ElmesElmes 11

SemesterSemester GenapGenap 20132013SemesterSemester GenapGenap 20132013

Steam TurbineSteam Turbine

Pompa SentrifugalPompa Sentrifugal

Gear BoxGear Box Gear BoxGear Box

Pulley & BeltPulley & Belt Pulley & BeltPulley & Belt

Chain & SprocketChain & Sprocket

Crank ShaftCrank Shaft

dlldll dlldll

F

F

F

F

Fx

FFy

Fx

FF

FF

F

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Strength is a property of a material (S)Strength is a property of a material (S)

The designer must allow the strength toThe designer must allow the strength toexceed the stress by a sufficient margin soexceed the stress by a sufficient margin soexceed the stress by a sufficient margin soexceed the stress by a sufficient margin sothat despite the uncertainties, failure is rare.that despite the uncertainties, failure is rare.

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MNSTMNST Brittle MaterialBrittle Material MNSTMNST Brittle MaterialBrittle MaterialSySy/N ≥/N ≥ σσmaxmax

MSST (MSST (TrescaTresca)) Ductile materialDuctile material MSST (MSST (TrescaTresca)) Ductile materialDuctile materialSySy/2N ≥/2N ≥ ττmaxmax

Distortion Energy (VonDistortion Energy (Von MisesMises))((SySy/N)/N)22 == σσ 22 ++ σσ 22 ── σσ σσ((SySy/N)/N)22 == σσ11

22 ++ σσ2222 ── σσ11σσ22

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3838

τmax

3939

JikaJika hanyahanya tegangantegangan normalnormal padapada sumbusumbu xxdandan tegangantegangan gesergeser padapada xyxy sajasaja yangyangdandan tegangantegangan gesergeser padapada xyxy sajasaja yangyangbekerjabekerja,, makamaka ……bekerjabekerja,, makamaka ……

• Diameter untuk mengecek kekuatan• Defleksi, slope untuk mencegah misalignment• Defleksi, slope untuk mencegah misalignment• Kekauan untuk menjaga torsi kontinu• Kekauan untuk menjaga torsi kontinu

• MSST dan Soderberg

• DET dan Soderberg

• Ksb dan Kst diberikan pada tabel di halaman342 (akibat kondisi Shock)342 (akibat kondisi Shock)

• Kf dan Kfs diberikan pada Appendix B, Gambar• Kf dan Kfs diberikan pada Appendix B, GambarB-1 (tergantung tipe Pasak)

• M = 0 (karena Momen berulang)• Mm = 0 (karena Momen berulang)• Tr = 0 (karena kondisi Steady)• Tr = 0 (karena kondisi Steady)

Bab 12 Shaft DesignMachine Elements in Mechanical DesignMachine Elements in Mechanical Design

• Titik B: HP = 30; n = 360 rpm• Titik C: 40% power• Titik C: 40% power• Titik E: sisa power• Titik E: sisa power

• MB = 10.351,77 lb-inT = 5250 lb-in• TB = 5250 lb-in

Definisi Shaft MisalignmentDefinisi Shaft Misalignment

Misalignment

Terjadi ketika sumbu rotasi dua (atau lebih) Terjadi ketika sumbu rotasi dua (atau lebih) poros mesin tidak berada dalam satu garis.

Offset & Angularity Misalignment

• Offset: jarak antara sumbu rotasi poros

• Angularity: sudut antara kedua sumbu putar porosputar poros

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Model Shaft MisalignmentModel Shaft Misalignment

1. Parallel Misalignment (Offset) 3. Combination Misalignment

2. Angular Misalignment (Angularity)2. Angular Misalignment (Angularity)

Target melakukan alignment adalahTarget melakukan alignment adalahmengatur posisi mesin sedemikian hinggapenyimpangan offset dan angularityberada di bawah batas nilai toleransi.berada di bawah batas nilai toleransi.

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Dampak Shaft MisalignmentDampak Shaft Misalignment

• Kerusakan seal • Kerusakan Kopling • Konsumsi Energi Lebih Besar

Bearing, seal, shaft, dan Bearing, seal, shaft, dan kopling cepat rusak/bocor

Kopling aus, baut patah

• Getaran Tinggi • Temperatur Tinggi

Pemborosan energi 2-17%.

• Getaran Tinggi • Temperatur Tinggi

Casing, oli, atau area sekitar bearing menjadi panas

Getaran aksial & radial besar. Baut base plate, shim packs atau

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bearing menjadi panasBaut base plate, shim packs atau dowel pins lepas

• To transmit power uniformly and with asteady motion.steady motion.

• Machinery shafting: 0.08 deg/ft of length• Transmission shafting to 1 deg in a length of• Transmission shafting to 1 deg in a length of

20 times the shaft diameter20 times the shaft diameter• Camshafts should be less than 0.5 deg

regardless of the shaft lengthregardless of the shaft length

Torsi InternalTorsi Internal

Ingat denganIngat denganPerjanjian tandanya

Untuk mengetahui distribusi torsi internal sepanjang poros makaperlu digambarkan diagram torsiperlu digambarkan diagram torsi

A key is a small piece of metalimbedded partially in the shaft andpartially in the hub to prevent rotationpartially in the hub to prevent rotationof a gear or pulley on a shaft.

The key prevents relative rotationbetween the two parts andbetween the two parts andenables torque transmission. A key isused for temporary fastening. For a keyused for temporary fastening. For a keyto function, the shaft and rotatingmachine element must have a keyway,also known as a keyseat, which is aalso known as a keyseat, which is aslot or pocket the key fits in.

SQUARE KEYS-The width is usually one-fourth of the shaft diameter. OneSQUARE KEYS-The width is usually one-fourth of the shaft diameter. Onehalf of the key is fitted into the shaft and one half is fitted into the hub.GIB HEAD KEY-Except for the gib head, this key is identical to the squarekey. The gib head provides easy removal.key. The gib head provides easy removal.PRATT & WHITNEY KEY-The ends are rounded and this key is fitted into aslot on the shaft of the same shape.slot on the shaft of the same shape.WOODRUFF KEY-A woodruff key is semi-circular in shape and fits into akeyseat of the same shape. The top of the key fits into a keyway in themating part.mating part.

Dimensi dariDimensi dariPasak

Lihat Tabel7-6 sd 7-87-6 sd 7-8

l pasak paling tidak harus 25% lebihpanjang dari d shaftpanjang dari d shaft

Lihat Example 7-2 di halaman 366Lihat Example 7-2 di halaman 366

Lihat Example 7-2 di halaman 366Lihat Example 7-2 di halaman 366