Choosing a rubber supplier or manufacturer can be difficult, especially if you are not exactly sure what you are looking for. Whether you are looking to source an automotive part, industrial seal, or a natural rubber dog toy, there are many different types of rubber polymers from which rubber products can be made as well as many different types of molding methods to make rubber parts. So where do you begin? Below, we will explain in detail what to look for in choosing the right rubber supplier for your needs.
Perhaps the most important question you need to ask yourself in the beginning of this process is what requirements are there for my rubber product?
- Will my rubber product be exposed to any kind of chemical environment? (rubber seals, gaskets, etc.)
- How tough will my rubber need to be?
- Do I need very flexible rubber or harder, less flexible rubber?
These are all important questions that your rubber supplier will need to know the answers to so that, by working together, you can achieve the best rubber product possible.
Rubber Polymer Types
Who would have thought there were so many different types of rubber? Rubber science actually has a lot to do with chemistry and polymer science. In order to pick the right rubber type for your application, you should be aware of the following general guidelines for each rubber type in the chart below.
|Fluoroelastomers generally have a wide chemical resistance and have high service temperature ranges. Due to a fluoroelastomer’s polarity, it can withstand interactions with non-polar substances (i.e. hydrocarbons, oils, and fuels).|
|EPDM is a synthetic, non-polar polymer that is compatible with polar substances like water and ketones. EPDM exhibits outstanding resistance to heat, ozone, steam, and weather. It is an electrical insulator.|
|Nitrile or NBR is a synthetic copolymer of acrylonitrile and butadiene. The higher the acrylonitrile (ACN) content of the polymer, the more resistant it is to oils and non-polar solvents. However, the lower the ACN content, the lower the glass transition temperature. Most applications requiring both oil resistance and low temperature flexibility require an ACN content of 33%.|
|HNBR differs from NBR only by a saturation of its double bond. HNBR is known for its physical strength and retention of properties after long-term exposure to heat, oil, and chemicals. The high temperature rating allows for HNBR to be used in many automotive and industrial applications in things like dynamic and static seals, hoses, and belts.|
|Natural rubber is a polymer of isoprene which is harvested in the form of latex from rubber trees. Natural rubber has many applications and is useful due to its resistance to water, its high elongation ratio, and resiliency.|
|SBR is used heavily in tires due its good abrasion resistance and aging stability. The higher the styrene/butadiene ratio, the harder and less rubber-like the polymer is.|
|Silicone rubber exhibits good resistance to a wide range of temperatures, typically -100 C to 300 C. Silicone differs from other rubbers in that its backbone is made up of silicon and oxygen instead of carbon. This allows for silicone to have a good resistance to UV and ozone whereas other polymer types cannot.|
|Neoprene has good chemical stability and exhibits good flexibility across a wide temperature range. It resists degradation more than synthetic and natural rubbers and also resists burning better than hydrocarbon-based rubbers.|
|Polyurethane is considered to be one of the most abrasion resistant polymers for rubber. It also shows good resistance to ozone, UV, and radiation. It is compatible with aliphatic hydrocarbons and fuels.|
|Perfluoroelastomers contain an even higher fluorine content than FKMs. These compounds have an improved resistance to an even larger array of chemicals at higher temperatures.|
For example, if you are making a large rubber seal that will spend most of its time underwater, you will most likely want to make that seal out of EPDM rubber due to its compatibility with water applications. Choosing the right polymer type sometimes can be tricky and you will want to lean on the expertise of your rubber supplier’s team of experts to make the right selection for you. This is why communicating all of your requirements for the rubber product will effectively aid in selecting the best rubber polymer.
Rubber Manufacturing Methods
When it comes to producing rubber products, many different manufacturing processes exist. Each method has its own pros and cons that make it the ideal choice for manufacturing certain types of products. Knowing a little about each process can help in understanding cost implications and tradeoffs.
- Extrusion: This method begins with an unvulcanized (uncured) rubber compound being fed into an extruder. Once it is inside the extruder, it gets carried to a dye, which is a specialized manufacturing tool used to shape the rubber. Once 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, or cured. It is important to note that any rubber compound must have a “cure package” already blended into the compound prior to vulcanization. Extrusion manufacturing has the advantage of being able to produce products in high volumes at a lower production cost. Most extruded products typically have a continuous cross section so some of the common rubber products produced from extrusion include cords, tubing, and gaskets.
- Compression molding: In this method, a rubber compound is formed into a blank (preform of uncured 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 parts to several hours for thicker parts. Some advantages of this method include being suitable for rubber compounds with large surface areas and the ability to be used for rubber compounds with high viscosity and poor flow properties. On the down side, the process is time consuming with a low production rate. Some common products made with compression molding include seals, o-rings, electrical insulators, and silicone wrist bands.
- Transfer molding: In transfer molding, the process starts with a blank being loaded into a mold’s pot, which is then pushed by a plunger and distributed into several cavities. In this beginning stage, pre-heating takes place in the rubber, forcing the rubber to flow through channels. This pre-heating reduces the curing time and allows the rubber to flow easier and fill mold cavities efficiently. However, the molds can be more complicated and expensive.
- Injection molding: This method can allow for the quickest production times for high volume part manufacturing. Rubber is fed into a screw which is used to pre-heat the rubber and inject it into a mold’s cavities. With no rubber preforms being required, this method is typically the most cost-effective when manufacturing rubber products on a large scale. However, tooling and molds can be quite expensive when using injection molding but this can be offset by better production efficiency.
- Calendering: This method works by forcing softened rubber between counter-rotating rollers. Rollers compact the material and the overall thickness of the product is determined by the gap distance between cylinders, which can be adjusted for varying product thicknesses. Once the material passes through cooling rollers, it can be vulcanized. This process works best to produce sheets or films of rubber. Benefits of calendering include control over product thickness and the ability to produce parts thinner and wider than with the extrusion. However, calendering can have high operating costs compared to other processes.
Finally, make sure your rubber supplier has a good inspection process of finished parts it will be sending to you. The last thing you need is bad product arriving at your door. Does the supplier have rubber testing and qualification capabilities? Does the manufacturer have certifications, such as ISO 9001? These will be important things to consider when choosing the right partner.
Reach out to Wayne Rubber and see how our experts can supply you with the best rubber product for your application!