US20080176487A1

US20080176487A1 - Portable cleaning and blasting system for multiple media types, including dry ice and grit

Info

Publication number: US20080176487A1
Application number: US11/941,924
Authority: US
Inventors: Jay T. Armstrong
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-01-19
Filing date: 2007-11-16
Publication date: 2008-07-24

Abstract

Blast-cleaning systems are disclosed, which enable a single system to handle different classes of particulate blasting media, such as grit, powder, and dry ice, and to deliver controllable mixtures of different media types during a blasting operation. This “multi-media” system includes a hopper having two chambers or other supply assemblies that are isolated from each other, for holding two different types of blasting media. Both chambers provide their particulates to a metering control device, which supplies a compressor. For example, by combining grit with dry ice, extremely efficient cleaning can be accomplished, with greatly reduced production of solid waste. Tests have shown that combinations of dry ice (at roughly 90%) with a grit or powder can provide far greater cleaning efficiency than either media type by itself.

Description

RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No. 11/625,260, filed on Jan. 19, 2007.

BACKGROUND OF THE INVENTION

This invention is in the field of mechanics and machinery, and relates to machines that use sand, dry ice pellets, or other particles that are pumped through a hose and nozzle, to clean structural surfaces.
The process commonly known as sand-blasting has been used for decades, to clean or otherwise prepare various types of structural surfaces. In this process, a supply of sand (or certain other types of particles, as described below) is mixed with a fast-moving stream of air being pumped through a hose. The sand becomes entrained in the air, and the air-sand mixture emerges at high speed from a nozzle at the end of the hose. The mixture is highly abrasive, and sand-blasting can be used to remove even strongly-adhering compounds (such as paint, etc.) from various types of structural surfaces.
The phrase “structural surfaces” as used herein needs to be explained, to clarify both what is intended to be covered, and what is intended to be excluded. This requires several different factors to be taken into account, and it is easier to understand these factors when someone realizes that typical and intended uses for the cleaning systems and processes described herein include to remove paint or similar coatings, rust or other corrosion, or grime that has accumulated over a span of multiple years, from one or more exterior or interior surfaces of a large and immobile structure, such as a building, bridge, pipeline, storage tank, etc. Other typical uses for such cleaning systems and processes include the cleaning of wooden, dry wall, or other surfaces of a building that has been damaged by a fire, or that have become coated by one or more colonies of mold, fungus, or other unwanted microbes.
In accord with that type of use, the cleaning systems and processes disclosed and claimed herein are designed for cleaning relatively large areas (defined herein as areas larger than a square yard or square meter, during a single typical operation.
In addition, the types of cleaning systems designed herein specifically exclude machines that use blast-cleaning as part of a manufacturing operation. For example, the types of cleaning systems used to clean semiconductor wafers and other electronic components or devices are not relevant herein, and are specifically excluded from any discussion or coverage herein. There are a number of reasons for this, including the following:
(1) The types of cleaning systems used for manufacturing operations typically operate in a stationary mode, and the pieces or components that are being cleaned will be passed through (or otherwise temporarily inserted into) a high-tech cleaning machine. By contrast, the vast majority of blast-cleaning machines that are designed for non-manufacturing use, such as for removing paint or rust from buildings or bridges, need to be portable, so that they can be moved to a series of different work sites at a series of different locations.
(2) The economic and operating requirements for fixed cleaning systems that are designed and used for high-tech manufacturing, versus systems designed to remove old paint or rust from buildings or similar structures, are totally different. The types of systems and methods that have been developed for sophisticated cleaning of electronics or other sensitive devices use very expensive machines that often require installation, debugging, and optimization for days or even weeks, by highly skilled engineers and technicians. By contrast, the types of blast-cleaning machines used to remove old paint or rust from buildings or other structures must be designed for rapid setup and operation, by semi-skilled laborers.
In addition, the phrase “structural surfaces” as used herein excludes living and/or biological surfaces (including teeth). In particular, because of the power levels involves, the volumes of grit or other particulates, and the frequent need for using dry ice as particulate material, the types of machines disclosed and claimed herein are not suited for medical, veterinary, or dental work. Certain types of highly specialized “entrained abrasive” cleaning systems have been developed for cleaning teeth in humans (such as described in U.S. Pat. No. 5,334,019, Goldsmith et al 1994). However, those types of units are very expensive high-precision medical devices, which are designed to handle only very small quantities of extremely small abrasive particulates which have very uniform sizes (the range of differences between particle diameters must be kept very low, and tightly controlled). Because of the major differences in operating scales, volumes that are used, differing requirements for portable versus nonportable operating equipment, and other factors, and because the per-pound or per-ton costs for particulate media must be kept as low as possible, when thousands of pounds of particulates will be used to blast-clean a large wall, bridge, or other structure, the types of high-precision medical systems that have been developed for dental cleaning and similar uses are irrelevant to the types of large industrial-type equipment that are used to blast-clean walls, bridges, and similar structures.
