SPRING (PEGAS)

Pegas dapat digolongkan atas dasar jenis beban yang dapat diterimanya yaitu :• Pegas Tekan• Pegas Tarik• Pegas PuntirSedangkan jika dipandang dari segi bentuk, maka pegas dapat dibedakan menjadi lima bagian, yaitu :o Pegas Voluto Pegas Dauno Pegas Piringo Pegas Cincino Pegas Batang Puntiro Pegas Spiral atau Pegas jam

KLASIFIKASI PEGAS

Types of springs

1. Helical springs2. Conical and volute springs3. Torsion springs4. Laminated or leaf springs5. Disc or bellevile springs

1. Helical Spring

A helical spring is made up of a wire coiled in the form a helix

- Circular- Square- Rectangular-Compression helical springs

-Tension helical spring

Helical Springs Closely Coiled HS

Open Coiled HS

1. Helical Spring

1.Fungsi : a. Menyimpan gaya yang selanjutnya dikonversikan menjadi energib. Peredam

2. Penggunaan : a. Persenjataanb. Sistem suspensic. Pembatasan Gaya (pada pengepresan)

Compression Spring (Pegas Tekan)

Pegas Tarik (Tensile Spring)

1.Fungsi : a. Penyiman gayab. Penyimbang

2. Penggunaan : a. Timbanganb. Standrtc. Tromol

1. Helical Spring

2. Pegas Kerucut (Volute Spring & Conical spring)

1.Fungsi : a. Memberi reaksi dan mengatur tekanan

2. Penggunaan : a. Penutup cup mobileb. Pembersi kaca di mobil

2. Pegas Kerucut (Volute Spring & Conical spring)

Conical Spring

Volute Spring

2. Pegas Kerucut (Volute Spring & Conical spring)

The characteristic of volute / conical spring is sometimes utilised in vibration problems where springs are used to support a body that has a varying mass.

1.Fungsi : a. Menerima beban dan memberi reaksi puntiranb. Penyeimbangc. Suspensi

2. Penggunaan : a. Handle mobilb. Penjepit

3. Torsion Springs

1. Helical Torsion Spring

2. Spiral torsion spring

3. Torsion Springs

Helical Torsion Spring

Spiral Torsion Spring

The Analysis of Compression Springs

1. Solid Length When the coils contact with each other2. Free Length The normal condition of compression springs3. Spring Index Ratio of mean diameter of the coil & the diameter of the wire4. Spring Rate The load required per unit deflection of the spring5. Pitch the axial distance between adjacent coils in uncompressed state. (P)

Equilibrium under the action of two forces (W) and the Twisting moment (T)

D = Mean diameter of the spring coild = Diameter of the spring wiren = Number of active coilsG = Modulus of rigidity for the spring materialW = Axial load on the spring fs = Shear stress induced in the wire due to the twisting momentC = Spring index = D/dp = Pitch of the coilsδ = Deflection of the spring, as a result of an axial load.

Ot only shear stress induced in the wire, the following stresses also act on the wire :1. Direct shear stress due to the load W2. Stress due to curvature of wire.

The Analysis of Compression Springs

The Analysis of Compression Springs

The direct stress due to the load W = Load / Cross-sctional area of the wire

The maximum shear stress

Substituting D/d=C

- Direct Shear- Curvature of the

wire

A shear stress factor (K) / Wahl Stress factor

The effect

Dimana K yaitu :

The Analysis of Compression Springs

The values of K for a given index C

Wahl’s stress factor oncreases very rapidly as the spring index decreases. In machinery the mostly used spring index above 3.

The Analysis of Compression Springs

The standard size of the spring wire may be selected from the following table

The Type of End Connections for Helical Springs

Plain ends

Ground ends

Squared ends

Squared & Ground ends

The Characteristic of End Connections for Helical Springs

1. Inactive Coils The part of the coil which is in contact with the seat does not contribute to spring action.

2. Active Turns The part of the springs that action.

The Connections of Tensile for Helical Springs

- Large stress concentration is produced at this point.

- Attaching device of tension spring

The Connections of Tensile for Helical Springs

A Compression Spring Tensile Spring

Deflection of helical springs of circular wire

Axial deflection of spring

Spring Rate / Stiffness of the Spring

Constant

Energy stored in helical springs of circular wire

Asumtion load is applied gradually

V = Volume of the spring wire

If : P = loadh = height

Stress and deflection in helical springs of non-circular wire

Helical Torsion Springs

- The ends are shaped to transmiit torque.- Bending stress- The radius of curvature of the coils

changes when the twisting moment is applied

Bending Stress

Total Angle of Twist /

Angular Deflection

Deflection

Flat SpiralSprings

Long thin strip of elastic material wound like a spiral.- Watches - Gramaphone

Since the radius of curvature of every spiral decreases when the spring is wound up, therefore the material of the spring is in a state of pure bending.

