What Questions Will My Anodiser Have For Me?

Anodising, while in principle a straight forward process, is full of pitfalls that can effect the final outcome.  It is therefore important for your anodiser to find out as much about your anodising job as they can.  This will ensure the best anodised finish is achieved  and it will also highlight any potential issues which may affect the final finish.  When you call your anodiser they will have some standard questions that they will ask you;

1.  How big are the items to be anodised?

Each anodiser will operate anodising tanks of a certain size and dimension.  If the items are too large to fit in the anodising tank this will limit the ability of the anodiser to do the job.  While it is certainly possible to double anodise items that are larger than the tank, it is not recommended and wont do it, particularly if a decorative look is desired.  Please see our services page for our tank sizes.  Effectively the maximum length we can handle in our anodising bath is 2.8 meters.  For our exact tank sizes click here.

We will also ask you if there are any areas on your items that are dimensionally sensitive i.e. bearing housing.  Anodising will change the dimensions of your items to some degree.  The total dimensional change will depend on 2 factors; the first is the amount, if any, of caustic etching and second the total thickness of the anodized coating.  For standard anodising you could typically expect a dimensional change of about 1/3 the total coating thickness e.g. Typically if you are after a 21 micron anodised coating the dimensions of the item will change by approximately 7 microns.  In the vast majority of anodising work done this is not an issue.  With regards to hard anodising this dimensional change is about 1/2 the coating thickness e.g. For a 50 micron coating you can expect a dimensional change of about 25 microns.

The size and number of items to be anodised will impact on the final cost of the anodising job.

2.  What alloy or alloys are the items made from?

This is very important in determining the final outcome of the anodising.  If you are able to tell us what the parts are made from then it is fairly easy to predict the outcome of the anodising.  Bought or second hand parts can be more of an issue, as these are typically an unkown alloy.  If these parts are already anodised and are needing a change of colour or a new anodised coating then at least we know that those parts should achieve an anodised finish at least as good as the original.

If different alloys are supplied, this may impact on the final cost of the anodising job, as not all Aluminium alloys are compatible in the anodising processing tank.  For example, we could not anodise 2011 Aluminium alloy at the same time as 6063 alloy as these are not compatible.  In the event several different alloys are supplied these may require seperate anodising runs.

For more information read our article - 'Choose the right Aluminium alloy for anodising'   or otherwise contact us direct to discuss your requirements.

In addition to knowing the alloy type it is important to note what the temper of the alloy is.  While in most cases the temper has little or no effect on the anodising in some instances it can impact on the finish, particularly when a chemical etch is required for a matt finish.

It is also important to know if there are any items that have metal attachments or inserts made from Steel, Copper or other non-Aluminium metal, as this will have a major impact on the anodizing process.  The presence of these other metals will effect the electric current profile in the anodising bath affecting the growth of the anodising.  In addition the anodising process will either damage or destroy the non-Aluminium part.

3. What anodised finish are you after?

Gloss or matt, coloured or plain.  This is in part determined by the alloy as some will have a tendency toward a more matt finish.

4.  What anodised coating thickness do you require?

Anodised coatings is measured in microns (Mil in the US, 1 mil = 0.001 inch).  The overall thickness you require will be determined by the required functionality of the anodising.

• Couple of microns for bright car trim
• 10 microns for decorative low wear indoor use
• 12 micron (0.5 mil) used for window frames etc
• 20 micron used for both high wear and corrosion resistance ie. window frames in coastal regions
• 25 micron (1 mil)  - Marine coat for marine applications i.e window frames within a few hundred meters of the sea or those in geothermal areas
• 50+ microns  (2 mil) - Hard coat

This is a guide only and for most decorative applications 12-20 microns is more than adequate.

5.  Are there any welds on the items?

This can have a major impact on the final look of the anodising job.  There are two basic types of welding rod available for Aluminium welding, 4000 series (e.g. 4043) and 5000 series (e.g. 5356).  A lot of welders prefer to use the likes of 4043 welding rod because it has good welding performance, i.e. flows better than 5356, due to it containing silicon.  This silicon, while improving ease of welding, does not aid anodising.  Any weld made from 4000 series welding rod will anodise either black or dark grey, which will adversely affect decorative anodising.  5000 series welds anodise well and match much better colour wise to the rest of the item being anodised.

