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  1. What You Need to Know About Molded Rubber Tolerances

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    All materials and industrial manufacturing processes create some degree of variability from one product to the next, no matter how automated the processes are. Depending on the materials and the needs of the project, these tolerances can be relatively large or incredibly minute so the products meet their required quality standards. Metals can often hold tighter tolerances as they can be cut or formed, without too much deformation. Compared to metals, different types of rubber offer different porosities, strength levels, and degrees of malleability, each of which can affect the tolerance of the final product.

    What Are Tolerance Schedules?

    Manufacturers use tolerance schedules that denote acceptable size variations and the degree to which a product’s dimensions can differ from the original design; these numbers are given as plus or minus (±) values. However, to account for the elasticity and flexibility of rubber in different conditions, manufacturers and engineers need a standardized approach to deciding the molded rubber tolerances for a project.

    You cannot use metal tolerance schedules when working with rubber. The tolerances used in metal or even plastic fabrication are just too tight to be applied to many rubbers and gasketing materials. A soft sponge rubber will have a much harder time staying within a tolerance as its shape will distort and change to to its soft and malleable nature. In fact, many elastomers are designed to expand and contract. This is essential for products like gaskets, as they need to squeeze into specific cavities and re-expand. Because many of these elastomers simply cannot meet metal tolerances due to their very nature, you could be wasting money and time trying to create a product to meet metal tolerances. Therefore, engineers need to consider common rubber tolerance schedules in their drawings.

    Learn more about the differences between metal tolerance schedules and the Rubber Manufacturers Association’s (RMA) rubber tolerance schedules, as well as how to make sure your products are manufactured according to your preferred standards.

    RMA Rubber Tolerance Schedules vs. Metal Tolerance Schedules

    Metals and alloys have stricter tolerance schedules because of the rigid nature of these materials. However, thermoset molded elastomers like rubbers cannot be made according to the same tolerances because, unlike metals, elastomers do not stay the same shape when compressed or under other conditions. Creating elastomer products using metal tolerance schedules would result in wasted money and time.

    RMA rubber tolerance schedules apply to elastomers like natural rubbers, ethylene propylene rubber, silicone elastomers, nitrile rubbers, and others. Each one reacts differently during the manufacturing processes based on molding temperatures, batch or compound variations, cure times, anticipated shrinkage, and even the textural features of the mold.

    Below are crucial considerations that influence elastomer and rubber tolerances.

    Mold Design

    The design of a mold itself should account for the variances in the rubber material. A mold is designed to create a part by pressing two plates (or more, depending on the complexity of the mold) together with a cavity in the middle that forms the rubber material into a shape. There are a few dimensions to consider in a mold’s design: the fixed and closure dimensions. The actual size of the plates themselves needs to be factored in (fixed dimension tolerance) as does the gap created when the plates are pressed together to form the product (closure dimension tolerance).

    Trim and Flash

    The flash (extra material) that is created in the parting lines of the mold where the rubber prevents it from closing needs to also be measured and controlled. If a material is prone to shrinkage, manufacturers can add more material to fill the mold. It is important to not only account for the outside flash but also be aware of any internal flash that might develop; if there is too much material on a critical part of the product, this can affect the functionality.

    Distortion/Shrinkage

    The inherent characteristics of different elastomers will result in different types of distortion and shrinkage based on how sensitive they are to heat or their ability to spring back to their original shape after being flexed (tensile strength). Many rubbers expand when heated and shrink when cooled, but the degree of size change varies. If a rubber shrinks after cooling, this is also essential to know when filling a mold.

    Environment

    To control for variances, manufacturers can manage humidity and temperature conditions, especially for rubber substrates that are more likely to absorb moisture from the air and swell.

    RMA Rubber Tolerance Schedules

    The Rubber Manufacturers Association (RMA) establishes standardized rubber tolerance schedules so manufacturers and engineers can effectively communicate and produce goods that meet all necessary standards. These rubber tolerance standards denote four tiers of necessary precision, ranging from a very high level of control to relatively lax (but still precise) standards. The levels are:

    • A1, High Precision: This is the most tightly controlled tier, and manufacturers must take all possible steps to reduce variance and distortion. It requires very precise molds, molds with fewer cavities, closely monitored mixing, and extensive inspections.
    • A2, Precision: This is a step down from A1 but still requires tightly controlled manufacturing and machining. Inspections are mandatory but less in-depth.
    • A3, Commercial: Commercial-grade rubber products are the most common, and they must generally fall within reasonable tolerances based on the industry and type of product.
    • A4, Non-Critical: These products have the least amount of precision and inspection. For this level, cost is often a priority over tolerance control.

