WO2012084293A1

WO2012084293A1 - Coated ceramic bursting disc

Info

Publication number: WO2012084293A1
Application number: PCT/EP2011/068156
Authority: WO
Inventors: Marcus Franz
Original assignee: Sgl Carbon Se
Priority date: 2010-12-22
Filing date: 2011-10-18
Publication date: 2012-06-28
Also published as: DE102010063997B3

Abstract

The invention relates to a process for producing a bursting disc, wherein at least one surface of a porous unimpregnated section of the bursting disc having a pressure surface and a surface arranged opposite to said pressure surface is coated with silicon carbide or silicon-infiltrated silicon carbide.

Description

Coated ceramic bursting protection

The invention relates to a method for producing a coated Keramikberstsicherung.

Bursting devices are used in apparatus engineering against overpressure or underpressure. This is intended to reliably prevent undetected pressure levels in apparatuses from being exceeded or exceeded by bursting the central rupture disk as a disposable membrane as a kind of "sacrificial material." The membrane is usually a thin metal foil consisting of steel, stainless steel or Graphite, other materials may be used to adapt the rupture disc to a particular application.

Bursting devices provide a quick response to a change in system pressure. Once the membrane has been destroyed, it can not be closed again.

These fuse components are subject to strict type testing. The components must therefore be manufactured with particular care and also retain their original properties during use.

In corrosive applications, especially oxidizing applications Berstsicherungen must be made particularly robust to meet the security requirements.

Anti-burst devices are made of resin-impregnated fine-grained graphite as standard. This resin impregnation, which makes the production-related porous graphite gas-tight, is generally resistant to acid corrosion.

Bursting protection made of carbon or graphite have good corrosion resistance. The production-related porous graphite bodies are impregnated for sealing with synthetic resins, such as phenol, formaldehyde or furan resins and the decomposition temperatures of the impregnating resins determine the maximum achievable operating temperature.

Another disadvantage of resin-impregnated rupture protection is that the strength decreases considerably with increasing temperature, with an increase in temperature of 0 to 150 ° C on average by about 20%. Temperatures above 20 ° C already lead to a drop in strength, which must be taken into account in graphite materials for the construction of pressure equipment.

The operator of equipped with rupture fuses made of impregnated graphite containers is thus forced to hold for each operating temperature special rupture fuses.

For high-temperature applications and highly corrosive applications, therefore, inadequate solutions of impregnated graphite are available which, moreover, can only be used up to a maximum of 200 ° C. Depending on the application medium, the maximum operating temperature can be greatly reduced. Metallic materials are inadequate for high temperature applications as metals lose their strength as the temperature increases.

Resin-impregnated graphite is not resistant to extremely strong solvents or oxidizing media such as sulfite, hot oxygen (T <300 ° C) or other oxidizing media.

Graphite is a material that does not lose its strength when the temperature increases. In terms of strength losses, impregnation poses a particular problem at higher temperatures because the resin and / or graphite structure is oxidatively attacked. So oxidation-resistant coatings are required, which protect effectively against oxidative attack.

It is known to cover graphite disks for burst protection with a layer of pyrolytic carbon. Pyrocarbon is gas impermeable, temperature resistant dig and the strength is up to temperatures of about 1000 ° C practically independent of the temperature.

However, the deposition of pyrocarbon is not limited to the surface of the graphite disc, a portion of the carbon is deposited on the inside of the disc at the pore walls. The extent of such deposits influencing the strength of the graphite disk is determined primarily by the pore structure of the graphite and by the reaction conditions. In these cases, these factors have a greater range of variation, and the breaking strength of pyrocarbon-coated graphite disks also varies considerably, making it especially impossible to calculate the respective bursting pressure.

It is also known to cover existing Berstsicherungen from graphite discs with a glassy carbon layer. Glassy carbon layers are made by mixing liquid synthetic resins, e.g. Phenol, formaldehyde resin, applied to graphite discs and cured in situ and carbonized. The liquid resins also partially penetrate into the pore system of the graphite and increase its strength to an unpredictable extent.

Significant disadvantages of bursting of metals are often not satisfactory resistance to corrosive media and especially at an elevated temperature, the deformation of the foil-like bursting disc.

So it must be found a material that is resistant in an extreme atmosphere and maintains its strength even with a temperature increase.

It is an object of the invention to avoid the disadvantages of the known Berstsicherungen to reduce the dispersion of the effective bursting pressures and generate bursting with large, temperature-independent Berstgenauigkeit. This problem is solved according to the invention by a method according to claim 1, which even surprisingly makes it possible to reliably protect high-temperature applications by means of bursting protection. The surface reaction of a portion of the porous, non-impregnated rupture arrestor with silicon carbide or silicon-infiltrated silicon carbide creates a strong composite material that is resistant to higher temperatures.

Particularly preferably, the bursting is gas-impermeable.

In a preferred variant, silicon can be deposited on the surface of the rupture disk before the application of the layer of silicon carbide or silicon-infiltrated silicon carbide. Any silicon excess on the surface can be removed by using acids such as hydrogen chloride vapor at temperatures between 1200 and 1400 ° C. The HCl reacts with the silicon to form a silane, but does not react with the silicon carbide.

