Trouble Shooting Blades
Core Cracks
One of the most common blade failures is core crack failure. Core cracks are a result of the stress put on the core at the root of the notch or gullet from the segments being pushed into the material at the point of initial contact and being pulled out of the cut at the end of contact with the material. This is analogous to bending a piece of wire back and forth until it breaks. Core cracking cannot be stopped or eliminated. Blade manufactures design the blade core system to not begin core cracking until well after the expected life of the blade under normal operating conditions. If during cutting operations the blade is subjected to pounding, twisting, overheating, or other abnormal stresses, core cracks will develop prior to the blade being worn out. The presence of a visible core crack renders the unusable.
The danger in using a core cracked blade is that for every visible crack there are several cracks that are not visible. Continuing to use a core cracked blade will result in catastrophic failure of the core causing large sections of the core to fly off at energy levels equal to a 22 caliber bullet. A core cracked must not be used. Fig 1 shows a core cracked blade that has major cracks and several small cracks that under visual inspection may not be visible.
Figure 1
Fig. 2 shows the progression of the two major cracks toward each other and the subsequent loss of the segment and attached core fragment.
Figure 2
This failure occurs almost instantaneously because the cracks progress slowly until the material separating the cracks can no longer withstand the stresses imparted to it and then failure occurs at the speed of sound in steel which is 19,553.81 ft/sec.
One of the leading causes of core cracks is that the blade specification is too hard for the material being cut. The saw operator has a tendency to push the blade very hard to in order to ''make''it cut. Eventually something has to give, and many times it is the steel core which cracks. The solution is to check the blade specification and make sure it is the correct one for the material the user is cutting. If the blade has become dull, sharpen it by cutting some soft abrasive material such as asphalt, block or mortar before sawing again.
A misaligned saw or excessive side pressure put on the blade while cutting can cause core cracks. A misaligned saw or excessive side pressure can be detected by uneven signs of wear on one side of the blade core. To prevent this problem, make sure that your saw is properly aligned and cuts in a straight line. If, for whatever reason, the blade begins to saw ''off-line'', it is easier on the blade (and generally faster), to take the blade up out of the cut and restart the cut on-line. Continually trying to make alignment correction while the blade is in the cut will cause core cracks.
A worn blade shaft or blade shaft bearing can set up a ''pounding'' effect. Be sure that your saw is properly maintained and that worn blade shafts or blade shaft bearings are replaced immediately.
Segment Loss
Except for rare instances such as bad weld or undercutting, the reasons that diamond blade segments are lost are impact damage or extreme stress. Let’s look at some of the common causes for segment loss.
Material slipping and jamming itself against the blade is a common cause for segment loss, particularly in masonry or tile sawing applications. Many times the break itself will appear very jagged, and damage to the core itself will be obvious. To prevent this type of damage, the saw operator must make sure that the material is ''seated'' securely on the saw, and that he holds the material firmly through the entire cutting stroke.
A worn blade shaft or blade shaft bearing is another common cause of segment loss. In addition to loose or broken segments, these blades will sometimes show signs of eccentric or uneven segment wear caused by the ''pounding'' effect of the blade in the cut.
A worn blade shaft can be the result of blades spinning on the shaft which wears a groove in the shaft at the point where blades are normally mounted. With a grooved shaft, the blade drops into the groove when it is mounted on the saw. This means the blade is mounted ''off center'' and will be jumping up and down in the cut.
This same type of ''pounding'' effect can be caused by worn blade shaft bearings which allow the blade shaft to move up and down inside the bearing housing.
Both the blade shaft and the blade shaft bearing should be checked regularly. At the first sign of wear or damage, those parts should be replaced.
Inadequate water supply or air coolant is a frequent cause of blade damage. If diamond blades are not properly cooled, they can generate a tremendous amount of heat from friction in the cut. It is critical that saw operators constantly monitor water flow on wet cutting diamond blades, and the entire water system should be checked regularly, including the water pump, water tubes and water jets in the blade guard.
For dry cutting diamond blade, the operator’s sawing techniques is critical in making sure that there is plenty of cooling air flow around the blade. Dry cutting diamond blades should not be used for one-pass, deep cutting or subjected to continuous cutting pressure. It is important to remember that dry cutting blades are cooled with air, and must be given periodic rest periods (i.e. removal of cutting pressure) to allow air to remove the heat generated in the cut.
