BEST PRACTICES OF POLISHING STONE WITH DIAMONDS: DISK POLISHING

Posted by Monday, October 8th, 2012 @ 10:10 am

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Almost all diamond disks in use today for polishing stone consist of diamonds embedded in a resin (plastic) matrix. Diamonds are mixed with the resin to form blocks rather like the lug pattern on the soles of shoes. The diamonds are randomly scattered throughout the resin matrix to a specified depth. As the resin matrix is worn away, the diamonds are gradually exposed.

Disk Use

A wide variety of diamond disks is available today. Popular sizes for the fabrication shop are 3″, 4″, and 5″ diameters, where 4” is by far the most popular and larger and smaller sizes are typically reserved for specialty uses.

The most popular grit sizes for electroplated disks are #70, #120, #220, and #400. Beyond that, there is ample demand for both the coarser #30 and #50 grits and well as the much finer #600, especially for marble work.

Grit sizes for resin bonded disks commonly range from the coarsest #30 to a very fine #8000. Typically, #50, #120, #220, #400, #800, #1800, and #3000 are most commonly used in the shop for processing granite surfaces. Marble processing is less stringent and the combination of grits #50, #220, and #800 usually yields the desired finish.

A point has to be made on the abrasiveness of the stone itself. Marble is soft, but tends to yield a more abrasive slurry than granite, which is harder but less abrasive in slurry form. Some shops try to polish both types of stone with a single set of disks, and this is a mistake. Disks are recommended for specific materials based on grit size, plus the bond (electroplate, metal, or resin), the number of diamonds that are working at any given time, and the hardness and abrasiveness of the material. Some disks work well with marble and poorly with granite, just as a marble diamond saw works well on marble and inadequately on granite. There are no universal disks any more than there are universal saws.

Flexibility vs. Rigidity

There is a trade-off between the flexibility and the rigidity of diamond polishing disks. Flexibility is usually achieved with the use of a rubber universal joint mounted on the spindle of a right-angle grinder, or by using a flexible disk attached with a hook and-loop fastener.  Rigidity is the result of a rigid disk attached with a snail-lock fastener.  A good compromise consists of a rigid disk and a hook-and-loop fastener.

Flexible disks tend to conform to the surface of the material, polishing high and low areas with equal ease. In heavily veined marble or on extensive granite surfaces, the flexible disk will tend to ride over the hard areas and dig into the softer portions. The job may go quickly, but the finish will be wavy. Moreover, the flexible disk will not do a good job of levelling untrue surfaces.

Rigid disks, on the other hand, will do a better job of levelling and have less tendency to dig into soft areas. The rigid disks are also less forgiving; the slightest inconsistency in the polishing procedure will show up as a flaw when the work is completed. The novice can usually obtain better results with a flexible disk. The experienced craftsman will generally prefer the rigid setup. Rigidity prevents rounding of the edges and produces a flatter desirable surface. In all cases, a slight cushioning is necessary to prevent rapid wear of the diamonds due to vibrations generated during the rapidly rotating polishing sequence.

Water

Water is a desirable component of diamond polishing, since it efficiently cools both the work and the disk. (Resin bonds especially are quite intolerant of heat build-up.) Beyond its cooling properties, water flowing over the work at a steady rate yields other advantages: the job will go faster with less effort because the slurry helps remove material, there won’t be any dust, and the finished surface will be superior to anything that can be done dry. This is just as true for hand-held grinders as it is for large production machines.

Rotation Speeds

For diamond abrasives, the best speeds are typically 3000-7000 RPM for a 4″ disk. Higher speeds allow the diamonds to do the work rather than relying on pressure. In fact, excessive pressure will noticeably shorten the life of a diamond disk.

Break-in

All resin-bonded disks need to be broken-in, a process that exposes the diamonds enclosed in the plastic matrix on the surface of the disks. This is easily done for all grit sizes on the rough surface of the material being worked.  With the coarse grits, simply attach the disk and start grinding. For the finer grits, e.g., #3000, break-in is best done on a surface that would be produced by a coarse grit of #120 or so.

