Rubber has made a name for itself as being one of the most versatile and impressive materials for manufacturing available. With a reliable build and operational flexibility, manufacturers in different industries make use of it to develop different products, all with the aim of meeting consumers’ needs.
However, the process of creating the traditional rubber material is even more impressive. And, one of the most pivotal processes here is rubber mixing. In this article, we’ll look into how a rubber mixer works, the intricacies of rubber mixing, and all you need to know about it.
The Fundamentals of Rubber Mixing
Now, let’s go into an introduction to the rubber mixing process itself:
What Is Rubber Mixing?
As explained earlier, rubber mixing is one of the most critical parts of the manufacturing process of rubber. Also known to some as rubber compounding, the process focuses on combining different raw materials to create a uniform blended mixture which itself serves as the basis for rubber products.
While rubber is a very functional material, it is actually not suitable for use in manufacturing in its raw form. The material’s inherent properties make it a bit challenging to work with, and this necessitates the use of other materials to optimize its performance and processability.
With rubber mixing, you’re ensuring that all ingredients in the rubber material are properly blended to create the homogenous composition. You can have a silicone rubber mix, which incorporates different ingredients such as the silicone polymer itself, curing agents, additives, plasticizers, and more.
Each of these ingredients will serve a particular purpose, all with the goal of enhancing the properties of the final rubber compound you get.
Considering that the quality of the silicone rubber mixer and other equipment used in the process will eventually determine the properties of the products, it should go without saying that you want to put a particular focus on getting the process right. Keep an eye on the ingredients used, from the type to the quantities. Just as well, ensure that you keep to tie when mixing silicone rubber, and that the processing conditions are optimal.
Types of Rubber Compounds
The entire purpose of using a rubber mixing machine to conduct this process is to create a rubber compound. These are essentially mixtures of rubber polymers and other additives that have been carefully formulated to meet specific production and performance requirements.
Your rubber type and additives used will generally depend on factors such as your required mechanical properties and more. However, here are some of the most prominent rubber compound types:
- Natural Rubber (NR) Compounds: Natural rubber is gotten from the background latex material of rubber trees. When tapped right, this latex gives way for rubber that offers optimal flexibility, resilience, and tear strength. In applications where high elasticity is needed, natural rubber is the go-to option.
- Styrene-Butadiene Rubber (SBR) Compounds: This is a synthetic rubber that operates as a copolymer of butadiene and styrene. It is easy to produce, and its abrasion resistance makes it perfect for making shoes, gaskets, and more.
- Nitrile Rubber (NBR) Compounds: NBR is a synthetic rubber that perfectly resists fuel and oil. It is mostly used to produce components that would need to interact with oil in one way or the other.
- Neoprene (Polychloroprene) Compounds: Manufacturers love neoprene because it offers good weather resistance, flame resistance, and moderate oil resistance.
- Ethylene Propylene Diene Monomer (EPDM) Compounds: With optimal resistance to UV rays and ozone exposure, EPDM rubber is perfect for making tools that need to be used outdoors.
- Chloroprene Rubber (CR) Compounds: Like many other rubbers, CR also offers resistance to flame and chemicals.
- Butyl Rubber (IIR) Compounds: Optimal gas impermeability is what sets Butyl rubber apart, making it perfect for applications that require airtight builds.
- Fluoroelastomer (FKM) Compounds: Known to some as Viton®, this rubber compound is notable for its ability to withstand high temperatures. From automotive to industrial applications, the rubber is perfect in situations that require resistance to high temperatures and chemicals.
- Silicone Rubber Compounds: One of the most prominent rubber variants, silicone rubber is known for its electrical insulating properties and resistance to outer factors. The use of injection molding and more also make silicone rubber especially flexible, and you can also use silicone rubber color mixing to achieve the right aesthetic properties for your rubber product.
- Acrylonitrile-Butadiene Rubber (NBR) Compounds: This is a specialty rubber that comes in handy in applications that require oil and fuel resistance.
Each rubber compound can be tailored to meet your specific performance needs. And, manufacturers such as we at Legenday can easily customize formulations by tweaking the quantity of polymers and additives.
The General Rubber Mixing Process
Equipment Needed For Rubber Mixing
For rubber compounding to work, rubber mixing companies will need to make use of a blend of raw materials. However, this process also requires the use of rubber compounders and several other tools.
Companies generally have their different toolsets. However, at Legenday, we believe that the following should be part of your setup if you’re looking to create the best soil mix for rubber plant.
