Section
5 Forgings for gearing
5.1 Scope
5.1.1 Provision
is made in this Section for carbon-manganese and alloy steel forgings
intended for use in the construction of gearing for main propulsion
and for driving electric generators.
5.1.2 Gear wheel
and rim forgings with a specified minimum tensile strength not exceeding
760 N/mm2 (760–910 N/mm2 acceptance range)
may be made in carbon-manganese steel. Gear wheel or rim forgings
where the specified minimum tensile strength is in excess of 760 N/mm2, and all pinion or pinion sleeve forgings, are to be made
in a suitable alloy steel. Specifications for alloy steel components
and for quill shafts, giving chemical composition, heat treatment
and mechanical properties, are to be submitted for approval.
5.1.4 Manufacturers'
test certificates for forgings may be accepted where the transmitted
power does not exceed 220 kW (300 shp) for main propulsion and 100
kW (150 shp) for auxiliary drives.
5.2 Manufacture
5.2.1 All forgings
are to be made with sufficient material to allow an adequate machining
allowance on all surfaces for the removal of unsound or decarburised
material.
5.2.2 The hardenabilty
of the forged material is to be checked at random intervals using
an end quench test complying with a National or International Standard.
5.2.3 The grain
size is to be checked on a random basis in accordance with the testing
and reporting procedures of ASTM E 112, or an equivalent National
Standard, and is to be within the range 5 to 8.
5.2.4 The microstructure
of the hardened case is to be mainly martensite, with a maximum content
of 15 per cent of retained austenite.
5.3 Chemical composition
5.4 Heat treatment
5.4.2 The delivery condition shall meet the design and application requirements. It is the
manufacturers responsibility to select the appropriate heat treatment method to obtain
the required mechanical properties. Where forgings for gearing are not intended for
surface hardening, lower tempering temperatures may be allowed.
5.4.3 Where forgings
are machined prior to heat treatment, the allowance left for final
machining is to be sufficient to remove the decarburised surface material,
taking into account any bending or distortion which may occur.
5.4.4 When the
teeth of a pinion or gear wheel are to be surface hardened, i.e. carburised,
nitrided or induction hardened, the proposed specification together
with details of the process and practice are to be submitted for approval.
For purposes of initial approval, the gear manufacturer is required
to demonstrate by test that the surface hardening of the teeth is
uniform and of the required depth and that it does not impair the
soundness and quality of the steel.
5.4.5 Where induction
hardening of nitriding is to be carried out after machining of the
gear teeth, the forgings are to be heat treated at an appropriate
stage to a condition suitable for this subsequent surface hardening.
5.4.6 Forgings
for gears which are to be carburised after final machining are to
be supplied in either the fully annealed or the normalised and tempered
condition, suitable for subsequent machining and carburising.
5.5 Mechanical tests for through hardened, induction hardened or
nitrided forgings
5.5.1 At least
one tensile test specimen is to be taken from each forging in carbon
or carbon-manganese steel, and at least one tensile specimen from
forgings in alloy steel. Sufficient test material is to be provided
for this purpose and the test specimens are to be taken as follows:
-
For pinion forgings
where the finished diameter of the toothed portion exceeds 200 mm,
tests are to be taken in a tangential direction and adjacent to the
toothed portion (test position B in Figure 5.5.1 Test positions for forgings for
gearing). Where the dimensions preclude the preparation of tests
from this position, tests in a tangential direction are to be taken
from the end of the journal (test position C in Figure 5.5.1 Test positions for forgings for
gearing). If, however, the journal
diameter is 200 mm or less, tests are to be taken in a longitudinal
direction (test position A in Figure 5.5.1 Test positions for forgings for
gearing).
Where the finished length of the toothed portion exceeds 1250 mm,
tests are to be taken from each end.
-
For small pinion forgings
where the finished diameter of the toothed portion is 200 mm or less,
tests are to be taken in a longitudinal direction (test position A
in Figure 5.5.1 Test positions for forgings for
gearing).
-
For gear wheel forgings, tests are to be taken from each forging in a
tangential direction (from one of the test positions A or B in Figure 5.5.2 Test position A or B).
-
For gear wheel rim forgings, tests are to be taken in a tangential
direction (from one of the test positions A in Figure 5.5.3 Test position A). Where the finished diameter exceeds
2500 mm or the mass (as heat treated but including test material) exceeds 3
tonnes, tests are to be taken from two diametrically opposite positions (test
positions A in Figure 5.5.3 Test position A).