When used as a blast-cleaning media, sand suffers from various problems, including the creation of very small “free silicate” particles that become airborne and that can create severe lung problems among workers and others. Therefore, various other types of “blasting media” have been developed, and are available from various suppliers such as Kramer Industries (e.g., www.kramerindustriesonline.com/blasting-media.htm). As described in more detail below, these types of particulate media can be grouped into three major categories, which are grit, powders, and dry ice. All three types of blasting media are particulates rather than liquids. Accordingly, any references herein to blasting, blast-cleaning, blasting media, or similar terms, refer to operations that accelerate particulates (such as grit, powders, or dry ice pellets) to high speeds.
Ice particles made of water (often called “water ice” in the industry, to distinguish it from dry ice) are not favored or commonly used for blast-cleaning, for a number of reasons, including:
(1) When particles of water ice are used for blast cleaning, the particles immediately melt, when they impact against a surface at high speed. Therefore, whenever water ice is used, it creates a heavy and wet form of waste, containing water mixed with dust, specks, chips, flakes, and other particles of paint, rust, charred wood, or any other material being removed from a surface by blast-cleaning. That type of wet and heavy waste (which can be referred to as a mud, slurry, etc.) creates substantial and potentially severe problems of hazardous and potentially toxic waste that must somehow be washed away or otherwise disposed of.
(2) If a wet slurry accumulates on a floor or other surface where workers must move around and walk, the floor likely will become slippery and dangerous, especially since the workers will be handling and maneuvering hoses that are blowing materials out through pressurized high-speed nozzles.
(3) Water from melted ice poses a substantial danger of permeating into and damaging or degrading various types of surfaces that may need to be blast-cleaned (such as wood, as one example).
(4) Water also tends to evaporate slowly, especially in cool or cold weather, and it clings to wood and many other surfaces in ways that can impede a refinishing operation. For example, many types of paint and other coatings should not be applied to a surfaces that has become wet, unless the surface has dried out for at least a full day or two. Accordingly, the use of water ice can interfere with a repainting or similar operation that could be carried out immediately, if the blast cleaning operation uses only dry ice, or dry particulates.
Accordingly, even though a mixture of water ice particles and dry ice particles was disclosed in a 1987 patent (U.S. Pat. No. 4,655,847, Ichinoseki et al) for a highly specialized use (i.e., for cleaning surfaces or equipment in nuclear power plants). When used in that manner, the water ice particles converted into an airborne mist, which reportedly reduced potentially radioactive airborne particulates, and which also reportedly improved visibility, by suppressing the type of “vapor cloud” that is often created when very cold carbon dioxide gas (from sublimated dru ice pellets) causes the normal airborne humidity to condense into droplets suspended in midair. However, the Ichinoseki process was never been widely adopted or used, because of several reasons. First, the inclusion of water in a blast-cleaning mixture will create increased quantities of waste, compared to blast-cleaning methods that use dry particles only. Because of the extremely high costs and risks of handling radioactive wastes, anything that would increase volume and weight of such wastes must be avoided, if at all possible. Second, when water and carbon dioxide are mixed together, they form carbonic acid. Although it is only a relatively mild acid, it is nevertheless classified as corrosive, and if added to radioactive waste, it would require an additional set of requirements and safeguards.
The third major problem with any blast-cleaning system that uses particles of water ice is that the ice particles encounter a highly-compressed and fast-moving air stream, while still in a pressurized hose. This will create some quantity of melting and water, within the hose and nozzle system. If dry ice particles are also being carried by the same hose and nozzle system, the liquid water droplets can trigger a highly undesirable type of agglomeration and clumping of the dry ice particles, which can create or severely aggravate problems of clogging and loss of flow. Therefore, after people realized the drawbacks of the Ichinoseki approach, it was dropped. Indeed, because of the increased risks and problems of clogging, to the best of the Applicant's knowledge and belief, mixtures of water ice and dry ice are not used or recommended by any companies that provide equipment or supplies for blast cleaning. The mixing of water ice and dry ice, in a blast-cleaning operation, would violate a set of “best practice” procedures that are known to those who work with these types of cleaning equipment and methods.
Returning to the basic types of equipment and methods that are normally used in blast-cleaning, to aid in explaining the invention, and to explain and illustrate certain terms that are used within the blast-cleaning industry, FIGS. 1-3 illustrate items of known and conventional prior art. FIG. 1 is a cross-section cutaway view of a device that is usually called a hopper, or bin, which holds a supply of particulate media that will be fed into a pumping or compressor system. FIGS. 2 and 3 depict single-hose and dual-hose applicator gun systems. These types of devices and systems are sold by companies such as CryoKinetics (www.cryokinetics.com), the assignee and applicant herein.
