Silicone rubber: The material of choice to meet new challenges.

Silicone rubbers are providing answers to new and more challenging application and specification requirements across industries. Around the world and in virtually every industry, the transition to silicones has been dramatic due to their high performance, wide temperature range, chemical resistance and environmental benefits.

New regulations and market trends are presenting new challenges for automotive, electrical and consumer manufacturers. This article will address the unique properties and performance characteristics that make silicone rubber the material of choice to meet the wide range of new application challenges presented by these market and regulation changes.

Unique combination of HCR/FSR for turboeharger hoses

In the automotive industry, closed engine and exhaust systems cause higher chemical contents in air and fluid hoses, requiring materials to perform under increased temperatures and harsher chemical environments. Additionally, automotive producers and their suppliers are especially price driven due to increasing global competition from low-cost component makers.

Advances in silicone technology are meeting those challenges, while also improving performance. One example is in turbocharged engines, which has spurred demand and performance improvements for the materials used in turbocharger components. In particular, flexible hose sections such as those used in the turbocharger and air-to-air heat exchangers--commonly known as a charge air cooler (CAC), or intercooler--are being challenged to perform in harsh environments of high temperatures and pressures, hot exhaust containing aggressive petrochemicals and other combustion by-products (figure 1).

[FIGURE 1 OMITTED]

While the developments and data presented are centered on the turbocharger hose, these findings can facilitate further understanding of the flexibility and performance characteristics of fluorosilicone for other oil, solvent and fuel resistant applications.

The typical construction for turbocharger hoses uses VMQ silicone with a fluoroelastomer liner (FVMQ fluorosilicone or FKM fluorocarbon). To contain the combination of pressure, vibration and high temperatures, single or multiple layers of a high temperature fabric (e.g., aramid) are part of the overall reinforced hose assembly.

Turbocharger hoses are among the highest-cost hoses under the hood due to the large number of layers required and the cost of the elastomer needed for proper fluid delivery. A plot of temperature performance against the cost (function of manufacturing process, number of hose layers and material selection) of different automotive hoses is shown in figure 2.

[FIGURE 2 OMITTED]

To maintain their performance at increasingly elevated temperatures, many hoses that previously used acrylic rubbers, such as AEM, have transitioned to silicone rubber. However, this has necessitated a fluoroelastomer liner to provide oil resistance.

In most cases, aramid fabrics are used in hose construction to provide the hose's shape and underlying strength. Silicone rubber serves to protect the fabric and gives the finished hose its flexibility and resistance to extreme temperatures. In the case of silicone rubber in turbocharger hose applications, a one-part high consistency rubber (HCR) is used. The rubber is normally calendered onto the fabric to prepare the material for hose construction. Due to continuous temperatures in excess of 170[degrees]C, it is generally necessary to employ dimethyl-vinyl silicone rubber (VMQ) in the middle and outer layers. When specifying the fluoroelastomer liner, fabricators and/or end users will have to choose either fluorosilicone rubber (FVMQ) or fluorocarbon (FKM).

[FIGURE 3 OMITTED]

The hose liner has multiple service requirements, including temperature resistance, oil resistance, fuel resistance, interlayer adhesion and processing characteristics (calender and/or co-extrusion).

Temperature resistance

The fluoroelastomer liner will experience similar temperatures to the HCR layers, so a similar level of heat resistance is required. Typical specifications call for good retention of physical properties after continuous exposure at a target temperature. A common baseline requirement is the successful demonstration of minimal change in durometer, tensile strength and elongation at break for seven days at 200[degrees]C. The typical range of property changes of FVMQ (FSR) materials are shown in figure 4.

[FIGURE 4 OMITTED]

With a loss in tensile strength of 15-20% and a loss in elongation ranging 5-10%, the data illustrate that many commercially available FSR materials already exhibit reasonable stability to this heat aging regime. Several experimental formulations demonstrate materials that have been formulated to produce minimal changes in tensile strength and elongation (typically approximately 5% property change in both cases).

Recognizing that the target hose may experience significant temperature excursions above 200[degrees]C, we also have generated a data set based on exposure to seven days at 225[degrees]C. Selected results are shown in figure 5.

[FIGURE 5 OMITTED]

The increased severity at a test temperature 25[degrees]C higher is immediately apparent. Commercial materials now show a wide range of property changes, with tensile strength loss anywhere between 40% and 80%. Again, however, we have several experimental candidates that restrict this loss to 25-30% while also showing minimal change in elongation at break. These data clearly suggest that these materials will retain excellent elastomeric properties even under extreme heat.

