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This chapter will cover the definition of rubber sheets, their production methods, and their various applications.
Rubber sheets are essentially flat pieces made from rubber or cloth coated with rubber, designed to enhance the mechanical properties of the material, such as improved tensile strength and reduced elongation.
This high-quality, versatile material is widely used in applications involving oil and petroleum, including fuel pumps, control valves, and similar components. It is adaptable for various purposes and suitable for many different uses.
The production of rubber sheets varies based on factors such as length, width, thickness, color, size, and the intended application.
The primary types of rubber sheets include recycled rubber, reclaimed rubber, synthetic rubber, and natural rubber. Recycled rubber is typically produced from crumb rubber derived from old tires, which are reassembled using adhesives. This should not be confused with reclaimed rubber, which is also sourced from discarded tires but undergoes de-vulcanization before being re-vulcanized to create new rubber sheets.
Synthetic rubber is primarily made from butadiene and styrene, by-products of petroleum, and can be combined with various other materials to produce sheets with diverse chemical and physical properties suitable for many uses. Lastly, natural rubber is obtained from the latex of the Hevea brasiliensis tree found in South America, Africa, and Asia. The latex is harvested from the tree, allowing it to regenerate, and is processed to create natural rubber.
These are polymers used independently, such as Polystyrene, Polyethylene, and Polypropylene. They are relatively easy to reuse, and recycling can be performed multiple times without significant degradation in quality.
Compounded and blended polymers, such as PVC and ABS, are less stable and more prone to deterioration during recycling. Although additives can be used to improve their stability, these enhancements are costly and not widely applied.
As their name states thermoset plastics are differentiated by the fact that when processing they are ‘cured’ and form a 3-dimensional network. Whilst thermoplastics can be described as long thin molecules laid out in a random manner but without any firm bond between the molecules. The curing process changes the thermoset plastics from a similar state to that of thermoplastics into a state where permanent bonds are formed at various points in the chain with some other molecules.
These materials are considered a specific class of thermosets. Before vulcanization, they are mostly thermoplastic, meaning they can be physically reshaped without significantly losing their properties. Vulcanization involves molecular cross-linking, but the process of de-vulcanization is not yet fully understood. Due to various unique challenges in the rubber industry, most research has focused on recycling issues. The two main forms of recycled rubber are Reclaim and marketed-Crumb. However, the problem of de-vulcanization remains unresolved and unexplored.
Optimal characteristics of various polymers are achieved through compounding with mineral fillers and other polymers. By incorporating a variety of compounding ingredients, a wide range of properties can be obtained. This approach is particularly effective for rubbers, thermoset plastics, and PVC, which is categorized as a thermoplastic.
When selecting materials for making rubber sheets, several considerations must be taken into account:
There are four primary methods for producing rubber sheets: molding, extrusion, latex dipping, and calendaring.
Molding involves shaping a compound by using a mold to achieve a specific form. This method is generally cost-effective for producing more complex items, as it allows for customized, smaller quantities, potentially lowering the costs compared to other methods. However, it is less commonly used compared to extrusion.
Molding consists of three main manufacturing processes: compression molding, transfer molding, and injection molding. Compression molding is the oldest and less expensive method. With compression molding, a rubber compound is made into a blank (a chunk of rubber); the blank then gets placed into a mold cavity to be shaped. The heating time is slow, which results in a long curing time; the heating can vary from three minutes for thin walls to a few hours for thick walls.
Some advantages of this method include being suitable for rubber compounds with large surface areas and therefore the ability to be used for rubber compounds with high viscosity and poor flow properties. On the negative side, the process is time consuming with a low production rate. The compression molding process is utilized in the manufacture of products like O-rings, seals, silicone wristbands, and electrical insulators.
Transfer molding represents an advanced step in manufacturing designed to address some of the limitations of compression molding. Initially, a blank is placed into the chamber and then distributed across multiple cavities. During this phase, the rubber is pre-heated, which aids in its flow through the channels. This pre-heating process shortens curing time and enhances the rubber's ability to fill the mold cavities effectively. Nonetheless, this method involves higher costs and more complex mold designs.
