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Gear Materials
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The materials used for the manufacture of gears depends upon the
strength and service conditions like wear, noise etc. The gears may be
manufactured from metallic or non-metallic materials. The
metallic gears with cut teeth are commercially obtainable in cast iron, steel and bronze. The non-metallic
materials like wood, rawhide, compressed paper and synthetic resins like
nylon are used for gears, especially for reducing noise.
The cast iron is widely used for the manufacture of gears due to its good wearing properties, excellent machinability and
ease of producing complicated shapes by casting method. The cast iron gears with cut teeth may be employed, where smooth
action is not important.
The steel is used for high strength gears and steel may be plain carbon steel or alloy steel. The steel gears are usually
heat treated in order to combine properly the toughness and tooth hardness.
The phosphor bronze is widely used for worms gears in order to reduce wear of the worms
which will be excessive with cast
iron or steel.
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The following table shows the properties of commonly
used gear materials.
Materials |
Condition |
Brinell Hardness
Number |
Minimum Tensile
Strength (kglcm2) |
Malleable cast iron
a) White heart castings, Grade B
b) Black heart castings, Grade B
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--- |
217 max.
149 max. |
2800
3200 |
Cast Iron
a) Grade 20
b) Grade 25
c) Grade 35
d) Grade 35
Cast steel |
As cast
As cast
As cast
Heat treated
--- |
179 min.
197 min.
207 min.
300 min.
145 |
2,002
2,500
2,500
3,500
5,500 |
Carbon steel
a) 0.3% carbon b) 0.3% carbon
c) 0.4% carbon d) 0.4% carbon
e) 0.55% carbon f) 0.55% carbon |
Normalised Hardened and tempered
Normalised
Hardened and tempered
Normalised Hardened and tempered |
143 152
152 179
201 223 |
5,000 6,000
5,800 6,000
7,200 7,000
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Carbon chromium steel
a) 0.4% carbon
b) 0.55% carbon |
Hardened and tempered
Hardened and tempered
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229
225 |
8,000
9,000
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Carbon manganese steel
a) 0.27% carbon
b) 0.37% carbon |
Hardened and tempered
Hardened and tempered
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170
201 |
6,000
7,000
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Manganese molybdenum steel
a) 35 Mn 2 Mo 28
b) 35 Mn 2 Mo 45 |
Hardened and tempered
Hardened and tempered |
201
229 |
7,000
8,000
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Chromium molybdenum steel
a) 40 Cr 1 Mo 28 b) 40 Cr 1 Mo 60
Nickel steel
40 Ni 3
Nickel chromium steel
30 Ni 4 Cr 1
Nickel chromium
molybdenum steel
40 Ni 2 Cr 1 M0 28 |
Hardened and tempered Hardened and tempered
Hardened and tempered
Hardened and tempered
Hardened and tempered
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201 248
229
444
225
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7,000 9,000
8,000
15,400
9,000
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Surface hardened steel
a) 0.4% carbon steel
b) 0.55% carbon steel
c) 0.55% carbon chromium steel
d) 1% chromium steel
e) 3% nickel steel |
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145 (core) 460 (case)
200(core) 520(case)
250 (core) 500(case)
500 (case)
200 (core) 300 (case)
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5,512
7,086
8,661
7,086
7,086
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Case hardened steel
a) 0.12 to 0.22% carbon
b) 3% nickel steel
c) 5% nickel steel
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650 (case)
200 (core) 600 (case)
250 (core) 600 (case)
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5,039
7,086
8,661
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Phosphor bronze castings
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Sand cast
Chill cast
Centrifugal cast
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60 min.
70 min.
90
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1,600
2,400
2,600
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