Sound absorbers are custom acoustic insulation that absorbs sounds instead of blocking or damping them. They’re made of foams and facings and used at the source of the sound and at its receiver. To choose the right noise control solution, engineers need to understand how sound absorbers work, which types are available, what questions to ask during material selection, and how sound absorbers are made.

How Sound Absorbers Work

Sound absorbers are made of open cell acoustical foams that can be combined with specialized facings. The sound energy that passes through the foam’s cells is converted into small amounts of low-grade heat that’s dissipated easily. The foam’s acoustical performance is predictable because the material’s manufacturer carefully controls the uniformity of each cell.

The facings that are used with these acoustical foams are like control knobs that allow sound absorbers to tune-out specific frequencies. Examples include the low-frequency rumble of a diesel engine or the high-pitched squeak, squeal, or whine of industrial machinery. A sound absorber’s facing can also provide a decorative, durable, or cleanable finish.

Sound Absorber Types

Most sound absorbers are made of polyester, polyurethane, urethane, or melamine foams. To meet fire safety requirements, some sound absorbers use polyimide foams instead. Vinyl and aluminum foils are common facing materials. Vinyl can absorb low frequencies and supports ease-of-cleaning. Aluminum foil reflects radiant heat and provides thermal insulation.

With mobile equipment, a vinyl-faced sound absorber might be used in the cab while a foil-faced sound absorber is used in the engine bay. Other examples of sound absorbers include:

• Un-faced polyester or polyurethane foams for maximum sound absorption
• Aluminized polyester faced foams for hostile environments that must remain clean
• Urethane faced foams that reduce the ingress of dirt, particles, and debris
• Convoluted foams with increased surface area for enhanced sound absorption

These are just a few of the many sound-absorbing solutions that are available.

How to Select Sound Absorbers

To choose the right sound absorber, engineers need to ask and answer a series of questions about acoustic insulation. Each application is different, but this list is a good place to begin.

• What is the maximum insulation thickness that your application can support?
• Are you trying to insulate an area where there’s air flow resistance, or can air flow in and out?
• Do you need facing materials that can absorb a specific frequency or frequencies?
• Do you need facing materials for protection? If so, what are you protecting against?
• If the sound absorber must provide flame resistance, what is the flame rating you need to meet?
• Will the acoustic insulation remain stationary, or be subjected to opening, closing, and bending?
• Will you add sound absorbing materials to structural components where there’s vibration?

How Sound Absorbers Are Made

Sound absorbing materials are supplied as sheets or rolls in various lengths, widths, and thicknesses. Using water jet cutting, a fabricator can cut materials to size without knives or dies – tooling that adds costs to projects. First, however, the fabricator can laminate different sound absorbing materials together to create an insulation “sandwich” with particular properties.

For example, a fabricator can laminate a vinyl facing to a polyurethane foam. Then, on the other side, the fabricator may apply a pressure-sensitive adhesive (PSA) with a removable liner. The resulting product looks like an insulation “sandwich” with the facing on top, the liner on the bottom, and the foam in the middle. This sound absorber stops low-frequency sounds and is easy to install and clean.

Find Sound Absorbers for Noise Control

The article you’ve been reading is the second in a series about how to stop noise with custom acoustic insulation. Future articles will examine barriers and dampers. In the meantime, please contact Elasto Proxy for more information. You can also ask for the Elasto Bag to see samples for yourself.

Custom acoustic insulation absorbs, transmits, or redirects sound waves – vibrations in the air that pass-through objects and result in audible sound. Noise, or unwanted sound, is measured in decibels (dB) and has a specific frequency distribution that’s measured in Hertz (Hz).

Unlike some noise control products, custom acoustic insulation can be “tuned” to address specific frequencies. Examples include the low-frequency rumble of a big diesel engine and high-frequency sounds like squeaking and squealing.

Custom insulation can strengthen product designs, but engineers need to know which questions to ask and what types of solutions are available. In this introductory article, you’ll learn about the basic elements of noise control. You’ll also learn about the basic types of acoustical materials and how they’re fabricated.

Three Elements of Noise Control

There are three elements to noise control: source, path, and receiver.

