Stainless steel heat break

In all metal hot end, why is the threaded stainless steel tube which connects the heat sink to heater block, called a 'heat break'?? It is a metal which conducts heat...How is it a heat break?

Stainless steel is actualy transfering heat pretty badly. Thanks to it's high strength it can be thin so over all it is a pretty good choice for a heatbreak.

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[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

Thank You, Also why is brass used as nozzle even though aluminium is twice a better conductor than brass?

Brass has a higher capacity to store heat, leading to more evev heating. Also the aluminum oxid that builds up on aluminum is a bad heat conducter.

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[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

Lots of other materials have been tried, there was a thread on here where someone was using a ceramic fuse as a heat break. I think the problem is they're either not strong enough or they are too rough to stop the filament sticking on retraction. Sure you can line anything with ptfe but then you get the problems of pfte breaking down after prolonged moderate temperatures or short high temperatures, which is the point of all-metal heatbreaks.

What's often suggested is to use thermal compound such as copper grease or heatsink paste between the heatbreak and heatsink but use none between the heatbreak and the heater block. Also to insulate the heater block with kapton/fibreglass mat or something similar to keep the heat in the heater block.

There are hot end designs which overcome these problems using less common materials. Such as Srek's merlin hot end or the genuine J Head.

Edited 1 time(s). Last edit at 04/24/2016 04:24AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

If aluminium oxide is build upon aluminium, how is there efficient heat transfer between heater cartridge and heater block?

You have way more surface area that connects the cartridge and the block and you have a pretty high force pressing them together. This is quite different inside of the nozzle. Also it can work, it is just not very good and in the end not worth the effort.

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[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

Quote
Pawan
Thank You, Also why is brass used as nozzle even though aluminium is twice a better conductor than brass?

Brass is also a little harder wearing than aluminum, so the critical nozzle bore region lasts longer.

There are also one-piece stainless steel nozzles, that combine the nozzle and the heat break onto a single component. I find them reliable and hard wearing, but of course you can't swap nozzle sizes so easily.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Have you got a link for those they sound like a good idea.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Here's one: [emaker.io].

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

The role of the heat break is to make a transition of temperature as neat as possible and so, limiting the heat transfer to the upper part of the hotend.
Austenitic stainless steel have a thermal conductivity 3 times lower than carbon steel, which help to limit the heat transfer.

So, the groove you see in heat break is there to reduce heat transfer.

But austenitic stainless steel have a property which is often overseen, when submitted to very high pressure, they harden very significantly, so they became a very high strength material. This is the reason why they are difficult to machine, and quite impossible to machine with high speed steel, as they tend to became harder than the tool.

So, if machined in a way that the tool exert intense pressure (notably with negative tool angle), the skin of the machined part increased it strength to 2 to 3 times the nominal strength and so the remaining skin could be thinned.

The external slot shall be machined first, and the hardening due to the machining will make the hole drill bit to self-center while drilling.

The steel 303, less common than 304 or 316, does have better hardening properties while machined.

Practically, the pressure reinforced skin thickness is very low, so the resistance of this weak tube does noy vary much with its thickness, and you are limited to practicability of the machining.

Personal experience (more than 25 years old) have shown 304 SS tensile strength increased from 500 MPa to more than 1200 Mpa for a skin of ~0.2 mm.

So, if properly machined (and this is a big if), the reduced thickness of the tube under the heat break groove is much stronger than most think and rupture side load on the nozzle may be more than 20 kg.

Edited 1 time(s). Last edit at 04/24/2016 02:33PM by PRZ.

Why do we need a machined heat sink with active cooling like the E3Dv6? Cant we have a ceramic hollow cylinder with a threaded end into the tapped heater bloc?

Quote
Pawan
Why do we need a machined heat sink with active cooling like the E3Dv6? Cant we have a ceramic hollow cylinder with a threaded end into the tapped heater bloc?

That would not cope well with the heat rising up inside the filament. Depending on the hotend, the extrusion speed, retract and the material printed you can get away with minimal cooling without a fan. To make sure xtrusion works reliable active cooling is useful.
With my Merlin hotend the M10 thread on the outside is sufficient for cooling, no extra machined aluminum is neccessary.

Edited 1 time(s). Last edit at 04/24/2016 04:59PM by Srek.

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[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

Hello,

Actually, you don't need a machined heat sink with active cooling. Genuine J-Head hot-ends have been printing without active cooling for years.

Best Regards,

Brian

Quote
Pawan
Why do we need a machined heat sink with active cooling like the E3Dv6? Cant we have a ceramic hollow cylinder with a threaded end into the tapped heater bloc?

I had my E3D v6 crash into a part on the print bed and it bent the heat break. I bent it back straight again and continue to use it, and ordered a spare.

Quote
PRZ

Personal experience (more than 25 years old) have shown 304 SS tensile strength increased from 500 MPa to more than 1200 Mpa for a skin of ~0.2 mm.

So, if properly machined (and this is a big if), the reduced thickness of the tube under the heat break groove is much stronger than most think and rupture side load on the nozzle may be more than 20 kg.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]