Many standard tests involve heat aging of the material and subsequent measurement of physical properties. Typically, these properties are determined after the material has equilibrated back to ambient temperature. In the real world, we might expect a part to fail while at its service temperature, not when it has cooled back down to room temperature conditions. Figure 6 represents data from a series of products tested at an independent rubber test facility at Rapra Technologies. Two FKM compounds and two FSR compounds were compared at ambient and elevated temperatures. The corresponding elongation test data demonstrate the superior retention of FSR compound to FKM.

[FIGURE 6 OMITTED]

Oil resistance

One key requirement in turbocharger hose liner applications is the ability to survive extended contact with hot engine oils. At a basic level, the liner must act as a barrier layer and prevent oil from seeping into the medium and outer layers of the hose. Beyond this primary requirement, further testing is usually based on a total immersion method at oil temperatures of 150[degrees]C to 200[degrees]C or higher. Modern engines increasingly use fully synthetic grade oils with additive packages, which yield excellent anti-corrosion properties and extended service intervals. These additives include materials such as zinc alkyl dithiophosphate, alkyl or aryl modified amines and alkyl phenols.

Most of our recent testing has focused on Total MA3, a common oil for this application, due to its reputation as a highly aggressive test oil and its widespread use in Europe as factory fill oil for diesel and gasoline engines.

Initial testing with Total MA3 at 175[degrees]C confirmed the aggressive nature of these test conditions. Both the oil type and the temperature impact material degradation during typical oil immersion tests at 150[degrees] C. Rates of rubber degradation increase dramatically as temperature is ramped from 150[degrees]C to 175[degrees] C.

Further investigation, however, has highlighted some very significant differences that can be related back to the FSR formulations and structures.

While our initial experiments gave tensile strength loss of as much as 80%, we now have many candidate formulations that have reduced the change in tensile strength to between 10% and 30%. Figure 7 shows some selected data arranged in order of percentage loss in tensile strength and elongation.

[FIGURE 7 OMITTED]

We have observed that the stronger FSR materials demonstrate higher susceptibility to degradation in oil. For example, an FSR such as LS5-2040, with initial tensile strength of 12 MPa, is quite often degraded to about 3 MPa alter the relevant exposure to MA3; i.e,. a loss of around 75% after seven days immersion at 175[degrees]C. Conversely, our most successful FSR grades are those with a starting tensile strength of 9-10 MPa. Test data indicate that these will typically retain the majority of their initial strength after the same oil exposure. The same tests report even higher property stability in FSR materials LS5-8740, LS-2380 and LS4-9038, depicted in figure 7.

Fuel resistance

Resistance to gasoline fuel is required in hose liner applications, although to a much lesser degree than oil. Specifications typically call for a Fuel C immersion test, through which a variety of fluorosilicone rubber formulations deliver satisfactory results.

Volume swell is perhaps the most relevant parameter for fuel resistance, with values of less than 25% accepted, and easily achieved, after seven days immersion at ambient temperature (usually specified as 23[degrees]C).

Interlayer adhesion

Along with satisfactory oil resistance, adhesion represents the other critical parameter for successful adoption of a fluoroelastomer hose liner. Integrity of the finished hose not only depends upon acceptable initial bond strength, but also upon the ability to survive the influences of temperature, oil and the effects of pulsation/vibration experienced during service.

Representative adhesion testing involves joining together uncured sheets of the appropriate HCR and FSR layers (each 3 mm thick). This composite is then press cured at 170[degrees]C under moderate pressure only and cut into strips (25 mm wide) for peel testing to quantify the bond strength between the two materials. Usually, a small piece of plastic film is used to hold an initial section apart, and hence allow the two ends to be clamped in the jaws of the tensometer.

Unmodified materials will frequently yield a peel strength of 1 N/mm or less. In some cases, this may be acceptable, but quite often this type of result translates into borderline adhesion in a finished hose. However, through a comprehensive screen of additives, we have been able to demonstrate up to a three-fold improvement over this baseline bond strength (figure 8).