The effects of inadequate water or air coolant on a diamond blade are obvious. Blades will typically have black and blue discolorations around the edge of the blade. An overheated blade can also show other signs of damage such as segment loss, loss of tension and core cracks.
Preventing overheating problems on wet cutting diamond blades is really very simple. The operator must make sure that he has adequate water flow on both sides of the blade at all times. Many times it only takes a few seconds without water for blades to be damaged.
For dry cutting blades, saw operators should make intermittent shallow cuts. If full depth cutting is required, the operator should make several shallow passes (step cut). Dry cutting diamond blades should be used only for intermittent sawing. This means that the blade should be allowed to run free by taking cutting pressure off the blade every few seconds and allowing it to run back up to full speed. The operator must allow air to flow around the blade core to keep it cool.
An improperly mounted diamond blade or loose blade flanges can cause segment loss. The nut or bolt which holds the flanges and blade shaft together on the shaft must be ''wrench tight''. If the blade shaft bolt or nut is not tightened securely, the blade may ''flutter'' on the shaft at high speed. Diamond blades which have lost segments due to loose flanges will sometimes have damaged or distorted arbor holes or drive pin holes.
If foreign material such as dirt or sand is between the blade core and flanges, or if the blade is improperly mounted on the shaft, the blade still may ''flutter'' on the shaft even though the blade shaft nut or bolt feels ''tight''. Often there is evidence of debris on the blade or flanges, or marks around the arbor hole as evidence of improper mounting.
Excessive Wear
Sooner or later everyone involved in using diamond blades hears about this one… ''the blade wore out too fast''. Before you get too far, make sure that you do indeed have a problem. Every user seems to have a different opinion about what is acceptable diamond blade life. Just make sure that you understand what is considered good blade life, and what is considered bad blade life.
Assuming there is a problem, the most common cause is simply using the wrong blade specification. If you buy a ''hard cured concrete'' blade specification, and then uses it to cut asphalt, the blade will wear out very fast. Check the application and then check and make sure you have the right blade for the job.
Insufficient water supply or cooling air can cause excessive diamond blade wear. Make sure that there is plenty of water for cooling wet cutting diamond blades, and make sure proper sawing techniques are used with dry cutting diamond blades. Saw operators need to get into the habit of making sure that there is proper coolant on the diamond blade.
Another cause of excessive diamond blade wear is insufficient power or speed to the blade. Whenever a blade is turning well below the recommended speed range, the blade will tend to wear fast. This condition can be caused by loose drive belts, a lack of power from the engine, or low voltage/amperage going into the electric motor.
To correct this condition, make sure that you have adequate voltage and amperage going into your electric motor. Also check belt tension regularly. Voltage and amperage should be checked at the motor. For gas or diesel engines, make sure that they are properly tuned and that they are running at full speed when sawing. The blade user should make sure to match the diameter of the blade to the blade shaft speed of the saw. While it is acceptable to use a slightly smaller blade on a given capacity saw, [such as using a 12'' (300mm) diameter blade on a 14'' (350mm) capacity saw], a substantially smaller blade used on a larger capacity saw will cause the smaller diameter blade to be turning at a very low speed, decreasing blade life.
Undercutting
Undercutting is a common condition following in almost every blade application involving the sawing of abrasive materials. Undercutting is caused by abrasive slurry wearing away the steel core, just beneath the diamond segment. The steel core can wear to a ''knife edge'' which will cause the diamond segments to separate from the core. This condition is found mostly on diamond blades used for asphalt or green concrete pavement sawing. Undercutting can be greatly accelerated when the diamond blade cuts completely through the pavement and into the loose sub-base.
While the undercutting problem on a diamond blade is easy to diagnose, preventing undercutting on diamond blades is impossible. A certain amount of undercutting is normal and acceptable on green concrete or asphalt sawing. Further, by adding some type of undercut protection, such as recessed segment blade cores or undercut retardant inserts, the undercutting wear can be slowed down to the point that the user can get full use out of his diamond segments before the steel core wears completely through.
