This article will take an in-depth look at rubber to metal bonding.
The article will bring more understanding on topics such as:
This chapter will cover the topics of rubber-to-metal bonding, the characteristics of bonded rubber, and the methods for gluing rubber to metal.
Rubber-to-metal bonding is a process that creates a strong and durable connection between rubber and metal components. Common adhesives used in this process include rubber-based adhesives, silicone adhesives, two-component adhesives, polyurethane polymers, and epoxy resins.
Rubber-based adhesives are frequently used due to their strong bonding capabilities and flexibility. For applications requiring a more robust and secure bond, two-component adhesives and polyurethane polymers are preferred. The choice of bonding agent depends on the specific environment in which the part will be used and the requirements of the industry manufacturing the component.
Metal and rubber can be combined using methods such as molding and adhesion. The choice of process depends on factors like production volume, available manufacturing space, speed of production, and equipment costs.
Several processes can be employed in molding methods, including the following:
This process involves molding rubber over a metal substrate, resulting in a part where both the rubber and metal are visible. It allows for the creation of multiple layers of metal and rubber if required. One of the most common applications of this method is in the production of seals.
In complete encapsulation, a metal inert will be placed in a mold before the rubber is added. This process is also well known as the insert molding. The final output will be a part in which the metal is barely noticeable. Encapsulation is common in parts where wiring is used, and these include o-rings.
The two most commonly used molding methods for rubber-to-metal bonding are transfer molding and injection molding.
In transfer molding, metal components are placed into a heated mold. Solid rubber is then introduced into the mold using a heated plunger, which pushes the rubber around the metal parts to create a bond.
The mold is then cured and vulcanized under high pressure and elevated temperature.
This method, similar to transfer molding, involves placing a metal component into the mold during the initial stage.
Next, a liquid elastomer is injected into the mold. The part is then removed after the mold has been cured and vulcanized under high pressure and temperature.
Compression molding is a closed-mold process where an uncured rubber preform or profile is placed into a heated mold. High-pressure clamps apply pressure to fill the mold cavity, causing the uncured rubber to conform to the shape of the mold. The heat and pressure liquefy the rubber, which then cures in the mold.
Once the curing process is complete, the rubber solidifies and is ejected from the mold. The final step involves trimming the part before it undergoes testing.
The steps involved in rubber to metal bonding are:
Most vibration isolation mounts are produced using either natural rubber or neoprene. Upon receiving natural rubber latex or neoprene, various fillers and additives are mixed in to achieve the desired properties. The rubber is then processed through rollers to ensure uniform distribution of these ingredients throughout the material.
The blended rubber is then formed into pellets. These pellets can be used for transfer molding or cut into strips for injection molding. The rubber is stored in a climate-controlled environment, remaining in an uncured state until it undergoes curing during the molding process.
After the vulcanization or curing process, natural rubber exhibits excellent mechanical properties such as high tensile strength, abrasion resistance, tear strength, impact resistance, and durability. These qualities make it suitable for use in environments with temperatures ranging from -40°F to 190°F.
Neoprene, a synthetic elastomer, is produced by polymerizing chloroprene. After the vulcanization process, neoprene's mechanical properties are comparable to those of natural rubber.
One of neoprene's advantages is its superior oil resistance compared to natural rubber. Due to its properties, neoprene is suitable for use in environments with temperatures ranging from -30°F to 212°F. Both neoprene and natural rubber are commonly used in various industrial applications, including pumps.
To ensure a strong bond, the metal surface must be slightly rough and free of oil. A common method for surface preparation is phosphate dipping, which removes oils and creates an ideal surface while also serving as a rust inhibitor. Alternative preparation methods include grit blasting, tumble blasting, or wiping down the surface.
Alkaline cleaning processes or solvent degreasing methods are used to remove oils from the bonding surfaces. If rust and debris are present, they can be removed using aluminum oxide grit blasting or machining. Once cleaned, metal components should be stored and protected in a low-humidity environment.
Various metals are used for rubber-to-metal bonding, including steel, aluminum, brass, beryllium, and copper. The choice of metal depends on the intended application and the environment where the bonded metal will be used. For cost efficiency, manufacturers often select inexpensive yet durable metals.
Once the metal surfaces are cleaned, the adhesive can be applied. Often, a two-coat adhesive system is employed for bonding natural rubber or neoprene to low carbon steel. This system typically consists of a primer layer and an adhesive topcoat.
