Masking for Anodizing: An overview of products
Masking for anodizing requires some specialized materials and even techniques for successfully stopping off the altered metal surface that occurs during the process as well as dyes sometimes used in this process. What masking will work best for you?
Stock Caps and Plugs
Starting with an easier aspect of masking, caps and plugs work very well for masking holes, studs and pins in aluminum parts that are anodized. Both silicone and EPDM rubber are excellent materials for this. Silicone can be either clear or colored, and because it is cured, will not leach into Type II or Type III anodizing tanks with sulfuric acid baths. EPDM rubber is typically black and is also perfectly acceptable.
Anodizers can choose from a wide range of plugs for masking, including standard tapered plugs, straight walled caps and even specialty items like pull plugs, flanged pull plugs and plugs with handles and a ribbed design to fit tightly and seal out liquids.
Custom molded masking
Of course, not every anodizing job can use a stock, standard part. In such cases, anodizers may use wax or UV-cured liquid to apply a maskant to parts. (Viadon does not carry wax or liquid masking products.) This is certainly an appropriate option, especially when the anodizer does not know if they will see the same job again or if it is a short-run quantity.
But when a recurring job requires labor-intensive paint-on masking, costs can skyrocket due to the labor required to complete the job. In these cases, we may be able to assist with custom parts that save time and money, such as this one (see photo above) where a steel insert was placed inside an aluminum part and had to be masked so the sulfuric acid would not attack the steel during anodizing. The originally-attempted paint on masking was inconsistent and had poor line definition. Viadon’s custom masking was not only faster to apply, it provided a clean, sharp masking line that the customer appreciated – and the best part was there were zero defective parts every time the job was run.
Type II Anodizing Tapes
Utilizing appropriate masking tapes is a great way to stop off anodizing on flat/machined surfaces. But there is a secret to successful masking with tape during anodizing: Pressure!
This is why: All the adhesive tapes we carry have what are called pressure sensitive adhesives. That “sticky” part of the tape requires some application of pressure to activate the adhesive. After it is activated, it really does “flow” into the microscopic crevices of a part – but – and this is the important part – that takes a bit of time, as the adhesive doesn’t flow everywhere instantaneously.
Therefore, the tape must be allowed to dwell on the part after the adhesive is activated. Ideally, 24 hours is best, but some anodizers have success with as little as 8 or 12 hours. This provides the necessary stop off for anodizing as it seals off not just the surface but the first few layers of aluminum below the surface – right where anodizing occurs within the metal.
Below are several popular tapes used in anodizing. Green polyester is by far the most popular one that we carry.
Top tapes for Type 2 Anodizing
Type 1 Anodizing Tape
Chromic acid is a harsh environment for most any tape, and if you have struggled to mask aluminum with tape for Type 1, you know the issues. 3M has developed a tape that survives remarkably well in these specialized baths that often see critical aerospace parts that sometimes require certain areas to be masked off. It is purple in color, transparent for easy application of die cuts and applied to a liner to it is ready-made for in-house, custom die cut designs you can make on a plotter cutter.
And we carry that tape – you can learn more about it at the link below.
3M 8985L purple chromic acid anodizing tape
Anodizing tape die cuts
Tape die cuts are a great way to speed up masking efficiency and save on labor costs. Small round circles may be used to cover holes or areas requiring a grounding surface area. Larger ones or squares/rectangles may be used to mask open areas or the surfaces around a milled out cavity.
And we can make custom die cuts too – need a specific size or shape? Give us a call – we can likely help. We make die cuts all day, every day – right here in house. Check out some of our standard and custom die cuts that are using in anodizing. And if you do not see what you need, just ask. Viadon has made die cuts from the 8985L purple tape, along with just about every other tape we carry.
VGD Green Polyester Disks
Custom Die Cuts
Viadon has been assisting anodizers with their masking needs since September of 2000. While we do not carry all masking products anodizers may use like UV cured masking or wax, if you need tape, caps or plugs – stock or custom – we can help you. Give us a call or send us an email to discuss your current masking challenge.
See the video below to watch these processes in action with green polyester tape, along with how Viadon slits the tape to width, die cuts it to size, and how you can get the most out of it when applying it to parts.