Another means of slowing down undercutting action is to be sure to use plenty of water on the diamond blade. This will help keep abrasive slurry washed out of the cut. When sawing, the user should take care not to cut completely through the pavement into the sub-base. One way for the operator to keep the blade out of the sand and dirt is to watch the color of slurry which flows up out of the cut behind the blade. When this slurry starts becoming very muddy and sandy, he should raise the cutting height of the blade until the water starts to run more clearly. The operator can then proceed with the cut, checking the slurry coming out of the cut frequently.
Other Blade Problems
The problems we have discussed over the most common blade problems encountered. The following are a list of other blade problems that you will encounter and are presented in a cause and remedy format:
Loss of Tension
| Cause |
Blade is used on a misaligned saw. |
| Remedy |
Check for proper saw alignment. |
| Cause |
Blade is excessively hard for the material being cut, creating stress on the steel center. |
| Remedy |
Make certain that the blade is correct for the material being cut (Consult manufacturer’s recommendation chart or see your dealer) |
| Cause |
Material slippage causing the blade to twist and become kinked or bent. |
| Remedy |
Maintain a tight grip on the material while sawing |
| Cause |
Utilizing blade flanges that are under size or not the same diameter, creating uneven pressure on the center. |
| Remedy |
Make certain that the blade flanges are of proper size and identical diameter |
| Cause |
Blade is used at improper RPM, over-speeding. |
| Remedy |
Make certain the blade shaft is turning at the proper RPM by using a Tachometer. This is especially important with concrete saws. |
| Cause |
Blade is improperly mounted on the arbor shoulder and becomes bent when the flanges are tightened. |
| Remedy |
Hold the blade securely on arbor shoulder until the outside flange and nut are firmly tightened |
| Cause |
Blade is overheating from lack of side clearance due to uneven or too rapid segment wear. |
| Remedy |
Specify a blade with a greater side clearance or a specification more suited to the material being cut |
| Cause |
Blade core is overheating from lack of adequate coolant. |
| Remedy |
Check water supply system for even water flow on both sides of the blade. For dry cutting, make more shallow, intermittent cuts allowing time for air to cool the blade |
Undercutting
| Cause |
Undercutting is a condition in which the steel core wears faster than the diamond segment, especially in the areas where the segment and core are joined. The condition is caused by highly abrasive material grinding against the blade during the sawing operation. Usually materials containing and are responsible for causing this condition. (See section on Segment Loss). |
| Remedy |
The flow of slurry (abrasive cuttings) must be distributed over a wider area, away from the critical segment area. On most occasions this can be accomplished by using undercut protectors specially positioned around the steel core to change the pattern of abrasion. Although successful in most cases, undercut protectors do not provide 100% protection. Use high water flow to thin the slurry and flush away sand particles. |
| Cause |
With a floor saw, sawing all the way through the material, allowing the blade to pickup sub-base material. |
| Remedy |
Set the cutting depth slightly less than or equal to the total thickness of the slab. |
Uneven Segment Wear
| Cause |
Segments worn on one side reducing side clearance. Usually caused by misalignment of the saw or a lack of sufficient water on both sides of the blade. |
Remedy |
Check the saw alignment. Clean the water system, making certain that water is properly applied to both sides of the blade. Check to see if the pump is supplying sufficient water. (See Excessive Wear section). |
| Cause |
Blade is worn out of round due to bad bearings, worn arbor, missing bushing, arbor hole larger than arbor, cleanliness of or damage to flange surfaces or excessively dull condition. (See section on Excessive Wear) |
Remedy |
Replace the bearings or worn arbor as required. Inspect the flanges for damage and foreign materials, replace if necessary. Do not remove drive pins when supplied with blade flanges. |
Excessive Wear
| Cause |
Using the wrong blade on highly abrasive material. (Example: hard concrete blade used on asphalt) |
| Remedy |
Recommend the proper blade specification for abrasive material. |
Cause |
Lack of sufficient water to the blade. Often detected by examining the segment and noting overexposed or highly exposed diamonds. |
| Remedy |
Clean up the water systems. Make certain the water pump is functioning properly. |
Cause |
Wearing out of round accelerates wear. Usually caused by bad bearings, worn shaft or using a blade too hard for the materials being cut. |