[FIGURE 8 OMITTED]

Processing

Properties of a liner, such as hardness, green strength, etc., are suitable for calendering and/or co-extrusion techniques. In addition, features such as cure speed and the cure process (steam or hot air; pressure or open oven) are some of the variables that must be considered when optimizing a compound. Fluorosilicone rubber is available in a wide range of properties and is suitable for applications involving both calendering and extrusion. Durometer can range from as low as 20 up to 80. This allows considerable flexibility in matching a material to the required processing characteristics. Proper formulation can produce the appropriate level of green strength to minimize hose sag in an extrusion-based process.

One key advantage of the HCR: FSR combination is the ability to closely match the cure speed of both layers. This is an important factor with respect to interlayer adhesion, where fully developed adhesion is achieved during the co-curing process. In the event of mismatched cure speeds, adhesion must develop while one layer has at least a partial cure. This reduces the potential for intimate contact and interpenetration of the two materials. The ability to closely match the durometer of both HCR and FSR is again a contributing factor in the interpenetration of two material layers.

Liquid fluorosilicone--the solution for fluid resistance and productivity

As performance requirements increase, so do pressures for automotive component manufacturers to find more efficient production methods. Liquid silicone rubber (LSR) is designed to produce rubber parts more efficiently and economically than high consistency rubber (HCR). In general, LSR offers the fabricator faster cycle times, clean operations resulting from enclosed systems, and automated processing. Fluorosilicone rubber is a high-performance elastomer particularly suited to environments where fuel, oil or solvent is present. Advances have been made in silicone rubber technologies that allow the process efficiencies of LSR to be coupled with many of the fluid resistance capabilities of fluorosilicone rubber. In the case of liquid VMQ silicone, even with a price premium typically realized (vs. HCR types), there are many advantages to the rubber fabricator, particularly in high volume parts.

Fluorosilicone liquid rubber molding provides the ability to perform long production runs with minimal manual intervention. Nearly unattended, automatic operation is possible. Even with the difference in price between the high consistency fluorosilicone, and liquid fluorosilicone rubbers (FLSR), the prospect of a single operator maintaining an entire bank of liquid injection molding machines can justify a transition, particularly in regions of the world with high labor costs.

Industry scientists have been advancing the science of a lull range of liquid fluorosilicone and fluorosilicone dimethyl silicone copolymers in the laboratory to evaluate their mechanical and chemical resistance properties.

Technology development of FLSR

The benefits of a liquid silicone rubber are well recognized; the challenge was to develop liquid silicone rubber with exactly the right oil and solvent resistance to meet customer needs. There are two approaches to tailoring the oil resistance properties, including blends and copolymers.

* Blends of fluorosilicone and dimethyl silicone polymers exhibit a range of swelling characteristics between that of dimethyl and fluorosilicone.

* However, because of the difference in performance characteristics of the two polymers and their poor miscibility in one another, blends of dimethyl and fluorosilicone polymers exhibit lower properties than copolymer.

In table 1, copolymers and blends were compared in a standard formulation without individual optimization. Until high concentrations of fluorosilicone polymer are reached, the dimethyl phase remains continuous with isolated pockets of fluorosilicone rubber. Because of this effect, even at blends of 60% fluorosilicone, the dimethyl rubber remains continuous and the material exhibits typical swelling properties of the dimethyl phase, but with reduced mechanical strength properties due to the fluorosilicone rubber component.

The solution to this problem is to create a new polymer consisting of a copolymer of both dimethyl and trifluoropropylmethyl. This copolymer is produced from the polymerization of the respective components by controlling the ratio of the monomer feedstocks. One is able to tailor the level of dimethyl to the level of trifluoropropylmethyl, to dial-in exact swelling characteristics, while retaining the best properties possible. Because this mixing takes place on a molecular level, there is a high degree of interaction between the dimethyl and trifluoropropylmethyl. Excellent properties are retained to 80% substitution. This gives it broad range of possible formulations. The swelling characteristics for these liquid silicone rubbers can be tailored to the level needed for the fluid of choice. The comparison of the fluid resistance and various levels of fluorine substitution are shown in the graphs of figure 9. At equivalent fluorosilicone levels, copolymcrs exhibit reduced swell. As a result, swell characteristics can be balanced against the cost of increased fluorosilicone content to meet a cost/performance profile that exactly meets the need (table 2).

