(19)

(11)

EP 0 031 355 A1

(12)

(43) Date of publication: 08.07.1981 Bulletin 1981/27 (21) Application number: 80901337.0 (22) Date of filing: 04.07.1980

(51) International Patent Classification (IPC):  E21B 10/ 46( . ) E21B 10/ 56( . ) E21B 10/ 62( . ) E21B 10/ 42( . ) E21B 10/ 567( . ) (86) International application number: PCT/SE1980/000187 (87) International publication number: WO 1981/000131 (22.01.1981 Gazette 1981/02)

(84) Designated Contracting States: AT CH DE FR GB LI LU NL (30) Priority: 04.07.1979 SE 19790005845 (71) Applicant: Atlas Copco Aktiebolag S-105 23 Stockholm (SE)	(72) Inventors: ANDERSSON, Kurt Holger S-135 00 Tyresö (SE) LEWKOWICZ, Josef S-130 10 Ektorp (SE) EKWALL, Carl Gösta Bernhard S-133 00 Saltsjöbaden (SE) (74) Representative: Aslund, Roland, et al  c/o Atlas Copco Aktiebolag Patent Department S-105 23 Stockholm S-105 23 Stockholm (SE)