A #3500 disk can be broken-in during the normal polishing routine, i.e., on a surface produced by a #1800 disk, but it will take some time. A disk is broken-in when all the grinding surfaces have lost the gloss they had when they came out of the package.

Costs

On the basis of materials only, diamond polishing tools are significantly more expensive than silicon carbide tools. The overall advantages, however, clearly favor diamonds: less grinding time, improved production rates, better finished surfaces, and longer disk life.  These important benefits lead to improved profitability.

For disk polishing with hand-held grinders, the advantages of diamonds include:

• A 50% reduction in polishing time.

• A cleaner shop without the dry grinding dust.

• Reduced worker fatigue with lighter tools requiring less pressure.

• Increased production throughput.

For more information about grinding and/or polishing stone, visit our website or feel free to Ask an Engineer080 about your specific needs.

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JACK OF ALL BLADES: DIAMOND SAW BLADE TO THE RESCUE

Posted by Monday, September 17th, 2012 @ 12:09 pm

As we were testing (playing with) the Jack of ALL Blades™, we naturally began to wonder about the potential uses for this kind of diamond grinding wheel. Two specific factors helped to drive the idea of using this blade for rescue work:

  1. My brother is a local fireman who is involved with the rescue unit in central Ohio
  2. The earthquake that devastated Haiti occurred while we were developing this blade and we couldn’t help but think it could be useful for rescue teams to be able to quickly cut through rubble made of a variety of construction materials including concrete, rebar, other metals, wood, etc.

In an effort to test this blade for rescue conditions, I made a few molds and used them to make concrete blocks with rebar running through them.  I contacted my brother to see if we could go to the junkyard with the local firemen while they were training and cut on cars & school buses… yeah it was fun!

Through this “real world” rescue & construction type testing we learned a few things:

  • this type of blade can dry cut concrete very rapidly, and it lasts quite awhile cutting only concrete.
  • it cuts automotive glass very effectively with almost no wear on the blade.  We also learned that it will cut steel pretty well, but it dramatically reduced the life of the blade compared to just concrete and other common construction materials.
  • as the blade wears from metal cutting, it degrades the cutting ability of the blade on softer materials like wood.

These lessons led us to another natural progression… how can we make the Jack of All Blades™ cut metal effectively without killing the overall life/effectiveness of the blade for other materials?

Next up, development of a metal (specifically steel) cutting saw blade using man-made diamond superabrasives.  Check back in a week or subscribe to our blog in the box to your right.

If you or someone you love is a First Responder and you think this solution could help, Ask an Engineer  about details regarding the mixed-material cutting solution: Jack of All Blades Now!

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SHARING ELECTROPLATED BOND TECHNOLOGY WITH FUTURE ENGINEERS

Posted by Friday, September 14th, 2012 @ 10:09 am

Abrasive Technology welcomed students from The Ohio State University College of Engineering to its Central Ohio headquarters for a Shadow Day.  Students spent a hands-on day with AT engineers and team members learning about how a superabrasive tool is manufactured – from the order first being placed all the way to the finished diamond tool leaving the facility.

Students ended the day with a basic understanding of the electroplated bonding process, as well as their own personalized diamond saw blade.

Abrasive Technology and The Ohio State University share a commitment of excellence in the field of engineering and a passion for continuing education for a smarter manufacturing workforce.

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FIXING OD GRINDING INCONSISTENCIES

Posted by Friday, August 31st, 2012 @ 9:08 am

A reoccurring challenge I confront when visiting customers using superabrasive OD (outer diameter) grinding wheels is variations in performance among wheels.  They want a consistent, sustainable (both in price and wheel life) wheel that grinds the same every time.

To produce an OD grinding wheel with a width of greater than 2”, individual 1” wheels are made and then glued together to form the desired width (with a goal of producing identical 1″ pieces for consistency).

