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When it comes to rubber mixing in industrial applications, choosing the right equipment is crucial for achieving optimal results. Two primary types of machines commonly used in rubber compounding and mixing processes are open mills and internal mixers. Understanding the differences between these two types of equipment can help manufacturers make an informed decision on the best option for their specific needs.
What Are Open Mixers and Internal Mixers?
First of all, we need to figure out what types of machines are the open mixer and the internal mixer. Open mills, also known as two-roll mills, have been a traditional choice for rubber mixing for many years. These machines consist of two counter-rotating rolls that create a shearing action to blend and process rubber compounds. Open mills offer versatility in terms of batch size and material processing, making them suitable for small to medium-scale operations. They allow for manual control of the mixing process, making adjustments and monitoring relatively straightforward.
Internal mixers are developed from open mixers. they have a enclosed mixing chamber containing a pair of rotors. The materials to be processed are put into the chamber, and the rotating rotors rotate to each other at a constant friction ratio to apply continuous shearing and squeezing forces to the rubber compounds to finally complete the masticating or mixing. Internal mixers are often preferred for larger production volumes and more demanding mixing applications.
Pros and Cons of Open Mixers and Internal Mixers
Labor requirements
The open mill utilizes the nip between two exposed rolls rotating at a fixed different speed to process the rubber mixture. This feature determines that its operation cannot be separated from the intervention and monitoring of the operator during the mixing process. When you operate a open mill, you need to manually add base rubber and feed various required compounding agents when needed. During the mixing process, you need to use a handheld scraper to constantly fold, cut and turn the rubber material wrapped on the front roll to enhance the mixing effect. Therefore, the use of a mixing open mill has high requirements on the operator’s physical strength and labor.
The internal mixer uses a pair of motor-driven rotors to process rubber compounds in a sealed chamber. The mixing process does not require operator intervention. The machine allows you to set the processing time and speed in advance. After the preset time is reached, the machine automatically stops for inspection, which greatly reduces the labor intensity of the operator. Especially in large-scale production, workers using internal mixers rarely need to do too much physical labor once the mixing parameters are set, they only need to ensure the normal operation of the equipment.
Operational safety
As mentioned above the difference in the way of operating with an open mixer and internal mixer determines that it is safer for the operator to use an internal mixer than an open mixer. The two rolls that act directly on the material in an open mixer are exposed. When you add material or manually cut or turn the rubber compounds on the rolls during the operation of the machine, it is possible for a scraper or fingers to get caught in the roll gap if you are not paying attention. Of course, to prevent this from triggering even worse hazards to the operator’s body if it happens, every open mixer is equipped with several emergency stop buttons and devices. However, the rotor of the internal mixer is located in a closed chamber that is isolated from the outside world while the machine is running and does not require hands to touch the area, so there is no danger to the operator when the rotor is churning the material.
Production Capability
While an open mixer uses the shear force generated between two oppositely rotating rolls to masticate or mix the rubber materials, an internal mixer puts the rubber materials into a sealed chamber and then uses two rotors to disperse and mix the material components. The smallest laboratory internal mixer has a mixing chamber with a capacity of 1L, which is a very large capacity compared to an lab open mixer. Experimental open mixers can accept smaller volumes of material at a time, and are suitable for small batch prototyping and trial production so that no material is wasted. In general, Open mixers have a simpler design and are typically used for smaller production runs and for mixing materials that do not require intense blending or processing. Internal mixers are commonly used in larger-scale production processes where high mixing consistency is required.
Processing Efficiency
In terms of working efficiency, internal mixers generally offer higher Processing efficiency compared to open mixers for several reasons:
Continuous Mixing: Internal mixers, such as Banbury mixers, are available in being designed for continuous mixing of materials, which can result in higher throughput and efficiency compared to batch mixing in open mixers. This continuous mixing process allows for a more streamlined production flow and reduces downtime associated with batch mixing.
Better Mixing Control: Internal mixers offer better control over the mixing process, including temperature, mixing speed, and material flow. This superior control allows for more precise blending of materials, resulting in consistent product quality and reduced material waste.
Reduced Labor Requirements: Internal mixers are often equipped with automated controls and monitoring systems, which help streamline the mixing process and reduce the need for manual intervention. This can lead to fewer labor requirements and increased process efficiency.
Temperature Control
When the open mixer processes rubber, the two rolls are exposed to the outside. The temperature of the processed rubber material generally does not rise to a very high level when the machine is working. The heat generated by the rubber material during processing is easily released to the external environment. If the temperature of the rubber material is relatively high, it can be stopped for a period of time to let it cool down before mixing. In addition, cooling water can be passed through the rolls of the open mixer to cool the material when needed.
When the internal mixer is working, the rubber material is processed under certain pressure conditions in the mixing chamber, and the faster the rotor rotates, the stronger the shearing effect on the material, and the higher the temperature naturally generated. Although cooling water is allowed to pass around the chamber and the rotor of the internal mixer to cool down, the high temperature is not easy to release in the enclosed chamber. Generally, internal mixers are equipped with advanced heating and cooling systems that allow for precise temperature control during the mixing process.
The low temperature control of the internal mixer is not as good as that of the open mixer. For temperature-sensitive rubber materials, scorching is easy to occur if using an internal mixer, and it is more suitable to be processed by the open mixer.
Energy consumption
When mixing rubber in an internal mixer, about 95% of the energy can be utilized, which can greatly save energy costs compared to an open mixer. The internal mixer adopts a sealed mixing chamber structure, which can cause the rubber raw materials to be subjected to a large amount of shear in a short period of time, thereby achieving a faster mixing effect. The internal mixer has higher working efficiency. To achieve the same mixing effect, the internal mixer takes less time, thus saving more energy costs.
Environmental Pollution
The open-type characteristics of the two rolls of the open mill expose the working area to the outside. During processing, when the materials and some additives are added to the upper area between the two rolls, it is easy to cause dust to fly, pollute the air in the working area, and even harm the health of the operator, and also cause material loss.
There is no need to worry about this problem when using an internal mixer, because the materials are fed into a sealed cavity for processing, and they cannot escape into the air, so naturally there will be no material loss.
In short, using an internal mixer is more friendly to the site environment than using an open mixing mill, which is more beneficial to the health of the operator, and can reduce material waste.
Procurement Cost
In general, internal mixers are more expensive compared to open mixers. Here are some reasons why internal mixers tend to have a higher cost:
Complexity and Technology: Internal mixers, such as Banbury mixers, are more sophisticated and technologically advanced than open mixers. They are equipped with features like automated controls, precise temperature regulation systems, and complex mixing mechanisms, which all contribute to their higher manufacturing and maintenance costs.
Material Handling and Applications: Internal mixers are capable of handling a wider range of materials, such as rubber compounds, plastics, and elastomers, which may require specialized mixing processes and equipment. This versatility and ability to handle complex materials contribute to the overall cost of internal mixers.
Precision and Control: Internal mixers offer better control over the mixing process, including temperature control, mixing speed, and material flow. The advanced control systems and monitoring capabilities of internal mixers add to their overall cost but result in more consistent product quality and higher efficiency.
Conclusions
In conclusion, the choice between an open mill and an internal mixer for rubber mixing depends on various factors such as labor requirements, operational safety, production volume, processing efficiency, temperature control, energy consumption, environmental pollution, budget, etc. Both types of equipment have their own advantages and limitations, and the decision should be based on the specific requirements of the manufacturing process. Ultimately, manufacturers should evaluate their needs, consider the pros and cons of each option, and select the machinery that aligns best with their production goals and priorities.
