Rocket coating – an extreme challenge for material and process
Ruggedness is an essential condition for economic operation in almost all industrial applications. Because damage of installed pumps may quickly result in the shut-down of entire production lines, resistant materials as well as durable components and very quiet running are very important when designing the pumps. Vibrations, translating into permanent strain on all components, must be avoided at all costs, especially when long service lives shall be achieved. The high viscosity of any medium represents a special challenge here. Depending on the delivery technology, it may possibly have a very uneven distribution causing imbalances which may result in mechanical damage to the pumps.
The delivery principle of volumetric displacement on which the progressing cavity pump is based works nearly without pulsation and can be regulated precisely via the rotational speed. In addition, engineering design permits numerous configuration versions regarding materials and geometries. Thus, the right pump can be put together for any use to ensure long service life and high efficiency in spite of the challenging conditions.
Task
For a very special and demanding application, was this ruggedness of the pump was the decisive feature for the operator. His task was the delivery and metering of special paint for coating rockets. After adding hardeners, this medium reaches a viscosity up to 3,000,000 mPas – comparable to molten glass or very tough paraffin oil. As a result, the delivery pressure lies at a very high 48 bar; still, a delivery amount of only 0.01 to 0.1 m³/h was supposed to be metered for the order with an accuracy of 95 percent. To be able to meet this requirement a special version of the NEMO® pump was configured just for this purpose
Solution
The experts combined a basic body of corrosion-resistant stainless steel coupled with a PTFE stator. The high viscosity of the medium was used to build the sealing line between rotor and stator, and the pump was thus able to generate the required pressure. The extremely low-friction PTFE prevents wear and reduces the required breakaway torque. The high axial loads generated from the high pressures were compensated by using a bearing block of a larger pump size. As a result, the pump was able to reach pressures up to 50 bar. In addition, inspection windows were installed in the pump housing allowing to check the motion of the tough special paint exactly. The delivery volume can be adjusted exactly to the required volumes via the speed to ensure optimal ink application.