A typical hopper system for use in cleaning the insides of homes or other buildings (or for similar projects) usually is designed to hold at least 25 pounds (and often 50 pounds or more) of particulate material, and it usually is mounted on a wheeled cart (such as a dolly, hand-truck, etc.) that one or two people can maneuver when the hopper is empty. Most blast-cleaning operations are done by two-man crews, partly because of safety reasons (carbon dioxide is a dangerous gas that can quickly asphyxiate and kill someone, if a respirator malfunctions), and partly because holding and moving around a hose with a high-speed nozzle at the end, for hours at a time, is a physically difficult and tiring operation, which can be performed best by alternating periods of hose work and support work.
Taking a portable hopper and other related equipment up or down a stairway often becomes necessary for indoor blast-cleaning operations, such as in a home or apartment that has suffered fire damage or a major mold infestation. In addition, the equipment usually needs to be small enough to be loaded into a van that can be closed and locked, to protect against rain, theft, and other hazards. These types of usage requirements establish practical upper size and weight limits for the types of portable equipment used for that type of blast-cleaning.
There is no substantial market or need for hoppers that hold less than about 25 pounds of blasting media. Smaller hoppers could be made if desired, but they would require more frequent reloading, which would disrupt and delay a cleaning operation. Accordingly, any references herein to hoppers or bins generally are intended to refer to the types of devices that can hold at least about 10 pounds of at least one type of blasting media (which distinguishes them from the types of miniaturized systems used for dental cleaning). For practical reasons, any such hoppers preferably should be designed to hold at least about 20 pounds of dry ice.
Very large systems have been developed for municipal or other government uses, such as cleaning bridges or similar structures. For example, very large hoppers often can hold several tons of particulate blasting media. These systems usually are mounted on flat-bed trailers designed to be pulled behind a truck or tractor, or on support frames designed to be lifted and carried by forklifts, cranes, or other heavy equipment.
FIG. 1 is a side (elevation) cutaway depiction of the main components of a hopper 100. When used properly, the term “hopper” refers to a complete device, assembly, or subassembly, while the term “bin” refers to either or both of the chambers or compartments that are provided by a hopper. However, those terms are not always used consistently, and some people refer to the complete device or assembly as a bin.
The “bin” that is created by the walls and floor of hopper 100 is divided by a slanted wall-type device 102, which is often called a diverter tray, into a first (loading) chamber 104 and a second (outlet) chamber 106. Diverter tray 102 does not descend all the way to floor 108 of the hopper 100; instead, a gap 110 is provided, which allows particulate media 112 to leave the first chamber 104 and travel through second chamber 106 toward outlet 120, which is coupled to an outlet 122 (which can be a pipe, hose, etc.).
Hopper floor 108 can have any desired shape; for example, it can be sloped or slanted, if desired, to promote particulate travel toward outlet 120, which usually is placed near one wall, near the center of that wall.
Above the level of floor 108, outlet 120 usually is surrounded by a collar 124, which typically is provided with vertical slots 126 that are sized to block the passage of any small pebbles that might be contained in sand or other grit media.
As mentioned above, a hopper of this type usually is mounted on a wheeled cart, to enable a worker to move it into or close to a building or other structure that needs to be cleaned. The mounting components that affix the hopper to the cart contain pieces made of rubber or other elastomeric material, often called vibration isolators. These allow the hopper to be vibrated, by means of a reciprocating piston 140 or similar device affixed to hopper floor 108 at an angle. The vibrator operates at a speed of roughly 30 or more cycles per second, creating a vibrating motion that helps the particulate media move out of first chamber 104 (via gap 110) and across hopper floor 108, until the media reaches outlet 120 and enters outlet hose 122, aided by gravity flow.
As mentioned above, hopper 100 is open and non-pressurized. Depending on the type of media being used, pressurized hoppers also are used, as illustrated by hopper 210 in FIG. 2, which has a closed top 214 and a valve-type inlet control 216. Pressurized hoppers can be loaded either continuously or intermittently, using loading systems known in the art.
Two different types of applicator systems are used in blast-cleaning operations, and an understanding of this invention requires a working knowledge of both types of systems. These two different systems are referred to as (1) single-hose systems; and, (2) dual-hose (or double-hose) systems. As explained below, single hose systems are more powerful and efficient, when they are working properly; however, they also are much more prone to clogging, in ways that can be difficult and even dangerous to unclog. The advantages of higher power, greater efficiency, and reduced working times, in single-hose systems, quickly become apparent to anyone who has worked with both types of systems; however, the higher frequency of clogging problems in single-hose systems, and the time-consuming and potentially dangerous chore of unclogging a single-hose system (under the prior art) also becomes apparent to anyone who has used single-hose systems on multiple occasions.