| Remedy |
Check the bearings and arbor. If worn, replace with new parts before installing another blade, select the proper blade for the application. |
Cause |
Insufficient power caused by loose V-belts, inadequate voltage/amperage, or improper RPMs. |
| Remedy |
Tighten belts (taut). Replace worn belts. Check voltage/amperage. Use proper size extension cord. |
Cause |
Blade is not perpendicular to material being cut |
| Remedy |
Check blade shaft and flanges ensure proper alignment of the blade and equipment. |
Cause |
Blade shaft RPM is too low. |
| Remedy |
Check the operating RPM of the blade shaft. If necessary, change equipment or modify the blade shaft speed. |
Cracked Segments
| Cause |
Blade is too hard for the material being cut. |
| Remedy |
Use a blade with a softer bond. |
| Cause |
Blade is being flexed in the cut by misaligned saw, or operating making dramatic saw course corrections. |
| Remedy |
Align saw. If cut has slightly wandered off line, gradually steer the saw back on line. If the cut is way off line, remove the blade from the cut. Align the saw/blade with the cut line, plunge the blade to proper cut depth and resume sawing. |
| Cause |
Blade is overheated. |
| Remedy |
Apply proper cooling. |
Cracked Core
| Cause |
Blade is too hard for the material being cut. |
| Remedy |
Use the correct blade with a softer bond. |
| Cause |
Excessive cutting pressure, or jamming or twisting the blade in the cut can cause the blade core to bend or flex. When subjected to extreme stress and metal fatigue, the blade’s steel core will eventually crack. |
| Remedy |
The saw operator should use steady, even infeed pressure, and be careful not to twist or jam the blade in the cut. |
| Cause |
Overheating through inadequate water supply or improper use of dry cutting blades. |
| Remedy |
Use adequate water to cool wet cutting diamond blades (for example, 2 to 5 gallons per minute (7-18 liters per minute) for concrete saws). Allow adequate airflow around dry cutting diamond blades to prevent overheating. |
| Cause |
RPM is too high. |
| Remedy |
Check the operating RPM of the blade shaft. Change equipment or blades if necessary. |
| Cause |
Blade is out of tension. |
| Remedy |
Replace the blade or have the blade retensioned by manufacturer. |
Eccentricity (Blade out of Round)
| Cause |
The bond is too hard for the material being cut. The hard bond retains the diamonds, which begin to round off, causing the blade to become dull. Instead of cutting, the blade begins to pound, causing the blade to wear out of round. |
| Remedy |
Change to a softer bond, which will wear away more readily, allowing the dull diamonds to be released and sharp, new cutting edges to become exposed. |
Cause |
The blade shaft may have a groove scored in it, caused a blade spinning between the flanges. A new blade, installed on the arbor shaft, will seat into the groove, and immediately run eccentrically when the saw starts. |
| Remedy |
Replace the worn shaft. |
Cause |
If the blade shaft bearings are worn, the shaft and mandrel will run eccentrically, causing the blade to wear out of round. Can happen with concrete saws with proper lubrications of the bearings is neglected. |
| Remedy |
Install new blade shaft bearings. In some cases it might also be necessary to replace the blade shaft if it is worn or out of alignment. |
Segment Loss
| Cause |
Blade is too hard for the material it is cutting, causing excessive dullness, which causes the segment to pound off or fatigue. |
| Remedy |
Use a softer blade specification. |
| Cause |
Worn blade flanges fail to provide proper support, causing the blade to deflect. |
| Remedy |
Replace both blade flanges. |
| Cause |
Out of round blade rotation results in pounding, caused by a worn arbor or bad bearings in the shaft. |
| Remedy |
Replace worn arbor and/or bearings |
| Cause |
Overheating. Usually an easily detected bluish color on the steel center, generally confined to the area where the segment was lost. |
| Remedy |
Check the water system for blocked water passages. Test the pump to see if it is functioning. For dry cutting it may be necessary to make shallower cuts and allow the blade to run free every few minutes to let their air cool it. |
| Cause |
Segment is subjected to sudden, sharp joking while moving the machine or when contacting the material being cut. |
| Remedy |
Avoid jarring the blade when transporting the machine. Contact the material with slow, even movements |
| Cause |
Undercutting. |
| Remedy |
See Undercutting section above. |
Repair Note:
It is possible to replace two or three missing diamond segments,
providing the steel center is not cracked or undercut badly. If many segments are missing, or if there is less than 50% blade life remaining, repairing the diamond blade may not be economical. Be certain to eliminate mechanical or operational problems before installing replacement blades.
