The second most important part of the plating process, after safety, is cleaning and part preparation. The importance of cleaning cannot be understated. How dirty or clean a part is will drastically affect the result of the newly electroplated layer. If time and care has been taken and an item has been polished to a mirror finish and is immaculately clean, then the deposited metal surface will reflect this. It will be smooth, lustrous and free from flaws. Alternatively, if little time and effort has been placed into the cleaning and preparation stage then plating will be dull, it will have blisters, it will peel and ultimately will need removing; causing a lot of wasted time and frustration. The best thing to do therefore, is to spend the time properly cleaning and preparing your item.
An item, no matter its condition will have something on the surface that should not be there. This is commonly known as soils. Soils cover a wide range of surface dirts and contamination from shop dust and lubricating oil, to finger prints and oxides. The types of soils on an item, as well as the base metal will dictate which cleaning methods need to be used. This guide will walk you through the steps involved in properly preparing a part and cleaning it ready for electroplating.
The usual steps involved in cleaning items ready for electroplating are:
Remove thick oil and grease with a degreaser
Remove oxides mechanically; sanding, buffing or polishing
Remove any polish or cleaning residue with a solvent
Remove solvent traces with detergent and hot water
Dip or electroclean in GP1 Alkaline Cleaner
Rinse in very clean water
Activate prior to plating
However, if there is old plating on an item, you will need to follow these steps and then remove the old electroplated layer. This is known as stripping and will be the first section covered.
When cleaning and preparing items, it is important to clean the surface to reveal the base metal, to strip any existing material. This may be old dull zinc plating, it may be multi-layered nickel plating, or it could be chrome plating that has started to bubble and peel.
If the old surface is covered with heavy soils, you may need to first clean these with the methods described in later sections and then return to stripping to reach the base metal later.
The most effective way to strip unwanted plating is using an acid solution. This can be used as either a soak cleaning, where items are simply immersed in the solution, or as an electrocleaner, where items are wired up similar to electroplating.
The strength, type, temperature and need for electrolysis will be determined by the type of old plating that needs removing. In the stripper guide, there is a table containing different metals and the ways in which they can be removed.
3. Alkaline Cleaning
Alkaline cleaning can be an extremely effective method to clean metals for electroplating. Our GP1 Alkaline cleaner is a specially formulated and balanced combination of basic salts in solution with applications in a variety of metal cleaning operations. Primarily it is used as a soak cleaner or electrocleaner prior to acid activation and electroplating. With this alkaline electrocleaning process, rust, oils, grease, and paint will be removed. GP1 is economical to use, giving a long and effective bath life.
We offer two versions of the alkaline cleaner; Light Duty and Heavy Duty. The light duty cleaner is less corrosive and is intended to be used for softer metals such as zinc, copper and their alloys. The heavy duty alkaline cleaner is formulated to be used on harder metals such as steel, nickel and its alloys. The way in which these cleaners can be used are the same.
To use GP1 as a soak cleaner, simply mix in a suitable container, the PP tub that came with the kit is ideal. The mixture should be at the rates in the table above depending on the type of metal you are cleaning. When mixed and at temperature, the parts should be immersed in the GP1 solution and left there for the required time.
In anodic electrocleaning, the item being cleaned is connected to the positive side of the DC power source; it is made the anode. It is then suspended in the cleaner and steel or lead anodes are hung round the side of the tank and attached to the negative side of the power source, becoming the cathodes. Whenever possible, use anodic electrocleaning as the final cleaning process before acid activation. For anodic cleaning using low voltages, between 3 – 12 volts DC, is normal. Current densities vary from 10–15 A per square foot, depending on the metal being cleaned and cleaning time allowed. Cleaning times of 30 seconds to 2 minutes generally suffice. While anodic alkaline electrocleaning is best for preparing many metals, it shouldn’t be used for cleaning aluminium, chromium, tin, lead, brass, magnesium or any other base metals that are soluble or are etched by alkaline electrocleaners. Cathodic cleaning is generally used to clean these metals and to clean buffed nickel prior to chromium plating. A diagram for an anodic cleaning setup is below.
