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How to determine the
rough casting tolerance?
Sometimes, our clients will be wondered
how to determine the
rough casting tolerance.
According to our experience, the
standard of
BS6615:1996 and
SFSA 2000 can be used for solving
this issue.
Please
see the following standard BS6615:1996,
this standard is also as same as
ISO 8062:1994, which has been
taken as the standard for the rough
castings. In addition, please see the
following standard SFSA 2000, although
this standard is for
steel
castings, it is also suitable
for
iron castings. Actually, we also
have Chinese standard, which is as same
as the description in this SFSA 2000.
From these two standards, you can see
that
investment casting is 5-7
degree. The highest tolerance for sand
casting is 8-10 degree, which means
shell molding process can reach
CT8 degree. The machine molding and
automatic molding can reach CT9
degree. The
resin sand casting can reach CT9
to CT10 degree. The
manual green sand casting can
reach CT10 to CT12 degree.
However, this standard can not represent
all dimensions. Sometimes, as for some
mounting dimensions, the clients will
have special requirements. Then the
foundries should consider it, and can
try to meet the special tolerance by
grinding or machining.
The
deviation of rough casting dimensions
are related with the strength of molding
sand, compactness of sand mold, liquid
iron temperature, chemical components,
moisture of sand and workers' operation.
Any small factor may cause the deviation
of dimensions. Sometimes, too strict
requirements are not realistic. Some
level of deviation is inevitable
although we also try our best to control
the deviation as small as possible.
The
following is the
ISO 8062 1994 inches and SFSA
2000 standard. Please click here to see
the
ISO 8062 1994 millimeter
(mm).
Table 1. Casting dimensional
tolerances adapted from ISO 8062-1994,
(inches), also used for SFSA 2000 steel
casting tolerances.
| Raw Casting basic dimensions (inch) |
Total casting tolerance (inch) |
| Over |
Up to ＆including |
Casting tolerance grade CT |
| 1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
-
0.4
0.6 |
0.4
0.6
1 |
0.01
0.01
0.01 |
0.01
0.01
0.01 |
0.01
0.01
0.01 |
0.01
0.01
0.01 |
0.01
0.02
0.02 |
0.02
0.02
0.02 |
0.03
0.03
0.03 |
0.04
0.04
0.05 |
0.06
0.06
0.07 |
0.08
0.09
0.09 |
0.11
0.12
0.13 |
0.17
0.17
0.18 |
-
-
0.24 |
-
-
0.32 |
-
-
0.39 |
-
-
0.47 |
1
1.6
2.5 |
1.6
2.5
4 |
0.01
0.01
0.01 |
0.01
0.01
0.01 |
0.01
0.01
0.01 |
0.01
0.01
0.02 |
0.02
0.02
0.02 |
0.03
0.03
0.03 |
0.04
0.04
0.04 |
0.05
0.06
0.06 |
0.07
0.08
0.09 |
0.1
0.11
0.13 |
0.14
0.16
0.17 |
0.2
0.22
0.24 |
0.28
0.32
0.35 |
0.35
0.39
0.43 |
0.43
0.47
0.55 |
0.55
0.63
0.7 |
4
6
10 |
6
10
16 |
0.01
-
- |
0.01
0.01
- |
0.01
0.01
0.02 |
0.02
0.02
0.02 |
0.02
0.03
0.03 |
0.04
0.04
0.04 |
0.05
0.06
0.06 |
0.07
0.08
0.09 |
0.1
0.11
0.13 |
0.14
0.16
0.17 |
0.2
0.22
0.24 |
0.27
0.32
0.35 |
0.39
0.43
0.47 |
0.47
0.55
0.63 |
0.63
0.7
0.79 |
0.79
0.87
0.98 |
16
25
40 |
25
40
60 |
-
-
- |
-
-
- |
-
-
- |
0.03
-
- |
0.04
0.04
- |
0.05
0.06
0.06 |
0.07
0.08
0.09 |
0.1
0.11
0.13 |
0.14
0.16
0.18 |
0.2
0.24
0.28 |
0.28
0.32
0.35 |
0.39
0.43
0.57 |
0.55
0.63
0.7 |
0.7
0.79
0.91 |
0.87
0.98
1.14 |
1.1
1.26
1.46 |
60
100
160
250 |
100
160
250
400 |
-
-
-
- |
-
-
-
- |
-
-
-
- |
-
-
-
- |
-
-
-
- |
-
-
-
- |
0.1
-
-
- |
0.15
0.17
-
- |
0.21
0.24
0.28
- |
0.32
0.35
0.39
0.43 |
0.39
0.47
0.55
0.63 |
0.59
0.67
0.79
0.91 |
0.83
0.95
1.1
1.26 |
1.02
1.18
1.38
1.58 |
1.3
1.5
1.73
1.97 |
1.65
1.93
2.21
2.52 |
Table 2. SFSA 2000 for steel
casting tolerance long-production series
| Production Conditions |
Select Tolerance Grades |
| All sand molding process fully capable, most appropriate
for large castings |
CT 12 - 14 |
| Appropriate for most casting types and sand molding
processes |
CT 10 - 12 |
| With in process capabilities, but not appropriate for
all casting types and sand molding processes |
CT 8 - 10 |
| Investment Casting |
CT 5 - 7 |
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