Metal Finishing Guide Book

2013

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increased, producing an electropolish action activation at the surface, which can be helpful for all alloys, but is extremely critical on 7000 series. These alloys tend to set up corrosion cells very quickly before anodize is even initiated during the ramp cycle. This manual pulse early in the run is considered a secret technique and used by many top anodizers. Pulse – Step – Ramp (Slow PSR Preferred): Pulse-Ramp technology should be mandatory on all type II – III – 23 and 123 anodizing, in order to achieve maximum quality and efficiency along with additional energy savings. Pulse-Ramp should always be applied as Slow Pulse – Step – Ramp initiated during the ramp cycle. Slow pulse specifications have been proven acceptable for more than 30 years on all aluminum alloys with improved quality (hardness), efficiency (anodize time) and energy savings (KWH). An additional slower pulse system, which gives even greater time and energy savings, can be used on most aluminum alloys, after the specified slow – pulse – step – ramp and for the duration of the anodize run cycle. The current (amperage) is pulse ramped in the voltage mode, in 0.1–0.3 volt increments and in 2–15 second steps, which cannot be confused with the dwell periods. They may be referred to as small ramp steps and longer dwell periods or steps. Increased Dwell Times (3-7): Slow Pulse – Step – Ramp procedures must have dwell times or periods while running to constant current density. These dwell periods have been overlooked or thought not to be important due to the lack of a full understanding of the anodize pore structure development. They are, however, very important during the ramp cycle as related to final quality, efficiency and energy savings. The number and length of dwell periods for type II, 23 and type III anodize are as follows: Type II Clear Anodize: Dyed Black: Type 23 Hard Type II: Type III Hard Anodize: Type III Hard 3 – 10 mils: 2 – 4 Dwell Periods 3 – 5 Dwell Periods 3 – 5 Dwell Periods 4 – 10 Dwell Periods 4 – 10 Dwell Periods 30 sec – 3 min dwell 30 sec – 3 min dwell 30 sec – 3 min dwell 45 sec – 5 min dwell 1 – 10 – 20 min dwell The number of dwell periods along with their times of duration play an important role in Amperage Decay (ADO), which is the secret to actual coating formation. Amperage Decay / Drop Off (ADO): The Amperage Decay or (ADO) is one of the most important factors/requirements necessary for maximum quality, efficiency and energy savings. It must be used on all Slow Pulse – Step – Ramp – Dwell Periods and throughout the anodize run cycle. The secret is: amperage must be controlled in the voltage mode in order to develop amperage decay; do not use the CC control knob! Constant Current Density Ranging (CCDR): The current is Pulse – Step – Ramped by increasing voltage (voltage mode) until a calculated current (amperage) is reached, which represents a running constant current density dependent upon the square ft area in the tank and the required current density (ASF) for the alloy. For example – A tank load of 25 sq feet to be run at 40 ASF would be calculated and set for 1000 Amps (25 x 40 ASF) for the duration of the run. A steady constant current density should never be used in 226

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