    In addition to adhering to RMA standards, it’s also important to consider how the inherent characteristics of different materials affect final product tolerances. For example, soft rubbers with a 30 durometer hardness or lower can shrink by 3 to 4%. Harder rubbers between 65 and 85 durometers, on the other hand, only shrink up to 2% and thus can have tighter tolerances.

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    Rubbermill Manufacturing Tolerances for Fabricated Rubber Parts

    High-Quality Rubber From RubberMill

    Rubber goods manufacturers, engineers, and product designers should adhere to and communicate through RMA rubber tolerance schedules to keep everyone on the same page throughout production. At RubberMill, our processes and products adhere to RMA standards, and we work with every client to engineer and produce rubber goods that fulfill their needs. We prioritize clear communication regarding molded and die-cut rubbers to guarantee project success.

    Contact us today to learn more about molded rubber tolerances or to start your project.

  2. Common Elastomer Properties

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    What Are Elastomers?

    Elastomers are synthetic or natural materials capable of repeated stretching without losing their original shape. Natural rubber is one of the most widely known elastomers. Choosing the best elastomeric material for your industrial needs requires understanding the different types of elastomers on the market. Below are common elastomers and how they fall into various categories, with some overlap based on their appropriate applications.

    These general-purpose elastomers are some of the most common in use today:

    • Neoprene
    • Natural Rubber
    • SBR
    • Silicone Rubber

    Examples of high-temperature elastomers include:

    • Neoprene
    • Viton®
    • Silicone Rubber
    • EPDM

    Low-temperature elastomers include:

    • Silicone Rubber
    • Butadiene
    • Butyl
    • Natural Rubber

    High-performance engineered elastomers, such as neoprene and butadiene, have a higher price point and offer greater durability in harsh operating environments. These oil- and hydrocarbon-resistant elastomers are also essential, such as for pressurized seals in chemical manufacturing.

    Because the properties of many elastomeric materials have significant overlap, choosing exactly the right elastomer for your application requires working with a specialist in elastomer applications.

    Common Elastomer Properties

    An elastomer’s properties are the combined result of several performance factors.

    Specific Gravity

    Specific gravity refers to the elastomer’s density compared to water. This property provides several indications of the elastomer’s strength, weight, and the media it can contain. Knowing the material’s specific gravity helps manufacturers evaluate the product’s ability to withstand heavier loads without becoming brittle, its wear resistance over time, and the rate at which it absorbs solvents and oils.

    Most elastomers have a specific gravity between 0.9 and 2.0. Viton®, urethane, and neoprene have the highest specific gravity out of all rubber materials at 1.86, 1.25, and 1.25.

    Durometer Range

    The durometer rating provides a relative comparison of hardness for materials. For example, most rubber materials are measured by either the Shore A or Shore D durometer scales. Shore A durometer ratings cover soft materials to certain semi-rigid and inflexible plastics. Shore durometers measure harder materials, including semi-rigid plastics and hard rubbers and plastics.

    Silicone rubber has one of the lowest durometer ratings (Shore A 20-30) of any elastomer, making it suitable for cushioning or molds. Nitrile has a higher durometer rating (Shore A 60-70), which makes it effective for high-pressure seals and gaskets.

    Strength

    There are several measures of elastomeric strength. It’s important to know what type of strength your elastomer application requires.

    • Tensile Strength measures the elastomer’s breaking point.
    • Elongation at Break indicates how much the elastomer will deform before it reaches the breaking point. A higher elongation at break value normally comes at the expense of lower tensile strength.
    • Tear Resistance denotes the level of force required to tear the material.
    • Impact Strength measures how well an elastomer resists sudden impacts and shock loads. Other variables, like the elastomer’s temperature and thickness, can affect its impact strength. Elastomers with the highest impact strength include natural rubber, SBR, and urethanes.
    • Abrasion Resistance shows how well the elastomer resists scraping, rubbing, erosion, and other mechanical forces. Examples of elastomers with exceptional abrasion resistance include polyurethane, nitrile, and SBR.
    • Compression Set Resilience is a measure of an elastomer’s height loss or deformation after withstanding a compressive force for some time. It also relates to how well the elastomer returns to its original shape. Seals, gaskets, and O-rings face continual compression, so they require elastomers with the best compression set resilience. Natural rubber generally has a very high compression set resilience, although this depends on the formulation.