-
For pinion sleeve forgings,
tests are to be taken in a tangential direction (from one of the test
positions C in Figure 5.5.4 Test position C). Where
the finished length exceeds 1250 mm, tests are to be taken from each
end.
-
For forged rings, the directions and positions of the set of tests to
be taken from each ring are to comply with the requirements of Ch 5, 3.4 Mechanical tests 3.4.4.
Figure 5.5.1 Test positions for forgings for
gearing
Figure 5.5.2 Test position A or B
Figure 5.5.3 Test position A
Figure 5.5.4 Test position C
5.5.3 Table 5.5.1 Mechanical properties for
acceptance purposes: carbon-manganese steels for gear wheel and rim forgings to Table 5.5.3 Mechanical properties for
acceptance purposes: alloy steel gear forgings - Quenched and temperedgive the minimum requirements for yield
stress and elongation corresponding to different strength levels, but it is not intended
that these should necessarily be regarded as specific grades. The strength levels have
been given in multiples of 40 N/mm2, or 50 N/mm2 in the case of
alloy steels, to facilitate interpolation for intermediate values of specified minimum
tensile strength.
Table 5.5.1 Mechanical properties for
acceptance purposes: carbon-manganese steels for gear wheel and rim forgings
Tensile strength
N/mm2
(see Note)
|
Yield stress N/mm2 minimum
|
Elongation on 5,65
% minimum
|
Hardness Brinell
|
Rims
|
Wheels
|
400 -
520
|
200
|
26
|
22
|
110 -
150
|
440 -
560
|
220
|
24
|
21
|
125 -
160
|
480 -
600
|
240
|
22
|
19
|
135 -
175
|
520 -
640
|
260
|
21
|
18
|
150 -
185
|
560 -
680
|
280
|
20
|
17
|
160 -
200
|
600 -
750
|
300
|
18
|
15
|
175 -
215
|
640 -
790
|
320
|
17
|
14
|
185 -
230
|
680 -
830
|
340
|
16
|
14
|
200 -
240
|
720 -
870
|
360
|
15
|
13
|
210 -
250
|
760 - 910
|
380
|
14
|
12
|
225 - 265
|
Intermediate values may be obtained by interpolation.
|
Note When the specified minimum tensile strength exceeds
700 N/mm2 forgings are to be supplied only in the
quenched and tempered condition.
|
5.5.6 Where more
than one tensile test is taken from a forging, the variation in tensile
strength is not to exceed the following:
|
Specified minimum tensile
strength N/mm2
|
Difference in tensile
strength N/mm2
|
|
<600
|
70
|
|
≥600 <900
|
100
|
|
≥900
|
120
|
5.5.7 Hardness
tests are to be carried out on all forgings after completion of heat
treatment and prior to machining the gear teeth. The hardness is to
be determined at four positions equally spaced around the circumference
of the surface where teeth will subsequently be cut. Where the finished
diameter of the toothed portion exceeds 2500 mm, the number of test
positions is to be increased to eight. Where the width of a gear wheel
rim forging exceeds 1250 mm, the hardness is to be determined at eight
positions at each end of the forging.
Table 5.5.2 Mechanical properties for
acceptance purposes: alloy steel gear wheel and rim forgings - Normalised and
tempered
Tensile strength
N/mm2
|
Yield stress
N/mm2 minimum
|
Elongation on 5,65 % minimum
|
Hardness Brinell
|
Rims
|
Wheels
|
600 –
750
|
330
|
18
|
16
|
175 –
215
|
650 –
800
|
355
|
17
|
15
|
190 –
235
|
700 –
850
|
380
|
16
|
14
|
205 –
245
|
750 –
900
|
405
|
15
|
13
|
215 –
260
|
800 –
950
|
430
|
14
|
12
|
235 –
275
|
850 – 1000
|
455
|
13
|
11
|
245 –
290
|
Intermediate values may be obtained by interpolation.
