bab 05 plain bearing
TRANSCRIPT
Bab V Plain Bearing
Training on Bearing and Lubrication
Bab V Plain Bearing
5.1 Pendahuluan1. AplikasiKompresor, pompa, motor berkapasitas besar Turbine Generator dll.
2. Jenis-jenisJournal/Radial Bearing beban radial poros Thrust Bearing beban aksial poros Guide/Slipper Bearing pengarah gerakTraining on Bearing and Lubrication 2
Bab V Plain Bearing
3. Prinsip KerjaSliding Murni tanpa ada cairan/gas pelumas (contoh: Teflon, Nylon, Graphite) Hydrodynamic terdapat lapisan batas antar permukaan Hydrostatic terdapat pelumas bertekanan yang memisahkan kedua permukaan Kombinasi Hydrodynamic dan Hydrostatic
Training on Bearing and Lubrication 3
Bab V Plain Bearing
4. Perbandingan Umum vs Roller BearingKelebihan:Bentuk yang kompak Operasi lebih halus Lebih murah untuk produksi massal Lebih kaku Umur relatif tidak dibatasi fatigue
Kekurangan:Gesekan besar untuk start awal Memerlukan pelumas kualitas tinggi Rentan terhadap lingkungan buruk (partikel asing dll.)
Training on Bearing and Lubrication 4
Bab V Plain Bearing
5.2 Sliding Bearing1. Requirement Material untuk sliding: Fatigue resistanceKemampuan material untuk menahan beban berulang tanpa mengalami keretakan/kegagalan
EmbeddabilityKemampuan material untuk menyerap partikel asing dalam pelumas sehingga scoring/aus dapat dihindari
Training on Bearing and Lubrication 5
Bab V Plain Bearing
Anti-scoring tendencyKemampuan material untuk menahan galling atau seizing pada kontak metal-metal saat start-up
ConformabilityKemampuan material untuk mengalami creep atau perubahan bentuk menyesuaikan kontour permukaan maupung pembebanan yang tidak uniform saat running (misal: misalignment)
High thermal conductivityKemampuan material untuk mengeluarkan panas yang timbul dari gesekan sehingga temperatur stabilTraining on Bearing and Lubrication 6
Bab V Plain Bearing
Wear resistanceKetahanan material terhadap aus, berhubungan dengan umur
Corrosion resistanceKetahanan material terhadap zat korosif yang kadang terkandung/terbentuk dalam pelumas
Load capacityKemampuan material untuk menahan beban tekan
Thermal Expansion coef.Untuk menghindari pemuaian dan thermal stress yang berlebih
Lain-laincosts, availability, machinability
Training on Bearing and Lubrication 7
Bab V Plain Bearing
2. Jenis MaterialLogamAluminium Babits (tin alloys) Copper alloys Zinc Iron
Non-logamPlastics Carbon/graphites Cemented carbides Self-lubricated materialsTraining on Bearing and Lubrication 8
Bab V Plain Bearing
3. Perbandingan Material Sliding
Training on Bearing and Lubrication 9
Bab V Plain Bearing
Training on Bearing and Lubrication 10
Bab V Plain Bearing
Training on Bearing and Lubrication 11
Bab V Plain Bearing
5.3 Hydrodynamic Bearing1. Mekanisme Kerja Komponen:Journal / Poros Bushing / Bantalan Pelumas
Pressure Distribution & Pemodelan
Training on Bearing and Lubrication 12
Bab V Plain Bearing
2. Mode OperasiKondisi pelumasan yang terjadi pada sistem hydrodynamic bearing Tergantung dari pelumas, rancangan bantalan dan kecepatan putar poros Terdiri dari:Full-film Boundary Lubrication Mixed
Training on Bearing and Lubrication 13
Bab V Plain Bearing
