Changing the seal wires on your heat shrink wrap machine isn’t difficult but if not done right, can cause a lot of frustration. Follow these 5 steps to get the job done the right way.

Here’s how nichrome seal wire works: the machine applies a voltage to the wire, the wire creates electrical resistance which causes it to get hot. When it gets hot, it expands (gets longer) until the seal cycle ends, the voltage is removed and the wire cools returning it to its original length. The constant expansion and contraction can over time weaken the wires causing them to break.

Every machine is a bit different but the principles are all the same. Generally speaking, you change the seal wires on your shrink wrap machine when one or both breaks. And when a wire does break, I recommend changing them both because if one broke, the other isn’t far behind. While you have your tools out, you might as well do both.

Remember the expansion and contraction thing? To keep the wire straight when it expands, it is kept under tension by a compensator mechanism that is spring loaded to keep the wires straight when they expand.

A Clamco might look different than a Seargent which looks different than a Pack-All, Shanklin, etc. The principles are always the same. With this in mind, here’s what I do when I change seal wires:

Step 1: Carefully remove the old wires. One or both wires may be under tension by a spring-loaded compensator mechanism at the far end of the seal jaw. Make a note or better yet take a picture of how the wire attaches. You’ll need to know this when installing the new wires.

While holding the wire with a pair of needle-nose pliers, detach it from it’s mounting point in corner of the seal jaw closest to you. While holding the wire with the pliers, gently relieve the tension. Remember, if you just clip the wire, the spring mechanism may fly off the machine and could injure nearby personnel.
L-bar sealer nichrome wire.jpg

Step 2: There is a narrow insulator strip that runs the length of each seal wire. It keeps the wire from touching the metal seal jaw. The strip may be covered with Teflon tape to make it last longer. If the strip and/or teflon tape is severely burned or broken, it must be replaced. Once you’ve checked the insulator strips, it’s time to re-string the wires.

Step 3: Replace the longest wire first. This is important because how the wires overlap at the corner of the seal jaw can have a big effect on how the machine seals and cuts the film.

Basically, you measure out a piece of wire that’s about a foot longer than you need. Attach the wire to the compensator mechanism (see your notes or pictures) and pull the opposite end until the spring-loaded compensator is completely compressed.

Use a pair of needle-nose vice-grip pliers if you have them. Otherwise a regular pair of needle-nose pliers will work. Wrap the wire around its mounting screw a couple of times and then tighten the screw but don’t overtighten. You don’t want to damage the screw or strip out the screw hole.

Step 4: Clip off the excess wire as close to its mounting point as possible. Be careful – the ends of the wires can be sharp. Also, make sure the end of the wire doesn’t touch the machine’s metal frame. This will cause it to spark and most likely break.

Step 5: With new seal wires, your L-Bar sealer’s heat settings will change. Set your compensator (or time/temp dial if your machine has one) to its lowest or coolest setting. With some shrink film pulled across the seal area, close the jaw. Gradually bring the temperature up until the film is sealed and the sealed film cleanly breaks away from the roll.

That’s it! It sounds complicated but the more times you do it the easier it gets. And if you get stuck, send me an email or give me a call and I will help talk you through it.

Footnote: While you’re doing this job, it’s a good idea to check out the lower seal pad and replace it as necessary.