THE STRENGTH OF HOT-DIP GALVANIZED HIGH-STRENGTH SCREWS

ZUM FESTIGKEITSVERHALTEN FEUERVERZINKTER HV-SCHRAUBEN

HV SCREWS OF STRENGTH CLASS 10.9 (42 CR M04) TO DIN 6914, NUTS OF STRENGTH CLASS 10 (C 45) TO DIN 6915 AND WASHERS TO DIN 6915 AND WASHERS TO DIN 6916 WERE EXAMINED. NO SIGNIFICANT EFFECT OF THE ZINC LAYER ON THE NOTCH IMPACT TEST AT ROOM TEMPERATURE OR AT - 60 DEGREES C WAS FOUND. TENSILE TESTS SHOWED NO SIGNIFICANT DIFFERENCES IN LOADING CAPACITY, IE 0.3 LIMIT OF THREADS WITH TOLERANCES ACCORDING TO DIN 13 AND DIN 267, IN UNGALVANIZED AND GALVANIZED STATE. IN TIGHTENING TESTS USING LUBRICATION (M0S2 PASTE) THE ABRASION RESISTANCE OF THE SCREW THREAD WAS EXCEEDED. THE TEST VALUES FOR TIGHTENING TORQUE AND INITIAL STRESSING FORCE FOR UNGALVANIZED AND GALVANIZED SCREWED JOINTS DIFFER ONLY SLIGHTLY. PRE-STRESSING TESTS SHOWED NO EVIDENCE OF A POSSIBLE HYDROGEN EMBRITTLEMENT. UNDER VIBRATIONAL STRESS A LARGE PART OF THE DROP IN INITIAL STRESSING FORCE OCCURS IN THE FIRST LOAD CYCLE (CA. 2% OF THE INITIAL STRESSING FORCE) WHEREBY STILL NO OBVIOUS EFFECT OF THE ZINC LAYER IS YET RECOGNIZABLE. UP TO 300 000 CYCLES THE AMOUNT OF LOSS IN INITIAL STRESS FORCE IS DOUBLED FOR GALVANIZED SCREWED JOINTS WHEREAS IT INCREASES BY ONLY HALF IN THE CASE OF UNGALVANIZED SCREWS.