However, consistency can prove challenging.  Assuming that the bond and superabrasive are properly prepared, the manufacturing process will likely include variations in:

  1. Mold setup when multiple molds are used
  2. Hot press equipment used
  3. Uniformity of pressure around the molded band
  4. Temperature ramp up & consistency
  5. Procedure of loading the molds
  6. Procedure of pressing the mold
  7. Bond density when compacting the loose powder matrix

Add the facts that different operators run machines at different times and there’s limited QC domumentation of the pressing cycle from wheel to wheel, it is easy to see that achieving absolute consistency in each 1″ piece is difficult.  And when multiple wheels are then glued together to make one large wheel, it’s no wonder machinists can encounter variations in wheel performance.

In order to solve these inconsistencies, I suggest using a solution that:

  • Is computer-controlled
  • Develops one uniform wheel rather than several individual wheels pressed together
  • Creates uniform density from OD to ID and from side-to-side
  • Relies on QC process documentation, which shows the precise process for each individual wheel. 
  •  A whole-system approach to ensuring consistency is your best bet when OD grinding.  By using a solution that follows these guidelines, you can be assured that each wheel is the same as the one that you ordered last time.

    vflex-wheel1-resized-600Abrasive Technology’s patented VFLex® OD Grinding Wheel is made with a computer-controlled process to achieve uniform density throughout the entire abrasive section.  Learn about the VFlex® process by selecting Centerless Grinding Wheel Flyer.

    If you have a question about a grinding or tooling challenge, please don’t hesitate to  Ask an Engineer  now!

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WHY CUSTOM GRINDING SOLUTIONS ARE BEST FOR FRICTION MATERIALS

Posted by Wednesday, August 29th, 2012 @ 3:08 pm

About a year ago I decided I needed reading glasses – my arms got too short.  I went to the big box discount store and picked a pair.  Yep, I could read better.  However, I still had sore eyes and headaches, so I made an appointment to visit an optometrist.  He checked my eyes and asked about my reading and computer use habits, then tailored a prescription exactly to my needs.  Now, I can not only read better, but I no longer have eye pain or headaches.

Choosing a grinding solution for your friction materials is no different.  You can purchase an off-the-shelf grinding wheel that will do the job, but to maximize your process and throughput, it’s best to work directly with the grinding wheel manufacturer to build a custom wheel.

Identifying your needs and goals – grinding cost (wheel price/parts ground), process output (parts/minute) and wheel set up time – will help narrow the field of choices.  Once the main conditions are identified, you’re on your way to an optimized grinding wheel solution.

drum Going with a custom wheel will allow you to choose between bond types — electroplated and braze bond -– to improve flexibility and function.  Electroplated grinding wheels can have a lower purchase price and are more easily re-plated (further reducing price) than braze bonds.  However, braze bonds can have longer wheel life and faster cutting speeds due to their higher bond strength and the ability to vary diamond concentration over a wide range.

Specifying the best wheel for a given grinding process also requires an understanding of the friction materials properties and the grinding process conditions.

Friction Materials Properties:  Friction materials are materials used to generate frictional forces.  There are two main categories — sintered materials and paper materials.  Sintered materials consist of a blend of various metal and non-metal powders that are pressed and heated to form a rough shape. This is often the first step in manufacturing a brake pad or brake shoe.  Paper products are combinations of pulp and resins more commonly used for clutch plates. Variation in materials and consolidation process conditions yield end products which require different grinding wheel constructions.

Grinding Process Conditions: Diamond abrasive grinding products, mainly drums, face wheels and saw blades, are used to successfully finish friction materials.  Diamond grinding wheel constructions are as wide ranging as the friction materials themselves.  Common variables include diamond type, diamond mesh size, amount of diamond per area, slotting and bond type (electroplated vs. brazed).

Delivering custom grinding solutions takes expertise and the ability to manufacture a wide range of grinding wheels. This process yields the best results when there is collaboration between the friction material manufacturer and the grinding wheel manufacturer.

