Why Regular Cleanings of your Thermal Transfer Rolls are Important
Transferring heat either to or from the web is a vital part of your production process. You’ve spent plenty of time and research into developing an efficient system. Including quite a few investments in your various rollers and machinery parts. Proper maintenance of these parts is vital to keep a smooth running shop. Particularly your thermal transfer rolls since they are subjected to heavy internal corrosion and sediment buildup (hard-water buildup) that isn’t obvious on the outside.
Failure to maintain proper maintenance on a thermal transfer roll may result in various problems:
Defects in the web
There are some substrates/processes that are more tolerant of temperature fluctuations. Yet other processes like web stretching, also known as machine direction orientation (MDO), require the temperature across the web remain extremely consistent.
Deterioration of Passageways
Over time the fluid being used can cause corrosion to the base metal of the interior of the roll. This deterioration of passageways can cause contamination in your cooling, or heating systems causing higher maintenance costs, unplanned downtime, and possible leaks within your heat transfer roll over time.
Reduced Flow Rate & Inconsistent Temperatures
In addition to corrosion, the fluid running through the roll may leave behind residue that can cause buildup inside the passageways. This build-up can reduce the flow rate, affecting the consistency in surface temperatures. In addition to reducing the flow rate mineral deposits, having lower thermal conductivity than steel, also reduce the heat transfer from the water to the roller shell. The reductio nin heat is usually in a non-uniform way, creating either hot spots or cold spots.
On new thermal heat transfer rolls, there is an option to have the interior of the passageways protected with a nickel plating. While this option is more expensive up front, the thermal heat transfer roll becomes significantly less prone to rusting, thus extending the life of the roller. For existing rolls, however, we do not recommend nickel plating. The nickel doesn’t adhere to the corroded steel and will flake off and plug up filters and deposit nickel into the waste stream.
Even with nickel plating on the inside of a heat transfer roll, preventative maintenance programs such as acid flushing are still just as important. While the chance of corrosion is significantly reduced, the roll will still be susceptible to clogging from sediments in the fluid causing buildup.
Acid Flushing for Thermal Transfer Rolls
We will cover Acid Flushing in more depth on a future post, but at a high level, it is the process of breaking down the sediments within the heat transfer roll passages. This method of cleaning is the most effective and proper way to clean your heat transfer rolls. However, acid flushing is not always 100% effective. The acid will have some success in removing corroded metal unless the inside is corroded too far. No amount of acid flushing that can revive a roll subjected to too much corrosion. Another important factor in acid flushing to remember that all passageways must have some flow to be effective. Even just one clogged passageway can prevent the acid flushing from being effective.
To maintain the efficiency of your thermal transfer rolls, a schedule for roll cleaning should be established for each installation. In our experience, proper maintenance requires cleaning at least every six months. When the water has high solids content, hardness, or acidity, cleaning should be scheduled more often, at least every 60 days. If you wait too long to begin a routine maintenance schedule, acid flushing may no longer be an effective solution. At this point, a new roll would need to be purchased.
Don’t end up with thermal transfer rolls beyond repair.
Waiting too long to begin routine acid flushings, results in rolls like in these photos below: