Homebrew PCBs

Ancel,

I am not sure I understand why slowing the rollers causes them to pick 
up more heat energy. In my  laminator (Harbor Freight) there are two 
heaters, placed on opposite sides fo the rollers. The heaters are 
attached to aluminum structures that enclose the roller assembly all 
around, except for the slots for the paper path. Slowing down the 
rollers does not change their exposure to the heat source when there is 
no board traversing the path. With a board in place, the board would act 
as a heat removal path, changing the temperature of the rollers. I would 
think that slower speed would allow more heat to bleed out the otherwise 
closed heater area. Does the Apache/Trulam have an open structure that 
allows visibility by the FLIR camera? It would be difficult to get a 
good reading on the Harbor Freight unit  because of the close spacing 
(~1/8") of the paper path. The rollers are recessed far inside, and the 
slots are actually a fairly deep aluminum structure.

Less accurate control systems in the cheap units is an understatement. 
The temperature control for my unit is a thermoswitch mounted on the 
heater. This is a single heat unit, so no more control is needed for 
normal lamination. I got curious to see what temperature the thermal 
fuse is rated for. This fuse is clamped to one of the aluminum heater 
fins, and is covered by a flexible plasticized glass fiber filled 
sleeve. The fuse is marked as 185�C. By mounting it in the thermally 
insulating sleeve, the heater temperature can go higher without tripping 
the fuse. I had it operating at approximately 210�C for an extended 
period without any complaint from the fuse. The only thing that fuses 
was the gears.

I have not yet had the time to determine the softening temperature of 
the structural plastic that supports the roller assembly. This outcome 
will determine whether there is any point in continuing with this 
particular laminator. The Brother toner supposedly fuses around 370�F, 
or 188�C. I have measured a 20�C temperature difference between the 
heater fins and the roller, making operation around 210+�C a necessary 
condition for my use of this laminator.

Harvey

On 12/31/2016 7:45 AM, AncelB mosaicmerc@... [Homebrew_PCBs] wrote:
>
> When a laminator's net roller speed is modified, you also modify the
> heat energy transfer to the rollers as the same surface of the roller
> sees more radiant heat in a given time. Thus it gets hotter without even
> upgrading the heater.
> Now if you run the rollers too slow, the roller area being heated vs the
> roller area being sensed will have a hi temperature delta and you could
> burn the rollers. If the gears are exposed to some of this heat
> conducted by the roller shaft, thermoplastic gears can 'become' plastic
> and fail.
>
> I encountered this heat delta effect when I was developing & monitoring
> my Apache/Trulam mod with a FLIR camera. To eliminate this heat spike,
> whenever the mod. reverses the roller it cuts the heater. This seems to
> work well to date with no roller damage and good transfers. Thus running
> the laminator at 'normal' speed during the heat up phase and then
> 'slowing' the rollers just for the Toner Transfer phase and returning
> the laminator to normal speed afterward keeps the rollers from seeing
> too much of a heat delta cycle and they suffer less degradation.
>
> For the different laminators being modified, cheaper units seem to have
> cheaper materials in them, with less accurate controls. Thus it's trial
> and error as to how slow and how hot you can go before you exceed the
> design spec enough to destroy the laminator and make a fire hazard.
>
> Rob's approach eliminates this risk but is not 'over the counter'
> repeatable for everyone and is certainly more time consuming when you
> have a batch to run!
>
> I shipped a built Apache/Trulam mod. to Italy yesterday based on the
> newer layout with the SMT PIC. It uses low ESR SMT bypass caps and wider
> power rail traces as well to mitigate PIC resets due to transient power
> spijes as are generated from the relay and heater switching.
>
>