WO1997032109A1 - Dual pitch connecting joint - Google Patents

Abstract

A drill rod has a first and second threaded end. The threads on the two ends have a different thread pitch so as to provide a different degree of joint tightness (torque) when the ends are threaded into a matching coupling. The different degree of joint tightness at each rod end causes a breaking of the joint connection in a predictable sequence, thereby facilitating drill string removal from a drill hole. An alternate embodiment achieves a different degree of joint tightness by having different thread lengths at each end of the drill rod and coupling, instead of different thread pitches.

Description

DUAL PITCH CONNECTING JOINT

BACKGROUND OF THE INVENTION This invention relates generally to the connection of drill string components used in percussive drilling, and more particularly to drill rods and couplings used to connect to each other in a way that is readily detachable.

Percussive drilling means the top hammer is rotating while generating impact waves that travel down through the drill string to perform work on the formation being drilled.

In drilling hole construction and mining, it is sometimes necessary to connect several drill rods together to achieve the desired drill hole depth. The most popular type of drill string connection in percussive drilling is by the use of threaded drill rods having the same pitch thread on both ends, with the rods threaded into what is known as a semi-bridge coupling. This coupling has the same pitch thread on both ends as the drill rod.

In modern drilling machines, the drill rod is stored in a rod changer with a coupling screwed onto the top, so that when the drill rod is held in-line with the actual drill string, in-line with the hole being drilled, the percussive top hammer can rotate the male threads of the drill rod into the female threads of the coupling on the top end of the last drill rod extending out of the drill hole. The drill string connections become tightened due to drilling rotation and impact.

To withdraw the drill string from the drill hole, it is necessary to uncouple two adjoining drill rods from each other, in the proper order. That is, the bottom end of the top-most drill rod must first uncouple from its coupling, so that the drill rod can be raised to storage. The next length of drill rod, with the coupling connected to the top end of tne drill rod, is raised to expose the next coupling join- for uncoupling. This procedure is repeated so that each drill rod becomes uncoupled from its coupling so that the coupling remains on the top end of the drill rod for the next cycle of usage. Frequently, impacts from the drifter are used to help loosen the connections, a procedure known as "rattling". When rattling is used, is it difficult to have the drill string connection break loose at the top drill rod first .

The foregoing illustrates limitations known to exist in present drill string connection components. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.

SUMMARY OF THE INVENTION A dual pitch drill rod comprising: an elongated tubular body having a centerline axis therealong, said body terminating in a first end and a second end; a bore extending along said centerline axis for providing passage therethrough for a fluid; said first end being threaded on an external surface with a thread having a first pitch; said second end being threaded on an external surface with a thread having a second pitch; and said first and second pitches being sufficiently different from each other to permit tightening to different torque values, when threaded into a coupling.

The foregoing and other aspects will cecome apparent from the following detailed descriptio of the invention when considered in conjunction with tne accompanying drawing figures. BRIEF DESCRIPTION OF THE DRAWING FIGURES

Fig. 1 shows a cross-sectional schematic view of a prior art coupling and rod connection,

Fig 2 shows a cross-sectional schematic view of a coupling and rod connection of this invention, and Fig 3 shows a cross-sectional schematic view of an alternate embodiment coupling and rod connection of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMODIMENTS Referring to Figure 1, a prior art coupling and drill rod connection 1 is shown Each rod 3, is an elongated tubular body 5, having a centerline axis 7 therealong Bore 8 extends along centerline axis 7 for providing passage therethrough for a fluid Body 5 terminates in a first (or upper) end 9 and a second (or lower) end 11 Threaded into an external surface of each end 9 and 11 is a threaded portion having a thread pitch 15. As is well known "pitch" refers to the distance between individual threads, and can be stated in length (inches, centimeters, etc) or threads per unit length The pitch 15 at each end 9 and 11 is substantially identical

Two consecutive rods 3 are connected together by a coupling 20 Each coupling 20 comprises an elongated tubular body 22 having a centerline axis 24 therealong Bore 26 extends along centerline axis 24, forming an internal surface 27 m coupling 20 Bore 26 provides passage therethrough for receiving threaded ends 9, 11 of drill rods 3 Body 22 terminates m a first end 28 and a second end 30 Threaded into internal surface 27 of each end 28 and 30 is a threaded portion having a tnread pitch 32 In prior art connections, pitch 32 at each end 28 and 30 is substantially identical, as well as being substantially identical to pitch 15 on ends 9 and 11 of drill rods 3 This similarity m geometry between threads in rods 3 and coupling 20 results m substantially similar tightening (or torque) being formed m all joints, when connections are made and operated There is no assurance that the connections will become uncoupled in any particular sequence, making the breaking of drill string connection random and unpredictable.

Figure 2 shows one embodiment of this invention. Elements having names similar to the prior art elements of Figure 1 carry the same numbers as set forth for Figure 1. Threaded into an external surface of upper end 9 is a threaded portion having a first thread pitch 40. Threaded into an external surface of lower end 11 is a threaded portion having a second thread pitch 42. Threaded into internal surface 27 of end 30 of coupling 20 is a threaded portion having a first coupling pitch 41 substantially identical to thread pitch 40. Threaded into internal surface 27 of end 28 of coupling 20 is a threaded portion having a second coupling pitch 43 substantially identical to second thread pitch 42. First thread pitch 40 and second thread pitch 42 are sufficiently different from each other so as to permit tightening into coupling 20 at different torque values

Table I shows the preferred thread pitch 40, 41, 42 and 43 for three rod diameters.

