The role of the 3D Printer Nozzle
The 3D printing nozzle is a crucial part of the 3D printer, the last printer part that touches the material before it is deposited on the object being built. It needs two critical characteristics: high wear resistance and good thermal conductivity.
Wear resistance of the nozzle.
The wear of the nozzle is the cause of many 3D printing issues and failures. Some filament materials degrade the nozzle faster than others, but there is constant friction between the laid material and the nozzle during print. For nozzles made of brass, the most popular type of nozzle thus far, a degradation that reduces the quality of the part will occur after printing pure PLA for a hundred hours or after printing carbon-fibre-filled
As you can see from the picture above, the geometrical parameters of the nozzle tip change significantly, which leads to many issues for the printed part.
It might come as a surprise to many people that the leading cause of so many 3D printing issues and failures is a worn-out nozzle. That little thing at the end of the extruder often makes the difference between a good and bad print.
Thermal conductivity of the nozzle.
The conduction of heat energy from the heating element to the filament is essential and, perhaps, one of the most misunderstood physical phenomena during 3D printing.
Temperature is the degree of hotness or coldness of a material. It's a measurable matter property which characterizes molecules' speed and amplitudes of vibrations and is measured in degrees. (C, F or K)
On the other hand, heat is not a characteristic of a material. Heat transfer is a process quantity and represents the energy which transfers from one object (or medium) to another during the "heat transfer" phenomenon.
Heat transfer cannot be measured directly but can be calculated using other measurable properties. The "heat transfer" moves the energy from the heat block to the nozzle and further to the plastic material, causing it to melt and get to the adequate viscosity to 3D print properly. Being energy transferred in time, we measure it in Joules per hour or Watts.
To understand what happens during a 3D printing job, we will consider the formula that describes the heat transfer through conduction:
From this, we can see that the amount of heat transferred from the heat block to the filament is directly correlated with the coefficient of thermal conductivity of the nozzle material.
To appreciate the importance of this observation, let's consider the following example: printing regular PLA using a brass nozzle versus using a tool steel nozzle.
To print at the same speed with the same quality, we need to transfer the same amount of heat per time. The equation will look like this:
so, we have
T2B is the temperature of the heat block when printing with a brass nozzle (220C);
kb is the coefficient of thermal conductivity of brass (92 W/(m*k));
ks is the coefficient of thermal conductivity of tool steel (27 W/(m*k));
T1 is the temperature of the melted PLA filament material (200C)
It is a known thing that if you use a tool steel (or other steel) nozzle, you need to bump up the temperature. Still, few people realize how much you need to bump it up to accomplish speeds comparable to a brass nozzle. And while it is okay to use these temperatures while printing fast, at the time of positioning travels and retractions, when the extruder is not pushing filament, the temperature in the melted filament might get over the limit of the polymer degradation.
The following table shows the thermal conductivity coefficients for some common nozzle materials.
Replitech cemented tungsten carbide nozzles
Our cemented tungsten carbide nozzles have a unique combination of high wear resistance and good thermal conductivity and thus constitute the most versatile material for 3D printing nozzle applications. While the complicated manufacturing process causes a higher initial cost than the other nozzle alternatives, the value is significantly superior to any other options when you consider that it will last and function correctly longer than the life of a typical 3D printer.
Our nozzle also withstands deformation, corrosion, heavy load, high temperature and high pressure – as it is made from one of the few materials that can fulfill all these demands.
The unique properties of our cemented carbide nozzles offer a more dependable solution than any other nozzle material to the most challenging problem encountered in 3D printing – reliability.