The discharge pump is installed under the reactor. The actual polymerization takes place in this reactor. The prepolymer melt has a very low viscosity due to the addition of solvents. In the polymerization stage, the solvent is evaporated under high vacuum and polymerization continues. As a result, the viscosity increases sharply.
Conveying from the vacuum
Due to the high vacuum, the polymer enters the pump only by gravity. To avoid fluctuations in the delivery flow, the interdental spaces must be filled evenly. This also avoids air bubbles in the delivery flow. Due to the process, the liquid column should be kept as low as possible, as should the residence time of the polymer in the pump.
The challenge
The challenge in this process stage is the constant filling of the interdental spaces for an optimum product result. The pump is filled with polymer only by gravity, as the reactor is under a high vacuum. The pump must be absolutely vacuum-tight to prevent the entry of oxygen at all costs. The product quality would suffer considerably from the entry of oxygen and, in the worst case, ruin the complete product.
This POLY pump is therefore operated with a threaded vacuum seal, which is additionally designed with a buffered stuffing box. For other applications, a version with a double flange seal including nitrogen overlay or a weld lip seal is also available. If this is not sufficient, a double cover gasket with nitrogen blanketing can also be installed in an additional modification step.
