Common Questions

Common Anodising Questions - Including repairing damaged anodising, white anodising and anodising steel, and others

 

Here are some common question we are asked about anodising;

 

Can you repair my damaged anodising?

The answer is both no and yes.  NO, we cant fix the existing anodised coating but yes we are able to strip of the existing anodising and re-anodise the part to look like new.  We frequently see parts that are faded or damaged due to age & general wear and tear.  We able to strip these parts, tidy if required and then re-anodise and colour.  For example we are commonly sent motorbike rims that are natural anodised, we strip, buff, anodise and lastly colour these to the colour of the customers choice.  This is a great way of avoiding having to spend extra money buying new coloured rims and also making the rims look like new.

As mentioned above the answer can also be YES.  Where a surface has been re-machined, spot anodising can be done.  A new layer of anodising will readily grow on the machined surface as the overall resistance is much lower than the rest of the surface.  However the new anodising will not stitch with the old anodising and so a boundary mark/line will be present.  In a lot of instances it may be easier to strip the whole part and start again.  Although care will be need to be taken where there are critical dimensions.  Surface finish will need to be another consideration as stripping anodising may result in the finish becoming more matt.  Obviously not an issue for items already mat but it could be if a bright/glossy finish is required - Extra polishing may be required.

 

Can my parts be anodised white?

Unfortunately the answer is no.  You are able to get most any other colour but white is not available for anodising.  If you would like to read more about what colours are available, please go to 'colours' page

 

Can you anodise steel?

Steel or any other iron based metal cannot be anodised.  Anodising is effectively controlled oxidation.  For Aluminium the anodising process leads to the very hard and corrosion resistant Aluminium Oxide.  Iron on the other hand would turn to Iron Oxide (rust) which would just flake off the surface - not good.  There is a process for 'anodising' stainless steel, although technically not true anodising as it is not a conversion coating but rather a type of chrome plating.  This process covers the stainless in a very thin coating of Chrome and a range of colours can be achieved - brown, blue, yellow, reddish brown, purple and green.  This so called 'anodising' of stainless steel does not enhance in any significant way the corrosion or wear resistance of the stainless steel and is purely done for the look.  We are not aware of this process being available in New Zealand.

 

Do you anodise car trim?

All original car trim was bright anodised and if you are looking at restoring that classic look then you will need to get this redone.  Bright anodising involves putting the parts through a chemical polishing tank called 'bright dip' prior to the parts being anodised.  Excellent surface preparation is required prior to ensure the best possible look.

 

While a high gloss finish can be achieved with mechanical polishing alone followed by anodising the look achieved by this on car trim can quite often be milky or cloudy.  While glossy it will lack the evenness and brightness that can be achieved with the bright dip process.  Advanced Anodising is not able to offer bright dip as an anodising option, so in answer to the question,we do not anodise car trim.

 

Can you colour match?

To be suitably vague, the answer is that is depends.  Yes we can try to match a colour but we will need a sample of the colour.  If the colour sample is not an anodised one then we amy only be able to achieve something that is close or will go with the sample.  If matching to something that is already anodised then to better achieve a match the most important factor is the alloy being anodised as this is most critical factor in determining how the item will dye.  If you are going to be supplying several different alloys then it is very likely that there will be some colour variation.

 

Yes we can colour match but this can not be guaranteed.  If in doubt give us a call to discuss your requirements and read our page on colour anodising

 

If you would like to know more about the anodising process, we would recommend you read our page on 'what questions will my anodiser have?' .

Marine Anodising

Marine Anodising

So what is marine anodising?  It is the same as standard anodising except that the specified coating thickness is 25 microns with a minimum coating thickness of 20 microns.  For some marine grade anodising the coating requirement will be greater.  Basically marine anodised coatings give greater corrosion resistance over standard anodised coatings.

 

For most fresh and salt water based applications a standard marine coating thickness of 25 microns is all that is required.  For application that involve extreme/constant exposure to salt water then a hard anodised finish or other coating option may be a better option.

 

When considering a job that requires marine grade anodising, there are a few things to consider;

 

Choice of alloy for marine anodising

Certain alloys of Aluminium are more resistant to corrosion than others and are therefore more suited to marine applications, while other alloys would certainly be a poor choice.  The best alloys for corrosion resistance are those found in the 5000 series of alloys, followed by those in the 6000 series.  A poor choice for corrosion resistance are the 2000 series of alloys and this is due to their high copper content.

 

Do I need marine anodising on my parts?

If your parts are for indoor use or outdoors away from coastal areas then standard 12 micron anodising will suit most applications, although sometimes more will be required for colour work.  If the parts are used in a coastal environment, geothermal areas or directly in salt water then marine grade coatings are recommended.  Marine grade anodised coatings are still suitable for the full range of anodised colours.

 

Maui Kanu are a Rotorua based company that make custom outrigger canoes for both the New Zealand and international market.  They use 6000 series Aluminium alloy tube, specially bent and shaped, to join the main canoe with the outrigger.  Maui Kanu have found that marine grade anodising is the most suitable finish for their product and have been very impressed by the performance and available colour range of the anodised coating.

 

For parts that have more continuous exposure to salt water then either hard coating or other coating options need to be considered, however for most applications standard marine anodising will give excellent results.

