Asbestos Plastic Electrical Properties
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Electrical properties of molded plastic or formed plastic asbestos-based products: This article describes the electrical properties of asbestos-based molded or formed products.
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, the Vanguard rocked nose cone, automobile parts & housings, electronic equipment (radar scanner), asbestos-filled Teflon, rocket motor parts, plastic drop tanks for the Hawker Sea Hawk, and hundreds of other products.
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NEMA [Electrical] Properties of Asbestos-Reinforced Plastic Products
The National Electric Manufacturers' Association (NEMA) has standard specifications for lam- m ated thermosetting asbestos (Grade A and AA) sheets, tubes and rods used in the manufacture of electrical ap- paratus and supplies. The maximum NEMA properties are low in comparison to those of the more recently developed asbestos felts and sheet materials or higher asbestos content fabrics treated by improved methods.
Grade A sheets (asbestos paper base) are identified as being more resistant to flame and slightly more resistant to heat than other laminated grades because of high inorganic content. They are not recommended for primary insulation for electrical applications involving commercial power frequencies at voltages in excess of 250 V. Grade AA sheets (asbestos fabric base) are more resistant to heat and stronger and tougher than Grade A. It is not recommended for primary insulation for electrical applications at any voltage.
Electrical Properties of Asbestos-Reinforced Plastics & Molded Products
Asbestos filled phenolic and urea formaldehyde resins are used in different electrical applications, particularly where high heat resistance is desired. Asbestos filled polyester and diallylphthalate premix compounds are readily used in electrical applications.
Asbestos is used as a filler and/or reinforcement with the various resins in order to produce different electrical properties. See Figure 9.4 below.
Figure 9.4. High-speed radar scanner manufactured from high-pressure asbestos-phenolic plastic. Applications are ground control approach, airfield radar, sector surveillance for harbor control, marine navigation and coastal defense. - Courtesy The Bristol Aeroplane Co. Ltd.
[Click to enlarge any image]
The asbestos moldings offer advantages such as availability on a mass production scale of complicated shapes and sizes normally difficult and expensive to fabricate in other dielectric materials; moldings can very readily be made with metal inserts; moldings can be made with an exceptionally high degree of accuracy; and variations in the molding compound can be made with various grades and amount of asbestos filler.
Silicone-asbestos molding compounds have been prepared with such special fillers as titinates in order to produce electrical transmission properties for radar which permit no electrical change for temperatures of 500°F and higher.
The electrical properties can be made to vary by changing the proportions of asbestos, silicone and filler. With the proper proportions, the electrical thickness remains constant with change in temperature.
Data have been reported on high temperature properties of asbestos filled "Teflon." * In the electronic industry, "Teflon" in the pure state is recognized for its excellent dielectric properties. This fact coupled with low water absorption, heat resistance to 300°C and a low coefficient of friction makes "Teflon" an attractive material in high temperature or missile radome applications.
The aforementioned attributes of this insulating material are overshadowed by mechanical drawbacks which are amplified at increased temperatures. Most undesirable of these properties is Teflon's extremely high coefficient of linear expansion and low resistance to deformation under load. By combining Teflon with asbestos, it was found that thermal expansion and heat of distortion were greatly improved.
* Marshall, R. F. and Ritt, P. E., "High Temperature Properties of filled Teflon," The Institute of Radio Engineers, University of Pennsylvania, Phila., Pa. (June 4-5, 1957).
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Citations & References
In addition to any citations in the article above, a full list is available on request.
- [1] ASBESTOS HISTORY & PROPERTIES [Book online] D.V. Roasato, engineering consultant, Newton MA, Reinhold Publishing Co., NY, 1959, Library of Congress Catalog No. 59-12535. We are in process of re-publishing this interesting text. Excerpts & adaptations are found in InspectApedia.com articles on asbestos history, production & visual identification in and on buildings.
- [2] "Asbestos in Plastic Compositions", A.B. Cummins, Modern Plastics [un-dated, pre 1952]
- [3] "Asbestos in Your Home," Spokane County Air Pollution Control Authority, Spokane WA 509-477-4727 www.scapa.org provides a one-page image, a .pdf file drawing of a house warning of some possible sources of asbestos in the home. The sources are not ranked according to actual risk of releasing hazardous levels of airborne asbestos fibers and the list is useful but incomplete.
