Thermal Survey of a Cooling Water Drum
Case History Number 1

This case history is based on a thermal imaging survey that was carried out on two food wrapping paper laminator machines of identical design.
The machines were responsible for laminating an outer film to a food specification film by means of a molten plastic polymer that would bond the two films together. The machine was designed so that the food specification film would enter a bonding area where it would have a given mass of molten plastic polymer applied along its width as it passed over two drums, then a top film would meet as both film layers entered the cooling drum section, this is were the suspected problem lay.
The machines were identified numerically as the 120 and 150 machine, as far as we are aware the numeric identifier is due to the mass of molten plastic polymer which is laid between the two films.
The problem lay predominantly with the 150 machine and was in the form of "bubbling" due to inadequate "bonding" of the two layers of finished product. In the centre of the food wrapping, at what would appear to be equidistant of the linear length of the cooling drum, was a defect in the form of film separation between the two layers.
A thermal survey of the two machines was carried out at the plastic polymer bonding stage through to the cooling drum, and then the finished product drum. The findings were very interesting and conclusive.
The first survey was carried out on the 120 machine and involved a live scan of all accessible drums and areas to identify and obvious hot areas. The engineering department had already confirmed that the 120 machine was not, in there opinion, a problem, as it could operate through the full range of product throughput speeds with finished product skin temperatures between 22° C and 24° C.
The remainder of the drums that were scanned also exhibited acceptable temperature profiles and were also considered fit for service.
One thing we had to take into consideration during this survey was the fact that due to the difference in molten plastic polymer mass, then a longer cooling time for the heavier grade would be required, however, we were informed this was catered for by virtue of the product throughput speed being slower on the 150 machine.
The thermal scan of the 150 machine cooling drum and the finished product as it left the machine indicated a hot spot of 57° C with the rest of the drum being around 40° C see Figure 1.

Figure 1 - Indicated hot area on the cooling drum of the 150 machine.

The hot area on the face of the product was due to inadequate cooling from the water passing through the drum.
When the finished product leaving the machine was scanned, it was evident that the molten plastic polymer had retained some of its heat, with a recorded temperature of 56° C, and was responsible for the ineffective bond between the two films see Figure 2.

Figure 2 - Hot spot evident on finished product.

All other scanned drums around the 150 machine exhibited uniform temperature profiles and did not give any cause for concern.
A report was submitted to the company, recommending the cooling water distribution channels within the drum should be checked for blockages or restrictions as it would appear that insufficient cooling water was reaching that portion of the drum.
The drum was subsequently replaced and the machine was brought back on line with no further bonding problems encountered.

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