Below is an example of a part anodised with a 4000 series welding rod

It is important to point out that due to the high temperatures the Aluminium metal is subjected to around the weld area, that there may have been some structural changes to the grain of the Alumimium.  The effect of this can lead to different shades when dyeing.

If you are doing decorative anodising and you need to weld the item, this anodiser recommends using 5356 series welding rod.  Please note that it also recommended that any welding is done prior to getting the items anodised due to the high electrical resistance of the anodised coating.  For more information on welding and anodizing, please read our anodising guide & tips page.

A quick comment on spot welding - While we haven't yet anodised anything that has been spot welded, the impact will be similar to those items that have been rivited or have a press fit.  Having an overlapping joint can cause issues with the quality of decorative anodising.  Normally this is due to the inablity to clean properly in between  the surfaces or trapped processing chemicals.  Either way the effect is the same, with dye uptake failure around the edge of the joint.

6.  Is there any corrosion present?

Corrosion can be a serious issue, particularly pitting corrosion.  Areas that are adversely affected by corrosion wont necessarily anodise well and the resulting anodised coating may not offer great corrosion resistance.  Prior to any anodising the corrosion must be removed and this can add extra time and cost ot the anodising job.

Below is an example of extreme pitting corrosion.  The parts were originally anodised but had been used in a salt water environment for some years.  Initial visual inspection showed that surface was intact but that there was corrosion present that showed as a powdery bloom and surface discolouration.  Stripping the anodising revealed that corrosion was much more severe than initial appearances.  The parts were given a light bead blast to remove the corrosion and highlight the full extent of the problem.  These parts were sent to Scorpro Engineering to have the worst of the corrosion filled in prior to anodising.

In most cases the corrosion issues are superficial and are not a major issue for anodising, but if you have any questions please do not hesitate to contact us.

7.  Where on the item can we rack it?

All items that are anodised need to be suspended on a 'rack' in the electrolyte solution (Sulphuric Acid) for the anodising process.  Where the item being anodised is in contact with the 'rack' there will be no anodising.  In most cases it will be obvious where to rack and the racking mark can be reduced to the point where you are unable to find.  Regardless of this we will need to know what is acceptable and unacceptable for your product in the way of 'rack' marks.

8.  What is the purpose of the anodising?

Is it purely for protective or decorative purposes.  Once this is known we will ask where the item is being used? and if you are after colour how much sun exposure it will have.  Following on from this we will ask how thick you require the anodised coating - We measure the thickness in microns and different application require different thicknesses.  For example classic car trim of only a few microns, marine applications with a minimum of 25 microns and those very high wear application hard anodising to 50+ microns.

9. Do you require the anodising to coloured?

This is a fairly straight forward question to answer but it is important for us know in the context that your range of options may be limited by your Aluminium.  Most alloys will colour quite well but some are only suitable for dark colours.  In addition to the effect of the Aluminium is the environment to which the item will be exposed.  If the item is going to be exposed to high UV sunlight for an extended period of time, then this will limit your colour choices as some dyes will fade with high UV exposure.

If you are after a colour that is not listed on our services page, please ask anyway, as we may be able to source it for you.  Unfortunately, white is the one colour that is not at all available.

10.  When is the latest the job needs to be completed by?

We will work with you to ensure you get the best possible turn around time for your product.  Please note that while we will make every effort to ensure you get the turn around you require, it will not always be possible due the work load we have at the time.

11. The all important question - Cost of the anodising?

While this is not a question we will be asking you, it is certainly one we get asked all the time.  Before we can give a price we first require as much information as is possible, hence our list of questions.  It is our standard procedure to only give estimates of the work prior to receiving it, to cover us against the unknown.  It is not uncommon to receive an anodising job to find that all is not as was represented in the initial discussion.  This is typically due to the alloys being unknown or the pre-anodised surface not being suitable for the required final finish.  Prep work that is required can be hard to price exactly with at least first seeing the items.

We do however give quotes when drawings of parts have been provided and the alloy is known, along with all the other particulars.  Quotes are most often issued for work CNC or engineering workshops.

Please note that regardless of whether we give an estimate or a quote, the price always excludes GST and freight.

This is only a partial list and some of the above questions may lead to further questions as indicated.  Basically the more information you can give your anodiser the better they are able to help you achieve the finish you are after.