The primer can be applied using various methods, such as dipping, rolling, spraying, or brushing. Generally, a dry film thickness of 0.2 to 0.4 mil is recommended for the primer, while the adhesive layer should have a thickness of 0.5 to 1 mil. Proper agitation of the primer and adhesive before application ensures that the ingredients are evenly distributed throughout the product.
After application, the components should be allowed to dry at room temperature. To accelerate the drying process, a circulating air oven can be used. Once dry, the components should be used in the molding process as soon as possible to minimize the risk of surface contamination.
Natural rubber and neoprene are typically processed using either transfer molding or injection molding techniques. In these processes, the mold is heated to temperatures as high as 340°F. Metal components that have undergone the two-coat adhesive application are then loaded into the mold.
After the molding process is complete, samples from the production lot must be tested. This involves breaking a sample piece to ensure it meets the required tensile strength specifications. The break should occur through the rubber, not at the bond. Additionally, a load deflection test may be conducted to verify that the spring rate is accurate.
Bonded rubber serves as an alternative to traditional poured rubber surfaces. While it offers a similar seamless one-piece surface, bonded rubber is made from larger pieces compared to poured rubber. It provides a natural look for outdoor facilities by being applied as a single-layer system on-site. Bonded rubber is produced by combining shredded rubber mulch with a binding agent and smoothing it by hand. Like most unitary surfaces, bonded rubber excels in safety features. Its natural properties offer excellent impact absorption and help meet critical fall height requirements as specified by ASTM standards.
In addition to offering uniform impact resistance, bonded rubber provides several benefits. It does not conceal hazardous objects, and its textured surface enhances slip resistance. Unlike other materials, bonded rubber is resistant to being displaced or scattered on walkways, which helps prevent slip hazards. Its effectiveness remains intact even in high humidity or extremely cold temperatures due to its resilient properties.
Bonded rubber is non-toxic, meaning it does not pose risks if it comes into contact with the eyes or mouth. It also inhibits microbial growth, including mold, mildew, and bacteria. With a long lifespan and low maintenance requirements, bonded rubber often outperforms less expensive alternatives. It offers design flexibility and is ideal for playground surfaces or pathways within playgrounds.
Its appearance is more natural compared to poured rubber surfaces because it is applied in mulch-like pieces, which can be dyed in various colors.
Different properties of materials often result in a trade-off between rigidity and flexibility. The choice of adhesive for rubber to metal bonding can be influenced by the specific application area and the size of the surface to be bonded. These factors play a crucial role in determining the most suitable adhesive to ensure a strong and effective bond.
For small areas or strips, superglues such as cyanoacrylate adhesives can be effective. However, for larger surfaces, a two-component adhesive is generally preferred. Contact adhesives based on polychloroprene or chloroprene rubber are suitable for bonding larger areas, such as square meters.
Before bonding, the surfaces must be pre-treated to ensure proper adhesion between metal and rubber. This involves using solvents, cleaning agents, and other substances to remove any residues. Sanding is essential if the metal has been coated or treated. It's important to note that the effectiveness of the bond can be challenging to predict, as rubber may deteriorate or weaken over time.
To ensure the effectiveness of the rubber-to-metal adhesive, it is advisable to test it on a small area first and evaluate the results after a few days. If the test is successful, the adhesive can be confidently used for the entire surface. Once the adhesive has fully cured, modifications such as drilling and milling can be performed on the bond. Additionally, rubber-to-metal adhesives are effective for filling cracks, bumps, or holes, and are particularly useful in applications involving aluminum housings.
This chapter will cover rubber bonding techniques, the various rubber products available, and the specifics of silicone bonding.
Proper surface preparation is crucial for successful rubber-to-metal bonding. Contamination of the surface can occur during the bonding process due to improper application of the adhesive. Every step in the bonding process must be handled meticulously to ensure a strong and secure bond. Understanding the bonding agent, the type of metal, and the specific process is essential for successful bonding.
Before proceeding with rubber bonding, it is necessary to use a solvent degreaser to remove any mold release agents, slip additives, or other processing lubricants from the surfaces. A quick wipe with isopropanol alcohol is often effective. Acetone can also be used, but its aggressive nature may attack some types of rubber, so caution is required.
Even after wiping the surface clean, rubbers may still contain plasticizers that can migrate back to the surface over time, potentially leading to debonding at a later stage.
Cyanoacrylate instant adhesives are generally more effective for bonding rubber compared to epoxies. Epoxies can often peel the rubber off a surface. Cyanoacrylate adhesives cure quickly, allowing for immediate assessment of their effectiveness. It is best to apply a small amount and ensure that the components are tightly aligned and pressed together during the curing process.
