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Q2. (50p) An as-wound helical compression spring, made of steel wire (A227, Washburn & Moen), will be used to support 190 lb boxes (see Figure given below). It is needed that when box is placed on the tabletop, spring should deflect 2.5 in from its free length (Lo). Spring will be used in a 4 in diameter hole. Clearance between inner wall of the hole and outer edge of the spring is 0.23/2 = 0.115 in. Design criteria: • Ends are squared and closed. 10 SC s 11 (spring index) • 72 0.15 (linearity) a) (15p) Select the wire from available diameters (Table A-28) 0.115 in Determine, b) (10p) Coil diameter c) (5p) Spring rate d) (10p) Total number of turns e) (10p) Free and solid length 190 lb Lop 25 in 02 dhole = 4 in Lop >
Q1. (50p) An external speed-reducing helical gear set transmits the input power of 6 kW at 600 rpm. . Name Description pinion 1.25 gear 1.25 Ko overload Specifications: Material : Grade 1, through-hardened steel Hardness: 390 Brinell for pinion and 300 Brinell for gear. Normal module is 3, normal pressure angle is 20° and helix angle is 25°. They have 20 and 30 teeth. Face width is 35 mm. Kv dynamic 1.22 1.22 Ks size 1 1 Кн load-dist. 1 1 . Ye temperature 1 1 Yz reliability 0.89 0.89 Ке 1 1 rim-thickness bending geometry Y ? ONLY FOR THE GEAR: a) (5p) Find the geometry factors. b) (5p) Find the stress cycle life factors. c) (5p) Determine the hardness ratio factor d) (5p) Find AGMA strengths. e) (20p) Find the factors of safety. f) (10p) Compare the factors of safety and determine the cause of failure. YN bending life ? 15000 h, use the lower limit ZE elastic coef. ? for steel- steel ZR surface 1 1 Z wear geometry ? load- sharing, my=0.40 Zw hardness ratio ? ZN wear life ? 15000 h, use the lower limit