FIG. 2 illustrates a single-hose blasting system 200, which is prior art. In this system, hopper 210 supplies particulate media 212 through an outlet 220 into a metering supply device 230, which typically is a rotary valve having a rotor with chambers, analogous to a ferris wheel. This valve controls the supply of the particulates into a mixing compressor 240. As used herein, the term “metering supply device” refers to a device that is designed to convey particulate blast-cleaning materials into a compressor, blower, pump, blasting applicator, or other accelerating and/or pressurizing device, in a manner that provides control over flow rates (when particulates are involved, flow rates also can be referred to as transfer rates, or various other terms). If desired, a metering supply device can be separate from a compressor or similar device, allowing coupling of the two devices by means of a hose, pipe, or other conduit; alternately, a metering supply device can be part of a larger assembly that includes a compressor or similar device.
In a single-hose system, compressor 240 (which also can be called a mixer, mixing compressor, pump, or various other terms) receives air or some other gas supply via a first inlet, and particulates via a second inlet. A high-speed rotating impeller inside compressor 240 mixes the air and particulates, and ejects the mixture through an outlet, at high pressure. A flexible hose 250 delivers the mixture to an applicator 260 (which also can be referred to as a gun, wand, sprayer, nozzle, or similar terms), which in most cases will be held by a human operator. The operator moves nozzle 262 of applicator 260 in a smooth and even motion across a surface that is being cleaned, at an appropriate distance (usually a few inches). Depending on the type of particulates being used, nozzle 262 may allow the operator to adjust the shape and dispersion of the stream that is emerging from the nozzle.
Inside applicator 260, the mixed stream of air and particulates passes through a constriction device 264, usually called a “critical orifice”. This accelerates the stream to very high speeds, which in some cases can approach or even exceed the speed of sound. However, since the stream that enters orifice 264 carries a heavy load of particulates, the particulates tend to cluster together in ways that can form aggregated clumps, at the entry ramp where the larger flow channel in the entry portion of applicator gun 260 narrows down to a smaller constricted pathway, on the “upstream” side of orifice 264. This is where clogging commonly occurs.
Clogging is a major problem in single-hose systems, and it can grow worse as an applicator gun ages, due to two factors. First, even though extremely hard metal alloys are used to make critical orifices, the entry ramp that leads into the constricted orifice tends to become pitted and scarred, over time, as highly abrasive particles are blasted through the orifice for hours at a time. Second, the diameter of the critical orifice can be widened, over time, by the abrasive particles, creating a mismatch between the orifice traits and the outlet nozzle traits. Either of those types of gradual developments can create problems, and any such applicator gun eventually will need to be replaced.
A dual-hose (or double-hose) blasting system 300, which also is prior art, is illustrated in FIG. 3. It comprises a hopper 310 (which usually must be pressurized, to help ensure proper travel of the particulates through a relatively long hose), and a particle metering and supply device 320 with a particulate hose 322 connected to its outlet. It also comprises air compressor 330 with air hose 332, and applicator gun with critical orifice 342. Particulate hose 322 supplies the blasting media into a mixing zone 344 that is located inside applicator gun 340, downstream of the critical orifice 342. The media is drawn into the mixing zone by the creation of a vacuum at location 346, which is the outlet of hose 322.
Because an air stream that is clean (i.e., that does not carry blasting media) passes through critical orifice 342, dual-hose systems do not suffer from the relatively frequent clogging events that plague single-hose systems. However, as an offsetting disadvantage, dual-hose systems suffer from problems of reduced output velocity, which leads to reduced power and efficiency.
Reduced output velocity, in dual-hose systems, arises mainly from two factors. First, a substantial portion of the kinetic energy of the air that is emerging from orifice 342 must be diverted, spent, and used up, in creating a vacuum that will pull the particulate media out of hose 322, through interface 346, and into mixing zone 344. In effect, energy is being drained and sapped out of the high-velocity air, in order to run a secondary pumping operation that will draw particulates into the nozzle.
The second factor that leads to reduced speed and power in dual-hose systems arises from mixing of relatively slow-moving particles with high-speed air, in mixing zone 344. That mixing operation unavoidably creates some level of turbulence in the mixing zone, and the turbulence creates interference and disruption that prevent the mixture from passing through the applicator in an efficient “laminar flow” manner that could sustain higher velocities.
As a result, most operators who have worked with both single-hose and dual-hose systems quickly recognize that single-hose systems are more powerful and efficient than dual-hose systems. If asked to compare the two types of systems, most operators likely would estimate that a dual-hose system has only about 80% of the power and efficiency of a single-hose system. However, experienced operators also will report that single-hose systems do indeed suffer from much more frequent clogging than double-hose systems.
That completes a brief overview of the two main types of mechanical systems used for blast-cleaning operations, in the prior art. At this point, attention must be turned to different types of particulate media that are used in such operations.