Extrusion starts with an unvulcanized compound being put into an extruder. Once it is inside the extruder, it gets carried forward to a dye, which is a specialized manufacturing tool used to mold the rubber. When the compound reaches the dye, the pressure from the process forces it through the opening of the extruder. Then, the extruded product will need to be vulcanized before it can be deemed usable. It is crucial to remember that any rubber compound should have a “cure package” already blended in before vulcanization. During the vulcanization process, the rubber may swell or shrink, after vulcanization the length of the rubber extrusion could also be impacted. Extrusion manufacturing has the merit of being able to produce products with lower production costs and in high volumes. Some of the common rubber products produced from extrusion include profiles, cords, tubing, and gaskets.
Latex dipping involves immersing thin-walled molds into a latex solution and then gradually withdrawing them. To achieve a greater thickness, the item can be dipped multiple times in the latex compound. After dipping, the product is finished through a vulcanization process. Depending on the product’s requirements, additional post-treatments might be necessary. Custom dipping techniques can be employed to refine the final product to meet specific needs. Dip molding is advantageous for creating latex items with thin walls and intricate shapes, which are challenging to achieve with extrusion. Common examples of dip-molded items include grips, rubber gloves, balloons, bladders, and tubing.
Another widely used manufacturing technique is calendaring, where softened material is pressed between counter-rotating rollers. These rollers compact the material, and the thickness of the final product is determined by the spacing between the rollers, which can be adjusted to achieve different thicknesses. As the material moves through the cooling rollers, it undergoes vulcanization. Calendaring offers advantages such as precise control over product thickness and the ability to produce thinner and wider parts compared to extrusion. However, it is important to note that calendaring tends to have higher operating costs relative to other methods.
Rubber sheets can be assembled into cylindrical shapes for protective sleeves or cut and shaped into conical profiles for marine applications, such as mast boots. There are two primary methods for joining these sheets: using adhesives or through vulcanization. While high-quality adhesives are available and can create strong bonds between rubber surfaces and other materials, they may not always be suitable for all conditions. Adhesive joints may fail under extreme pressures or temperatures, degrade when exposed to certain chemicals, and may not be fully waterproof. In contrast, vulcanized joints offer enhanced durability and a better aesthetic finish, making them a preferred choice in demanding environments.
Creating a vulcanized joint involves several key steps. Initially, the rubber profile must be cut to optimize the strength of the bond; a simple perpendicular cut might not be sufficient. A dovetail joint is often recommended for its effectiveness. The next step is to prepare the material, typically through mechanical means such as buffing, to ensure proper bonding.
Before vulcanization, a bonding liquid compound is applied to the joint area. A mold or jig is then used to hold the components securely in place during the vulcanization process. For complex joints or profiled extrusions, the joint is subjected to pressure and heat to cure the rubber and establish a chemical bond through vulcanization. This method creates a bond distinct from those achieved with adhesives alone. The choice of method depends on the specific requirements of the bond. While vulcanized joints provide a strong bond, they may not achieve the dimensional precision of a fully molded product. This approach can be cost-effective and time-efficient, depending on production quantities. When joining extruded products into rings or other profiles, achieving consistency can be challenging, especially if the profile is deep and the internal diameter is small.
The two main specifications are:
This specification encompasses flexible cellular rubber products such as sponge rubber and expanded rubber. However, it does not include ebonite cellular rubber or latex foam rubber. The base material for these closed or open-cellular products can be composed of natural, synthetic, blended, or reclaimed rubber. Additionally, they may incorporate a variety of polymers and chemicals, with both inorganic and organic additives used to enhance their properties.
For manufactured products, the specification stipulates the use of synthetic rubber, vulcanized rubber, or rubber-like materials, either alone or in combination. It also outlines the methods for inspecting these products to ensure they meet the required standards.
The different types of rubber sheets are:
These materials exhibit excellent dynamic and rebound characteristics and are resistant to tearing. For packaging applications, they serve effectively as anti-vibration pads. They offer superior dynamic performance, rebound, elasticity, and mechanical strength. Additionally, these sheets are commonly used as general sealing materials. Their versatility makes them widely adopted in various environments without the need for specialized conditions.
