He said rigid foams made using the system “show increased isotropy with air or nitrogen as the nucleating agent. We also see good results in flexible polyurethane with carbon dioxide as the nucleating agent.”
The nucleating agent is supplied as small bubbles which become smaller by a combination of cross-cutting shear elements and relatively high flow through them. “The idea came from the food industry,” he explained.
In the DUT process, about an hour before production is due to start the nucleation begins. The nuceleating gas is added by weight, Fisselbrand said. During production, the level of nucleation is measured and maintained using a feed-back system, he added.
Once 10% of the nucleated polyol is consumed, it is replaced with fresh polyol and re-nucleated. Other producers’ systems may only nucleate the polyol once and so the level drifts with time, he said.
Fisselbrand said: “The maximum level of nucleation is 26 l/min with 45% air. “The nucleation bubbles are under 50 µm diameter,” and it takes “30 minutes to diffuse out of the polyol.”
“The traditional method produces bubbles of approximately 200 µm diameter using a static mixing element but, there are no bubbles on the inside wall of the tube because there is no flow. There are bubbles in the middle of the flow.
Cell variation in the finished foam is due to the variable sizes of bubbles in the flow. If the bubbles are not small enough then they wish to re-agglomerate into larger bubbles.”
Fisselbrand said his invention overcomes this problem by significantly increasing the flow rate and using a special mixing element which homogenise the flow and generates very small diameter bubbles.
The device is also available for continuous sandwich panel lines, he said.
“The goal is to produce small cells and it is being used by the Japanese panel producer Nippon Steel. They have found that can reduce panel density by 10 to 20% and is giving payback within about three months,” he concluded.
Yong-Chia Jiong, DUT Korea ceo, also used UTECH Asia 2016 to outline a range of new high-pressure resin transfer moulding equipment for the PU industry. This range of machinery includes products where resin is injected under slight vacuum, and follows Korean requests for a number of machines to do this. The machines are now available in Asia and they will be available in two years in Europe, Jiong said.
The mixhead of the machine is based on the company’s DTRC new generation mixheads. They can handle filled materials. There are four machines in the range which can handle chopped glass strands or carbon fibre injected into the mould. There is also a design with a more specialised mixhead for filled materials. A Long fibre LSI model is being used by a customer, according to Jiong.