Executive Summary
How an abrasive is constructed impacts how that abrasive performs. Depending on your purpose or application, you want to choose an abrasive built to achieve the results you want. There are three primary types of abrasives: 1) conventional mono-layer 2) multi-layer aggregates and 3) multi-layer engineered. The most sophisticated and advanced type is the multi-layer engineered abrasive, and it is most critical to use this type of abrasive when you need a very fine finish. Industries such as medical implants, automotive components, and plumbing parts will definitely benefit from a multi-layer engineered abrasive.
Defining Types of Abrasives
Let’s start by probing how different types of abrasives are built. A conventional coated abrasive is created using a backing, commonly made from polyester, cotton or other pliable material that has been treated with a coating to give the material strength. As the backing material runs through the coater, a layer of resin known as the make coat is applied. This allows the next ingredient, the abrasive grain, to adhere to the backing as it passes through an oven to dry the resin. Next, a size coat is applied; this covers the grain to provide a structure to hold the grain during grinding or polishing applications.
Conventional coated abrasives start out aggressively. As the grain fractures and becomes smaller, however, the grain loses its aggressiveness. The surface finish will thus decrease because the belt is polishing more than cutting.
A second type of abrasive construction is the aggregate. With their multi-layered structure, aggregate abrasives can extend belt life. However, the grains are randomly placed on the backing surface and offer less control of the contact area. (See Figure 2) Compared to conventional coated abrasives, aggregates have been shown to provide a higher material removal rate (MRR) in terms of grams removed per minute in a test finishing stainless steel.
When considering whether to use a conventional coated versus an aggregate abrasive, you’ll want to assess the amount of material that needs to be removed from the workpiece. Use an aggregate abrasive when you have a greater amount of material to remove, at least in the initial stage of cutting.
The third type of abrasive is a multi-layer construction known as the engineered abrasive. These abrasives are made with a different process that results in improved life and maintains consistent cutting performance from start to finish. The same cotton or polyester backings are used. However, the placement of grains is controlled during the manufacturing process. This creates evenly dispersed placement of the grains in a specific multi-layered pattern. Several different multi-layered patterns are available that address different application conditions.
During grinding, engineered abrasives provide a slow erosion of the bond and grain, consistently exposing a greater number of sharp, fresh grains over time.
Comparing Conventional Coated vs. Engineered Abrasives
Conventional coated abrasives have a few advantages over engineered abrasives: Initial cut rate, and belt cost are the main ones. The initial cut is high for conventional coated, which is required in specific applications. Conventional coated also has a coarser grit range than engineered abrasives, while engineered abrasives encompass a finer grit range. Due to the coating process, conventional coated is usually a lower cost per belt option. Lower cost per belt does not mean, however, lower cost per part.
By comparison, engineered abrasives can remove more stock over time and provide a more consistent workpiece surface finish. In some cases, this consistent cut and finish allows a reduction in the number of steps in the process, thus reducing grind time, the number of passes, and the quantity of products required to complete a project. An engineered abrasive belt can last three to 10 times the life of a conventional belt.
Engineered abrasives' advantages of consistent performance and longer belt life can lower the cost per part. Robotic applications also can benefit from engineered abrasive products because the program can be set up and run without constant human interaction to monitor part quality. Most engineered abrasives do not go coarser than 80 grit, however, they can go up to 6000 grit. This allows operators to use the same product in multiple grit steps to achieve up to a mirror finish before employing buffing wheels and compound.
Engineered abrasives can also be a better ecological alternative. Because fewer belts are needed to grind the same number of workpieces, there is less refuse to dispose of at the end of a project. Engineered abrasives also have a cooler operating temperature and require less pressure, improving operator ergonomics.
Emphasis on Application Demands
Engineered abrasives should be considered for applications where there are multiple material removal and polishing steps, surface finish requirements, and a need to improve consistency and efficiency in the operation. Different patterns are available to address applications with differing pressure levels.
The latest product in the Norton NORaX® line of engineered abrasive belts is the NORaX N899. This micro-structured engineered belt features a high-performance micron-graded aluminum oxide grain in a fine 3D pyramid pattern. Ideal for applications where belt flexibility is needed, N899 produces consistent finishes on all types of materials, even at low pressure, preventing uncontrolled scratches and producing more repeatable uniform finish throughout the entire part run.
NORaX N899 Case Studies
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Medical Implant
In one application, a major medical prosthetic manufacturer sought to improve part quality, increase throughput, and decrease overall cost per part while maintaining a robust and safe operation when polishing cobalt-chrome knee implants on a 5-hp Hammond backstand machine. Compared to a competing engineered-abrasive belt, the Norton NORaX N899 belt produced 40% more implants per belt, reduced the cycle time, and generated an excellent surface finish. As a result, the manufacturer reduced its total cost per part 28% by switching to the N899 belt.
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Marine Parts
Another manufacturer saw 24% improvement in the number of stainless steel boat propellers it could produce per belt after switching from a competitor’s engineered-abrasive belt to the N899 belt.
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Armaments
In another example, a manufacturer of brass rifle receivers increased the number of parts per belt by more than 30% with the new N899 belt compared to a previous generation of the belt.
The N899 belts are suitable for polishing auto and motorcycle parts, sinks and taps, golf clubs, hand tools and virtually all other metal parts where a very fine surface finish is required. The belts can be applied on various types of grinding equipment, including off-hand, robotic, and portable file belt machines. They are available in a variety of grit sizes including X6, X16, X22, X30, X45, X65, X80, and X100.
Summary
Coated abrasives can be categorized by the way they are built. Mono-layer conventional coated abrasives start aggressive but degrade faster than multi-layered aggregate or engineered abrasives. An engineered abrasive is the most advanced and sophisticated type, delivering longer life and the highest quality surface finish. Norton’s newest engineered abrasive, NORaX N899, has demonstrated clear superiority in a number of applications demanding a smooth surface finish.