These materials are ideal for corrosion-resistant coatings and are commonly used in power transformers and other electrical applications. They offer excellent resistance to petroleum products, oils, flames, acids, and alkalis. In industrial settings, neoprene rubber sheets are employed for cushioning external metal cases to protect their contents, as corrosion-resistant coatings, for noise isolation in power transformer installations, and for various other electrical uses.
Neoprene rubber with a 40A durometer rating is highly compressible and can endure minimal force or pressure, making it easy to compress.
Neoprene rubber with a 50A durometer rating also withstands lower levels of force or pressure and is similarly easy to compress.
Neoprene rubber with a 60A durometer rating offers a balanced hardness, suitable for applications involving water, oil, beverages, and food. It remains durable and weather-resistant.
Neoprene rubber with a 70A durometer rating provides greater hardness and strength, making it more resistant to compression compared to softer grades.
Nitrile rubber is specifically engineered to resist oil and solvent exposure, making it ideal for use in electrical transformers, sealing applications, the food industry, and in environments involving dielectric oils for electrical systems. It is commonly used in flange joints and other connections exposed to fluid or atmospheric pressures.
Hydrogenated nitrile rubber (HNBR) offers superior chemical and oil resistance compared to standard nitrile rubber. It can endure higher temperatures and provides outstanding resistance to fuels, oils, various chemicals, ozone, and steam. HNBR also boasts excellent tear and tensile strength, abrasion resistance, and elongation properties. However, it is more expensive and has limitations, such as poor electrical insulation, limited flame resistance, and incompatibility with polar organic solvents and aromatic oils. HNBR is predominantly used in the automotive industry for various applications, including hoses, static seals, and belts, among others.
Due to their resistance to acids, alkalis, and ketones, these materials are well-suited for outdoor and high-demand environmental applications.
These materials feature low permeability and resistance to high temperatures, weathering, ozone, and various chemicals. They are particularly well-regarded in the pharmaceutical industry for their reliability and durability.
This type of sheet is constructed from natural or synthetic rubber and includes one or more layers of fabric reinforcement. This layering provides enhanced strength and durability under high pressure, making the sheets suitable for a range of applications.
Styrene-butadiene rubber (SBR) is a cost-effective synthetic rubber known for its abrasion resistance, excellent impact strength, high tensile strength, and good resilience. However, SBR has limited resistance to ozone, sunlight, oils, and steam. It is primarily used in automotive components, tires and tire-related products, and various mechanical rubber goods.
Viton™ sheets are made from fluoroelastomer materials, widely used across various applications. This durable fluoropolymer elastomer offers temperature stability from -20°C to 205°C. Viton™ can handle fluorinated solvents but may degrade if the incorrect grade is used and tends to be expensive. It is one of the most popular elastomers for sealing applications, including gaskets, O-rings, and seals, alongside nitrile.
Developed in the 1950s for the space program, Viton™ fluoroelastomers are renowned for their exceptional heat resistance, withstanding temperatures above 204°C for over 10,000 hours and up to 325°C for shorter periods. Besides its thermal resilience, Viton™ also resists most chemicals, making it a versatile choice for demanding applications.
Butyl rubber is an excellent choice for shock absorption due to its superior properties. It exhibits outstanding moisture resistance, low gas permeability, and excellent durability against aging, heat, ozone, weather, chemical exposure, flexing, tearing, and abrasion. Additionally, butyl rubber is resistant to ester-based phosphate hydraulic fluids and provides exceptional electrical insulation. However, it may experience issues like blistering, creeping, and air entrapment during manufacturing. Common applications for butyl rubber include O-rings, sealants, tank liners, and seals for vacuum applications due to its gas-impermeable nature.
This chapter will explore the various applications and advantages of rubber sheets.