Source is the origin of the noise to control. For example, is the source of the sound a bell, a whistle, or a loudspeaker? Maybe you’re trying to silence traffic noises or industrial machinery instead. Low-frequency sounds, especially those that cause vibrations, are especially challenging. Yet failing to quiet them can result in damage to human hearing or mechanical failure.

Path describes how the sound is transmitted. In the case of a bell, whistle, or loudspeaker, the sound may travel through a factory’s interior wall and disturb the occupants of an adjacent room such as a front office. With mobile equipment such as logging trucks and military vehicles, engine sounds travel from under the hood to inside of the cab.

Receiver considers the listener’s requirements, expectations, or preferences. On a factory floor, some noise is expected as long as it doesn’t exceed regulatory limits. Passengers on a train, bus, or airplane want to be able to hear themselves talk. The owner of a sports car wants to hear the engine’s sounds, but without excessive amounts of road noise.

Four Types of Acoustical Materials

There are four types of acoustical materials: absorbers, barriers, dampers, and facings.

Absorbers are made of acoustical foams and used at the source and the receiver. As their name suggests, these materials absorb rather than block or dampen unwanted sounds.

Barriers are made from acoustical foams or extruded vinyl. They’re used at the source and along the path. Unlike sound absorbers, barriers block rather than absorb sound.

Dampers are made of extensional and constrained layer materials. Like barriers, dampers are used at the source and the receiver. Unlike barriers, dampers reduce sound energy instead of blocking it.

Facings are like control knobs that allow custom acoustic insulation to tune-out specific frequencies. They can also address environmental or aesthetic concerns.

How Custom Acoustic Insulation is Fabricated

The materials for custom acoustic insulation are supplied as sheets or rolls in various lengths, widths, and thicknesses. Using water jet cutting, a fabricator can cut materials to size without knives or dies – tooling that adds costs to projects. First, however, the fabricator can laminate different materials together to create an insulation “sandwich” with particular properties.

For example, a fabricator can laminate a facing to an absorber. Then, on the other side of the sound-absorbing foam, the fabricator may apply an adhesive with a removable liner for peel-and-stick installation. The resulting product looks like an insulation “sandwich” with the facing on top, the liner on the bottom, and the foam in the middle.

Stop the Noise with a Closer Look

The article you’ve been reading is the first in a series about stopping noise with acoustic insulation. Future articles will take a closer look at absorbers, barriers, dampers, and facings. In the meantime, please contact Elasto Proxy with your questions about custom acoustic insulation.

Cold bonding for finished gaskets joins cut lengths of rubber without the use of heat. This bonding technique isn’t performed under low-temperature conditions but is manual process that requires a brush and glue. By contrast, injection molding is a semi-automated process that uses a C-press machine with a heated barrel, metal plates, and tons of pressure. To join cut lengths, uncured rubber is used.

By understanding how these joining processes work, engineers can make better decisions about which types of finished gaskets to choose. It’s also important to understand the advantages of disadvantages of each bonding technique. In this week’s article, we’ll compare cold bonding with injection molding in terms of capabilities, costs, and quantities.

Cold Bonded Gaskets

Cold bonded gaskets are recommended for lower-volume projects because cold bonding doesn’t require tools or molds. Metal tooling can add significant costs to gasket fabrication – sometime as much as tens of thousands of dollars. Higher-volume projects can spread the costs of tools across many finished gaskets, but the per-gasket cost for a mold may be too high for a low-volume project.

Unlike C-press injection molding, cold bonding is an entirely manual process. First, production personnel clean and dry the surfaces of the cut lengths. To promote optimum adhesion, some rubber may need to be abraded. Next, a glue or adhesive is applied with a brush. There are many different rubber bonding systems, and some glues or adhesives are designed for specific elastomers.

For engineers, it’s important to understand that some glues crystallize when they contact water. All glues dry out over time. The right gasket fabricator can help with adhesive selection and also allocate labor resources to medium-volume jobs where cold bonding remains cost-effective. Cold bonded gaskets won’t last as long as other types of finished gaskets, but cold bonding offers important advantages.

