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SILICONE RUBBERS

General Characteristics of silicone rubbers

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(VMQ Vinyl MethylSiloxane)

Renowned chemist Frederick Kipping was a pioneer in the study of organic compounds with carbon and silicon molecules and was responsible for the name 'silicone'. Silicone is a combination of quartz rock and carbon at high temperatures, obtaining a silicon-based rubber. From this basic substance other physical states such as gels, oils and solids are formed.

Silicone has a high transparency, is versatile and has an excellent behaviour in different physical and chemical working conditions. It can be transformed by injection, compression moulding, extrusion, autoclave, casting, etc.

Thermal Resistance: Silicone rubberus have an excellent behaviour and stability at temperatures from -55 ºC up to +225 ºC and our THT silicones can work up to +320 ºC in dry heat. There are silicones which can reach working temperatures of -90 ºC, such as the Phenyl-Vinyl-Methyl-Siloxanes (PVMQ). We have special vapour resistant (wet heat) silicones which are stable up to +150 ºC constant temperature.

Non toxicity standards:Inert material which can comply the following international standards for medical, pharmaceutical and foodstuff contact:: FDA CFR 177.2600 (US Food and DrugAdministration), BgVVBfR cap.15 (Bundesinstitut für Gesundheitlichen Verbraucherschutz Und Veterinärmedizin), USP Clase VI (US Pharmacopoeia), EC 1935/2004 Regulation, Journal officiel de la Republique Française brochure 1227.

Non porous Surface: Non adherent to most products and adhesives, silicone is water repellent and water- proof.

Dielectric properties: Silicone rubbers are one of the best electric insulators with the possibility of working from -40 ºC to +180 ºC. We can supply special conductive silicone formulations.

Mechanical properties: Compared to other organic elastomers, silicone does not stand out for its mechanical properties, but combined with its high temperature resistance it is unbeaten by other rubbers. We have specific formulations for high mechanical strength, abrasion resistance, high elasticity, high tear strength, etc.

Weather resistance: Offers excellent resistance to all weather conditions, ozone, pyralene and UV radiation.

Chemical resistance: Silicone rubbers have a good response when in contact with most chemical compounds, but are affected by fats, solvents and petrols.
With fluorosilicones we obtain superb anticorrosion results in most conditions.

Colours: Standard silicone is translucent, but can be pigmented with foodstuff contact approved colours to achieve any RAL upon request. We can also supply luminescent, fluorescent and metallic colours. We transform platinum- cured silicones for those items exposed to sun rays, that need a high transparency or to avoid yellowing due to ageing.

Vulcanisation: Silicone rubbers are vulcanised with different catalysts depending on the process used to vulcanise them. The most common catalysts are:
DBPH (2,5-Dimethyl-2,5-di (tert-butylperoxy) hexane), mostly used for moulding.
DCBP (2,4-dichlorobenzoyl peroxide)
and addition catalysts commonly known as platinum curing, being especially suited for medical, pharmaceutical applications and foodstuff contact used in extrusion.

Post-curing: Peroxide- or platinum-cured silicones must be post-cured at +200 ºC for a minimum of ten hours in air recirculating ovens to remove all volatile residues and make them suitable for foodstuff contact, as well as certifiable as medical grade.

Hardness and density: We offer from 25 Shore A to 90 Shore A hardness in compact silicone(our standard being 65 Shore) and 0.25 gr/cm3 to 0.8 gr/cm3 density in sponge silicones (our standard is 0.25 gr/cm3). 20 shore A compact silicones and 0.15 gr/cm3 are in development and approval stages.

Main products and shapes: Tubes, reinforced tubes, hoses, cords, profile, flat die-cut gaskets, moulded seals, inflatable seals, heat-vulcanised seals, encapsulated o-rings, rectangular profiles, square profiles, moulded parts, sheets, rolls, with textile or metal inserts, multicomponent parts, etc.

Main applications: Pharmaceutical, chemical, medical, aeronautics, space industries, laboratories, foodstuff, cosmetics, packaging, fluids, metal carpentry, construction, lighting, electronics, car industry, machinery manufacturing, etc.

