x so� baùnh ñai T 1 tuoåi thoï cuûa ñai giôø N o so� chu kyø cô sô� N o 10 7 σ

X so? baùnh ñai t 1 tuoåi thoï cuûa ñai giôø

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x: soá baùnh ñai. T 1 : tuoåi thoï cuûa ñai, giôø N o :soá chu kyø cô sôû, N o = 10 7 σ No : giôùi haïn cuûa ñai öùng vôùi N o = 10 7 Neáu i 1, ñieàu kieän laøm vieäc cuûa ñai nheï hôn, vì öùng suaát uoán treân baùnh lôùn coù trò soá nhoû hôn neân tuoåi thoï taêng: T = Ψ .T 1 Heä soá Ψ phuï thuoäc vaøo i vaø loaïi ñai (tra soå tay) Tuy nhieân do chöa coù soá lieäu ñaày ñuû vaø kinh nghieäm veà tính ñai theo ñoä beàn laâu neân ngöôøi ta thöôøng tính ñai baèng caùch haïn cheá soá voøng quay cuûa ñai trong 1 giaây. Vôùi vaän toác laøm vieäc yeâu caàu V, ta coù theå giaûm soá voøng chaïy u baèng caùch taêng chieàu daøi L vaø ñöông nhieân ñeå ñai laøm vieäc laâu daøi phaûi coù ñieàu kieän: max min max u V L L u L V u = = (6.27) 6.4. TRÌNH TÖÏ THIEÁT KEÁ TRUYEÀN ÑOÄNG ÑAI 6.4.1. Xaùc ñònh khoaûng caùch A vaø chieàu daøi ñai L Chieàu daøi toái thieåu cuûa ñai (theo 6.27): 5 3 u vôùi , u v L max max min ÷ = = Tính A theo L min (duøng coâng thöùc (6.3)) Ñoái vôùi truyeàn ñoäng thöôøng ñeå α ñuû lôùn, do ñoù A caàn thoûa ñieàu kieän: A 2.(D 1 + D 2 ) (6.33) Neáu A tính theo L min khoâng thoûa (6.33) caàn taêng A ñeå: A = 2(D 1 + D 2 )
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Giaùo Trình CÔ HOÏC ÖÙNG DUÏNG CHÖÔNG 6. TRUYEÀN ÑOÄNG ÑAI 135 Vaø tính laïi L theo A (coâng thöùc (6.2)). Ñeå noái ñai, sau khi tính xong caàn taêng theâm chieàu daøi ñai khoaûng (100 ÷ 400) mm tuøy theo caùch noái. 6.4.2. Tính goùc oâm α 1 (theo (6.1)) vaø kieåm nghieäm ñieàu kieän α 1 150 o (6.34) Neáu α 1 < 150 o , caàn taêng A hay duøng baùnh caêng ñai. 6.4.3. Xaùc ñònh tieát dieän ñai Choïn tröôùt chieàu daøy ñai theo tyû soá δ /D, quy troøn theo tieâu chuaån (Baûng 6.7) Chieàu roäng ñai tìm theo coâng thöùc (6.24) vaø quy troøn theo tieâu chuaån (baûng 6.6) Baûng 6.6 Vaûi cao su Da Deät Loaïi A Loaïi B Loaïi B Ñôn Keùp Sôïi vaûi Sôïi len 20 20 20 20 - - - 25 25 25 25 - - - 30 30 30 30 - - - - - - 35 - - - 40 40 40 40 - 40 - 45 45 - 45 - - - 50 - 50 50 - 50 50 60 - 60 60 - 60 60 (65) - (65) - - - - 70 - 70 70 - - - 75 - 75 75 - 75 75 80 80 80 80 - - - 85 - 85 85 85 - - 90 90 90 90 90 90 - - - - 95 95 - - 100 - 100 100 100 100 100 (115) - - 115 115 115 115 (120) - - - - - -
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Giaùo Trình CÔ HOÏC ÖÙNG DUÏNG CHÖÔNG 6. TRUYEÀN ÑOÄNG ÑAI 136 125 - 125 125 125 - 125 150 150 150 150 150 150 150 (175) - - 175 175 175 175 200 200 200 200 200 200 200 (225) - - 225 225 225 225 250 250 250 250 250 250 250 (275) - - 275 275 - - 300 300 300 300 300 - 300 - - - - - - 350 - 375 375 - - - - 400 400 400 - - - 400 - 425 425 - - - - 450 450 450 - - - 450 500 500 500 - - - 500 (550) - - - - - - 600 - - - - - - 6.4.4. Xaùc ñònh chieàu roäng B cuûa baùnh ñai Xaùc ñònh chieàu roäng B cuûa baùnh ñai theo coâng thöùc: B = 1,1.b + (10 ÷ 15) , mm (6.35) Ñoái vôùi truyeàn ñoäng thöôøng vaø laáy troøn theo tieâu chuaån (baûng 6.8) 6.4.5. Tính löïc caêng vaø löïc taùc duïng leân truïc S1 S2 R S1 S2 Hình 6.6
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Giaùo Trình CÔ HOÏC ÖÙNG DUÏNG CHÖÔNG 6. TRUYEÀN ÑOÄNG ÑAI 137 Goïi 2 1 S S R G G G + = γ + + = cos S S 2 S S R 2 1 2 2 2 1 (6.36) vôùi daãn nhaùnh caêng löïc : 2 P S S daãn nhaùnh caêng löïc : 2 P S S 0 2 0 1 = + = S 0 : löïc caêng ban ñaàu 2 sin S 2 2 cos S 2 2 cos 1 P 2 cos S 4 R 1 2 cos 2 4 P S 2 2 P S 2 R 1 o o 2 / 1 2 2 2 o 2 / 1 2 2 2 0 2 2 o α = γ
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