Molding is a manufacturing process that uses a mold - the latter being a solid container used to give shape to a piece of material. It is a forming process. The form is transferred from the mold to the material by...
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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 discuss what rubber to metal bonding, bonded rubber and glue rubber to metal bonding.
Rubber to metal bonding is a process where a permanent and durable connection is produced between rubber and a metal part. Bonding adhesives include rubber based adhesives, silicone bond, two component adhesives, polyurethaned polymers, and epoxy.
The most common form of adhesive is rubber based since it bonds well and is flexible. Two component adhesives and polyurethane polymers are used when a very strong and secure bond is required. The factor that determines the type of bonding agent is the environment where the part will be used and the industry that produces the part.
There are ways in which metal and rubber can be combined, such as through molding and adhesion. One may choose a process based on product volume, manufacturing space, speed, and price of equipment.
There are several processes that can take place in the molding methods, and these include:
This process takes place when rubber is molded over a metal substrate. With an over molded part, both the rubber and the metal is noticeable. This creates enough room to create multiple layers of metal and rubber if they are to be needed. One of the most common over-molded parts are 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.
For rubber to metal bonding, the two most common molding methods are the transfer molding and the injection molding.
In transfer molding, the metal parts are inserted into a mold that is heated. Solid rubber is then pushed into the mold and this is done using a heated plunger where it fills around the metal parts.
This mold is then cured and also vulcanized at a high pressure and high temperature.
This method used in rubber to metal bonding is also similar to transfer molding in the process they both use. In this first stage, a metal piece is inserted into the mold.
After a liquid elastomer is injected into the mold. The part is later removed once the mold has been cured and vulcanized at a high pressure and a high temperature.
Compression molding is a closed mold process that involves placing an uncured rubber preform or profile in a heated mold. Pressure from high pressure clamps fills the mold cavity, which causes the uncured rubber to take the shape and form of the mold such that it covers every aspect of the mold cavity. The uncured rubber liquifies in the process and is cured by the pressure and heat.
At the completion of the process, the rubber returns to a solid state and is ejected from the mold. The final step in the process is trimming the part before it is sent on for testing.
The steps involved in rubber to metal bonding include:
The majority of vibration isolation mounts are made using either natural rubber or neoprene. When natural rubber latex or neoprene is received, various fillers and other ingredients are added to get the desired properties of the natural rubber or neoprene to be used. Using rollers, the rubber is then fed in so that the entire contained ingredients are uniformly dispersed throughout the rubber.
The mixed rubber then comes off the rollers and is taken to be made into pellets. The rubber can be used in transfer molding or is made into strips if the rubber will be used in injection molding. The rubber in the molding process is then stored in a climate controlled room. Neoprene or natural rubber is considered to be in an uncured state, so these rubbers will not out produce any of their characteristics until they go through the curing which is done during the molding.
When the vulcanization or the curing process is complete, natural rubber will be containing the best mechanical characteristics such as tensile strength, resistance to abrasion, tear strength, impact resistance, and the ability to be durable. Because of such advantageous characteristics, rubber can be used in environments which have temperatures ranging from -40°F to 190°F.
Neoprene is a synthetic elastomer and is produced through the process of polymerizing chloroprene. When completing the vulcanization process, the mechanical characteristics of neoprene are similar to those of natural rubber.
Neoprene is advantageous as it offers better oil resistance than the natural rubber. Because of its properties, neoprene can be used in environments where temperatures range from -30°F to 212°F. Neoprene and natural rubber are widely used for general industrial uses such as pumps.
The surface of the metal has to be a little rough and oil free to ensure a secure bond. A common surface preparation is a phosphate dip that removes oils and leaves an ideal surface. The phosphate acts as a type of rust inhibitor. Other methods include grit blasting, tumble blasting, or a wipe down.
Using an alkaline cleaning process or solvent degreasing methods, the oils on the bonding surfaces are removed. In some cases, rust and debris may need to be removed, which can be achieved using aluminum oxide grit blasting or machining. After being cleaned, metal components are stored and protected in a low humidity environment.