Flat SpiralSprings

Bending Moment

B at max distance from the application of P Bending Moment Max

Maximum bending stress

Deflection (angular) Asumtion : both ends of the spring are clamped

Deflection

Strain energy

stored in the spring

4. Pegas Daun / Leaf Spring (laminated or carriage spring)

Application :For heavy vehicles, they have the advantage of spreading the load more widely over the vehicle's chassis, whereas coil springs transfer it to a single point.Thereby saving cost and weight in a simple live axle rear suspension.

4. Pegas Daun / Leaf Spring (laminated or carriage spring ) Flat spring

Deflection :

4. Pegas Daun / Leaf Spring (laminated or carriage spring )

Bending Stress Full length

graduated

Nipping Equalised Stress

Stress in full length = 50% Stress in graduated

Should be equal

The Steps :1. Making full length smaller thickness than the graduated leaves.2. Given greater radius of curvature to the full length than graduated.

4. Pegas Daun / Leaf Spring (laminated or carriage spring )

Nipping The Value of initial Gap (Nip C)

The Load on the clip bolt Wb

Final Stress = Stress in the full length due to applied load minus the initial stress

1. The final stress equal to graduated due to applied load plus initial stress.2. The deflection due to applied load is same as without initial stress

4. Pegas Daun / Leaf Spring (laminated or carriage spring )

The lenght of the leaf spring leaves

The effective

Band is used

U-Bolts is Used

The length of leaves

Smallest leaf

Next leaf

Length of (n-1)th leaf

4. Pegas Daun / Leaf Spring (laminated or carriage spring )

Length of master leaf d = diameter of eyet = thickness of master leaf

Standart sizes of automobile suspension springs

1. Standart nominal widths : 32, 40*, 45, 50*, 55, 60*, 65, 70, 80, 90*, 100 & 125mm.

2. Standart nominal thickness : 3,2; 4,5; 5; 6; 6,5; 7; 7,5; 8; 9; 10; 11; 12; 14; & 16mm

3. The recommended eye bore diametrs : 19, 20, 22, 23, 25, 27, 28, 30, 32, 35, 38, 50, & 55mm.

4. The diameter of centre bolts:

4. Pegas Daun / Leaf Spring (laminated or carriage spring )

5. Clip section and sizes of rivets & bolts

4. Pegas Daun / Leaf Spring (laminated or carriage spring )

Materials for leaf springs

1. Automobiles : 50Crl, 50Crl V23,55Si2 Mn90 (Hardened & Tempered)

2. Rail road C 55 (water – Hardened), C 75 (oil – Hardened), 40 Si2 Mn 90 (Water – Hardened), 55Si2 Mn90 (oil – Hardened)

3. All values are for oil quenched condition and for single heat only.

B. Bahan Pegas (Material) Depends on what they are used

1. Severe service2. Average service3. Light service

Severe service Rapid continous loading Ratio of minimum to maximum load is one half Automotive valve springs

Average service Intermittent operation loading Ratio of minimum to maximum load is one half Engine - Governor springs

Light service Very infrequently varied Load Safety valve springs

B. Bahan Pegas (Material)

B. Bahan Pegas (Material)

B. Bahan Pegas (Material)

B. Bahan Pegas (Material)

-The material treatment of helical springs both Cold Formed or Hot Formed.

-The material treatment depends on the size of the wire.

-Wires : < 10 mm Cold > 10 mm Hot

- The Srength size- Small size have greath strength & less ductility cold working

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Sumber

A semi-elliptical laminated vehicle spring to carry a load....kg is to consist of seven leaves .....cm wide, two of the leaves extending the full length of the spring. The spring is to be 110 cm in length and attached to the axle by two U-bolts .... Cm apart. These bolt hold the central portion of the spring so rigidly that they may be considered equivalent to a band having a width equal to the distance between bolts. The leaves are to be silico-manganese steel. Assuming an allowable stress of 3500 kg/cm2, determine :a. Thickness of the leavesb. Deflection of the springc. Diameter of the eyed. Length of the leaves e. Radius to which leaves should be initially bentAssume modulus of elasticity as 2,1x10^6 kg/cm2