MY130222A - Fastening screw with self-tapping thread - Google Patents

Abstract

THE INVENTION RELATES TO A RETAINING SCREW (1) PRODUCED BY COLD ROLLING, HAVING A SELF TAPPING THREAD (2, 11) AND DESIGNED TO BE SCREWED FOR EXAMPLE INTO THERMOPLASTIC MATERIAL. SAID SCREW HAS A VIRTUALLY END-TO-END CYLINDRICAL THREAD (8) AS WELL AS THREAD TEETH (10), THE THREAD CREST (47) OF WHICH HAS THE SAME HEIGHT ON THE WHOLE LENGTH, WHILE THE FREE SPACE BETWEEN TWO TEETH REMAINS THE SAME ALL ALONG THE THREAD. THE SCREW (1) PRESENTS THE FOLLOWING CHARACTERISTICS: EITHER 1) THE THREAD OUTER DIAMETER DO AND THE THREAD INNER DIAMETER DK GIVES A RATIO Q1=DO/DK, IN A MAGNITUDE OF 1.25 TO 1.65; 2) THE AXIAL DISTANCE P BETWEEN TWO THREAD TEETH GIVES WITH THE HEIGHT H OF THE LATTER A RATIO Q2=P/H, IN A MAGNITUDE OF 2.35 TO 2.7; 3) THE OUTER THREAD FLANK ANGLE (α) OF THE THREAD TEETH IS ABOUT 30°; 4) THE FILLET FLANK SURFACE (26, 28; 31/33, 34/35; 37, 38) FEATURES AN INWARD CURVE IN ITS CENTRAL THIRD AND FORMS AN OUTER AND AN INNER THREAD FLANK ANGLE (α, β), WHEREBY THE INNER THREAD FLANK ANGLE (β) IN THE CENTRAL PORTION IS SUBSTANTIALLY EQUAL TO OR LARGER THAN ONE THIRD OF THE OUTER THREAD FLANK ANGLE (A).(FIG 1)