Blade wear microscopic analysis specific analytical tool for the diagnostics of yankee coating protective performance

As you know, a variety of techniques are used to evaluate the capability of the yankee coating to shield the cylinder surface, going from on-line monitoring blade vibrations to the determination of the roughness and run-out of the yankee surface in shut down.

The analysis of blade wear is maybe one of the oldest practices used by tissue makers to understand if the attrition between the blade and the cylinder is properly controlled or not. The control of the deterioration is usually more meaningful when done on creping blades made in steel.

When analyzing a steel creping blade after use, the attention of the observer will be mainly concentrated on:

• evenness or unevenness of the blade wear across the whole blade;
• appearance of the blade wear in machine direction;
• extent of the wear;
• eventual signs of overheating of the blade itself.

All this will have to be contextualized on the basis of the duration of the blade life and of the conditions met during it, such as kind of pulp, system pH and cationic demand, refining intensity and many others. In the following case history, the assessment of creping blade wear has been very important to highlight a significant improvement in the protective effect of the yankee coating. A double size, high speed, premium tissue machine suffered from limitations in speed due to instability of the yankee coating.

Picture 1 shows a 60X image of a creping blade used to produce ECF toilet paper. Analyzing the picture, we can see that:

• the total extent of the wear is 0,79 mm; this had been developed on 315 km of revolving yankee surface, coning to 0,26 mm/100 km of specific blade wear;
• the worn beavel shows severe damages, with micro-fragments of metal chipped out of the beavel;
• clear signs of overheating are visible (blue-brownish area). This means most probably the ‘chipped’ missing pieces have been transformed in micro-weldings on the yankee surface.

Picture 2 shows a 60X picture of a sample of tissue sheet coming from the first roll produced with the blade shown in Picture 1. You can see a minimal creping is developed in the tissue body. Picture 3 shows a 60X picture of a sample of tissue with the third (and last) roll produced with the blade of Picture 1. In this case tissue creping is very difficult to identify. On the basis of the blade wear analysis, as well as of the assessment of vibrations on the creping blade and other observations on the yankee surface and creping performance of tissue paper, the customer agreed to run a test with a coating chemical package from MARE, comprising:
MARECOAT A 598: a base coating with excellent stability to moisture changes and peaks, soft behavior and providing an excellent doctorability of the tissue sheet;
MARERELEASE R 250: release agent based on synthetic molecules, contributing to the stability and the softness of the coating layer while providing excellent release control;
MAREMOD P 600: inorganic aid providing a stable deeper protective layer on the yankee surface.

Mare Dynamics can supply the whole of the paper industry with its process chemical requirements

Picture 4 shows a 60X image of a creping blade used to produce the same grade of ECF toilet paper mentioned in Picture 1, while MARE chemicals were on the machine. Analyzing the picture, we can see that:

• the total extent of the wear is 0,72 mm. This had been developed on 461 km of revolving yankee surface, coning to 0,15 mm/100 km of specific blade wear;
• the wear edge is very smooth and even, no damages nor chipping off of any micro-fragment can be observed;
• there are no signs of visible overheating.

Picture 5 shows a 60X picture of a sample of tissue sheet coming from the fourth (and last) roll produced with the blade shown in Picture 4. You can see a well-developed creping wave can be observed in the tissue body.
Due to excellent results in coating stability, increased yankee protection and improved sheet doctorability, the customer could solve the speed limitations suffered so far. We hope you found this new article interesting for your business. If so, please do not hesitate to contact the nearest MARE representative for further information on our chemical programs.

Mare was founded in 1979. Since its conception, the company has grown both organically and through acquisition