Ideas for closing plastic bags

Hi I'm working on a bag in bag machine I have come to the last section on the machine witch is closing the bag. At the moment I'm using 2 resistance on the bottom and 2 on the top to melt and close the bag. The resistances are enclosed with an aluminum part and covered with Teflon to keep the bag from sticking to the aluminum.

The problem I'm facing is that the I don't get a constant temperature on the heating area and because of this my bag opens or melts on some parts. I have seen machines using a copper wire (5mm width) to a temperature and then closing the bag with it. Have anyone got any experience which way is better?

The bags a thin LDPE and at the moment I need 150 degrees c and a closing time of 400ms.

Thanks in advance

How are the resistances controlled?

Thimmonier uses a FSM controller in conjunction with an electric resistance element to seal liquid-filled bags.

http://www.fsm.ag/en/production-transformer-relay-tsrl.php

you can use a static relay to control the resistance, a thermocouple or RTD to get the actual Temp. and PWM output to control the relay

We have used a Ropex controller in the past with TOSS heating elements. Try to search for TOSS heating elements and/or Ropex resistron controller. These worked very well with excellent temperature control.

You need a very small straight line with uniform heat, Use a heat wire (for example out of a toaster)
put a teflon tape over it.
the other side a simple piece of tape, over rubber or alike.
control the temp by using a PWM set (for example a arduino,
when the thing is closed the power must be ON. full.
another way is to use a heated wheel.
In my kitchen drawer is a very simple bagsealer working on a battery.

slp530 said:

We have used a Ropex controller in the past with TOSS heating elements. Try to search for TOSS heating elements and/or Ropex resistron controller. These worked very well with excellent temperature control.

Click to expand...

+1 for the Ropex setup.

...and make sure that the area being sealed is not subject to blasts of air from another part of the machine or nearby doors opening and closing.

tarik1978 said:

How are the resistances controlled?

Click to expand...

I use solid state contractors to control the resistance via a PID function

Thanks for all your answers. This is for an industrial application so I need something rugged and already made.

I think I wasn't clear enough. I can control the resistances to an accuracy of +-1 degree C with resistances integrated with thermocouple J, but when I measure the surface of the aluminum then it differs quite a bit depending on where I'm aiming the temperature controller (from left to right see exmaple bellow)

R1 ------------------------- R2
^ ^ ^ ^
170 185 185 170


This is why I'm searching for a more reliable and constant heatingsource for example a thin wire. I like the idea with a heat wire but I can't deliver a machine with parts from a toaster to my costumer, so if anyone have any idea where I can buy one for industrial use and the electrical components needed for heating it and controlling the temperature.

Thanks for all your answers. This is for an industrial application so I need something rugged and already made.

I think I wasn't clear enough. I can control the resistances to an accuracy of +-1 degree C with resistances integrated with thermocouple J, but when I measure the surface of the aluminum then it differs quite a bit depending on where I'm aiming the temperature controller (from left to right see exmaple bellow)

R1 ------------------------- R2
***^****^****^******^
**170***185**185*****170


This is why I'm searching for a more reliable and constant heatingsource for example a thin wire. I like the idea with a heat wire but I can't deliver a machine with parts from a toaster to my costumer, so if anyone have any idea where I can buy one for industrial use and the electrical components needed for heating it and controlling the temperature.

The lower temps that you see near the ends of the aluminum would indicate that there is more surface are to dissipate the heat near the ends than there is in the center. you may need to insulate the aluminum to prevent losing so much heat into the ambient air.

the toaster was just an example, it is the principle.
the wire is available in several sizes.
you will have to play with time, temperature and closing pressure.
it is tricky, and you will need a lot of experience, special if the foil is thin.
always have the machine moving, and only close when need sealing.
if yu want to close loose bag from a box, use 2 finers to keep the bag tight, not having rinkels.
keep the closing area by filling with a pipe.

Nickel-Chromium or NiCr.

http://kanthal.com/en/products/materials-in-wire-and-strip-form/wire/resistance-heating-wire-and-resistance-wire/list-of-nicr-alloys/