Show drill dra 11 bits and drill dra 11 steel BY GEORGE H OILMAN too much importance cannot be attached to the problem of determining the quality of drill steel that is best suited for the ground the best drill steel is not necessarily the highest priced nor is a cheap steel the best for all conditions in general it may be said that the best steel to employ for a fixed set of conditions is the steel that will withstand the duty imposed upon it without undue breakage and will withstand the abrasive action of the rock with the least amount of wear hollow drill steel which is now gener ally used throughout the united states in combination with hammer rock drills embodying an air or water jet for the purpose of ejecting the sludge or rock cuttings from the bottom of the drill hole is a comparatively new departure in steel making and the manufacturers have experienced some difficulty dif f in meeting the requirements owing chiefly to the fact that the hole throughout the length of the bar introduces especially in the high carbon steel difficulties of manufacture that have not been easy to overcome and for this reason it is a generally accepted fact that hollow drill steel is more susceptible to breakage than solid steel of corresponding sectional area however there are now on the market many excellent hollow drill steels that may be procured in a great variety of shapes and sizes the chemical composition of drill steel eel is a matter that has been subjected to a great deal of experiment by the drill steel manufacturers the ining dining industry and the jurers aers of rock drills it is an acred accepted ce fact that steel of a low car on content will withstand more abuse by the he ecksmith blacksmith ack smith and lends itself more readi ly y to welding than steel embodying a greater percentage of carbon on the other hand d it has been determined by experience covering bering a great r nany many years that the higher carbon steel steal will better withstand the vibratory oratory shocks to which it is subjected III n hammer drill service and furthermore th e cutting bit although requiring more care n the working and tempering may be made ta 0 last much longer than is possible with the blower carbon steel the following blowing specifications for straight I 1 ear boll hollow allow drill steel to meet ave average rage shei led it mine and quarry guarr for aul july cuts fu fur r by C 70 c burte 18 of machinery pany 33 the sullivan ti 10 or of if calago this article is a continua 1917 1117 and papers ch appeared in the june julle 1 15 5 blevie eve alay y 30 30 1918 issues of the mining n g conditions of ground and air pressure C conform on with present day practice chemical composition I 1 per cent carbon to manganese to phosphorus under sulphur under silicon to the forging heat of this steel should not be higher than 1600 F the quenching heat should be approximately 13 1300 F critical or decalescence point to secure this re Ws top lofs off n n 1 LJ firebrick 11 I 1 41 if tr i 14 1 angle iron kon 0 1 SE deitan A itan 0 7 alb oloa I 1 0 I 1 I 1 i support for drills L L 21 made TO from 14 ap P ipe ve if A A back of furnace same as n front 7 w back sides and front except no opening 1 bottom of boiler for oil plate lined with i Fi firebrick oil is fed from one side only n using efly oil 0 burners from L denver fire day clay co ca furnace fig 16 oil burning drill heating furnace IM air exhaust JJ air cylinder iff aise for gripp grip 1 n g pipe drill steel bushior Cushi or ned i funch 01 base plate fig 17 punch for hollow hollo w drill steel bits and shanks sult suit the hardening furnace should be set secure a heat of from 1420 F to 1440 F the following specifications for drill steel as applied to workmanship of the bar stock are fair and reasonable to both the steel user and to the manufacturer bars shall be free from injurious defects shall have a workmanlike finish and shall not be defaced by stamping melt numbers or symbols except within four inches binche s 4 I 1 of one end of bar the hole must be of such size and shape that a steel ball of the size specified by the mini minimum murn limit may be passed throughout the entire length it must not exceed in ara that of the maximum limit and in the case of the hole being elliptical the long diameter must not exceed the d diameter la limit plus one s sixteenth of the maximum inch the hole must not be more than one thirty second inch off center from the axis of the bar and sharp corners in the hole seams flaws or cracks in the bar will be sufficient cause for rejection the outside diameter of bars must not exceed the ordinary commercial limit of stock of this nature and must not be more than one sixty fourth inch under or over the specified size the hole throughout the length of the bar must come within the following limits size of size of hole drill mini maxi steel in dia Di deain aIn in dia Di deain aIn in ag 1 4 I 1 1132 38 the drill steel sharpening shop no man on the job deserves more consideration than the drill steel blacksmith for upon him depends in a great greaf measure the entire success of drilling A few minutes carelessness by a blacksmith may undo many days work of a careful in hardening naturally results in a soft drill steel while uneven heating beating Z or heating for too short a time will result in a soft soft center bit with danger of breakage when the steel is put into service pres ent day practice is sounding the death knell of the old style coal or coke forge for heating rock drill steel for forging and tempering and it is being rapidly supplanted with the gas or oil furnace which has a great many points in its favor chief among them the facts that it may be adjusted to approximately maintain the proper temperature in the heating chamber and thus obviate overheated or burnt drill steel A word of caution should be introduced against the common practice of allowing the bits to remain