MIL-G-45204 Technical Information
With MIL-G-45204, there are several properties that are associated with the part finish:
- Type – Percentage of gold in the deposit
- Type I – 99.7% gold Type II – 99.0% gold Type III – 99.9% gold
- Hardness Grades – Deposited gold’s resistance to a localized deformation force
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Grade A (90 Knoop) Grade B (91-129 Knoop) Grade C (130-200 Knoop) Grade D (201+ Knoop)
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- Relationship between Type and Hardness:
Since more impurity results in higher hardness values, the following are acceptable combinations per MIL-G-45204:
a. Type I (99.7% gold) can be Hardness Grade A (90 Knoop), B (91-129 Knoop), or C (130-200 Knoop)
b. Type II (99% gold) can be Hardness Grade B (91-129 Knoop), C (130-200), or D (201+ Knoop)
c. Type III (99.9% gold) can ONLY be Hardness Grade A (90 Knoop)
- Gold Class – MINIMUM gold thickness required
NOTE: Any Gold Class is acceptable and must be specified by the customer.
Class 00 – 20 microinches
Class 0 – 30 microinches
Class 1 – 50 microinches
Class 2 – 100 microinches
Class 3 – 200 microinches
Class 4 – 300 microinches
Class 5 – 500 microinches
Class 6 – 1500 microinches
Example: How to interpret the blueprint note “Type I, Grade A, Class 3”
99.7% gold, 90 Knoop Hardness, 200 microinch thick gold deposit
Strikes and Underplating:
Silver or copper plus silver may not be used as an underplate. When gold is applied to a copper rich surface such as brass, copper, bronze, or beryllium copper, an anti-diffusion underplate such as nickel shall be applied.