Types of rubbers such as natural rubber, silicone rubber, and EPDM can be challenging to bond, often resulting in joints that fail even after ample curing time. For difficult rubbers like EPDM and natural rubber, specialist cyanoacrylate adhesives, such as Permabond 105, are recommended. These adhesives can effectively bond without the need for a primer. For silicone rubber bonding, it is advisable to use a primer like Permabond POP in conjunction with Permabond 105. For applications requiring flexibility, Permabond 2050 Cyanoacrylate is recommended. This adhesive maintains flexibility in the joint, which is especially useful for bonding soft o-rings.
While cyanoacrylate adhesives offer several advantages, they are not the only option for rubber bonding. Their benefits include excellent adhesion, which often results in the rubber tearing rather than the bond breaking. The rapid curing time of cyanoacrylate makes it ideal for high-speed assembly processes on production lines. However, drawbacks include its inability to realign joints after bonding, as it sets in seconds. Additionally, cyanoacrylate has a limited gap-filling capacity (up to 0.5mm) and cannot cover large areas effectively. Its strong odor can be off-putting, which is why contact adhesives might be preferable for larger surfaces, though they can also be challenging to align.
For a cost-effective bonding solution, solvent-based rubber bonders can be used. However, silicone-based adhesives are better for silicone rubber bonding, though they can be messy and slow to cure, making them less suitable for rapid production lines.
Permabond TA46XX series are two-part structural acrylic adhesives designed for bonding difficult plastics such as polypropylene, polyethylene, and PTFE. These adhesives also provide good adhesion to some rubbers, though not to silicone rubber. Compared to cyanoacrylate, structural acrylics offer accurate alignment and spreading due to their slower cure time. They are not solvent-based and have a less pungent odor. The TA46XX series is also suitable for applications where rubbers may later be submerged in water, thanks to their excellent environmental durability.
Rubber products are typically categorized into three major classes: tires, industrial rubber goods used in motor vehicle and ship construction, and consumer goods such as footwear and mats. These products are made from various forms of rubber, including hard, raw rubber, latexes used for seamless gloves with thin walls, rubber threads, and foam rubber used in automotive seats and furniture.
The production of rubber products from raw rubber involves two main stages. In the preparation stage, rubber stock is created by mixing raw rubber with essential ingredients using machines like internal rubber mixers or milling machines.
In the final stage, the semi-finished rubber product is vulcanized. This process involves heating the rubber to temperatures between 140°C and 200°C and applying pressures ranging from 0.3 to 20 meganewtons per square meter.
The equipment used in the vulcanization process includes presses, boilers, and various other machines, depending on the type of rubber products being manufactured. To ensure strong bonds between the rubber and any textile materials or metals used in the product, these materials must be pre-treated before the vulcanization process. This pre-treatment is crucial to achieving optimal performance under operational conditions.
Textile materials are bonded to rubber using rubber cement or other adhesives in specialized machines, followed by coating with a rubber stick-on coating. Metals are degreased using organic solvents and then coated with a layer of cement or brass. This process, known as brass plating, is accomplished through electroplating in a bath.
Industrial rubber goods are typically categorized into major groups: molded goods, unmolded goods, conveyor belts, hoses, and belts.
These goods are produced through a process that simultaneously molds and vulcanizes rubber stock. This is accomplished using a compression mold mounted on a press or through injection molding. Examples of molded industrial rubber goods include packing parts, shock absorbers such as gaskets, dust protection components, and rings with various cross-sections.
Unmolded industrial rubber goods are used for sealing doors and windows in motor vehicles, aircraft, and for hermetically sealing construction panels. These goods are produced by extruding rubber stock into cords of various shapes, lengths, and cross-sections. The semi-finished products are then vulcanized either in continuous action apparatus or through periodic batching in boilers. The resulting seals can be either monolithic or porous.
These are many types of conveyors and made for the transportation of friable and other materials. Using fabrics made from synthetic fibers, cotton, or other fabrics which can contain a tearing stress of about 65 to 300 kN/m reinforcement of conveyor belts is possible. A strong conveyor belt needs brass plated steel lines. The production of rubberized fabric belts includes assembling the core with the required thickness of rubber stock. The vulcanizing of the belt takes place in a press which has plates with a length of about ten meters.
