Masking materials

Question - I’m new to masking and there seem to be a lot of different materials available for masking caps and plugs. Can you explain the differences between them and suggest which material should be used in which application?

There are a lot of materials available for standard masking products, due mainly to the diverse processes that are used in finishing products. In terms of choosing a material the first thing to consider is the temperature of your process. Next look at what materials can withstand that temperature. If you are plating products, you must also look at whether or not the material can withstand the chemicals in your process. Here is an overview of materials that are used for masks, along with some information on what material can be used in which finishing process.

Silicone – for high temperature applications such as powder coating and E-Coat.

When it comes to high temperatures, silicone rubber is hard to beat. Able to withstand temperatures up to 600°F / 316°C, silicone stretches easily, resists compression and is available in a number of different hardnesses, making it ideal for masking parts. It can be produced relatively cheaply and it can be molded to almost any form. Caps and plugs made from silicone are readily available and are typically manufactured by compression molding. Silicone plugs and caps can be made in different colors and different hardness. Different colors can help you identify the size of a cap or plug. Hardness can impact how the paint sticks to the cap or plug. A lot of paints do not adhere as well to softer plugs and caps, which can help you with cleaning the masks.

Neoprene - a good choice for plating and wet paint applications.

Neoprene is a very versatile rubber, like silicone it can be color coded and parts are made by compression molding. Neoprene, however, can only withstand temperatures up to 350°F / 177°C. Neoprene can be formed into caps and plugs and has its place in both plating and low temperature painting or dry film lubrication applications. Neoprene’s ability to resist abrasion also makes it a good choice for use in blasting, cleaning, deburring and polishing processes.

Flouroelastomer (FKM) – a chemical-resistant rubber for aggressive chemical processes.

FKM can withstand high temperatures, but temperature isn’t the reason for choosing this material for your masking products. FKM is a rubber that was developed to resist aggressive chemicals, so it works well for masks in chemical treatment applications. Molding with FKM can be a specialized process and it’s important to check your masking supplier is used to dealing with this material.

Vinyl - ideal for wet paint applications.

Vinyl caps are a mainstay of the wet paint industry for masking studs, screws or shafts. Vinyl is available in numerous colors and can handle temperatures up to 350°F / 177°C. Vinyl isn’t as flexible as silicone rubber, so it’s a little more important to get the size of the cap correct. Also, with vinyl caps, there is a larger tolerance on the outside diameter of the cap. That tolerance is perfectly normal as it is caused by the manufacturing process. Naturally, the inside diameter of the cap is consistent. Vinyl tapered plugs are also available.

High temperature vinyl – a high temperature option.

If you cannot use silicone in your process, then a high temperature vinyl is worth considering. High temperature vinyl masking products are available and can resist temperatures of 475°F / 246°C.

LDPE – a low temperature plastic.

Most masking suppliers have a range of protection products, which are made from LDPE (low density polyethylene). While LDPE parts are generally used for protecting products during shipping, they can be used for masking. LDPE is a relatively hard plastic material compared to the typical rubber masking caps and plugs. As LDPE is able to withstand temperatures up to 175°F / 79°C it can be used in low temperature masking applications. A number of LDPE protection parts are threaded, so they can be screwed onto threaded studs.

Paper – wet paint applications.

Paper caps and plugs are available and are generally made from a blend of virgin and post-consumer recycled paper. Both tapered and straight-sided paper caps are available. In addition to the caps, tapered paper plugs are available to use for masking.

Cork – wet paint applications.

Cork plugs are available for wet paint applications and are able to withstand temperatures up to 300°F / 149°C. Although not quite as flexible as silicone or neoprene tapered plugs, cork plugs have their place in low temperature finishing processes.

Nylon – for plating applications.

Nylon is a very hard material, which makes it a useful masking product in plating applications where you have to protect internal threads. The nylon plugs can be screwed into the thread and will form a seal to keep the solution out. Nylon plugs are able to withstand temperatures up to 175°F / 79°C.

This is just an overview of the main materials for standard masking parts. Most masking suppliers have additional materials, which they can use for specific applications. A good masking supplier will be able to help you choose the most suitable material for your application and supply a sample to test in your process.

Written by John the article was published in Products Finishing Magazine.

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Masking materials differences