2022.09.30
Obviously, various raw materials have different foaming ratios and foaming speeds. For various raw materials, its foaming ratio and foaming speed are inconsistent. For various types of pre-expanders, the foaming ratio can be controlled by adjusting various parameters.
Taking the continuous pre-expansion machine as an example, under the condition of a certain body volume and steam flow rate, we can control the pre-expansion bulk density of EPS by adjusting the feeding speed and adjusting the height of the discharge port.
Intermittent pre-expanding machine means that after the machine throws EPS material once, after the material is pre-distributed to a certain volume, the material in the machine is finished and blown. Then feed, pre-deliver, and discharge… and so on. Figure 5-3 is a schematic diagram of an intermittent pre-engine. Since the feeding amount of each batch is certain, the pre-release volume of each batch is also certain, so the bulk density after pre-release is guaranteed, and after pre-release, the change in bulk density of the material is also small, generally kept below 3%. Excessive foaming agent content will lead to uneven pre-foaming, foam blooming, product deformation and cracking, and it is easy to reduce the foaming ratio, the heating time is too long, and the cohesion between the EPS beads during the molding process is poor. As well as product shrinkage and particle drop, etc. The content of the best foaming agent should be 4.8%~7%. Since the foaming agent of the domestic material is volatile, the content of the foaming agent of the raw material that has just left the factory is less than 4%, and the vapor pressure does not increase (or the temperature increase), the density will not be low (generally above 23kg/m3), so it is required that the raw material warehouse must pay attention to the temperature not too high (the requirement is lower than 20oC), and the storage time should not be too long.
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