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Centerless Grinding
centerless grinding
What is Centerless Grinding
Centerless grinding processes the outer periphery of a cylindrical workpiece using a centerless grinding machine. A workpiece is supported between a fixed blade and a rotating adjusting wheel and a grinding wheel. The rotation and feed of the workpiece are then adjusted by rotation of the adjusting wheel to grind the outer circumference of the workpiece. Centerless grinding requires neither a center hole in the workpiece nor the workpiece’s installation on and removal from the grinding machine. These advantages make it suitable for mass production.
Centerless Grinding Wheels
Conventional centerless grinding wheels / Superabrasive diamond & cbn wheels Centreless (centerless) grinding can perform excellent roundness of the work piece.The workpiece is supported by a work rest blade and set between a rubber regulating wheel that rotates the workpiece and a rotating grinding wheel.
Centerless grinding
centerless grinding
The grinding wheel and the smaller one is the pressure or regulating wheel.
The regulating wheel is a rubber-bonded abrasive having the frictional characteristics ta rotate the work at is own rotational speed. The speed of this wheel, which may be controlled, varies from 50 to 200 ft/min(0.25-1.02 m/s). Both wheels are rotating the same direction. The rest assists in supporting the work while it is being ground, being extended on both sides to direct the work travel to and from the wheels.

The axial movement of the work past the grinding wheel is obtained by tilting the wheel at a slight angle from horizontal. 
In centerless grinding, the workpiece rotates between a grinding wheel and a regulating drive wheel. The work is supported from below by a fixed work-rest blade. The two basic modes of centerless grinding are "thru-feed" and "in-feed" or "plunge" mode. In the thru-feed mode, the work proceeds in the axial direction through the slowly narrowing gap between the grinding wheel and the regulating wheel. Work is advanced by the axial force exerted on it by the rotating surface of the regulating wheel. This is a highly productive form of grinding in that a number of workpieces can be ground simultaneously and in a continuous stream. The "infeed" mode is used for work with projecting heads that would prohibit "thru-feeding," the work is placed on the work-rest blade while one wheel is retracted and fed to an end stop. The wheel is then brought back, reducing the gap between the wheels, grinding the work.

Three types of grinding for centreless cylindrical grinding machines 

- Pass-through centreless grinding. The workpiece is fed in the direction of the grinding wheel axis for grinding. The axial feed of the workpiece is achieved by adjusting the slight inclination of the guide wheel axis. Suitable for grinding long, thin cylindrical workpieces. Short shafts and bushings without a central bore, etc.
- Plunge-cut centreless grinding. The workpiece is supported in a certain position on the pallet with an axial positioning pivot point and is ground by plunging the grinding wheel or guide wheel. For grinding workpieces with shoulders or bosses, cones, spheres or other rotary workpieces.
- Pass-through/Plunge-cut centerless grinding is a combination of these two types of grinding. In addition, there is tangential feed grinding and end-feed grinding where workpieces with steps are moved in and out of the axial direction. Centreless cylindrical grinding machines are highly productive. They are mostly used for mass production and can be easily automated.
Operation procedure of the centreless grinding machine

1. Before starting the machine, check the surrounding conditions of the machine, whether the oil level of the oil tank is normal, the water level of the cooling water tank, whether the clearance between the grinding wheel and guide wheel and the supporting blade is normal, and whether there are working objects or debris in the machine tool. Before starting the machine, check that the switch is reliable and that safety guards such as guards are effective. 
2. Observe whether the hydraulic gauge pressure of the machine tool is normal. Before starting, the grinding wheel and guide wheel must be wiped clean.
3. The centreless cylindrical grinding machine does not have a spindle box and tailstock. Instead, the workpiece is supported by the support plate and guide wheel, and ground by the grinding wheel.
4. The upper surface of the support plate is inclined by 30 ~ 50° so that the workpiece is pressed tightly against the guide wheel by the cutting force. The axis of the guide wheel has an inclination angle α (1 ~ 5°) with respect to the axis of the grinding wheel, and it mainly consists of three mechanisms: the grinding wheel, the adjusting wheel and the workpiece support, in which the grinding wheel actually performs the grinding work and the adjusting wheel controls the rotation of the workpiece and the feed speed of the workpiece.
5. Due to the inclination angle α between the axis of the guide wheel and the axis of the grinding wheel, the workpiece is not in linear contact with the guide wheel. A centreless grinding machine that grinds the rotating surface of the workpiece by centreless grinding is usually called a centreless cylindrical grinding machine, where the workpiece is placed between the grinding wheel and the guide wheel and supported by the support plate and the guide wheel, rather than being centred and supported by the centre. The grinding wheel is generally mounted at the end of the spindle, while a grinding wheel with a width greater than 250 mm are mounted in the middle of the spindle, with grinding wheels up to 900 mm wide.

Maintenance of centreless grinding machines:
Limit the spindle oil pressure to between 8-10 KG/CM
Lubricate the machine properly with an oiler before starting the machine each day
Keep the slide clean (clean, free of debris and impurities and in a lubricated state).
Regularly check the tightness of the zip
Regularly check the tightness of the grinding wheel drive belt
Replace the spindle once every 2000 hours of use
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