Ceramic has a unique microcrystalline structure that is self-sharpening. Because of this is is sharper and harder than some other abrasive grains. It provides a significant cooling action and also has less need for the grinding wheel to need dressing.
Silicon Carbide is a very versatile material and harder than standard aluminum oxide with a very sharp abrasive grain. Cast iron and aluminum are considered relatively soft materials that grind well with Silicon Carbide. However, it can also be sued on extremely hard materials such as cemented carbide as well.
Zirconia Alumina has a grain that is associated with high-tech resin bonds. It is used for rough grinding applications. It is used best for high stock removal.
Aluminum Oxide is a naturally occurring material that is refined through a refractory process in order to create block and trough-shaped abrasives. There are several types of aluminum oxide is white, brown, pink, however, white is the most popular. This is because white aluminum oxide is the purest. It is typically used in JF4top which is stainless steel finishing applications.
For premium woodworking applications, pink aluminum oxide such as KP947. Emery boards are a handheld application that you will find brown aluminum oxide on. It is used for applications that are working with soft materials.
Zirconium Oxide (also called Zirconia)
Zirconium Oxide (also called Zirconia) is great for machining and grinding applications because it is significantly more abrasive than pink or brown aluminum oxide, however, this doesn’t make it a good choice for mill scale. It has a good heat resistance and works best in 24-120 grit. It is good for grinding and steal applications. Because of this, you will find Zirconium Oxide (also called Zirconia) you find this material is commonly found in steel fabrication shops on abrasive discs and belt. It is good for stainless steel applications as well.
Ceramic Grit Abrasives
Ceramic Grit Abrasives have an extended range of applications because they have a more micro-crystalline structure than zirconia abrasives or aluminum oxide. It is used in aerospace applications, titanium alloys, stainless steel, aluminum casting, and mild steel mil scale.
In order for ceramic grit to be an option, it is important that you understand that it is sensitive to pressure and heat.
Silicon Carbide Abrasives
Silicon Carbide Abrasives have been described as a belt or disc covered in a bunch of tiny sharp knives. This is because the molecular structure of silicon carbide is long, very sharp, and thin. However, this material is more friable than some of the other options and because of this, they break down rather quickly. It is not a good option for those that are looking for a nice clean cut and it is not good for high-pressure grinding applications. Polishing stone and cutting back lacquers are not applications that should be done with silicon carbide abrasives.
As a whole, the public uses abrasives all the time without giving them much thought. However, selecting the proper abrasive for your particular application can be important in many cases. Not all abrasives are created equal, meaning not all abrasives can be interchanged for different applications. The goal of this guide is to help you determine what abrasives are best for your application.
WHAT ARE ABRASIVES?
Abrasives are materials that smooth surfaces through friction. It is a material that is used to finish many different products. The general public often calls abrasives sandpaper, however, that isn’t exactly the case. Sure some of the abrasives used to be made of glass and sand, however, in this day and age they are made of different materials. Abrasives are used for many different applications in the technological, consumer, and industrial industries. Abrasives can be used in sanding, honing, buffing, lapping, sharpening, drilling, polishing, grinding, and cutting amount other applications. Because of the vast number of ways to use abrasives can be used, there have been a number of new ones formulated.
HOW DO ABRASIVES WORK?
Abrasives are used to smooth out workpieces and remove material. Two materials, after being rubbed together, will smooth out the surface, no matter the materials. However, abrasives are formulated for this and are harder and last longer. Abrasives have grains or grit that are used to grind down various materials. There are some factors that are considered to determine if how effective the abrasives will be, such as:
- Use of lubricant, metalworking fluid which is used to keep things cool, and coolant.
- Contact Force (Faster abrasion will happen when there is more force applied.)
- Loading (How often the abrasives are changed affects the effectiveness.)
- Adhesion between the grains determines how fast the grains are worn.
- The relative hardness of the material to the abrasion. The harder the material, the longer it will take the abrasive to work.
HOW ARE ABRASIVES PRODUCED?
Abrasive grains are produced by chemically treating minerals and heat to create hard materials. Hard materials are needed in abrasives to be the most effective. Each abrasive material is created a bit differently. To determine what grain size you need, you should know that the smaller the grain size, the more smooth the finish.
Once the grains are produced, they are crushed, washed and a magnet is used to remove any metal components that might remain. For abrasive wheels, these grains will have to be bonded to the wheel with an adhesive:
- Oxychloride of magnesium
- Silicate of soda
- Vitrified and Ceramic
Coated abrasive products have grains bonded to the back of fabric or paper with varnish, glues, and resins. They are made originally on large rolls and then cut into the finished product.
WHAT ARE THE DIFFERENT TYPES OF ABRASIVES?
The most common abrasive products are sanding rolls, sanding sheets, sanding discs, and sanding belts.
Sanding rolls are used on drum sanders or are cut into sanding sheets. To put a nice fine finish on your projects, drum sanders are a perfect choice. While drum sanders can be used on metal workpieces and plastic, they are mostly used on wood products.