Several types of metals are used for rubber to metal bonding and include steel, aluminum, brass, beryllium, and copper. The type of metal is dependent on the application where the bonded metal will be used as will as the environment. For cost savings, manufacturers look for inexpensive, durabla metals.
The adhesive can now be properly applied after the surfaces of the metal components have been cleaned. In some cases, a two coat adhesive system is used to bond natural rubber or neoprene to the low carbon steel. This two coat adhesive system contains a primer layer and an adhesive topcoat.
The primer can be applied using several methods and some of them include dipping, rolling, spraying, and brushing. In common cases, the recommended dry film thickness for a perfect bonding performance is usually 0.2 to 0.4 mil for the primer and for the adhesive it is usually 0.5 to 1 mil. The proper agitating of the primer and the adhesive before the spraying process enables the settled ingredients to become uniformly spread throughout the product during its use.
After the spraying process, we consider the temperature to be at room temperature for proper drying. This drying process can be sped up using a circulating air oven. After the drying process, the finished components should be used in the molding process instantly. This helps in decreasing the probability whereby the surface contamination is quickly noticeable.
The natural rubber and the neoprene are usually produced by the processes which include the transfer molding process or the injection molding process. A mold is heated up to as high as 340 °F and metal components which have gone through the two coat adhesive process are loaded into it.
When we are done with the molding process, samples of the production lot must be tested, and this can be done by breaking a piece and testing if it meets the requirements of the specific tensile strength. The break should not be in the bond, but through the rubber. A load deflection test can also be done to ensure that the spring rate is in perfection.
Bonded rubber is used as an alternative to traditional poured rubber surfaces. It has an ability to provide the same highly accessible one-piece surface, but bonded rubber uses larger pieces than poured rubber. It can achieve a natural experience for an outdoor facility as it is poured in a single layer system onsite. Bonded rubber is created by combining rubber mulch which is shredded together with a binding agent and then troweling smooth by hand. Like most unitary surfaces, bonded rubber has excellent ratings for their safety characteristics. Because of its natural properties, it is able to provide superior absorption to impact and also allows the surface to easily meet the critical fall height requirements according to the ASTM.
Despite just providing and maintaining a uniform impact resistance, bonded rubber also has some benefits. These include the ability not to hide harmful objects, its textured surface aids in the slip resistance, the bonded rubber surface cannot be thrown or displaced as well as be scattered on walkways thus creating a slip hazard. High humidity and very cold temperatures are not able to reduce its effectiveness due to its characteristics.
Bonded rubber does not get in eyes or mouth and at the same time it has an ability of not supporting microbial growth which includes the growth of mold, mildew, and bacteria. Bonded rubber contains a life span that is durable and because also of its low maintenance requirement it outperforms less expensive options. The bonded rubber offers flexibility in the design, and it can be perfectly be used for playground surfacing or for pathways through playgrounds.
Due to it being imposed on mulch like pieces, it has a more natural appearance than rubber which is poured in place. These mulch-like pieces can be dyed different colors.
Because of the different properties in the elements, one is associated with rigidity and the other one with flexibility. The right rubber to metal adhesive can be affected due to the area of its application. The size of the area to be glued can be another affecting factor.
Superglues such as cyanoacrylate adhesives can be suitable for small areas or small strips, whereas for larger areas a two component adhesive is usually placed as a first preference. Contact adhesives which are based on polychlor pores or chloroprene rubber can be used for areas for large square meters areas.
The affected surfaces need to be pre-treated when gluing metal and rubber. For proper sticking of metal to rubber adhesive, it is best to work with solvents, cleaning agents, and other substances to remove residues and contain them as much as possible. Sanding the metal is essential if the metal has been coated or treated in some way and must be further cleaned. It is difficult to evaluate if the bonding process will succeed, as rubber can be damaged or weakened after time.
To counter this, one may resort to the idea of testing the rubber to metal adhesive on a small area and then assess the results obtained after a few days. If the results are positive in their nature, therefore the rubber to metal adhesive is a good choice, and it can be used for the whole surface. After the adhesive has been hardened, alterations can be made on the bond and these include drilling process and milling process. The rubber to metal adhesive can also be used in the filling of cracks, bumps, or holes and in some cases this can be experienced in aluminum housings.
