Post on 01-Feb-2016
description
Elemen Mesin
Pertemuan ke-3:
POROS (SHAFT)
Pokok Bahasan Hari Ini
Definisi dan fungsi poros Jenis-jenis poros Material poros Kekuatan poros akibat puntiran/torsi
Definisi
A shaft is the component of a mechanical device that transmits rotational motion and power (Mott, 2004)
A shaft is a rotating machine element which is used to transmit power from one place to another (Khurmi & Gupta, 2005).
A shaft is a rotating member, usually of circular cross section, used to transmit power or motion (Shigley, 2008).
Shaft/Poros
Beban pada Poros
Serupa Poros
axle (as/gandar) adalah elemen mesin yang tidak bergerak dan berfungsi sebagai pendukung bagi beberapa bagian yang berputar seperti: roda, puli/kerekan.
Axle
Serupa Poros
spindle merupakan poros transmisi yang relatip pendek, misalnya pada poros utama mesin perkakas, yang memutar pahat (bor, milling) atau memutar benda kerja (bubut)
Spindle
Shaft Materials
It should have high strength. It should have good machinability. It should have low notch sensitivity factor. It should have good heat treatment
properties. It should have high wear resistant properties.
Shaft Materials
Types of Shafts
Transmission shafts. The counter shafts, line shafts, over head shafts and all factory shafts are transmission shafts. Since these shafts carry machine parts such as pulleys, gears etc., therefore they are subjected to bending in addition to twisting.
Machine shafts. These shafts form an integral part of the machine itself. The crank shaft is an example of machine shaft.
Counter Shaft
Crank Shaft
Standard Sizes of Transmission Shafts
25 mm to 60 mm with 5 mm steps; 60 mm to 110 mm with 10 mm steps ; 110 mm to 140 mm with 15 mm steps ; and 140 mm to 500 mm with 20 mm steps. The standard length of the shafts are 5 m, 6
m and 7 m.
Stresses in Shafts
1. Shear stresses due to the transmission of torque (i.e. due to torsional load).
2. Bending stresses (tensile or compressive) due to the forces acting upon machine elements like gears, pulleys etc. as well as due to the weight of the shaft itself.
3. Stresses due to combined torsional and bending loads.
Design of Shafts
The shafts may be designed on the basis of Strength, and Rigidity and stiffness.
In designing shafts on the basis of strength, the following cases may be considered :
Shafts subjected to twisting moment or torque only, Shafts subjected to bending moment only, Shafts subjected to combined twisting and bending
moments, and Shafts subjected to axial loads in addition to combined
torsional and bending loads.
Shafts Subjected to Twisting Moment Only
Solid Shaft
Hollow Shaft
Hollow Shaft
Hollow Shaft = Solid Shaft
Power in watts
Belt drives
Contoh-1
Contoh-2
Contoh-3
Contoh-3
Pokok Bahasan Minggu Depan
Kekuatan poros akibat lenturan/momen lengkung
Kekuatan poros akibat lenturan dan puntiran Daya pada poros
Referensi
Machine Elements in Mechanical Design 4th Edition by Robert L. Mott (2004)
A Textbook of Machine Design by R.S. Khurmi and J.K.Gupta (2005)
Shigley’s Mechanical Engineering Design 8th Edition (2008)