design of toggle jack
TRANSCRIPT
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L.D. college of engineering• Subject: Machine Design and Industrial Drafting
• Topic: Design of toggle jack• Year:2014-15
Sr.No. Name Enroll No. Roll No
1 Kuralkar Hemant Yogeshbhai 140283119009 419245
2 Shinde Kunal Bharatbhai 140283119024 419259
3 Sabalpara Nilesh 140283119023 419258
4 Rathod Jaydipsinh 140283119022 419257
5 Patel Sagar 140283119019 419254
6 Vaghela Kanu 140283119025 419260
7 Jadav Vipul 140283119007 419243
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Content:
• Mechanism of toggle jack• Design of the screw• Design of the Nut• Design of the Pin• Design of spanner• Design of the Link
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Design of toggle jack
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Design of toggle jack- Assumed data
• Lifting load = 4KN • Number of Link = 8• Length of the link = 110 mm• Materials for the screw, Nut and pins = M.S.• for M.S. = 100 MPa• 𝞽 for M.S. = 50 MPa• Limited bearing pressure = 20 MPa• Pitch of the screw thread = 6 mm• Co-efficient of the friction = 0.20
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Toggle Jack
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Design of screw
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Design of Square threaded screw
• Maximum load on screw occurs when the jack is in the bottom position.• From figure = → Ѳ = 35.1°
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Design of Square threaded screw
• Each nut carries half the total load on the jack• Link CD is subjected to tension
while the square threaded screw is under pull.• F = = = 2846N• This similar pull acts on other
nut,therefore total tensile load on square threaded rod
→= 2F =5692N
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Design of Square threaded screw
• Now considering tensile failure of the screw
→= * *→5692= * *100→ = 8.5 mm say 10 mmSince the screw is also subjected to shear stress, therefore let→ = 14 mm
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Design of Square threaded screw
• Outer Diameter of screw → = + P = 14+6→= 20 mm.Mean Diameter of screw→d = - = 20 – 3→d = 17 mm
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Checking of the screw for principal stress• = = = 0.1123• Effort required to rotate the
screwP = *) P = () = 5692()P = 1822N
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Checking of the screw for stress
• Torque required to rotate the screw
→T = P* = 1822*17/2 →T = 15487 N.mmShear stress due to torque→𝞽 = 16х = →𝞽 = 28.7 N/
• Direct Tensile stresses in the screw
→ = = → = 37 N/
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Checking for maximum principal stress• Maximum Principal stress→ = + + 4→=+→= 52.6 N/
• Maximum shear stress→ = + 4→ =→ = 34.1 N/
Since the maximum stresses are within limit, therefore design of square threaded screw is safe.
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Design of Nut
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Number of threads
• Let n is the number of the threads, which can be find by considering bearing failure of nut.
=20= =→ n = 1.776Inorder to have good stability and to prevent rocking of the screw let n = 4
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Dimensions of the Nut
• Thickness of nut→t = n*p = 4*6 →t = 24 mm.• Width of the nut→b = 1.5*=1.5*20→b = 30 mm
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Length of the screw
• To control the movements of the nuts beyond 210mm , rings of 8mm thickness are fitted on the screw with the help of set screw.
→length of screwed portion = 210 + 24 + 2*8 = 250 mm• Since screw is operated by spanner, therefore
extra 15 mm length both sides are provided.
→Total length = 250 + (2*15) = 280 mm
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Length of spanner
• Assuming that a force of 150 N is applied by each person at each end of the rod,
→T = 150*2*Length of spanner→15487 = 150*2*L→ Length of spanner = 51.62 mmWe shall take length of spanner as 200 mm in order to facilitate the operation
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Design of the pins in the Nuts
• Let is diameter of the pin.• Considering double shear of the
pin.→ F = 2**𝞽→2846 = 2**50→ = 6.02 mm ≈ 8mm
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Design of the Links
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Load acting on Link
• Load on the link = F/2 = →2846/2 = 1423 NAssuming factor of safety = 5→ = 5*1423 = 7115 N
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Dimensions of the link• Let = thickness of the link• Let = width of the link• Assuming .• cross sectional area of the link ,A→A = * = • Moment of inertia of the cross
section ,I→I = ** = 2.25• Radius of gyration k→K = = 0.866
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Buckling of the link in vertical plane• In buckling in vertical plane link
is considered as hinged.Therefore, L = l = 110 mmRankine’s constant a = According to Rankines formula for column,
=
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Buckling of the link in vertical plane
• 7115 = • = = 25.7• = 5.07 mm≈ 6mm and• = 3*6 = 18 mm
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Buckling of the link in plane perpendicular to vertical plane
• I = *3* = 0.25 • A = * = • K = = 0.29 • Since the buckling of the link in
plane perpendicular to the vertical plane, the ends are considered as the fixed.
→ L = l/2 = 110/2 = 55mm
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Buckling of the link in plane perpendicular to vertical plane
• According to Rankine's formula = = Taking = 6 mm = 9532 N.Since buckling load is more then the calculated value,
link is safe in design.
So dimension of the link• = 6mm and• = 18 mm