MIL-DTL-45204

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With MIL-DTL-45204, there are several properties that are associated with the part finish:

  1. Type – Percentage of gold in the deposit
    1. Type I – 99.7% gold Type II – 99.0% gold        Type III – 99.9% gold
  2. Hardness Grades – Deposited gold’s resistance to a localized deformation force
    1. Grade A (90 Knoop) Grade B (91-129 Knoop)
      Grade C (130-200 Knoop) Grade D (201+ Knoop)
  1. Relationship between Type and Hardness:

Since more impurity results in higher hardness values, the following are acceptable combinations per MIL-DTL-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)

  1. 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.