Abrasive Technology is a leading manufacturer of electroplated and P.B.S.® brazed grinding wheels.  If you would like our expert engineers to address your Friction Materials Grinding challenges,Ask an Engineer  and someone will be with you in 24 hours.

 

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WE CHAMPION SUPERABRASIVE GRINDING WHEELS EXPO

Posted by Thursday, August 23rd, 2012 @ 5:08 pm

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An entrance washed in color.  Banners flying in the air.  Diamonds as far as the eye could see.

A crowd gathered.  There were big winners.  And others who left with only what they brought with them.

The Summer Olympics you ask?  No, it was the “We Champion Superabrasives” event at Abrasive Technology’s Lewis Center headquarters.

The event, attended by AT associates, highlighted products and processes from AT facilities across the globe for the aerospace, medical, general industrial, oil & gas, and stone markets.  AT Sales and Business Development associates served as hosts at each expo station, helping to make a connection between the tools the company produces and the resulting end products.

Stone Grinding at Abrasive Technology

Associates mixed and mingled throughout the event, learning more about the extensive AT product line and enjoying prizes, a photo booth and refreshments.

Golden memories for all.

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DIAMOND OR CBN WHEELS?: BEST PRACTICES FOR GRINDING CARBIDE AND STEEL

Posted by Monday, August 20th, 2012 @ 4:08 pm

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Grinding a combination of carbide and steel can be a particularly difficult problem when using superabrasives. The main question is: Should Diamond or CBN be used to grind this combination of materials?

Punch dies used specifically in the plastics and printed circuit board industries and known as “lamination dies” are most commonly made of both materials. The cost of making very large lamination dies would be prohibitive, if made completely of carbide and would wear very quickly if made just from tool steels. Therefore, the most common practice is to make the punches and the areas around the holes being punched in carbide for maximum wear resistance, while the rest of the die plate is made of various tool steels.

Now, back to the original question; should diamond or cbn be used to grind a combination of carbide and steel? The answer is actually simple: CBN can’t and will not ever grind carbide. Whereas, diamond can grind steel and easily grinds the carbide.

Of particular importance, Abrasive Technology provides a very effective wheel specification for this application utilizing “XD” type diamond which is a tougher, blockier, and stronger type of diamond. When this diamond is bonded with our B170 resin bond and used in wet grinding applications our product is an excellent choice for customers to use.

Have a question about grinding carbide and steel?   Ask an Engineer  Now!

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A DISTINCT CLASS OF MATERIALS: CERAMIC GRINDING AND TOOLING

Posted by Friday, August 10th, 2012 @ 3:08 pm

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When visiting customers I am most commonly approached with the statement, “We are grinding ceramics”.  The word “ceramic” is a very generalized statement covering a broad spectrum of materials. 20 years ago ceramics literally defined a material that was always alumina based with no other additives. Today, if someone were to say “Ceramic” it would be much like going to your favorite coffee shop and asking for a “Coffee”.  The barista will then ask, “What type of coffee, whole/skim, grande/tall, iced/hot?”

Below, are the technical definitions for each material that could be referred to as “ceramic” and my interpretation of these terms as they apply to the industrial diamond grinding world.

Ceramic is a non-conducting material, often used as an insulator for electronics.  The challenge in grinding ceramic is that, because it is non-conducting, the heat that is generated during the grinding process returns to the wheel.  When the wheel absorbs this heat, particularly when using resin bonds, the heat can cause the resin to soften and glaze the wheel.  Therefore, the grinding wheel must be dressed and sticked often to re-expose the crystals.

Alumina Based Ceramic is typically 99% pure alumina and is very easily ground with diamond wheels typically resin bond.

Silicon Nitride is much more chip-prone than alumina based ceramics and requires the use of a special micro-crystalline diamond in the grinding process.

