Anodizing to perfection need the designer as well as the engineer to be efficient and effective in choosing the process that will give a good result. Efficiency means that you can carry out an obligation in such a manner that there is no underutilization or wastages.
It means handling the process with skill and perfection such that there are no lost in material and product while no stone is left unchanged. Engineers with those engaged in designing have to consider some factors that play crucial parts in the process and Endeavour to direct the work properly. Effective, in other words, is the act of creating the effect, using what is available to achieve one’s goals.
They need to select a treatment for surfaces due to the properties. Hence, they should have little knowledge of the plating process. Therefore, you have to forgive me if I should go through the process in step by step method since knowledge of it is necessary for your choice and the perfect result. Here are some of the facts you should know about this whole business.
Anodizing is another name for electroplating. It means using another metal to coat or design another. This involves the covering of the surface of either aluminum or titanium with the substance that is below its oxidized surface layer. You can’t use substances like sulfur or copper in this process. Aluminum is used because it is cheap and can do the work at hand, but titanium is better due to its power to reject having to strip off films formed after every process. Aluminum being more active than hydrogen chemically, should not be electroplated out of a solution of water or acidic hydrogen such as esters, ammonia, acids, primary amines, secondary amines as well as alcohols. Rather you can successfully do so from organic and inorganic salt solutions as well as compounds containing aluminum. Hence, anodizing is a critical topic that needs carefulness, expertise, and experience. But my advice is, in the majority of the cases, preferably titanium. Now we have known little of anodizing. We also need to find out what jigging or racking process has in common with anodizing, since we are considering it for use in anodizing.
So, what do you think jigging is?
Jigging is a method in which the parts to be anodized are held firmly while electrical contact is provided. By this, two important things have been achieved. The point of contact should not be anodized but left free since the anodized area is not electrically conductive but, an insulator in nature. This anodic process on aluminum that possesses electrical insulating characteristics, even while it’s being processed should be chosen carefully and followed with precaution.
We have to keep the contact points practically hidden and small yet to a limit. During the coating process, there is always occurrence of 13 volts drop across the coating and 3 volts from the outer layer of that coating to the cathode via the electrolyte especially if the acid medium is operating at 16 volts and if it is the sulphuric acid solution.
Electrical closeness between the work that is being done and the jig holding it is necessary. This should be made compulsory because the provision of the solid electrical relationship between the workpiece and the jig that anchor the main work would ensure continuity in jigging process on the aluminum. You can add some tooling holes so that while anodizing is on, the parts can still be held and the jig areas will be left out.
In all, avoid airlock as well as cavities which is a condition where there is no possibility of escape for evolved gases thereby hindering the thickness of the coat, poor coat formation, keeping chemicals in the cavities and poor dying. This condition analyzed is otherwise known as the effect of geometry of parts.
The material for jigging may be titanium or aluminum depending on the duration and type of anodic coating that is required. Titanium is preferable and more appropriate for the anodic coating of up to 12-15 micrometer thicknesses, but the probability of the material losing its electrical contact when it comes to thicker coatings is high except on the condition where heavy-pressure screw clamps are used. So, in cases where very thick coatings are required aluminum is to be used. Titanium acquires light anodic coating while racking process is going on, owing to the anodizing conditions on the ground and this causes a color change from yellow to purple.
You don’t need to strip off the thin coating after every anodizing activities; it breaks off on its own once the jigged job presses hard on it.
Care must be taken to ensure that the current has enough power to do its work. The capacity should be enough to supply current for the total work area on the well-loaded rack is sufficient when you are designing the racks.
The standard for choosing the cross sections for the wires and titanium rack stems must be based at a maximum current load of 0.2 amp per mm² while that of aluminum should be 1 amp per mm². This condition applies when aluminum and titanium are not immersed in an electrolyte but is in the air. If they are in an electrolyte, there will be rise by the factor of 5.
Aluminum is very cheap when you compare it to titanium which is very costly. The expensive nature of titanium makes it less preferable in comparison to cheaper aluminum and thereby restricts its use to only the production of adjustable racks which can make do with a short run of different sizes or on a long run working purpose.
But when you crosscheck the amount of money saved during the process and how consistent as well durable it can be, you will now notice that the high cost is negligible. It is also worthy of note that titanium being less conductive than aluminum demands that jig design with it should proceed with caution. All contact points and jig marks should be very large so that there won’t be contact burns.
Racking Methods for Anodic Coating
In jigging or racking, articles for anodizing should be suspended. The suspension of these articles for anodizing bath should be carried out in such a way that it will meet some conditions which include:
- First, you as a designer need to ensure that all the surfaces that are prone to anodic coating are in close contact with the solution.