TABLE I

ROD DIAMETER PITCH 40,41 PITCH 42,43 RANGE (INCHES) (INCHES) 'INCHES) VARIATION

1.5 0.615 0.500 ±10%

1.75 0.727 0.615 ±10%

2.0 0.800 0.727 ±10%

Thus, it can be understood tnat the finer pitch threads 42 (of the same pitch diameter) at the lower end 11 can be torqued to a higher value ,i.e. tighter) than the coarser pitched threads 40 at upper end 9. The coarser pitch threads will break connection before the finer pitch threads.

Figure 3 shows an alternate embodiment of this invention. Instead of changing the pitch 40, 42 of the threads of rods 3 and pitch 41, 43 of threads of coupling 20, it is possible to achieve different torque values buy using different thread lengths, while keeping the pitch 40, 42, 41 and 43 the same.

As shown in Figure 3, a first, long thread length 50 in coupling 20 engages a similar, first long thread length 52 on lower end 11. A second, short thread length 54 in coupling 20 engages a similar, second short thread length 56 on upper end 9 of rod 3. Thread lengths 50, 52 are longer than corresponding thread lengths 54, 56.

Table II shows the preferred thread length 52, 56 (and pitch) on rod 3, for three rod diameters.

TABLE II

THREAD LENGTH 56 THREAD LENGTH 52

ROD RANGE DIAMETER VARIA¬

TOTAL TOTAL TION

INCHES THREADS INCHES THREADS

1.5 3.0 4.9 4.0 6.5 ±20%

1.75 3.2 4.4 4.3 5.8 ±20%

2.0 3.6 4.5 4.8 6.0 ±20%

Table III shows the preferred thread length 50, 54 (and pitch) on coupling 20 for three rod diameters. TABLE III

THREAD THREAD

ROD LENGTH 54 LENGTH 50 RANGE DIAMETER VARIATION

TOTAL TOTAL

INCHES THREADS INCHES THREADS

1.5 2.9 4.7 3.9 6.3 ±20%

1.75 3.0 4.1 4.0 5.5 ±20%

2.0 3.5 4.4 4.7 5.9 ±20%

Thus, it can be understood that the longer thread length 52 (of the same pitch diameter) at the lower end 11 can be torqued into coupling 20 to a higher value (i.e. tighter^ than the shorter thread length 56 at upper end 9. The snorter thread lengtn combination 54, 56 will break connection before the longer thread length combination 50, 52. Coupling thread lengths 50, 54 will be substantially similar to drill rod thread lengths 52, 56, but need not be identical .

Claims

WHAT IS CLAIMED IS:

1. A dual pitch drill rod comprising:

(a) an elongated tubular body having a centerline axis therealong, said body terminating in a first end and a second end;

(b) a bore extending along said centerline axis for providing passage therethrough for a fluid; (c) said first end being threaded on an external surface with a thread having a first pitch;

(d) said second end being threaded on an external surface with a thread having a second pitch; and (e) said first and second pitches being sufficiently different from each other to permit tightening to different torque values, when threaded into a coupling.

2. The drill rod of claim 1 wherein said first pitch and said second pitch are in the range as follows :

ROD DIAMETER PITCH 40,41 PITCH 42,43 RANGE (INCHES) (INCHES) (INCHES) VARIATION

1.5 0.615 0.500 2:10%

1.75 0.727 0.615 ±10%

2.0 0.800 0.727

3. A dual pitch drill rod comprising:

(a) an elongated tubular body having a centerline axis therealong, said body terminating in a first end and a second end; (b) a bore extending along said centerline axis for providing passage therethrough for a fluid; (c) said first end being threaded on an external surface with a thread having a first pitch,

(d) said second end being threaded on an external surface with a thread having a second pitch; and

(e) said first pitch being capable of being tightened into a coupling to a first torque value; and

(f) said second pitch being capable of being tightened into a coupling to a second torque value .

4. A dual thread length drill rod comprising: (a) an elongated tubular body having a centerline axis therealong, said body terminating m a first end and a second end;

(b) a bore extending along said centerline axis for providing passage therethrough for a fluid;

(c) said first end being threaded on an external surface with a thread having a first thread length;

(d) said second end being threaded on an external surface with a thread having a second thread length; and

(e) said first and second thread lengths being sufficiently different from each other to permit tightening to different torque values, when threaded into a coupling.

5. The drill rod of claim 4 wherein said first thread length and the second thread length are m the ranges as follows: THREAD THREAD

ROD LENGTH 56 LENGTH 52 RANGE DIAMETER VARIATION

TOTAL TOTAL

INCHES THREADS INCHES THREADS

1.5 3.0 4.9 4.0 6.5 ±20%

1.75 3.2 4.4 4.3 5.8 ±20%

2.0 3.6 4.5 4.8 6.0 ±20%

6. A dual thread length drill rod comprising:

(a) an elongated tubular body having a centerline axis therealong, said body terminating in a first end and a second end; (b) a bore extending along said centerline axis for providing passage therethrough for a fluid;

(c) said first end being threaded on an external surface with a thread having a first thread length;

(d) said second end being threaded on an external surface with a thread having a second thread length; and

(e) said first thread length being capable of being tightened into a coupling to a first torque value; and

(f) said second thread length being capable of being tightened into a coupling to a second torque value .