Thermoplastic pellets for large scale 3d printing explained
CEAD’s large scale 3D printing technology uses thermoplastics. Thermoplastics are plastics that, after applying a specific heat, melt and can be reformed. The thermoplastic material for large scale 3D printing comes in “pellets” or also called “granules”. These pellets typically have somewhat the same shape. However, how the pellets are manufactured determines largely how they look and whether they can be processed.
By understanding more about the material, you can better determine what is applicable for your production process. In this blog we therefore explain more about the shape, sizes and application of different thermoplastic pellets.
Average size of thermoplastic pellets
Typically these pellets have a tubular form shape. The average size is about 2 mm in diameter and 6 mm in length. However, wider (up to 5mm) and longer (up to 10mm) can be processed as well. Though smaller can also be processed, the processing becomes challenging when the pellets are too small.
An example of those really small particles are the industry standard, dust-like pellets for rotational moulding. These are so fine that air filters in the system are quickly saturated with the particles, obstructing the air filters and consequently making the system less productive.
Another example of the processing becoming challenging with smaller pellets, is when materials do not have enough mass. The material transport may be less efficient in that case. Smaller pellets (especially very long but narrow shapes) can easily obstruct the funnel or other feeding mechanisms which rely on the gravity forces as well.
Average shape of thermoplastic pellets
While generally speaking, anything called a granule or pellet by the industry will work, some pellet shapes can have a tendency to “bridge” when stacked closely together. This is often the case with pellets cut when the material is still hot. To prevent this, most pellets have a pillow shape, with pointed corners that ultimately make it possible for the pellets to stack up efficiently.
Vibrating motors are integrated in the 3D printing systems to overcome this “bridge” issue. For the above mentioned issue, where the very long and thin materials “strand”, the vibrating motors form a solution too. The vibration makes sure that the pellets do not form a closely stacked block and obstruct the funnel by holding its own weight.
Application of recycled (shredded) thermoplastics
Recycled materials can also be processed, and yes thermoplastics can be recycled. An example would be when you have scrap or a failed print from a previous project. This can be recycled using a shredder and feeding it into the system again. Our 3D printing systems are capable of processing the so-called shredded material, which makes recycling quite easy.
Another way of using recycled materials is purchasing recycled grades from suppliers. In such a case, the materials are sorted, cleaned, and repelletized for future use. These materials are often recycled using an extruder which means that the material is supplied in pellets again.
In both cases it is important to take into account the effect recycling has on the material. It is almost always impossible to retain the same quality as the virgin material. Therefore, either the material is used for less structural or critical purposes, or the recycled material is combined with a certain amount of virgin material to retain the same quality. The amount of virgin material needed heavily depends on the type of thermoplastic, the application and the fillers in the material.
In the end, both recycled materials shapes are directly processable by the equipment. In the case of the mechanically recycled material the “shards” need to be small enough to pass through the system without obstructing the hoses and openings.
Understanding the large scale 3D printing process
Thermoplastics are used to a great extent in other processes such as injection molding, plastic extrusion, rotational molding, vacuum forming and in small scale printing such as FDM (extrusion based process) and SLS (laser Sintering process). With the addition of large scale 3D printing, more possibilities open up. It is therefore good to understand more about the material and the large scale 3D printing process.
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