Mixing Machines:
Of course, it goes without saying that you’d need the rubber mixing machine. Generally, the roller mixing machine can be broken down into the following:
- Internal Mixers (Banbury Mixers): This is most likely the most common machine in the rubber mixing process. The internal mixer for rubber consists of a chamber with spinning rotors that mix and knead the rubber compounds with any additives you throw in.
The mechanical shear generates heat, which optimizes additive dispersion and ensures a consistent blend. - Open Mill (Two-Roll Mill): These mills are known for their versatility and they facilitate both semi-automatic and manual rubber mixing. Here, you have two counter-rotating rolls that process the rubber during the mixing process.
In most cases, these mills are used to process smaller batches of rubber, although they can also involve a great deal of labor.
Weighing and Measuring Equipment
Throughout the process of using a kneader rubber mixer, you want to make sure that you have the right measurements of raw materials – as well as additives. So, be sure to get balances and scales to weigh all components and ensure that they are placed in the right proportions.
Mixing Tools and Accessories
For mixing tools, you will most likely need to get paddles and bowls.
If you’re handling the mixing process manually, the paddles or spatulas will be needed for optimal blending. This way, the rubber compound and any additives can be properly put together.
Then, you might need to get mixing bowls with rubber bottoms. The rubber bottom mixing bowls hold and mix the compound ingredients before they are sent into the mixing machine, thus ensuring a homogenous combination. So, rubber mixing bowls are a necessity
Temperature Control Equipment
The rubber mixing process relies heavily on proper temperature control. Once the mixing process is done, you want to cool the rubber mixture to prevent any premature curing. So, you need proper cooling systems to achieve the right temperature.
Safety Equipment
Every mechanical process involves a risk component, and rubber mixing isn’t left out. With personal protective equipment like goggles and gloves, you can keep yourself safe at all times during the process.
Testing and Quality Control Equipment
Viscometers, rheometers, and other testing tools will be required to assess the properties of your compounds following the mixing process. With the, you ensure that your compound meets the right specifications.
Automation and Process Control Systems
For automated rubber mixing, control panels on the mixing machines need to be in optimal condition. They will be needed to help you set parameters such as temperature, rotor speed, and mixing duration.
Dust Collection and Ventilation Systems
The rubber mixing process is notable for its dangerous by-products – fumes, dust, et. with ventilation systems and extraction units, you can take out these by-products and maintain a healthy working environment for everyone.
Roller Equipment
For open mill mixing, you’d need roller mixing equipment. Calendar machines are perfect, allowing you to further process the rubber compound through smoothing, sheeting, and more.
Once again, it is important to note that the specific tools you use will depend on your production scale and the type of rubber compounds you’re workin with. You can engage a combination of automated, semi-automated, or manual mixing equipment to get the right process and achieve high-quality compounds.
Looking At The Rubber Mixing Process
So, now we know about the tools needed for rubber mixing. Let’s go ahead to examine the overall process involved in getting this job done.
Per usual, you want to keep in mind that the details of a rubber mixing process can easily vary based on factors such as the available equipment, production sale, and even the type of rubber being used. However, at Legenday, we follow these steps to create the proper blend for our clients:
Raw Material Preparation
First, you start with selecting the appropriate rubber polymers and additives. This is done based on the final product and the properties you have in mind.
In most scenarios, the raw materials can be lubricants, plasticizers, and more. And as expected, their job is to enhance the properties of the rubber product itself.
Weighing and Measuring
It is also important to ensure that every raw material you’re putting into the mix is properly measured. So, before making an addition, measure it right to see if it fits your formulation recipe.
Pre-Mixing
In some cases, you can find the process starting with a pre-mixing step. Here, you blend specific ingredients together before introducing them into the rubber mixing machine.
The purpose of the pre-mixing step is to ensure that additives are properly dispersed more evenly during the major mixing phase. And, it can go a long way in helping you achieve proper formulations.
Mixing Stage
Now, we get to the real meat of the matter. With a rubber mixing mill machine, you conduct the mixing process.
Remember – internal mixers come with a chamber and counter-spinning motors. Also known as a Banbury machine rubber mixer, this product’s rotors intermesh and mix the compound along with additives, creating forces that optimize the mixing process. The generated by this process helps to soften the rubber, while dispersing additives and raw materials in a uniform manner.
As for open mills, the compound is also passed through two counter-rotating rolls. These rolls blend and shear the rubber, leading to a proper spread and mix of additives with the compound.