Different Types of Blasting Media

Blasting that uses natural sand (obtained from sources such as sandbars in rivers, desert areas, offshore dredging operations, etc.) has been used for decades, for purposes such as removing old paint from surfaces that are too rough to be sanded effectively using sandpaper (such surfaces include, for example, asphalt, unfinished concrete, exposed steel girders on bridges and overpasses, etc.). However, sandblasting suffers from several problems and shortcomings that have limited its use. Those problems include, for example:
(1) sandblasting cannot discriminate between the surface layer or contaminant that should be removed (such as old paint, etc.), and underlying material that should not be altered. Because sandblasting is so powerful and abrasive, it often “scars” the surface of the underlying material, creating problems such as an undesired roughened appearance, weakening of the material, and increased susceptibility to corrosion;
(2) high-velocity sand generates heat, when the sand smashes against a surface and bounces off. In some cases, heat production can be very undesirable; for example, paint that is being removed may soften and melt, forming a sticky mess rather a clean surface;
(3) if sand is used to clean a surface, any sand that remains scattered around the work area, after the blasting operation has been completed, can pose serious problems; and,
(4) when natural sand is used for blast-cleaning, it can generate microscopic airborne “free silicate” particles, which pose a serious risk of health problems among workers who do this type of work.
For those and other reasons, numerous efforts have been made to develop and use alternatives to sand, for operations that use blast-cleaning. Some efforts have involved controllable mineral compounds other than sand, such as aluminum oxide, “white” aluminum oxide, silicon carbide, pumice, glass beads, etc. Other efforts have focused on the use of materials that are softer and less abrasive than sand, and that will not aggressively alter and scar an underlying material, such as plastic beads, ground-up walnut shells or corn cobs, and particles derives from wheat plants, usually referred to as wheat starch.
Still other alternatives involve the use of dry powders, such as baking soda (i.e., sodium bicarbonate, often referred to in the blasting industry simply as soda, since baking is not involved). It should be noted that soda and other chemical powders tend to be sensitive to both temperature and moisture; they will form clumps, “cakes”, and other unwanted aggregates if too much moisture is present, or if subjected to temperatures higher than certain preferred ranges. These constraints pose not just one but two complicated and potentially competing challenges, because of two important factors: (i) compressors will heat up any air they handle; but, (ii) if a conventional cooling device is used to chill heated air that emerges from a compressor, the cooling action can increase the relative humidity of the air, in ways that can create moisture problems. Specialized systems that address and overcome those problems, to enable effective blasting using powdered soda as the media, are sold by companies such as ProBlast. Information on those systems is available from the ProBlast website, www.problast.ca.
Since roughly the mid-1980's, particles of dry ice (frozen carbon dioxide) also have been used for abrasive cleaning. Blasting with dry ice offers two major advantages over hard particles. First, the very cold particles of dry ice prevent any heating of the surface, and in many cases can render surface layers or contaminants brittle (also called friable, which indicates that something can be easily broken). In some cases, this can make it easier and faster to remove an unwanted layer of paint or other coating material, leading to improved results. As one example, dry ice blasting is ideal for cleaning the types of large sanding belts and planing devices that are used in manufacturing furniture, veneers, and various other wood products. A sanding belt or planing drum will become “loaded” with gummy, sticky residues that contain wood sap. However, the freezing effects of dry ice blasting will render the sap-laden material hard and brittle, so it can be efficiently removed from the sanding belt or planing drum.
The second major advantage is that when dry ice pellets smash against a surface that is being cleaned, the dry ice will “sublimate” (i.e., it will convert directly into gas form, without passing through a liquid phase). This eliminates the problem of cleaning up grit or powder that remains scattered around a work area after a blasting operation has been completed.
However, dry ice blasting has its own limitations and shortcomings. The cost of the machinery and power to run a dry ice blasting system is relatively high, since dry ice is more expensive to obtain (or create) and store, compared to inert particulate materials. Also, since dry ice pellets are softer than sand or other mineral particulates, it takes a larger quantity of dry ice, applied for a longer period of time, to completely clean some surfaces; indeed, due to its lower levels of abrasiveness, dry ice blasting simply cannot clean some types of coatings, from some types of surfaces that need to be cleaned.
Under the prior art, no one adequately figured out how to create and provide a blasting system that can reliably handle a “wide variety” of different media types. As used herein, the term “wide variety” refers to a blasting machine or system that can handle each and all of the three major classes of blasting media, which are referred to herein as grit, powder, and dry ice.
As used herein, “grit” includes any hard particles with average sizes that can be readily seen by the naked eye, and that can be readily felt when a single typical particle is rubbed hard between a finger and a thumb. This includes sand, and most conventional preparations of aluminum oxide, glass beads, etc.
By contrast, “powder” refers to particulates with average particle sizes that are too small to see readily with the naked eye, and too small to be felt as individual particles, when rubbed between a thumb and finger. Baking soda offers an example of a compound that is a powder rather than a grit.
“Dry ice” refers to frozen carbon dioxide; blast-cleaning systems that use dry ice usually handle pellets that are roughly the size of grains of rice.
Although they have different sizes and contents, all three classes of blasting media are particulates (as distinct from water or other liquids, which are used in processes that are referred to as washing or power-washing, rather than blast-cleaning). Accordingly, as mentioned above, any references herein to blasting, blast-cleaning, blasting media, or similar terms, refer to operations that accelerate particulates (such as grit, powders, or dry ice pellets), rather than liquids, to high speeds.
