Mike Howell
EASA Technical Support Specialist
One of the least popular tasks to perform related to winding treatment processes is preparation and cleanup of fits, threaded holes and machined surfaces. Many service centers invest additional time in the preparation stage so as to minimize the cleanup stage. The most common approach to protecting these surfaces during winding treatment is to utilize masking compounds or dry release sprays.
In the last year, EASA’s technical support staff has received a number of inquiries from members seeking replacement recommendations for Famous Lubricants' “Special Masking Compound” which is currently unavailable. It is believed at this time that the manufacturer intends on continuing production at some point in the future though the time frame is not known. This specific problem leads to a more general question: What is a good practice for choosing a product to mask these surfaces?
Risk of contamination
The single biggest risk with introducing any material to your resin or varnish supply is contamination. For this reason, EASA suggests that you contact your resin or varnish manufacturer for recommended masking products. Most of the manufacturers already have masking products for the various varnishes and resins they produce.
When evaluating cost, also consider that materials having established compatibility with your varnishes and resins may pose less risk of damage to them. Additionally, it is critical with materials that are expensive per unit to avoid waste. For example, some brush-on masking products, while relatively expensive by volume, are effective with minimal application. (See Figure 2.)
Verify use of product with manufacturer
There are of course many general industrial masking products available in the marketplace and some of them are commonly used in service centers. If using some of these general materials, EASA recommends either verifying that they are listed in the resin or varnish manufacturer’s documentation as acceptable or contacting the manufacturer directly to verify that these products should not damage your varnish or resin. As a starting point with some general products, PTFE (Teflon® or similar polytetrafluoroethylene) masking compounds or sprays work well with many resins and varnishes. On the other hand, there are interactions between silicone release agents and epoxy that are known to be problematic, so silicone based release agents may not be a good choice.
Some industrial grease compounds intended for masking may work well with your dip & bake varnish, but not with your vacuum pressure impregnation (VPI) resin. So, when verifying suitability, make sure you evaluate the material against all your winding treatment products and place restrictions as necessary.
Plan ahead
If products can be found that work with all your winding treatment processes, that could prevent accidental misuse of the wrong material. It is worthwhile to determine at least two different product alternatives for any process in the service center. Material unavailability can cause delays in production and sometimes lead to rush decisions to use alternatives that are not suitable for the application. Whatever masking products are used, it is important not only to determine compatibility but also to follow the manufacturer’s instructions as cure times, temperature ratings and other characteristics can also affect processing requirements.
In the event a surface is not masked or poorly masked, use a cutting torch with the oxygen lever depressed to burn off the cured resin without heating or damaging the fits. This is especially useful for threaded holes.
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