- Secondly, there should be good and firm electrical contact between the conductor which connects to the source of current.
- Thirdly, the solution neither gets corroded nor contaminated by the jig or rack.
- Airlock conditions must be strictly avoided and entrapping of chemicals in the cavities also by making sure that an air space is made available to those components being designed.
- Avoid digging holes, making folds, or keeping difficult points to make the process easier.
- If it involves architectural industries use of aluminum racks may be advisable since there are screws through which current passes and due to it, covers the holes from anodizing.
- Choose the anodizing material that is not costly and consumable as well as does not require much stripping after use. Always use rectifier in the anodizing process such that only some parts and not all are anodized. See, titanium is very costly, but the cost price is normally offset by the length of time the work lasts and other things which we will consider in this process analysis.
- Constant rinsing at as many stages as possible is necessary for the anodizing process for a more effective and attractive finish.
- Titanium should be preferable to aluminum since it can withstand more heat than aluminum and it does not form films that need stripping off after every use.
- The contact points should not be burnt by overheating and loading as well as offloading should be made easy.
- Copper or sulfuric metals though they possess high conductivity should not be thought of because they will have a bad result.
- Finally, there should be freedom of circulation of the solution to ensure thorough work.
These same conditions are also required when you are brightening as well as polishing the baths. This is a practice that is rampant in rack brightening and anodic coating especially when it is void of intermediate re-racking. There are rules to follow also for the actualization of a good result.
Here are some of those standard rules. Please, you should follow them if you are dealing with these aspects stated below:
When you are dealing with alloys of aluminum, the general rule to be followed is, you should never process different alloys of aluminum at the same time and in the same bath since this will lead to differences in current densities, and variations are resulting to a final thickness of the film. Also, don’t put strange materials into the base metal. If you do it, you will contaminate the anodized coating.
It is wise to tender the part for coating for the mechanical finish before anodizing because this process does not cover scratch marks, pits or scares. When anodizing on aluminum, steel should be treated separately. Otherwise, the aluminum will be made out of place, and that material that was inserted will also be damaged completely.
Contact Area of the current flow is of vital consideration because if it is wide, there might be too much of heat and if it is too narrow, current will not pass.
Therefore, the contact area should be as little and as open enough to allow the flow of current with moderate heating on the metal surface since excess heat will give a poor result.
Large articles should be bolted to the jigs or be attached to the current source at various points.
In choosing a point of contact, you should choose that which is not easily corrosive and is at a hidden position. If it not, corrosion will take place and will damage the beauty of the work especially in such cases as in decorative work and when it concerns the dying process, Hence, the points of contacts to be chosen, since the anodic film is not present should not be conspicuous or prone to corrosion.
The rigidity of contact should be of paramount consideration if you need avoid swinging into contact with one another. Once the solution is agitated, the articles must be kept in sufficiently firm and electrically good contact condition such that there won’t be collusion with the others.
The method of arrangement of articles should be in such a way that there is sufficient gap between them. This is so because insufficient space between the articles may lead to overheating of the electrolyte as well as burning of the surface of the anodized item or a deposit whose quality is not reliable. All vital surfaces for anodizing must experience cathodes effect at the same distances of at most 15 cm, and this will bring about a deposit of reliable quality.
The recessed parts must be kept facing upward to stop the formation of air pockets or gas. The auxiliary cathode(s) will be hung inside or close to it at the right position and inner agitation made available so that there will be total and even formation of a film on the internal part of the recessed article with a narrow space. Conductors to this type of cathode(s) should be converted to insulators with porcelain beads or glass from any small circuit that has anodic workpiece.
Composite articles formed with aluminum as well as other metals except titanium anodize only if other metals are shut off from the operation. There is a wide range of stop-off lacquers that are resistant to pickling, anodic solutions as well as etching solutions that are obtainable in a commercial quantity for covering the area where anodizing is not needed.
The electrical conductivity of jigs and racks must be good since it is part of the circuit that carries anodizing current. Square, circular rod or wire like metals such as aluminum alloy 6063, which forms good spring contacts, titanium as well as pure aluminum might be welded or riveted. For the formation of racks or baskets, expanded aluminum is used while soft aluminum in its pure condition is for twisting circular articles. Where jigging is not suitable, the twisting technique is used as against the other types where it wastes time, material and space.
Aluminum, when in contact with Electricity becomes worse while the anodic coating process is going on as against electrodepositing especially when the contact is not sufficiently tight. And immediately the contact is broken, it can’t be made again. Jigs and clamps of aluminum make get an anodic film that should be erased from the point of contact before it can be used again. To achieve a better result in this process, you have to put the jig into a solution containing chromic or phosphoric acid or a much faster-in-action caustic soda solution which melts the jig more quickly provided the solution will not stick in the crevices.
