Beating chrome in Yankee Metallizing

Damaged Yankee cylinders in tissue machines impede production output and can have a detrimental impact on tissue quality. Cylinders with damaged surfaces are often metallized, particularly if the remaining cylinder shell is not thick enough or if further grinding may affect production capabilities. A recognized risk of metallizing is that during the process, potentially harmful hexavalent chromium is created. Chromium is a fundamental component of almost every iron-based hard-facing alloy.

Having recognized the potential risks associated with the thermal spraying of ferrous materials, Valmet embarked on a program to develop new alloys to beat chrome in Yankee metallizing. The new Valmet Infinikote-2 Yankee Metallizing process contains no chrome and generates no hexavalent chrome during application. It is the most environmentally safe and durable Yankee metallizing coating available.

For the safety of people and the environment 

Yankee metallizing is on-site field services work on the customer’s premises. “We identified the need to change the system to better ensure safety for customers and our employees, and to anticipate future environmental legislation. This led to the decision to invest in the development of new, safer materials for Yankee thermal spray coatings,” says Marko Heino, Director of Field Services at Valmet.

A collaborative development team from Valmet’s hard-coatings research and development group in Jyväskylä, Finland joined with Valmet’s partners to create an outstanding team of world-class material scientists, metallurgists and manufacturing supply-chain partners.

The same performance, but without chrome 

The plan was to create a new generation of Yankee cylinder metallizing alloys, which must display quality attributes at least as good as those for our current Yankee metallizing process, but should contain no chromium-bearing constituents. Valmet Infinikote-2 Yankee Metallizing should equal or surpass the competition in all measured criteria for Yankee thermal spray coating performance.

The main goals were stable creping surfaces while still addressing environmental and safety concerns, with the same application process and a wider application window.

Key structural and surface characteristics for optimal Yankee performance were painstakingly reevaluated to ensure fundamental improvements in all crucial areas: wear and corrosion resistance, heat transfer, and surface tension.

“Groundbreaking collaborative development procedures enabled us to quickly design new alloy materials, optimize microstructures, and achieve our target performance metrics,” says Andrew Cross, Senior Operations Manager at Valmet’s Global Yankee Services. 

Intensive development and exhaustive trials led to the identification of candidate materials best suited to the objectives. From these, the final formulation for the new chrome-free thermal spray material was created. “The test results with the new material are convincing, demonstrating significantly improved application characteristics, and meeting or exceeding all our key objectives,” says Cross. 

Published in Forward 1/2018