JPS5939303B2 - Manufacturing method of anti-corrosion asbestos joint sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a corrosion-resistant asbestos joint sheet that is attached to a flange joint of a corrosion-resistant piping system to prevent corrosion of the flange joint surface.

Conventional asbestos joint sheets use asbestos fiber as the main raw material.
Rubber materials, vulcanizing agents, and fillers are mixed and kneaded with this, and this is heated and rolled and laminated between rolls, but since the content of asbestos fibers is extremely large (more than 70% by weight), The composition is non-uniform, with asbestos lumps and rubber lumps coexisting locally, and asbestos fibers and rubber materials contain corrosive components such as chlorine and chlorine compounds.This asbestos joint sheet is made of stainless steel. When installed as a gasket on a flange joint, internal fluid may enter between the asbestos and rubber lumps mixed in the gasket, and corrosive components such as chlorine in the gasket may be extracted onto the flange joint surface. In addition, various conditions such as internal fluid temperature and pressure interact,
As a result, a local battery (
Concentration battery) has occurred, and pitting corrosion and groove corrosion have occurred on the flange surface. As a countermeasure to this problem, treatments have been taken to reduce the chlorine content in asbestos fibers, but this is not a sufficient method.

The present invention solves the above-mentioned defects by combining asbestos fiber with a rubber material, a vulcanizing agent, a filler, etc., a metal powder having a large ionization tendency of 0.5 to 30 q6 (by weight), and a metal powder of 0.1 to 10" (by weight).
The present invention provides an anticorrosion-proof asbestos joint sheet that prevents corrosion of flange joints by blending and kneading the following compounded chemicals having the ability to form a protective film.
Zinc powder, copper powder, iron powder, magnesium powder, etc. are used as the metal with a large ionization tendency (sacrificial metal powder), and nitrite, permanganate, etc. are used as the compounded agent (inhibitor) that has the ability to form a protective film. Acid salts, iodates, chromates, dichromates, polymer phosphates, quinones, amines, amides, thioureas, etc. are used.

The metal with a higher ionization tendency acts as an anode in the battery combination and is subject to accelerated corrosion, whereas the metal with a lower ionization tendency acts as a cathode and is electrically protected against corrosion.

In addition, the corrosion resistance of stainless steel is obtained through passivation.
This passivation forms a protective coating on the stainless steel surface.

Therefore, asbestos fibers are mixed with rubber materials, vulcanizing agents, fillers, etc.
This is mixed with a metal powder with a high ionization tendency and a compounded agent (inhibitor) that has the ability to form a protective film to produce an asbestos joint sheet, which is then cut to form a gasket. When used in a flange joint, the gasket contains metal powder that has a high ionization tendency, and the stainless steel of the joint has a small ionization tendency, so the metal powder contained in the gasket is used as an anode, and the stainless steel flange joint is used as an anode. Uses as a cathode to prevent corrosion of stainless steel flange joints.

In addition, the gasket contains a compounded drug (inhibitor) that has the ability to form a protective film, and this compounded drug forms a protective film on the stainless steel flange joint by adsorption, deposition, etc.
Stainless steel becomes difficult to dissolve and acts as a corrosion protector for stainless steel flange joints. The present invention achieves the purpose of corrosion protection of stainless steel flange joints by incorporating both a metal powder with a high ionization tendency and a compounding agent with the ability to form a protective film.

If the sacrificial metal powder is mixed in a weight ratio of 30 (!l) or more, it will interfere with the sealing function of the asbestos joint sheet, so if it is less than this, a comparable product BZ can be obtained.

A preferable value is 3 to 5#). The metal powder may have a density of 20 meshes or less, but is preferably 100 meshes or less.

If the amount of the compounded agent capable of forming a protective film is more than 10% by weight, it will be difficult to produce an asbestos joint sheet, so the amount should be less than this, preferably 2 to 3%.

Next, Example 1 is a combination of a metal powder with a high ionization tendency, a protective coating, and a compounded drug with film-forming ability.
- and Example 1 of the present invention in which both are blended.

Reference example 1 Asbestos fiber 65-80q6 (weight) Rubber material 11-14q1) (〃) Vulcanizing agent 0.
8~25#) (〃) Filler etc. 3.5~23.2q1) (〃
) 300 mesh of zinc powder 3% (〃) Mix and knead the above materials and heat this between rolls (100~
1400 kneading C) Rolling and laminating for 5 to 15 minutes to produce an asbestos joint sheet.

A pitting corrosion comparison test was conducted between this asbestos joint sheet and a conventional asbestos joint sheet manufactured without incorporating zinc powder.

The test method was to attach an asbestos joint sheet to a SUS3O4 flange (JISlOK-65A), apply an internal pressure of 0.1 kf/Cm with an aqueous solution containing halogen ions after 30 minutes, hold it for 168 hours, and then disassemble the flange. The judgment was made by observing the surface and gasket surface with a magnifying glass. When zinc powder was mixed with 6 (by weight) and 15 (I) (by weight), the results were similar to those with 3% (by weight) as described above, but when 0.5% (by weight) was mixed. Several points of pitting corrosion were observed on the flange surface, and several brownish spots were observed locally on the gasket surface where it had come into contact with pitting corrosion.

Reference Example: Changed the zinc powder π from Reference Example 1, added 0.1(f) of NaNO2,
0.2%, 1.51! ), 5(f) (weight) to produce an asbestos joint sheet, and the sheet and these N
When we conducted a pitting corrosion comparison test with a conventional asbestos joint sheet manufactured without adding aNO, we found that the pitting corrosion rate was 0.1.
%, pitting corrosion occurred at several points on the flange surface, and the gasket surface was locally brownish where it came into contact with the pitting corrosion area.
In the case of No. 1.5) and No. 5 (No. 16), there was no change in the flange surface or gasket surface.

Example 1 Instead of the zinc powder in Reference Example 1, 1.5q1 zinc powder
) (weight) and NaNO2l. 5(f) (weight), and zinc powder 5q1) (weight) and NaNO25.
A comparison test of pitting corrosion was conducted between an asbestos joint sheet produced by blending with #) (weight) and an asbestos joint sheet produced without these. There was no change in the flange surface or gasket surface.

Claims (1)

[Claims] 1 Rubber material, vulcanizing agent, filler, etc. to asbestos fiber, 0.5~
An anticorrosive asbestos joint sheet prepared by mixing and kneading 30% (by weight) of a metal powder with a high ionization tendency and 0.1 to 10% (by weight) of a compounded chemical having the ability to form a protective film.