(19)

(11)

EP 0 230 417 A1

(12)

(43) Date of publication: 05.08.1987 Bulletin 1987/32 (21) Application number: 85905445.0 (22) Date of filing: 22.10.1985

(51) International Patent Classification (IPC):  E21B 1/ 26( . ) E21B 6/ 00( . ) E21B 1/ 00( . ) E21B 6/ 02( . ) (86) International application number: PCT/SE1985/000411 (87) International publication number: WO 1986/002694 (09.05.1986 Gazette 1986/10)

(84) Designated Contracting States: AT BE CH DE FR GB IT LI LU NL SE (30) Priority: 22.10.1984 ZA 19840008213 (71) Applicant: Atlas Copco Aktiebolag S-105 23 Stockholm (SE)	(72) Inventors: MAZZALUPI, Giovanni Clarenspark Edenvale Transvaal (ZA) SPORNDLI, Peter, Paul Highway Gardens Edenvale Transvaal (ZA) STRYDOM, William, Denvil Sunnyridge Germiston Transvaal (ZA) (74) Representative: Molin, Alexis, et al  c/o Atlas Copco Aktiebolag Patent Department S-105 23 Stockholm S-105 23 Stockholm (SE)