The absence, in the prior art, of any systems that can handle all three major classes of blasting media (grit, powder, and dry ice) is important, and is not merely an oversight. People who work in this field have realized for years that if a single system could be developed that can handle all three types of media, such a “multi-media” or “omni-media” system could be more useful and valuable than blasting machines that can handle only one of those classes.
This point requires specific attention. People who work with sand or dry ice blasting have known and recognized, for years or even decades, that each media type has only a limited range of effective uses. At the hardest, most abrasive end of the spectrum, sand and other grit media are very powerful, but they have several major problems and limitations, including: (i) they will scar and damage most underlying materials; (ii) they generate levels of heat that can interfere seriously with some uses; and, (iii) they leave behind large quantities of gritty residues, which can create problems that range from annoying, to unacceptable.
In the center of the spectrum, powders tend to be more expensive than sand; they tend to suffer from clumping and caking problems; and, because they are less abrasive than grit, they usually require longer blasting times, and greater volumes.
At the softest end of the spectrum, dry ice creates no heat and leaves no residue, but it is the most expensive blasting media, and it is not strong enough or abrasive enough to remove some types of coatings that need to be removed.
Accordingly, people who work with blast-cleaning have openly wished and asked for a single blasting system that could handle a broader range of blasting media than can be provided by any systems known under the prior art. Such a system would allow a single machine (with a fixed cost, and with reasonable and practical training and use requirements) to be used for a broader variety of jobs than can be handled by current blasting machines.
These issues are becoming even more important within the industry, as new uses for blast cleaning are being developed and used. As one example, it has been realized that blast cleaning using dry ice and possibly some powders can be very effective at removing charred and damaged layers from wood or other relatively soft surfaces, after a fire, without damaging the underlying layers of wood. In such uses, sand or other hard grit would rapidly degrade the undamaged soft materials, and should not be used. Similarly, blasting using dry ice or some powders can be used to remove mold from soft materials such as pine wood, dry wall, and sheetrock, without damaging the soft supporting material; however, grit cannot be used for such purposes, since it would rapidly destroy soft wood, drywall material, etc.
In other situations, if a blasting machine could handle all three classes of blasting media, it would be able to provide better results than a machine that can handle only grit, only powder, or only dry ice. In many situations, a “first stage” blasting process that uses grit can “break the surface” of a layer of paint or other coating material, in ways that can render the underlying material more susceptible to “second stage” cleaning, using less abrasive media that can be effective without seriously scarring or damaging the underlying material. This type of two-stage blasting process would be comparable to using coarse sandpaper to rapidly achieve an initial level of partial smoothness, and then switching to fine-grit sandpaper to achieve a level of smoothness that cannot be achieved by coarse sandpaper.
In addition to providing a single system that can handle multiple types of blasting media, the invention described herein also provides other advantages. In particular, the hose and nozzle system described herein discloses and embodies an anti-clogging mechanism that is highly useful for rapidly and conveniently dislodging and removing clogs, clumps, or other problems that may arise inside the hose and nozzle system, without having to shut down the system and manually dislodge such clogs and clumps. As a result, this system provides improvements and advantages over prior systems, even if only a single type of blasting media is used.
Finally, it must be noted that various problems mentioned above are often aggravated by the working conditions encountered in blasting operations. Many blasting jobs need to be done at a job site that must be reached by truck, rather than in controllable factory-type settings, and blasting machines often are operated by semi-skilled manual laborers, rather than highly-trained specialists. If any equipment breaks or supplies run out, the operation often comes to a halt until a specialist can fix the problem, or until new equipment or supplies are delivered.
In addition, operators must wear protective gear for the eyes, ears, and skin, as well as breathing gear (which may include filter masks, oxygen tanks if dry ice blasting is being used, etc.). These requirements lead to additional clutter and complications, and the plastic lenses used in goggles often become: (i) spattered with paint or other material that is being removed from a surface, and/or (ii) pitted and degraded, if grit is used as a blasting media. Because the blasting media emerge from the nozzle at very high speed, the hose pushes against the holder with considerable force, and it is tiring on the arms, chest, abdomen and legs to have to hold a heavy reinforced hose and point the nozzle in carefully controlled directions, for long periods of time. In view of all of these factors, it tends to be difficult and uncomfortable work, and laborers who do this kind of work usually just want to get finished as quickly as possible, and then get cleaned up and leave. If they could be provided with better systems, with options that would help them accomplish a desired goal more rapidly and efficiently, the final results in many cases would be considerably improved.
Therefore, one object of this invention is to provide a blasting machine and system, for cleaning large structural surfaces, that can handle a wide variety of blasting media, which must be broad enough to include grit, powder, and dry ice pellets.
Another object of this invention is to disclose a blasting system for cleaning structural surfaces, with improved means for rapidly and conveniently dislodging any clogging that may occur inside one or more hoses, nozzles, or other components.
These and other objects of the invention will become more apparent through the following summary, drawings, and detailed description.

