Mounted Wheels: As the name suggests these are small grinding wheels mounted to steel shanks and are primarily used on portable hand grinding machine and clamped in position by means of a collets. They are ideal small tools both for coarse, heavy duty work and for superfine grinding work on precision parts. Internationally standardized in the shapes A, B and W
A = Non Cylindrical mounted points, 6mm shank diameter
B = Non Cylindrical mounted points, 3mm shank diameter
W = Cylindrical mounted points
Factors When Selecting A Grinding Wheel: n Material to be ground - type and hardness, Stock to be removed, Work piece geometry, Surface finish required, Grinding machine - type, horsepower and condition, Wheel speeds and feeds, Grinding contact area, Grinding fluid - wet or dry, Severity of operation, Dressing method
Mounting of grinding wheels: The grinding wheel rotate at high speeds. If they are not properly mounted on the spindle it is dangerous to the operator. Before mounting, all grinding wheels should be inspected by ringing test. On light taping with a metal bar inspected by ringing sound. A cracked wheel gives a dull sound.
While mounted the wheels, the following point are considered:-
1. The abrasive wheel should have a sliding fit on the spindle. The wheel should not be forced on spindle.
2. A liner lead bush is used in the bore of the wheel. The bush should not project beyond the wheel face.
3. Flanges of equal diameter are fitted at both sides of the wheel. The flange diameter must be at least equal to half of the wheel diameter.
4. The side of the wheel and the flange should be perfectly flat.
5. Flanges should have clearances only on their faces.
6. The inner fixed flanges is keyed to the spindle, the outer flange has a sliding fit with the spindle.
7. Thick compressive washers are placed on both sides between the wheel faces and the flanges. This helps proper gripping of flanges on the wheel.
8. The nut should be tighter firmly enough to hold the wheel.
9. Wheel guards should be placed in position before starting the grinder.
Work holding devices: The work holding devices used in grinding are: Magnetic chuck, Vice, Angle plates’` blocks, clamps.
Magnetic chuck: Magnetic chucks are of two types: Electromagnetic chuck, Permanent magnetic chuck.
The magnetic power of the electromagnetic chuck can be varied according to the size of the work. But not so in the case of a permanent magnetic chuck.
Cutting speed: The cutting speed (V) is the relative speed of the wheel V (peripheral speed) and the work pieces. It is expressed in meter per minute.
V= ^dn/1000 meter per minute.
Where
d= diameter wheel in ‘mm’.
N =speed of the wheel in r.p.m.
Work speed:-
The work speed is expressed in meter per minute and is determined by the formula:-
Vp = cdpz/ tntxsy meter per minute.
Where, c= coficient
T= wheel life in mm
dp = work diameter in mm
t=derth of cut
s= feed par work revolution in mm per revolution.
Formula of work in speed in r.p.m.
[NP= 1000Vp/^dp]
Feed: The feed (s) in cylindrical in the longitudinal movement of the work pieces per revolution. It is expressed in mm per revolution of the work pieces.
Depth of cut: The depth of cut (t) is the thickness of the layer of metal removed in one pass. It is expressed in ‘mm’. The depth of cut is taken in a range from 0.005 to 0.04. It is the thickness of the material removed in surface grinding for one cut. Depth of cut in grinding depends on the: Cutting load, Power of the machine, Finish required.
Machine time in grinding: Machining time for cylindrical grinding is determined from the formula:-
Tm = Li/ Si np k.minutes.
Where, L= the length of longitinal travel in mm.
i= the number of pass.
Si = longitudinal feed in mm per revolution.
Np = the speed of the work piece in r.p.m.
O.P.G (optical profile grinding): Optical profile grinding in present age becomes one of the most accurate machine tool develop in recent year. It is now being universally used and its takes places with other specified manufacturing techniques.
The difference models have been produced by various manufactures but they all have the same results. These types of grinding profile or shape accurately. An optical profile grinding machine comprising a work piece support, a grinding wheel support and means for producing relative movement between the grinding wheel and a work piece, a platform supporting an enlarged layout of a profile to be reproduced on the work piece, a microscope for viewing the layout through a reducing lens and the grinding wheel in superimposed relationship so that an operator can reproduce the profile on the work piece.
Grinding work: There are two types of working area:
Direct working area: The magnification of projector is 50 x or 25 x and the effective range of the projection screen is 500 x 500 mm. there are grinding range of the actual range is limited to 10 mm x 10 mm or 20 mm x 20 mm accordingly. This is referred as the “direct working area”.
Indirect working area: If the grinding range of the actual contour of the work is larger than the 50 x or 25 x magnifications divide the entire contour into several parts so that each part can be put in the range of either 50 x or 25 x magnification. Start the grinding of 1st parts and move the table longitudinally and cross both direction to grinding next part. This is called the range of “indirect working area”.
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