Preferably, the bursting protection consists of graphite. Particularly suitable are all graphite bodies obtainable by processes such as pultrusion, dry pressing or isostatic pressing.

Preferably, a rupture protection made of graphite or of carbon black and graphite is coated with slip, the slip containing finely divided silicon carbide, finely divided carbon and binder. The slip is preferably dried, the binder is destroyed by heating and the coating with the carbon bodies is siliconized by contact with liquid silicon.

The thickness and composition of the slurry layer can be used to vary the physical properties of the composites.

Further, it is preferred that a bursting of graphite or carbon black and graphite is provided with a CVD coating of silicon carbide. Preferably, the rupture protection is machined to the desired size or shape before or after coating.

Preferably, the silicon carbide is formed by reducing a silicon and carbon-containing gas mixture. The silicon is preferably formed by reduction of halogenated silanes.

Preferably, the coating is impermeable to chemical attack (e.g., most preferably oxidative agents) and erosion.

As the relief space of graphite bursting fuses is usually a natural environment, e.g. the atmosphere, it is not mandatory to coat both sides of the rupture disk with SiC.

The coating of at least one surface of a porous impregnation device which is not impregnated surprisingly achieves a high safety increase, since it is now possible to observe from this side whether the side facing the extremely corrosive medium corrodes. This can be done purely visually, by inspection, or by simple electronic devices. Such devices are e.g. Conductivity meters or thin wires, which emit a signal to the safety controller in the event of wire breakage, after which the system can be moved to a safe mode. Such signaling devices then need only be coated by coatings, e.g. made of PFA or vapor-deposited metals, to be protected against corrosion from the atmosphere. Surprising are so preferred

Use temperatures of 300 ° C-1200 ° C in, for example, extremely corrosive media to realize.

Regardless of whether signaling devices are to be used or protected, it is also preferable to use plastics such as cyanate esters, synthetic resins such as phenolic resins, or coatings of the family of polysilazanes to protect the graphite from air-atmosphere. In a preferred variant, a bursting protection against overpressure up to about 1 bar (g) must also be protected against vacuum. These are so-called vacuum rupture disks, which are provided with vacuum supports. These vacuum supports are preferably designed according to FIG. Here, two support bars made of SiC or coated with SiC graphite are glued to the rupture disk with SiC adhesive and then sintered on.

The almost identical contour can, however, particularly preferably be milled into the graphite immediately. Such a composite is much more stable and is ready for use after coating with silicon carbide.

Preferably, all coatings or infiltrations can also be carried out with the so-called LPI process. The so-called CVI process for coating and surface infiltration of the graphite with SiC can also be used with particular preference.

The invention further provides a rupture protection in which at least one surface of a porous unimpregnated portion of the rupture protection is coated with a pressure surface and a surface arranged opposite thereto with silicon carbide or silicon-infiltrated silicon carbide.

Particularly preferably, a vacuum support is milled into burst protection and / or a signal wire is inserted.

Claims

claims

1 . A method for producing a rupture protection, characterized in that at least one surface of a porous unimpregnated portion of the rupture protection with a pressure surface and one of these oppositely arranged surface with silicon carbide or silicon-infiltrated silicon carbide is coated.

2. The method according to claim 1, characterized in that the rupture is gas-impermeable.

3. The method according to one or more of the preceding claims, characterized in that a bursting protection of graphite or carbon black and graphite is coated with slurry.

4. The method according to one or more of the preceding claims, characterized in that the slurry contains finely divided silicon carbide, finely divided carbon and binder.

5. The method according to one or more of the preceding claims, characterized in that the slurry is dried, destroys the binder by heating and the coating with the carbon bodies is siliconized by contact with liquid silicon.

6. The method according to one or more of the preceding claims, characterized in that a bursting protection of graphite or carbon black and graphite is provided with a CVD coating of silicon carbide.

7. The method according to one or more of the preceding claims, characterized in that the bursting protection is processed before or after the coating by machine to the desired size or shape.

8. The method according to one or more of the preceding claims, characterized in that the silicon carbide is formed by reduction of a silicon and carbon-containing gas mixture.

9. The method according to one or more of the preceding claims, characterized in that the silicon is formed by reduction of halogenated silanes.

10. The method according to one or more of the preceding claims, characterized in that the coating is tight against oxidative agents.

1 1 .Verfahren according to one or more of the preceding claims, characterized in that the use temperature is 300 to 1200 ° C.

12. The method according to one or more of the preceding claims, characterized in that the coating takes place with an LPI and / or CVI method.

13. Bursting device, characterized in that at least one surface of a porous non-impregnated portion of the bursting protection is coated with a pressure surface and one of these oppositely disposed surface with silicon carbide or silicon-infiltrated silicon carbide.

14. Bursting device according to claim 13, characterized in that this

is gas impermeable.

15. Bursting device according to one or more of claims 13 and 14, characterized in that in the bursting a vacuum support is milled.

16. Bursting device according to one or more of claims 13 to 15, characterized in that in the rupture a signal wire is inserted.