Tech Talk
What are the “Seven Factors for specifying a grinding wheel”?
Certain conditions cause grinding wheels to perform differently. To determine the most effective abrasive product for any grinding application, all seven factors need to be considered as they relate to each other. Some factors can be weighted more heavily than others in assessing optimum wheel performance. The following is an overview of the general rules for each of the separate factors involved in proper wheel selection during the grinding process. Abrasives have a natural tendency to become dull. Dulled abrasives cause most of the grinding problems so the longer the abrasive remains sharp or the quicker it re-sharpens itself the more effective the product becomes.
The material to be ground. There is a tremendous array of materials ground with abrasive products. Some materials are best ground with aluminum oxide while others are best ground with silicon carbide. The hardness and/or toughness of the work piece affects how quickly the abrasive will dull. This affects the specification selection process.
The Severity of the Operation.The primary purpose of grinding is to remove material. The speed with which the material is removed is a function of the amount of force applied to the product. When the forces are high, the abrasive product must withstand those forces and when the forces are light, the specification is selected based on keeping the abrasive sharp and not dull.
Finish and Accuracy. When fine finishes and tight tolerances are important to the work piece, the specification becomes more critical. Accuracy means tighter tolerances and the abrasive can not break down and lose form or the tolerance will be lost. Finish means smooth surfaces and metallurgical integrity so the abrasive product has to act mild and not be too aggressive.
The Area of Grinding Contact.Area of contact affects the number of abrasive particles physically in contact with the work piece at a time. As the area of contact increases, the force per abrasive particle decreases and the abrasive will tend to become dull quicker. On the other hand, as the area of contact becomes smaller, the forces per grain increase and the abrasive will act more aggressively, cutting more freely because there are fewer abrasives in contact with the work.
Wheel Speed.The working speed of an abrasive product is measured in Surface Feet per Minute (SFPM). This speed affects the size of the chip the abrasive can make and, therefore, affects the grinding action of the abrasive product. Typically the faster the abrasive moves the harder the product will act and as the abrasive travels slower the product will act softer and more aggressive.
Wet or Dry Grinding.While making chips, abrasives are subjected to friction. This friction has a tendency to dull the abrasive if not dealt with. Therefore, any medium that can help to reduce friction will extend the time it takes for the abrasive to become dull. Coolants are used to reduce friction, clean chips from the grinding contact area, cool the part and the abrasives, prevent rust, and generally extend the life of the abrasive product.
Horsepower.When an abrasive product makes contact with the work piece, it has a natural tendency to stop moving. Depending on the forces applied, the product may require a lot of power to maintain its speed. If there is insufficient power to keep the product in motion, a softer acting product is needed. On the other hand, harder acting products can be used when there is plenty of available horsepower to keep the product in motion.
