Liquid Silicone Rubber Basics LSR Specific Options Dosing
Liquid Silicone Rubber Basics LSR Specific Options Dosing Equipment Control system Closed loop metering control Minimum - maximum material pressure limits Capacity Amount of material to be processed per hour 5 gallon / 55 gallon capabilities Molding controls Feed system sized correctly for injection unit size Static mixer, filter pack, material dosing valve
LSR vs. HCR vs Thermoplastics Vacuum Feed Injection Mold LIMS Molding Process Mold Heated electrically or with fluid: 300 - 430F Cold Runner: 70 F Vacuum
Liquid Silicone Rubber Viscous fluid, centipoise from 500,000 2,000,000 5 gal or 55 gal drum Mixing ratio 1:1 Component A Methyl Vinyl Polymer Platinum Catalyst Silica Filler Additives A
Injection Molding Machine Standard Injection Molding Machine Special injection unit Optimized non-return valve B LSR Mixing Unit Pneumatic, hydraulic or servo Material pressure 100 - 200 bar Third stream additive Component B Methyl Vinyl
Polymer Hydride Crosslinker Inhibitor Silica Filler Additives LSR Dosing Equipment Equipment Mounted on the Injection Molding Machine (IMM) Mixing block Equipped with non-return valves Static Mixer Water cooled, sized properly
Pressure reducing valve Stabilizes pump pressures Material isolation valve Isolate material pump pressures from the injection unit Filter assembly With pressure transducer LSR Dosing Equipment Static Mixers Static Mixers work by splitting/folding the A, B & third stream option(s) with the desired result being a
homogenous mix Cooled mixer is preferred to slow the vulcanization of the mixed silicone Static mix is the preferred method of mixing as dynamic tends to create heat Ratio of mixing elements will need to be considered for proper utilization; Too many = residence time of mixed material & pressure drop Too less = incorrect ratio of LSR LSR Specific Requirements Injection unit Water cooled static mixer
Dosing Valve Pressure Transducer mounted below filer element Water cooled abrasion resistant barrel Pneumatic shut-off nozzle Zero compression screw
Material seal with brass back plate BSPP ORB feed throat interface Barrel flange with M36 x 1.5 thread Cooling sleeve Material seal, brass back plate LSR Specific Requirements - Screw LSR Plasticizing Screw Zero compression, feeding only, minimal mixing
LD = 20/1, ideally not less than 16/1 Surface hardened 2 mm thickness, except for smaller diameters Screw specifications: S8 through hardened chromium steel LSR Screw: LD16 without compression Plasticizing screw LSR Specific Requirements - NRV LSR Non-Return Valve Valve body Shut off platen Coil spring
Assembly nut Advantages No injection movement needed to shut off LSR Plate NRV with spring Nut Spring Platen Valve body LSR Specific Requirements Injection Units Hydraulic drive Standard injection drive system
Proven repeatability & precision Profiled speed control for process control Improved performance with the addition of servo valve Operating range of 20 75% capacity for best resolution Lower Initial investment LSR Specific Requirements Injection Units Servo Electric drive Best possible resolution for shot to shot consistency Dynamic speed control Force transducer for actual injection pressure
display Due to Servo drive, injection unit works independent from clamping system Zero hydraulics, no heat up time or fluctuations resulting in parameter changes Larger operating range due to higher resolution measurement Higher initial investment LSR Specific Requirements Clamping Unit Clamping Unit Mold area for peripheral equipment, core pulls, automation, connections Tonnage Requirements for Silicone, part surface area, 2-3
tons per square inch. Clamp force is required to overcome expansion of LSR during vulcanization Thicker parts need higher clamp to overcome expansion Thinner parts have less expansion Always discuss mold construction with mold builder, preloaded inserts, springs and needed land size of cavities Hydraulic or Electric clamping unit Tie-bar vs. Tie-barrless design LSR Specific Requirements Vacuum System with Monitoring Vacuum system
Dedicated vacuum pump, 25, 40 or 60m3/hr Vacuum valve switchable in machine software System monitoring Vacuum release valve Vacuum Sensor, analog or digital LSR Specific Requirements LSR Tooling Hot Runner Technology Built for low volume Short production runs, mostly operator driven Higher material waste
Extended cycle times to ensure runner is fully cured Sprue bushing on mold, Typically radius nozzle for hot runner molds Lower tooling cost Faster tooling changes LSR Specific Requirements LSR Tooling Cold Runner Technology Open nozzle vs. valve gate design Direct Injection Reduced material waste Reduced cycle time Typically 15mm diving nozzle needed
for cold runner technology Higher tooling cost Increased preventative maintenance LSR Specific Requirements Clamping Unit Tonnage requirements Part Surface area of each cavity needs to be calculated for required machine Example: .520in^2 (x) one cavity = 1.5Tn LSR Specific Requirements Clamping Unit Tonnage requirements Part Surface area of each cavity needs to be calculated for required machine Example: .082in^2 (x) 64 cavity = 16Tn
LSR Specific Requirements Cooling water Water cooling circuits Cooling water manifold, (0-10L & 0-30L), to distribute cooling to plasticizing components & cold runner mold Bulkhead option for convenience, setting up mold Number of circuits required should be considered to ensure enough cooling for all auxiliary equipment Cooling water filter, important for cold runner molds
LSR Specific Requirements Mold heating Euromap 14 Standard Multi pin connector, all zones on one plug Execution in standard, 230V with 12 amps each zone is standard (other specifications are available) Male/Female connectors for heating current and T/C temperature reading Set-up errors reduced
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