01 The role of cold and hot mixing equipment

Cold mix and hot mix work differently. Hot mixing is generally not equipped with external heating, mainly relying on high-speed rotating blade pulp to drive the material to collide with each other, friction and shear with the barrel, and generate mechanical energy to convert heat, so that the normal temperature material becomes a hot mixture.

The barrel of the cold mixer has an interlayer, and the interlayer is filled with cooling water. And generally, the volume of the cold mixer is about three times that of the hot mixer. After entering the cold mixing machine, the hot mixing material is continuously stirred in a relatively spacious environment and the rotating blade slurry is slow, and the heat is exchanged by the cooling water in the interlayer of the inner wall of the barrel, and it gradually cools down.

02 Cold Mixing and Mixture Quality Evaluation

The role of cold mixing

The material should be cold mixed immediately after hot mixing to prevent the mixed material from degrading when stored at high temperature for a long time. If the mixture is not cold-mixed, it is easy to re-absorb water when cooled in a natural state, increasing the water content of the mixture and causing adverse effects on extrusion. In fact, hot mixing of materials is an endothermic process, and cold mixing of materials is an exothermic process.

Cold mixing can not only prevent the material from cooling and absorbing water at high temperature, but also the process of further discharging the intermolecular water during the exothermic reaction of the material.

The discharge temperature of cold mixing after hot mixing plays an important role in ensuring the quality of the mixture. This is also often overlooked.

Relevant personnel of some enterprises believe that: the mixture is to be plasticized in the extruder anyway, it is not good to add it while it is still hot, why should it be cooled again? , the quality of its products is difficult to guarantee. Generally, the rated temperature of cold mix discharge is 40-45℃. The temperature of the cold mixed cooling water is usually controlled at 13-15°C.

Assessment of Mixture Quality

The quality requirements of the dry mix are: loose and not agglomerated, no grease on the surface, micro-elasticity by hand, no impurities, etc. It can also be tested by the following simple method: squeeze a handful of dry mix by hand and let it flow down freely. It is better to have less powder and less adhesion on the hands when falling. Another method is to observe the initial plasticization state of the material in the vent hole of the extruder. The color of the parison is consistent, with a certain luster, the material is uniformly discharged, the hand-kneading has good elasticity, the current of the extruder is stable, and the pressure display is normal and stable, indicating that the mixing quality of the material is good.