CS203954B2 - Method of producing anticorrosive coat on exhaust systems of internal combustion engines - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing exhaust systems of internal combustion engines, in particular exhaust silencers and exhaust pipes, with increased corrosion resistance, which are used in particular for vehicles powered by internal combustion engines under atmospheric and adverse road conditions.

At present, the individual parts of exhaust systems are made of sheet steel and structural carbon steel tubes with a ferritic or ferritic-copper structure, low-alloy steels and, in some sparse cases, high-alloy steel sheets. The outer surfaces of the individual parts of the exhaust systems, which are still joined to form a single exhaust system, are covered with a lacquer layer to protect the assembly against corrosion.

In some special cases, exhaust systems are also manufactured from aluminum sheets by means of an immersion process in a continuous manner. (Poliakov J. Je., Lieberm, an EN, Tichonov Jv. A .: On the Problem of Choosing the Appropriate Material for Mufflers for Motor Vehicle Exhaust Systems, Avtomobilnaya Promyslenost, 1977, No. 2, pp. 44-46; Tums V .: What the Exhaust Endures, Engine World, 1978 No. 10, p. 10).

The methods of manufacturing exhaust system components that are still in use have some disadvantages. For example, the protection of individual parts of the exhaust system by a coating of a layman or a layer of silicone plastic is susceptible to damage or destruction caused by impacts of gravel and thrown stones, ice or frozen snow thrown from the road surface during vehicle movement. The effect of these factors is increased by the state of stress in the coating caused by rapid changes in the temperature of the external surfaces of the individual components of the exhaust system, especially when driving in the autumn or summer season.

The aforementioned coatings also wear prematurely due to excessive heating of the individual parts of the exhaust system. This is particularly true of the exhaust pipe leading superheated exhaust gases directly from the exhaust ports in the engine head. The temperature of these gases is in the range of 600 to 750 ^Q C ·

The silicone lacquer coatings and layers used hitherto are only moderately resistant to elevated temperatures; can withstand temperatures of the order of 400 ° C to 450 ° C for a short period of time and consequently cannot provide sufficient protection for hot parts of the exhaust system.

A considerable disadvantage of the methods of protection of exhaust systems which:. is still in use, it is also the fact that the coating or the si203954 liquid layer of the exhaust system only protects the outer surfaces, while all the inner surfaces of the system are subject to corrosion which is. particularly intense on all internal combustion engines with indirect ignition of the fuel mixture.

Also . The known drafting process of continuously producing exhaust systems from aluminum sheets and pipes has serious disadvantages. The continuously aluminum-coated sheets are coated on both sides with a diffusing aluminum coating, but in the case of cutting individual parts of the exhaust system from such sheets, the protective coating is necessarily cut off at the edges along with the sheet. On the other hand, deep pressing causes considerable thinning of the coatings and, in many cases, discontinuity of the coating. Thin patches, micro-cracks, and gaps in the coating cause corrosion between the iron alloy base and the aluminum coating. The electrical potential of these corrosion sources can reach 1.22 volts. The application of continuously aluminum sheets is also the most unfavorable due to their low corrosion resistance due to the high silicon content of the aluminum alloy bath, which is 10%. This silicon content, which forms the Al-Fe-Si phase in the outer layer of the aluminum coating, greatly increases the electrochemical corrosion of the coating due to potential differences between the Al-Fe-Si crystallinity and the diuterine eutectic containing a significant amount of aluminum. structural components of the outer layer.

The above drawbacks are overcome by the method of manufacturing an anti-corrosion coating on internal combustion engine exhaust systems or on internal combustion engine exhaust system components according to the invention, which consists in that the exhaust system components or the ready assembled and filled exhaust immersed in closed openings for 60 to 240 ° C and at 700 to 760 ° C in an aluminum bath containing traces of up to 2% by weight of chromium and traces of up to 0.2% by weight of titanium individually; or in combination with each other and further containing traces of up to 1% by weight of iron.

Exhaust system components exposed to temperatures above 400 ° C during operation are immersed in an aluminum bath containing traces of up to 2% by weight, chromium and traces of up to 1%. .'meat, iron.

Exhaust system components exposed to temperatures below 400 ° C during operation are immersed in an aluminum bath containing traces of up to 0.12% by weight, titanium and traces of up to 1% by weight of iron.

