Usually the hardness of the material is considered primary for nozzles used with abrasive filaments. Has friction between between nozzle material and abrasive filaments been considered? It seems that friction as well as hardness would play a roll in how long the nozzle lasts. Perhaps, this is considered with ruby tipped nozzles.
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$\begingroup$ How is friction not just wear in progress? $\endgroup$– Zeiss IkonCommented Jun 18, 2021 at 14:25
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$\begingroup$ @Zeiss So you are saying friction is accounted for by measuring the wear of the abrasive filament on the nozzle rather than measuring the friction properties between the nozzle material and the filament material at extrusion temperature. If so, you could put that in an answer. $\endgroup$– Perry WebbCommented Jun 18, 2021 at 14:32
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$\begingroup$ No, I'm saying they're effectively the same process -- friction measures the force and energy it takes to wear away the nozzle material. $\endgroup$– Zeiss IkonCommented Jun 18, 2021 at 14:34
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2 Answers
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Yes, Friction between nozzles and the material plays a part in the printing process. Eventually, the nozzle diameter will widen if the printer is using an abrasive filament that is using things like carbon fibre or iron. The ruby nozzle is essentially a catch-all that won't wear out no matter the filament you buy. However, the steel nozzle is good enough when it comes to most abrasive filaments; and it has the added bonus of insulating the molten filament from the outside air much better than the much more thermally conductive brass nozzles.
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$\begingroup$ But insulating isn't what we generally want the nozzle to do -- rather, we'd usually want to see it conducting heat from the heat block to the filament to ensure proper melting at useful feed rates. $\endgroup$ Commented Jun 18, 2021 at 14:36
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1$\begingroup$ @ZeissIkon, actually no. By the time the filament gets to the nozzle, it should already be molten. There are hot end socks that cover the heat block as well as the nozzle: fabbaloo.com/wp-content/uploads/2020/05/… $\endgroup$ Commented Jun 18, 2021 at 14:40
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$\begingroup$ Ruby is chromium doped sapphire. I assume ruby is desired because of visibility, the reason it is desired for mechanical watches. $\endgroup$ Commented Jun 18, 2021 at 14:56
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$\begingroup$ @user77232 Generally, there are only a few millimeters of heat break in which the filament ought to come into contact with hot metal before reaching the nozzle -- and that only if you have an all metal hotend. Otherwise, if the filament is melting significantly in the PTFE tube, isn't that "heat creep" that can lead to clogs, retraction failures, etc.? $\endgroup$ Commented Jun 18, 2021 at 15:12
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$\begingroup$ Remember the ruby tips are on brass nozzles, which have better heat conduction than steel, except for the ruby. However, some people who have used both say the steel works fine and the ruby isn't worth it. $\endgroup$ Commented Jun 18, 2021 at 15:41
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Friction is known to differ and it has been considered at least in some products: here Micro-Swiss sells a plated nozzle with reduced friction and increased hardness.
It is not clear from any known measurement whether the friction plays any role in the print performances, since so far lower friction coatings (Nickel) are also harder, therefore you never know whether the increased lifespan is due to the reduced friction or the harder coating.
Also, I am not aware of any test where a lower friction nozzle results in higher flow rate and print speed. I am only aware of a diamond-filled PLA which claims higher printing speed, confirmed by CNC kitchen (last graph).