Dispersion and Homogenization
One of the most important parts of the process involves achieving proper additive homogenization and dispersion. This should also extend to the fillers and rubber, with heat and mechanical shear breaking down any agglomerates and ensuring proper material distribution.
Temperature Control
One of the biggest risks of rubber mixing is compound curing. To prevent this, you need optimal temperature control. Get cooling systems to ensure suitable temperatures and temperature stability, and you should be good to go.
Monitoring and Testing
Al through the mixing process, you would need to constantly take mixed rubber samples to test them and ensure proper quality control. Lab equipment like tensile testers and rheometers are useful here, allowing you to get a good assessment of the compound’s overall properties.
Cooling and Storage
With the mixing process itself being completed, you move ahead to cool the rubber compound in order to prevent any additional reaction. Then, store it in an appropriate container to keep its quality optimal for long.
Further Processing
If the need arises, you might need to conduct some additional processing. Your rubber compound is used as a base material, and you can mold and shape it however you like to create the perfect final form.
Quality Assurance
The process doesn’t stop here. You want to make sure that your rubber compound is up to code, and this means checking for batch consistency and performance capabilities. At the end of the day, rubber is no good if it doesn’t perform up to expectations.
Cleanup and Equipment Maintenance
Once the mixing process is done, remember to clean your tools and store them appropriately to prevent any cross-contamination.
The Different Rubber Mixing Techniques
When it comes to rubber mixing, one of the things you need to keep in mind is understanding the perfect type of mixing technique to work with. If you’re a newbie to this, here are a few notable options you could go with:
Open Mill Mixing
Open mill mixing is probably the most prominent form of rubber mixing available. Also known as two-roll mill mixing, the rubber compounding process makes use of a pair of rotating rolls to process rubber compounds.
In most cases, you’d find open mill mixing in labs and small-scale production environments. Equipment needed here include the rolls themselves, a roll gap, the feed hopper, and simple control systems that oversee the entire process.
For open mill mixing, the process breakdown is as follows:
- Loading: Weigh the raw material and additives, then introduce them into the open mill’s feed hopper. Then, the material is ded into the roll gap between the rolls.
- Mixing: The rotation of the rolls will lead to shearing and kneading of the rubber compound, combining it with fillers and additives.
- Sheet Formation: Then, the rubber compound is slowly compressed and spread into a thin sheet as it goes through the roll gap.
- Cutting and Folding: The sheet is constantly folded and fed back into the roll gap, so you can ensure uniformity across the board.
- Sheet Formation and Collection: Gradually collect the mixed rubber compound at the end of the open mill in the form of a sheet. You can roll the sheet up manually and cut it into smaller sections for further testing and processing.
In general, open mill icing provides several benefits – including, but not limited to, its cost-efficiency and simplicity. You’d also be able to use it for small batch processing, which makes it perfect for most operations.
That said, the process is also labor-intensive compared to more automated methods. So, keep that in mind.
Internal Mixer (Banbury Mixer)
The Banbury rubber mixer is an internal batch mixer that is used for blending rubber compounds with additives. It handles larger quantities of materials quite well – especially compared to open mills. And, it provides a more automated operating system.
In the Banbury mixer, you have the following components:
- Mixing Chamber: This is an enclosed space with a cylindrical shape that handles the blending of the rubber compounds and additional components.
- Rotors: In the mixing chamber, you have two rotors. They rotate in countering positions, with specialized shapes that are designed to properly shear and knead the rubber compound for uniformity.
- Drop Door: A drop door in the mixing chamber can be opened to release the resultant compound upon the completion of the mixing process.
- Cooling System: Finally, all Banbury mixers come with cooling systems that help release heat generated during the mixing process.
On to the mixing process, you have something that looks like this:
- Loading: load the polymer and any other additives into the mixing chamber after they’ve been weighed.
- Mixing: Once they’re all in the chamber, the rotors begin rotating in opposite directions. This causes a kneading and shearing of the material, which ensures uniformity.
- Heat Generation: The mechanical forces generated by the rotating rotors will create some heat and friction in the rubber compound. This will soften the rubber material and optimize dispersion. Fortunately, the cooling system can help with temperature control as well.
- Discharge: Once the mixing is complete, the drop door at the bottom of the mixing chamber is opened, and the mixed rubber compound is discharged.
Continuous Mixers
For optimal rubber mixing, you can also take advantage of continuous mixers. In particular, consider single screw and double screw extruders, which forcibly process materials by pushing them through a die to create continuous profiles.
Both machines use the principles of pressure and shear to mix, melt, and shape raw materials, allowing you to get the perfect shape.
