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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.
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.