Injection Molded Gaskets

Injection molded gaskets are recommended for sealing applications that require rounded joints, the ability to withstand stretching, or high cycle times. This bonding technique is more expensive than hot splicing or vulcanizing (two other joining methods), but injection-molding can create radiused corners instead of the right-angle corners found in bezel or picture-frame gaskets.

Unlike cold bonding, injection molding requires metal tooling and a C-press machine. First, uncured rubber is heated and then injected into channels in the bottom half of the mold. The top half of the mold is then pressed down on the bottom half. Cut lengths are positioned in each half of the tool. The corners are formed, the top plate or mold half is removed, and cooling occurs.

C-press injection molding is used only with solid rubber profiles – and not with sponge rubber or silicone elastomers. Engineers need to consider the cost of tooling, but gaskets with molded corners support reduced cycle times and cost-effective processing. Injection molding also supports gaskets in a range of sizes and provides an enhanced appearance.

Finished Gaskets and Custom Fabrication

Elasto Proxy is a gasket fabricator that provides cold bonding, C-press injection molding, hot splicing, and vulcanizing services. If your project requires finished gaskets, we can also add value by providing design assistance and help with material selection. We use water jet cutting and abrasive water jet cutting to create fine, fast cuts that are ready to bond with whatever joining method you require.

Elasto Proxy has three C-press molding machines at its headquarters near Montreal, Canada. Once your mold is made, Elasto Proxy can store it for you and use it repeatedly. If you need cold bonded gaskets instead, we can help you with adhesive selection and even allocate additional labor resources for higher-volume quantities. Our Simpsonville, South Carolina (USA) facility also has bonding or joining capabilities.

For more information, contact us.

Hot splicing uses heat, pressure, and a film splice to join the ends of rubber profiles into bonded gaskets. This joining technique uses either a conventional heating source or infrared (IR) light and polyethylene (PE) film. Hot splicing creates strong bonds at the molecular level and generally provides better results than vulcanization, a bonding technique that uses uncured rubber instead of a film splice.

Choosing the best way to bond rubber gaskets can be a complex decision, however. The profile material is just one of many considerations. You also need to consider the size and shape of the seal, production quantities and costs, and the way that lengths of rubber are cut. In addition, it’s important to inspect and install your gaskets properly to ensure reliable sealing and prevent avoidable waste.

Is hot splicing better than vulcanizing for the rubber gaskets that you need? Let’s take a closer look.

Vulcanized Gaskets

Vulcanizing uses heat, pressure, and uncured rubber to join the ends of sponge or solid profiles. Applications include O-rings, tubing, and rubber gaskets that need a space for the free-flowing passage of air. Vulcanization is best-suited for low-volume quantities instead of high-volume production. This splicing technique is also a good choice for joining lower-quality cuts like those made with guillotine cutting.

With vulcanization, the uncured rubber compound that’s used is the same type of elastomer as the profile itself. First, the uncured rubber is applied to the length of profile. The ends are pressed together, and the joint is placed into a hot mold. The uncured compound flows into any gaps and fills them. The result is a strong bond between profile surfaces. When bonding is complete, cooling is required.

Hot Spliced Gaskets

Unlike vulcanization, hot splicing always uses a PE splice instead of an uncured rubber compound that’s made of the same material as the profile itself. Hot splicing also requires clean, straight cuts such as those made with water jet cutting or abrasive water jet cutting. Ultimately, these smooth edges are easier-to-bond. Automated cutting is also faster than manual cutting and offers greater consistency and accuracy.

Compared to vulcanization, hot splicing is better for higher-volume quantities. Most hot spliced joints are 90° but this bonding technique also supports 45° miter cuts and endless gaskets. The type of profile – sponge or solid – usually determines whether conventional hot splicing or IR splicing is used. Some materials, such as silicone, support traditional hot splicing but not infrared splicing.

IR splicing is a good choice for sponge rubber profiles because infrared light won’t burn the elastomer. Infrared splicing equipment can also accommodate very large profiles, such as the bonded gaskets that are used as gate seals in water filtration systems. IR splicing also requires significantly less trimming, a post-production activity that’s performed manually. This video provides a demonstration.

