Dimensional Tolerances for Rubber Products

Dimensional tolerances for rubber products are allowable variations in part or material size. They’re expressed as plus or minus values, or as a range of measurements. During the seal design process, engineers record tolerances on part drawings so that vendors can source materials and fabricate products that meet or approximate the required dimensions.

If parts or materials are out-of-tolerance, seal failure can occur. For example, if a door seal is too large, the door may not shut. If the seal is too small, water or weather could enter. Coils and cut lengths also need to have the proper dimensions. That’s why your part drawing represents a contract that your distributor or fabricator needs to keep.

Yet engineers have an important responsibility, too. If the tolerances you specify are impossible to achieve, you won’t be able to get the sealing solutions that you need. It’s not because you selected the wrong vendor or manufacturing process. It’s because rubber isn’t like metal.

Rubber vs. Metal

Sometimes, designers specify tolerances that are too tight for rubber products. This leads to confusion and frustration during the seal design process. Typically, these engineers are used to working with metal – a material with different properties. Because metal parts support tight tolerances, it’s assumed (incorrectly) that rubber also supports a high degree of precision.

Rubber has many useful properties, but it can’t match metal’s tolerances. That’s because rubber is more sensitive to environmental conditions such as heat, cold, and humidity. The kind of tooling and equipment that’s used with rubber affects tolerances, too. If you’re used to working with sheet metal or metal profiles, you may find there’s a learning curve with rubber materials.

Fortunately, there’s a resource that explains what you can expect.

The RMA Handbook

The RMA Handbook is a technical publication that contains dimensional tolerances for molded and extruded rubber products. The U.S. Tire Manufacturers Association (USTMA), an organization formerly known as the Rubber Manufacturers Association (RMA), publishes the RMA Handbook and shares this information with distributors and fabricators of industrial rubber products.

If you’re wondering whether this resource is authoritative, consider the organization’s membership:

  • Bridgestone Americas
  • Continental Tires, The Americas LLC
  • Cooper Tire & Rubber Company
  • Giti Tire (USA) Ltd
  • Goodyear Tire & Rubber Company
  • Hankook Tire America Corp.
  • Kumho Tire U.S.A., Inc.
  • Michelin North America, Inc.
  • Pirelli Tire North America
  • Sumitomo Rubber Industries
  • Toyo Tire Holdings of the Americas
  • Yokohama Tire Corporation

Across the supply chain, the RMA Handbook provides a common language that’s easy to understand. Dimensional tolerances are organized into tables and assigned classes. By adding an RMA class to your part drawing, you can clearly explain what a distributor or fabricator needs to know.

RMA Drawing Designations for Molded and Extruded Parts

It also helps to have a basic understanding of how the RMA Handbook is structured. Molding and extrusion are both rubber manufacturing processes, but they subject elastomers to physical changes in different ways. Consequently, molded parts and extruded parts are covered in different chapters. Moreover, there are different RMA classes for molded parts and extruded parts.

Chapter 1 of the RMA Handbook describes four levels of dimensional tolerances for molded rubber products. There’s a separate table for each class along with information about dimensional terminology.

A1 High Precision
A2 Precision
A3 Commercial
A4 Basic

Chapter 2 of the RMA Handbook describes three levels of tolerances for extruded rubber products.

1 Precision
2 Commercial
3 Non-Critical

There are also separate tolerance tables for spliced extrusions (cut and spliced lengths) and for unspliced extrusions (cut lengths). Spliced extrusions use drawing designations S1, S2, and S3. Unspliced extrusions use drawing designations L1, L2, and L3 instead. Complete this form to see these tolerance tables.

Get Help with Dimensional Tolerances for Rubber Products

Elasto Proxy is a distributor and fabricator that can help you specify dimensional tolerances for rubber products. To get started, contact us.

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Seal Design Starts With This Formula

Seal Design

Finished gaskets follow a formula. Seal design begins with compound, hardness, and profile selection. Custom seals and gaskets that account for these factors can fill the gap, withstand the environment, and meet business and technical requirements.

Let’s take a closer look at what you need to know. Continue reading Seal Design Starts With This Formula

Seal Rounded Corners by Starting with These Three Measurements

Seal Rounded Corners with Bulb Trim Seals Do you need to seal rounded corners against wind, water, dust, or dirt? Bulb trim seals are industrial rubber products that provide sealing and insulation for machine doors, vehicle hatches, and equipment enclosures. They’re designed to seal rounded corners and have separate bulb and retainer sections. Each of these sections can use a different material and have a different durometer or hardness.

With bulb trim, the bulb section compresses to form a seal when the door, hatch, or enclosure is closed. The trim or retainer section attaches to a flange or substrate. To choose bulb trim for your application, you need to specify the bulb size, bend radius, and flange thickness. By choosing the right bulb size, you can avoid over-compression. The right bend radius and flange thickness help to avoid kinking and leakage. Continue reading Seal Rounded Corners by Starting with These Three Measurements

Vibration Dampers for Structure-Borne Noise

Vibration DampersVibration dampers dissipate the energy that causes resonant vibrations in built structures. Vibration, a back-and-forth movement or oscillation, produces structure-borne noise in machine enclosures, engine bays, generator sets, heavy trucks, military vehicles, and many other applications. Vibrations can also damage parts, loosen fasteners, weaken soldered connections, and suggest poor quality.