 

Please be aware that no matter what the coating is, salt water is extremely corrosive and it will eventually work its way through a coating causing corrosion damage.  So the coatings must always be correctly looked after;

 

  • Always rinse off any salt water after use
  • Clean only with non-abrasive and neutral detergents
  • Avoid scratching the coating as this opens a pathway for corrosion (Note - Anodised coatings are scratch resistant but not scratch proof)
  • If corrosion does begin, get it seen to as soon as possible before any major damage is done.  Anodising can easily be re-done.  Below is an example of pitting corrosion showing the devastating effect it can have on an item -

corrosion_example

This  particular part is of a bilge pump.  The part on the initial inspection only showed minor surface corrosion and discolouration.  A light bead blast removed all the soft corroded areas highlighting the true extent of the corrosion.  The pitting corrosion is quite extensive and in some spots has travelled almost all the way through the metal.

 

Call Advanced Anodising now to discuss your marine anodising needs.

 

 

Shipping guide

Shipping your Anodising

Shipping is a very important consideration for any anodising job.  Damage to goods that occur in transit to the anodiser can result in costly extra prep work as anodising does not hide any scratches or marks that are present.

 

Here is our guide to help you get your anodising job arriving in the same condition it left in;

 

1.  Avoid having parts in direct contact with each other

2.  If the parts are bare Aluminium alloy, you will need to ensure that the parts are clean and dry.  Finger prints and moisture can adversely affect the surface of the metal that may be present after anodising.  It is amazing how quickly bare Aluminium alloy can show stains, marks or even show the early stages of corrosion.  Below is an extreme example of some parts we received that were not properly cleaned of the cutting fluid used during the machining process.  The damage was only superficial and the parts came out OK.Incorrect storage of aluminium results in corrosion

 

3.  Wrap parts in several layers of news paper (cheaper than bubble wrap)

4.  When using tape avoid putting the tape directly on the metal surface. 

5.  If using box ensure it is sturdy, if the parts do not all fit snug in the box, add newspaper to ensure that there is minimal movement during the shipping

6.  Write or printout a list of items that have been sent and the anodising details i.e. colour.   We quite often do not receive a list of parts and this can lead on occasion to issues with insuring we have all the parts for a job.  Some customers will include a picture of all the parts as a reference.

7.  Include contact name, company, phone number and a return address for the anodising.  We still receive jobs that have NO information on them at all, which leaves us waiting until the customer contacts us to find out the progress on their job.

8.  Always ensure you have a tracking number for anything sent by courier

 

Upon arrival;

 

1.  We will start a job sheet

2.  Check the details of the initial phone or email enquiry with the parts that actually arrived

3.  Any discrepancies with information provided and the job or the item list does not match what actually arrived will be noted

4.  You will be called to let you know the job arrived, any issues relating the job will be discussed and agree on a completion date for the anodising job

 

Please note that while Advanced Anodising Ltd does what it can to ensure parts are securely packed, it does not take any responsibiility for the freighting of parts.  All freight is at the customers own risk.

How to get the best out of your Anodising and other tips

How to get the best out of your Anodising and other tips

 
Here are some general pointers to take into account when getting anodising done:

 

1.  Anodising does not hide marks present on the surface of the Aluminium before anodising e.g. scratches, clamp mark , die lines etc.........  These marks must be removed before anodising.  In some instances chemical etching can be used to reduce the impact of these marks but you will end up with a matt finish.  Etching will blend in fine lines but will have virtually no impact on more pronounced marks that may be present.

 

2.  When sending your job away to be anodised, make sure the parts are packaged in a way that they cant be easily damaged or marked during transit.  We have had instances where brand new parts have been sent to us with all the parts able to rub together in the packaging.  Needless to say there a cost involved in getting the parts ready to anodise.

 

3.  If the parts need to be welded, do this before the product is anodised.  The anodised coating has very high electrical resistance, effectively stopping welding and the anodizing needs to be removed before welding can take place.  (To remove the anodized layer for welding either use mechanical means or apply caustic based chemical e.g. oven cleaner - please take all safety precautions)

 

4.  If welding , then use 5356 welding rod for the best looking results.  TIG welding is generally considered to be more suitable for aluminium to be anodised than MIG.  MIG welding generally results in very high localised heat around the weld that cools very quick after welding.  The result of this very quick cooling are structural changes to the Aluminium around the weld that wont anodise properly and wont take dye - No good for that decorative look.  This problem can be reduced or eliminated by preheating the aluminium around the area to be welded and works by slowing the rate of cooling after welding is completed.  As TIG welding typically requires pre-heating, problems with anodising are less common.

 

5.  If you have a product that needs to be formed or shaped in any way, then this needs to be done BEFORE anodising.  While the anodised coating is very hard and resistant to wear, it does not like excessive tension.  Should an anodised layer be bent past a critical point the anodising will get fracture marks.  These fractures can become openings to corrosion.

 

6.  If you have a colour sample available, please send this either with the job or email a photo.  This will help us to get the colour you are after.

 

NOTE:   While every effort will be made to match the colour this cannot be guaranteed as there are many variables that impact on the final colour.
 
NOTE:   'White' is not available as a colour, this is due to the fact that the particles that make up white dye are too big to fit into the pores generated by anodising.

 

7.  When packaging avoid putting any tape directly on the Aluminium, as it is difficult to clean off and is not removed by the anodising process.

 

8.  Remember that anodising is only suitable for Aluminium and its alloys, this is because anodizing is an oxidation process.  Iron products such as steel would just turn to rust if they were to be anodised.

 

9.  If the product has any non-aluminium metal attached, this either needs to be removed prior to sending the product or let the anodiser know so they can mask it before anodising.

 

10.  Avoid leaving finger print marks on un-coated Aluminium products as these can become imprinted on the surface of the metal.  In some cases these marks will show through in the final product.

What questions will my anodiser have for me?

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

Anodised welding example

 

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.

 

Pitting corrosion on Aluminium part

 

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/hang 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 colours 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.

 

For more information see our pricing page.

 

NOTE:  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.