Masking is important to any kind of finishing and often viewed as a necessary evil, one that is frustrating, time-consuming and labor-intensive. But the benefits of masking are numerous, including improving line speed, product quality as well as providing a competitive advantage.
There are several techniques to use for masking specific parts such as strippable coatings, tapes as well as masking devices such as caps, discs and plugs. Strippable coatings are used to mask large and small areas of objects. Adhesive tapes are used on small- to medium-sized objects and sometimes in conjunction with sheets of paper or plastic on large objects. Caps adhere by friction and are used to cover openings on the ends of or protrusions on products. Adhesive backed discs are used to cover spots on the surface of objects. Plugs adhere by friction and are used in holes of objects.
Custom masking is a growing facet of the masking industry. Rather than buying a generic plug or cap and hoping that it fits the part, finishers can take their part to a custom masking supplier and come away with a mask designed exclusively for that specific item—ensuring a proper fit.
In order to obtain the proper finish, all plugs and seals need to be compatible with the coating materials. This means the sealing device cannot leach any material into the bath. All seals meant for reuse cannot be destroyed by the process, and, therefore, must be compatible with the temperature and bath.
For painting and coating applications, most reusable sealing devices withstand any commercial paint or powder. However the drying and curing processes require that the rubber sealing portion withstand temperatures in excess of 400°F. Another option is to design lines with masking in mind and plan to remove masking devices before curing. In addition, for applications where the seals will be cleaned, it is important that the seal resist acidic cleaners.
For electrocoat, since the method of coating requires dipping the part in a liquid bath, you have the potential to create large pressure differentials at the interface of the masking and the part surface, which can lead to leaks. To protect the surfaces from electrocoating, several methods have been tried and tested including: high-temperature silicon plugs, aluminum plugs with silicon O-rings, grease, mating parts, blind holes, etc. Each method has its advantages in different applications.
For plating applications, the rubber seal needs to be compatible with the applied bath material.