Full-filmPelumas mampu memisahkan secara sempurna kedua permukaan gesek Koefisien gesek rendah ( = 0.001 0.005) Keausan rendah Parameter yang harus dipenuhi meliputi:Pemilihan pelumas yang tepat untuk kondisi operasi Aliran pelumasan yang terpelihara baik Perancangan dan pemilihan bantalan yang tepat Kecepatan relatif kedua permukaan terjaga sekira 25 feet/min
Training on Bearing and Lubrication 14
Bab V Plain Bearing
Boundary LubricationPermukaan sliding saling bergesekan dengan hanya dibatasi oleh lapisan pelumas yang sangat tipis Cukup baik untuk peralatan dengan gerak osilasi atau rotasi putaran rendah (< 10 feet/min) Koefisien gesek, = 0.08 0.14 Umumnya menggunakan pelumas grease atau oli dengan maintenance regular
Training on Bearing and Lubrication 15
Bab V Plain Bearing
Mixed Film-Boundary LubricationMode operasi terjadi antara mode full-film maupun boundary, tergantung kondisi operasi bearing Terjadi pemisahan sebagian antar permukaan sliding Koefisien gesek, = 0.02 0.08 Rotasi putaran minimal 10 feet/min
Training on Bearing and Lubrication 16
Bab V Plain Bearing
Perbandingan tiga mode operasi
Training on Bearing and Lubrication 17
Bab V Plain Bearing
Dalam operasi, semua mode pelumasan terjadi:Saat journal berhenti, terjadi kontak antar permukaan sliding Saat start-up dan stop, terjadi mode boundary lubrication Seiring bertambahnya kecepatan putar, terjadi mixed film-boundary Pada kecepatan rancangan, terjadi full-film lubrication
Training on Bearing and Lubrication 18
Bab V Plain Bearing
3. Journal BearingMenahan beban radial journal/poros Grooving:Untuk menjaga agar pelumas tetap berada diantara journal dan bantalan Juga berfunsgi sbg pendingin pelumas Lokasi pemasukan pelumas ke dalam bearing haruslah pada daerah bertekanan rendah
Training on Bearing and Lubrication 19
Bab V Plain Bearing
KonstruksiCircumferential grove alur pada sekeliling bantalan Cylindrical overshoot alur lebar untuk pendinginan bearing aplikasi kecepatan tinggi Pressure dengan tambahan alur setengah lingkaran untuk mengatur tekanan pelumasan Multiple groove beralur banyak untuk memperlancar aliran pelumasTraining on Bearing and Lubrication 20
Bab V Plain Bearing
EllipticalTerdiri dari 2 bagian membentuk penampang ellips
Elliptical overshootModel Ellips dengan alur melebar
Three-lobeMirip elliptical tetapi dengan 3 rongga yang lebar
Pivoted ShoeBearing dengan 3 atau lebih permukaan yang terpisah dengan titik putar pada sumbu poros
Nut-crackerBearing terdiri dari 2 bagian dengan bagian atas bisa bergerak bebas dalam arah vertikal
Training on Bearing and Lubrication 21
Bab V Plain Bearing
Parameter Performans Journal Bearing:Bearing load capacity Frictional losses Lubricant flow requirement Kenaikan temperatur
Training on Bearing and Lubrication 22
Bab V Plain Bearing
Journal Bearing Notation
Training on Bearing and Lubrication 23
Bab V Plain Bearing
Procedure for Lubrication Analysis
Training on Bearing and Lubrication 24
Bab V Plain Bearing
Training on Bearing and Lubrication 25
Bab V Plain Bearing
Training on Bearing and Lubrication 26
Bab V Plain Bearing
Training on Bearing and Lubrication 27
Bab V Plain Bearing
Training on Bearing and Lubrication 28
Bab V Plain Bearing
Training on Bearing and Lubrication 29
Bab V Plain Bearing
Training on Bearing and Lubrication 30
Bab V Plain Bearing
Training on Bearing and Lubrication 31
Bab V Plain Bearing
Training on Bearing and Lubrication 32