Inspecting and Installing Spliced Gaskets

If hot splicing is the right choice for your application, you’ll need to follow the proper installation and inspection methods. When installing a spliced gasket onto your product, always start with the joint. Then move six inches to the left and six inches to the right, as this video shows. By securing the joint, you can then continue to install the gasket without breakage.

Inspecting a spliced gasket is simple. Hold the bonded gasket on each side and pull away from the joint. If you don’t see a break, your gasket is sealed and ready to install. Do not inspect the gasket by folding it at the joint. Doing so will break the rubber gasket in half. Folding the gasket in this way is unrealistic; it’s not how your seal will operate.

Get the Bonded Gaskets You Need

Elasto Proxy uses hot splicing, vulcanizing, cold bonding, and molding to create bonded gaskets. We also use water cutting and abrasive water jet cutting so that the edges of rubber profiles are smooth, straight, and easy-to-bond. If you need hot spliced gaskets, we offer both conventional hot splicing and infrared splicing. To get the bonded gaskets that you need, ask Elasto Proxy.

Rubber profiles come in lengths that are cut-to-size and fabricated into finished gaskets. Examples include picture frame or bezel gaskets, O-rings, and gaskets with rounded corners.

There are four ways to bond or join the ends of rubber profiles.

• Hot Splicing
• Vulcanization
• Cold Bonding
• Molding

Each bonding or joining method has its advantages, but what’s the best choice for your application? Let’s examine each method in detail so that you can make the right decision.

Hot Splicing

Hot splicing uses heat, pressure, and a thin PE film splice to join the ends of rubber profiles. This bonding technique is called “hot” because it uses either a conventional heating source or infrared light (IR). Traditional splicing takes longer than IR splicing, but both methods create strong bonds. Most film splices are 90°, but hot splicing also supports 45° miter cuts and endless gaskets.

Hot splicing requires clean, straight cuts but supports higher production volumes. The type of profile usually determines whether a conventional heat source or IR light is used. IR splicing is a good choice for sponge rubber profiles because IR won’t burn the elastomer. IR splicing can also accommodate larger profiles and requires less post-production trimming. With silicones, however, traditional splicing is used.

Vulcanization

Vulcanization uses heat, pressure, and uncured rubber that’s made of the same elastomer as the profile itself. Compared to hot splicing, this bonding technique is more forgiving since the cuts don’t have to be smooth and precise. With vulcanization, uncured rubber is applied to the profile’s ends. After the ends are pressed together, the joint is placed into a hot mold.

Applications for vulcanization include O-rings, tubing, and other industrial rubber products with a space for the free-flowing passage of air to the gasket. Vulcanization can’t match hot splicing in terms of results, but vulcanized seals and gaskets are good for low volumes.

Cold Bonding

Cold bonding is a manual process that’s performed with a brush and an adhesive or glue. This technique is called “cold” because no heat is applied to the ends of the gasket. Bonding systems include low, medium, and high viscosity adhesives in cyanoacrylate, silicone, and epoxy formulas. Glues may be designed for specific types of rubber or crystalize when they contact water.

Cold bonding or gluing doesn’t require metal tools called dies, but cold bonded gaskets won’t last as long as hot spliced ones. Plus, cold bonding is more expensive than hot splicing. Compared to molding, however, cold bonding costs less because there’s no metal tooling. Gasket fabricators can add labor to projects, but most cold bonded gaskets are produced in low-volume quantities.

Molding

Molding is the only bonding technique that can create rounded corners for rubber gaskets. This joining method is also recommended for gaskets with corners that will be stretched or pulled. Compared to hot splicing, molding produces stronger joints and offers increased resistance to leaking. Molding is also recommended for bulbs with difficult shapes.

Molded gaskets require tooling and C-press injection molding equipment. The cost of a metal mold can be significant, but tooling that’s used across higher volumes of gaskets has a lower unit cost. Molding is generally used with larger production runs; however, molding is not recommended for silicone or sponge profiles.

Get the Sample Kit

Elasto Proxy is a gasket fabricator that provides a choice of joining methods. Our capabilities include hot splicing, vulcanization, cold bonding, and molding. We also keep hundreds of profiles in stock and use water jet cut cutting or abrasive water jet cutting. To see samples of our rubber products – including spliced corners – ask for our Sample Kit.