Grinding Journal - Summer 2007 - (Page 20)

The HOW WHY of conventional vitrified grinding wheel selection A dvances in grinding wheel technology over the past decade make choosing the right grinding wheel for your specific application a crucial piece of the solution puzzle. Yet industry has fewer and fewer personnel with the necessary knowledge. With that in mind, let’s cover grinding wheel basics and how varying wheel specifications affect your grinding process. & Abrasive Grain Types: The first position in the grinding wheel marking system references the type of mineral used for the abrasive grain. We will cover the three major grains: Aluminum Oxide, Ceramic Aluminum Oxide and Silicon Carbide. 1. Aluminum oxide (Al2O3) is by far the most common of these three and is the “first choice” for many grinding applications. It is a bulky, hard grain (when compared to typical ferrous materials) adaptable to a variety of grinding conditions. This grain will typically be called out by an “A” in the first position of the marking system. Examples would include 38A, 86A, 57A, 64A, 25A etc. So you are probably asking yourself: “If ‘A’ calls out aluminum oxide, what do all the numbers mean?” Well, the numbers are the wheel manufacturer’s way of denoting different types of aluminum oxide. Aluminum oxide has many different varieties (Saint-Gobain Abrasives alone has over a dozen) that can be applied depending on the application. The biggest factor separating different types of aluminum oxide is a property we call “friability.” Friability is a measure of the grain’s ability to fracture and break down during use. This property is achieved by varying the internal structure in the abrasive grain itself. White aluminum oxide (typically a white wheel – think a manual tool and cutter wheel) is the most friable type of aluminum oxide (i.e. breaks down easiest). A brown aluminum oxide (typically a gray wheel – think a bench grinder) is the least friable (i.e. the most durable). (Note that I am referring to the durability of the grain, not the wheel. All vitrified wheels are basically made of glass and extremely fragile.) We’ll concentrate on conventional vitrified grinding wheels. These wheels use a vitreous glass to bind traditional abrasive grains (Aluminum Oxide, Ceramic Aluminum Oxide and Silicon Carbide) in a controlled porosity matrix. You often see examples of these wheels colored white, blue, green or pink. These colors differ by manufacturer and were traditionally helpful in identifying the abrasive grain in the wheel. But this isn’t the norm anymore, especially when discussing Ceramic Aluminum Oxide and Aluminum Oxide grinding wheels. To determine the wheel type, you must look at the wheel marking system. The wheel marking system was developed in the 1940’s and the vast majority of grinding wheel suppliers follow the basic guidelines. This system uses a series of letters and numbers that combine to make six basic positions: Abrasive Grain Grit Size Grade Structure Bond Type Bond Modification Example: 5SG 60 – L 8 V HP These positions can have many different possible combinations of letters and numbers and we will refer back to them and how they affect your process throughout the article. 20 Grinding Journal

Table of Contents Feed for the Digital Edition of Grinding Journal - Summer 2007

Contents My Thoughts Exactly When Lives Are at Stake Walter Consolidating Production The Art of Grinding: Knowing the Source of Grinding Errors and How to Fix Them The How and Why of Conventional Vitrified Grinding Wheel Selection Grinding Glass Flat Problem Solver

Grinding Journal - Summer 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.