THE UTILITY OF TREATMENT FOR DRYING OR DEHUMIDIFICATION OF THE RAW MATERIAL
Starting from the fact that, for some materials it is essential the treatment of drying or dehumidification, we would like to highlight here the importance of this process for those materials that classified "Not Hygroscopic" do not require any preventive treatment.
Let’s consider, as example, the PE for extrusion (film or pipes). This material, when used pure, is considered "Not Hygroscopic" but when the material get in contact with very humid air, it is possible that this humidity condense on the pellet surface entering in this way in plasticization process, and, transforming itself in steam, can modify considerably the transformation parameters and the mechanical and aesthetic properties of manufactured product.
This happens when extruder barrel does not have the degassing device. In fact in this case the steam entrapped in the barrel increase the backpressure, lowering productivity, increasing the effort on the screw and therefore increase the consumption and costs. In addiction the steam bubbles prevent a steady stream of the material in extruder causing a pulse production.
This problem increases exponentially in the presence of a Co-extruder. In this case in the head, where the materials must match and weld, the presence of steam particles act as a disruptive, causing the separation of the layers or even the mixture of different materials. This because it is possible that the space occupied by steam in one material can be easily occupied by second layer material, causing the spots effect.
We handled this problem in the co-extrusion of corrugated tube with small thickness, where a layer occupied parts where others missing. After several attempts to correct the defect by making changes on the extruder head, the problem was solved simply drying the material in advance.
Even in the production of sheet in PS by thermoforming, also in the not co-extruded sheet, several problems on the stability of thickness were resolved simply drying the material. In this case there was not any aesthetical defect so it has been quite difficult to understand that the problem was caused from the presence of small percentages of humidity.
Trying to solve the problem, our WM Control was installed. The WM (weight meter) control have been studied for the automatic determination of the average thickness of the pieces, and the constantly maintenance during all production.
The WM showed that even if the material entered regularly in the extruder with constant RPM on screw, sometime there was a suddenly increasing of pressure in the head that in a few seconds disappear. Comparing data provided by WM Control with the production data, we came to the obvious conclusion that it was the characteristics of the material to change.
Drying the material for one hour at 70 C°, the problem was finally resolved, and the production, that with this problem decreased around 8-15%, besides being stabilized, is increased by 4% with equal consumption electricity.
In blow moulding process, the prior drying of FPVC, increased gloss and transparency of containers, almost eliminating the need for continuous polish of mould for the presence of moisture in the material which develop chlorine that attacks the surface of the mould making mat. Even in this case, the productivity increased of a few percentage point.
In addiction to these productivity advantages, we have to consider also the not less important qualitative advantages of manufactured goods as a better surface appearance and increasing of mechanical strength characteristics. This last one would be even better if it would be used a process of dehumidification instead of drying
Let’s consider, as example, the PE for extrusion (film or pipes). This material, when used pure, is considered "Not Hygroscopic" but when the material get in contact with very humid air, it is possible that this humidity condense on the pellet surface entering in this way in plasticization process, and, transforming itself in steam, can modify considerably the transformation parameters and the mechanical and aesthetic properties of manufactured product.
This happens when extruder barrel does not have the degassing device. In fact in this case the steam entrapped in the barrel increase the backpressure, lowering productivity, increasing the effort on the screw and therefore increase the consumption and costs. In addiction the steam bubbles prevent a steady stream of the material in extruder causing a pulse production.
This problem increases exponentially in the presence of a Co-extruder. In this case in the head, where the materials must match and weld, the presence of steam particles act as a disruptive, causing the separation of the layers or even the mixture of different materials. This because it is possible that the space occupied by steam in one material can be easily occupied by second layer material, causing the spots effect.
We handled this problem in the co-extrusion of corrugated tube with small thickness, where a layer occupied parts where others missing. After several attempts to correct the defect by making changes on the extruder head, the problem was solved simply drying the material in advance.
Even in the production of sheet in PS by thermoforming, also in the not co-extruded sheet, several problems on the stability of thickness were resolved simply drying the material. In this case there was not any aesthetical defect so it has been quite difficult to understand that the problem was caused from the presence of small percentages of humidity.
Trying to solve the problem, our WM Control was installed. The WM (weight meter) control have been studied for the automatic determination of the average thickness of the pieces, and the constantly maintenance during all production.
The WM showed that even if the material entered regularly in the extruder with constant RPM on screw, sometime there was a suddenly increasing of pressure in the head that in a few seconds disappear. Comparing data provided by WM Control with the production data, we came to the obvious conclusion that it was the characteristics of the material to change.
Drying the material for one hour at 70 C°, the problem was finally resolved, and the production, that with this problem decreased around 8-15%, besides being stabilized, is increased by 4% with equal consumption electricity.
In blow moulding process, the prior drying of FPVC, increased gloss and transparency of containers, almost eliminating the need for continuous polish of mould for the presence of moisture in the material which develop chlorine that attacks the surface of the mould making mat. Even in this case, the productivity increased of a few percentage point.
In addiction to these productivity advantages, we have to consider also the not less important qualitative advantages of manufactured goods as a better surface appearance and increasing of mechanical strength characteristics. This last one would be even better if it would be used a process of dehumidification instead of drying
