Vacuum-soldered mixing elements –
The manufacturing process of static mixers with gapless soldered mixing elements has been tested and developed over a period of several years. It starts by producing a special tube for the corresponding inner diameter. The mixing elements to be soldered are furnished with a longitudinal slot on the side where the solder is subsequently introduced. After this, the mixing element chain is inserted into the tube which is subsequently warmed up in the vacuum oven in specified temperature levels to over 1000°C. This is the melting phase. The solder is diffused during this process into the tube material and into the elements – a crystal transition takes place. In the crystallisation and maturing phase the gapless connection between mixing element and tube interior is created.
Each year, several hundred pieces of these gapless mixing tubes are integrated for instance into tube bundle heat exchangers in order to significantly improve the heat transfer and avoid caking. Other applications can be found for instance where dead spaces have to be avoided. This is a frequent demand in the pharmaceutical industry. For processes which generate large axial forces due to the product characteristics (very high viscosity), soldered mixing elements are also frequently used as this enables the forces to be fully delivered to the tube.
By using measurement technology (e.g. X-ray, ultrasound) it is not yet possible to prove gap clearance. During specified test procedures the elements case confusing shadows, thus no definitive statement is possible. Up until now, only a visual assessment of the components has been possible.
Viscosity – The term viscosity relates back to the typically viscous juice from berries in the botanical systematics of mistletoes (viscum spp.) from which birdlime was gained. Viscosity is a physical value and gives information about the siziness of a liquid. Its reciprocal value is fluidity, measuring the flowability of a liquid. The larger the viscosity, the more viscous or the less fluid the medium is. We differentiate between dynamic and kinematic viscosity. Dynamic or absolute viscosity is measured in Pa.s or mPa.s and is usually determined with the aid of a rotation viscometer. The dynamic viscosity of most liquids reduces as the temperature increases. The kinematic viscosity is specified in m2/sec. It is the measurement for the internal friction of a liquid and describes the resistance of liquids against shear stress. Here, the term shear viscosity is used as opposed to bulk viscosity which results for instance from a consistent pressure to liquids. Kinematic viscosity can be calculated by dividing the dynamic viscosity by the density of a liquid. STRIKO process technology requires specifications on viscosity from its customers if for instance it is about choosing the right type of mixer in the static mixer product range for a special application. The more precisely the existing process parameters are known the more effectively a static mixer can be designed and produced. In the area of custom-designed STRIKO demisters, viscosity also has a role to play. Amongst others, important influencing factors for an efficient separation here include the density and the viscosity of the liquid. The viscosity has an indirect effect on the performance in that – alongside the formation process – it plays a massive part in determining the droplet size.
Volume flow rate – The volume flow rate, less precisely referred to as flow rate, is a physical value from the field of fluid mechanics which indicates how much volume of a medium is transported through a defined cross-section in a defined time frame. For STRIKO it is an important parameter for designing heat exchangers, demisters and static mixers.