Polyurethane mixing process

Polyurethane, also known as PU or PUR, is a foam plastic that offers a wide range of applications. The foam forms due to a chemical reaction in which isocyanate and polyol, as well as a blowing agent, are mixed together. The reaction starts immediately after mixing and thus forms the foam plastic. Depending on the intended use, the foam is used in blocks or sheets, which are then shaped.

 

 

The mixing process is one of the standard applications in the chemical industry. Two or more substances are to react by mixing to form a new substance. The polyurethane synthesis from the starting chemicals isocyanate and polyol is outlined here as an example. For high and consistent product quality, it is of great importance that both starting materials are accurately and reproducibly metered into the mixing head.

Landscape

Isocyanate pump

Isocyanants are highly reactive esters of isocyanic acid. They are used to produce polyurethanes by adding alcohols in a polyaddition reaction. The materials and design of the CHEM pump are therefore specially adapted to this application.

Thus, due to the low viscosity of the isocyanates, plain bearings and the gear shafts made of low-friction and low-wear material pairings are used in this application. By using special stainless steels as housing material, efficiency improvements can be realized even at operating temperatures above ambient temperature, as well as tight clearances.

The toxicity of the isocyanates requires the pump to be designed with a technically tight shaft seal in accordance with TA Luft. Hermetically sealed magnetic couplings are preferred, but the use of buffered mechanical seals is also possible.

Operating parameters

Pump type
CHEM 2,78
Flowrate l/min
0,2 up to 2
Possible seals for this application
Magnetic coupling or double, buffered mechanical seal
Heating
hydraulic if required

Process setup

  • Metering pump
  • Isocyanate storage tank
  • Volume flow meter
  • Mixing head
  • Control station

  • Metering pump

    The metering pump of the CHEM series is responsible for delivering the exact amount of isocyanate required to the mixing head. The isocyanate is stored in the feed tank.

  • Isocyanate storage tank

    The storage container must be absolutely clean and airtight. Isocyanates are highly reactive and can change their aggregate state in a very short time on contact with air, water or other substances. The reaction can manifest itself in the form of coating formation, gelation or thickening or clumping. These then cause problems in the further course of the process.

  • Volume flow meter

    The pump is coupled to a volume flow meter, via which the pump or motor is precisely adjusted. In the mixing process, it is extremely important that the exact mixing ratio of the two components is maintained.

  • Mixing head

    In the mixing head, the two components are mixed together to previously defined parts, thereby initiating the desired reaction. In this case, the mixing of isocyanate and polyol leads to the formation of PUR, a foam plastic.

  • Control station

    The entire process is monitored via the control station, in particular the performance of the pumps and the filling levels of the feed containers. Here, it is possible to react at an early stage and take corrective action if there are deviations from the standard operation.

WITTE Zahnradpumpen | Isocyanat-Pumpe