Anodizing Amperage Calculator

What is Anodizing Amperage?

Anodizing is an electrochemical process used to increase the thickness of the natural oxide layer on aluminum surfaces. The anodizing amperage refers to the electrical current required to achieve the desired oxide coating thickness within a specified time. Getting the amperage right is crucial for producing consistent, high-quality anodized finishes.

The Anodizing Amperage Formula

The formula for calculating anodizing amperage is based on the "720 rule," which is an industry standard:

$$\text{Amperage} = \frac{720 \times \text{Surface Area}}{\text{Time}} \times \text{Thickness}$$

Where:

• Surface Area is the total surface area being anodized (in square feet)
• Time is the anodizing duration (in minutes)
• Thickness is the desired coating thickness (in mils)

The constant 720 represents the amp-minutes per square foot needed to produce 1 mil of anodic coating.

Metric Conversion

For metric units (square meters and microns):

$$\text{Amperage} = \frac{720 \times \text{Surface Area} \times 0.092903}{\text{Time}} \times \frac{\text{Thickness}}{25.4}$$

Calculation Example

Let's calculate the required amperage for a typical anodizing job:

Given:

• Surface Area = 10 sq ft
• Time = 20 minutes
• Thickness = 2 mils

Calculation:

$$\text{Amperage} = \frac{720 \times 10}{20} \times 2$$

$$\text{Amperage} = \frac{7200}{20} \times 2$$

$$\text{Amperage} = 360 \times 2$$

$$\text{Amperage} = 720 \text{ amps}$$

You would need 720 amps for this anodizing job.

Understanding the 720 Rule

The 720 rule is derived from Faraday's laws of electrolysis applied specifically to aluminum anodizing. Here's why it works:

1. Electrochemical basis: Aluminum oxide forms at a predictable rate based on current density
2. Industry standard: This constant has been validated through decades of practical application
3. Linear relationship: Doubling the surface area doubles the required amperage

Tips for Successful Anodizing

1. Temperature control: Maintain bath temperature between 68-72°F (20-22°C) for Type II anodizing
2. Current density: Aim for 12-24 ASF (amps per square foot) for standard anodizing
3. Ramp-up time: Gradually increase current at the start to prevent burning
4. Agitation: Keep the bath agitated for even coating distribution

Common Anodizing Types

Understanding the required amperage is essential for achieving consistent results across all anodizing types.