Heat Transfer Rolls & Effects of Temperature
There is one primary goal when it comes to the design of heat transfer rolls: to transfer heat from the web to the roll or from the roll to the web.
Utilizing concepts within the first law of thermodynamics where heat transfer occurs through a temperature difference, heat transfer rolls play an important part in various applications within the web converting process. There are many different designs of heat transfer rolls, one design of heat transfer rolls are manufactured with a dual shell construction: special inner flow chambers and (sometimes) special finishes. As a result, the procurement of heat transfer rolls often requires a significant investment and proper maintenance becomes essential. Periodic maintenance is required to maintain effective heat transfer performance over the life span of the heat transfer roll. To lessen the risk of diminished heat transfer performance and reduce the likelihood of roll repair or replacement, C.R.E.W. recommends the following tactics:
- Use of proper fluids
- Periodic cleaning & flushing
- Remember the rust inhibitors
- Follow best practices for storage
Use of Proper Fluids
If the heat transfer roll uses thermal oil, it is best to follow the oil manufacturer’s guidelines. Water solutions have proven to be detrimental to a heat transfer rolls performance as suspended solids, water pH, and organics can eventually coat or clog its interior fluid channels. The water may even cause rust on the rolls inner surfaces.
For best results using water, it is highly recommended to run a 25-50% mixture of ethylene glycol with rust inhibitors to clean water.
Periodic Cleaning & Flushing
If your heat transfer roll is maintained with water solutions periodic flushing is essential in minimizing mineral scale build-up. There is a risk of scale, rust, and suspended matter resulting in restricted fluid flow.
The condition of the water or fluid typically dictates the roll flushing schedule:
- In areas that have hard water, heat transfer rolls should be cleaned once every 6-9 months.
- Installations that service a closed-loop system or use a 50-50 water/ethylene glycol mixture should be cleaned every 12-18 months.
- Allow up to a day for recirculating flushing to achieve maximum effect.
The roll flushing process typically employs a pump-through method where the cleaning solution is prepared in a drum and run through the roll. C.R.E.W. recommends following the solution manufacturer’s directions carefully. It is advised to not pump the same solution through more than one roll at once unless a filter is used between each flushing to screen out any solids or scale deposits.
Acidic solutions are commonly used as effective flushing agents for heat transfer rolls. As most heat transfer rolls are manufactured of carbon steel, an acid flushing will not damage internal parts or surfaces. A couple of acid solution manufacturers’ include:
Part 2 of How to maintain your heat transfer rolls will define the importance of remembering rust inhibitors and how to follow best practices for storing your heat transfer rolls. In the meantime, please contact C.R.E.W. with any questions; we’d love to hear from you.