Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
2001-10-19
2004-11-16
Morgan, Eileen P. (Department: 3723)
Abrading
Abrading process
Utilizing fluent abradant
C451S039000, C451S040000
Reexamination Certificate
active
06817927
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to methods for removing adherent materials, for example, paint, flashes, photoresists, contaminants, and other materials from external surfaces. In particular, the method employs an improved media comprising core/shell particles.
BACKGROUND OF THE INVENTION
For various types of structures, it is often desirable to remove a coating that has been formed on an exterior surface area. In one case, the coating may be unwanted contamination. In another case the coating may be an intentionally applied material such as a decorative or protective layer. Numerous techniques exist for removing paint, sealants, lacquers, rust, scale, biogrowth and other adherent materials from virtually any type of surface. Surface cleaning or stripping methods range from mechanical abrasion to the use of strong chemicals and involve varying degrees of time, effort and expense. For any given type of coating, the character and function of the substrate material from which a coating is to be removed usually dictates the stripping method, at least in industrial settings.
In view of the environmental and health hazards involved in the use of solvents for cleaning surfaces, in particular, large exterior surfaces, it has become common practice to use an abrasive blasting technique wherein abrasive particles are propelled by a high pressure fluid against the solid surface in order to dislodge previously applied coatings, scale, dirt, grease or other contaminants. Hard, durable surfaces, such as heavy steel plating can be cleaned or stripped by a hard abrasive such as sand. Softer metals such as aluminum or more delicate surfaces such as polymer composite layers may require the use of a softer abrasive material during blasting such as plastic pellets or sodium bicarbonate.
Sand blasting of steel plate or other hard surface to remove adherent coatings and the like, while successful in removing the coatings, has several disadvantages. For one, the sand abrasive is very friable such that upon contact with the surface, a vast amount of silica dust is formed. There is a concern that the minute air-borne free-silica particles which are formed during blasting present a substantial health hazard, in particular, if ingested into the lungs. Secondly, very large amounts of sand are required for cleaning large structures such as bridges, stacks, etc. such that after blasting, this sand remains and must be removed from the blast cleaning area adding substantially to the time and expense of the blasting process.
Alternative abrasives for blast cleaning hard surfaces are known. For example, U.S. Pat. No. 3,775,180 is directed to a method for descaling steel in which the steel is descaled by spraying a mixture of a solid such as aluminum oxide or silicon carbide with water and a gas such as air under specified conditions onto the steel. In removing a coating or a scale on the surface of a metal, however, it is important that the anchor pattern (surface roughness) of the metal surface be uniform and not too extensive such that the surface and even the metal structure is damaged. A blast media composed only of hard aluminum oxide and silicon carbide can be detrimental to the metal structure.
Hard abrasives such as alumina, silicon carbide, or glass bead, or a soft abrasive such as a walnut shell flour has been blasted at a high speed onto molded products to remove flashes. U.S. Pat. No. 4,548,617 describes the problems associated with using these abrasives.
For certain surfaces such as metals softer than steel, a softer abrasive can be used with the blast stripping method. An example of such is disclosed in U.S. Pat. No. 4,878,320 to remove coatings from aluminum, fiberglass or carbon fiber laminate. As disclosed in the patent, an abrasive particle is used which has a Mohs hardness of about 3. Sodium bicarbonate is a preferred material.
Other patents which disclose cleaning metal surfaces with an abradant other than sand include U.S. Pat No. 2,624,988 which utilizes a mixture of Tripoli paste and a liquid vehicle to which mixture can be added sponge rubber fragments which carry the abradant to the metal surface and which provide a rubbing action to polish and buff the metal surface.
U.S. Pat. No. 2,710,286 discloses a method of removing fluorescent and other materials from viewing screens of cathode ray tubes in which sodium and potassium carbonate are used as the abrasive material. U.S. Pat. No. 4,588,444 discloses removing calcium from polymeric contact lenses by using as an abradant sodium chloride, sodium bicarbonate or a mixture of same. U.S. Pat. No. 4,731,125 discloses a method for removing adherent material from composite surfaces made of a reinforced matrix material using a granular media composed of particles which have a Mohs hardness of lower than 3.5. Preferably the abradant is polymeric particles.
Polymer particles are commercially available for use as non-abrasive stripping, cleaning, deburring, and deflashing media. These non-abrasive media are particularly useful when the substrate is susceptible to damage. Such substrates include aircraft and aerospace components, dye castings, computer housing panels, vehicle and boat bodies.
U.S. Pat. Nos. 5,505,749 and 5,509,971 to Kirshner et al. disclose the use of a major amount of a granular relatively soft abrasive having a Mohs hardness of less than 4 and a minor portion of a granular hard abrasive having a Mohs hardness of greater than 5. U.S. Pat. No. 5,234,470 to Lynn et al. discloses a granulated composite, in particular, a flexible open cell water-foamable material and an abrasive mineral such as garnet.
PROBLEM TO BE SOLVED BY THE INVENTION
It would be desirable to be able to clean an external surface more rapidly without damaging the underlying surface. It would also be desirable to be able to more finely control or tailor the abrasive properties of the media to balance its ability to remove a particular coating without attacking a particular surface material. It would be desirable for the media to be durable and non-friable and not produce dust during use. It would also be desirable for the media to flow through the propelling equipment without clogging nozzles or requiring special treatment to prevent static cling.
It would be desirable to be able to economically manufacture and customize such particles for a particular application.
It would be desirable to accomplish this without using chemicals that present environment or health problems. It is an object of the invention to remove surface materials without harming the underlying surface of the structure and which is more effective than other known non-abrasive media.
SUMMARY OF THE INVENTION
The above objects are achieved by providing an abrasive media that comprises a polymeric core surrounded by a layer of inorganic particles. The media can be propelled against or along an external surface by a gaseous or liquid carrier medium or a mixture of gas and liquid to remove the unwanted surface material. By the term “external surface”, with respect to the surface being cleaned, is meant a surface that, during use, is not enclosed but rather is freely open or exposed to the ambient atmosphere, as it will be exposed to the cleaning composition of the present invention. Thus, internal surfaces, such as the concave surface of a conduit or an enclosed tank, is excluded. Typically the abrasive media of the present invention is applied by shooting or blasting the media through air, specifically the air space between the external surface to be cleaned and the means for shooting or propelling the particles.
This invention can be used for removing adherent materials, for example, paint, flashes, burrs, photoresists, contaminants, biogrowth, and other materials from various surfaces. Contaminants to be removed from a surface may include any foreign substance attached to or carried by the surface such as scale, soil, grease, oil, soot, solvents and other objectionable deposits. In another type of situation, the surface material may be a previously applied material such as
Gruszczynski David W.
Puccini Christopher J.
Smith Dennis E.
Eastman Kodak Company
Konkol Chris P.
Morgan Eileen P.
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