Single Screw Extruder
As the name suggests, the single screw extruder comes with just one rotating screw within a cylindrical barrel. The screw here is the main component that melts, transports, and mixes the material, delivering the perfect end result.
With a single screw extruder, the raw materials – usually flakes, powders, or pellets – are directly introduced into the extruder hopper. Then, the screw moves the material forward while also applying heat and compressing it.
With the material moving along the screw, it is subjected to pressure and temperature, eventually melting. Once it melts, the screw’s design will help mix in colorants and other additives.
Over time, the molten material gets homogenized as it is pushed through the screw’s flights and the barrel’s groves. And, at the end of the barrel, the material is forced through a die that finally shapes it into the right form.
Twin Screw Extruder
The difference here, of course, is that the twin screw extruder comes with two intermeshing screws that spin within a barrel. You can find different configurations of twin screw extruders, from co-rotating to counter-rotating screws.
A twin screw extruder pretty much operates in the same manner as the single screw variant. However, these ones offer several advantages – such as:
- Enhanced Mixing: Thanks to intermeshing screws, you have a more effective material mixing process that better disperses additives and achieves uniformity.
- Greater Flexibility: Twin screw extruders also process a broader range of materials – many of which will be impossible with the single screw variants.
- Higher Throughput: With their improved mixing, twin screw extruders also come with higher processing rates.
Process Control and Optimization
In the general rubber mixing process, it is important to implement proper techniques and strategies to ensure consistency and quality in the overall process. By incorporating these steps, you will be able to create a more seamless environment that allows you to achieve the right output across the board:
Formulation Design
The first thing you need to do is develop the right compound formulations. Be deliberate about the type and quantity of polymers you want to be in your compound, as well as the structure of the overall mix.
Raw Material Handling
You also want to ensure that the quality and consistency of the raw materials are of the highest caliber. Work with reputable providers like Legenday, and ensure that you conduct regular material testing to ensure that they meet your standards of operation.
Weighing and Measuring
You want to ensure accuracy in measurements if you hope to get the perfect end result. So, incorporate a structure where you weigh and measure everything.
Mixing Equipment Calibration
Like it is with testing, you also want to ensure that mixing equipment are regular calibrated to ensure that all settings are properly tuned.
Process Monitoring
Real-time process monitoring systems will also help to check the important parameters as the mixing process goes on.
Statistical Process Control (SPC)
SPC techniques will help you to monitor process data over time and identify any possible anomalies across the board.
Preventive Maintenance
As always, you want to establish a thorough and effective maintenance schedule for all of your mixing equipment to prevent any possible breakdowns and ensure that performance is optimized all through the mixing process.
Applications of Rubber Mixing
Rubber mixing plays an important role in different applications and industries. And over the past few years, the process’s role has only expanded even more. As long as rubber compounds are used to create products, rubber mixing will find use.
Some of the areas where the process is currently notable include:
Tire Manufacturing
Rubber compounds help in making different tire components – sidewalls, treads, liners, etc. Just as well, compounds can be formulated to meet specific requirements like durability and traction to optimize the functionality of these tires.
Automotive Industry
From producing gaskets and seals to belts and other components, rubber mixing helps broadly in the automotive industry. The process is especially ideal as these components require specific formulations to ensure optimal sealing across their operation.
Industrial Seals and Gaskets
Rubber mixing helps in producing compounds that help create gaskets and seals that optimize the operation of different industrial equipment.
With these products, you get considerable sealing against fluids, gases, and other materials.
Conveyor Belts and Power Transmission Belts
The development of conveyor belts has also benefited from rubber mixing – especially since these materials are made of rubber in the first place. Today, these belts are used across different industries, from transport to mining and more.
Footwear and Shoe Soles
Rubber mixing helps in developing the soles of rubber shoes. In turn, these rubber soles offer cushioning and grip, while ensuring that the shoes last as long as possible.
Construction and Building Materials
In the building space, rubber mixing helps to create rubber roofs, waterproofing membranes, and sealants.
Medical Devices and Equipment
Many products used in the medical space – from diaphragms to gloves and more – can be developed using this technique as well. Of course, it is worth remembering that any medical-grade rubber will need to meet strict quality standards – from biocompatibility to wear resistance and more.
Consumer Goods
You can easily find rubber compounds in different consumer goods – from kitchen utensils to rubber bands and more. For most of these products, specific properties such as elasticity need to be put into consideration.
