Viscotec presents some of the main questions you should ask prior to acquiring dosing technology, especially with abrasive media.
Fine tuning application parameters prior to sourcing phase ensures the accuracy and quality of the dosing process. The basis of each process revolves around the medium and the method of application. After successful selection of a medium, it is necessary that it is dosed, applied, or filled with high precision and high repeatability to ensure process reliability. For such applications, various factors must be considered when selecting the dosing technology, especially when it comes to the handling of abrasive media.
Dosing systems can be grouped into two functional units, dosing valves and dosing pumps. The valves may include means of pressure-time, volumetric, and gravimetric dosing, whereas the pumps can be found in rotating and oscillating systems.
In an oscillating pump, the medium is transported by changing the chamber volume, increasing and decreasing it. Typical examples include piston or diaphragm pumps. Dosing components in rotating systems displace a more consistent volume.
ViscoTec Pumpen Dosiertechnik makes use of the endless piston principle of the eccentric screw pump in all its dosing applications. This type of rotary positive displacement pump feeds the medium in a self-contained cavity. The combination of a rotor made of hardened stainless steel and a soft elastomer stator can, for instance, gently doses and promotes highly filled media. The sealing line between the rotor and the elastomeric stator also produces minimal shear on the medium and at the same time ensures a seal effect without valve. In this way, abrasive media with particles of high-grain hardness can be dosed without increased wear, volumetrically accurate on any one part.
However, there are a number of criteria that must be observed even when selecting the correct pump type from ViscoTec.
Essential questions that must be asked, from selecting the material to acquiring a new dosing technology, especially in the application of abrasive media:
What criteria must be set prior to the sourcing of dosing technology?
Before a dosing technology is selected, it is necessary to contact the manufacturer of the medium to be applied. The medium can either specify a defined process or the process might have been previously defined by the end user.
In any case, information, such as viscosity, density, and filler content are just as relevant as pot life, the type of cross-link, and the mixing ratio for two component applications. In this context, the rheological behaviour of the medium plays an essential role and is subject to various factors, including amount and duration of a load and processing temperature.
Particularly non-Newtonian fluids require high application and processing know-how, as their viscosity can vary during the dosing process. After the selection of the medium, the size of container to be delivered is to be considered, particularly if a material is to be removed directly from the delivery barrel.
What basic components should be included in the dosing process?
As a system provider, ViscoTec refrains from selling individual components but puts significant emphasis on a coordinated, functional process technically specified in close consultation with the customer.
As a result, components of the dosing process structured depending on the application in terms of supply of material, material preparation, and dosage. Supply of material can be from any kind of container, such as cartridges, cans, buckets, or barrels and ensures a reliable removal without air being trapped in the medium.
Material preparation is necessary if the media already contains air pockets, if it has a tendency to set the filler content, or if it must only be fed continuously. Depending on these requirements, material processing plants buffer, circulate, homogenise or degas the fluid. The heart of the process is dosing, which is also the focus of this sourcing guide.
Dosing can include any one medium, but can also consist of a mix of two components, which are dosed before application. In particular, an indication of the required cycle times, the required dosing quantity, the application type, and the ambient temperature are of importance for the application. The required dosing and repeatability of the application is to be determined.
What information is required concerning set-up of the dosing technology?
Existing knowledge of the material, the container type, and the parameters of the application are agreed in an individual consultation with a member of ViscoTec’s sales staff. Details of any open questions are also discussed, including the required hoses, adapters, and connectors of the dosing components. Restrictions of space in the end process are also observed, such as the mechanical mounting of the components. Signal access of the controls and electrical connections represents another important aspect in this detail-collecting stage.
A semi-automated stand-alone solution with ViscoTec controls is equally achievable as a fully-automated system controlled via a programmable logic controller (PLC), whether via Profibus, PROFINET, or digital input / output (I/O).
For particularly demanding dosing tasks, testing in Viscotec’s in-house laboratory can be carried out in consultation with the customer. These tests provide an important insight into the process and help to erase any last doubts that the customer may have. Based on information gathered, a customised solution will be prepared and an individual offer submitted.
What are the technical challenges to be aware of when dosing abrasive media?
When it comes to the processing of abrasive media, there are a number of details to consider. ViscoTec offers a broad selection of different elastomers that can be used depending on the medium and its mechanical aggressiveness. A multi-tiered qualification process will be used to specify the correct elastomer for the stator to significantly increase its service life despite mechanical load.
In addition, it is also important to take into account, and minimise friction of the particles in the medium onto the dosing components. The wear of both the rotor and the stator can be reduced by adjusting a comparatively low flow. High-flow velocities such as abrupt reversals or narrow openings in the dosing pump geometry should also be avoided.
These measures can counteract a so-called cavitation in the dosing pump. Short inlets with large diameters equally prevent the build-up of high pressures and thereby reduce the friction on the inside of the pipe. To prevent a blockage of particles in the dispensing needle, a conical dispensing needle, with a diameter of at least the size of the largest grain cross-section, should be chosen.