Technical Data Sheet

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COMPACT SILICONE RUBBER STANDARD SERIES FOR EXTRUSION
Propierties Standard Units 135 160 175 180
General
Characteristics
Appearance Transparent
Density ISO R1183 (g/cm3) 1,11 1,14 1,18 1,21
Heat stability Good heat stability up to + 200°C
Mechanical
propierties
after cure
Catalyst type Peroxide
Catalyst content (parts) 1,1 1,25 1,25 1,25
Post cure 4 hours at 200 °C
Hardness Shore A ASTM D 2240 41 62 75 81
Tensile strength ISO R37 (MPa) 8,2 11 9,3 9
Elongation at break ISO R37 (%) 420 385 260 200
Secant modulus at 100% elongation ASTM D 412 (MPa) 1,1 2,2 3,4 5,3
Tear strength ASTM D 624A (kN/m) 17 21 21 19
Compresion set
(22h/177°C/25%)
ASTM D 395B (%) 39 35 37 49
Rebound Resilience ISO 4662 (%) 53 53 45 46
Linear shrinkage (%) 3,1 2,6
Dielectric
Propierties
After cure
Dielectric strength (1mm thickness) kV/mm 29
Dielectric strength (2mm thickness) kV/mm 21
Breakdown voltage Kv
Dielectric constant 2,5
Dissipation factor 3,4 x 10-3
Transversal resistivity Ohm·cm 2,6 x 1015


COMPACT SILICONE RUBBER HIGH TEAR STRENGTH SERIES FOR EXTRUSION (H.T.S)
Propierties Standard Units 345 360 370
General
Characteristics
Appearance Transparent
Density ISO R1183 (g/cm 3) 1,1 1,16 1,18
Heat stability Good heat stability up to + 200°C
Mechanical
propierties
after cure
Catalyst type Peroxide
Catalyst content (parts) 1 1,25 1
Post cure 4 hours at 200 °C
Hardness Shore A ASTM D 2240 45 62 70
Tensile strength ISO R37 (MPa) 7,2 9 9,3
Elongation at break ISO R37 (%) 460 430 440
Secant modulus at 100% elongation ASTM D 412 (MPa) 1,2 2,6 2,9
Tear strength ASTM D 624A (kN/m) 31 35 40
Compresion set
(22h/177°C/25%)
ASTM D 395B (%) 42 48 52
Rebound Resilience ISO 4662 (%) 48 47 36
Linear shrinkage (%) 3,2 3,4 3,3
Dielectric
Propierties
After cure
Dielectric strength kV/mm
Breakdown voltage kV
Dielectric constant
Dissipation factor
Transversal resistivity Ohm·cm


COMPACT SILICONE RUBBER INDUSTRIAL SERIES FOR EXTRUSION
Propierties Standard Units 940 950 960 970 980
General
Characteristics
Appearance Translucent Transparent Translucent
Density ISO R1183 (g/cm 3) 1,11 1,11 1,15 1,17 1,18
Heat stability 225 °C 200 °C 200 °C 225 °C 200 °C
Thermal Conductivity (W/ºC·m) 0,25
Mechanical
propierties
after cure
Catalyst type Peroxide
Catalyst content (parts) 1,25 1,25 1,25 1,25 1,25
Post cure 4 hours at 200 °C
Hardness Shore A ASTM D 2240 46 50 61 70 78
Tensile strength ISO R37 (MPa) 7,8 7,4 7,0 8,3 8
Elongation at break ISO R37 (%) 515 365 250 350 230
Secant modulus at 100% elongation ASTM D 412 (MPa) 1 1,5 2,25 2,3 3,8
Tear strength ASTM D 624A (kN/m) 13 13 11 18 16
Compresion set
(22h/177°C/25%)
ASTM D 395B (%) 27 34 25 42 34
Rebound Resilience ISO 4662 (%) 61 56 57 54 60
Linear shrinkage (%) 2,8 2,8 2 3
Dielectric
Propierties
After cure
Dielectric strength kV/mm 19 23 21 23
Breakdown voltage kV 45,4 45 44
Dielectric constant 2,8 2,8 2,8 2,9
Dissipation factor 0,007 3,5 x 10 -3 3,5 x 10 -3 3 x 10 -3
Transversal resistivity Ohm·cm 2 x 10 14 2,2 x 10 14 2,2 x 10 14 1,2 x 10 15
 

