Diamond Blade Technical Facts
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Diamond Blade Technical Facts

A Diamond Blade is a circular steel disc with a diamond bearing edge. The edge of the blade may be smooth or textured, continuous rim, or a segmented rim with smaller, individual sections. The blade core is a precision-made steel disc and may have a continuous or slotted rim. The slots (also called "gullets") provide faster cooling by allowing water or air to flow between the segments. The slots also allow the blade to flex under cutting pressure. Most blade cores are tensioned at the factory, so the blade will run straight at cutting speeds. Proper tension also allows the blade to remain flexible enough to bend slightly under cutting pressure and "snap" back into position. Diamond segments or rims are made up of a mixture of diamonds and metal powders. Diamond used in blades is almost exclusively manufactured and is available in various grit sizes and quality grades. In the manufacturing process, the metal powder and diamond grit mixture is melted at high temperatures to form a solid metal alloy (called the bond or matrix) in which the diamond grit is suspended. The segment or rim is slightly wider than the blade core. This side clearance allows the cutting edge to penetrate through the material.

To attach the diamond rim or segments securely to the steel core, several different processes are used.

  1. Brazing - Silver solder is placed between the segment or rim and the core. At high temperatures, the solder melts and bonds the two parts together
  2. Laser welding - The diamond segment and steel blade core are welded (fused) together by a laser beam
  3. Mechanical bond - A notched, serrated or textured blade core may by used to "lock" the diamond rim or segments onto the edge of the blade. Mechanical bonds usually also include brazing or other metallurgical bonding processes to hold the rim or segments in place

* This information applies to diamond blades, diamond bits and other diamond grinding wheels

Diamond blades don't really "cut" like a knife… they grind. During the manufacturing "break-in" (grinding) process, individual diamond crystals are exposed on the outside edge and sides of the diamond segments or rim. These exposed surface diamonds do the grinding work. The metal "matrix" locks each diamond in place. Trailing behind each exposed diamond is a "bond tail" (also called "comet tail"), which helps support the diamond.

While the blade rotates on the arbor shaft of the saw, the operator pushes the blade into the material. The blade begins to cut through the material, while the material begins wearing away the blade.

Exposed, surface diamonds score the material, grinding it into a fine powder. Embedded diamonds remain beneath the surface. Exposed diamonds crack or fracture as they cut, breaking down into even smaller pieces. Hard, dense materials cause the diamonds to fracture even faster. The material also begins to wear away the metal matrix through abrasion. Highly abrasive materials will cause the matrix to wear faster.

This continuous grinding and wearing process continues until the blade is "worn out". Sometimes, small unusable parts of the segments or rim may remain. It is important to understand that the diamond blade and the material must work together (or interact) for the blade to cut effectively.

In order for a diamond blade to work properly, the diamond type, quality and grit size must be suited for the saw and the material. The metal matrix must also be "matched" to the material.

Blades for cutting hard, dense (less abrasive) materials (tile, hard brick, stone, hard-cured concrete) require a softer metal matrix. The softer metal matrix wears faster, replacing worn-out diamonds fast enough for the blade to keep cutting.

Blades for cutting soft, abrasive materials (block, green concrete, asphalt) must have a hard metal matrix to resist abrasion and "hold" the diamonds longer.

Blade performance is a combination of both cutting speed and blade life. Selecting the right blade (for the saw, the material and the job) is the most important factor in getting maximum performance. Many other variables also affect blade performance. Changing any variable will have an effect on cutting speed and blade life. Here are some examples:

Variables Which Affect Diamond Blade Performance
Variables Change Result
Cutting Speed Blade Life
The Blade Segment Bond Hardness Harder
Softer
Slower
Faster
Longer
Shorter
Diamond Quality Lower
Higher
Slower
Faster
Shorter
Longer
Diamond Concentration Lower
Higher
Faster
Slower
Shorter
Longer
Segment Width Thinner
Thicker
Faster
Slower
Shorter
Longer
The Saw Horsepower Lower
Higher
Slower
Faster
Longer
Shorter
Blade Speed (SFM) Lower
Higher
Faster
Slower
Shorter
Longer
The Job Water Volume Lower
Higher
Faster
Slower
Shorter
Longer
Cutting Depth Shallow
Deep
Faster
Slower
Shorter
Longer
Cutting Pressure Lower
Higher
Slower
Faster
Longer
Shorter
The Materials Material Hardness Harder
Softer
Slower
Faster
Shorter
Longer
Material Abrasiveness More
Less
Faster
Slower
Shorter
Longer
Aggregate Size Smaller
Larger
Faster
Slower
Shorter
Longer
Steel Reinforcing Less
More
Faster
Slower
Longer
Shorter