For engineers, it’s important to understand that objects have a frequency at which vibration occurs. With resonant vibrations, multiple objects vibrate at the same frequency. For example, the low-frequency rumble of a big diesel engine can cause a vehicle’s windows to rattle. These vibrations don’t just produce unwanted sounds. They can also damage the window glass.

In this article, the last in a series about custom acoustic insulation, Elasto Proxy explains what engineers need to know about the different types of vibration dampers. You’ll also learn how this type of custom acoustic insulation is cut from sheets and bonded to other types of materials.

Types of Vibration Dampers

Vibration dampers are made of extruded vinyl, asphalt-impregnated paperboard, metal foil, or fiberglass.

Extruded vinyl dampers are flexible, lightweight, and available in grades that meet specific standards. For example, vinyl that meets UL 94 V0 flammability requirements is used in hospital equipment, kitchen appliances, and computer housings. Vinyl that meets ASTM E662 for the optical density of smoke and ASTM 162 for surface flammability is used in buses, trains, and subways.

Asphalt-impregnated paperboard dampers are odorless, wear-resistant, waterproof, lightweight, and  cost-effective. Like extruded vinyl, they’re supplied in sheets that can be cut to size and then laminated to other materials. For example, asphalt-impregnated paperboard can be laminated to sound barriers. Asphalt-impregnated paperboard can also be bonded to flat or curved panels in built structures.

Metal foil dampers can be applied directly to structural components or bonded to other types of insulating materials. For example, aluminum foil can provide the facing for a sandwich-like structure that includes a sound absorber and a heat blocker. To support vibration damping, metal foils can be embossed so that raised features in the foil disrupt sound waves as they travel across the surface.

Fiberglass dampers are made of a reinforced plastic that’s composed of glass fibers embedded in a resin matrix. These thin, composite materials include laminates with a viscoelastic compound that’s sandwiched in the center. For optimum damping performance, both outer layers of the fiberglass may have the same thickness. Applications include acoustic hoods and housings.

How Vibration Dampers are Made

Vibration dampers are cut from sheet materials and can be laminated to other types of insulation. They can also feature a release liner with a pressure-sensitive adhesive (PSA) for peel-and-stick installation. For engineers, it’s important to understand how choosing the right fabrication method affects cost, consistency, and quality.

Cutting can be done in-house or by a custom fabricator. Manual cutting with a knife, saw, or other hand tools may seem cost-effective, but poor-quality cuts can result in rework and material waste. By contrast, water jet cutting creates fine, fast, consistent cuts that maximize material yields. Plus, unlike die cutting, there’s no paying for or waiting for tooling with water jet technology.

Laminating combines vibration dampers with other types of materials in a sandwich-like structure. To avoid delamination, this bonding process requires the right adhesives and the efforts of skilled production personnel. Some vibration damping materials, such a fiberglass with a viscoelastic core, are laminated when they’re manufactured. Other vibration dampers are laminated during custom fabrication.

Find Vibration Dampers for Structure-Borne Noise

The article you’ve been reading is the last in a series about how to stop noise with custom acoustic insulation. For more information, please contact Elasto Proxy. You can also ask for the Elasto Bag to see some sample insulation for yourself.

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Sound Barriers for Noise Control

Sound BarriersSound barriers are custom acoustic insulation that blocks sounds instead of absorbing or damping them. They’re made of dense materials and are used at the source of a sound and along its path. To choose the right noise control product, engineers need to understand how sound barriers work, how they’re made, and the different types that are available. Continue reading Sound Barriers for Noise Control

Sound Absorbers for Noise Control

Sound AbsorbersSound 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. Continue reading Sound Absorbers for Noise Control

Stop the Noise with Custom Acoustic Insulation

Custom Acoustic InsulationCustom 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. Continue reading Stop the Noise with Custom Acoustic Insulation

Cold Bonding vs. Injection Molding for Finished Gaskets

Finished Gaskets - BlogCold 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. Continue reading Cold Bonding vs. Injection Molding for Finished Gaskets

Window Channel Selection Tips

Window ChannelWindow channels are rubber gaskets that hold window glass in place and help to secure window frames. They also eliminate rattling and provide protection against wind, water, dust, and debris. Applications for window channels include mobile equipment, defense, medical and health, stainless steel and food equipment, infrastructure, and aerospace.

For engineers and product designers, window channel selection begins by understanding the types of products that are available. It’s also important to define your application requirements and to compare product specifications. In this article from Elasto Proxy, you’ll learn how to select window channels that provide the sealing and insulation you need. Continue reading Window Channel Selection Tips

Four Common Shapes for Extruded Rubber Seals

Shapes for SealsThere are four common shapes for extruded rubber seals. Do you know which shape is the right choice for your gasket application? Engineers and seal designers can choose P-shapes, D-shapes, E-shapes, and lip seals. Purchasing agents can either order cut lengths or buy spliced gaskets.

In this article from Elasto Proxy, you’ll learn when to choose and how to use the four common shapes for extruded rubber seals. We also invite you to stay tuned for a series of short videos that will explain what you need to know about P-seals, D-seals, E-seals, and lip seals. Continue reading Four Common Shapes for Extruded Rubber Seals