[FIGURE 9 OMITTED]

Automotive industry summary

Correct selection of the appropriate fluorosilicone base requires formulation expertise in the areas of heat stability additives, secondary fillers and adhesion promoter technology. These building blocks produce optimum results for physical property retention after relevant exposure to dry heat and hot oil. Laboratory and customer tests reveal the physical properties of FVMQ to be much less sensitive to testing at elevated temperatures when compared to FKM. Additionally, adhesion improvements have yielded VMQ-FVMQ bond strengths comfortably in excess of typical specifications.

FVMQ offers high temperature and hot oil resistance while maintaining total cost. We see tremendous potential for these optimized FVMQ materials to satisfy the increased performance and quantity demands of turbocharged system components.

Dow Corning, like much of the industry, is focusing on new advancements that FLSR technology is offering in process improvements. FLSR offers advantages to the rubber fabricator, particularly for applications in harsh conditions. Enhanced flexibility is available to the fabricator through FLSR products formulated to meet various solvent or oil resistance needs and through the addition of ingredient packages to enhance release or lubrication. Compressed fuel permeation rates of FLSR have been shown to be comparable to LoPerm VMQ and significantly better than uncompressed rates. The addition of mold release and ease-of-assembly additives allows the manufacturer to take full advantage of the higher-speed processing of FLSR. While an optimum solution that is able to reap the full benefits for both FSRs and LSRs has not been introduced, the industry is moving quickly to find better, more exact, solutions to meet performance and processability demands.

Electrical industry: HCR and LSR--the light choice for insulators

In comparison with traditional porcelain and glass insulators, composite insulators are becoming more popular in both long rod and hollow core applications. The use of composite insulators has accelerated in the past five years as the benefits of composites have become more widely recognized. These benefits include the lighter weight of the composite insulators, greater mechanical strength, less breakage when in transit or installation, and greater seismic resistance. Additionally, the unique surface characteristics of silicone rubber differentiate composite insulators made with this housing material from those made with organic rubber housings in difficult environments.

Greater mechanical strength

In substation applications, the explosion behavior of composite surge arrestors, breakers and insulators is becoming widely recognized due to the fact that they cause less damage to neighboring installations when compared to porcelain housed apparatus.

Lower maintenance costs

In areas of moderate to high contamination, there has been a strong trend towards the use of silicone housed composite insulators due to the increased performance in the suppression of leakage currents and the reduced maintenance of the line.

Areas affected by coastal contamination, industrial contamination and agricultural areas benefit from the unique surface ability of silicone-housed insulators to retain and recover their hydrophobicity. This ability to produce and retain a non-wetting surface interrupts the normal contamination-induced flashover mechanism, leading to improved system reliability and lower cost to the utility companies.

Lower total line costs

Silicone composite insulators can also help in the reduction of the total line cost due to their lower weight in new constructions. The lower weight may allow more environmentally sensitive line designs and the upgrading of existing lines to higher voltage without the need for extending the right-of-way access (ref. 1).

It has been shown previously that the use of silicone composites can reduce the installation costs of line apparatus (ref. 2). When installing a switch and fuse unit, the Los Angeles Department of Water and Power saw significant savings in the time needed by field labor for assembly and installation when compared with a porcelain unit (table 3).

Material types

Silicone rubber as a generic family of materials encompasses a wide range of materials and applications; consequently, it is important to understand the difference in performance of different types of materials under this generic heading. Within each family of silicone, many formulations exist, some of which have been specifically designed for high voltage applications. High consistency silicone rubbers have been used extensively for both insulators and cable accessories. They are processable by high pressure molding (compression or injection) or by extrusion techniques, and require high temperatures for the curing of the parts. Recent advances in cure technology have enabled fast cure times using a new rapid cure system. This enables better process utilization and total cost benefits Typically for high voltage applications these materials are highly filled with tracking resistant fillers and show a high hardness and relatively low physical properties.

For the production of insulators, several techniques are utilized. These include direct injection of the silicone rubber over the glass fiber rod, separate molding of the sheds (which are then fixed to the insulator in a second operation), or extrusion techniques to coat either rods or hollow core tubes.

Liquid silicone rubbers have to be divided into two distinct areas, RTV (room temperature vulcanizing) silicones and LSR or LIM (liquid injection molding) silicones. Recent advances in the combination of tracking resistance and viscosity have blurred the distinction between these two types of silicones. Typically these materials show good flowability due to their low viscosity and fast cure properties. They are suited for making complex shaped or large parts. Applications for liquid silicone rubbers include large hollow core bushings, distribution and transmission insulators, and cable accessories.

