Possible alternatives to asbestos as a friction material

Our plain-English summary of Possible alternatives to asbestos as a friction material, by D. Hatch (The Annals of Occupational Hygiene, 1970).

The study

• Author: D. Hatch
• Journal: The Annals of Occupational Hygiene
• Published: 1970;13(1):25-9
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

This paper, presented at a March 1969 conference on exposure to asbestos during brake and clutch maintenance, discussed possible alternatives to asbestos in friction materials. The author, from the friction-material maker Ferodo, traced brake linings from oil-impregnated cotton to woven and then moulded asbestos. He argued that no substitute could replace asbestos in conventional drum brake linings without loss of performance and strength. He noted that disc brake pads, oil-immersed automatic transmission clutches and spider clutches allowed less asbestos or none. He stated that friction materials used chrysotile, that heat converts chrysotile to non-fibrous olivine minerals, and that about 1 per cent of asbestos remains in wear products, much of it ground to less than 5 µ. In tests on employees' cars and company trucks, brake drums were cleaned with a compressed-air jet in an unventilated garage, and instantaneous samples were taken from the dust cloud. Across seven samples, counts of fibres above 5 µ ranged from 2.1 to 8.2, against non-fibrous counts of 109 to over 2000, with a 10-minute average of 0.8. The author did not recommend compressed-air cleaning but concluded that wear products were probably no more dangerous than many other dusts. He listed glass fibre, steel wool, mineral wool, carbon fibres, and sintered metals and cermets as possible substitutes, each with drawbacks, and judged sintered metals and cermets probably the best eventual possibility.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This 1970 paper is the text of a talk given at a 1969 conference on asbestos exposure during brake and clutch maintenance. The author worked at Ferodo, a friction materials company. It was not a study of disease in people. The author argued that no fibre then available could replace asbestos in ordinary drum brake linings without loss of performance. Disc brake pads, oil-immersed automatic transmission clutches and some heavy-duty clutches could use less or no asbestos. The author stated that the chrysotile in friction materials breaks down with heat into non-fibrous minerals, and that about 1 per cent asbestos remains in wear products. The author also reported tests in which brake dust from cars and trucks was blown out with compressed air in a garage with no forced ventilation. In seven instant samples from the dust cloud, counts of fibres longer than 5 microns ranged from 2.1 to 8.2 (units not stated). The author concluded that brake wear dust was probably no more dangerous than many other dusts, while not recommending compressed-air cleaning.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Conference presentation (technical commentary by an author from a friction materials manufacturer), including air sampling during brake cleaning
• Who was studied: Brakes of employees' private cars and company fleet trucks cleaned in the company garage over recent weeks before the 1969 talk; the table lists seven tests plus a 10-minute average sample
• Exposure: Chrysotile (white asbestos) in brake and clutch friction materials; dust from brake drums and back plates blown out with a compressed air jet in a garage with no forced ventilation, sampled instantaneously by hand-pump from the centre of the dust cloud
• Main results:
  • In the instantaneous samples taken in the dust cloud during compressed-air brake cleaning, fibre counts above 5 microns ranged from 2.1 to 8.2. Fibres of 2 to 5 microns ranged from 11 to 306, and non-fibrous particles above 2 microns from 109 to 2000+. Units of the counts were not stated.
  • A 10-minute average sample gave 181 non-fibrous particles above 2 microns, 5.0 fibres of 2 to 5 microns, and 0.8 fibres above 5 microns (units not stated)
  • The author interpreted the counts as showing a very small percentage of asbestos among dust particles of similar size
  • The author stated that asbestos has only rarely been detected in wear products by X-ray diffraction, and that about 1 per cent asbestos remains in wear products, much of it ground down below fibre length
  • The author stated that chrysotile decomposes under heat at around 600°C into non-fibrous olivine-series minerals
  • The author stated that no substitute for asbestos in normal drum brake linings existed without loss of performance and strength. The author listed glass fibre, steel wool, mineral wool, carbon fibres, and sintered metals and cermets as possible replacements, each with drawbacks; sintered metals and cermets were judged probably the best eventual possibility.
• The authors' conclusion: The author concluded that, although raw asbestos must be tightly controlled, wear products from friction materials are probably no more dangerous to health than many other dusts. The author did not recommend blowing out brake drums with compressed air.
• Limitations the authors state:
  • No corresponding dust data were available for clutches
  • The author was unsure whether the proposed explanation (very high temperatures at contact points) for the scarcity of asbestos in wear products was correct

Topics

The National Library of Medicine indexes this study under subjects our site covers: Auto mechanics and brake work.

Medical terms in this study, explained in our Lexicon: Brake Lining, Chrysotile, Olivine.

Related studies

• Control of the use of asbestos-containing friction materials — M.L. Bentley (1970)
• History and evolution of warning labels for automotive friction products — L.M. Kopelovich, K.A. Thuett, et al. (2014)
• Environmental history of a factory producing friction material — J.W. Skidmore, B.L. Dufficy (1983)
• Malignant mesothelioma among employees of a Connecticut factory that manufactured friction materials using chrysotile asbestos — M.M. Finkelstein, C. Meisenkothen (2010)
• Discovery and application of the Yoshida effect: nano-sized acicular materials enable penetration of bacterial cells by sliding friction force — N. Yoshida (2007)
• Effects of Alkyl-Substituted Polybenzoxazines on Tribological Properties of Non-Asbestos Composite Friction Materials — A. Wongpayakyotin, C. Jubsilp, et al. (2021)

Browse more research in The Annals of Occupational Hygiene, or return to medical research.