Differences in Masking and Plug Materials

Q. I’m new to masking, and there seems to be a lot of different materials available in masking caps and plugs. Can you explain the differences between them and suggest which materials should be used in which applications?

A. There are a lot of materials available for standard masking products, mainly due to the diverse processes that are used in finishing. In terms of choosing a material, the first thing to consider is the temperature of your process. Next, look at which 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 plating process. Here is an overview of materials that are used for masks, along with some information on which materials can be used in which finishing processes.

Silicone is suited for high-temperature applications such as powder coating and electrocoating. When it comes to high temperatures, silicone rubber is hard to beat. Able to withstand temperatures as high as 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 is a good choice for plating and wet paint applications. Neoprene is a very versatile rubber, and like silicone, it can be color-coded and the parts are made by compression molding. Neoprene, however, can only withstand temperatures ranging to 350°F (177°C). It 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.

Fluoroelastomer (FKM) is a chemical-resistant rubber for aggressive chemical processes. It 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 that your masking supplier is used to dealing with this material.

Vinyl is 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 to 350°F (177°C). It isn’t as flexible as silicone rubber, however, 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 is worth considering if you cannot use silicone in your process. High-temperature vinyl masking products are available and can resist temperatures ranging to 475°F (246°C).

Low-Density Polyethylene (LDPE) is a low-temperature plastic. Most masking suppliers have a range of protection products that are made from LDPE and are generally used for protecting products during shipping, although they can also be used for masking. LDPE is a relatively hard plastic material compared to the typical rubber masking caps and plugs. As it is able to withstand temperatures 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 is suited for wet paint applications. Paper caps and plugs are generally made from a blend of virgin and post-consumer recycled paper. Both tapered and straight-sided paper caps are available, as well as tapered paper plugs for masking.

Cork is also suited to wet paint applications. Cork plugs are able to withstand temperatures up to 300°F (149°C), and although not quite as flexible as silicone or neoprene tapered plugs, have their place in low-temperature finishing processes.

Nylon can be used for plating applications. It is a very hard material, which makes it a useful masking product in plating applications in which internal threads must be protected. 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 as high as 180°F (82°C).

This is just an overview of the main materials used for standard masking parts. Most masking suppliers offer additional materials that can be used 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.

John Gill is an engineer with Caplugs. For more information, visit caplugs.com.