Silane metering with LEWA pumps and LEWA smart control

Metering silanes with LEWA systems has the following advantages:

• Closed and weatherproof systems for outdoor installation (frost and rain proof)
• Open system for indoor installation (stationary or mobile)
• Safe for installation in ex-zone
• System can be adjusted to supply voltage, system hierarchy as well as metering quantity and pressure
• System is adapted to meet requirements regarding flammability, toxicity, and corrosiveness of various silane types. (Already metered silanes include: trichlorosilane, tetrachlorosilane, vinyltrimethoxysilane, dimethyldichlorsilane)
• Metering of silane with inert gas blanketing (nitrogen) to avoid humidity of air and crystallization
• If required, the system can heat up or cool down the silane in the metering process
• Metering with diaphragm pump technology (hermetically tight and resistant to abrasion)
• Safety valve protects the system from overpressure and damage
• Pressure gauge for the surveillance of pipes on suction and pressure side
• Mass flow meter
• Integrated diagnostic function indicates deviations and disturbances
• High system availability; even wear of pump is recognized to enable timely maintenance
• Exact metering through continuous monitoring: LEWA smart control conducts plausibility tests between the signal of the mass flow meter (actual value) and guide signal (setpoint value). Thus, the silane flowrate is adjusted to the speed of the extruder or the plastic melt mass
• LEWA smart control makes it possible to choose between centralized (multiple extruders controlled by one operating terminal) or decentralized (multiple separate smart control units) operation

Process scheme silane metering

What is important when metering silane?

In order to meet the production requirements (reproducibility, consistency, product purity etc.) of plastic cables and plastic pipe compounds for the manufacture of cable and/or wire insulation, metering must be precise, easily adjustable, and unaffected by external influences.

The extremely precise metering is effected via a hopper into the extruder (almost pressureless in laboratory applications) or into the process zone of the extruder by an injection pipe which places silane in the melt polymer. The choice of silane type depends on polymers. Special type organosilanes open new possible applications because they are important components of paints and coatings and their adhesion to various grounds is guaranteed for years.

The speed of silane crosslinking in polyethylene of cables can be influenced by:

• Silane type
• Size of the component that has to be crosslinked
• Temperature
• Pressure
• Amount of existing water molecules
• Efficiency of grafting
• Amount of catalyst

Source: Wacker Chemie AG, EVONIK Industries