Flooring and roofing applications are the most popular uses of rubber sheets in the industry. Rubber provides good resistance to substances like oil and petroleum, ultra violet lights, and oxidizing elements. Furthermore, it has the capacity to maintain flexibility even in cold temperatures. It is elastic and that even makes it suitable for various kinds of shock absorbers and for specialized machinery mountings designed to reduce vibration.
Rubber sheets are utilized across a wide range of applications, including industrial buildings, agricultural machinery, and Original Equipment Manufacturer (OEM) parts. They are also commonly used in commercial and residential settings such as storerooms, gyms, dance studios, garages, under shower pans, in drainage systems, and for weather stripping, as well as various construction and remodeling projects.
These sheets find applications in virtually every industry, including scientific, footwear, medical, engineering, railways, automotive, defense, aerospace, and marine sectors. Examples include their use in railroad tank cars, as linings for storage tanks, and in the creation of floor mats, gaskets, bearing pads, horse stall mats, sandblasting equipment, orthopedic footwear, and heavy-duty curtains. Rubber sheets are also used in wet areas like under showerheads and in washrooms to enhance slip resistance.
As the use of rubber sheets continues to expand, their demand is expected to grow significantly. Rubber sheets offer a cost-effective alternative to other materials and their versatility in combining with various products further enhances their appeal in the industrial market.
The benefits of rubber sheets are:
Protection of Work Surfaces – Rubber sheets provide excellent cushioning and impact absorption, making them effective at safeguarding work surfaces in industrial environments from damage.
Safety – Rubber is known for its safety benefits, being user-friendly and suitable for public areas. Its non-slip and shock-absorbing properties contribute to a safer environment for both users and staff.
Protection of Equipment – Rubber is an ideal material for protecting machinery due to its shock-absorbing qualities, helping to reduce wear and tear on equipment.
Anti-Vibration – Rubber effectively dampens vibrations from machinery, which helps prevent annoyance and reduces the risk of damage from excessive vibrations.
Resistance – Rubber is resistant to electricity, discoloration, and rust, enhancing its durability and longevity in various applications.
Versatility – Rubber sheets can be cut into a variety of shapes and sizes, including pads, washers, and gaskets, making them highly adaptable to different needs.
Availability – Rubber sheets come in various materials and colors, making them suitable for numerous settings, including retail and commercial applications. They can be customized into various forms, such as gaskets, washers, and pads.
Natural rubber has limited resistance to hydrocarbons, fats, oils, and greases, which can lead to swelling or dissolution upon contact with these substances. Ethylene propylene rubber (EPDM) sheets are unsuitable for food applications or exposure to aromatic hydrocarbons. They are commonly used for high-temperature water vapor seals, bathroom equipment seals, brake system components, and radiator seals in automotive applications. Silicone rubber sheets, though effective, are generally more expensive. Additionally, some rubber sheets can be affected by moisture and may not have a long lifespan. They may expand with temperature fluctuations, so they should be used in environments where these properties can be managed appropriately.
Rubber sheets can have a long service life with proper care and maintenance. This includes initial cleaning, regular upkeep, and the application of suitable finishes. It is advisable to use doormats at main entry points and to perform daily cleaning with a wet vacuum to remove dirt particles from the grooves of the sheet.
Avoid using chemicals on rubber sheets as they may cause adverse reactions. In healthcare settings, such as labor rooms and neonatal units, rubber sheets should be washed with running water and treated with an antiseptic solution. After cleaning, they should be hung to dry, then powdered before being rolled and stored.
If cracks, scratches, or thinning are observed on the rubber sheet, it may no longer maintain its insulation properties and should be replaced promptly. To prevent aging and deterioration, avoid exposing the sheets to direct sunlight, sharp metal objects, or excessive heat. Additionally, keep them dry and clean, and prevent contact with acids, alkalis, and other corrosive substances to avoid damage and maintain effective insulation performance.
Therefore, rubber sheets are basically material that is made from rubber. They are cost effective and safe for use by the public. Manufacturing rubber sheets is a lucrative business as they have immense and various uses in every industry worldwide (chemical, biological, commercial, environmental, and physical). They can be molded into various shapes and in various colors.
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