Adhesion measurements at Tampere University ICE Laboratory

Novia UAS and Tampere University met again as part of the collaboration around their anti-icing coating. This time it was planned to do the measurement of the woodchips adhesion by shear test from the previously coated boxes and the centrifugal adhesion test from the coated sample plates.

Researchers Katrin Asplund and Julien Walser from Vaasa drove to Tampere for a week to proceed to the experimentations with woodchips and coated boxes. The experimentations took place at Tampere University ICE laboratory in the cold room set at -10°C and around 40% humidity. There were 6 tests with the boxes, different polyethylene (PE) surfaces and 2 steel boxes sprayed with coating. The measurements were recorded at room temperature to determine how long it would take to separate the frozen woodchips from the boxes. A pressure was applied every 5min by a Kern-SAUTER FK 25 force gauge to determine also the force needed to remove the wall.

Picture 1. The project group preparing box samples. From left to right; Julien Walser (Novia UAS), Jari Oja (TAU), Heli Koivuluoto (TAU) and Ruqaya Khammas (TAU).
Picture 1. The project group preparing box samples. From left to right; Julien Walser (Novia UAS), Jari Oja (TAU), Heli Koivuluoto (TAU) and Ruqaya Khammas (TAU).
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Picture 2. Filled boxes with woodchips sitting at -10°C in the ice room.
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Picture 3. PE (on the left) and Slippery Lubricant Infused Porous Surface SLIPS + silicon oil (on the right) boxes at room temperature (21°C) after shear tests.

Centrifugal ice adhesion tester CAT is used to determine the adhesion. In principle, this machine shows the relation between the adhesion strength of an ice cube frozen on the CAT blade and the rotation speed at a constant angular acceleration. When the samples detach, they hit the dome and activate a sensor recording the time and the rotation speed.

With smaller sample sizes, the CAT allowed more testing. Altogether, 9 surfaces were tested with similar surfaces as in the box tests, e.g., polyethylene surfaces, steel surface with added chemicals and Teflon tape for reference. A cube of woodchips and water mixture were frozen on top and then put in the CAT to determine the adhesion.

Picture 4. CAT machine
Picture 5. CAT samples

Measurements show promising results concerning surface coating for frozen woodchips adhesion on containers. Simple solutions, like environmentally friendly or antifreeze lubricants, keeping a liquid layer between woodchips and surface at cold temperature are a good step forward. Further investigation should be made to study the durability of those coatings by cyclic measurement. More tests would be required as well to see the behavior of those coatings on larger scale containers.

Sample preparations at the Thermal spray lab at Tampere University

As a part of the icing research conducted at Novia UAS, one aim is to help forest and bioenergy companies with finding new solutions and ways of decreasing the freezing and adhesion of wood chips to storage container walls during cold weathers. In order to do so, close cooperation with the thermal spray and icing laboratories at project partner Tampere University has begun, where experimentation setup and work with different anti-icing and icephobic coatings and surfaces has started.

During a week in August, project personnel from Novia and Tampere University met at the thermal spray laboratory at TAU in order to prepare for and start up the collaborative experimentation work. As the goal of the experimentation is to investigate wood chip freezing behavior on differently coated surfaces, the first part of the preparations consisted of treating and coating the surfaces of test boxes and sample plates. These will later be filled with wood chips and placed in a cold room, after which different centrifugation, cycling and adhesion tests will be performed.

The project personnel from Tampere University and Novia UAS in front of a flame-sprayed polyethylene metal plate
Picture 1. Flame spraying of polyethylene coatings on metal plates in the thermal spray lab at Tampere University. From left to right: Jari Oja (TAU), Heli Koivuluoto (TAU), Anssi Metsähonkala (TAU), Jarkko Lehti (TAU), Julien Walser (Novia UAS) and Katrin Asplund (Novia UAS).

The coatings were done by flame spraying LD-PE powder onto the sides of the metal test boxes with the help of a robot (ABB IRB 4400/60), gun (CastoDyn DS 8000) and the powder feeder (Sulzer Metco 4MP). By carefully programming and adjusting pretreatment conditions as well as parameters such as temperatures, pressures, powder feeding rates and layers, a dense polyethylene coating could be created.

Thermal coating setup and equipment
Picture 2. The setup and equipment used for thermally coating the box sides (on the left), and a thermally sprayed polyethylene coated test surface (on the right).

Test plate thermally sprayed with PE- coating


For the box tests, three metal boxes will be used: one box coated with the flame spayed polyethylene (FS-PE), one flame sprayed with SLIPS and one untreated box for reference. Furthermore, a box made of PE- Quicksilver will used. In addition to the boxes, small sample plates for the centrifugation adhesion tests (CAT) were also prepared with the flame sprayed polyethylene coating (FS-PE), whereas more CAT samples will be made with other surface coatings, ie. FS-SLIPS, hydrophobic coatings, and oils such as silicon and rapeseed and tested out with the frozen wood chips in the icing laboratory.

Samples ready to be coated
Picture 3. CAT samples ready for coating (on the left), coated test box and logos (on the right).

Coated test box