    Temperature Resistance

    Elastomers also deteriorate under excessive heat. Heat aging and other temperature resistance tests can simulate the elastomer’s behavior under extreme temperatures and help establish its expected service life under particular conditions. Viton® and silicone rubber have the best flame resistance and highest operating temperatures, up to 400-485 °F.

    Low temperatures render elastomers brittle and stiff, and rubber crystallization is a risk mostly for non-vulcanized rubber. Silicone rubber has the best low-temperature resistance, as low as -180 °F.

    Elemental Resistance

    This property refers to an elastomer’s resistance to outdoor elements. These tests (and associated standards) help determine the material’s elemental resistance:

    • Dielectric Strength – ASTM (D-149)
    • Heat Aging – ASTM (D-573)
    • Ozone – ASTM (D-395)
    • Water – ASTM (D-1149, D-1171)

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    Properties of Elastomers

    Premium Elastomers From RubberMill

    With more than 30 years of experience in the industry, RubberMill provides OEMs across diverse industries with the high-quality nonmetallic parts they need. Our technical, engineering, and sales teams work together to help customers determine which elastomers will best meet their goals. We consider every design factor, delivering reliable custom gaskets, insulation, and acoustic and vibration control solutions.

    To learn more about which types of elastomers are most suitable for your specific product or application, contact us or request a quote today.

  3. ASTM Testing Methods for Elastomers

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    American Society for Testing and Materials (ASTM) is a global organization with thousands of members who are technical experts in different fields. They work to develop and publish comprehensive standards, consisting of test methods, specifications, classifications, guides, and best practices for different materials, products, and systems used in many industries.

    Ensuring the elastomers used in your products meet ASTM standards is a major step toward meeting product performance and safety requirements, quality expectations, and longevity.

    To aid in the classification of materials and products, all ASTM documentation uses a system of letters. The letters A through G designate broad material categories. Most elastomers are grouped under ASTM D, “miscellaneous materials and products.”

    In this article, we’ll focus on some of the many common ASTM testing standards for elastomer materials.

    Common Elastomer ASTM Test Methods

    ASTM test standards describe why and how to conduct specific tests on materials or processes. The standards explain the scope of the test, what it measures or observes, specifications for equipment used in testing, specimen requirements, and procedures for the test.

    Generally, the tests listed below allow manufacturers to measure and observe the properties, behaviors, changes, and limitations of different types of vulcanized thermoset rubbers and thermoplastic elastomers. To obtain accurate results, all tests must be performed under controlled conditions with specialized and properly calibrated machinery.

    Some of the most common tests for elastomers include, but are not limited to:

    • ASTM D412 (Tensile/Elongation). This is a test of the material’s ability to withstand tensile forces. Tensile properties including tensile strength, tensile stress at a given elongation, ultimate elongation (the point of rupture), and tensile set or residual deformation are measured before and after applying force. This test is conducted using a universal testing machine, also referred to as a tensile testing machine or pull tester.
    • ASTM D624 (Tear Resistance). This test measures resistance to tears by finding the force per unit thickness required for the specimen to rupture or tear. Typically, any materials that are tested to D624 also undergo ASTM D412 testing to measure tensile strength and elongation.
    • ASTM D395 (Compression Set). This test observes the material’s compression set, or its ability to retain elasticity after prolonged exposure to compressive stress. The test can be performed with a static force applied to the material or a rapid repeated deformation and recovery. This test is particularly applicable to elastomers used in seals, vibration dampers, and machinery mountings.
    • ASTM D2240 (Durometer). This is a method for measuring the durometer hardness of rubber materials. The material is compared to 12 established, universal reference scales called shore hardness scales (Types A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R). The test is performed by measuring the depth of an indentation made in the specimen under controlled conditions.
    • ASTM D573 (Heat Resistance). This test assesses physical and chemical changes to the material when exposed to heat. Elastomers must be able to resist deterioration of physical properties caused by thermal and oxidative aging. This testing procedure offers a way to assess certain performance characteristics of rubber under the specified accelerated conditions. Properties are measured before and after exposure.
    • ASTM D1171 (Ozone Resistance). This is a test to determine molded or extruded rubber products’ resistance to ozone cracking and outdoor weathering. The test does not apply to hard rubber materials but can be adapted to extruded or molded soft rubber materials, as well as sponge rubber used for automotive applications (i.e. window weatherstripping).
    • ASTM D471 (Fluid Resistance). Elastomers used for gaskets, seals, diaphragms, sleeves, and hoses are often exposed to fuels, greases, oils, and other fluids during operation. This test assesses a material’s ability to withstand the effects of these liquids by simulating operating conditions via controlled accelerated testing.
    • ASTM D297 (Chemical Analysis of Rubber). This is a group of quantitative and qualitative tests used to analyze the composition of natural and synthetic crude rubbers. The methods are divided into general and specific testing categories. Part A tests look at the type and amount of major constituent compounds, while part B tests determine the specific polymers present.

