6 1 4 1 1 σ σ σ 823 Khi raêng laøm vieäc ca� hai maët chu kyø öùng suaát ñoái

6 1 4 1 1 σ σ σ 823 khi raêng laøm vieäc ca?

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] .[ ). 6 , 1 4 , 1 ( ] [ 1 σ σ ÷ = σ (8.23) - Khi raêng laøm vieäc caû hai maët (chu kyø öùng suaát ñoái xöùng):
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Giaùo Trình CÔ HOÏC ÖÙNG DUÏNG CHÖÔNG 8. TRUYEÀN ÑOÄNG BAÙNH RAÊNG 171 Nu u K n K . ] .[ ] [ 1 σ σ = σ (8.24) vôùi : σ -1 laø giôùi haïn moûi chu kyø ñoái xöùng (baûng 8.2). Baûng 8.2 Ñaëc tính cô hoïc cuûa moät soá loaïi theùp duøng cheá taïo baùnh raêng Ñaëc tính cô hoïc N/mm 2 Ñoä raén Phaïm vi öùng duïng Maõ hieäu theùp Daïng phoâi Nhieät luyeän Ñöôøng kính phoâi, mm σ B σ C σ -1 HB HRC 40A Ñuùc Thöôøng hoùa Baát kyø 520 294 224 147 - Baùnh lôùn bò truyeàn taûi nheï 100 503 294 253 100-300 569 284 245 45 Reøn Thöôøng hoùa 300-500 608 304 262 167-217 - Baùnh lôùn caùc boä truyeàn 100 647 324 278 100-300 628 314 270 55 Reøn Thöôøng hoùa 300-500 608 304 262 186-229 - Baùnh nhoû vôùi v 8 m/s 150 637 363 274 50 Γ Reøn Thöôøng hoùa 150-400 608 314 262 190-229 - Baùnh nhoû vaø baùnh lôùn vôùi v 8 m/s 60 981 785 437 100-200 765 490 362 40X Reøn Thöôøng hoùa 200-300 736 490 352 200-230 - Baùnh nhoû vaø baùnh lôùn v 100 m/s 40X Reøn Toâi caûi thieän 120 948 656 450 257-255 - Nt 40X Reøn Toâi caûi thieän Baát kyø 736 490 351 500-550 51-55 Nt
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Giaùo Trình CÔ HOÏC ÖÙNG DUÏNG CHÖÔNG 8. TRUYEÀN ÑOÄNG BAÙNH RAÊNG 172 K σ laø heä soá taäp trung öùng suaát ôû chaân raêng. Ñoái vôùi baùnh raêng keùp thöôøng hoùa: K σ =1,8, toâi beà maët K σ = 1,2; vôùi baùnh raêng gang K σ = 1,2. [n] laø heä soá an toaøn cho pheùp. Ñoái vôùi baùnh raêng reøn thöôøng hoaù [n] = 1,5; reøn toâi [n] = 2,2; baùnh raêng ñuùc thöôøng hoùa [n] = 1,8. K Nu laø heä soá cheá ñoä taûi troïng khi tính toaùn raêng theo uoán. 9 6 10 . 5 CK Nu N K = (8.25) ÔÛ ñaây N CK xaùc ñònh theo (8.19), trò soá nhoû nhaát K Numin = 1, lôùn nhaát K Numax = 1,65. ÖÙng suaát quaù taûi cho pheùp: - Vôùi baùnh raêng theùp: + Ñoä cöùng 350HB: [ σ ] uq = 0,8. σ c (8.26) + Ñoä cöùng > 350HB: [ σ ] uq = 0,36. σ b /K σ (8.27) - Vôùi baùnh raêng gang: [ σ ] uq = 0,6. σ BK (8.28) 8.2.3. Tính toaùn boä truyeàn baùnh raêng 8.2.3.1. Tính toùan boä truyeàn baùnh raêng truï Löïc taùc duïng taïi ñieåm aên khôùp luoân truøng vôùi phaùp tuyeán cuûa beà maët raêng taïi ñieåm ñoù (boû qua löïc ma saùt khi aên khôùp vì nhoû). 8.2.3.1.1. Ñoái vôùi baùnh raêng truï raêng thaúng α Hình 8.12
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Giaùo Trình CÔ HOÏC ÖÙNG DUÏNG CHÖÔNG 8. TRUYEÀN ÑOÄNG BAÙNH RAÊNG 173 a) Löïc taùc duïng taïi ñieåm aên khôùp: Taïi cöïc aên khôùp P: n P G laø hôïp löïc cuûa caùc löïc taùc duïng khi raêng aên khôùp nhau treân ñöôøng aên khôùp. Ñeå tính toaùn raêng, truïc vaø oå truïc, P n ñöôïc phaân thaønh hai thaønh phaàn: - Löïc voøng: P = P n .cos α = A i M d M ) 1 ( 2 1 1 1 + = (8.29) - Löïc höôùng taâm: T = P.tg α (8.30) ôû ñaây M 1 laø moment quay treân baùnh nhoû.
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