SPONGE SILICONE RUBBER STANDARD SERIES FOR EXTRUSION
Propierties Standard Units White Silicone
General
Characteristics
Appearance White
Density BS-EN-ISO 845 g/cm 3 0,250±0,040
Heat stability ºC -50ºC / +200ºC
Hardness Shore OO ASTM D2240 45±5
Hardness Shore A ASTM D2240 5±2
Mechanical
propierties
after cure
Compresion stress BS-EN-ISO 3386 parte 1.2 kPa 90±40
Tensile strength BS-EN-ISO 1798 (0,75min.) N.mm -2 1,2
Tear strength BS-EN-ISO1798 (100min.) % 200
Compresion set BS-EN-ISO 1856 (22h/70ºC) % 10
Brittle point ASTM D746 ºC -80
Oxygen limit index BS 2872 Parte 1 % 24
Thermal Conductivity VDE 0304 W.m -1.K -1 0,24
Radiation Resistance >10 5 Grays (10 5 Rads)
Dielectric
Propierties
After cure
Dielectric Coefficient VDE 0303 2,9
Dielectric strength VDE 0303 kV.mm -1 23
Dissipation factor at 50c/s VDE 0303 3x10 -4
Volume Resistivity VDE 0303 3x10 15 Ohm.cm

Chemical Resistance Chart

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ACIDS
Acid Resistance
Acetic acid 5% Good
Concentrated acetic acid Good
Hydrochloric acid 10% Good
Concentrated Hydrochloric acid Good
Chromic acid 10% Good
Chromic acid 50% Good
Citric acid Good
Formic acid below 87% Good
Nitric acid 10% Good
Concentrated nitric acid Mediocre
Oleic acid Good
Oxalic acid Good
Phosphoric acid 10% Good
Concentrated Phosphoric acid Quite good
Stearic acid Good
Sulphuric acid 10% Good
Concentrated Sulphuric acid Bad


ALKALIS
Alkali Resistance
Ammonia 10% Good
Concentrated Ammonia Good
Potash 10% Good
Potash 50% Good
Caustic Soda 10% Good
Caustic Soda 50% Good


SALINE SOLUTIONS
Saline Solution Resistance
Ammonium acetate Good
Ammonium carbonate Good
Barium chloride Good
Calcium carbonate Good
Calcium chloride Good
Calcium Hypochlorite Good
Iron sulphate Good
Potassium chloride Good
Sodium disulphate Good
Sodium disulphite Good
Sodium carbonate 2% Good
Sodium chloride below 23% Good
Sodium cianide Good
Sodium trisulphate Good


SOLVENTS
Solvent Resistencia
Butyl acetate Quite good
Acetone Quite good
Amyl Alcohol Good
Butyl Alcohol Quite good
Isoprolylic Alcohol Mediocre
Methyl Alcohol Good
Diacetone Alcohol Mediocre
Essence Mediocre
Turpentine Mediocre
Ether Mediocre
Carbon tetrachloride Mediocre
White Spirit Mediocre


OTHER CHEMICAL AGENTS
Agent Resistance
Liquid ammonia Good
Aniline Good
Phthalic anhydride Good
Sulphur anhydride Mediocre
Bromium Quite good
Chlorine Good
Chlorine water Good
Phtalic dibutyl Good
Dichlorobenzene Good
Diphenyl chloride Good
Water at room temperature Good
Boiling water Good
Water vapour Good
Hydrogen peroxide 80-85% Good
Ethylene glycol Good
Ethylene oxide Good
Freon 12 Mediocre
Freon 114 Mediocre
Glicerine Good
Methyl chloride Mediocre
Nitrocellulose Good
Paraffin Mediocre
Pentachlorophenol 10% (in alcohol) Good
Phenol 85% Good
Phosphate trichloride Mediocre
Silicon Tetrachloride Mediocre
Tricresyl phosphate Good

Tolerances

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During silicone rubber extrusion processes, the tolerances needed are higher than during moulding as when silicone is extruded and goes through the die it expands and during vulcanisation and post-curing it contracts and deforms.

