AU753579B2

AU753579B2 - Thread coupling for a drill string for percussive rock drilling

Info

Publication number: AU753579B2
Application number: AU10880/00A
Authority: AU
Inventors: Christer Gustafsson
Original assignee: Uniroc AB
Current assignee: Uniroc AB
Priority date: 1998-09-28
Filing date: 1999-09-22
Publication date: 2002-10-24
Anticipated expiration: 2019-09-22
Also published as: SE515517C2; AU1088000A; WO2000019057A1; SE9803268D0; CA2345707A1; EP1117898A1; SE9803268L; ZA200102511B

Description

1 THREAD COUPLING FOR A DRILL STRING FOR PERCUSSIVE ROCK

DRILLING

This present invention relates to a thread coupling for a drill string for percussive rock drilling.

In previously known thread couplings for percussive rock drilling prestressing of the drill string elements at the contact surface between them is obtained. The increased load depends on a combination of the material deformations, which are obtained when a shock wave passes through the thread coupling, and the applied torque. The increased load increases the risk for breakage in either or both of the connected drill string elements.

The present invention aims at achieving a thread coupling where the above mentioned load increase near the contact surface between the two drill string elements is avoided. Through this one can increase the drill rate without deteriorating the service life compared to previously known equipment. This is 15 achieved by providing a thread coupling for a drill string for percussive rock drilling including a male thread and female thread cooperating therewith, said male thread being arranged on a first drill string element and said female thread being arranged on a second drill string element that said first drill string element includes a first impact surface that said second drill string element includes a 20 second impact surface and that said first and second impact surfaces during drilling are intended to abut against each other, characterized in that said male thread has a variable pitch in its axial direction and that said female thread has a thread opening which is wider than a crest of the male thread.

A preferred embodiment of the invention is described below with reference 25 to the accompanying drawings in which Figure 1 shows a drill string with a thread coupling according to the invention. Figure 2 shows a thread joint partly in section. Figure 3 shows a part of the thread joint on a larger scale with exaggerated variation of the thread pitch.

The drill string shown in the drawings includes a drill bit 1, a drill rod 2 and a shank adapter 3. Instead of a dtill rod as shown one can have several. Drill bit, drill rod and shank adapter are drill string elements. A first drill string element 3 is provided with a male thread 4 and a first impact surface 6. A second drill string element 2 is provided with a female thread 5 and a second impact surface 7. The impact surfaces 6, 7 abut against each other during drilling. In the shown example the abutment is situated at the outer end of drill string element 2, socalled shoulder abutment. One can of course have the abutment at the outer end of drill string element 3 instead, so-called bottom abutment. As is best shown in Figure 3 the male thread 4 has an axially varying thread pitch. Furthermore the female thread 5 has a thread opening which is wider than the crest 9 of the male thread 4. The female thread has substantially constant pitch. Through these features the thread coupling can be tightened in spite of the threads not having the same pitch. If e.g. the female thread has a pitch of 15 mm the male thread can have a pitch which is 15+(x/15)*0.2 mm where x is a running coordinate in the longitudinal direction of the thread. In the shown example the pitch of the thread is largest near the outer end 10 of the thread 4. This means that the thread coupling is prestressed near the outer end 10 so that one avoids oooo overloading adjacent the contact surfaces 6, 7. If one instead of shoulder 15 abutment, as shown, has bottom abutment the thread 4 has the smallest pitch near the outer end o*

Claims

1. Thread coupling for a drill string for percussive rock drilling including a male thread and female thread cooperating therewith, said male thread being arranged on a first drill string element and said female thread being arranged on a second drill string element that said first drill string element includes a first impact surface that said second drill string element includes a second impact surface and that said first and second impact surfaces during drilling are intended to abut against each other, characterized in that said male thread has a variable pitch in its axial direction and that said female thread has a thread opening which is wider than a crest of the male thread. DATED this 19th day of August, 2002 UNIROC AB WATERMARK PATENT TRADE MARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA P19320AU SKP/PCP P1°2AU0 °PPc ooo oooo :*AEMR AET&TAEMR TONY 29*UWODRA HATOR ICOIA32