    Related Resources

    At RubberMill, we provide testing services for several of the ASTM tests commonly required for new product development.

    View our elastomer physical and analytical testing chart here.

    A chart of chemical resistance information for nine common elastomers is available here.

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    Elastomer Testing Services

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    Chemical Resistance of Elastomers

    Elastomer Products by RubberMill

    RubberMill is an ISO 9001:2015 certified non-metallic component manufacturer with over 30 years of experience. We are a trusted resource for ASTM testing as well as materials for custom die cutting, lamination, and more. A variety of die cut and molded parts are also available in stock.

    Please contact us or request a quote to learn more about our capabilities or to talk with an expert about your next project.

  4. The Industrial Flatbed Lamination Process

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    Flatbed lamination is a process that involves using pressure and heat to join multiple materials, producing a multi-layered composite with improved properties. Compared to PSA lamination, which involves creating a sticky, adhesive surface to bond materials with, industrial flatbed lamination can create specialized laminates such as multi-layered sheets or rolls.

    Industrial flatbed lamination is used across diverse industries for applications such as automotive components, packaging, insulating panels, and molding precursors. This process not only produces a high-quality finish but also can improve the appearance of products, add a protective barrier, and to reduce material thickness when desired.

    The Basics of Industrial Flatbed Lamination

    Flatbed lamination is used to combine different materials such as foam, film, fabric, and nonwoven materials to produce a composite material with improved characteristics. The main goal of industrial flatbed lamination is to create materials with highly specialized properties, such as enhanced structural integrity or insulation.

    This process is especially beneficial for creating products with a smooth, level surface from raw, uneven substrates. As such, it allows for the use of more economical materials compared to other lamination processes. Flatbed laminators also facilitate precise thickness reduction and material densification of certain foams, nonwovens, and other substrates.

    Depending on your particular needs, the adhesion between the materials being laminated can be achieved using thermoplastic adhesives in the form of webs, powders, and films. Some materials can even be laminated without the need for additional adhesives due to their inherent thermoplastic characteristics.

    Types of Industrial Lamination at RubberMill

    At RubberMill, we utilize highly advanced Pressurized Flatbed Laminating technology that employs zoned heating, cooling, and pressure to produce unique material composites. Using a range of material combinations as well as adhesive films and webs, we can create the desired end product. For example, we can combine nonwoven materials with films or fabric with foam.

    If the main goal is the application of pressure sensitive adhesives, RubberMill also offers PSA lamination services using dedicated equipment. The finished PSA laminated product can be converted into continuous rolls of stripping or cut into separate parts.

    With over three decades of industrial lamination expertise, RubberMill can deliver innovative solutions to meet the needs of various industries and applications. This level of experience allows us to provide finished laminated products that adhere to specific OEM requirements.

    The Technology Behind RubberMill’s Lamination Process

    Our advanced belt press lamination machine uses a horizontal flat conveyor run, allowing it to accommodate materials of various thicknesses and widths. By applying customized amounts of pressure, heating, and cooling, our machine enables precise control over the properties of the end product.

    To meet the needs of sensitive applications, RubberMill’s lamination process includes continuous full-width thickness monitoring, including product-specific settings that can be stored electronically for the duration of the laminating process. Our machinery is also capable of creating sheets with specific dimensions and can automatically trim the edges to ensure uniform roll width.

    Our lamination technology is highly cost-effective due to its high speed and minimal energy and adhesive consumption. This makes it a sustainable option for all of your industrial lamination needs.

