Rubber to Metal Bonding

Bonding rubber to metal to produce metal and rubber products involves gluing rubber to metal by way of various adhesives. A mold is also used to give the rubber a certain shape when the rubber is bonded to the metal. While steel was originally the most common metal to use, today aluminum bonding is popular because it saves on both cost and weight without compromising the product's quality or seal strength. Metal bonding is used to fabricate products for many different applications within the automotive, aerospace, construction, plumbing, electric, industrial machinery, vibration absorber and medical industries, as well as rubber roller manufacturers. Silicon bonding is mostly used to make surgical instrument handles as well as other products including rubber lined rollers, engine mounts, gaskets, reinforced tires, bearings, rubber lined tanks/pipes, conveyor belts, electrical cables and plugs. Rubber bonding can take place with materials other then metal, although bonded metal is the most well-known, since all grades of steel, aluminum, copper, beryllium and brass adhere to bonded rubber. Glass, fabric and a variety of plastics are also utilized. However, the metal must be able to handle the high heat and pressure involved in the bonding process. The rubber material can be natural or synthetic, and includes silicon, neoprene and nitrile. 

In the rubber metal bonding process there are three main components: the rubber material, the bonding agents and the metal substrate. Any type of rubber can be used, providing that the material can flow into the mold without developing a significant level of cross-linking and that the substances making up the rubber material will not bleed rapidly to the surface of the uncured stock. The bonding agents consist of solutions based on solvent or water, with a primer coat based on phenolic-style resins and a topcoat of polymers and other materials. If the part will not be exposed to high heat, humidity or pressure, sometimes a single coating of bonding adhesive will work. Most of these solutions are patented. The thickness of the bonding layer depends on the nature of the rubber formulation. The application of the bonding agents typically requires the spraying of a gray primer coat over a slightly wider area than the black topcoat, using a low pressure, high volume barrel spraying machine. Before the substrate can be coated in adhesive, it must be cleaned well of all dust, grime and oils leftover from the fabrication process. The specific type of adhesive material is determined by a couple of different factors; the operating conditions of the finished part and the rubber and metal chosen as the materials.
 
The science behind the rubber metal bonding process is varied and complex; rubber to metal bonding is often referred to as a sophisticated industrial process because it takes both skill and patience. Often the type of polymer (rubber) chosen depends on what type of metal is to be used and/or the part being manufactured. Determining the appropriate bonding agent is critical. The selection process depends on the rubber to be used, the component design and the elasticity of the rubber. The traditional metal used in rubber metal bonding services is steel in all its forms and grades, but recently, an increasing amount of products are made of aluminum alloys and polyamides because they are less expensive and lighter in weight without compromising quality or durability. Almost any material can be bonded to rubber, provided that it can withstand the heat and pressures of the rubber molding process. However, the results of bonding rubber to alloys, such as bronze and brass, greatly depend on the composition of the alloys. Environmental factors have also changed the bonding material. Originally, solvent-based adhesives were used, but today they have mostly been replaced by water-based adhesive, an environmentally friendly alternative that has been proven to provide the same sealing properties that are able to withstand the same conditions and last just as long.

The bonding process, no matter what type of metal, bonding adhesive and rubber are chosen, is similar in almost all cases. After the substrate has been fabricated, it must be cleaned of all dust, debris, grime and oil using a sand blaster, chemicals and degreasers. Next, the bonding agents are sprayed onto the surface in coats. The rubber molding process is next, which is considered the most important and difficult step in the bonding process. The metal component is positioned within a mold, which is most likely injected with uncured rubber that is heated and almost molten. Sometimes, plated inserts are added for more strength. The rubber is left to cure, and when it has completely dried, the part is finished. Sometimes the mold itself is just slightly larger than the substrate, and the rubber forms a thin coating around the metal, while other products require complex rubber part designs that greatly differ from the substrate's dimensions. The products made by rubber metal bonding services are used in various areas of the industrial, commercial and medical fields. Many of the components are used for the isolation of vibration and noise in manufacturing applications. The motor vehicle industry in particular uses a large number of bonded rubber to metal parts. The steering wheel is joined to the steering column by various rubber bonded parts. Foot pedals and bumpers are examples of common items that have rubber/metal characteristics. Because of the wide variety of parts used today consisting of bonded rubber to metal, most of the shops that specialize in the manufacturing of these parts are custom shops that work with customers from the design level through production.

Images Provided by Timco Rubber Products, Inc.

Rubber to Metal Bonding Types

• Aluminum Bonding is a specific metallic material used in rubber and metal bonding; aluminum is a very popular choice because it is strong and corrosion resistant as well as being low in cost and very light weight.
• Bonded Metal may be a variety of different metallic substances or their alloys that are bonded with rubber to produce specific products such as vehicle tires, industrial parts such as gaskets or medical supplies.
• Bonded Rubber may be synthetic or natural rubber that is bonded by way of heat and an adhesive to metal, fabric or glass in order to create specialized products with specific characteristics such as strength and flexibility.
• Bonding rubber to metal is a process that requires adhering or molding the rubber to sandblasted metal.
  
