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A behind the scenes blog covering the goings on at ESTechnical. Expect my ramblings about R&D, CNC, fixing machines, reflow and wave soldering... Ed Simmons

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Frankengluegun: Making a low cost temperature controlled glue gun

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Until recently, the Bosch glue gun has served me well - it's now 3 or 4 years old and has started to get hotter than it's meant to.

I think these glue guns have some sort of positive temperature coefficient heater, this regulates the temperature just by changing its resistance according to temperature. However this has stopped happening recently and the glue is getting dangerously hot.

Hot glue is used in the ESTechnical reflow controllers to support the display as it is only soldered onto the controller PCB at one corner (this is done is a specially made jog to ensure everything is help in the correct spacing). After being on for several hours during a production run of Reflow Controllers, the glue was boiling and smoking. Something had to be done about this - someone was going to get burned - it was dripping from the nozzle and smelled awful.

At this point I searched for temperature controlled glue guns and was horrified by the cost of them. I decided that since they were so expensive and 'normal' glue guns are not designed for the kind of abuse we give them during a production run of controllers, that I should make my own temperature controlled glue gun.

Since the glue gun wasn't drawing far more than it's normal heating up current, I thought I should try fitting a thermocouple to the heater barrel assembly and powering the glue gun with a cheap PID temperature controller from ebay. I had a few of these lying around so I got straight to it.

Inside the glue gun I found that the heater is a cartridge in hole in the glue barrel casting. I was able to slide the heater out, cover the inside of the hole with thermal paste and slip the heater back in. There was a convenient hole in the casting at the full depth of the heater tube, I covered the tip of a thermocouple in kapton tape and slid this into the hole with more thermal paste.

b2ap3_thumbnail_glue-gun-thermocouple-added.jpg

I also managed to fit the thermocouple cable neatly through the rubber cable glad in the handle of the glue gun, then cable tied the thermocouple cable along the length of the power cable.

b2ap3_thumbnail_glue-gun-cables.jpg

I cut off the plug of the glue gun and connected fork crimps to the end of the wires. All the connections were made to the back of the controller using crimps fastened in the screw terminals. A short section of cable with a plug was used to supply power to the controller. Until I fit the controller into a box, the connections are covered in lots of electrical tape.

b2ap3_thumbnail_glue-gun-thermocouple-cable-routed.jpg

The end result is excellent, the PID controller means I can set it to 140°C and it stays there even when pumping lots of glue through it in regular bursts. 140°C is perfect for our application, I'm sure it was slightly hotter than this when operating normally originally. The glue runs less and is easier to work with as it is firm enough to hold very quickly.

b2ap3_thumbnail_completed-franken-glue-gun.jpg

Due to the great level of interest in the temperature controlled glue gun, please contact us for a quote if you would like to order one (or more!).

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Electronic designer, hardware hacker, programmer, machine geek, father of two and owner of ESTechnical.

Comments

  • Jdm8
    Jdm8 Sunday, 17 August 2014

    Looks nice. Does it heat up any quicker than it did before? By how much?

  • Ed
    Ed Sunday, 17 August 2014

    My guess is that it's slightly slower to heat since the controller is trying not to overshoot the set tempterature - that said, it doesn't matter since it doesn't drip glue much at 140°C - waste is minimal!

  • Guest
    Jdm8 Sunday, 17 August 2014

    OK, thanks. One of my desires is to get a quicker warm-up. It seems to take my dual-temp hot glue gun about five minutes to warm up. My soldering iron takes maybe a minute, so I was hoping to achieve something about that quick.

  • Ed
    Ed Sunday, 17 August 2014

    Well - you could put a more powerful cartridge heater in the cast barrel. The problem with glue gun heaters is they're designed to self regulate the temperature - it's a big Positive Temperature Coefficient (PTC) resistor - as it gets hotter, it's resistance increases, thereby reducing its power. Since mine had stopped doing this somehow, I got something like full power all the time. This makes it ideal for PID control - I don't think the PTC characteristic of the 'normal' glue gun element will help the PID controller - it's probably better with something like a 200W cartridge heater, these are at least more predictable for the PID controller to tune to.

    Your soldering iron only has to heat a very small tip and it is probably temperature controlled so can be a much higher power than a typical iron - this allows it to achieve a very fast heat up, but requires careful temperature control to be safe.

    The glue guns achieve temperature control by making the heater self-regulating at approximately the right temperature - the power drops from something like 200W to about 15W at operating temperature. The heaters must be similar design to the self regulating heater strip they use to prevent industrial freezer doors freezing up...

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Guest Thursday, 18 September 2014