Grinding Journal - Summer 2007 - (Page 27)

Summer 2007 Grade/Structure Shifts Structure can affect wheel life positively or negatively. This creates a problem when adjusting more than one wheel parameter at a time. In general, shifting the structure by three points is equivalent to one letter grade. So if you move from an “E” grade “18” structure to an “F” grade in a “21” structure you will have two wheels which act the same as regards hardness. The below chart demonstrates this fact: Harder • Excellent resistance to abrasion from the part • Good form holding ability • Free cutting bond (porosity) • Excellent ability to draw coolant into grind zone • “Self sharpening” bond (releasing of dull abrasive grains) Bond Modification: Abrasive Grain Grit Size Grade Structure Bond Type Bond Modification 5SG46 M8VHB = 5SG46 N11VHB 5SG46 J5VHB = 5SG46 K8VHB 5SG46 E12VHB = 5SG46 F15VHB 5SG 60 – L 8 V HP The 6th and last position in the wheel marking system is what we call the bond modification. This is basically the wheel manufacture’s way to internally identify the differences in the bond system. It designates, among other things, bond traits, speed limitations, and specialty bonds for specific abrasives. And wheel manufacturers generally do not release the meanings of each modification. Softer Bond Type: Abrasive Grain Grit Size Grade Structure Bond Type Bond Modification 5SG 60 – L 8 V HP The bond type is called out by the 5th position in the marking system. Besides the vitrified bond we’re discussing, there are several other bonds available in conventional grinding wheels, including resin, rubber, shellac, and plastic. The vitrified call-out letter is almost always a “V,” while the others vary depending on the grinding wheel manufacturer. One of the most important things to remember when using vitrified grinding wheels is that they are extremely fragile. The manufacturing process is very similar to that of china dinner plates. It is a glass bond fired in a kiln at high temperatures (approximately 2300° F) for a set time. As the wheel size increases, so does the “burn time,” or length of time in the kiln. Vitrified bonds wear by pressure breaking the bond posts in the grinding wheel. The majority of vitrified grinding wheel wear comes from the truing process. This is why an increase in parts per dress is directly related to an increase in wheel life. Other key points to remember about vitrified bonds versus other bonds: Conclusion We’ve covered a lot of information in this article and putting it all together can take time, testing, and a deep understanding of the grinding application. Once successfully combined though, you will reap the rewards of a high performance wheel that has been designed for your specific application. The grinding wheel is a unique part of the grinding process. Abrasive cost is typically only 2-4% of the entire process cost. But that 2-4% can affect more than 15% of your process cost by improving cycle times, improving quality, and combining operations. When you look at the grinding process as a system you can permanently improve it, leading to meaningful savings: The type of savings that will help you compete in the global economy. Author Pat Baliva is OEM Manager, North America, Corporate Application Engineering, for Saint-Gobain Abrasives. Pat has been with Saint-Gobain for 6 years. He earned his Engineering degree from Clarkson University in NY and resides in Birmingham, AL. INFO grinding.com Pat Baliva • 205.427.3699 Patrick G. Baliva@saint-gobain.com Grinding Journal 2 http://www.grinding.com

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

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