SUMMARY OF THE INVENTION

Blast-cleaning systems are disclosed, which enable a single system to handle two different types of particulate blasting media simultaneously, and which enable an operator to adjust the ratio (or percentages, relative content, etc.) of the two types of media, to achieve optimal results for a specific cleaning job. In one preferred mode of operation, one of the blasting media types will be dry ice pellets, while the other type will be a grit or powder.
In one preferred embodiment, this type of “multi-media” system includes a hopper having two chambers that are isolated from each other, for holding two different types of media. Each chamber is coupled to an outlet with a valve-type control that allows an operator to control and adjust the quantity (or flow rates, etc.) for each media type, at any given time during a blast-cleaning operation.
In an alternate preferred embodiment, this type of “multi-media” system uses a pipe, hose, duct, or other injection conduit which passes through a hopper system, and which is be coupled directly to a valve-controlled outlet. This can enable media that requires specialized “upstream” equipment or processing to pass through the upstream equipment and then be delivered directly to metering or dispensing equipment, without being diverted into hopper-type storage for a brief period. Media types that can benefit from “upstream” processing followed by direct delivery to a metering or applicator system include, for example: (1) baking soda or other powders that require dehumidifiers, to prevent caking, and (2) dry ice pellets, which require specialized equipment.
Regardless of which particular design is used, a human operator preferably should be provided with a control system that will enable him or her to adjust and control the ratio (or percentages, relative content, etc.) of the two different types of blasting media during a cleaning job, to achieve optimal results for that particular job. This will allow the operator to make adjustments (which will depend on various factors, such as the type and thickness of the paint or other coating material that must be removed from a surface, the type of underlying structural material that is being cleaned, the temperature and humidity conditions in the room or other area at the time of the cleaning operation, etc.) that can optimize the results of the cleaning operation, which can be monitored and adjusted in a relatively simple and straightforward manner, merely by watching and monitoring how rapidly and effectively the coating material is being removed from the structure that is being cleaned, and adjusting the flow rate of either or both media types until an apparently optimal blend or ratio is achieved, as shown by optimal removal of the coating material as a wand, gun, or other applicator nozzle is moved across its surface. In dual-bin or dual-hopper systems, maximal flexibility and control can be provided by enabling valve-type adjustment of the flow rates for both of the two different types of media. Alternately, if one type of blasting media is being supplied to an applicator at a relatively constant rate (for example, dry ice pellets generally should be pumped to an applicator through an insulated conduit, without any delays for temporary storage in a bin or hopper), then a single adjustable control over the other media type can allow the operator to conveniently create a desired ratio of the two media types.
Tests to date indicate that blasting mixtures containing about 90% dry ice (by volume) mixed with about 10% of harder particulates can be extremely effective in removing even difficult coatings from surfaces. These systems also generate much lower quantities of waste, compared to blasting systems that use only a single particulate media with no dry ice. In some cases, when dry ice was combined with a harder grit, waste production levels were reduced to only about 10 to 20% of the waste levels that were created using the harder media type alone.
In addition, the systems disclosed herein will provide an operator with an additional type (or dimension, parameter, etc.) of control that can help an operator efficiently remove a coating from an underlying material, with minimal scarring, pitting, or other damage to or degradation of the underlying material.