Electronics and Electrical Insulation
You can find rubber compounds being used to create electrical insulation components like connectors and cable jackets. As long as they offer electrical insulation properties, they can work.
Sports and Recreation Equipment
Of course, we shouldn’t also forget the use of rubber in sports tools like golf grips, sneakers, and inflatable products.
Factors That Affect Your Rubber Mix
At the end of the day, the mix of your rubber compound and its additives will be the key to ensuring a seamless rubber mixing process. And, as we pointed out, finding the right combination is non-negotiable.
To that end, keep the following in mind when you’re in the mixing process as they just might be the key to success:
Raw Material Quality
The first thing that can easily affect your rubber mix is the raw material itself. The polymers, additives, curing agents, plasticizers, and more need to be of top quality to achieve a final rubber product that meets your requirements.
Mixing Time and Temperature
You also need to carefully control the duration of mixing and the temperature at which the process occurs. Overmixing can easily cause heat to accumulate and degrade the rubber product altogether.
Just as well, insufficient mixing time can lead to suboptimal component dispersion, which will also affect the end product.
Mixing Equipment and Parameters
Of course, the type of mixing equipment and the parameters of the mixing process will affect efficiency and compound quality. This is why we recommend optimal equipment maintenance and calibration to achieve the right results.
Additive Dispersion and Homogenization
When additives and fillers are properly dispersed, you get uniform properties in your rubber compound.
Filler Loading and Type
Different filler types – as well as their quantities – can easily affect the properties of the compound; such as abrasion resistance, hardness, tensile strength, and more.
You also need to remember that inadequate filler loading can cause the final compound to get too soft.
Chemical Reactions and Curing
It’s often to find curing agents and accelerators in rubber compounds. These agents optimize cross-linking, and you need to ensure that they are accurately added into the mix to help achieve the right curing characteristics.
Operator Skills and Training
All of this won’t be possible without the person handling the entire mixing process. And, if the operator isn’t adequately skilled, you might end up with a subpar end product. To wit, ensure proper training and see to it that the operator adheres to standard operating procedures.
Environmental Factors
Ambient temperature and the presence of excess humidity in the production environment will most likely affect the behavior and material properties of the mixing process. As much as you can, keep these factors under control going forward.
Operational Challenges For Rubber Mixing
While the outcome is quite functional, rubber mixing is a complicated process that rings in different materials – all of which need to operate under varying parameters. It’s possible to run into several operational challenges that can impact the quality of the final compound and affect the process’s efficiency. Some of those include:
Inconsistent Material Quality
Differences in the properties and the qualities of the raw materials can lead to inconsistencies in mixing. When you get materials from different suppliers or get them in batches, you could end up with varying characteristics that will affect overall compound performance.
Poor Dispersion of Additives and Fillers
Inefficiencies in additive dispersion and filler incorporation will result in a lack of uniformity across the properties. And, if this isn’t checked the compound’s performance will also be compromised.
Overheating and Premature Curing
As we stated earlier, excessive heat during the mixing process will only lead to premature rubber curing. This will lead to processing challenges and affect the compound’s properties. As such, keep a close eye on the mixing process and temperature to avoid heat buildup.
Inadequate Mixing Time
If the mixing time isn’t enough, the mixing will be incomplete. As such, you’d be left with an inadequate dispersion and subpar ingredient blends. This means it is important to optimize mixing time as much as you can.
Equipment Malfunctions
All the tools you use need to be in top shape. Any operational errors, and you could throw the entire mixing process out of whack. This is why you need to implement proper equipment maintenance and troubleshooting when you can.
Material Contamination
If you’re mixing in batches, you need to be especially wary of cross-contamination, which could happen when remnants of a previous batch are added to the next. These foreign particles will affect the compound’s properties, so ensure to thoroughly clean your equipment after each mixing process and adhere to industry-standard cleaning protocols.
Operator Skill and Training
Anyone handling the rubber mixing process will need to be thoroughly trained to ensure that they conduct the job well.
Poor Quality Control and Testing
Quality control is a critical step of any rubber mixing process. You want to ensure that every batch meets your required specifications, and testing ensures that you can identify issues and treat them immediately.
Environmental Factors
Finally, keep a close eye on environmental conditions like humidity and temperature. Each of them can affect material behavior and the mixing process, so maintain consistency in environmental and atmospheric conditions as you go.
Conclusion
In general, rubber mixing is an interesting process that shouldn’t be taken for granted. A lot needs to go into making the right rubber compound, and we at Legenday can help ensure that your rubber products meet the desired specifications across the board.
Need to get started? Give us a call!