Seal of approval for low-voltage system

Edited by the Engineeringtalk editorial team Sep 2, 2003

Microtherm (GB) has cut cycle times, reduced maintenance requirements and improved seal integrity by replacing its impulse wire sealing machine with an LVH sealing system.

Microtherm (GB) has cut cycle times, reduced maintenance requirements and improved seal integrity by replacing its impulse wire sealing machine with an LVH sealing system.

Robert Holmes, Plant Engineer at Microtherm (GB), says replacing the company's impulse wire sealing on one of their machines, with an ingenious, low-voltage system, saved the fridge freezer insulation-panel manufacturer up to three man hours a week.

The impact on productivity at the Merseyside company was considerable.

"The LVH system incorporates a sealing blade with a tough, non-stick coating which immediately appealed to me because I could see the time-saving possibilities", Holmes says.

"The LVH made a big impression".

Holmes first saw Ceetak's LVH low voltage heating system at a trade show over two years ago.

At that time, Microtherm was using an impulse-sealing machine to close outer barrier bags containing insulation cores made of precipitated silica.

The vacuum-insulated panels, known as Microtherm VIPS, are designed to be four times more efficient than traditional insulation methods and are used to thermally protect cold storage applications such as top-of-the range fridge freezers.

Holmes explains that the outer bags are presealed on three sides before the rectangular core is placed inside and then finally sealed within a vacuum chamber.

The bags are closed by sealing the forth side of the bag, thereby creating a highly efficient thermal insulation panel.

Holmes explains that Microtherm has manufactured the vacuum-insulated panels for four years but wanted to improve the production process by reducing operational inefficiencies.

"The impulse heater would take quite a while to complete a cycle because it only started to get hot when it reached the bag.

There were also problems with the heater ribbon snapping due to expansion and contraction.

The impulse heater was certainly less reliable than the LVH and took about 20s per cycle longer to heat up".

As the LVH system's low-mass blade conducts heat constantly along its contact face, it can create high-integrity seals quickly and evenly.

It also features thermal insulators that ensure heat is conveyed directly to the sealing area rather than into the surrounding environment.

This significantly reduces energy loss and ensures greater heat concentration along the highly conductive sealing blade.

It also means the ground-breaking LVH system can operate on a low voltage (max 40V), which reduces running costs and simplifies maintenance.

Installed in July 2001, Microtherm's LVH system welds a variety of seal lengths at approximately 150C, although Holmes says the company has tested the system at 200C.

"We're very pleased with it mainly because it has helped us reduce our cycle time by over 20%.

The low-maintenance blade has also saved approximately three man-hours a week, which would have been spent replacing broken elements on the impulse machine.

In over 18 months, we haven't had to replace a blade".

All Microtherm's sealing processes are tested using a tensile machine that measures the force required to break the welded seem.

Holmes notes that many of the seals created using the impulse-heating machine failed close to the force threshold of 67N.

"The LVH's seals reach 100N", he adds.

"This is what we were looking for; a reliable sealing system that creates strong welds consistently with a fast cycle time".