    Benefits of Contract Lamination with RubberMill

    By outsourcing your industrial lamination needs to RubberMill, you gain access to the following benefits:

    • Cost savings.Outsourcing your lamination process reduces costs associated with investing in additional machinery and manpower.
    • Speed. Our level of expertise ensures a fast and efficient manufacturing process. This results in a quicker time-to-market for your laminated products.
    • Turn-key. Our in-house die-cutting capabilities allow RubberMill to provide a turn-key lamination solution. This eliminates the need for you to transport your laminated materials for further converting.
    • Eco-friendly. Industrial lamination is a more environmentally friendly alternative to flame bonding and other lamination processes that emit toxic fumes.

    Take Your Industrial Lamination to the Next Level: Contact RubberMill Today

    Contract laminating helps companies save significant amounts of time and money on specialized material finishing processes they’re likely unequipped for. At RubberMill, we offer contract flatbed lamination and well as other lamination services to deliver the unique composites you need. For more information about our industrial lamination capabilities, or to get started on your contract laminating solution, request a quote from us today.

  5. Thermal vs. Acoustic Insulation

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    Many types of heavy machinery, appliances, and other equipment require thermal and acoustic insulation to prevent excessive heat and noise. These products protect operators and keep machinery working reliably. As a leading provider of quality thermal and acoustic insulation products, RubberMill can help you better understand how these products work and the different types available.

    Thermal vs. Acoustic Insulation

    Thermal and acoustic insulation serve different functions but are used throughout many similar applications. Let’s explore what exactly these products are, their benefits, and the materials options available.

    What is Thermal Insulation?

    Thermal insulation is a product used to reduce heat transfer between solid objects, fluids, or gasses. It works by forming a lower temperature barrier between heat-producing components that prevents heat transfer. Thermal insulation is used throughout many industries, including medical, energy, industrial, and more. These applications all involve machinery that requires an optimal thermal environment for efficient performance.

    Benefits of Thermal Insulation

    Thermal insulation products provide a number of advantages:

    • Energy conservation
    • Hotspot prevention
    • Surface temperature reduction
    • Operator protection and comfort
    • Electronic component protection

    Common Types of Thermal Insulation

    There are two primary types of heat-resistant materials: heat reflection and insulation. Insulation keeps heat confined within a space, minimizing convective and conductive heat flow. Radiant materials, on the other hand, reflect heat energy from traveling in a straight line, thereby reducing heat gain.

    Thermal insulation products are made using many types of materials:

    What is Acoustic Insulation?

    Also known as sound insulation, acoustic insulation reduces the transfer of noise. Sound is made up of vibrations and acoustic insulation products reduce noise by either redirecting it, absorbing it, or transmitting it. These products can be designed to target specific noise frequencies.

    Benefits of Acoustic Insulation

    When acoustic insulation materials are used to line hard objects like engines or heavy machinery, the porous material prevents sound waves from reflecting back at workers and the nearby environment. These materials are utilized in automotive, HVAC, and appliance applications to provide quiet operation of the device.

    Common Types of Acoustic Insulation

    There are two main types of acoustic insulation: absorbers and barriers.

    Absorbers

    Absorbers take in and trap sound waves, reducing the amount of noise in an area and improving its acoustic conditions. Absorbers can be applied to walls, ceilings, floors, and even objects. They can be made from several materials:

    • Open-cell elastomeric foam
    • Melamine
    • Nonwoven fiber materials
    • Cellulosic fibers
    • Dimensional fabrics
    • Urethane
    • Glass fiber materials
    Barriers

    Acoustic barriers block noise from transmitting between locations. In this instance, sound is not absorbed by the material but bounced back to the original location. Common types of acoustic barriers include steel or concrete. While durable, these options can be expensive to manufacture and ship and are not very eco-friendly. This type of insulation is also limited in the sense that it is for larger projects such as construction walls, whereas foam absorbing materials can be used in tight-fitting appliances and automotive parts.

    Thermal and Acoustic Insulation Products From RubberMill

    Thermal and acoustic insulation products are used throughout numerous industries, including automotive, consumer appliances, heavy machinery, and more. Each of these applications requires reliable, high-quality products to ensure operator and equipment safety. RubberMill has over 30 years of experience meeting OEM needs for quality and precision insulation products. To learn more about our solutions, contact us or request a quote today.

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