Bab V Plain Bearing
Training on Bearing and Lubrication 33
Bab V Plain Bearing
Training on Bearing and Lubrication 34
Bab V Plain Bearing
Training on Bearing and Lubrication 35
Bab V Plain Bearing
Training on Bearing and Lubrication 36
Bab V Plain Bearing
Training on Bearing and Lubrication 37
Bab V Plain Bearing
Dari hasil penghitungan & Grafik, kondisi cd yang dapat diterima:d 1 : cd min. 200 mikroinch 1 d 4 : cd min. 500 mikroinch d 4 : cd min. 750 mikroinch
cd ditentukan pada T = 400 F dari kurva oiltemperature jika dalam manual tidak terdapat persyaratan khusus Toleransi pembebanan dari manufacturer bisa dimodifikasi asal masih dalam range h0 dan T
Training on Bearing and Lubrication 38
Bab V Plain Bearing
Contoh Soal
Training on Bearing and Lubrication 39
Bab V Plain Bearing
Training on Bearing and Lubrication 40
Bab V Plain Bearing
Training on Bearing and Lubrication 41
Bab V Plain Bearing
Training on Bearing and Lubrication 42
Bab V Plain Bearing
Training on Bearing and Lubrication 43
Bab V Plain Bearing
Training on Bearing and Lubrication 44
Bab V Plain Bearing
Training on Bearing and Lubrication 45
Bab V Plain Bearing
4. Thrust BearingFungsi:Menahan poros arah aksil Memposisikan poros pada arah aksial
Konsep
Training on Bearing and Lubrication 46
Bab V Plain Bearing
Klasifikasi berdasarkan Geometri1.
Parallel/FlatPaling umum, sederhana dan murah Aplikasi beban/energi rendah Umum untuk
positioning devices2.
StepSederhana, relatif murah Sensitif terhadap
misalignmentDimensi kecil
Training on Bearing and Lubrication 47
Bab V Plain Bearing3.
Tapered-landKapasitas besar Performance bagus untuk dimensi besar Perlu alignment yang bagus Relatif mahal
4.
Tilting padKapasitas besar Relatif mahal Mampu mengakomodasi misalignment
Training on Bearing and Lubrication 48
Bab V Plain Bearing
Load range applications
Training on Bearing and Lubrication 49
Bab V Plain Bearing
Thrust Bearing Notationa b b2 B c D e f g h i J= radial width to pad, inches = circumferential length of pad at pitch line, inches = pad step length = circumference of pitch circle inches = specific heat of oil, Btu/gal/oF = diameter, inches = depth of step, inch = coefficient of friction = depth of 45o chamfer, inches = film thickness, inch = number of pads = power loss coefficienTraining on Bearing and Lubrication 50
Bab V Plain Bearing
K
= film thickness factor
Kg = fraction of circumference occupied by the pads;usually, 0.8
l M N O p ps Pf Q
= length of chamfer, inches = horsepower per square inch = revolutions per minute = operating number = bearing unit load, psi = oil-supply pressure, psi = friction horsepower = total flow, gpm
Qc = required flow per chamfer, gpm Qc0 = uncourrected required flow per chamfer, gpm QF = film flow, gpmTraining on Bearing and Lubrication 51
Bab V Plain Bearing
s t U V W YG YL YSZ
= oil-groove width = temperature rise, oF = velocity, feet per minute = effective width-to-length ratio for one pad = applied load, pounds = oil-flow factor = leakage factor = shape factor = viscosity, centipoises = dimensionless film-thickness factor = taper = kinetic energy correction factor
Note : In the following, subscript 1 denotes inside diameter and subscript 2 denotes outside diameter. Subscript i denotes inlet and subscript odenotes outlet.