Table from Cardinal Saws & Blades, Inc.™

Diamond Blade Operating Speeds
Diameter Recommended Operating Speed (RPM)* Maximum Safe Speed (RPM)**
4" 9072 15000
4 1/2" 8063 13300
5" 7257 12000
6" 6048 10185
7" 5184 8730
8" 4536 7640
9" 4032 6790
10" 3629 6115
12" 3024 5095
12" High Speed 6300
14" 2592 4365
14" High Speed 5400
16" 2268 3820
16" High Speed 4725
18" 2016 3395
20" 1814 3055
22" 1649 2780
24" 1512 2550
26" 1396 2350
28" 1296 2185
30" 1210 2040
32" 1134 1910
36" 1008 1700
42" 864 1455
48" 756 1275

*Based on 9,500 SFPM (Surface Feet Per Minute) - the general optimum performance range for cutting concrete and masonry products, + or - 10%. For hard, dense materials such as stone and tile, the optimum performance speed is 10 - 25% less than the speeds shown above.
Blade shaft speeds (RPM's at no load) for most tools will be higher than the recommended operating speeds shown above. Under normal sawing conditions, the actual blade shaft speed of the tool will slow down under load, and should fall within the optimum speed range.

**This speed (RPM) represents the maximum safe speed (in revolutions per minute (RPM)) at which each blade can be used. Before using any blade, make sure the blade shaft (arbor) speed of the tool is within the "maximum safe" limit of that blade.

Core Drill Operating Speeds
 Diameter  Minimum Operating
Speed (RPM)
 Recommended Operating Speed (RPM)  Maximum Safe Speed (RPM)
 1"  2400  3200  4000
 2" 1200  1400  2000
 3"  800  1000  1300
 4"  600  900  1000
 5"  500  700  800
 6"  400  550  665
 7"  350  450  600
 8"  300  400  500
 10"  250  300  400
 12"  200  265  330
 14"  170  225  285
 16"  150  200  250
 18"  130  175  220
 20"  120  150  200
 24"  100  130  165
 30"  80  105  130

 

Maximum Blade Cutting Depths
Blade
Diameter
Cutting
Depth
Concrete Saw Blades
12" 3 5/8"
14" 4 5/8"
16" 5 5/8"
18" 6 5/8"
20" 7 5/8"
24" 9 5/8"
26" 10 5/8"
30" 11 5/8"
36" 14 3/4"
42" 17 3/4"
48" 20 3/4"
Cut-Off Saw Blades
12" 4"
14" 5"
16" 6"
Wall Saw Blades
18" 6 1/2"
24" 9 1/2"
30" 11 1/2
36" 14"
42" 17 3/4"
48" 20 3/4
Masonry Saw Blades
14" 5"
18" 7"
20" 8"
Tile Saw Blades
6" 1 3/4"
7" 2 1/4"
8" 2 3/4"
9" 3 1/4"
10" 3 3/4"
Power Hand Saw Blades
4" 1"
4 1/2" 1 1/4"
5" 1 1/2"
7" 2 1/2"
8" 3"

 

Note: Diamond blade cutting depths listed above are approximate. Actual cutting depth will vary with the exact blade diameter or saw type (or brand), or the exact diameter of the blade flanges. Cutting depth will also be reduced if saw components extend below the blade flanges.

When cutting concrete, several factors influence your choice of diamond blades. These include compressive strength, hardness of the aggregate, size of the aggregate, type of sand, steel reinforcing and green or cured concrete.

The guidelines in this section are for general reference only. Your best source for information on the characteristics of the concrete you are cutting is from the original contractor. Contact your local Department of Transportation or City Hall for help in tracking down this information.

Compressive Strength

Concrete slabs may vary greatly in compressive strength, measured in pounds per square inch (PSI).

Concrete Hardness PSI
Critically Hard 8,000 or more
Hard 6-8,000
Medium 4-6,000
Soft 3,000 or less

 

Concrete slabs may vary greatly in compressive strength, measured in pounds per square inch (PSI).

Most concrete roads are 4-6,000 PSI, while typical patios or sidewalks are about 3,000 PSI.

