Gaskets have many essential responsibilities. In fluid processing and handling equipment, they create a pressure-tight seal between two surfaces — preventing fluids from escaping and preventing contaminants from intruding. Plus, they insulate, cushion, and reduce noise. Not much to ask, right?
Materials used to perform all of these functions have included rubber, cork, electrical insulation, EMI/RFI shielding materials, foam, felt, plastics, and other high-temperature materials. The material you choose depends on the performance demands of the intended application: What is the temperature range? What pressure range is expected? Will it be exposed to corrosives? Will it be exposed to UV radiation? Are there industry-specific requirements?
Whichever material is selected, the second essential function of a gasket is to partner with an adhesive to create a reliable bond on the two surfaces. That’s what today’s article is all about: the best adhesive material for gaskets.
1. Explore Your Options; Start With PSA’s
Before we start, you’re encouraged to review two articles specific to gaskets and adhesives: the advantages of adhesive transfer tape for gasket applications and a guide to foam gaskets and foam gasket tape.
Speaking of tape, pressure sensitive adhesive (PSA) tape is a category that all engineers should explore and understand because it’s easy to use, cost-effective, and can be converted into custom sizes and shapes.
PSA’s typically comes in three formulations that match up with various gasket materials:
• Acrylic Based — Being thermoplastics by nature, acrylics typically soften slightly when exposed to heat and harden when cooled, offering a wide operating temperature range: -50°F (-46ºC) to +350°F (+177ºC). This allows acrylics to flow under light pressure and adhere to most gasketing materials and surfaces, which is vital when bonding to irregular or rough surfaces.
• Silicone Based — Offering the broadest operating temperature range: -80°F (-62ºC) to +450°F (+232ºC), silicone-based adhesives adhere well to most surfaces and best to silicone elastomers, yet are also the highest cost. However, the holding power may not be high enough on non silicone applications. Standard silicone sealants require a 2- to 24-hour curing time (anaerobic sealants cure in about an hour). Without curing, the seal’s integrity can be compromised.
• Rubber Based — Usually available at a lower cost (with lower performance), rubber based adhesive is a general use adhesive and works best on aluminum, bare metal, stainless steel, and non-polar substrates: polyolefins, EPDM’s (ethylene propylene diene terpolymers), and silicones. Operating temperature range: +50°F (10ºC) to +150°F (10ºC).
Because a PSA is vital to a gasket’s short- and long-term success, there are severe consequences for choosing a poor PSA.
2. Tapes of Various Types
Each adhesive type offers advantages, depending on what performance is required. Of all the types of adhesive available for gaskets — liquid, spray, tape — only tape (double sided, adhesive transfer, and VHB™) can be pre-applied to gasketing material before die-cutting to make the right parts.
The majority of available silicone, rubber, and acrylic gaskets are sold and shipped with a pressure sensitive adhesive backing. These “peel and stick” gaskets feature double sided backings, with the release liner remaining in place until the gasket is installed.
Adhesive Transfer Tape
With high conformability, initial adhesion, and overall strength, adhesive transfer tape’s liner stays in place on the gasket until the second substrate is ready. Depending on the exact gasket performance demands, other advantages may be useful:
• Flexibility — Thin (sub 1 mil) and conformable; bonds to irregular shapes and sizes
• No Carrier — Not limited to the temperature resistance of a carrier
• Low Profile — Easily stacked atop one another if needed
If an optional priming solution is used to help the adhesive transfer tape stick to the gasketing material, these gaskets should be used within a year without a priming solution (note: transportation and storage conditions can affect shelf-life).
Double Sided Tape
A carrier within double sided tape enables the bonding of two similar or completely different substrates (perfect for gaskets). It also provides stability that makes the tape easier to handle and convert. The carrier’s material may be paper, plastic, foam, or film — again, depending on what the gasket needs to do — thicknesses can range from a fraction of a millimeter up to a thick foam.
3M VHB™ tapes, a double-sided foam tape made from high-performance acrylic adhesives, contour to various shapes, including gaskets. In fact, some of these high-strength tapes can replace rubber or foam gaskets because their closed-cell construction creates a watertight barrier between two flat parts. In these cases, VHB tape is easily die-cut into whatever shape is needed.
3. Spray Adhesives
Both solvent- and water-based adhesives can be sprayed (or applied with a brush or roll). Advantages include being fast to apply and economical, and being able to cover irregular shapes. Difficulties include applying evenly, which could cause quality concerns, even when a specialized applicator is used. Spray and liquid (see below) adhesives can be messy and require specialized application processes.
4. Liquid Adhesives
Liquid adhesives are strong but, again, applying them can be difficult, either done using an automated machine or manually. Gasket processing could be slowed by the adhesive’s curing time (can usually reach handling strength in 5-30 seconds). Liquid adhesives, commonly used on rubbers and plastics, come in handy for tight spaces, although they’re more expensive and dripping glue requires clean-up after application.
In some specialized applications, one-part anaerobic liquid adhesives can be applied between complex metal shapes and cured, completely replacing preformed gaskets.
Flexible Material Converters Help Choose Adhesives for Gaskets
Although this article suggests four available adhesive types, choosing the exact right gasket adhesive isn’t as simple as picking one of four options. Each type has hundreds of products on the market, and the ultimate success of your gasket is at stake!
The important thing to remember is that it’s not simply choosing an adhesive type, it’s how that adhesive is used. An expert and experienced converter can be a true partner, doing upfront research and providing critical advice that ensures the gaskets will perform as needed.
Strouse, a 3M Preferred Converter, die cuts and converts flexible materials to exact sizes, shapes, and formats. Gaskets are second-nature to us, and choosing the right adhesive is something we’re true experts at. Bring your products and needs to adhesive conversion specialists today.