US 3666022 A
A striking bar of a type utilized in a percussive tool, such as a hammer rock drill, and more particularly a striking bar having a bearing portion thereof provided with stress distributing means such that stresses in the bearing portion of the striking bar due to bending and impact occur primarily in sections of the bearing portion other than sections thereof where heat cracking or friction welding can occur.
Description (OCR text may contain errors)
111i States 1 1 3,666,022
ailey et a1. 1 1y 30, 1972 54 STRING BAR 3,074,381 1/1963 Osgood ..173 105 1 1 Edwm- W 33233252 11132; 3Z;if?'.f.'?.f..i.:.: iii/i3;
port, NH. 03773; James F. Ordway, 10 Floyd Ave., Lebanon, N.H.A03784 Filed: Nov. 23, 1970 App1.No.: 92,033
U.S. C1 ..l73/80, 173/105, 175/320 Int. Cl. ..E2lc 7/00, E21c 15/00 Field of Search ..173/80, 105, 128, 109, 132,
References Cited UNITED STATES PATENTS 12/1964 Fulop ..173/109 Primary Examiner-James A. Leppink Attorney-E. Wallace Breisch 57 ABSTRACT A striking bar of a type utilized in a percussive tool such as a hammer rock drill, and more particularly a striking bar having a bearing portion thereof provided with stress distributing means such that stresses in the bearing portion of the striking bar due to bending and impact occur primarily in sections of the bearing portion other than sections thereof where heat cracking or friction welding can occur.
10 Claims, 1 Drawing Figure Patented May 30, 1972 IIVVE/VTO/PS EDWARD A. BAILEY 8 JAMES E GROW/l) STRIKING BAR Some common striking bars of a type utilized in percussively actuated rock drill assemblies include an elongated generally cylindrical member which comprises: a striking end portion supported in a chuck bushing; a splined or lugged portion adapted to be in driving engagement with a known chuck driver gear; a threaded portion axially spaced from the splined portion and adapted to be coupled to a length of drill steel; and a bearing portion axially intermediate the splined portion and the threaded portion and which is rotatably supported within a suitable support bushing. In operation of a striking bar of a type described hereinabove there is relative axial and rotative'movement between the striking bar and the adjacent supporting and driving elements thereby resulting in the occurrence of rubbing friction. Forces from three primary sources are acting simultaneously on the striking bar. Such sources include: a cyclic axial force resulting from the hammer impacting on the end of the striking bar; a torque load delivered through the splines to the threaded steel; and cyclic bending loads caused by drill steel alignment and whip. As a result of these loads, cyclic temperatures are generated at the rubbing surfaces of the striking bar, particularly around the front bushing and large temperature variations are generated in the striking bar often causing heat cracking or friction welding in the bearing areas of the striking bar adjacent the front bushing.
Various striking bar structures have been conceived to take care of the cumulative stresses at the bearing portion due to bending and cyclic temperature. Standard designs teach a striking bar with a bearing portion proportioned to have sufficient strength to withstand the bending and cyclic temperature stresses at the front bearing area thereof. Such a structure often results in the bending moment acting on the reduced section area in the threaded portion and often causes bending thereat resulting in the striking bar breaking in the thread or thread neck.
By means of the present invention which includes a striking bar with stress distributing means at the bearing portion thereof, the surfaces where heat cracks or friction welds occur are separated from the sections where the stresses due to impact and bending are highest.
These and other objects and advantages of this invention will become more readily apparent from a reading of the following description and drawing which illustrates a striking bar constructed according to the principles of this invention.
An elongated generally cylindrical striking bar is of a type utilized in percussively actuated rock drill assemblies (not shown) wherein the rearward end 24 thereof is periodically struck by a reciprocating hammer member and the forward end thereof is adapted to be coupled to a drill string (not shown). For a detailed description of-a rock drill assembly of a type which can utilize the striking bar of this invention reference is hereby made to a copending application Ser. No. 59,290, filed July 29, 1970 and assigned to the same assignee as this invention.
For purposes of the hereinabove and hereinafter set forth description, forward and rearward shall refer respectively to the right and left of striking bar 10 as viewed in the sole illustration thereof.
Striking bar 10 comprises: a rear bearing portion 16; a driver portion 17 forwardly adjacent portion 16; a forward bearing portion 12 located forwardly adjacent portion 17; and
a threaded portion 14 forwardly adjacent portion 12. Portions 16, 17, 12 and 14 are all coaxial with respect to the longitudinal axis XX of striking bar 10.
As shown driver portion 17 is of a known construction having a plurality of circumferentially spaced radially outwardly extending splines or lugs 19 about the outer periphery thereof which are adapted to be in rotatable driving engagement with a known chuck driver gear (not shown) thereby providing suitable means for the rotating of striking bar 10. In use, bearing portions 16 and 12 are encompassed by suitable bushings (not shown) to provide for the alignment and supporting of striking bar 10 within a rock drill assembly of a type illustrated in the above mentioned application. Threaded portion 14 is also of a known construction which is adapted, in any suitable manner, to be threadably coupled to a drill string (not shown), for example by means of rope threads 22 around the outer periphery thereof.
A plurality of radially outwardly open stress distributing grooves 18 of this invention are longitudinally spaced along bearing portion 12 and as shown each individual groove extends around the periphery of portion 12. Grooves 18 are shown as having a generally wide U" shaped cross section, however, they can be of any suitable cross-section. It is preferred that whichever cross-section is chosen by grooves 18, the configuration thereof provides for no sharp edges at the reduced diameter portions thereof for the presence of such sharp edges would become areas of high stress concentration which could lead to premature failure of striking bar 10. The sections of the outer periphery of portion 12 intermediate adjacent grooves 18 define bearing surfaces 20. It is to be noted that in addition to groove 18 providing stress distributing means they also improve lubrication of the front bearing region by providing reservoirs for lubricating oil.
