We have been selling mainly to industrial accounts but also to the DIY hobbists these days. Anodizing is not fun because you need to handle nasty chemicals. The fun part comes in coloring of anodized aluminum. People will find this process interesting and satisfy in coloring parts. These colors can be mixed into different ratios to achieve many shades across the whole color spectrum. Sealing is the last step to give a protection on the anodic surface against attack from different environmental conditions.
MECHANICAL PRE-TREATMENTS - You can do all sort of things before the chemical finishing process. Buffing and sandblasting are the usually methods being used. The surface defects can usually be removed by either process. If your surface is good enough, you do not need any kinds of mechanical pre-treatment process.
CLEANING - The most important part of metal finishing is to clean the surface prior to subsequent processes. Cleaning can be done be simple dipping as well as ultra-sonic. Neutral pH cleaner is usually used to avoid etching of the aluminum surface. Our non-etch cleaner 161 D can be used to clean off oils and dirts without damaging the surface. It can be used for either dipping or ultra-sonic bath.
ETCHING - We do not sell these chemicals because they are DG goods and difficult to ship around these days. Etching is achieved by using sodium hydroxide in a concentration of 50-60 grams/liter for a dipping time of 3-5 minutes at a temperature of 50 – 60 C.
DESMUT/DEOX - Again, we do not sell these chemicals because they are DG goods and difficult to ship around these days. Desmut/deox is achieved by using 10% of nitric acid for a dipping time of 1 minute at room temperature.
ANODIZING - Since anodizing is exothermic, it gives out heat during thie process. A temperature range of 21– 23 C is needed to maintain during the anodizing process to produce a good quality anodic film. If there is no temperature regulation, thicker film cannot be achieved and deep shades are not possible. So, if you are serious enough, better get yourself some form of cooling during the anodizing process. Some basic figures are given here. Anodizing current density of 1 - 1.5 A/sq dm is typical for normal application. Higher current density will generate greater risk of soft coating or “burning”. The higher the current density the greater the heat generated at the coating/electrolyte interface and the cooling needed. You can find it here or many of guides can be found in other websites..
COLORING - It is the most fun part of anodizing. Different shade depths can be controlled by process variables. These process variables are anodic coating thickness, dye concentration, dye temperature, dye time and pH values. If light shade is desired, keep these variables at lower figures with pH at around 5.5 – 6.0. If deep shade is desired, keep these variables at higher figures with pH at around 5.5 – 6.0.
COLOR MIXING - Color mixing to produce stable shades is not easy in an industrial scale. Usually, color shift is result after some batches of operation. In small scale operation, this is not so important because not many parts are produced in a period of time. However, there are some advices to minimize the shift in color when dyeing in a color mixture. Try to use low make up concentration, i.e., 1 – 2 g/l. Try to dye at room temperature, i.e. around 25 C & maintain the pH at around 6.0 +/- 0.2. The pH can be lower by diluted acetic acid and higher by diluted sodium hydroxide solution.
SEALING - Sealing is usually done at a temperature above 85 C to achieve a good sealed surface. For color anodized aluminum, Hot Sealant CK must be selected at 5g/l concentration. A sealing speed of 1 um per 3 minutes can be achieved at a sealing temperature of 90 C. Typically, sealing at 85 C for 8 to 10 minutes are usually enough for most colors. Cold Sealant SE is only good for clear anodized part without coloring.
STRIPPING - If you do not like the colors, you need to strip it and do it all over again. Strip it in a 50 -60 g/l sodium hydroxide solution at 70 C for a couple of minutes and repeat the steps from the beginning. So, if you do not want any re-works, be careful for the coloring process.
RINISE & WATER - The rinse is an important step in the finishing operation. If not removed, acid residues clinging to the dyed parts are liable to cause spot dyeings. The contaminates can shorten the lifetime of dyebaths. As tap water contains minerals as well as many impurities, please do not use them. Get yourself some DI water if possible or bottle waters from convenient stores.
Why do I know all of these, because I sell these chemicals & colors for many years. If you have questions about anodizing, you can E mail me. If I do not know the answers, I will ask experts around for answers.
For industrial users, please visit our parent company website : www.ckchem.net . We developed a full distribution network in China as well as South East Asia countries including Thailand, Malaysia, Singapore as well as Vietnam. The local partners can provide solutions for turnkey projects of equipment & chemicals. Free feel to contact us anytime for your enquires.
A free anodizing basics guide can also be found HERE for customers to use as a good reference for the aluminum finishing process.
CLEANERS, COLORS, SEALANTS, FUME SUPPRESSANT
PLACING AN ORDER
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Delivery can be made usually in three days after confirmation of payment. During any holidays through out the year, delay of shipments can be expected as this is outside our own control. If possible, we prefer all shipments are shipped by EMS door to door service.