The dipping aluminum technology used to aluminum parts of exhaust systems aims to significantly increase their corrosion resistance; this is particularly important if these parts operate at elevated temperatures, in an aggressive environment, and · accelerating the corrosion process, and in particular for all sodium chloride solutions and condensates. The alumination process also has to be resistant to those exhaust system components that are in contact with the exhaust gases in the exhaust zone and therefore have the highest temperature. These notes relate, in particular, to the exhaust pipes to direct the exhaust from the engine head.

For this reason, the aluminum process parameters of the exhaust system components should be selected to provide a two-layer diffuse aluminum coating on the surface of each component, while the outer layer thickness should be in the range of · 40 to 100 μΐη, ensuring its corrosion resistance as at normal temperature and at elevated temperatures due to the even formation of a protective layer of alumina on the surfaces to be coated.

In order to maintain a constant concentration or limited decrease in the aluminum content of the alumina components of the exhaust system, elevated temperature treatment and alloying alloys should be used, thereby reducing aluminum diffusion into the Fe-C aluminum base during system operation.

If the aluminum concentration in the alumina surface layer is kept fairly high, then the alumina layer on the surface of the aluminum coating will always be regenerated during operation of the system. The most preferred alloying component is chromium, which forms a secondary solution with the FeAb phase during the silting process taking place in the Al-Cr alloy bath containing up to 2% by weight of chromium.

On the contrary, in order to obtain significant corrosion resistance for those parts of the exhaust system which are less exposed to elevated temperatures and which, like the entire exhaust system, operate in an extremely aggressive environment such as saline mist fog of sodium chloride solution present on roads during the winter season, the alumination process should be carried out in a bath of pure aluminum or Al-Ti alloy containing up to 0.2% by weight. Ti.

Extreme The use of silicon as an aluminum bath additive is also harmful; the use of silicon in an amount of up to 10% by weight is common in known continuous aluminization processes.

The process for producing the exhaust system coating according to the invention is further described by way of examples.

Example 1

The components of the exhaust, then when their surfaces were appropriately prepared for aluminum, were suspended on conveyors and immersed in an aluminum alloy bath at a rate of 12 m per second. The components to be in contact with the exhaust gases at temperatures ranging from 400 to 66600, i.e. the exhaust pipes or exhaust pipes of the front silencer, were provided with an aluminum layer in the aluminum alloy bath containing up to 1.5% by weight, chromium and 1% by weight, iron, at 720 ° C for 140 s.

The components for contact with the exhaust gases at a temperature of less than 400 ° C, i.e. the components of the silencer body and the exhaust pipe, were aluminum-coated in an aluminum alloy bath containing 0.1 wt. titanium and 1% him. The iron was heated at 700 ° C and aluminum was pumped for 120 s. The surfacing was half a meter per minute. The individual components of the exhaust systems thus aluminized were then joined together to form a complete exhaust system by welding, welding under pressure by bending.

Example 2

The complete exhaust system after assembly was

Claims (3)

A method for producing an anticorrosive coating on internal combustion engine exhaust systems or internal combustion engine exhaust system components, characterized in that the exhaust system components or ready-assembled and filled, closed-hole exhaust systems are immersed for 60 to 240 s at a temperature of 700 to 760 ° C in an aluminum bath containing traces of up to 2% by weight of chromium and traces of up to 0.2% by weight of titanium, individually or in combination, and further comprising traces of up to 1% by weight of iron. ready for submersible aluminum. The inlet and outlet openings were blinded, additional loads were suspended to overcome hydrostatic pressure, all exterior surfaces were appropriately prepared for aluminum, and finally the entire exhaust system was hung on suitable booms. The thus prepared exhaust system was then immersed in a rate of 15 to 2 (0 m / min. In a bath containing an aluminum alloy to 0.2 wt% titanium, up to 1 wt.% _Chro: 1 to him and why. Masses of iron, at a temperature at 700 to 760 DEG C. The system was aluminum dipped in an aluminum alloy bath for 60 to 240 seconds, then lifted to the bath surface at a rate of 1 m / min. The excess liquid aluminum alloy was removed by centrifuging the aluminized exhaust - system over the aluminum bath. VYNALEZU 2. A process according to claim 1, wherein the components of the exhaust systems of internal combustion engines exposed to temperatures above 400 DEG C. are immersed in an aluminum bath containing traces of up to 2% by weight of chromium and traces of up to 1% by weight of iron. 3. The method of claim 1, wherein the components of the exhaust system of the internal combustion engine, exposed to temperatures below 400 DEG C., are immersed in an aluminum bath containing traces up to 0.2% by weight, titanium and traces up to 1% by weight. irons.