It is easier said than done, that highly viscous materials can be dosed reliably and precisely, but it is possible with ViscoTec products, which are all based on the endless piston principle. The viscosity-independent dispensers impress with their shear-sensitive, high-precision material handling.
Application example LOCTITE SI 5970
The thixotropic 1-component silicone LOCTITE SI 5970, which cures at room temperature on contact with moisture, is a difficult to process material due to its high viscosity. ViscoTec dosing systems have proven themselves in extensive dosing tests for the handling of this 1-component sealant. In particular, the 1-component dispensers of the RD series.
The curing of this material is comparatively fast: after only approx. 25 minutes at 23 °C and 50 % humidity, a skin is formed, and the surface is tack-free. Since methanol is released during curing, LOCTITE SI 5970 is one of the neutrally crosslinking silicones.
The properties of the 1-component silicone cause great problems, e.g. with time-pressure systems, when dosing a smooth and even bead, as there can be an excess of material at the beginning of the dosing process and a strong thread pulling and dripping at the end. The material is thixotropically formulated, which in principle reduces the viscosity during shearing and simplifies processing due to improved flow behaviour. Nevertheless, an initial viscosity of approx. 1.5 million mPas remains in the low shear range – the dosing material therefore still poses challenges, especially in its behaviour at the start-up of the systems. After application, however, the silicone relaxes again very quickly, and the viscosity increases almost abruptly, which in turn prevents it from running.
LOCTITE SI 5970 is mainly used for sealing applications, e.g. as a sealant in a groove or as a closed sealing bead on the flat surface of a flange, a casing cover or an oil pan. The high oil resistance of silicone makes the material particularly suitable for sealing applications in these areas. LOCTITE SI 5970 can also be used for sealing covers for gear units in contact with gear oil.
At the same time, the material naturally offers all the advantages of silicone in general: high temperature resistance, thermal shock resistance and high expansion/elasticity. This allows different thermal expansions of the components to be bonded to be compensated. The sealing of the system is therefore guaranteed.
The complete system from one source
ViscoTec offers the complete dosing system from one source: typical systems for this silicone consist of a hobbock removal (in some cases with additional separating plate degassing to prevent air from entering the system during container change), a hose line and a 1-component dispenser. The 3RD12 or 3RD10 dispensers of the RD series are perfect for this material and its typical applications.
Advantages of ViscoTec dosing systems for the processing of highly viscous materials
- Viscosity-independent dosing thanks to progressive cavity technology – particularly important for highly viscous materials
- Error-free dosing bead possible thanks to continuous dosing even with different sealing geometries which is a decisive factor in the case of sealing beads. If a piston dosing unit would be used, a small defect could occur due to the “reloading” or switching of the piston. ViscoTec dosing systems on the contrary, allows for more flexibility should the customer change the component geometry for example.
- No contamination of the components with dosing material: Clean bead ends through prevention of thread pulling and re-compression
Find more information on Loctite’s 1-component silicone on Loctite’s website.
ViscoTec‘s 1-component dispensers are explained in detail here.