Training on Bearing and Lubrication 52
Bab V Plain Bearing
Procedure for Thrust Bearing Lubrication Analysis1. Flat Plat Bearing
Training on Bearing and Lubrication 53
Bab V Plain Bearing
Training on Bearing and Lubrication 54
Bab V Plain Bearing
Training on Bearing and Lubrication 55
Bab V Plain Bearing
Training on Bearing and Lubrication 56
Bab V Plain Bearing
Training on Bearing and Lubrication 57
Bab V Plain Bearing
Training on Bearing and Lubrication 58
Bab V Plain Bearing
2. Step Bearing
Training on Bearing and Lubrication 59
Bab V Plain Bearing
Training on Bearing and Lubrication 60
Bab V Plain Bearing
Training on Bearing and Lubrication 61
Bab V Plain Bearing
3. Tapered
Training on Bearing and Lubrication 62
Bab V Plain Bearing
Training on Bearing and Lubrication 63
Bab V Plain Bearing
Training on Bearing and Lubrication 64
Bab V Plain Bearing
Training on Bearing and Lubrication 65
Bab V Plain Bearing
Training on Bearing and Lubrication 66
Bab V Plain Bearing
Training on Bearing and Lubrication 67
Bab V Plain Bearing
Training on Bearing and Lubrication 68
Bab V Plain Bearing
Training on Bearing and Lubrication 69
Bab V Plain Bearing
Training on Bearing and Lubrication 70
Bab V Plain Bearing
4. Tilting Pad
Training on Bearing and Lubrication 71
Bab V Plain Bearing
Training on Bearing and Lubrication 72
Bab V Plain Bearing
Training on Bearing and Lubrication 73
Bab V Plain Bearing
Training on Bearing and Lubrication 74
Bab V Plain Bearing
5.4 Hydrostatic BearingPada Hydrodynamic bearing, perlu kecepatan relatif permukaan yang tinggi untuk membentuk film pelumas yang bertekanan Jika bearing dengan beban besar tetapi dengan kecepatan relatif permukaan rendah, maka perlu tekanan eksternal agar tidak terjadi kontak langsung antar permukaan gesek Khususnya pada saat start up atau shut down, aplikasi Hydrostatic diperlukan, yaitu dengan menambahkan tekanan eksternal pada bearing
Training on Bearing and Lubrication 75
Bab V Plain Bearing
Mekanisme pembentukan film pada hydrostatic bearing
Training on Bearing and Lubrication 76
Bab V Plain Bearing
KelebihanKoefisien gesek sangat rendah Dapat menerima beban yang sangat tinggi, tidak tergantung kecepatan Akurasi tinggi pada kecepatan tinggi, beban rendah Kekakuan bearing tinggi
KekuranganMemerlukan pompa tekanan dan kecepatan alir tinggi
Training on Bearing and Lubrication 77
Bab V Plain Bearing
AplikasiTeleskop besar, radar tracking unitBeban sangat besar Kecepatan sangat rendah
Machine tools dan giroskopBeban rendah Kecepatan sangat tinggi
Training on Bearing and Lubrication 78
Bab V Plain Bearing
Gas-lubricated hydrostatic bearing
Training on Bearing and Lubrication 79
Bab V Plain Bearing
KelebihanGesekan dan viscous resistance yang sangat rendah Pelumas gas/udara, sehingga sederhana dan bersih Tidak ada kontaminasi pelumas terhadap permukaan Pelumas dapat bekerja baik range temperatur yang sangat besar Tidak terjadi fenomena kavitasi
Training on Bearing and Lubrication 80
Bab V Plain Bearing
KekuranganKapasitas beban rendah Pengerjaan permukaan harus halus Alignment harus sangat baik Dimensi dan clearance harus sangat akurat Stabilitas relatif rendah
AplikasiGas-cycled machinery Gyroscope Food-processing Textile processingTraining on Bearing and Lubrication 81
Bab V Plain Bearing
5.5 Ringkasan Plain Bearing1. PerbandinganCondition General Comments Bearing Type Hydrodynamic Hydrostatic Self-acting Gas Externally Presurised
High temperature
Attention to differential expansions and their effect on axial clearance is necessary Attention to differential expansions and starting torque is necessary
Attention to oxidation lubricant is necessary resistance of Excellent
Excellent
Excellent
Low temperature
Lubricant may impose limitations; consideration of starting torque is
Lubricant may impose limitations
