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Old 07-19-2020, 12:08 PM   #1
cook
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Question Airgap in soldering iron tip

Some soldering tips do not fit on the heater element very tightly and you end up with an air gap between the tip and the heater core.

What experiences has anyone had using high temp copper paste or silicone grease to fill the air gap and get better heat conductivity on the tip?
Did it work well over time?
Or maybe you used something else to fill the air gap?
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Old 07-19-2020, 01:28 PM   #2
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Default Re: Airgap in soldering iron tip

I've only seen the airgap issue with Hakko tips for 900 and FX888, whose tips I measured are a few thou smaller ID than 900 series tips. I guess Hakko tried to improve the heat transfer.

The airgap is there for two reasons - manufacturing tolerances and thermal expansion.
The thermal expansion coefficient of the ceramic heater compared to a iron/copper tip, it seems to be about half ref. Kyocera. This means the metal (tip) changes size twice as much as the ceramic and I imagine a cold tip should not crush the ceramic, or squeeze out during warm up when the heater is hot but tip cold. You don' want to crack the heater.

Silicone (based) grease was tried and does not work because it can't take the high temperatures and becomes a huge mess. https://www.mcmaster.com/heat-transfer-paste/

I wonder if a copper foil wrap would work better?
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Old 07-19-2020, 01:47 PM   #3
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Default Re: Airgap in soldering iron tip

I bought a piece of thin copper with the idea to make a thin tube, then I discovered T12 tips and irons, so didn't bother with the upgrade.
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Old 07-19-2020, 02:11 PM   #4
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Default Re: Airgap in soldering iron tip

OP could try even aluminium foil. It's better than air for conducting heat.

Cement has 1/10 the heat transfer, it's largely an insulator so the T12 construction is still not the greatest. Especially with all the cheap chinese tips that contain almost no copper in the core.
My old Weller is still king for heat, sadly.
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Old 07-19-2020, 03:03 PM   #5
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Default Re: Airgap in soldering iron tip

no shortage of copper in my last tip,
maybe the cement is zinc-loaded.

so @cook:
what make/model iron is it??
most transfer heat from the sides - only weller afaik transfer from the end of the element
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Old 07-19-2020, 07:04 PM   #6
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Default Re: Airgap in soldering iron tip

I have a Yihua 939D. I will be using a genuine Hakko tip on it - T18 BR02
I also have a RadioShack Pro Line 70W -- similar style iron.

One post suggested copper paste, an anti-seize compound that can take high heat. I have not tried the paste myself, but I was wondering if anyone had tried it and if it made much difference. Maybe that post was specifically addressing the air-gap in a Weller iron.
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Old 07-20-2020, 04:05 AM   #7
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Default Re: Airgap in soldering iron tip

T18 tip is for the 888 iron isnt it?
the 939 i'm pretty sure is a 900m clone - slightly differrent size iron
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Old 07-20-2020, 04:57 AM   #8
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Default Re: Airgap in soldering iron tip

I believe I may have gotten the wrong Hakko tip. Somehow I thought the T18 was the same as a 900M. But I am seeing now they are slightly different and the T18 is just a tad shorter than a 900M. Is that the only difference? I am hoping that although they are different, I may not really notice the same as long as I am very careful and don't over tighten nut that holds the tip on.
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Old 07-20-2020, 07:28 AM   #9
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Default Re: Airgap in soldering iron tip

the main difference between the 888 iron and the 900m is the diameter of the element
if you try to use 900m tips on an 888 they are slightly loose.
so i imagine an 888 tip will be a tight fit - or not fit on a 900m element.
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Old 07-20-2020, 04:40 PM   #10
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Default Re: Airgap in soldering iron tip

My Yihua 939D uses the 900M tips, as listed in their documentation that comes with the unit. When I use my 939D to compare the 900M tip with a real Hakko T18 tip, I notice the following 2 differences.
1. The hole in the T18 tip is just slightly more narrow than a 900M, but it still easily slides on the ceramic heating element.
2. The T18 is about 1mm shorter than a 900M. When you put on the T18 tip, it does not slide all the way down ceramic heater to where it should meet the metal sleeve. I think I will make a small metal spacer to fill the gap so that when I tighten the nut for the element cover, the tip will be pressing small spacer which is pressing on the metal sleeve. Without the spacer the tip would be pressing on the ceramic heater and I don't want to do that for fear of breaking it.

Regarding my original question about using copper paste to fill the air gap in the tip, I no longer think I want to do that. The T18 tip does not leave hardly any air gap to worry about.
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Old 07-22-2020, 03:03 PM   #11
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Default Re: Airgap in soldering iron tip

Quote:
Originally Posted by redwire View Post
I wonder if a copper foil wrap would work better?
I don't know about copper, but I think The_Unique (or someone else here a long time ago) suggested aluminum foil. However, if I remember correctly, there was a warning that once this is done, the tip may get permanently stuck on the heating element. So it may or may not be a good idea, depending on how often you like to change tips.

On irons that use 900M tips, I don't usually use anything less than a 3 mm chisel or bevel tip, as even the genuine tips don't have enough thermal mass or good conductivity for heavier joints.

Quote:
Originally Posted by redwire View Post
OP could try even aluminium foil. It's better than air for conducting heat.
Yup, that's the suggestion I've been seeing elsewhere as well.

Quote:
Originally Posted by redwire View Post
Cement has 1/10 the heat transfer, it's largely an insulator so the T12 construction is still not the greatest.
True.
But even then, this is still better than a thin layer of air.

So I'm thinking perhaps ceramic/clay can be used to fill the gaps, too.

On another note, I have built a "clay solder pot" before and it did work:
https://www.badcaps.net/forum/showpo...5&postcount=33
This was before I got my 75-Watt soldering station, I think. So I was trying all kinds of crazy experiments to make a device that can tackle large solder joints.

Last edited by momaka; 07-22-2020 at 03:05 PM..
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Old 07-22-2020, 04:10 PM   #12
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Default Re: Airgap in soldering iron tip

if you do intend to use a packing substance, think about how it changes with time or heat.
i packed a tip once with arctic-ceramic.
when i had to replace that tip i had to use pliers to remove it!!
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