|
Table 5.5.3 Mechanical properties for
acceptance purposes: alloy steel gear forgings - Quenched and tempered
Tensile strength
N/mm2
(see Notes 1 and 2)
|
Yield stress
N/mm2 minimum (see Note 2)
|
Elongation on 5,65 % minimum
|
Hardness Brinell
|
A
|
B
|
C
|
600 –
750
|
420
|
18
|
16
|
14
|
175 –
215
|
650 –
800
|
450
|
17
|
15
|
13
|
190 –
235
|
700 –
850
|
480
|
16
|
14
|
12
|
205 –
245
|
750 –
900
|
530
|
15
|
13
|
11
|
215 –
260
|
800 –
950
|
590
|
14
|
12
|
10
|
235 –
275
|
850 –
1000
|
640
|
13
|
11
|
9
|
245 –
290
|
900 –
1050
|
690
|
13
|
11
|
9
|
260 –
310
|
950 –
1100
|
750
|
12
|
10
|
8
|
275 –
330
|
1000 –
1150
|
810
|
12
|
10
|
8
|
290 –
340
|
1050 – 1200
|
870
|
11
|
9
|
7
|
310 –
365
|
|
= |
Column A is applicable to tests from gear rims and
to longitudinal tests from pinions.
|
|
= |
Column B is applicable to tests from gear wheels
and to tangential tests from pinions.
|
|
= |
Column C is applicable to tests from pinion
sleeves.
|
|
Intermediate values may be obtained by
interpolation
|
Note
1. For gear wheel and rim forgings the
specified minimum tensile strength is not to exceed 850
N/mm2.
Note
2. For carburised gear forgings the
requirements for minimum yield stress and maximum tensile strength are
not applicable.
|
5.5.8 For small
gear forgings which are batch tested, at least one hardness test is
to be carried out on each forging.
5.5.10 On nitrided
or induction hardened components, hardness tests are also to be made
on the teeth when surface hardening and grinding have been completed.
The results are to comply with the approved specification.
5.6 Mechanical tests for carburised forgings
5.6.1 Sufficient
test material is to be provided for preliminary tests at the forge
and for final tests after completion of carburising. For this purpose,
duplicate sets of test material are to be taken from positions as
detailed in Ch 5, 5.5 Mechanical tests for through hardened, induction hardened or nitrided forgings 5.5.1, except that,
irrespective of the dimensions or mass of the forging, tests are required
from one position only, and in the case of forgings with integral
journals are to be cut in a longitudinal direction. The test material
which is to be used for measurements of case depth, hardness, grain
size and residual austenite as well as mechanical properties is to
be machined to a coupon of diameter of or 30 mm, whichever is less, where D is the
finished diameter of the toothed portion.
5.6.2 For small
forgings, where a system of batch testing is adopted, the test material
may be prepared from surplus steel from the same cast provided that
the forging reduction approximates to that of the actual gear forgings.
The test samples are to be correctly identified and heat treated with
the forgings they represent.
5.6.3 For preliminary
tests at the forge, one set of test material is to be given a blank
carburising and heat treatment cycle simulating that which will be
subsequently applied to the forgings.
5.6.4 For final
acceptance tests, the second set of test material is to be blank carburised
and heat treated together with the forgings which it represents.
5.6.5 At the discretion
of the forgemaster or gear manufacturer, test samples of larger cross-section
than in Ch 5, 5.6 Mechanical tests for carburised forgings 5.6.1 may be either carburised
or blank carburised, but these are to be machined to the required
diameter prior to the final quenching and stress relieving heat treatment.
5.6.6 At least
one tensile specimen is to be prepared from each sample of test material.
5.7 Non-Destructive Examination
5.7.1 Magnetic
particle or liquid penetrant testing is to be carried out on the teeth
of all surface hardened forgings. This examination may also be requested
on the finished machined teeth of through hardened gear forgings.
5.7.2 The manufacturer
is to carry out an ultrasonic examination of all forgings where the
finished diameter of the surfaces, where teeth will be cut, is in
excess of 200 mm, and is to provide the Surveyor with a signed statement
that such inspection has not revealed any significant internal defects.
5.7.3 On gear forgings
where the teeth have been surface hardened, additional test pieces
may be required to be processed with the forgings and subsequently
sectioned to determine the depth of the hardened zone. These tests
are to be carried out at the discretion of the Surveyor, and for induction
or carburised gearing the depth of the hardened zone is to be in accordance
with the approved specification. For nitrided gearing, the full depth
of the hardened zone, (i.e. depth to core hardness), is to be not
less than 0,5 mm and the hardness at a depth of 0,25 mm is to be not
less than 500 HV.
|