A comparison of the performance and processing of these types of material is shown in table 4.

Viscosity behavior electrical performance for LSRs

The viscosity of the LSR material can range from 20 Pa-s to over 500 Pa-s. From pourable liquids to paste-like materials. this viscosity influences the processes that can be used for the production of articles. At the higher range of viscosities, an injection molding process must be used, whereas in the medium range, low pressure casting can be utilized (figure 10).

[FIGURE 10 OMITTED]

Recent advances in the electrical performance of these materials have meant that the traditional compromise between processability and end-part performance is no longer valid. In the past, constraints on formulation meant that to achieve the high tracking resistance of 4.5 kV in IEC 60587 inclined plane testing, the viscosity o[ the LSR had to be tit the top of the spectrum for liquid systems. As the viscosity decreased, so did the tracking performance. The low viscosity materials used for casting processes could only achieve a tracking resistance of 3.5 kV, which also limited the applications of these materials and their competitiveness against other materials.

In addition, this latest generation of material demonstrates some excellent erosion resistance in both standard inclined plane tests and in arc tests (ASTM D 495). Previously, excellent arc resistance was only possible with high consistency rubber, due to its high filler content. Recent work has shown that low viscosity silicone rubbers can achieve erosion resistance similar to highly filled silicone rubbers.

As can be seen in figure 11, it is now possible to get a range of materials suitable for different processes and applications that all exhibit the ability to reach 4.5 kV in the IEC 60587 tracking test.

[FIGURE 11 OMITTED]

These advances allow the user to select from a range of materials that achieve the same electrical performance. They also offer fabricators several process options to meet equipment availability, total cost and quantity requirements.

Safety cable designs

Because nearly 35% of all fires are started from electrical equipment, proper protection and insulation of power supply plays a key role in fire prevention. Safety cable regulations fall under UL standards. These requirements cover 60-250[degrees]C (140-482[degrees]F) single- and multiple-conductor cables for use as fixed wiring within buildings (some are also marked for direct burial), principally for power-limited fire-alarm circuits.

The material properties of insulation material influencing fire safety performance of cables include the lowest oxygen index (LOI), combustion heat, smoke density and smoke toxicity. To provide adequate protection, safety cables must meet the fob lowing requirements:

* Resistance of the cable to ignition:

* low fire propagation of cable bunches:

* low smoke density and smoke toxicity:

* low corrosivity of smoke;

* isolation maintenance of cables; and

* function maintenance of power supply assemblies.

Fire resistance

Compared with PVDF or PVC, silicone rubber has only average flame retardancy. Nevertheless, due to its low combustion heat and the low smoke density and toxicity, silicone rubber offers a very advantageous combination of properties for insulation materials for safety cables.

Despite its extraordinary short-term heat stability above 400[degrees]C, even silicone rubber does not withstand the conditions that may occur in a fire. One has to assume temperatures up to more that 1,000[degrees]C in case of fire, which no known elastomer can withstand without damage. In order to maintain the supply of power under these circumstances, additional measures must be taken to insulate the different conductors from one another.

The performance of cables under fire conditions is tested according to specification DIN VDE 0882-1 resp. IEC 331. A piece of cable is heated to 750[degrees]C in an open flame.

The performance of power supply systems (including assembly and mounting system) is tested according to DIN 4102 part 12. Under these test conditions, temperatures can go up to 1,050[degrees]C.

To achieve fire resistance, tapes of mica or glass fiber were used in the first safety cables to provide additional insulation. By developing combinations of fillers that combine with the main combustion product of silicone rubber (quartz) to form a stable, insulating layer, it has been possible to significantly increase fire resistance and function maintenance, without compromising processability (figure 12).

[FIGURE 12 OMITTED]

With the latest generation safety cable, the combination of elastomeric and ceramifying properties has been further improved to reduce wall thickness without losing performance under special wire tests (table 6).

Future work is targeted to enhance ash stability and processing speed, requiring close cooperation between fabrication and material supplier.

Electrical industry summary

The typical silicone attributes of UV and weathering resistance, as well as hydrophobicity, make silicone rubber ideal for usage in electrical applications. Recent advances in liquid silicone rubber formulations have increased electrical performance in terms of tracking and erosion resistance. As a result, they simultaneously offer good erosion resistance and meet the tracking resistance requirements of 4.5kV according to IEC 60587.

