Formers

Yankee dryer operation and maintenance

The Yankee dryer is one of the most essential parts of the tissue machine. This pressure vessel serves as a base for creping, pressing and drying of the paper sheet. Because of its importance to the tissue-making operation, mills should provide regular maintenance services to the Yankee dryer to maintain high runnability and ensure top-notch quality. On the Yankee dryer, the paper goes from approximately 40 % dryness to just over 95 % dryness, and is then doctored off into the sheet transfer area. In terms of paper quality, there are a lot of parameters that depend on the Yankee dryer’s performance, such as dryness, dryness profile, sheet quality, and so forth. In order to minimize downtime due to poor Yankee dryer performance, it is imperative that mill personnel pay close attention to the operating condition of the Yankee dryer.

Review Yankee dryer condition and performance In order to maintain good Yankee dryer operation, machine operators should follow some basic steps. Some points to pay close attention to are:

• An uneven moisture profile can cause insufficient coating. Mills should check to see if the doctor blades are properly adjusted and/or if any Yankee wear can be spotted.
• Periodic inspections are required to determine if the complete Yankee surface is coated, otherwise the doctor blades will wear the Yankee surface where coating is missing.
• Uneven wear on the doctor blades indicates that there probably is something wrong with the coating or unnecessary Yankee wear.
• The profile of the doctor blades should be aligned after the Yankee surface to achieve even wear.
• Although Yankee surface edge wear does not directly affect production, it leads to an unnecessary amount of material that must be grinded off the Yankee the next time it is reground, in order to achieve the correct crown curve.

Drying: Yankee dryer

The Yankee is the heart of the tissue machine. It works as a press roll, dries the sheet together with the hood, and finally provides the surface for the creping process.

The drying operation is a short and intensive process and the Yankee dryer must perform well in all its functions. For conventional dry crepe machines the system consists of a Yankee dryer and associated high velocity, high temperature impingement hood. It is a complex mechanical structure, exposed to steam pressure, and there are extremely high demands on safety and operational reliability.