Filled Foam on Maxfoam

The demand of filled foam is increasing in some parts of the world. It was produced quite successfully on conventional machines to a very limited height.

The use of an organic fillers in foam are an important tool to produce cheap quality foam without to much damage to the foam properties provided it is well applied and produced.

Years ago producers were satisfied to reach a block height of 26 inches or 650 mm but today a Maxfoam technology can produce a foam of almost 42 inches high by a width of 84 inches with 100% filled polyol.

In general the production of the foam type is not so difficult provided certain points are well noticed.

1. Type of Filler

Fillers must meet the following requirements;
a) The particle size must be very small, approx 5 micron.

b) The water content should not exceed 0.2% and the filler itself should not be hygroscopic.

c) The filler should not contain free metal parts to destroy the catalyst activity.

d) The filler must be easily dispersed in the polyol. In a weight ratio one to one the slurry must have a low enough viscosity to be pumped, preferably by means of a Monyo screw pump. One of the organic filler that meets all these requirement is Barium Sulphate with a specific gravity of 4.2 grams/cm3 in its purest foam.

Barium sulphate is to be used in preference to calcium carbonate due to the 55% higher specific gravity.

For this reason this report will continue on this type of filler.

2. How much filler can be used?

Any percentage from 0-100% or beyond this limit.

More important is the water rate/freon level in combination with the filler percentage/block height, because these four factors will determine the limit in which the production becomes critical. Also in the machine in particular the fallplate setting determines if it is possible to produce fault free foam.

For the sake of reproducibility it was found out that a 100% Barium filler with 2.35 water, 8 Freon and a block height of 42 inches will come pretty close to this limit of producing high density medium soft foams.


3. If conventional polyether foam is compared WITH FILLED foam what properties can we expect by filler increase percentage?

Elongation at tear strength reduced from 205% to 170%.
Tear strength reduces from 0.82 to 0,78Kg/cm2
Compression set shows 11.8% instead of normal 2.8 %.

4. What are the difficulties?

a) Very narrow tin spread by increasing filler percentage. Expressed in pph a spread of 0.025 pure stannous octate is possible for a 100% filled foam.
b) Mechanical faults can be made very easily in this type of foam due to somewhat different rise pattern.

The catalyst level on a filled foam is higher than on a conventional foam and still a total rise time of 270 seconds can be expected in a 3 lbs/cft density.

The trained observer soon finds out that the foam will almost reach a height in less than 120 to 150 seconds, it is very delicate at this stage and it is therefore easily damaged. Therefore a good fall plate settings which follows downward expansion of the foam and a smooth lay down are very essential, despite the little lost in the profile shape.

c) The index should not be lower than 106

d) A homogeneous slurry together a narrow range in specific gravity is required.

e) The water content of the slurry should be established before the production.

f) Preferably a machine box test should be made before any foam is poured onto the conveyor.

Unifoam’s standard start procedure can be used to obtain optimum shape and quality.


5. Description of additional equipment.

To produce a filled foam the following items are required.

a) The batch or slurry tank

Depending on the duration of the run, the tank volume has to be determined, an average output on slurry in approx. 500-600 lbs/min with a specific gravity of 1.3~1.6.

It is recommended to use a closed tank with a removable lid on the top. The bags containing fillers have to be emptied very carefully through a sieve into a predetermined quantity of polyol and during the preparation the slurry has to be circulated through metering circuit and the agitator (two blade propellers) has to run on a maximum speed of 55 revs/minute.

As soon as the filler is mixed in, the agitator speed can be turned down to 15~20 revs/minute and the metering pump keeps the running while the tank is closed.

Keep preferably dry air supply onto the when agitating.

b) Agitator

Two speed motor 8~10 H.P
Low speed 15~20 revs/min.
High speed 55 revs/min.

c) Propellers.

They can be made of metal sheets which are firmly connected to the axle with a clearance to the tank wall of not more than 12 inches.

The lowest propeller has to be installed close to the bottom and the second one 3 feet from the bottom.

The outlet opening of the tank into the feed line of the pump has to be provided with a coarse grid or sieve.

The return line must hit the wall of the tank on the top and splashing must be prevented.

d) Metering pump for polyol filler

Accurate metering at an output of 250 kg/min is achieved with a Monyo pump CDQ which is delivered by Robins and Meyers Springfield Ohio USA.

If some parts of nonhyrdolysable silicone oil are mixed into the slurry, the life of the pump will be extended.




e) Metering lines and filters

4 inch suction line and 3 inch delivery lines are required.
An oversized 6 inch filter in the pressure line will act as a strainer.


f) Temperature Control

The working temperature should not exceed 73F, a higher temperature will cut back on catalyst level but the major disadvantage of using heat as a catalyst lies in the fact of a long curing time and subsequently thick top skin with damage to the side skin.

When the slurry is prepared, it is obvious that the agitator is running.

The friction heat which is developed will raise the temperature of the slurry which is checked with a pyrometer or probe. Automatic temperature controlling the equipment can be used on the outside of the tank wall. Cooling on the outside and heat development on the inside will result in condensation if the slurry tank is open. Therefore it is better to have a closed tank with a dry air supply on the top.

6. Procedure

The best way to establish a stable formulation is to do some trials on lab scale, as described in the Maxfoam instruction book. Premix polyol and the desired quantity of Barites a couple of hours before that trial, for air will be trapped and it must have the chance to escape from the slurry.

Virgin foam formulation can be used to determine the catalyst levels.

If the density is within specification and if the ILD value is rather on the high side then it becomes worthwhile to prepare the machine for box trial.

From this point one can continue with short machine runs during which exact catalyst levels can be established and optimum fall plate setting can be determined.

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