To strip off the anodic film seal easily using caustic soda, dip the jigs for fifteen minutes into 20% nitric acid. For anodic film removal using mechanical techniques, use the fine file, steel scratch-brush or abrasive paper that is coarse. When you want to reduce the area to be stripped after completion of each cycle, coat and anodize the aluminum jigs with inert material on the areas that do not need such contacts. Then, skillfully strip off the exposed parts.
An alternative method in which stripping is not useful can be achieved by using PVC or chlorinated plastic to coat the aluminum jig portion or titanium points of contact. The jig will be ok till the rubber coating goes off. This will now require repairing the joints between the tips and the frame then coating the frame again.
Trichloroethylene as well as phosphoric acid solutions which has brightening effect and can react against plastics coatings that are, composite jigs, should not be used during the cycles.
For economic purposes, strength and durability, jigging and welding with titanium are preferable to mild steel.
Sometimes, the sheets that need an anodic coating on the two sides will require a single row of activity is loaded in the bath which leads to a less economical and low amperage load. For more frequent problems, the use of wider bath for anodizing to arrange another row of cathodes in the center takes place.
Presently, plastic made C-clamps that can tolerate much cleaning, anodizing, sealing, etching and coloring are frequently used though they are required in chemical activities like polishing solutions. The C-clamp since it is mechanical, an insulator to anodizing current and does not need stripping, will firmly hold the job against the titanium or aluminum bar.
This bar will still undergo stripping if it is of aluminum after every load contrary to racks with prongs having even spaces especially, C-clamp types which can be adjusted.
Riverts and articles that are similar to it are very closely packed in a punched aluminum, titanium or rubber basket with a tube with aluminum in its center. Many are against this due to the inappropriate coating on the places where the articles come in contact with others or zones where electrical contacts are minimal.
This, notwithstanding, a larger proportion of these particles, receive satisfactory treatment. Only in a commercial plant with a range of (0.2 to 6) %, and those with nest does reject occur while the ones that have no specific shape and are unable to provide contact opportunities like bayonet lamp fittings led to rejects below 0.5 %. A washer as well as flat surfaced items can undergo this process when mixed with irregularly shaped items. Maximum satisfaction is not granted.
If you want to prevent overheating, circulation of the electrolyte should be thoroughly done following these steps, especially when it concerns aluminum anodizing.
Polishing the material electrically which involves exposing the surface film to air such that it will not be a new thing to it when it is exposed to air as one travels or in the store. After that, treat it in alkaline solution in which the concentration of free alkali is known because that’s the only thing that will determine the success of the polishing process.
Note that, alkaline is not a major constituent of the solution but forms as a result of the reacting sodium with aluminum. Then, carry on with rinsing as many times as possible, then jigging and anodizing which involve what has been stated earlier in the preceding paragraphs, racking and rinsing again for neatness and a better result. The coloring is done for beauty sake using electropolishing method while sealing is to make the film highly resistant to corrosion and more insulating electrically.
Conclusion
My advice is that you should use titanium mostly since it can conduct electricity to the various points where they are needed and will not anodize, and you don’t need to strip often while in use unlike in the case of aluminum which does not last long due to constant stripping after use. Limit your work to aluminum and titanium only especially if it involves non-conducive materials or metals that can withstand acid and heat. Don’t look at how expensive titanium is since the quality of work done by it offset its cost. Then if you are anodizing, the decision as to which kind of rack to choose should depend on the work outlay, the cost of the metal to be used, the color of the finished product, the duration of the work, and the type and nature of the job.
You should also consider the experience of other engineers and designers who have to be on the job beforehand, the standard steps to be followed with the conditions stipulated. For example, aluminum racks are found to be preferable in situations where you need stripping like architectural extrusions in which the parts are attached to aluminum rack sheets with metal screws that are fixed inside holes onto the racks from where the conduction of current occurs.
The holes are not anodized because the screws covered them. Also worthy of note is the fact that additional surface area is very important in aluminum racking but not in titanium racking Some might also ask why they can’t use other metals that have high conductivity like sulfuric acid or copper in racking. The answer is that their racks will melt in the solution immediately the current for working passes through them. So, don’t aim at anything by using any metal you know, rather go for aluminum or titanium.
Now, the end of the matter is that you need quality in whatever you are doing and these guidelines if strictly followed will give you the quality of finish you desire, durability, beauty, satisfaction, experience and total service to humanity.