Apr 7, 2011

Gravure Cylinder Basics

The Universe is Governed
by Natural Laws

Your plating process is governed by
Faraday’s Laws of Electrolysis

1. The amount of chemical change produced by an electric current is proportional to the quantity of electricity that passes.

2. The amounts of different substances liberated by a given quantity of electricity are
proportional to their chemical equivalent weights.

Faraday’s Laws can be expressed as a formula

g = I e t /96,500

Current in Amperes
Chemical Equivalent
Weight Time in Seconds
Faraday’s Constant (coulombs)
Weight in Grams
g = (I e t/96,500)?

How can this be important

The entire electroplating process is governed by these laws Any problem solving must keep Faraday’s Laws as reference This carries through to all plated results If the engraving  characteristics are other than predicted it can be explained through Faraday’s Laws. If the thickness is other than predicted it can be explained through Faraday’s Laws.

In order to co-deposit additive, the deposition of copper must be limited.This is done through:

1. regulating the current density
2. controlling the concentration of copper ions
3. controlling the acid concentration
4. controlling the concentration of additive Not enough copper?
Either something other than copper is depositing. § Hydrogen § Garbage Or you’re missing something in your calculation. What can you do if your cylinder plating goes BAD? Go Back to Basics! Sulfuric Acid concentration Copper Sulfate concentration Current Density Anode to Cathode Distance Temperature Additive Dosing Filters Cleaners Sulfuric Acid Sulfuric Acid provides the conductivity to the bath.

Controlling the current controls the plating deposition at the cathode.The amounts of anything  plated vary according to Faraday’s Laws of Electrolysis. Controlling the current controls the deposition of copper and additive. Copper Sulfate Copper Sulfate (CuSO4) is dissociated in the bath as Cu++ [SO4]=.The concentration of the Copper Sulfate is in fact the concentration of Copper ions available to the cathode. Copper will tend to plate preferentially. Too high a concentration and deposition of the additive is blocked. Too low a concentration and too much
additive can be co-deposited. Current Density Current Density is a measure of total current
and the area to which it’s applied. The current determines the rate of deposition. Low current density…. Slow deposition. High current density…. Fast deposition. Higher current enables the deposition of additive.Too high…. Too much additive.Too Low…. Not enough additive.Anode to Cathode Distance

Resistance of the bath varies with the square of the distance.

The distance is also critical to even deposition Too close can cause banding, too far and
the voltage requirement is too high. Temperature Temperature also has multiple affects.
Higher temperature decreases resistance in the bath. Temperature affects solubility, low
temperature can cause precipitation or crystallization of bath components. The additive is an organic compound that can be damaged by high temperature. Additive Dosing The  concentration of the additive in the bath will affect the amount of additive codeposited.
If the bath is over-dosed with additive it will cause problems with brittleness also
additive that remains in the bath will breakdown and lead to organic contamination.
Filters It’s important to remember that the function of the filters is to keep the bath clean.
Elevated current density forces the codeposition of things other than copper.
A dirty bath has lots of things in it that can get on the cylinder and be the cause of
problems. Cleaners Cleaners are used to clean. If the cleaner becomes dirty and tired then
instead of cleaning it dirties.

Attention to the Basics Is Attention to the Process

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