In use striking bar 10 is subjected to stress from three primary sources which include: an axial force resulting from the hammer impact on end 24; a bending moment developed from forces acting transversely of longitudinal centerline XX and torsional force delivered through splines 17. As a result of the above mentioned forces coupled with the relative movement of the striking bar 10 with respect to the supporting bushings, frictional welding and heat cracking can occur at area 12.
For analysis purposes striking bar 10 can be viewed as a simple beam supported at bearing portions 16 and 12 and with a cantilever portion (i.e., portion 14 and the drill string secured thereto) extending forwardly therefrom.
Forces acting transversely of centerline XX intermediate bearing portions 16 and 12 will result in negligible bending moment at portions 16 and 12 because of the particular means of support of striking bar 10. The forces acting transversely of centerline XX forwardly of portion 12 will result in a stress in portion 12 due to the moment resulting from the cantilever supporting of striking bar 10 forwardly of portion 12. Portions 16 and 12 are also subjected to stresses from temperature as indicated above. Any heat cracking and friction welding on portion 16 can be readily resisted because negligible bending load is applied thereat. The heat cracking and friction welding on portion 12 would be aggravated by the stress due to bending moment thereat were it not for stress distributing grooves 18 and the bearing surfaces 20 disposed between grooves 18. With such a construction of portion 12 as indicated hereinbefore, the stress due to bending moment will be applied at grooves 18, which are the weakest sections of portion 12 for they have the least cross-sectional area thereof, and any heat cracks and friction welds, which are substantially localized at bearing surfaces 20, will be limited to the bearing surfaces 20. Hence, by means of the present invention the stresses due to bending and the heat cracks and friction welds are localized in specific independent areas and are not cumulative in any significant manner to produce premature failure of the bar 10.
Bearing surfaces 20 may be of any suitable diameter which is larger than the diameter of stress distributing grooves 18, however, for obvious reasons of fabrication convenience and machining such diameter would preferably be substantially equal to the outermost diameter of threaded portion 14. The innermost diameter of grooves 18 must be proportioned such that the moment due to any transverse forces applied forwardly of bearing portion 12 will produce a greater stress at grooves 18 than at any bearing area 20 where heat cracking and friction welding can occur. The bending stress at 18 should also be greater than at any section of the threaded por tion. In this regard it is to be noted a substantially uniform inner diameter bore 25 extends coaxially longitudinally through striking bar 10 for conducting a pressurized flow of air therethrough for discharge at the drill bit end of a drilling string (not shown) secured to striking bar 10. It is this uniform diameter of bore 25 which permits the hereinabove discussion of diameter proportions for if bore 25 was of a varying diameter along sections 12 and 14 the consideration would have to be directed to a viewing of the section moduli at grooves 18, bearing areas and threaded portion 14.
Inasmuch as the invention herein resides in providing a striking bar having stress distributing means at bearing portions thereof to distribute stress due to bending in areas which are not prone to heat cracking or friction welding, various changes can be made to the preferred embodiment described hereinabove without departing from the scope of this invention, for example; bearing portion 16 can additionally be provided with stress distributing grooves; stress distributing means can be of other configurations than the annular grooves 18 shown, for example, a continuous spiral groove, as long as the relationship of section moduli described hereinbefore is maintained; and a striking bar can be designed having only one primary bearing portion or more than two bearing portions with stress distributing grooves provided where necessary.
What is claimed is:
l. A striking bar of a type utilized in percussive rock drilling comprising: a member having a chuck driver portion, a threaded portion axially spaced from said driver portion for coupling to a drill string, and a bearing portion connecting said driver portion to said coupling portion; said bearing portion being coaxial with and extending axially between said driver portion and said threaded portion and being rotatably supportable by a bushing assembly adjacent the outermost periphry thereof; and stress distributing means extending inwardly from the outermost periphery of said bearing portion and along at least an intermediate section of said bearing portion.
2. A striking bar as specified in claim 1 wherein said stress distributing means comprise a plurality of axially spaced annular grooves coaxial with the central axis of said bearing portion.
3. A striking bar as specified in claim 1 wherein said stress distributing means comprises at least one annular groove intermediate the axial ends of said bearing portion.
4. A striking bar as specified in claim 1 wherein the section modulus at the smallest cross-section of the bearing portion is sufficient to withstand nonnal working bending stresses.
5. A striking bar as specified in claim 1 wherein said stress distributing means defines at least one section of said bearing portion across which at least a major portion of the bending applied to said bearing portion is distributed.
' 6. A striking bar as specified in claim 1 wherein said stress distributing means defines a plurality of sections of said bearing portion across which at least a major portion of the bending applied to said bearing portion is distributed.
7. A striking bar as specified in claim 1 wherein the respective outermost peripheral portions of said bearing portion are of a substantially equal diameter.
8. A striking bar as set forth in claim 7 wherein said threads on said threaded portion have substantially equal root diameters.
9. A striking bar as specified in claim 1 including a coaxial through bore extending axially through said member along the central axis thereof.
10. A striking bar as specified in claim 9 wherein said bore is of a substantially constant diameter.
UNIT-ET) STATES PATENT OFFICE QERTTFEQATE @F CORRECTION 3,666,022 Dated May 30, 1972 Patent No.
Inventor(s) Edward A Bailev and James F. Ordwav It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Claim 1, line 5, delete "coupling" and substitute threaded Signed and sealed this 1st day of January 197M.
RENE D6 TEGTMEYER EDWARD MQFIETCHERJR. Acting Commissioner of Patents Attesting Officer