1. Liquid Silicone Rubber Basics

2. 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

3. LSR vs. HCR vs Thermoplastics
Vacuum Feed
Injection
Mold

4. A B LIMS Molding Process Component A Component B Mold
Heated electrically or with fluid: °F
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 B
Component B
Methyl Vinyl Polymer
Hydride Crosslinker
Inhibitor
Silica Filler
Additives
Injection Molding Machine
Standard Injection Molding Machine
Special injection unit
Optimized non-return valve
LSR Mixing Unit
Pneumatic, hydraulic or servo
Material pressure bar
Third stream additive

5. 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

6. 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

7. 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
LD 16:1, 20:1
Spring loaded
check assembly

8. LSR Specific requirements – Injection barrel
Plasticizing barrel
Cooling sleeve
Material seal, brass back plate
Flange
LSR Plasticizing Assembly
Standard, M3 Bimetallic barrel
Cooling sleeve
Material seal with brass back plate
½” – ¾’ BSPP ORB feed throat interface
Barrel flange with M36 x 1.5 thread

9. LSR Specific Requirements - Screw
LSR Plasticizing Screw
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

10. LSR Specific Requirements - NRV
LSR Non-Return Valve
Valve body
Platen
Spring
Nut
Valve body
Shut off platen
Coil spring
Assembly nut
Advantages
No injection movement needed to shut off
LSR Plate NRV with spring

11. 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

12. 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

13. LSR Specific Requirements – 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

14. LSR Specific Requirements – Vacuum System with Monitoring
Dedicated vacuum pump, 25, 40 or 60m3/hr
Vacuum valve switchable in machine software
System monitoring
Vacuum release valve
Vacuum Sensor, analog or digital

15. 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 ½” radius nozzle for hot runner molds
Lower tooling cost
Faster tooling changes

16. 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

17. 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

18. 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

19. 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

20. 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