By tailoring both the physical property performance and the processing characteristics, it is possible tot the materials supplier to provide a number of solutions to the fabricator that maximize manufacturing efficiency and total cost. This allows the fabricator to utilize multiple production techniques, which, in turn, allows greater flexibility in terms of initial equipment investments, ability to produce small run tailored products and other customized solutions to the utility companies.

Silicone rubber also is an ideal material for safety cable applications. It provides the right combination of properties, including low fire propagation, low smoke density and isolation maintenance, to maintain electrical functionality under fire and heat exposure. This combination of design and materials provides improved performance without impacting productivity or total costs.

Consumer industry

A growing range of consumer products is demanding higher speed manufacturing to reduce costs. In addition, a range of food and skin contact applications is raising material demands for consumer goods. In infant care applications, such as baby bottle nipples and pacifiers, clarity and strong adherence to food contact standards are essential. LSR is exactly the material of choice to meet customer needs in terms of processability, clarity and mechanical properties without post cure.

Processability

Newly developed LSRs allow smooth production runs and optimize equipment throughput (figure 13). The short cycle time allows for more parts to be completed in a day. The long pot life of this new LSR reduces material waste.

[FIGURE 13 OMITTED]

Clarity

Clarity provides functional transparency in applications where unobstructed views are required, such as in swimming goggles. Furthermore, clarity also plays a safety and sanitation role, such as with baby bottle nipples.

New formulations are proven to provide much more superior transparency than previously available formulations (figure 14).

[FIGURE 14 OMITTED]

Consumer summary

New consumer applications are being developed that provide silicone rubber with a competitive edge over other materials. This is particularly true for applications that require increased processability and high specialty-performance requirements.

Summary

Silicone rubber is the material of choice lot new challenges in a variety of new markets. Whether it is hose liners and seals in automotive applications, insulators and safety cables in electrical systems or infant care and kitchenware consumer products, silicone rubber offers the properties required to overcome various application barriers. This article has demonstrated the variety of needs silicone rubber can fulfill through HCR, LSR or FSR application.

Future discoveries and investigations, such as the exploration of Mars, will further challenge this material to reach new levels of performance. Undoubtedly, silicone will play a key role in achieving these milestones.

This article is based on a paper presented at Silicone Elastomers 2006, a Rapra Technology conference. (www.rapra.net/ conferences)

References

(1.) M. Zimmerman, "Innovative compact line design at Energie Ouest Suisse," INMR, March-April 1999.

(2.) C. Heller and R. Rowe, "Switch assembly saves money," Transmission and Distribution World, May 1997. Other sources cited by the authors can be viewed by clicking here: (RW+)

by Steven Waier and Hans Peter Wolf, Dow Corning (www.dowcorning.com/content/rubber/)

Table 1--properties of lab examples of FLSR
prepared from fluoro/dimethyl copolymers or
polymer blends
                                                               Polymer
                                  Copolymer data               blends

Mol % trifluoropropyl *       0     40     60     80   100    40     60
Durometer (A)                40     38     37     36    40    33     35
Tensile (MPa)               8.0    6.4    6.5    6.0   4.0   5.5    4.9
Elongation (%)              460    347    387    338   290   519    379
Compression set (%)          13     NA     15     31    NA    NA     NA
Tear B (kN-M)              34.4   30.5   25.5   19.0   9.8  20.5   23.0
% resilience (Bashore)       54     38     32     22    21    33     23
Extrusion rate (gm/min.)    248     59     31     27    10    58     34

* e.g., 40 mol % trifluoropropyl = 40 mol % trifluoropropyl
methyl siloxane and 60 mol % dimethyl siloxane

Table 2--mechanical properties
of 40 mol and 100 mol% F-LSR

40% F-LSR properties

                                FL-45-9001
Durometer                             45.6
Tensile (psi)                          800
Elongation                             357
Tear B                                 108
C. Set 22h./1 77[degrees]C            19.1
Bashore %                               45

                                FL-65-9001
Durometer                             68.3
Tensile (psi)                          728
Elongation                             146
Tear B                                  71
C. Set 22h./1 77[degrees]C            14.8
Bashore %                               53

100% F-LSR properties

                                FL-30-9201
Durometer                               31
Tensile (psi)                        1,200
Elongation                             300

Table 3--comparison of field assembly times for
a fuse installation in silicone or porcelain