Sanding sheets require a lot of manual labor. It is used when you want to reach hard-to-reach surfaces or areas that cannot be reached by electric equipment. Sometimes, bladesmiths will turn to sand sheets after 220 grit. This allows them to have more precision in the finishing process.
Sanding discs are typically used for large sanding jobs. They are good for de-rusting metals, preparing surfaces, and finishing wood. They can be used instead of belts.
Sanding Belts are perfect for those jobs that need to remove a lot of material. Sanding belts are used for removing paint from flat surfaces, sharpening tools, sanding hardwood floors, and knife making.
CHOOSING THE RIGHT ABRASIVE FOR YOUR NEEDS
Abrasives are manufactured in various grits, weights, coating types, backings, and grit materials. Because of this, there are a lot of different variations.
ZIRCONIA OR ALUMINA ZIRCONIA (A/Z)
Zirconia was the most durable and aggressive grain on the market until ceramics came along. It is great for material removal for hardwoods and for heavy metal grinding/polishing. Zirconia is less costly than ceramics and only goes to 220 grit. It is the middle ground between ceramic and aluminum oxide in terms of longevity and price.
Ceramic abrasives are ideal for aggressive cutting hardwoods and metals. It is considered a premium abrasive grain and comes with a premium price. The grain on ceramic is very hard and sharp. However, it has a longer lifespan than some of the other abrasives, making the higher cost justifiable.
Ceramic is typically available in 120 grit to 204, with some places offering it to a max of 220 grit. It works best when high speed and pressure is applied. Caution must be taken when working with materials such as wood to prevent scorching.
SILICON CARBIDE (S/C)
Silicon carbide is perfect for finishing heat-sensitive applications, epoxy, resins, and finishing stab labialized wood without excessive heat build-up. It is also a great choice for automotive paint preparation. It is commonly used in finished work because of its intense consistency. The cut rate remains the same throughout the entire life of the belt and is sharper and harder than aluminum oxide. It also delivers more consistency than aluminum oxide, however, it is more expensive.
ALUMINUM OXIDE (A/O)
Aluminum oxide is the material of choice and the most popular among abrasive materials. It is used for finishing on all wood types, roughing, stripping, and planing. The tips of the grains have a high friable, meaning they fray overuse. It is one of the least expensive and most widely used abrasives on the market today.
Shop rolls, discs, and carbide belts are typically used with aluminum oxide. It is lower cost and lightweight which are some advantages over other backings. It can be infused with things such s latex to improve its durability and make it more flexible. There are different types of belts that are used for different applications. Paper backing can deliver a more delicate grit process.
CLOTH (COTTON, POLYESTER, POLY/COTTON BLEND)
Most standard-sized belts to cloth-backed. Polyester is waterproof. Typically premium abrasive products have synthetic backings or feature cloth. They are more superior to paper backing as well.
Plastic is popular for water sanding for obvious reasons, it holds up far better. It offers a more uniform finish and offers flexibility and strength.
FOAM AND SPONGE
For veneers and sanding moldings the best type of backing is foam or sponge. This allows the sander to get into the specific contour of the project.
What Does Grit Mean?
On the abrasive side of the abrasive item, there are differences in how course the abrasive side is. This is called grit. The lower the number of the grit, the more course the grit is. The higher number of grit, the more fine the grit is. When understanding grit, there is a grade that goes along with it. This is:
Grade Grit Size
Medium Coarse 80-100
Very Fine 240 and Up
Aluminum oxide is the material of choice when it comes to woodworking. It gets the job done and it is the most affordable on the market. Closed coat aluminum oxide is good for the harder woods such as hickory, oak, cocobolo, and African Blackwood. However, open coat abrasives are good for softer woods such as pine and cedar.
FOR KNIFE MAKING
Knives are often made up of different materials. The blade might be different than the handle of the knife. Because of this, there might need to be more than one type of abrasive used to make knives. Open coat aluminum oxide abrasives are good for use on the wooden handle if the handle isn’t made of too hard of wood. While the metal will need ceramic abrasives, Zirconia, or closed coat aluminum oxide. While aluminum oxide is mentioned, it does not hold up as well as the other options. If you use it a lot, then you might want to consider choosing one of the more expensive upfront options that tend to last longer. There are different grit levels as we have discussed previously.
Ultrafine grits such as P1000-P5000 are used to finish out and provide an ultrasmooth finish. Fine grits P180-P800 are used to start the honing processes. Course grits aP36-P150 are good for grinding away stock.
When it comes to metalworking there are generally two types of abrasives that are recommended which are ceramic and aluminum oxide. Zirconia Abrasive could also be used from time to time. These abrasives are less expensive than ceramic but are stronger than aluminum oxide. However, if you work a lot with the abrasives you really get more bang for your buck with ceramics.
BEST PRACTICES FOR ABRASIVE STORAGE AND USE
You should always store your abrasives in low humidity, moderate temperatures (60F-80F), and away from the ground. Joint adhesive and sanding belts can be damaged if they are not stored properly which can lead to a shorter lifespan. Sanding discs or wheels should be stored in boxes, drawers, bins, or racks. Sanding belts should be stored on racks.