“A typical Vertifoam machine runs at speeds of between 1.0 and 1.5 m/m as opposed to a horizontal machine which will run at between 4 and 7 m/m. It is a controlled process which gives time for the foam to build its strength in exactly the same way as it does in a horizontal machine,” said Brian Blackwell.
“Most big conventional slabstock lines run for 3-4 hours a day or an hour every couple of days. When they run they produce a great deal of foam,” Bill Blackwell said.
It's not a race
“With Vertifoam you can run it for 5 to 8 hours. Because it’s running slowly, start/stop losses and formulation changes are very inexpensive and you’re not wasting huge amounts of foam. A typical horizontal slab dispensing head is running at 300 kg a minute whilst a Vertifoam is running at 40 kg a minute,” Bill Blackwell said.
Brian Blackwell added: “They make up the difference by longer running.”
The amount of space Vertical machines need is much lower than conventional horizontal machines. They have a footprint of around 16m2, Bill Blackwell said. The foam rises vertically, is cut, tilted through 90 degrees and accelerated out.
The Vertifoam machines are slower than traditional horizontal machines and they can produce both a round or rectangular block of foam which must then be cut and removed from the machine.
“Round blocks are easy to peel,” Brian Blackwell added.
To win the Sheela contract, “we put together a technical group of experts for both equipment and process. The team, led by John Blackwell, Technical Director, included the man who invented Vertifoam in the mid-1980s, Tony Griffiths, and Andre Van de Velde an industry expert” said Brian Blackwell.
“Together with our expertise as machinery manufacturers and Sheela’s experience in foam processing and specialist knowledge of Vertifoam and VPF foaming, we devised a way of making two processes work together,” he added.
The big advantage is financial, said Blackwell, such variable pressure machines enable very low density foam, down to around 10kg/m3 (0.6 lb/ft3) with good physical properties and it is possible to formulate systems to closer stoichiometric balance than with horizontal machines.
Moreover, the density of the foam is uniform throughout the circular block and there is little or no skin.
Joyce Foam Products in Australia (owned by Sheela Foam) installed a horizontal VPF machine in 2010. Sheela/Joyce discovered it could make some unique foams and one of these was a very low-density, very soft foam to replace polyester fibre in mattress quilting. This lead Sheela to purchase the technology for India.
This unique low density polyurethane foam has replaced polyester wadding in 80% of the mattresses per year which Australia makes, said Bill Blackwell. Not only is the foam low density, it has excellent physical properties such as compression set, which is much lower than polyester wadding, he added.
“This can be a very profitable business for foamers,” Brian Blackwell added.
How the process works.
Isocyanate and polyol are mixed in a low/high pressure head which dispenses the reacting mixture into a horizontal trough at the bottom of a short tower.
As the foam rises, it expands horizontally until it comes into contact with a tube of polyethylene which forms around the outside of the rising foam.
This passes through a cure section and then comes into contact with a set of twelve vertically-oriented pinned conveyors. The pins puncture the polyethylene tube, enter the foam and convey the product up to the cut-off machine.
The block length is cut and the block is tilted through 90 degrees and passes through an airlock door. Once closed the outer airlock door is opened and the block accelerates out. Once clear of the outer door, the airlock is depressurised and the next block is cut and enters.
The system is designed with access doors for maintenance work, which is carried out at similar intervals to a conventional horizontal atmospheric machine. Aside from the pressure-resistant enclosure the other extra pieces of equipment is a blower system, used to evacuate the airlock quickly after the outer door closes and a smaller blower which continuously maintains a reduced pressure in the vertical process enclosure part of the machine.
Foaming under reduced pressure gives lower densities and improved physical properties reducing formulation costs.
In addition VPF can also operate at higher pressures than atmospheric equally improving physical properties and formulation savings.