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)