Twin screw extrusion is an advanced technology mainly known for its key role in the polymer processing sector. However, it is also widely used in other fields, such as the food and pharmaceutical industries.
The machine used to carry out the process, the laboratory twin screw extruder, melts, mixes, homogenizes, and shapes the material fed into it in a controlled way. It is a highly technical process that guarantees uniformity and reproducibility.
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A sophisticated technology
As mentioned, twin screw extrusion is a sophisticated technology, but it is also not very cheap. The investment required to purchase this machinery for industrial use, install it, and maintain it should be carefully estimated and budgeted.
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As a result, using industrial machinery only for product analysis or formulation testing would be inefficient due to the waste of raw materials and plant downtime.
The laboratory-scale twin screw extruder
A solution to this problem is the lab scale twin screw extruder. This is a highly sophisticated, very small machine capable of operating with minimal quantities of material.
It could be described as a sort of miniaturized twin-screw extruder, capable of recreating the operating conditions of the industrial process, but in the small setting of a laboratory, making tests cost-effective.
This kind of machine can be used in the research and development of new materials, in the feasibility assessments of production processes, and in many other types of analysis. Its importance comes from a tendency of organizations not to proceed by trial and error using industrial-scale plants.
It is also important to note that having a simulation tool that guarantees total accuracy can make all the difference in today’s difficult and competitive industrial market. The lab scale twin screw extruder, in fact, allows the feasibility of a given project to be tested, avoiding unproductive investments.
Twin-screw extruder: what are the main components
A twin-screw extruder is a particularly complex machine from a technological point of view. However, we can briefly highlight its main components. Apart from the engine, the other components are the hopper, the cylinder, the twin screws, and the die.
The hopper is a sort of “funnel” located at the beginning of the machine. It is where the ingredients (e.g., polymers) are poured.
Laboratory twin-screw extruders usually also feature a gravimetric dosing device, which allows the ingredients to be dosed with extreme accuracy. Precision is a key test requirement, as even the smallest differences in weight could affect the results.
A very important component is the cylinder, a sort of “tube” made of materials capable of withstanding high temperatures, pressure, corrosion, and wear. The cylinder is divided into various heating and cooling zones.
In twin-screw extruders, there are two screws that rotate inside the cylinder. They can be co-rotating or counter-rotating. The first ones rotate in the same direction, while the latter rotate in the opposite direction. Counter-rotating screws are more often used to process very hard materials. It is worth noting that the design of the screws varies, in fact, it changes according to the material to be processed and the size of the plant.
Lastly, the die is the final part installed at the extruder outlet that gives the material its profile. The shape of the material changes depending on the type of outlet. For example, circular holes produce “strands,” while flat slots produce films.
Extruders can be customized with downstream equipment to meet specific process requirements. One example is water bath or cooling belt systems, which allow solidification of the material coming out of the laboratory extruder to maintain its shape. Another typical example is machinery that conveys the extruded product into various types of containers.
Single-screw extruders and twin-screw extruders
Extruders can be divided into single-screw and twin-screw machines. These are two different systems, in terms of both cost and performance.
Compared to a twin-screw machine, a single-screw extruder has a simpler configuration. It is a suitable choice for applications where production volumes are low or medium-low and where simpler processing is required because the materials involved are less resistant and do not require special additives or mixtures. When it comes to cost, single-screw extruders are less expensive and maintenance is much less complex. Operation-wise, single-screw extruders are easier to manage.
A laboratory twin screw extruder is a more sophisticated and technologically advanced machine. Its blending power is significantly higher, which is essential when the work involved is more complex. In addition, it is capable of processing a wider range of materials, including those with higher viscosity and abrasiveness.
The choice between one technology and another is therefore mainly linked to the sector in which you operate and your production requirements.