The deformation at the exit of the extruder can be controlled via different supports, which in turn will depend of the degree of control, size and cross-section required. The characteristics of the profile will determine the tolerances applicable to each dimension. With certain synthetic rubbers it is not possible to achieve E1 class.

During longitudinal cutting, precision and tolerance will be dependent on the technology used in the process.

During moulding, all parts are manufactured with an excess of rubber to fill the shape completely and the excess material flashes. This flash makes the vertical dimensions (thickness) vary. To apply the standard correctly, we have to take into consideration the fixed dimensions which are: horizontal (H) and thickness (V), vertical. For vertical tolerances you need to use the highest dimension of the part.

There are 3 types if internationally accepted tolerances: “E” for extrusion, “L” for longitudinal cut and “M” for moulding:

  • Class E1, L1 and M1 = Maximum Quality
  • Class E2, L2 and M2 = Good Quality
  • Class E3, L3 and M3 = Not Critical
  • Class M4 = Medium Quality

EXTRUSION TOLERANCES FOR CROSS-SECTION OF UNREINFORCED SILICONE RUBBER PROFILES
( ISO 3302-1:1996(E) E CLASS )
from
(mm)
to
(mm)
Clase E1
(+ / - mm)
Clase E2
(+ / - mm)
Clase E3
(+ / - mm)
Nominal
Dimension
0 1,5 0,15 0,25 0,40
1,5 2,5 0,20 0,35 0,50
2,5 4,0 0,25 0,40 0,70
4,0 6,3 0,35 0,50 0,80
6,3 10 0,40 0,70 1,00
10 16 0,50 0,80 1,30
16 25 0,70 1,00 1,60
25 40 0,80 1,30 2,00
40 63 1,00 1,60 2,50
63 100 1,30 2,00 3,20

LONGITUDINAL TOLERANCES FOR CUTTING UNREINFORCED, EXTRUDED SILICONE RUBBER PROFILES
(ISO 3302-1:1996(E) L CLASS)
from
(mm)
to
(mm)
Clase L1
(+ / - mm)
Clase L2
(+ / - mm)
Clase L3
(+ / - mm)
Nominal
Length
0 40 0,70 1,00 1,60
40 63 0,80 1,30 2,00
63 100 1,00 1,60 2,50
100 160 1,30 2,00 3,20
160 250 1,60 2,50 4,00
250 400 2,00 3,20 5,00
400 630 2,50 4,00 6,30
630 1000 3,20 5,00 10,00
1000 1600 4,00 6,30 12,50
1600 2500 5,00 10,00 16,00
2500 4000 6,30 12,50 20,00
4000 --- 0,16% 0,32% 0,50%


SILICONE RUBBER MOULDING TOLERANCES
( ISO 3302-1:1996(E) M CLASS)
from
(mm)
to
(mm)
Clase M1
V (+ / - mm) H
Clase M2
V (+ / - mm) H
ClaseM3
V (+ / - mm) H
Clase M4
F(+/- mm)H
Nominal
Dimension
0 4 0,08 0,10 0,10 0,15 --- --- ---
4 6,3 0,1 0,12 0,15 0,20 0,25 0,40 0,50
6,3 10 0,10 0,15 0,20 0,20 0,30 0,50 0,70
10 16 0,15 0,20 0,20 0,25 0,40 0,60 0,80
16 25 0,20 0,20 0,25 0,35 0,50 0,80 1,00
25 40 0,20 0,25 0,35 0,40 0,60 1,00 1,30
40 63 0,25 0,35 0,40 0,50 0,80 1,30 1,60
63 100 0,35 0,40 0,50 0,70 1,00 1,60 2,00
100 160 0,40 0,50 0,70 0,80 1,30 2,00 2,50
160 --- 0,3% 0,4% 0,5% 0,7% 0,8% 1,30% 1,50%


CALENDERED SPONGE SILICONE SHEETING TOLERANCES
from
(mm)
to
(mm)
Tolerance
(+ / - mm)
Nominal
Dimension
1,6 7,00 0,50
7,50 10,00 0,80
11,00 11,50 1,00
>11,50 17,00 1,50
>17,00 19,00 1,90
>19,00 20,00 2,00
>20,00 25,00 1,60

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