Cermet contains high levels of metallic content such as titanium, nickel or both.  Because of the metallic mix, Cermet is the most difficult of this class of materials to grind.  The metals tend to load the diamond grinding wheel very quickly.  This causes increased wheel wear, the need for frequent dressing, and substantially lower stock removal rates in the grinding equation.

Ceramic vs. Cermet Materials in Cutting Tools

Ceramics used in cutting tool materials are based on aluminum oxide and silicon nitride. Ceramic tools can withstand higher cutting speeds than cemented carbide tools when machining hardened steels, cast irons and high-temperature alloys.

Whereas, Cermet cutting tool materials are based mostly on titanium carbonitride with nickel and/or cobalt binder. Cermets are characterized by high wear resistance due to their chemical and thermal stability. Cermets are able to hold a sharp edge at high cutting speeds and temperatures, which results in exceptional surface finish when machining most types of steels.

With these distinct qualities of “ceramic” materials in mind, you may be able to determine the grade of material you need to use in your grinding or tooling application.  Recognizing these qualities and applying the right solution, are crucial to the success of using a ceramic based product or derivative in your operations.

Have a question about Ceramic Grinding and Tooling? Ask an Engineer  Now!

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MIXED MATERIAL CUTTING CHALLENGE: ROADBLOCK OR OPPORTUNITY?

Posted by Wednesday, August 8th, 2012 @ 1:08 pm

In the process of remodeling my living room, I ran into an issue where I needed to cut through metal, brick and wood, all at the same time. At the joint where the back wall of the room met up against the fireplace, there was a 2×4 joined to brick with metal straps & screws. The screw heads were so corroded that it wasn’t possible to back them out to remove the board.  The only viable option was to find a way to cut through all three of these materials with the same cut.

It just so happens that I work for Abrasive Technology, a worldwide leader in a variety of superabrasive grinding and cutting products.  That said, we didn’t already have a product to tackle this multi-material,DIY job.  This challenge got my wheels turning.  I decided to talk with a couple of my fellow engineers at work about my idea to make something that could cut all of this stuff at once… the name “Jack of ALL Blades” immediately came to mind.

We discussed the required attributes of a diamond blade capable of cutting a wide variety of materials and settled on testing:

    • a relatively large grit abrasive
    • with a high level of fracture resistance
    • applying our P.B.S. brazing process

The key in this multi-material environment is using a low bond and low concentration of abrasive, while still having enough strength to prevent the abrasive from pulling out in use.  We also used a few other tricks-of-the-trade to increase the toughness of the bond to help maximize life, without reducing the aggressiveness needed to cut the softer materials like wood.

We took our initial ideas, made a couple of test blades, and then did some empirical testing on a variety of materials.  We had success cutting the following:

    • wood
    • concrete
    • brick
    • cinder block
    • nails / screws (in wood)
    • sheet metal (school bus)
    • automotive glass
    • rebar
    • aggregate filled cast fiberglass tubing

Here is the logo I created and a few quick photos I took of the Jack of All Blades.

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While it is pretty cool and interesting that we were able to make a working, useful product for this mixed-material cutting challenge, in a very short amount of time (from idea to end product in just days), the point of sharing this information is not really to focus on the end product. The point is that the culture of Abrasive Technology allowed us the freedom to take an idea (one that originated completely outside the context of work) and spend a little bit of time, resources and effort to see what we could come up with.

As one of the founders of our company has stated, “I wanted to create the kind of organization I wanted to work in. The kind of place that doesn’t get in the way of good ideas.”

Creating the Jack of All Blades for home use, got us thinking about what other markets could benefit from this mixed material cutting solution.  Because my brother is a local firefighter, we think this is a perfect tool for rescue crews.  Subscribe in the box on the right to be alerted about the next article I am writing, where I will put the Jack of All Blades to work in a simulated rescue environment!

If you’d like our experts to tackle your grinding and tooling challenges, with an innovative, custom grinding or tooling solution… Ask an Engineer Now!

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