The magic of flexible materials and the Shore scale
As a beginner 3D printer, your first steps probably led you to filaments such as PLA, ABS or ASA. They are generally easy to print with and have practical properties. But sooner or later you will definitely start to come across the concept of flexible materials - these are flexible filaments that open up new possibilities of use. There are rumors about these filaments that could discourage many 3D printing enthusiasts. Printing with them can be more demanding, so they are not suitable for beginners. Sometimes the printer settings need to be adjusted to suit the needs of the filament. And beginnings sometimes end in failure. But believe me, it would be a shame to leave the flexible filaments hidden in a drawer and deprive yourself of their charm. Because these materials combine two basic properties: they are flexible and strong at the same time. The degree of flexibility is determined by the Shore scale, which we'll get to later, but if you're eager, you can read more about it here.
A miracle called flexible filament
Just look around and you will immediately realize how often rubber material is used. Both for practical things in the home and in the industrial area. With flexible materials, you can print various prototypes, sample molds, various seals and covers, tires for RC models or even small upgrades to printers such as rubber feet. All these products share the same requirements - they should be flexible and malleable to a certain extent, but also resistant to mechanical damage.
First a bit of theory
On the filament market, you will come across two names - TPE and TPU. The abbreviation TPE hides the name for the material thermoplastic elastomer (sometimes you can meet the name thermoplastic rubber), the abbreviation TPU is used for thermoplastic polyurethane. TPE filament is actually the superior group under which TPU material falls. These materials are produced by a combination of hard plastic polymers (which can be, for example, the material PP - polypropylene, PA - polyamide or PU - polyurethane) and soft materials (for example, polyether).
You might be wondering what is the magic behind such good flexibility in flexible materials. The answer is the excellent adhesion of the individual layers. Thanks to this, models extruded from these materials can be flexible and do not break as easily as with other non-flexible materials.
Where do we meet flexible materials?
The most frequently used TPU material has found its application in various areas. One of the most widespread will probably be the automotive industry, also thanks to the fact that it is highly resistant to oil and other chemical substances. In industry, you will come across it in the production of various protective packaging, aids and vibration and shock absorbers. We also encounter TPU in everyday activities, for example watch bracelets can be made of it. Other areas where it can be used are sporting goods or, for example, in surgery.
Why include flexible materials among your favorites?
You will appreciate the flexibility of flexible materials when printing various practical gadgets, but also prints that you use as part of your hobby. All RC model enthusiasts will surely be excited by the filament specially designed for printing RC model tires from the TreeD Filaments brand.
Among the advantages of TPE or TPU is the often mentioned flexibility, but it is not the only advantage that this material can excite you about. Judge for yourself:
- it is soft
Thanks to its flexibility, you can easily bend and stretch it.
- will retain its original shape
If the prints are in a suitable environment, I can keep their original shape for a long time.
- minimal shrinkage and deformation
When printing, you don't have to worry about a high percentage of shrinkage and deformation.
- impact and chemical resistance
Prints are highly resistant to mechanical impact and chemicals.
- dampens vibrations and shocks
Thanks to the ability to dampen vibrations and shocks, this material is ideal for the production of components for various devices.
But to be fair, there are also darker sides:
During printing, the so-called stringing, or filament dripping from the nozzle, may occur a little more often (in printing slang, you might also come across the term "hairy print"). This manifests itself in the fact that small parts of the filament already stick to the printed model (mostly this is caused by the fact that the filament still flows out of the nozzle, even when the extruder moves to another position). |
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Flexible material needs to be printed relatively slowly, otherwise the nozzle could become clogged, which will manifest itself in an inconsistent flow of filaments, and this will immediately be reflected in the appearance of the printout. |
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- it is hygroscopic
TPU/TPE is among the materials that are more susceptible to absorbing moisture from the surrounding environment. It will therefore be necessary to put more emphasis on the correct storage of the filament. You can learn more about how to properly store filament and how to dry it if it gets wet in this article.
- requires special printer settings
Flexible materials have specific properties and these also require specific printer settings. Especially if you're going to print with it for the first time, you'll probably have to play around a bit with the ideal printer settings.
- more difficult post-processing
Post-processing of prints can be a bit more complicated than with other non-flexible materials.
- print at lower speed
You should print at a lower speed, which goes hand in hand with an overall longer print time.
- more difficult printing with supports
If you are going to print a model where some parts will stick out and not directly connect to the previous layer, you need to add supports to the model. Which could be a complication in the case of flexible materials.
Shore hardness scale
Although this scale was invented around 1920, it is still used today. It was invented by the American Albert Ferdinand Shore, after whom it earned its name. The scale shows the degree of resistance to mechanical compression, or how hard a particular material is, and how much effort is needed to squeeze it. It is an important indicator in case you decide to choose a suitable material for printing a functional model.
Hardness is measured using a hardness tester, which pushes a ball, cone or pyramid into the material and assesses how much resistance the material has to create. Thanks to this test, you can compare the hardness of different materials. Shore hardness is rated on the international rubber hardness scale from 0 to 100, with the higher the number, the greater the hardness. But to make it not so simple, there are different scales of hardness:
- The Shore 00 measures materials such as foams, gels and very soft rubbers
- The Shore 0 measures soft to medium rubbers and soft plastics
- The Shore A measures rubber for casting
- The Shore B measures mid-range rubbers and plastics (it's a convenient scale if you're working with a variety of materials)
- The Shore C measures from medium rubbers to hard plastics
- The Shore D measures hard rubbers, semi-rigid plastics and hard plastics
An example can be sealing rings, where it is important that they are sufficiently flexible, but at the same time strong. And in different proportions depending on the type of product material that we want to seal. The softer material is best suited for sealing rough surfaces, as its flexibility and malleability will ensure it can conform to uneven areas and allow for a precise seal. Harder material provides greater resistance to mechanical damage, but also offers less flexibility, which makes it the best choice for sealing even areas that are exposed to high pressure. Hard materials such as polyurethane are used for hydraulic seals and a good gauge to measure them would be Shore C or D.
If you need to convert between different hardness scales, this table will serve you well:
Shore scale - source: https://www.totallyseals.com
The often used Shore A hardness scale focuses on generally softer and more flexible materials. The scale indicates whether particular materials are extremely soft or harder. In addition to soft rubbers, semi-rigid plastics can also be tested on this scale (with higher results).
Examples from the Shore A scale:
Hardness 10A Shore: this is an extremely soft material, but it has the disadvantage that it wears out quickly.
Hardness 20A Shore: filament with this shore score is extruded smoothly, but its resistance is still not very high.
Hardness 40A Shore: the material is slightly more resistant than materials with a lower Shore degree. Its use is ideal for models that are not subjected to too much mechanical pressure. The hardness is similar to pencil eraser.
Hardness 70A Shore: this material combines excellent flexibility and strength.
Hardness 90A Shore: material that can withstand greater pressure. They have a longer lifespan and you can use them in dynamic applications.