In cathodic electrocleaning, the item being cleaned is connected to the negative side of the power source; it is made the cathode. It is then suspended in the cleaner and steel or lead anodes are hung round the side of the tank and attached to the positive side of the power source, becoming the cathodes. Cathodic cleaning solutions must be discarded and re-made more frequently than anodic ones. The same equipment, voltages and current densities specified for anodic cleaning are generally satisfactory for cathodic cleaning.A diagram for an cathodic cleaning setup is below.
Avoiding Hydrogen Embrittlement:
Any work negatively affected by hydrogen embrittlement (e.g. hardness exceeding 40 Rockwell C, such as spring steel) should not be cleaned cathodically unless adequate steps are taken after processing to relieve the hydrogen. Generally, heat treatment for one hour at 200°C immediately after processing will remove the hydrogen embrittlement.
Periodic Current Reversal Cleaning:
In periodic current reversal cleaning, the work is made alternately cathodic and anodic, using a current of 6–15v. PR cleaning in alkaline solutions containing sequestering or chelating agents removes smut, oxide and scale from ferrous metals. When PCR is the final electroclean, the parts should leave this station during the reverse-current part of the cycle. Work may be PCR cleaned on racks or in a barrel. One of the advantages of periodic-reverse cleaning to replace acid pickling is elimination of acid trapped by certain types of work such as hinges. In such applications acid from pickling can bleed out after alkaline electroplating (brass, copper, zinc, cadmium, tin). Oxides also may be removed without the danger of etching or the development of the smut usually associated with acid pickling.
Interrupted Current Cleaning:
The theory behind IRC cleaning is simple and logical. At the interface of the soil on the part and the cleaning solution, a reaction is occurring. This reaction depletes the concentration of the cleaning chemicals at the interface. By turning off the power momentarily, the reaction ceases and the cleaner concentration is restored. When the current comes back on, the solution concentration is what it should be at the interface. A typical cycle would be 8–9 seconds with current applied, followed by 1–2 seconds with power off.
4. Acid Activation
The final step before plating is an activation dip. An activation dip is required to prepare the surface of a metal for plating. The surface oxides and metals are stripped by an acidic solution leaving pure metal atoms at the surface. This is done using our dry acid pickle salts.
Dry acid salts are an off-white, carefully formulated blend of mineral acid salts that, when mixed with distilled water, produce a balanced acidic solution used as an acid cleaner and activator prior to electroplating for steel, zinc, copper, aluminium, and various other alloys. It can also be used for stripping chrome, activating stainless steel, activating nickel, removing rust and scale, and activating metals prior to chromate conversions.
Dry Acid Salts are economical to use, giving a long effective bath life with a reduction in maintenance periods. As the product is a powder, Dry Acid Salts are safe to use and store. The absence of fumes during operation improves working conditions and reduces equipment corrosion. They can be used at ambient or elevated temperatures by either soak or electrolytic application.
Dry Acid Salts are simply dissolved in water in the proportions indicated according to the application. While the product is readily soluble, up to 350 g/L at room temperature, for the initial make up warm water should be used since there Is a reduction in temperature on dissolution of the salts.
After the dip in an activation tank then rinse well in clean water and plate immediately after, doing so will prevent the build-up of oxides on the surface which can cause problems during plating.
Electroforming can seem daunting, especially when you see some of the amazing things people can create. Fear not, we have you covered! In this section of the website we will guide you through the entire process, from deciding what setup you need to setting up the kit and electroforming items.
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Another method that can be employed is a counterflow rinsing system and an reactive flow, shown in the image above. These will be more useful for larger systems where the amount of water used is conserved.
6. Testing Cleanliness
There are a few easy tests to check if a part is cleaned and ready for plating.
If you have a magnifying glass, use it to inspect the parts for any remaining traces of soils. Usually, if there are remaining oxides or dirt on an item a quick visual inspection will pick these up and more cleaning can be done.
Water Break Test:
This will detect if there is any grease or oil on the surface. Dip the part in clean water. If the water film is continuous and uninterrupted then the surface is clean. If the water beads, then this indicated the presence of soils.
White Cloth Test:
The white cloth test can also be used. This is simply the wiping of a clean white cloth along the surface of an item. If it comes away dirty, then more cleaning is needed.