Abrading – Machine – Sandblast
Reexamination Certificate
1999-03-15
2001-11-13
Rose, Robert A. (Department: 3723)
Abrading
Machine
Sandblast
C451S075000
Reexamination Certificate
active
06315648
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an improved high-capacity apparatus for rapidly pressure treating a large surface area, such as the hull of a cargo ship or a large storage tank, using high-pressure spray. The apparatus conforms to the surface to be treated and provides the treating power of multiple rotating or oscillating nozzles, or rotating brushes. Conformity is important in that optimal treatment requires spray nozzles to be spaced a predetermined distance from the surface being treated. Further, conformity allows for an improved seal around the treatment apparatus for collecting and recycling fluids, volatile emissions or abrasives used and for capturing any material removed from the surface during treatment. Multiple rotating nozzle units increase the area of coverage per pass of the apparatus, thus reducing the amount of time required to treat a large surface. The invention further relates to means for positioning the apparatus against a non-horizontal surface and moving the apparatus along the surface for continuous surface preparation.
2. Discussion of the Related Art
Cargo ships travel long distances through salt water. Over time the outer surface of the ship hull becomes covered with marine growth, which increases drag and reduces the operating efficiency of the ship. The corrosive action of salt water causes the hull to corrode, which can lead to metal fatigue and hull damage. It is thus necessary to periodically clean, prepare (e.g., etch), and repaint the hull of the ship. This requires lifting the hull from the water in a dry dock facility.
Dry dock work is both equipment and labor intensive. Hull surface cleaning and preparation prior to painting must be accomplished to a high level of quality, and must pass inspection by the ship's master. If a hull fails to pass inspection, it must be re-treated. The expense of re-treatment can cause the contractor to loose any profit he may have made on the contract.
Obviously, while the ship is in dry dock it is out of commission and not operating for profit. The longer the ship is in dry dock, the greater the economic cost to the ship owner. There is thus a need to clean and prepare a hull as quickly as possible. Equipment available today is not capable of rapidly treating large surface areas, particularly surfaces that are curved and/or non-horizontal.
Additional significant problems with hull preparation relate to concerns over pollution by material removed from the ship hull during the pressure treating. This material may be entrained in liquids or abrasives used in pressure treating the hull, or may be airborne particulate or volatile chemical matter. Environmental laws mandate strict measures for collecting this waste and then disposing of the collected waste. Many shipyards today are not capable of meeting these requirements.
Further yet, noise evolved by equipment used in high-pressure treatment can represent a risk to the health of the operator and other dock workers.
Other examples of structures that have large surface areas that need cleaning include buildings, elevated water tanks and storage tanks. Specifically, storage tanks of the type used for storing crude oil, chemicals and other large quantities of liquid or solid material. Storage tank cleaning is very much like cleaning the hull of a cargo ship. The owner of the storage tank must follow similar regulations with regard to the containment of the hazardous waste byproducts created during the cleaning process, i.e. paint, rust, sludge etc.
Presently, surface-treating jobs can take several days to several weeks. Most surface blasting machines (sand blasting, ball or shot peening, etc.) and abrasive cleaners in use today are designed to remove all coatings and rust down to bare metal. In most cases, such excessive cleaning is not necessary. The preparation of a ship hull for painting merely requires that surface materials are removed down to a good layer of paint or epoxy to which the new layer of primer or paint can bond. There is thus a need for a method for preparing a surface which is faster and which does not remove excessive amounts of material.
The pollution problem created when cleaning cargo ship hulls and storage tanks is so widespread that many governments (foreign, federal and state) regulations are requiring total containment of the structure during the cleaning process, e.g., by providing a framework around the structure and then draping canvas or shrink-wrapping plastic over the structure. This may take days or weeks to rig. Once the ship hull or storage tank is cover cleaning is done under the containment material. Even where the structure has been covered, there is no guaranteed against air-borne particulate and gaseous leakage and liquid runoff during the cleaning operation. Due to the large surface area, canvas or plastic are easily damaged or removed by the wind. Once the containment covering is blown off by the wind, it may takes several days to re-contain the ship or storage tank.
Yet another hazard associated with attempting to contain evolved hazardous materials stems from the accumulation and concentration of hazardous or flammable materials inside the containment zone. When cleaning or painting ship hulls or storage tanks using conventional apparatus, air-borne fine particulate material and evolved gasses accumulate within the containment material, usually in the upper areas. Most of these evolved materials are hazardous to- humans and/or highly flammable, and any type of igniter (e.g., arcs and sparks from electrical machinery, dropped molten metal from welding operations, etc.) coming in contact with the upper layer of the containment material can cause an explosion or fire. Further, in some cases other services must be performed by dockyard workers at the same time that the ship hull is being cleaned, that is, these personnel must work under the containment material. Personnel near the cleaning operation may wear protective garments and particulate filtration breathing gear. Workers inside the ship, in most cases, would not be wearing protective gear. Thus, as the concentration of hazardous or flammable materials increases, the risks to the safety of the personnel working inside the containment area increase. Finally, it has been found in practice that containment material does not prevent the waste materials from running off the ship and entering the ground or water around the shipyard.
Presently no apparatus is available which is capable of cleaning and preparing a large non-horizontal and non-planar surface areas in a short period of time, to the high standards required to pass the scrutiny of a marine inspection, without serious noise emissions, and without violating EPA standards. Even though violation of legally mandated containment standards can bring fines and jail time, violation continues to be the practice rather than the exception, since no equipment is presently available which can meet the environmental standards in a cost-effective manner.
Various specialized devices have been developed for surface treating metal surfaces. “Vactrax”, available from TMR Associates Inc., cleans surfaces to bare metal using 40,000 PSI water pressure at 6 GPM, has a cleaning width of 8 to 8.5 inches. The device uses 4 to 10 inches of mercury vacuum to suction adhere to the side of a ship, and can recover and capture waste. Such a device is not suitable for preparing ship hulls prior to repainting for four reasons. First, due to the very narrow cleaning width, it would take a very long period of time to surface treat a large hull. Second, the device is designed to completely remove paint from steel. Most ships merely require cleaning and preparation of surfaces, and do not require complete removal of paint. Third, as much as 225 horsepower may be required to maintain the vacuum required to suction adhere the device to a vertical surface. Such a machine is costly to operate and maintain. This is a waste of power. And fourth, any interruption in vacuum or any break in the seal betwe
Pendorf & Cutliff
Rose Robert A.
LandOfFree
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