5 reasons to upgrade to vit-CBN
Advice is given for switching from conventional vitrified grinding wheels to vitrified CBN when cylindrical grinding.
When upgrading a cylindrical grinding process from a conventional vitrified Al2O3 or ceramic wheel to vitrified cubic boron nitride, or vit-CBN, there are key points to consider.
Sometimes a grinding machine is designed to handle either conventional or vit-CBN, and other times it is necessary to add certain features to allow a machine to run vit-CBN. Additionally, to tune up a vit-CBN wheel, grinding and dressing conditions need adjustments.
But why use CBN instead of Al2O3 or ceramic grains at all? There are five main reasons that can justify the use of CBN over conventional abrasive grains.
Used primarily for automotive and bearing applications, Norton Winter Vitron7 is the newest vit-CBN wheel from Norton | Saint-Gobain Abrasives. Image courtesy of Norton | Saint-Gobain Abrasives
1. Cycle time. The desire to grind faster is a reason to consider CBN. Since it has a higher hardness and can stay sharp longer than Al2O3 or ceramic grains, it can be pushed harder and cut quicker. CBN grain hardness also helps maintain cutting ability for longer periods without redressing. The reduced frequency of dressing eliminates downtime.
2. Superhard materials. With some difficult-to-grind materials, such as M4, becoming more popular, it makes sense to use CBN instead of conventional grains. This is because sometimes the hardness of an alloy is close to the hardness of a conventional grinding wheel, which could glaze or damage the wheel.
3. Grinding stock. Having a high volume of material to remove may warrant using vit-CBN grinding wheels. For example, the high volume could be due to a large number of parts or a few parts with considerable grinding stock.
4. Cost per part or operational costs. Due to the hardness of CBN, it cuts longer and has a lower wear rate. A vit-CBN wheel reduces the amount of dressing and abrasive layer required to grind big batches. This can translate into lower overall operational costs.
5. Thermal stability. The thermal conductivity of the CBN grain is greater than Al2O3 or ceramic grains, which helps the CBN grain dissipate heat away from a grinding zone, preventing thermal damage to a workpiece.
When switching from conventional grinding to a vit-CBN process, it is important to review three principal areas: machine requirements, grinding wheel considerations and operator know-how.
Machine Requirements
Machine requirements involve the grinding wheel spindle, dressing, the coolant system, machine rigidity and safety.
The grinding wheel spindle needs rigid bearings to handle a heavier wheel. Vit-CBN wheels are heavier because of the steel used as the core material. The motor requires enough horsepower to spin the wheel and maintain the necessary grinding speeds. Spindles for vit-CBN call for higher operating speeds than for conventional wheels. Vit-CBN wheels usually run from 40 to 120 m/sec. (131 to 394 ft./sec.) or higher.
Norton Winter CarbonForce uses a carbon-fiber hub, which reduces the overall weight of the wheel. Image courtesy of Norton | Saint-Gobain Abrasives
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