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[February 2007]
Successful Development of a Gasket Substitute for Asbestos
Takeo Ebina (Senior Researcher) of Research Center for Compact Chemical Process of Japan's National Institute of Advanced Industrial Science & Technology, or AIST, and Japan Matex Co Ltd have combined a heat-resistant clay membrane and exfoliated graphite – a conventional material for gaskets – to develop a new gasket that is superior to existing non-asbestos products in terms of heat resistance, durability and chemical resistance in addition to offering the same ease in handling as asbestos products.This gasket offers a wide range of applications in facilities such as chemical plants (oil refineries, heat power plants etc), taking advantage of its ease in handling and thermostability. It has already obtained excellent results from the verification tests conducted in petrochemical plants.
This product is a result of the 'Emergency Project to Develop Key Technology for the Reduction of Asbestos' (Development of High-Temperature Non-asbestos Gasket and Packing) project of the New Energy & Industrial Technology Development Organization (NEDO).
Normally, non-asbestos products have limited heat resistance because they generally contain rubber. Gaskets made of exfoliated graphite have been used because they have a certain degree of heat resistance and excellent pressure tightness in addition to allowing for long storage and easy processing. However, graphite powder comes off the product surface because of poor binding between graphite powders, which then contaminate the interiors of the pipes.
In addition, clipping an exfoliated graphite gasket by a flange to replace it with a new one results in fixation between the graphite and the flange surface. This fixation is not easily undone, which makes piping maintenance a time-consuming job. To make up for this shortcoming, the surface of the graphite was coated with a resin. This product, however, can only be used at temperatures below 300°C because the resin has a low degree of heat resistance. At the same time, as one of the characteristics of graphite, the gasket thins down because as a result of oxygen degradation from oxygen in the atmosphere at temperatures above 400°C, making it no longer usable because of the decreased sealing ability.
AIST announced the successful development of Claist – a clay membrane of uniform thickness without a pinhole – in August 2004. Claist is a flexible gas barrier membrane material with high heat resistance that densely accumulates clay crystals about 1nm thick. Concurrently, Japan Matex, a producer and marketer of exfoliated graphite gaskets, proposed that an exfoliated graphite product be combined with Claist and started the basic research to assist regional medium-sized companies in 2005.
Now the team has developed the technology to form a protective, heat-resistant membrane on the surface of exfoliated graphite with Claist. After selecting several natural clay materials with excellent adhesion to exfoliated graphite, the team blended them and added a small amount of organic binder for homogeneous water dispersion to prepare an optimum coating paste. Also developed has been the production technology for composite gaskets with a uniform coated layer by optimising the detailed conditions of the dip coating method. Unlike asbestos, which has needle-shaped crystals, the clay selected for this research is harmless to humans because it has flat crystals.
Performance tests on the gasket obtained excellent results in every test regarding ease in handling, powder-off properties and fixation. The seal test proved that this gasket maintains excellent seal performance even after high-temperature processing at temperatures up to 420°C. This gasket can be used at temperatures down to –240°C as well. This gasket complies with JIS R3453:2001 "Joint Seat" standards in tensile, relaxation and bend tests. A verification test conducted in the high temperature piping division of actual petrochemical plants is currently under way. The results of a short-term evaluation are excellent and the efforts to obtain long-term evaluation results are in progress.
www.aist.go.jp
ENDS