Exellent: thorough drying of gas is necessary
Training on Bearing and Lubrication 82
Bab V Plain Bearing
Condition External vibration
General Comments Attention to possibility of fretting damage is necessary (exepts for hydrostatic bearings) -
Bearing Type Hydrodynamic Statisfactory Hydrostatic Excellent Self-acting Gas Normally satisfactory Externally Presurised Excellent
Space requirements
Small radial extent but total space requirement depends on lubricant feed system
Small radial extent
Small radial total space requirement depends on gas feed system Satisfactory
Dirt of dust
-
Statisfactory; filtration on lubricant is important
Sealing is important
Training on Bearing and Lubrication 83
Bab V Plain Bearing
Condition Vacuum
General Comments -
Bearing Type Hydrodynamic Hydrostatic Self-acting Gas Not normally applicable Externally Presurised Not applicable when vacuum has to be maintained Satisfactory
Lubricant may impose limitations
Wetness and humidity
Attention to posibility of metallic corrosions is necessary -
Satisfactory
Satisfactory
Radiation Low starting torque High starting torque Accuracy of radial location
Lubricant may impose limitations Satisfactory Satisfactory Good Excellent Satisfactory Excellent
Excellent Excellent Excellent Good Excellent Excellent Excellent
Training on Bearing and Lubrication 84
Bab V Plain Bearing
Condition Life
General Comments -
Bearing Type Hydrodynamic Theoretically infinite but affected by filtration and number of start - stops Hydrostatic Theoretically infinite Self-acting Gas Theoritically infinite but affected by number of start- stops Externally Presurised Theoretically infinite
Combination of axial and radial load capacity Silent running
-
A journal bearing surface must be provided to carry radial loads and thrust face to carry axial loads
-
Excellent
Excellent except for possible pump noise
Excellent
Excellent except for possible compresor noise
Training on Bearing and Lubrication 85
Bab V Plain BearingBearing Type Hydrodynamic Self-contained assemblies can be used with certain limits of load,speed and diameter; beyond this, oil circulation is necessary Good Hydrostatic Auxiliary high pressure is necessary Self-acting Gas Excellent Externally Presurised Pressurized supply of dry, clean gas is necessary
Condition Simplicity of lubrication
General Comments -
Availability of standard parts Prevention of contamination of product and surroundings Tolerance to manufacturing and assembly inaccuracies
-
Poor
Good Excellent
Poor Excellent
Normally statisfactory,but attention to sealing is necessary, exept where process liquid can be used as lubricant Poor Satisfactory
-
Poor
Satisfactory
Training on Bearing and Lubrication 86
Bab V Plain Bearing
Condition Type of motion Frequent Start-stops Unidirectional Bidirectional Oscillatory Running costs
General Comments
Bearing Type Hydrodynamic Hydrostatic Self-acting Gas Externally Presurised Exellent Suitable Suitable Some types are suitable Unsuitable Suitable Suitable Suitable
-
Good Suitable Some types are suitable Unsuitable
Suitable
Depends on complexity
Training on Bearing and Lubrication 87
Bab V Plain Bearing
2. Aplikasi PraktisPanduan Pemilihan Bearing dalam Grafik
Training on Bearing and Lubrication 88
Bab V Plain Bearing
Keterangan
Training on Bearing and Lubrication 89
Bab V Plain Bearing
Pemilihan Plain Bearing menurut operasi
Training on Bearing and Lubrication 90
Bab V Plain Bearing
Training on Bearing and Lubrication 91
Bab V Plain Bearing
Training on Bearing and Lubrication 92
Bab V Plain Bearing
Panduan Pemilihan Thrust Bearing
Training on Bearing and Lubrication 93
Bab V Plain Bearing
Training on Bearing and Lubrication 94
Bab V Plain Bearing
Training on Bearing and Lubrication 95
Bab V Plain Bearing
