Section
4 Castings for crankshafts
4.1 Scope
4.1.1 This Section
gives the requirements for carbon and carbon-manganese steel castings
for semi-built crankshafts.
4.1.2 Where it
is proposed to use steels of higher carbon content than is indicated
in Ch 4, 4.3 Chemical composition 4.3.1, or alloy steels, particulars
of the chemical composition, mechanical properties and heat treatment
are to be submitted for approval. For alloy steels, the specified
minimum tensile strength is not to exceed 700 N/mm2.
4.2 Manufacture
4.2.1 The method
of producing combined web and pin castings is to be approved. For
this purpose, tests to demonstrate the soundness of the casting and
the properties at important locations may be required.
4.3 Chemical composition
4.3.1 The chemical composition of ladle samples is to comply with the following
limits provided in Table 4.4.1 Chemical composition limits for
steel castings for crankshafts (%): C, C-Mn steels
Table 4.4.1 Chemical composition limits for
steel castings for crankshafts (%): C, C-Mn steels
Steel type
|
C (max.)
|
Si (max.)
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Mn
|
S (max.)
|
P (max.)
|
Residual elements (max.)
|
Total residuals (max.)
|
Cu
|
Cr
|
Ni
|
Mo
|
C,
C-Mn
|
0,40
see Note
|
0,60
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0,50-1,60
|
0,035
|
0,035
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0,30
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0,30
|
0,40
|
0,15
|
0,80
|
Note. See
Ch 4, 4.7 Rectification of defective castings 4.7.4.(d).
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4.4 Heat treatment
4.4.1 Castings
are to be supplied either:
-
fully annealed and
cooled in the furnace to a temperature of 300°C or lower; or
-
normalised and tempered
at a temperature of not less than 550°C, and cooled in the furnace
to a temperature of 300°C or lower.
4.5 Mechanical tests
4.5.1 Proposals
for the number of tests and the location of test material on the casting
are to be submitted by the manufacturer.
4.5.2 Not less
than one tensile test and three impact tests are to be made on material
representing each casting. The impact tests are to be carried out
at ambient temperature.
4.5.5 The results of all tests are to comply with the requirements of Table 4.4.2 Mechanical properties for
acceptance purposes: carbon - manganese steel castings for crankshafts appropriate to the
specified minimum tensile strength. For the impact tests, one individual value may be
less than the required average value provided that it is not less than 70 per cent of
this average value. See
Ch 1, 4.6 Re-test procedures for re-test procedures.
Table 4.4.2 Mechanical properties for
acceptance purposes: carbon - manganese steel castings for crankshafts
Tensile
strength N/mm2
|
Yield stress
N/mm2
minimum
|
Elongation on % minimum
|
Reduction of area
% minimum
|
Charpy V-notch
impact tests average energy J minimum
(see Note)
|
400 –
550
|
200
|
28
|
45
|
32
|
440 –
590
|
220
|
26
|
45
|
28
|
480 –
630
|
240
|
24
|
40
|
25
|
520 –
670
|
260
|
22
|
40
|
20
|
550 –
700
|
275
|
20
|
35
|
18
|
Note Impact tests are to be made at ambient temperature (i.e.
23°C±5°C), which is specified in ISO 148-1.
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4.6 Non-destructive examination
4.6.2 Each casting
is to be examined by ultrasonic testing, and the extent of examination
and defect acceptance criteria, using the DGS (Distance Gain Size)
technique, are to be as shown in Figure 4.4.2 Ultrasonic examination acceptance levels. Alternative ultrasonic procedures may be submitted for
approval.
4.7 Rectification of defective castings
4.7.2 Where castings
have shallow surface defects, consideration is first to be given to
removing such defects by grinding and blending or by machining the
surface where there is excess metal on the Rule dimension.
4.7.3 Subject to
prior agreement and submission of the detailed welding procedure for
approval by LR, welding may be carried out prior to the final austenitising
heat treatment.
4.7.4 Approval
for welding will not be given in the following circumstances:
-
For the rectification
of repetitive defects caused by improper foundry technique or practice.
-
For the building up
by welding of surfaces or large shallow depressions.
-
Where the carbon content
of the steel exceeds 0,30 per cent.
-
Where the carbon equivalent
of the steel, given by
4.7.5 Provided
that the Surveyors are satisfied that welding is justified, they may
also authorise welding to the surfaces of crankwebs, following the
final austenitising heat treatment, within the following limits:
-
In general, the volume
of the largest groove which is to be welded is not to exceed 3,2t cm3, where t is the web axial thickness, in cm. The
total volume of all grooves which are to be welded is not to exceed
9,6t cm3 per crankweb.
-
The welds do not extend within the cross-hatched zones marked on Figure 4.4.3 Areas of semi-built crankthrows to
which weld repairs are not permitted for semi-built crankthrows.
-
Larger welds on balance
weights may be permitted at the discretion of the Surveyor, provided
that such repairs are wholly contained within the balance weight and
do not affect the strength of the crankweb.
4.7.6 Subsequent
to the final austenitising heat treatment, welding may be authorised
in the surface of the bore for the journal (or pin) within the following
limits:
-
In general, the welds
are to be not less than 125 mm apart.
-
The welds are not to
be located within circumferential bands of from the edges of the bores, nor at any position within
the inner 120° arc of the bores, as cross-hatched on Figure 4.4.3 Areas of semi-built crankthrows to
which weld repairs are not permitted.
-
The volume of the largest
weld is to be not more than 1,1t cm3,
where t is the web axial thickness at the bore, in cm,
and not more than three welds are to be made in any one bore surface.
Figure 4.4.2 Ultrasonic examination acceptance levels
Figure 4.4.3 Areas of semi-built crankthrows to
which weld repairs are not permitted
4.7.7 After all
defective material has been removed from a region, and this has been
proven in the presence of the Surveyor by magnetic particle inspection
or other suitable method, the excavation is to be suitably shaped
to allow good access for welding.
4.7.9 Welding is
to be carried out by approved welders using approved procedures. The
welds are to be made by an electric arc process using low hydrogen
type consumables which will produce a deposited metal that is not
inferior in properties to the parent metal.
4.7.10 All castings
are to be given a preliminary refining heat treatment prior to the
commencement of welding. Before welding, the material is to be preheated
in accordance with the qualified procedure. Where possible, preheating
is to be carried out in a furnace. The preheat temperature is to be
maintained until welding is completed, and preferably until the casting
is placed in the furnace for post-weld heat treatment.
4.7.11 Where welding
is carried out after the final austenitising heat treatments, a post-weld
stress relieving heat treatment is to be applied at a temperature
of not less than 600°C, see also
Ch 4, 1.5 Heat treatment 1.5.2.
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