impulse sealer

[irondesk40]

anyone ever designed a impulse heat sealer. Looking at putting together a sealer bar using Nichrome 60 wire and automatically controlling it to cycle in the program on a protype machine i have built using a micrologix 1400 and Red Lion HMI unit.
Automatically cycling etc. is pretty straight forward but not had any experience with Nicrhome type heating wire etc.
the sealer bar will be 6 feet in lenght and need to operate at 600 degrees F.
I looked it up and the Nichrome 60 wire requires approx. 5.1 amps of current when stretched straight to reach 600 degrees.
I was looking at using a output of the plc to turn on relay to supply power to the primary side of a transformer.
If the output of the transformer is 24vac and i would need 5.1 amps then since P=V*I then it would require 122 watts.
If I take the 122 watts and divide it by a power factor of .6 then i would need a 200va transformer.
If i needed to pulse the heat to the heat bar I could just cycle the relay turning on the transformer on and off with a timer in the plc.
Am I way off base here? If so, could someone tell me what I may be overlooking?
Thanks

 

[iant]

Several Items come to mind.
1. Power Factor is for Inductive reactance
- this sounds ike a resistive load.
- Consider rectificaton to DC - Better Heating.
2. Transformer Switching of the Primary
- This is the trap to be aware of.
Switching the Transformer On will work easily, But when you turn it OFF.
The Back EMF spike will burnout the contacts of the relay and shorten it's life exponentially.

Consider using a selector or similar to enable or isolate the power.
Still use a relay from the PLC
Have the relay Switch a solid state relay to the Transformer.
there are other options - like switching a series potentiometer also

 

[HJTRBO]

The ones i have worked on in the past are pretty trick. Cant remember the name, but not to expensive.
The use a ssr to turn on and off the transformer. They have voltage feed back cables coming back from the ends of the nichrome wire, plus a current ct on the secondary of the transformer. Last piece of the puzzle is the thermal factor of the nichrome wire itself which is set in software.
With all this it manages to control the sealing temp to very precise tolerances using its in built alogarithim.

 

[milldrone]

anyone ever designed a impulse heat sealer. Looking at putting together a sealer bar using Nichrome 60 wire and automatically controlling it to cycle in the program on a protype machine i have built using a micrologix 1400 and Red Lion HMI unit.
Automatically cycling etc. is pretty straight forward but not had any experience with Nicrhome type heating wire etc.
the sealer bar will be 6 feet in lenght and need to operate at 600 degrees F.
I looked it up and the Nichrome 60 wire requires approx. 5.1 amps of current when stretched straight to reach 600 degrees.
I was looking at using a output of the plc to turn on relay to supply power to the primary side of a transformer.
If the output of the transformer is 24vac and i would need 5.1 amps then since P=V*I then it would require 122 watts.
If I take the 122 watts and divide it by a power factor of .6 then i would need a 200va transformer.
If i needed to pulse the heat to the heat bar I could just cycle the relay turning on the transformer on and off with a timer in the plc.
Am I way off base here? If so, could someone tell me what I may be overlooking?
Thanks

I have not designed one, but we have 23 sealer/cutters where I work. 16 of them are around 5 feet long. We use the wire for cutting only. The wire also has a tensioner because it grows about a 1/4 inch when hot. We also use 120V on the wire. A mercury displacement contactor is used to supply power The wire is pulsed about 100ms every 4 seconds to keep it ready before the actual cut.

For the seal part we use 1/2 " wide 18ga blue spring steel. On the spring steel we use a 1KVA buck boost transformer. I cannot remember if we use the 12 or 24 volt setting. A solid state relay supplies the power to the buck boost transformer

A heat resistant fabric that has a shiny finish is placed between the poly and the heat wire or spring steel. This fabric is incremented from one roll and wound on another every 250 seal events.

After the heat is applied but before the pressure is released, a blast of air is supplied to chill the hot plastic

 

[OkiePC]

What is the thickness and material you are sealing?

You can purchase seal bars from packaging machine makers of various widths and lengths built with thermocouple embedded, fire them with ssr and standalone PID heater controller, and apply them for a duration controlled by a PLC operated pneumatic cylinder.

Our bag making (think retail freezer bags of sausage) machine uses seal bars to close the bag then cuts it the film being fed from pre-printed roll stock.

We use "heat wire" for cutting only and only for thin shrink wrap film. I don't think our machine pulses the wire to keep it ready. That sounds like an easy enough upgrade, we do pop a lot of fuses and replace that wire quite often.

 

[_Woody_]

Have you considered using a power controller instead. We used several Omron G3PX power controllers to control Nichrome wire cutters for plastic film a few yrs back & they worked great. In this instance we controlled them from the PLC with a 4-20mA signal and a digital run/stop.
The G3PX is old now and the current series G3PW has comm's option. Haven't used the G3PW but it might be worth a look.


http://www.ia.omron.com/data_pdf/data_sheet/g3pw_j176-e1_5_2_csm2000.pdf