best air flow for 858D hotair station ?

[lordvader88]

IDK or remember much thermodynamics , so I just set the fan to 50%

What do you folks set fan speed to on these usually?

[aandrew]

I keep the airflow as high as possible but not so high it blows the parts off the board. :-)

Usually that means 6ish (60%?) for most things, but down at 3 or even 2 for very light/small components or when I'm trying to very very gingerly reflow an area.

[KL27x]

Mine is currently at 6.5/8 airflow, 316C, wearing the 8.3mm/320 mil nozzle. 

Stuff that has already been soldered is a lot harder to blow away... I mostly use mine for rework. And for QFN, but I'm pinning those down during the reflow.

[stj]

it's all relative to the nozzle diameter because your talking about the total volume leaving wand.

[KL27x]

^And the practical reason to avoid using lower airflow than necessary is that this puts higher temp in the heater for given amount of heating to the board. The cooler you run the heater, the longer it will last.

There was another thread discussing pluggng up the vent holes to reduce air flow. This can not only kill the heater coil, but you also might melt some plastics in the handpiece.

[stj]

you also might melt some plastics in the handpiece.

been there, done that!

[piguy101]

Will using a lower airflow actually cause the heater to be at a higher temperature? In theory, the power should be decreased at a lower airflow in order to maintain the same output temperature, so I do not see why the heater would be hotter at lower airflow.

Anyways, I use the airflow near the low settings when reflowing small components for the first time when using solder paste. Otherwise, they will blow away. However, for rework, I use a higher airflow simply to decrease the amount of time I need to heat the components. And for shrinking heat shrink, I max out the airflow.

[KL27x]

this puts higher temp in the heater for given amount of heating to the board.

I.e., with a lower air flow, you would generally need to turn the temp higher to get the solder to flow.

Take the extreme example of zero air flow, and the heater is just sitting in a small enclosed airspace. It can maintain 350C with very minimal power, maybe a few watts. But it doesn't heat the board up, at all. Once the air starts flowing, the current draw has to jump up to keep the heater at the same set temp.

So ignoring the numbers on the display, because they don't do the soldering, with lower airflow you will generally end up turning the knob higher to do the same job in the same amount of time.

It's the absolute temperature, not the amount of current draw, which kills the heater. If we blow enough cool air over it, we can run it at triple the max current and it will last for years. This is why the 858D has the autoshutdown routine which runs air past the heater.... even after the current draw is zero.