Training on Bearing and Lubrication 96
Bab V Plain Bearing
Panduan Pemilihan Material
Training on Bearing and Lubrication 97
Bab V Plain Bearing
Training on Bearing and Lubrication 98
Bab V Plain Bearing
Training on Bearing and Lubrication 99
Bab V Plain Bearing
Training on Bearing and Lubrication 100
Bab V Plain Bearing
5.6 Metode PemasanganFaktor-faktor yang harus dipertimbangkan:Keseragaman tebal dinding bantalan Kontak yang baik dan luas dengan housing, untuk perpindahan panas Perubahan bentuk bearing akibat kenaikan temperatur
Training on Bearing and Lubrication 101
Bab V Plain Bearing
Beberapa MetodePress / Shrink-fit Keys: Set screws, Woodwurf keys, bolted, threaded bearing, dowel pins, housing caps
Training on Bearing and Lubrication 102
Bab V Plain Bearing
5.7 Pelumasan1. Metode PelumasanPressure/pompaPelumas bertekanan diinjeksikan ke arah permukaan kontak melalui alur atau lubang Tekanan umumnya pada 50 psi Untuk mode film-lubrication, perpindahan panas cukup baik dan kemampuan pembersihan kotoran yg baik
Training on Bearing and Lubrication 103
Bab V Plain Bearing
Splash-fedPelumas dipercikkan ke bearing Biasanya digunakan untuk pelumasan bearing/bushing yang berselang (tidak terus menerus) Praktis untuk kondisi housing yang sempit dan bagian bergerak tidak dapat terendam pelumas
Oil-bathBushing/bearing terendam pelumas Kehandalan setinggi pressure lubrication Housing memungkinkan Putaran bagian berputar tidak terlalu tinggiTraining on Bearing and Lubrication 104
Bab V Plain Bearing
Oil-ringPelumas disuplai ke bantalan melalui ring yang berkontak dengan bagian berputar Rentang kecepatan tangensial 200 2000 feet/min.
Wick-packPelumas disuplai ke bantalan dengan prinsip kapiler melalui sumbu (wick) Jumlah pelumas yang dialirkan proporsional dengan ukuran sumbu
Training on Bearing and Lubrication 105
Bab V Plain Bearing
Grease packMenggunakan grease dan bantalan berpori Pelumasan permanen, tetapi hydrodynamic sulit tercapai Biasanya sampai mode boundary lubrication
Training on Bearing and Lubrication 106
Bab V Plain Bearing
2. PelumasNilai pelumasan untuk sliding bearing terutama tergantung pada kapasitas pembentukan lapisan film pelumas antar permukaan sliding Karakteristik terbentuknya film pelumas tergantung terutama pada viskositas Idealnya: pelumas dengan viskositas (kekentalan) rendah sehingga rugi gesek rendah tetapi tidak pecah pada film Kenyataannya kompromiTraining on Bearing and Lubrication 107
Bab V Plain Bearing
Satuan Viskositas
Training on Bearing and Lubrication 108
Bab V Plain Bearing
Pengaruh Temperatur terhadap viskositas
Training on Bearing and Lubrication 109
Bab V Plain Bearing
Faktor-faktor dalam pemilihan pelumasMode operasi yang diharapkan Kecepatan relatif permukaan gesek Beban yang bekerja
Misal: Bantalan dengan beban ringan, diharapkan terjadi mode full-film pada putaran 2000 rpm, maka pelumas yang cocok adalah: SAE 5
Training on Bearing and Lubrication 110
Bab V Plain Bearing
Training on Bearing and Lubrication 111
Bab V Plain Bearing
3. GreaseKondisi Operasi:Putaran rendah dan beban besar Boundary lubrication Koefisien gesek: 0,08 0,18 (rata-rata 0,12)
KelebihanPeriode pelumasan yang panjang Terhindar dari kontaminasi akibat kebocoran oli Efektif untuk lingkungan yang relatif kurang bersih
Training on Bearing and Lubrication 112
Bab V Plain Bearing
4. Solid LubricantMaterial dengan tahanan geser yang rendah Untuk peralatan yang bekerja pada temperatur tinggi Sifat pelumasan berubah drastis jika mendekati titik cair:Koefisien gesek bisa meningkat 5 10 kali Laju metal transfer meningkat 1000 kali
Training on Bearing and Lubrication 113
Bab V Plain Bearing
Training on Bearing and Lubrication 114
Bab V Plain Bearing
Training on Bearing and Lubrication 115
Bab V Plain Bearing
Training on Bearing and Lubrication 116