per minute is the upper limit. While this figure is a practical limit, trials using serrated contact wheels have shown maximum stock removal rates occur at surface speeds between 1300-2000 meters per minute. At speeds greater than 1700 meters per minute, even soft wheels tend to act hard, i.e. by increasing the speed, the soft backup can be made to perform like a hard back up.
Proper selection of surface speed of the abrasive belt is essential for economical and effective operation. Since the speed, size and form of the contact wheel also affect the speed of operation, we must consider these facts while selecting the operating speed. Contact us for further information.
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