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Properties of asbestos based or asbestos filled formed or plastic products: this article describes all major properties of asbestos-based plastic & formed or molded products except for electrical behaviours which are discussed separately at ASBESTOS PLASTIC ELECTRICAL PROPERTIES.
This articles series about the manufacture & use of asbestos-containing products includes detailed information on the production methods, asbestos content, and the identity and use of asbestos-containing materials.
This article series about asbestos plastics & molded materials describes the history, manufacturing process & uses of asbestos plastics and molded materials such as asbestos reinforced handles and hundreds of other products.. Page top photo: Rocket motor body asbestos-plastic exhaust cone and ring - Adapted from Rosato (1959) .
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Properties of asbestos reinforced or filled plastics will vary depending upon the various conditions of the asbestos and also of the resin or binders. Length of fiber is related to strength properties. In the commercial type of asbestosphenolic molding compound such as those listed in Military Specification MIL-M-14, the asbestos shorts and floats are principally used.
The strength properties are lower than those reported in Table 9.3 below, where longer fibers are given. In addition to length of fiber, it is important that contaminants or foreign matter generally associated with short fibers be considered as well as fiberization of longer fibers. Chrysotile asbestos is principally used. Its pertinent properties are as follows:
The percentage of asbestos used in plastic compounds is an important requirement. In all resin systems, there is a certain percentage required to give maximum mechanical strength. A different percentage may be used to produce such desirable properties as chemical resistance, thermal insulation, impact, erosion, and resistance.
These percentages will generally differ from one resin system to another. For example, with phenolic resin maximum strength is obtained with 25 per cent long fiber, but with silicone resin the percentage is approximately 45 per cent long fiber. With short fibers, there is a relatively small range in difference of properties; the percentage of fibers can range from 30 to 60 per cent.
High-Temperature Structural Properties of Asbestos-Based Plastics
Data and requirements for a basically structural type of asbestos plastics are given in Military Specification MIL-P-25770, entitled "Plastic Materials, Asbestos Base-Phenolic Resin, Low Pressure Laminates."
Table 9.4 lists requirements after room temperature testing. Table 9.5 lists requirements at high temperatures. Commercially available asbestos-phenolic plastics data are shown in Table 9.6. These data are for parallel layup with tests conducted in a longitudinal or high strength direction.
TABLE 9.4. LONGITUDINAL MECHANICAL PROPERTIES OF Low PRESSURE LAMINATED ASBESTOS BASE PHENOLIC RESIN PLASTIC (0.125 ± 0.010 INCH THICK) AT STANDARD CONDITIONS * - [Click to enlarge]
TABLE 9.5. LONGITUDINAL MECHANICAL PROPERTIES OF LOW-PRESSURE LAMINATED ASBESTOS BASE PHENOLIC RESIN PLASTIC (0.125 ± 0.010 INCH THICK) AT ELEVATED TEMPERATURES * [Click to Enlarge]
TABLE 9.6. PROPERTIES OF ASBESTOS-PHENOLIC RESIN LAMINATES* [Click to Enlarge]
The principal reason for developing asbestos-silicone products has been to produce high temperature strength, heat insulation, and good electrical properties which will operate for long periods of time. Table 9.7 shows the prop- erties obtained with using principally asbestos sheet with such resins as Dow Corning's DC-2106 and DC-R-7141.
TABLE 9.7. PROPERTIES OF ASBESTOS-SILICONE REINFORCED PLASTICS [Click to enlarge]
Chemical Properties of Asbestos Reinforced Plastics
With regard to the chemical or acid resistant properties of asbestos plastics, contributions have been made in solving chemical problems as well as operating problems in the textile fibers manufacturing plants by the use of asbestos-phenolic parts. Early spinning buckets for rayon spinning machines were made of molded hard rubber, aluminum and plastic lined aluminum.*
However, they were unsatisfactory and asbestos-phenolic parts were substituted. Polyester resin systems are used in order to provide room temperature cure systems without pressure. However, phenolic resin systems have also been developed to meet similar curing conditions. Improved chemical resistant properties have been obtained with the relatively newly developed epoxy laminating resins.
Asbestos products are of particular interest where strong alkaline conditions are encountered or for exposure to chemical salts in high concentration.
The type of chemical parts or applications include tubes or pipes (with fittings), valves, tanks and liquid containers (tank liners), fume ducting and systems, pumps, towers, agitators and such miscellaneous parts as packing, trays, flooring, buhings, spinning buckets and chemical splash guards. In addition to asbestos plastics being used, asbestos millboard is used as aprons or as guard plates on which fluids in glass containers can be heated.
Thermal Properties of Asbestos-Reinfoced Plastics, Laminates & Molding Compounds
The following thermal properties are based on laminates or molding compounds. The density of these materials ranges from 1.6 to 1.8.
Phenolic Asbestos Properties
Specific heat, room temperature to 500°F: C, = 0.308 Btu/lb/OF
Specific heat determinations were made by means of a dry-type adiabatic colorimeter. Specific heat for laminates exhibit straight-line temperature enthalpy curves.
Thermal conductivity determinations were made in a guarded hot-plate apparatus (ASTM Specification Cl 77-45). Thermal coefficient, room temperature to 600°F: 2to4 X 10 6 / 11 °F
Silicone Asbestos Properties
Specific heat, 100 to 200°C: Ct = 0.292 to 0.355 Cal/gm/°C
Thermal conductivity (100°C): 6.5 x 10-4 Cal/cm/cm°/sec/°C.
Thermal coefficient (room temperature to 310°C: 2 x 10 -5 /°C
Table 9.2 - general information concerning asbestos felts.
In molding compounds, short asbestos fibers such as "shorts and floats" can produce attractive surface finishes and satisfactory molding properties. Long asbestos fibers tend not to produce highly attractive surface finishes and have inferior flowing characteristics. To remedy these problems, shorter asbestos fibers are generally mixed with the long fibers.
Increasing filler content increases the viscosity of the resin systems. For example an unfilled polyester resin system with a viscosity of 2,500 centipoises at 75°F would increase to 60,000 centipoises with 20 per cent asbestos filler. Actually thick and stiff putties or pastes can be made with a high percentage of asbestos fillers in the various resin systems.
In many of the past applications, asbestos reinforced or filled plastics were not evaluated as basically structural materials. However, in the past decade there have been tremendous strides with regard to reporting and developing high strength and high modulus asbestos base plastics by industry. These types of plastics are gradually entering into such diversified fields as automotive parts, electronic parts, chemical equipment, aircraft, and missiles.
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Web search 01/20/2011, original source: http://epa.gov/asbestos/pubs/verm_questions.html
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