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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.
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.
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.
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.
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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 Asbestos, its Industrial Applications, 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.
 "Asbestos in Plastic Compositions", A.B. Cummins, Modern Plastics [un-dated, pre 1952]
 "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.
 The US EPA provides a sample list of asbestos containing products epa.gov/earth1r6/6pd/asbestos/asbmatl.htm
 "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_Exposuret.pdf ].
 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
 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
 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, 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).
 "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 Copy on file as - /hazmat/Asbestos_in_Your_Home_US_EPA.pdf - 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
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
Copy on file as - /hazmat/Asbestos_in_Your_Home_US_EPA.pdf - 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
[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
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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