In the previous blog, we were discussing large cellular glass boards, which are recently available. In that case, the own weight of a board may induce bending up to breakage and for that reason, we have to consider a minumum thickness.
Today, there are still small boards on the market. For example, in case of 59 x 46 cm boards with 140 kg/m³ density, the boards have to be only 4mm thick to sustain its own weigth with a span of 59cm. The minimum thickness is about 3cm, so bending under its own weight was never an issue. It explains why flexural strength gets much less attention than compressive strength.
But for GLAPOR boards 280 x 120 cm at 140 kg/m³ density, the situation is different. In this case, we need a thickness of 10 cm to have a safe resistance against bending under its own weight. Like shown in the previous post, the picture shows 10cm boards 280cm x 120cm.
For the same reason, people, dreaming about even larger boards to reduce even more production cost, have to be carefull. Indeed, for the case of 4m wide boards, we need 20cm thickness to have a safe resistance against bending. Like can be calculated, annealing of 20cm in continuous foaming involves a very long lehr due to the large annealing time. This case could be non realistic. We expect however that soon production lines will be built with two ribbons of about 3m width, which are foamed and annealed in the same furnace to reduce largely production and investment cost.
The above shows that flexural strength will become an important property for cellular glass due to the new large GLAPOR boards on the market. But we observe that large boards have to be thicker due to bending stress. In that perspective, it makes sense to consider cheaper cellular glass like GLAPOR boards with a slightly higher thermal conductivity, because thickness is already needed against bending stress.