This chapter will discuss rubber bonding, rubber products and silicone bonding.
Proper surface preparation is the key to the success of rubber to metal bonding. Even with the best efforts, a surface may become contaminated during the bonding process due to improper application of the adhesive. Every step of bonding has to be carefully handled to ensure a tight and secure bond. Understanding the bonding agent, metal, and process can ensure the success of bonding of the surfaces..
Before rubber bonding can be carried out a solvent degreaser is first required. This is due to the fact that surfaces may have mold release, slip additives, or other processing lubricants on them. To effectively remove lubricants a quick wipe with isopropanol alcohol is best. Acetone can also be used. A disadvantage of acetone includes its aggressiveness thus making other types of rubber prone to attack.
Rubbers may still contain plasticizers even after the surface has been wiped clean and these may travel back to the surface again as time goes on thus causing debonding at a later stage.
Cyanoacrylate instant adhesive is usually best for rubber compared to epoxies. Epoxies easily peel rubber off of a surface. Cyanoacrylate has the ability to cure fast, making it easy to tell if it is going to work or not. It is best to use a tiny drop and make sure that components are tightly aligned and squeezed together.
Types of rubbers such as natural rubber, silicone rubber, or EPDM can be more difficult to bond as these can result in the joint falling apart after the ample curing time. The use of specialist Cyanoacrylate can be used for difficult rubbers such as Permabond 105 and all other EPDM and natural rubber bonding. This results in negating the use of a primer. For the silicone bonding it is usually advisable to use a primer such as Permabond POP in combination with the Permabond 105. If flexibility is desired, POP and Permabond 2050 Cyanoacrylate should be used. This type is highly useful, especially for bonding o-rings which are soft in nature due to the ability to maintain flexibility in the joint thus making it hard to detect the joint.
Though it has many advantages, cyanoacrylate is not the only option for rubber bonding. The advantages may include good adhesion because if the bond is attempted to separate, it may lead to the rubber tearing. Because of the high speed in the cure process, the cyanoacrylate is an ideal element for assembly processes on production lines. Cyanoacrylate also has drawbacks which include it not being able to cater for the proper re-aligning of joints due to its ability of curing in seconds.
The cyanoacrylate also offers a limited gap fill of a maximum of 0.5mm and it cannot be spread over large areas. It also contains a pungent smell which can be off putting therefore contact adhesives can be used especially in offering a practical solution for larger areas. But these can also be hard to align also. For a low cost method of joining one may refer to the use of solvent based rubber bonders. For the bonding of silicone rubber, silicone based adhesives can be used but some find them to be messy and also to be slow to cure therefore they are no longer practical for small items assembled on a rapid line of production.
Permabond TA46XX series are two part structural acrylics which are used for bonding plastics which are difficult to bond such as polypropylene, polyethylene, and PTFE. These have also shown to have a good adhesion to some rubbers but exclude the silicone type of rubber. Accurate alignment and spreading is possible in structural acrylics adhesives as compared to cyanoacrylate as it offers a slower cure. They are also not solvent based and their odor is less pungent than many other adhesives used. The TA46XX series adhesives can be used in applications where rubbers can be needed to be later submerged in water thus they contain an excellent environmental durability.
Rubber products are usually divided into three major classes such as tires, industrial rubber goods used in motor vehicle or ship construction, and consumer goods like footwear and mats. These rubber products are usually made from rubber which is hard and raw and from latexes like gloves which are seamless and with thin walls, rubber threads, and foam rubber seats for automobiles and furniture.
The technological process used in the production of rubber products when they are extracted from hard raw rubber consists of two major stages. In the preparation stage, rubber stock is produced from the mixing of raw rubber with the necessary ingredients in machines like internal rubber mixers or milling machines.
The semi finished rubber product is then later vulcanized in the final stage. This is done using temperatures of 140 °C to 200 °C and pressures of 0.3 to 20 meganewtons per square meter.
The equipment used in the vulcanization process includes presses, boilers, and other equipment depending on the type of rubber products manufactured. In order to provide strong bonds between these materials and the rubber in any operational conditions, the textile materials and metals used in the rubber product’s production need to be preliminary treated.
