What is Rubber Mixing?
Rubber mixing is a vital process in rubber production. It entails adding special ingredients to a base polymer to form a uniform rubber mixture offering excellent service. Besides a polymer, a rubber mix typically contains:
- Reinforcing agents
- Accelerators and their modifiers
- Color fillers
- Crosslinking agents
Rubber Mixing vs. Rubber Compounding
Rubber mixing describes the fundamental rubber processing step in which additives and compounds are amalgamated. On the other hand, rubber compounding describes mixing and producing various rubber compounds.
Each rubber compound often requires specific ingredients depending on its application.
The Principles of Rubber Mixing Process
By rubber mixing compounds, you will make a rubber polymer amalgam which with consistent properties.
In other words, you can produce rubber compounds in more cost-effective way. Such compounds have excellent characteristics.
For instance, custom rubber mixing efficiency determines the cost of rubber manufacturing. Generally, excellent rubber mixing ensures consistent, high-quality products that meet market needs.
Another noteworthy point is that rubber is extremely thick and moderately elastic. Also, the additives come in liquid or powdery form. Thus, electrically-powered machinery like mixers and mills is essential to effectively blend the polymer and the additives.
Choosing Rubber Mixing Machine
When it comes to mixing of rubber, you can choose:
- Internal mixer for rubber
- Two roll rubber mixing mills
- Continuous rubber mixer
1. Internal Mixers
Internal mixers mainly comprise two rotors, cooling and lubrication systems, and a mixing compartment. Other internal mixer components include a feeding chute, unloading apparatus, and transmission mechanisms.
Internal mixers blend polymer and ingredients alternatingly. They produce high-quality, homogenous products. Internal mixes are more popular than rubber mills due to their quicker run cycles and large production capacity.
Internal mixers produce less dust and waste during a production cycle. So, another benefit of using internal mixers is a more hygienic production room.
Internal mixers also require less manning since most of their operations are mechanized.
You can choose:
· Tumble Blenders
Spinning tumble blender walls often cause collision between solid particles, steadily forming a consistent rubber mixture. Various companies manufacture different tumble blend brands with varied capacities and geometries. The common tumble blender shapes include a twin shell, double cone, Y-cone, and horizontal cylinder.
Besides their affordability, tumble blenders are preferable over other mixers because they are easy to assemble and operate. However, tumble blenders cannot mix large volumes of materials. Likewise, their mixing effectiveness needs to be improved.
· Blade Mixers for Rubber
These rubber mixers combine the action of a rotating screw and constant collision to displace particles. Their geometries determine their classification.
For instance, a U-shaped tank holds the rotor in trough mixers. As the rotor spins, it displaces the particles around the mixer, gradually mixing rubber compounds.
High-velocity propeller blade mixers mix particles quickly by pushing them into the high-speed airstream. Their operations are highly exothermic. Thus, they are only ideal for high-volume mixing.
· Air Mixers
Air mixers expose the rubber ingredient particles to a high-velocity air current that displaces them. Some air mixers can run continuously due to their huge fluidized beds, which allow high-volume processing.
2. Continuous Mixers
In most rubber production setups, mixing is a multiple-step process. In the first stage, the operators add inert rubber ingredients to an internal mixer. The ingredients incorporation occurs before the mixture is deposited into a second mixer or mill.
In the second stage mixer, the operators add vulcanizers as the mixer disperses the particles to achieve high homogeneity.
Nonetheless, these continuous mixers are rarely used since they do not fully incorporate material particles.
3. Two-Roll Rubber Mills
Although newer milling technologies have replaced the two-roll mills, manufacturers still use them to shred waste from other mixers. Besides, research on new rubber formulations is often conducted on these mills. Mills are also suitable for small-batch production.
Two-roll rubber mills’ low prices and faster startup time are ideal for mixing high-grade rubbers.
Step-by-step Rubber Mixing Process
The first stage involves deagglomerating huge ingredient heaps into tiny particles that can easily combine with the polymer to form a homogenous compound.
The second stage involves rigorous homogenization of the molecules. Here, the mixer cuts the rubber particles, imparting shear stress on the rubber polymer and tiny ingredient particles. As a result, it pulverizes them into ultra-tiny sizes that can move and mix rapidly.
However, the mixing process can be extremely time-consuming. Pulverizing the ingredients before mixing can help reduce the mixing duration. Pulverizing rubber ingredients increases their surface area, hastening their amalgamation into the polymer.
The next phase after the ingredients’ amalgamation is their dispersal. One easy way of achieving excellent dispersal of ingredients in the polymer is by lengthening the mixing period. The shear stresses imparted on the polymer particles also determine the ingredient’s dispersal rate.
Dispersion of ingredients considerably determines the rubber product’s characteristics. For instance, big carbon back lumps always form coarse grains, forming weak points in the structure.
Effects of Mixing Rubber
Mixing rubber with other ingredients has several impacts, such as:
- Inducing desirable properties: Mixing rubber produces compounds with distinct characteristics, such as hardness and vibration-damping.
- Increasing elasticity: Mixing rubber with other additives can enhance its elasticity for specialized applications.
- Make it easy to machine: Rubber mixing can increase flexibility, elasticity, and hardness. These properties ease its processing and adaptability to numerous applications.
- It makes rubber processing more sustainable: Adding compounds to rubber and recycling wastes makes it more renewable.
Practical Examples of Mixing
Silicone Rubber Mixing
Silicone rubber mixing entails blending rubber with carbon black and silica gel to form a compound with excellent mechanical and electrical properties. For instance, silicone rubber is chemically inert, resistant to extreme temperatures, and a superb insulator. These properties explain why silicone rubber is extensively used in manufacturing various healthcare, aviation, electrical, and automobile components.
Using powdered rubber to manufacture rubber compounds offers several advantages and disadvantages. Notably, preparing powdered rubber requires significant inputs in terms of handling equipment and additional power costs. On the other hand, powdered rubber mixing consumes less time, easing large-scale production.
The process involves mixing pulverized rubber with other ingredients to form a uniform material. The powdered rubber mixing requires less shear force to distribute material particles.
Future Rubber Mixing Systems
Rapid technological advances in rubber production mean that future rubber mixing technology will produce more cheap, homogenous, high-quality rubber compounds more hygienically. In summary, these ultramodern mixing setups will have the following unique capabilities:
- Automated scales that perfectly and flexibly weigh the rubber compound ingredients and additives.
- Modern mixers with adjustable hydraulic cylinder pressure or rotor speeds.
- Instrumentation and control systems that determine mixing duration based on the polymer’s properties like thickness and temperature.
- Robust dust-shielding systems, mechatronic components, and rotors to reduce downtime.
- Automated milling and forming setups to reduce workforce requirements.
- Real-time sampling and examination of all batches at the milling machine’s exit to inform changes to the process formula and post-mill processing.
- Cutting-edge control systems to enhance the compounding process. For instance, these systems will self-adjust, producing a more.
In short, custom rubber mixing plays an integral role in rubber part manufacturing process. For successful mixing of rubber, choose an efficient machine, understand the technique and select high quality rubber materials.