Oct 28, 2019
The Yankee cylinder is the heart of a tissue machine and its surface is critical to production output and creping quality. Unfortunately, constant exposure to chemicals, wet tissue, internal steam pressure and high surface temperatures leads to surface wear and corrosion.
A worn Yankee cylinder surface will reduce production output and can have a detrimental impact on tissue quality. Metallization is a proven method for protecting, refurbishing and prolonging the lifetime of the cylinder surface. But metallization is not perfect. Thankfully, new surfaces have been developed which now are safer for people and the environment.
Metallization – thermal spraying – is a well-proven method for applying a metallic, homogenous, hard-facing surface onto a Yankee cylinder. Besides improved creping, metallization will extend cylinder lifespan.
Metallization of cast iron cylinders is increasingly common, albeit optional. On these, metallizing decreases surface and/or heat-transfer defects, increasing durability and decelerating wear on cylinders. On the contrary, steel cylinders must undergo metallization before their use, hardening their soft surfaces.
Once a means of preservation, paper manufacturers now use metallization as a reconditioning method – after grinding – for maintaining production levels and avoiding expensive equipment replacement.
Unfortunately, metallization comes with associated health, safety and environmental risks. The method produces hexavalent chromium – a harmful component of most iron-based, hard-facing alloys.
To improve worker safety during thermal spraying, as well as sustainability of the coating to comply with potential future legislation both in the EU and the US, a chrome-free Yankee cylinder coating has been developed.
By collaborating with tissue industry experts, several new alloys now exist with optimized microstructures that achieve targeted performance metrics, such as a stable creping surface.
The new thermal spray coatings deliver numerous advantages over previous benchmarks.
Whilst 100% chrome free, they have been tailormade for the tissue industry to increase wear resistance, further extending cylinder service life. The uniform surfaces created are also ideal for running ceramic doctor blades and providing better sheet adhesion during tissue production.
For more information on this new coating, view this film
Find this story interesting? You can read more about tissue at www.tissuestory.com. If you want to know more about how Valmet helps its customers become best in tissue, go here to get information about our products and services.
Article type: Operations
Industry level: Advanced
Est. read time: 4 minutes
Summary: Metallization is an established method for protecting and refurbishing Yankee cylinders, but has traditionally entailed significant health and environmental drawbacks. This article presents the benefits of a newer, chrome-free coating process.