                           Switch unit            Fuse unit

                       Porcelain   Silicone   Porcelain   Silicone

Unit Cost                 $3,028     $3,444      $2,971     $2,000
Weight                    245 kg      59 kg      238 kg      59 kg
Typ. shipping cost           $98       $103         $98       $103
Field assembly labor    40 hours    0 hours    12 hours    0 hours
Field labor              5 hours    5 hours     5 hours    5 hours
Total labor             45 hours    5 hours    17 hours    5 hours

Table 4--comparison of material types
for usage in electrical applications

                                                            Materials
                                          RTV                     LSR

General                         In electrical         Two part liquid
Description              application-two part        systems with low
                          liquid systems with     to medium viscosity
                          ultra low viscosity    and heat cure system
                        and room (or slightly
                        elevated) temperature
                                  cure system

                        Processing parameters

As supplied                     2 part system           2 part system
Mix ratio                          Usually 10              1:1 system
                                  (or 9) to 1
Viscosity                          10-30 mPas             50-400 mPas
State                         Pourable liquid         Pourable liquid
                                                             to paste
Cure system                          Platinum                Platinum

Cure temp                       Room temp. to        90-170[degrees]C
                                 90[degrees]C
Cure time                     60 min.-24 hrs.          2 min.-10 min.
Processing                     Casting or low     Low-medium pressure
                           pressure injection       injection systems

                                   Product properties--physical

Hardness (durometer A)                     30                   44-55
Specific gravity                     1.1-1.13               1.09-1.14
Tensile (Mpa)                             7.5                       6
Elongation (%)                            500                 280-450
Tear (N/mm)                                30                      30

                                     Product properties--electrical

Volume resistivity                    6x10^14               1.8x10^15
Dielectric constant                       2.8                     2.7
Dissipation factor                      0.001                   0.001
Tracking resistance                     1A3.5                   1A4.5
Dielectric strength                        24                      27
Erosion resistance                       Poor                  Medium
Typical product                   HV 1540/20P             HV 1551/55P

                                                                  HTV

General                               Solid high consistency rubber--
Description                                  usually fully compounded
                                            complete with cure system
                                               (peroxide or platinum)

                                                Processing parameters

As supplied                     1 part system
Mix ratio                         1 component

Viscosity                      > 100,000 mPas
State                             Solid putty

Cure system              Peroxide or platinum

                                     Peroxide                Platinum

Cure temp                    150-200[degrees]C      120-160[degrees]C

Cure time                      3 min.-15 min.          2 min.-10 min.
Processing                       High pressure injection. Compression
                                        molding or extrusion systems.

                                      Product properties--physical

Hardness (durometer A)                  50-80                   50-80
Specific gravity                    1.53-1.63               1.53-1.63
Tensile (Mpa)                         2.5-4.5                   3.5-5
Elongation (%)                        150-300                 150-300
Tear (N/mm)                             13-17                   15-20

                                     Product properties--electrical

Volume resistivity                      10^14                   10^14
Dielectric constant                       3.6                     3.6
Dissipation factor                      0.017                   0.017
Tracking resistance                     1A4.5                   1A4.5
Dielectric strength                        17                      17
Erosion resistance                  Excellent               Excellent
Typical product                    HV 1660/65              HV 1760/65

Table 5--the following standards regulate
performance code requirements in Europe

                     International        Europa        UK          D
                               IEC    CENELEC/EN        BS    DIN/VDE

Flame retardancy           60332-1  EN 50265-2-1    4066-1   0482-267
of a cable
Burning behavior    60332-3 cat. C  EN 50266-2-4    4066-3   0482-266
  of cable bunches
Smoke density            61034-1+2      EN 50268     7622-1  0482-268
Smoke corrosivity          60754-2      EN 50267     6425-2  0482-267
Insulation          60331-11-21-23      EN 50200  6387(CWZ)  0482-814
  maintenance (FE)
Function                        --            --         --  DIN4102-
  maintenance of                                                   12
  cable assemblies

Table 6--effect of wall thickness reduction

Generation 3

Copper 1.32 mm - ceramifying material 0.4 mm (sp. gr. 1.63),
Insulation 0.73 mm (sp.gr. 1.34)
Material consumption 3.47 g, Isol 11.23 g = total 14.7 g/m cable

Generation 4

Copper (calc.) 1.32 mm, Insulation 0.76 mm (sp.gr. 1.34)
Material consumption 6.7 g/m cable