Operating temperature of polystyrene from -200 to +85 C. Water absorption foam Unlike other materials Styrofoam is not hygroscopic. Even under water, it absorbs little moisture. Since the walls of the cells are impermeable to water, it can leak out only through the channels between the individual associated with each other between the cells. Water absorption is measured by the standard method. Test samples are squares with the surface of 200×200 mm and the corresponding thickness, immersed completely in water.
The water absorption is virtually independent of the bulk density. It is reached after 24 hours up to 2-3% in terms of volume. Water absorption during curing under water not only plays a significant role for most of the material and is of interest only in special situations. Since polystyrene does not dissolve or swells in water, and because no coherent structure containing air cells, almost does not absorb water. The water in the liquid phase can, in principle, to penetrate the labyrinth between the granules fused together, mainly due to capillary action, but can always leave the maze, without affecting long-term adverse effects on the mechanical strength, size, physical appearance or the insulating properties of the material. In addition, by increasing the degree of fusion between the granules through optimization of molding, the capture of water is minimized. Water vapor phase able to penetrate, and polystyrene, although at a density of 30 kg/m3 and above, the rate of displacement less than 1% compared to the speed of movement of water through the stable layer of air of the same thickness.
Plasma cutting – one of the most effective methods of thermal cutting of metal. On the quality of the cut only slightly exceeded only laser cutting, but it surpasses laser cutting of economic indicators and more ample opportunities, especially concerning the maximum thickness for cutting metals. Duty cycle (MF,%) – one of the most important factors influencing the choice of a particular model of plasma cutting machine. This relationship time of the apparatus to the plasma cutting the time needed for its cooling. Some companies claim their vehicles for MF 100%, without specifying on which a stream of cutting it occurs at the maximum or nominal. At maximum current 100% duty cycle can in principle be based on the laws of physics. A current rating is just one in which the device can operate plasma cutting for a long time without stopping. Science, the duration inclusion should be considered based on the 10 – minute cycle, ie if the device PV 70%, 7 min plasma machine – cut the metal, and 3 minutes – to cool.
In practice, all slightly different: for the cycle takes 1 hour, ie 60 minutes, ie at DC in plazmoreza 70% per hour, he must cut metal 42 minutes and 18 minutes – cool. In addition, for manual cutting of cutting without interruption 42 minutes, almost impossible, because cutter must move with respect to the product, or move the product itself. Ie periodically turn off the ignition button on the plasma torch. And in these moments of idle time of machine plasma cutting already under way to offset the cooling, because cooling fans continue to blow transformers (if it is – not plazmorez inverter). Accordingly, the PV in practice may be somewhat higher than the nominal expressions.
We now turn to concrete examples. Among the devices manufactured by Power Engineering Concern Plasma is a model of the APR-60 which is designed exclusively for hand cutting sheet metal in the thickness range from 0.5 to 12 mm. We mean quality cut (without burrs), because as this machine cuts up to 18mm – the dividing cut. Apparatus Plasma APR-60 has infinitely adjustable current, it has 2 modes: 40A and 60A. Relative to these regimes, the stated duty cycle, 70 and 60%. What does this mean? This means that the steel 12mm (maximum value for quality of cut on this machine plasma cutting) APR-60 can be an hour to cut about 30 minutes without overheating. But at the same mode of smaller thickness (8-10mm) APR-60 will be cut longer, due to the higher cutting speeds, respectively, for by the fact that the cutter should be more stop for various subsidiary operations. Despite the fact that the plasma cutting machine APR-60 is designed for manual cutting, the experience of our customers tells us that small thicknesses of this plazmorez can be used in automatic mode as the plasma source in a small portal machine with CNC plasma cutting of metal. At the same PV at thicknesses up to 3-5mm grows to 100%, despite that the automatic plasma cutting length of cut is much more than the manual. Nevertheless, the selection for the client machines for automatic cutting, we recommend installing Plasma APR and APR-91-150, as these devices for just this and are designed and have more features than other models of production plazmorezov Power Engineering Group.