Đang chuẩn bị liên kết để tải về tài liệu:
Sổ tay tiêu chuẩn thiết kế máy P43

Tham khảo tài liệu 'sổ tay tiêu chuẩn thiết kế máy p43', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CHAPTER 36 WORM GEARING K. S. Edwards Ph.D. Professor of Mechanical Engineering University of Texas at El Paso El Paso Texas 36.1 INTRODUCTION 36.2 36.2 KINEMATICS 136.3 36.3 VELOCITY AND FRICTION 36.5 36.4 FORCE ANALYSIS I 36.5 36.5 STRENGTH AND POWER RATING 36.9 36.6 HEAT DISSIPATION I 36.12 36.7 DESIGN STANDARDS 36.13 36.8 DOUBLE-ENVELOPING GEAR SETS 36.18 REFERENCES 136.22 ADDITIONAL REFERENCE 36.22 GLOSSARY OF SYMBOLS ba Dedendum of gear teeth C Center distance d Worm pitch diameter d0 Outside diameter of worm dR Root diameter of worm D Pitch diameter of gear in central plane Db Base circle diameter Do Outside diameter of gear D Throat diameter of gear f Length of flat on outside diameter of worm hk Working depth of tooth ht Whole depth of tooth L Lead of worm mG Gear ratio Na Nw m Module millimeters of pitch diameter per tooth SI use mp Number of teeth in contact n Rotational speed of worm r min nG Rotational speed of gear r min 36.1 36.2 STANDARD HANDBOOK OF MACHINE DESIGN Na Number of teeth in gear Nw Number of threads in worm pn Normal circular pitch px Axial circular pitch of worm P Transverse diametral pitch of gear teeth per inch of diameter W Force between worm and gear various components are derived in the text X Lead angle at center of worm deg 4 Normal pressure angle deg j x Axial pressure angle deg at center of worm 36.1 INTRODUCTION Worm gears are used for large speed reduction with concomitant increase in torque. They are limiting cases of helical gears treated in Chap. 35. The shafts are normally perpendicular though it is possible to accommodate other angles. Consider the helical-gear pair in Fig. 36.1 with shafts at 90 . The lead angles of the two gears are described by X lead angle is 90 less the helix angle . Since the shafts are perpendicular X X2 90 . If the lead angle of gear 1 is made small enough the teeth eventually wrap completely around it giving the appearance of a screw as seen in Fig. 36.1b. Evidently this was at some stage taken