Textile materials are made one with rubber cement or other adhesives in special machines and then coated with a rubber stick on coating. With organic solvents, the metals are degreased and coated with a layer of cement or brass. This latter process is referred to as brass plating and is done in an electroplating bath.
These industrial rubber goods are usually divided into the major groups which are molded goods, unmolded goods, conveyor belts, hoses and then belts.
The process of simultaneously molding and vulcanizing rubber stock produces these types of goods. This is done in a compression mold mounted on a press or by the process of injection. There are several types of molded industrial goods, rubber goods and these include parts for packing, shock absorption namely gaskets, dust protection and rings which have various cross sections.
Unmolded industrial rubber goods are used for sealing the doors and windows of motor vehicles, aircrafts, and for the process of hermetically sealing construction panels. These goods are made in cords of various shaped lengths and cross sections by the extrusion of the rubber stock and the vulcanization of the semi finished product in the apparatus for enabling a continuous action or by periodic batching in boilers. The seals are 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.
These belts are the elements which are flexible in the belt drive of automobiles engines, agricultural machines and other various industrial devices. There are types of belts which include the v-belts and flat belts. In the production of flat belts the technology used is similar to that one used in the production of conveyor belts. The sheet is cut into strips in order to obtain belts of the required width, and this is done either before or after vulcanization. V-belts contain a closed design and a trapezoidal cross section. Belts are assembled on machines and these belts are then vulcanized in boilers or diaphragm vulcanizers. The length and the cross section of the belt are used to determine the proper selection of the vulcanization equipment.
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 divided into industrial footwear, athletic, and everyday footwear. Industrial footwear is usually made in a manner that protects the feet from the harmful effects of corrosive agents, low temperatures, and injury. Industrial footwear includes the boots used by miners, fishermen, and dielectric rubber footwear.
Rubber footwear can be distinguished also according to the production method used. Taking previously produced parts on conveyor lines, glued rubber footwear is assembled and glued. They are then lacquered and vulcanized in boilers. By impact stamping on special presses and vulcanizing in boilers, galoshes can be produced under stamped rubber footwear. Molded rubber footwear is also pressed in a mold and vulcanized.
This method can be used in the production of boots and footwear which have fabric upper sections. Injection molding involves the use of compounds which are polyvinyl chloride and thermo elastic plastics. Liquid molding is a modern method which involves the use of liquid oligomers including polyurethanes and plastisols.
Silicone is an elastomeric material with a high performance and flexibility. It can be used in seals and gaskets. In surface preparation not much is done to improve the surface of the silicone. This is due to the surface always having plasticizers which migrate to the surface to add to bonding issues.
For better preparation of the surface, a solvent wipe which contains isopropanol is used to prepare the surface for the bonding, to give a better binding surface, and remove any processing lubricants. There are other solvents which may be aggressive, including acetone and white spirits. This is an issue because these solvents leave a residue.
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 discuss the applications and benefits of rubber to metal bonding.
Metal bonding can be done on any rubber part and is therefore versatile and popular. Some of its applications include the automotive industry through making seal gaskets together with engine mounts. In agriculture, rubber to metal bonding can be used to make ball joints and stabilizers. O-rings which help in the better development of the medical field can also be made alongside with pump compressor isolations.
With the increased growth in the construction field conveyor belts are also produced from the rubber to metal bonding activity and help in swift construction as they are strong and durable. Valve seals and pedals are made in the mass transit field. Because of the bonding process of metal to rubber, parts can last longer thus keeping users and equipment safe. This achieves optimal outcomes as long as the correct materials are used.
When rubber to metal bonding has been done there is a reduction in the number of components required during assembly. This is because the rubber is bonded directly to the substrates and fewer components will be needed. This results in the betterment of the assembling process and also reduces the amount of labor and time given in for the production. There is a result of a stronger bond and this gives materials that can last for long. There is an element of resistance in the substrate as it can easily resist damaging elements like water and corrosion. Rubber is also an environment friendly element as it does not contain lead as compared to other bonding agents. The rubber to metal bonding accommodates a wide temperature range thus allowing the bonded elements to be used in hard conditions without any negative effect.
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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