Hardness of Aggregate

There are many different types of rock used as aggregate. Hardness often varies even within the same classification of rock. For example, granite varies in hardness and friability.

The Mohs scale is frequently used to measure hardness. Values of hardness are assigned from one to ten. A substance with a higher Mohs number scratches a substance with a lower number - higher Mohs scale numbers indicate harder materials. The scale below shows how some common minerals fall into the Mohs scale range.

Mohs Scale
1-Talc 5-Apatite 9-Corundum
2-Gypsum 6-Feldspar 10-Diamond
3-Calcite 7-Quartz
4-Flourite 8-Topaz

 

Most aggregates fall into the 2 to 9 range on the Mohs scale. Some commonly used aggregates measure this way on the Mohs scale:

Mohs Range
Range Description Aggregates
8-9 Critically Hard Flint, Chert, Trap Rock, Basalt
6-7 Hard Some River Rock, Some Granites,
Basalt, Quartz, Trap Rock
4-5 Medium Hard Some River Rock, Some Granites
3-4 Medium Dense Limestone, Sandstone,
Dolomite, Marble
2-3 Medium Soft Soft Limestone

 

Aggregate hardness is one important factor when cutting concrete. Because hard aggregate dulls diamond grit more quickly, segment bonds generally need to be softer when cutting hard aggregate. This allows the segment to wear normally and bring new, sharp diamond grit to the surface. Softer aggregate will not dull diamond grit as quickly, so harder segment bonds are needed to hold the diamonds in place long enough to use their full potential.

Size of the Aggregate

The size of aggregate affects diamond blade performance. Large aggregates tend to make a blade cut slower. Smaller aggregates tend to make a blade cut faster. The most common standard sizes of aggregate are:

  • Pea Gravel – variable in size, usually 3/8” or less diameter
  • ¾” – sieved size
  • 1 ½” – sieved size

Type of Sand

Sand is part of the aggregate mix, and determines the abrasiveness of concrete. "Small aggregate" is usually sand. Sand can either be sharp (abrasive) or round (non-abrasive). To determine the sharpness of sand, you need to know where the sand is from. Crushed sand and bank sand are usually sharp; river sand is usually round.

Green concrete is more abrasive than cured concrete. When the concrete is not fully cured sand can more easily be scraped off the surface being cut. More loose sand means more abrasiveness.

Amount of Steel Reinforcing (Rebar)

Heavy steel reinforcing tends to make a blade cut slower, while less reinforcing tends to make a blade cut faster. "Light" to "heavy" rebar is a very subjective term. Examples include:

"light" Wire mesh, single mat
"Medium" #4 rebar, every 12" on center each way (OCEW), single mat
wire mesh, multi mat
"Heavy" #5 rebar, 12" OCEW, single mat #4 rebar, 12" OCEW,
double mat

 

Green or Cured Concrete

The drying or curing time of concrete greatly affects how the material will interact with a diamond blade. Green concrete is freshly poured and has set up, but is not yet fully cured. It is softer and more abrasive than cured concrete. You need a harder bonded blade with undercut protectors to cut green concrete. You need a softer bonded blade to cut the same concrete in a cured state.

Typically, concrete defined as "green" is six hours from pour or younger, but this can vary widely. Weather, temperature, moisture in the aggregate, time of year and the amount of water in the mix all influence curing time. Also, additives in most new concrete can either shorten or extend curing time. Consult your mix design to find the relative curing time for your job. As soon as wet concrete sets up and does not spall or ravel, green cutting can begin.

Even though diamonds are the hardest substance known to man, they will eventually wear down and become dull. The material being cut should have enough abrasiveness to wear away some of the bonding matrix material to expose a new diamond grit. As the old diamond is worn away, a new diamond will take over the task of cutting.

Sometimes the material being cut is not abrasive enough to expose a new diamond. If the blade is not sharpened, it will rub against the surface resulting in heat build-up in the core. To prevent this it is necessary to Dress the Wheel.

To dress the wheel it is necessary to cut something that is abrasive in order to expose the new diamond grit. Good results can be achieved by cutting a concrete block or asphalt. Cut approximately 10-20 feet to adequately dress the blade.

Indications that the blade needs dressing are:

  • The diamonds in the matrix appear shiny because they are worn flat.
  • The blade stops cutting or noticeably slows down.

Always let the blade do the cutting. There is no need to apply excessive force on the part of the operator of the articular saw being used.

 

 

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