• Chemical curing is a method in which an agent is applied to the surface of the lining and allowed to permeate the lining over several days at room temperature. The chemical curing process that can be accelerated by the application of heat, is commonly used on tank repairs or large field lined vessels.
  
• Exhaust steam curing is a method in which the vessel is blanked off with blind flanges or tarped with live steam being bled into it. The exhaust steam method maintains the lining integrity and bond and is often used on field lined tanks that are too large to transport.
  
• Gaskets are pieces or rings of rubber or metal placed at a joint to make it leakproof. Gaskets are a type of seal made often with bonded to metal rubber.
  
• Glue Rubber to Metal refers to the adhesives used in the rubber to metal bonding process that creates a variety of products in multiple industries including the automotive industry and medical field.
  
• Induction heating provides reliable, repeatable, non-contact and energy-efficient heating in a minimal amount of time to very small areas within precise production tolerances without disturbing individual metallurgical characteristics. The closed-loop control of induction heating produces repeatable, rapid and accurate heating cycles, making it ideal for in-line production processes.
  
• Metal Bonding is specifically referencing the metallic substance, which can be aluminum, brass, copper, steel or a number of other metals that is utilized in the rubber and metal bonding process; different metals are used depending on what the application requires.
  
• O-rings are made of rubber or silicone and seal rotating or sliding shafts. O-rings, often made with a rubber coating on metal, are used in applications such as shock absorbers and differentials.
  
• Piping is sometimes bonded with rubber when the pipe line is required to be more insulated and vibration absorbent.
  
• Press bonding is a non-heat or chemical way of bonding rubber to metal that involves the bonding of a preformed rubber piece onto a piece of metal via a predetermined groove or space and a mild adhesive agent.
  
• Rubber bonded to metal gives the metal material elasticity and dampening abilities.
  
• Rubber bonding is a manufacturing process that adheres rubber to various materials in order to give the material elastic qualities.
  
• Rubber grommets are common devices made by the bonding of rubber to metal. Rubber grommets are used in the screen press process, in the hoisting of a flag and other applications in which an eyelet is needed for passing a line through.
  
• Rubber products are those goods made from natural and synthetic rubbers materials.
  
• Rubber rollers are used to squeeze the water out of pulp in the manufacturing of paper. The roll has a metal core, but to perform efficiently, the core is lined with rubber. 
  
• Seals are common types of products made with rubber bonding technology. Seals are often used as shut off pieces in hydraulic equipment.
  
• Silicon Bonding is a rubber bonding process involving silicon specifically, which is particularly common in the medical field as surgical instruments.
• Vulcanizer curing is a rubber to metal bonding method in which a rubber lined metal article is placed in a live steam vulcanizer and cured under pressure. The vulcanizer method results in the highest rubber to metal adhesion and yields the highest density for corrosive media.
  

Rubber to Metal Bonding Terms

Accelerators - Chemicals which are added to rubbers to accelerate the rate of vulcanisation. Rubber without accelerators takes 20-30 times longer to cure.
 
Activators - Chemicals added to rubber to activate curing.
 
Adhesion - The propensity of rubber to bond to a contact surface.
 
Adhesive - Material that can be used to adhere or stick one surface to another.
 
Bonding - Joining of identical or different types of material by means of an adhesive, creating a positive-substance bond throughout the entire surface of the joint.
 
Bond Strength - Unit load, applied in tension, compression, flexure, peel, impact, cleavage or shear, required to break an adhesive assembly with failure occurring in or near the plane of the bond. Rubber Metal Bonding strength is measured in pounds per square inch (psi).
 
Break-Out - Force necessary to actuate sliding. A high break-out value indicates the development of adhesion.
 
Coating - A uniform layer of chemical primers or adhesives that are used to produce chemical bonding between rubber and a substrate.
 
Cold Bond - The adhesion of a vulcanized rubber material to a contact surface through the use of suitable contact cements.
 
Contact Pressure - Pressure applied to the assembly to achieve a bond in contact adhesives.
 
Curing - Also known as "vulcanization," this is the permanent change that the rubber undergoes during molding.
 
Elastomer - Any material that when stretched more than twice its length is able to return to its original shape.
 
Flex Cracking - The tendency of some Rubber Metal Bonding materials to crack as a result of repeated bending or stressing at the same point.
 
Natural Rubber - Crude rubber obtained from organic sources, such as vegetables.
 
Nitrile - Also referred to as "Buna-N," it is the most commonly used elastomer for O-rings, due to its wide temperature range, resistance to petroleum fluids and good physical properties.
 
Polymer - General term used to describe all rubbers and plastics involved in Rubber Metal Bonding. Polymer is also the chemical term that refers to all organic materials that are formed from chains of repeated chemical units.
 
Primer - Chemical material that improves the bond of the sealant to the substrate.
 
Set - Also called "permanent set," it is the degree to which a rubber does not fully recover to its original shape after it has been deformed for a long period of time.
 
Substrate - Any surface to which a coating or sealant is applied.
 
Vulcanized Bond - A bond formed between an elastomer to a primed surface through the used of heat and pressure. The elastomer is vulcanized at the same time as the bond.