- [4] The US EPA provides a sample list of asbestos containing products epa.gov/earth1r6/6pd/asbestos/asbmatl.htm
- [5] "Characterization of asbestos exposure among automotive mechanics servicing and handling asbestos-containing materials", Gary Scott Dotson, University of South Florida, 1 June 2006, web search 3/9/2012 original source: scholarcommons.usf.edu/cgi/viewcontent.cgi?article=3505&context=etd [copy on file as /hazmat/Automotive_Asbestos_Exposure.pdf ].
- [6] Asbestos Identification and Testing References
- Asbestos Identification, Walter C. McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed the basis for current work by asbestos identification laboratories.
- Stanton, .F., et al., National Bureau of Standards Special Publication 506: 143-151
- Pott, F., Staub-Reinhalf Luft 38, 486-490 (1978) cited by McCrone
- [6] ASBESTOS IN YOUR HOME U.S. EPA, Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
- [7] Asbestos products and their history and use in various building materials such as asphalt and vinyl flooring includes discussion which draws on ASBESTOS, ITS INDUSTRIAL APPLICATIONS, ROSATO 1959, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print, text and images available at InspectAPedia.com).
- [8] "Handling Asbestos-Containing roofing material - an update", Carl Good, NRCA Associate Executive Director, Professional Roofing, February 1992, p. 38-43
- [9] EPA Guidance for Controlling Asbestos-Containing Materials in buildings, NIAST, National Institute on Abatement Sciences & Technology, [republishing EPA public documents] 1985 ed., Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
- EPA ASBESTOS MATERIALS BAN: CLARIFICATION 1999
- Basic Information about Asbestos, US EPA, web search 08/17/2010, original source: http://www.epa.gov/asbestos/pubs/help.html
- "Handling Asbestos-Containing roofing material - an update", Carl Good, NRCA Associate Executive Director, Professional Roofing, February 1992, p. 38-43
- EPA Guidance for Controlling Asbestos-Containing Materials in buildings, NIAST, National Institute on Abatement Sciences & Technology, [republishing EPA public documents] 1985 ed., Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
- EPA, ASBESTOS IN YOUR HOME [PDF] - U.S. EPA, Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
- Vermiculite:
Protect Your Family from Asbestos-Contaminated Vermiculite Insulation, U.S. EPA , web search 08/17/2010, original source: http://www.epa.gov/asbestos/pubs/verm.html
Web search 01/20/2011, original source: http://epa.gov/asbestos/pubs/verm_questions.html - Proteja su familia del aislante de vermiculita contaminado con asbesto, U.S. EPA HOJA INFORMATIVA - Proteja a su familia del aislante de vermiculita contaminado con asbestos, web search 08/17/2010, original source http://www.epa.gov/asbestos/pubs/verm-ques-sp.pdf
- [copy on file as /hazmat/Vermiculite_US_EPA.pdf/ Current Best Practices for Vermiculite Attic Insulation - May 2003, U.S. EPA
- [copy on file as] /hazmat/Vermiculite_Health_Canada.pdf] Vermiculite Insulation Containing Amphibole Asbestos - September 2009, Health Canada
- Managing Asbestos in Place, How to Develop and Maintain a Building Asbestos Operations and Maintenance (O&M) Program, U.S. EPA, web search 01/20/2011, original source: http://www.epa.gov/asbestos/pubs/management_in_place.html
- Asbestos Strategies, Lessons Learned about Management and Use of Asbestos: Report of Findings and Recommendations on the Use and Management of Asbestos, 16 May 2003, US EPA, web search 01/20/2011, original source: http://www.epa.gov/asbestos/pubs/asbstrategiesrptgetf.pdf
prepared by the: Global Environment & Technology Foundation, 7010 Little River Turnpike, Suite. 460, Annandale VA 20003 - Other US EPA Publications on asbestos: web search 01/20/2011, see http://www.epa.gov/asbestos/pubs/pubs.html
- In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
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