Cutting-Off Wheel Breakages - Causes and Cures

Roger E. Cloutier, Senior Product Safety Engineer

Saint-Gobain Abrasives, Inc.

 

We have received a call from a customer complaining that their cutting-off wheels were slipping and breaking during the cutting process. The customer reports the problem must be the wheels because they have used their machine for years without a problem therefore, it must be the wheel. Upon examination of the customer’s flanges it was determined that the flanges were distorted. Years of tightening and over-tightening the flanges cause them to distort. This distortion destroyed the “relieve” in the flanges and reduced the contact area of the flange onto the wheel causing the wheels to slip and break. Fortunately, proper guarding and cutting procedures prevented a personal injury.

It is amazing, when a wheel breakage occurs, how often a customer blames the wheel first without checking the equipment. All tools wear out. Tools not properly maintained can, and do, lead to wheel breakages. Customers must inspect their machines every time a new grinding wheel is mounted. Flanges should be checked for proper type, flatness, burrs, or any damage. Failure to properly inspect the flanges can lead to wheel breakage and personal injury.

 

To better understand the causes and cures of cutting-off wheel breakages read and follow the information below.

 

Wheel Breakages

The principal causes of wheel breakage on cut-off machines are:
 

(a.) Excessive Wheel Speed   

(b.) Improper Mounting of the Wheel

(c.) Work Improperly Clamped

(d.) Abusive Operation

(e.) Improper Machine Condition

(f.) Unequal Coolant Distribution

(g.) Excessive Wheel Feed Into Work

(h.) Wheel Grade Too Hard

   

(a.) Excessive Wheel Speed

The maximum speed specified by the wheel manufacturer for the particular wheel to be used must not be exceeded.

(b.) Improper Mounting of the Wheel

Investigation of breakages using abrasive cutting-off wheels have revealed the following conditions for improper mounting.

1. Flanges not matched either in diameter or recess. This causes a bending stress on the wheel that may distort the wheel or cause it to be broken (see Fig. 1). The flanges should be of equal diameter and recessed to produce equal and opposite clamping force on bearing areas (see Fig. 2). 

   

2.  Excessive tightening of the spindle end nut may distort the flanges and result in wheel breakage (see Fig. 3).

  Figure 3  

(c.) Work Improperly Clamped

The work holder should be of proper design and of adequate size for the complete range of work for which the cutting-off machine is designed. If the work is allowed to shift or the pieces cut off do not fall away properly, the wheel may be “pinched,” this is a major cause of wheel breakage. If the bar or tubing cut is slightly warped it should be clamped in such a manner that the convex side is down and is in contact with the work support. Otherwise when the piece is cut off, the bar or tubing may drop slightly, “pinching” the wheel (see Fig. 4).

  Figure 4  

(d.) Abusive Operation 

Cutting-off wheels are thin and do not have great lateral strength. Care should be taken to avoid twisting, cocking, cramping, or exerting any pressure on the side of the wheel.This is particularly true on portable cutting-off machines where the work is held and the wheel is guided by hand or on operations where the work is not clamped. On such operations only reinforced wheels should be used. Attempting to cut work beyond the capacity of the wheel or the machine may cause wheel breakage.

(e.) Improper Machine Conditions 

Loose wheel spindle, excessive end play, loose or vibrating machine parts such as the work table and the work holder may cause the wheel to bend in the cut and break. If the machine is underpowered for the job or has loose belts to the extent that the wheel slows down or stalls in the cut, there is a possibility of the wheel breaking. It is unsafe and uneconomical to perform cutting-off operations which exceed the capacity of the machine. Table saws normally used in woodworking operations should never be used for cutting-off operations with abrasive wheels. These machines are generally no properly guarded, flanges are inadequate, and work holding devices are not suitable.

(f.) Unequal Coolant Distribution

When cutting wet, adjust the jets to direct the coolant so that it flushes both the wheel and the work at the same time. Use a generous flow of coolant for best results in abrasive cutting. It is essential that equal amounts of coolant are applied to each side of the wheel; otherwise, the periphery of the cutting-off wheel will wear irregularly, as shown in Figure No.5. Excessive grooving of the wheel may be an indication that more coolant is required or possibly that the wheel grade is too soft. Coolant should be turned off before stopping the wheel so that the excess coolant will be centrifugally spun from the wheel.

Water, mixed with a reputable manufacturer’s grinding compound, is recommended as a coolant. The compound also acts as a rust inhibitor for both the cutting-off machine and the work piece. The coolant tank must be kept clean and filled to the top to insure that the pump will supply a generous flow.

  Figure 5  

Wheels Nos. 1, 2 and 3 will cut STRAIGHT. Wheel No.1 is good for cutting steel tubing. Unequal flow of coolant will result in irregular wear of the wheels on the periphery as shown in No.4 and No.5. Such wheels will NOT cut straight.

(g.) Excessive Wheel Feed Into Work

Jamming or feeding the work into the wheel too fast, will cause excessive strain on the wheel and may result in wheel breakage, particularly with machines which feed the wheel into the work hydraulically.

(h.) Wheel Grade Too Hard

The use of a wheel of too hard a grade will generate excessive heat which in turn will burn the bond on the wheel edges causing chipping and eventually, wheel breakage.

 

Information is the key to safety. Knowing and following the rules will keep you safe at the wheel.

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For additional information on this topic or if you need any other abrasive safety information, please review ANSI, OSHA and all literature provided by the abrasive wheel and machine manufacturer. You may also contact the Saint-Gobain Product Safety Department at Tel. (508) 795-2317 or Fax: (508) 795-5120 or contact your Saint-Gobain Abrasives, Inc. representative with any safety related questions.