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Tuesday, 26 November 2013

Center less Grinding Operation

Center less Grinding Operation Points : Center less Grinding Operation, Classes or Variations of Center-less Grinding, Through Feed Grinding, In-feed Grinding, End Feed Grinding Center-less grinding is a form of cylindrical grinding. It produces accurately: ground parts without requiring them to be mounted between centers. Parts are held in position on a work-rest blade which is located between a grinding wheel and a regulating wheel. The regulating wheel rotates the work which rests on the work-rest blade. At the same time, the grinding wheel grinds the surface. Straight or tapered objects may be ground in this manner.
Lathe centers, piston pins, roller bearings, and similar objects without center, holes are examples of objects ground by the center-less grinding method.

In Center-less grinding the work passes between the wheels, one a grinding wheel and other the regulating wheel. The grinding wheel rotates at high speed. Its purpose is to grind material off the surface of the cylindrically shaped work-piece. The regulating wheel is opposite the grinding wheel and it rotates at a low speed. The regulating wheel has three functions: (1) to rotate the work so the grinding wheel can grind over the entire surface, (2) to support the work against the horizontal thrust of the grinding wheel, and (3) to feed the work between the grinding and regulating wheels as it rests on the work rest blade.

Through feed is obtained by setting the regulating wheel at a slight angle. The action of grinding wheel exerts a pressure on the work down against the work-rest and regulating wheel. The regulating wheel, which is actually a rubber bonded abrasive wheel, rotates in a clockwise direction: the same as the grinding wheel causing the work to revolve in a counter clockwise direction and feeds the work through the machine. The grinding wheel operates at about 6000 s.f.p.m. where the regulating wheel can be operated at from 50 to 200 feet per minute or 12 to 300-rpm, To get the best rounding action, the work rest should be adjusted so that be center of the work is located one half (1/2) the work diameter above the centerline of the two wheels.
Classes or Variations of Center-less Grinding These center-less grinding princi5les lend themselves to almost unlimited applications through the use of machine setups involving special relationships between the grinding wheel, the regulating wheel, and the work-rest blade, combined with various types of work guides and feeding mechanism. 1. Through Feed Grinding This method can be only be used to produce simple cylindrical shapes. Work, is fed continuously by hand, or from a feed hopper, into the gap between the grinding wheel and the regulating wheel. The pieces drop off the work support blade when the grinding operation is completed. 2. In-feed Grinding Work is fed into the wheel gap until it reaches a stop in this centerless technique. The piece is ejected at the completion of the grinding operation. Work diameter is controlled by regulating the width of the gap between regulating wheel and grinding wheel. Work with a shoulder can be ground using this method. 3. End Feed Grinding This form of center-less grinding is ideally suited for grinding short taper and spherical shapes. Both wheels are dressed the required taper or shape and the work is fed in from the side of the wheel to an end stop. The finished piece is ejected automatically. Center less grinding is used when large’ quantities of the same part are required. Production is high and costs are relative because there is no need t drills center holes or to mount the work in a holding device. Almost any material can be ground using this technique.

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