Belts are flexible components used in belt drives for automobile engines, agricultural machines, and various industrial devices. There are several types of belts, including V-belts and flat belts. The production process for flat belts is similar to that used for conveyor belts: the rubber sheet is cut into strips to achieve the desired belt width, either before or after vulcanization. V-belts, which have a closed design and a trapezoidal cross-section, are assembled on machines and then vulcanized in boilers or diaphragm vulcanizers. The length and cross-section of the belt determine the appropriate vulcanization equipment needed.
Hoses are tubes which are flexible and they are used for conveying liquids, gasses, and other materials which are friable and this is done under excess pressure or under vacuum. The basic elements included are the inner sealing which is of rubber, a carcass of heavy duty and an outer layer which is also made of rubber. Suction hoses contain a possible vacuum of 80 kN/m² and are made with a metal spiral on top of adding the heavy duty carcass. Through extrusion, the inner and outer layers of a hose are made. The hose is either wrapped using a fabric brand or molded using a shell made of lead. It is then vulcanized in a boiler and then the shell is removed after vulcanization.
Rubber footwear is categorized into three main types: industrial, athletic, and everyday footwear. Industrial footwear is designed to protect the feet from harmful substances, extreme temperatures, and physical injuries. Examples include boots used by miners, fishermen, and dielectric rubber footwear.
The production method used for rubber footwear can also distinguish different types. For example, glued rubber footwear is assembled from previously produced parts on conveyor lines, glued together, lacquered, and then vulcanized in boilers. Galoshes, made using impact stamping on special presses followed by vulcanization in boilers, represent another production method for stamped rubber footwear. Molded rubber footwear is created by pressing rubber into molds and then vulcanizing the material.
Boots and footwear with fabric upper sections can be produced using these methods. Injection molding involves compounds such as polyvinyl chloride and thermoelastic plastics. Liquid molding, a more modern technique, uses liquid oligomers, including polyurethanes and plastisols, to create the footwear.
Silicone is an elastomeric material known for its high performance and flexibility, making it ideal for use in seals and gaskets. Surface preparation for silicone bonding is generally minimal, primarily because silicone surfaces often contain plasticizers that migrate to the surface, which can complicate bonding.
For improved surface preparation, a solvent wipe containing isopropanol is commonly used. This helps clean the surface and remove any processing lubricants, providing a better binding surface. However, some solvents, like acetone and white spirits, can be overly aggressive and may leave behind residues that could affect bonding quality.
There are not as many industrial adhesives which can properly be used in bonding with the silicone. To have a faster cure and exclude the use of isocyanate chemicals, polyolefin primer such as Permabond POP can be used. This primer can be used to prime the surface of the silicone and then take cyanoacrylate in the bonding of the parts. Permabond 2050 is usually preferred as it is flexible and doesn’t affect the feel of the silicone. The bonded joint can be hard to detect as it will remain soft like the original material. This result is great for the use in seals and o-rings as the design will not have a hard or crunchy part.
This chapter will explore the uses and advantages of bonding rubber to metal.
Rubber to metal bonding is highly versatile and widely used across various industries. In the automotive sector, it is utilized for creating seal gaskets and engine mounts. In agriculture, this bonding method is employed to manufacture components such as ball joints and stabilizers. Additionally, the medical industry benefits from rubber to metal bonding in the production of O-rings and pump compressor isolations.
With the expansion of the construction industry, rubber to metal bonding is also applied in the creation of conveyor belts, which are essential for efficient construction due to their strength and durability. In the mass transit sector, it is used for making valve seals and pedals. The durability provided by rubber to metal bonding ensures longer-lasting parts, contributing to both user safety and equipment reliability. The effectiveness of these applications depends on the use of appropriate materials.
Rubber to metal bonding streamlines the assembly process by reducing the number of components needed. By directly bonding the rubber to the substrates, fewer parts are required, which enhances assembly efficiency and decreases both labor and production time. This method results in a more robust bond, leading to durable materials with an extended lifespan. Additionally, the substrate gains resistance to harmful factors such as water and corrosion. Rubber is also a more environmentally friendly option compared to other bonding agents, as it is free from lead. Furthermore, rubber to metal bonding supports a broad temperature range, making it suitable for use in demanding conditions without compromising performance.
Rubber to metal bonding is a phrase that is generic in nature as it covers a number of interdependent processes. In general terms this includes combining the rubber element with a steel or metal element for it to attain properties which are advantageous in nature. Some of the rubber bonded elements obtained are used in areas like automotives and in other engineering applications. Larger units are used in construction to decouple movement in buildings in translation ways.
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