LSR injection moldingn | Chevalier, Cléret, Eltec

LSR means “Liquid Silicon Rubber” :

LSR consists of 2 components A and B contained in drums (20+20 litres or 200+200 litres) with a honey consistency.

LSR means ‘Liquid Silicon Rubber’.

LSR consists of 2 components A and B contained in drums (20+20 litres or 200+200 litres) with a honey consistency.

These platinum-catalysed silicones are automatically dosed by high-precision pumping units, guaranteeing dosing in the following proportions: 50%+50% or 49%+49%+2% colourant or other.

LSR A + B + any colourant are mixed in a static mixer before being dosed through the press screw (screw with a special profile, seal at the end of the screw, nozzle with obturator, …), the whole circuit being cooled to around 20°C.

The LSR must be injected into cavities in which the vacuum has been previously established at a satisfactory and controlled value: this requires a vacuum pump, a vacuum switch, a special and precise sequence for closing the mold before, during and after vacuuming, and also a very specific mold design.

The A+B+colourant mixture is usually injected through a cold runner injection system (injection time generally <1 s for small technical parts) into the mold heated to 180-200°C in order to vulcanise (combined effect of pressure and temperature) the parts in a few seconds.

Over the last 30 years, LSRs have gradually taken an ever-increasing place in the market, to the detriment of “paste” silicones. A large number of grades exist for a variety of uses:

Standard
High tear
Flame retardant UL94V0, yellow card
Heat resistant
With oil exudation (1% … 6% oil) to reduce seal insertion forces in housings

Low coefficient of dynamic friction
Low DRC
Resistant to steam, oils, coolants, …
High damping
High transparency

Self-adhesive on a wide range of materials: thermoplastics (PA + PBT); metals, glass and ceramics
Electrical conductor (9 Ohm.cm – 60 Ohm.cm)
Food contact (FDA, BfR)
….

LSR interface seal direct injection

LSR grommet direct injection

LSR interface seal direct injection

LSR grommet
direct injection

Fully automatic direct injection molding with no waste of material makes it possible to obtain a high degree of quality and productivity using :

High-quality molds
Continuous monitoring of the various parameters (pressure, temperature, flow rates, …),
Implementation and monitoring by professional, skilled teams.

The many advantages of LSR

Temperature range: -55°C to +210°C,
Very low volatile substance content,
“Burr-free” molding due to low viscosity A+B = no cryogenic deburring required: no extra cost, no risk of breaking the part, no risk of polluting the part,
Facilitates fully automatic molding,
Very short curing time (much shorter than paste silicones).

Manufacturers’ batches are several ton or even hundred of ton, which means that molding processes are highly stable and the characteristics of the molded products are linear.
Suitable for complex geometries
Possibility of bi-injection LSR / TP
FDA, drinking water, pharmaceutical, medical, … certification guaranteed by major chemical groups
Various agents can be automatically added to the A+B + colorant mixture: anti-microbial, temperature reactive, flame retardant, etc.
Easy and infinite coloring