TM 1-1500-204-23-9(3)Hardness.Hardness of a grinding wheelis a measurement of the ability of the bond to retain theabrasive grains in the wheel. Grinding wheels are saidto have a soft to hard grade, which indicate the wheelhas a large amount of bond (hard) or a small amount ofbond (soft).c.TypesofGrindingWheels.The selection ofgrinding wheels for precision grinding can be discussedgenerally in terms of such factors as the physicalproperties of the stock to be ground, the amount of stockto be removed (depth of cut), the wheel speed and workspeed, and the finish required. Selection of a grindingwheel is determined by considering one or more ofthese factors. The following paragraphs describe thetypes of wheels which can be used to grind metals withcertain general qualities.(1)Wheel abrasive type.An aluminum oxideabrasive is most suitable for grinding carbon and alloysteel, high speed steel, cast alloys and malleable iron. Asilicon carbide abrasive is most suitable for grindingnonferrous metals, nonmetallic substances, andcemented carbides.(2)Wheel coarseness.Generally, the softerand more ductile the substance being ground, thecoarser the grain selected should be. Also, if a largeamount is to be removed, a coarse grain wheel isrecommended (except on very hard objects). If a goodfinish is required, a fine grain wheel should be used.(3)Wheel hardness.For soft metals, smalldepth of cut, or high work speed, use a soft grade wheel.If the machine you are using is worn, a harder grademay be necessary to help offset the effects of wear ofthe machine. Using a coolant also permits the use of aharder grade of wheel.d.WheelInstallation.The wheel of a grinder mustbe properly installed. If it is not, the wheel may operateimproperly, and an accident may occur. Install a grinderwheel as follows (see figure 6-5):CAUTIONDo not use a metallic object for testingthe soundness of a grinding wheel. Thewheel may crack and disintegrate at anytime.(1)Test the wheel for soundness by tapping itlightly with a piece of hard wood. A good wheel givesout a clear, ringing sound when tapped. If the wheel iscracked, a dull thud will be heard.Figure 6-5. Grinding Wheel Installation(2)Ensure that the shaft and flanges areclean and free of grit and old blotter.(3)Install the inner flange on the shaft.NOTEThe blotter thickness for paper must beno thicker than 0.025 inch. A leather orrubber blotter must be no thicker than0.125 inch.(4)Place a blotter on the shaft and up againstthe flange to ensure even pressure on the wheel, and todampen the vibration between the wheel and the shaft.CAUTIONNever force the wheel on the shaft. Thismay cause the wheel to crack, or be outof alignment.6-4
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