in the furnace longer than is necessary to bring the heat up slowly and uniformly to the desired temperature pera ture which in practice is commonly termed soaking this has a tendency to open the grain of the metal by enlarging the crystals and produces brittleness the blacksmith should handle his steel in rotation by advancing each steel one step nearer the point of withdrawal when a new drill is inserted the furnace is preferably constructed with baffle plates or surfaces to insure the maximum heat of the blast being directed against or over the drill bit just prior to the point at which it is withdrawn from the fire the number of steels that can be heated in the furnace at one time is determined by the time required to bring the heat of the bit up to the proper point and the speed at which it is withdrawn for forging or tempering it is desirable to both forge and temper drill steel on the rising heat which necessitates the steel being withdrawn from the furnace the instant the required heat is obtained gas as fuel is rec recommended where it is accessible and cheap as it is the cleanest and costs least for installing if oil is used it is desirable to have the th e oil storage tank below the level of the burner as the fire risk is lessened A satisfactory grade of fuel oil may be procured at current prices ranging from 3 to 5 cents per gallon in isolated districts a great many of the mine blacksmith shops are equipped with homemade home made furnaces the burner only being purchased outside A sketch of such a furnace which may be made at comparatively slight expense with equipment to be found in the average smiths shop is shown in fig 16 if a pyrometer is used for determining and checking the heating furnace a base metal outfit is recommended on account of its simplicity and the fact that its I 1 upkeep is slight the tha pyrometer should be checked periodically if the base metal couple is used one of the fire ends can be kept as a standard and the fire end in daily use compared with this standard each month or so a new fire end can be used for the standard and the old standard put in 21 alrod J T i j M 14 STANDARD HEXAGON COLLARED DRILL SHANK FOR ROTATORS J 4 T 14 C 00 A W 1 jl j 31 l 1 fig 15 standard lugged drill shank for mounted hammer drills daily use u se the indicator or galvanometer should be adjusted daily for the zero reading if the temperature of the cold junction of the fire end is determined with an ordinary thermometer the indicator can be adjusted to this temperature for drill steel of the carbon content specified the forging heat should not exceed 1600 IF the forging operation should not be continued after the steel fades from a good red color as working a steel cold below its critical range di the refined structure and tends to produce brittleness it is better to reheat the steel to finish the forging operation than to chance a bit or shank breaking underground too much emphasis cannot be placed upon the desirability of forging the bit and shank end of the drill steel by subjecting it to percussive action instead of squeezing the part into shape on the principle of the bulldozer drill making machines are now on the market utilizing the hammer blow for both upsetting and swaging this method approaches more closely the results secured from hand sharpening which blacksmiths know is advantageous to the stand ingup ing up qualities of the bit it furthermore permits the forging operation to be done at a low heat as the conductivity of a rapidly reciprocating swage hammer has been found to be considerably less than that of a squeezing die for all hollow drill shanks equipped with a collar or lugs the length from the shoulder to the striking end should not be more than one sixteenth inch over or under the specified size and all transverse dimensions men should not vary more than one sixty fourth inch in either direction from the size specified see ee figs 14 and 15 the striking end should be kept square and smooth with both the inner and outer edges slightly rounded the hole in the shank for the of the water tube should invariably be kept central and open to the size specified for a distance of from three to three and a half inches from the tip this hole in the smaller sizes of hollow drill steel should not be less than five sixteenths inch and in the larger sizes three eighths inch otherwise a great deal of trouble will be experienced by broken water tubes device for keeping holes in shank and bit open for large installations it is recommended that a pneumatic punch be provided for punching out the hole in both the shank and bit end during the forging operation A number of successful devices have been developed for the purpose A sketch of such a pneumatic punch is shown in fig 17 which in general principle of design and operation has been adopted by a number of the mining companies in the southwest briefly Dri efly it consists of an air cylinder with its piston and piston rod to the front end of which is detachably secured a taper punch of the required size compressed air is admitted to the front and rear pis ton chambers by i a four fou rw r w way ay plug der the hand valve control of the operator erectly at the rear of the air operator 4 cushion cylinder with its cylindering cylinder attack ig to the extension exien extension sion piston rod piston atal of the al air inder this cylinder is filled fil ledwith with oil is displaced from one end to the through a small oa 3 bypass coll connection n eato in for r ward of the air cylinder is a clamping vice with suitable gripping jaws for at th drill steel this may be made hand han dope oper active or equipped with an air cylindering cylinder aj ind piston connected by a toggle with jax jm which assists materially in minimizing th manual operation with an apparatus apparatus e this kind steel may be punched satisfactorily while hot in from tour four to ve seconds to be continued |