Process for applying a coating resistant to temperature and to c

Details Process for applying a coating resistant to temperature and to c Process for applying a coating resistant to temperature and to c

1996-08-27

1999-08-24

Lusignan, Michael

Stock material or miscellaneous articles

All metal or with adjacent metals

Composite; i.e., plural, adjacent, spatially distinct metal...

148253, 148254, 427304, 427305, 427435, 428684, B32B 1500

Patent

active

059423390

DESCRIPTION:

BRIEF SUMMARY
The present invention concerns a coating applied to a sheet of steel or a pipe of common carbon steel.
When applied to common carbon steel, the referred coating provides it with special characteristics, allowing its use in the parts of vehicle exhaust systems, which by law regulations have to be fitted with catalytic converters.
Prior to PROCONVE (Program of Vehicle Emission Control) requirements, the primary pipe of an exhaust system could be made from common carbon steel. This material, when in use in the vehicle, underwent an oxidation process on its internal surfaces, due to the elevated temperatures (near the exhaust manifold, the temperature is around 800.degree. C., and far from it, it is approximately 600.degree. C.)
The result of iron corrosion, at elevated temperatures, is normally an adherent oxide, forming a film (inert to the exhaust gases) above the substrate (common carbon steel).
Due to the usage of the vehicle, the pipe undergoes thermocycles (warming and cooling), associated with the vibration of the motor, initially causes fissures to occur within the adherent film and later, the flaking of iron oxide from the substrate.
When the iron oxide detaches itself from the substrate, it leaves it susceptible to a new oxidation process by elevated temperatures, forming again the adherent film, as explained previously With the subsequent use of the vehicle, the film breaks once again and the process is repeated innumerable times, as follows: (a) corrosion of the substrate; (b) formation of the adherent film (inert); (c) fissuring and subsequent breaking of this film: (d) flaking of the oxide formed; and (e) substrate exposure and, in this way, the restarting of the corrosion process of the substrate.
The flaking of the oxide formed in the referred conditions does not affect the performance of the exhaust system, provided that the vehicle does not utilize a catalytic converter.
With the advent of the requirements of maximum emission levels for vehicles (PROCONVE), the use of a catalytic converter became necessary; and, in this way, the internal corrosion of the primary exhaust pipe, previously not objected to, now constitutes a limiting factor in the use of common steel piping, since the flaking of the iron oxide will block and interfere with the metals which exist in the absorbent bed of the catalytic converter, considerably diminishing its performance and no longer permitting it to abide by the requirements of PROCONVE.
This being the case, the use of catalytic converters requires the use of corrosion-resistant and high-temperature-resistant steel; and the most commonly used such steel is the stainless steel type SAE 51409.
This raw material to be made into pipes requires a specific chemical composition, such as: carbon 0.12% maximum, titanium (or niobium)=0.75% maximum and chromium=10 to 12%, it being the case that these elements are fundamental in order to acquire the properties necessary for the defined application (primary exhaust system pipe resistant to elevated temperatures and corrosion).
When carrying out welding operations which are required to produce the final configuration of the primary pipe, when stainless steel is used, the usage of special welded frames is required in specific cases, since during the melting process changes may occur in the microstructure of the metal base (stainless steel) that which significantly alter its chemical and mechanical properties.
One object of the invention is the possibility of the use of common carbon steel with a nickel coating which, when applied onto the internal areas of the pipe forms a common steel/coating system, resistant to elevated temperatures and corrosion produced by the exhaust gases.
A more specific object of this invention is the ease with which one can use common carbon steel and consequently have greater productivity due to the operational simplifications of the final configuration of the primary pipe, since it avoids the use of welded frames, and there are no significant alterations on the microstructure of the material.
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REFERENCES:
patent: 2774688 (1956-12-01), Girard
patent: 2876116 (1959-03-01), Jendrynski
patent: 3080643 (1963-03-01), Hanink
patent: 3887732 (1975-06-01), Parker
Patent Abstract, JPC-66, Dec. 5, 1979, vol. 3, No. 147, JP54 123539.
Patent Abstracts of Japan, vol. 9, No. 241 (C-306) (1964) Sep. 27, 1985, & JP,A, 60 100 685 (USUI Kokusai Sangyo K.K.) Jun. 4, 1985.
Patent Abstracts of Japan, vol. 11, No. 96 (C-412) (2543) Mar. 26, 1987, & JP,A, 61 246 374 (NEC Kansai Ltd) Nov. 1, 1986.

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