Coating processes – Interior of hollow article coating
Patent
1994-11-15
1996-08-13
Bell, Janyce
Coating processes
Interior of hollow article coating
427239, 427304, 427305, 427328, 427345, 427437, 4274431, B05D 722
Patent
active
055454330
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and an apparatus for precipitation coating of internal surfaces in tanks and pipe systems.
Usually, coating of internal surfaces in tanks and pipe systems has the purpose of protecting the base material against corrosion or mechanical wear and tear. In some cases it is desirable to protect the content of tanks and pipes, such as foodstuffs, against undesirable effects from the base material.
A coating may be applied in a plurality of ways. As known, paint is applied by means of a brush, a roller or a sprayer. Metal coating is e.g. applied through thermical spraying, through electrolysis or through precipitation of metals from a metal solution. Also, various forms of applying metal vapour in vacuum are known.
On a base material such as steel, metal coatings of e.g. chrome and nickel alloys are preferred for corrosion protection and resistance to wear and tear. Where a particularly large resistance to wear and tear is required, coatings of various carbides are used.
When immerging an object into a metalliferous solution, metal can precipitate on the surface of the object. In order to achieve a plain and smooth precipitation, temperature, acidity and concentration must be controlled. Good preliminary work, such as cleaning and removal of oxide coating, is important in order to obtain good adherence to the base material. The treatment may involve immersion into up to tens of baths having different chemical composition. When the object is moved from one bath to the next, the surface thereof is often very reactive. One has to work such that corrosive attacks do not arrise when the object is out of the baths.
Chemical coating through precipitation is difficult to accomplish on very large objects, i.a. because it requires many and large vessels to immerse the object into. Repair treatment involving disassembling, transport and immersion of tanks of e.g. two hundred cubic meters, is nearly unthinkable with prior art technique.
An object of the invention is to provide a method and an apparatus for precipitation coating of internal surfaces in tanks and pipe systems without immersion into vessels. Also, it is an object that surfaces to be coated are not subjected to corrosive environment between the various steps of the process.
The objects are achieved in that the object to be coated internally is filled with a liquid, the chemical composition, acidity and temperature thereof being varied. This replace the various steps of the immersion process. The surface to be coated undergoes approximately the same stages as in immersion into several vessels containing different chemicals.
BRIEF DESCRIPTION OF THE DRAWING
The drawing illustrates an embodiment of the invention whereby an electroless metal coating is applied to the inside of a tank.
The invention is described with reference to the enclosed figure, and with a starting-point of a tank of steel to be coated internally with e.g. a nickel alloy of a type known.
One embodiment of such a nickel alloy is nickel-phosphorous.
In the figure of the drawing, 1 denotes a tank where a first pump 2 is adapted to circulate a liquid into the tank through a filter 4. A blowing pipe 5 is adapted to supply gas or vapour to the liquid 3 for stirring purposes. One or more heating elements 6 are adapted to heat the liquid 3, and one or more thermometers 7 record the temperature of the liquid 3. A pH-meter 8 records the acidity of the liquid 3. A second pump 9 is adapted to pump acid 10 into the tank 1. A third pump 11 is adapted to pump a base 12 into the tank 1. A sensor 13 measures the concentration of dissolved metal in the liquid 3, and a fourth pump 14 is adapted to pump a concentrated metal solution 15 into the tank 1. Surplus liquid and gas are drained from the tank 1 through a drain pipe 16.
The tank 1 is assumed to be cleaned prior to the treatment commences. The tank 1 is coated internally in that metal dissolved in the liquid 3, in a manner known per se, is precipitated on the internal surface of the tank 1.
First, the tank 1 is filled with
REFERENCES:
Patent Abstracts of Japan, vol. 12, No. 237, C-509, abstract of JP, A 63-26376. Feb. 3, 1988.
Bell Janyce
Marcus Stanley A.
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