Overheated Blade
| Cause |
Adequate coolant was not provided. |
| Remedy |
Check the water supply for an adequate volume and for obstructions through water system. Use dry blades only for shallow cutting of 1 to 2 inches deep (2-5 cm) or step cutting. Allow the blade to run free every 10 to 15 seconds to increase cooling airflow. |
| Cause |
Using improper specification for the material being cut. |
| Remedy |
Consult the manufacturer’s specification chart for the proper blade. |
Arbor Hole Out of Round
| Cause |
Saw arbor badly worn due to blade being improperly mounted. |
| Remedy |
Be certain the blade is properly mounted on the arbor before tightening the flange. |
| Cause |
Blade flanges have been improperly tightened, permitting the blade to rotate on the shaft. |
| Remedy |
Always wrench tighten the arbor nut. Never hand tighten. Always use hexagonal nuts. Never use wing nuts. |
| Cause |
Blade flanges, drive pin or the arbor shaft are worn and not providing proper blade support. |
| Remedy |
Check the blade flanges, arbor shaft and drive pin for wear, foreign matter and proper tightness. Both flanges should be no less diameter than recommended by the manufacturer. Replace worn parts. |
Note: If the out of round condition of the blade is not too serious, return the blade to the factor for possibly repair.
Blade Will Not Cut
| Cause |
Blade is too hard for the materials being cut. (Examples: block or general purpose blade being used for extended period on hard brick. Asphalt lade being used to cut hard concrete.) |
| Remedy |
Consult the dealer or manufacturer for the proper blade to cut materials on the job. |
| Cause |
Insufficient power to permit the blade to cut properly. (Loose V-belts, low voltage, motor lacks horsepower). |
| Remedy |
Check belts, voltage/amperage and horsepower. |
| Cause |
Blade segments still appear to have plenty of life, but the blade will not cut. |
| Remedy |
Some blades have a non-diamond bearing section in a backing at the base of the diamond segment for better adherence to the steel core. A blade used to this stage has worn out in the normal manner and should be replaced. |
| Cause |
Blades become glazed due to excessive RPM. |
| Remedy |
Match blade specification and diameter to the machine RPM and cutting conditions. |
| Cause |
Blade becomes glazed due to inadequate pressure against the material being out. |
| Remedy |
Ensure proper pressure to keep the blade sharpened, while avoiding an excess of pressure. |
Glazed Blade
Glazed Blade: Surface of segment and diamond are smooth
Reasons:
- Diamonds are too friable
- Bond is too hard
- Blade speed is too high
Results:
- Blade initially cuts, slows and then stops cutting
- If cutting conditions are not modified, overheating, segment loss, segment breakage, core cracking or tension loss will occur
Over-exposed Diamonds
Over-exposed Diamonds: Diamonds protrude from bod with minimal support from bond
Reasons:
- Abrasive resistance of bond is incorrect for the material being cute
- Diamond concentrations and bond type are unsuitable for the application /li>
Results:
- Blade cuts fast
- Blade life is short due to premature loss of diamonds
Heavy Premature Diamond Loss
Heavy Premature Diamond Loss: Surface of segment has a high percentage of missing diamonds.
Reasons:
- Diamonds are not impact resistant, too low in quality
- Bond is overpowered by cutting conditions and high quality diamonds were used.
Results:
- Blade cuts very fast
- Blade wear is high
- Short blade life
Crushed Diamonds
Crushed Diamonds: Majority of diamonds show heavy fracture
Reasons:
- Diamonds are too friable
- Diamonds are too large
- Excessive pounding or vibration
Results:
- Blade cuts fast
- Blade life is short due to premature loss of diamonds if bond cannot hold the crushed diamonds
Polished Segment
Polished Segment: Diamonds are smooth or have flat tops and protrude fro the bond surface
Reasons:
- Diamonds have too high impact resistance
- Diamond size is too large
- Diamond concentration is too high
- Insufficient workload on diamonds
Results:
- Blade initially cuts, slows and then stops cutting
- If cutting conditions are not modified, overheating, segment loss, segment breakage, core cracking, or tension loss will occur