If a single-hose applicator gun is used, it preferably should be provided with a quick-connect attachment. This will allow the applicator gun to be quickly and easily disconnected from its supply hose, whenever clogging occurs. The clogged applicator gun can be quickly replaced by another applicator gun that has been cleaned out. This will allow the operator to quickly resume the blasting operation, while a support person cleans out the clogged gun (such as by using a surge of reverse-flow air), to get it ready it for the next quick-swap exchange.
Dual-hose applicator systems also are disclosed that are less prone to clogging than single-hose systems, and easier to clean and restart if clogging does occur. These units can be unclogged, without requiring any disconnections, by momentarily turning off the flow, pressing the nozzle of the gun directly against a hard surface, and starting flow again. This will divert the flow of compressed air into the particle supply hose, thereby breaking apart and dislodging any clumps that formed in the supply hose.
Integrated blasting systems also are disclosed that can include water-pumping components. This can enable an operator to use an intermittent water spray, out of the same applicator gun, to control dust problems, and it can enable an operator to convert back and forth quickly and efficiently between blast-cleaning, and power-washing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway side (elevation) view of a conventional hopper (which is prior art) with a slanted diverter tray that divides the hopper into two chambers, and a vibrator that promotes travel of the particulates to the outlet.

FIG. 2 is a schematic depiction of a single-hose blasting system (which is prior art), in which a rotary valve delivers a steady supply of particulates to a compressor-mixer. The mixture of air and particulates are delivered via hose to an applicator gun, which uses a constricted passage or “critical orifice” to increase the exit velocity of the abrasive mix.

FIG. 3 depicts a dual-hose blasting system (which is prior art), in which the particulate blasting media are sucked into a turbulent mixing zone, inside the applicator gun, by a vacuum created by high-speed air traveling through the gun.

FIG. 4 is a cutaway side (elevation) view of a dual-media hopper, in which a dividing wall divides the hopper into two chambers that are isolated from each other, with valve or gate components that allow either type of particulate media to pass through the outlet.

FIG. 5 depicts a dual-media hopper, with an injection tube that allows a second type of blasting media that has received any “upstream” processing (such as dry ice particles from a freezing unit, soda powder from a humidity control unit, etc.) to be injected into the blasting system via a hopper outlet that is already coupled to a particulate metering system.

FIG. 6 depicts two separate hopper units, simultaneously providing two types of blasting media to a metering supply device.

DETAILED DESCRIPTION

As summarized above, the disclosures herein relate to a blast-cleaning system that can simultaneously handle at least two different types of blasting media. Preferably, such a system should be designed to handle any and all of the three major classes of blasting media, which are grit, powder, and dry ice, as described in the Background section.
In one preferred embodiment, a system as disclosed herein should enable an operator to blast-clean a surface with a mixture of dry ice pellets, and a second selected media that can be either grit, or powder, depending on the needs of a particular cleaning task. In addition, such a system preferably should enable the operator to adjust and control the ratio (or percentages, relative content, etc.) of the two different media types, to achieve optimal results for a specific cleaning job.
This will allow an operator to make adjustments (which will depend on various factors, such as the type and thickness of the paint or other coating material that must be removed from a surface, the type of underlying structural material that is being cleaned, the temperature and humidity conditions in the room or other area at the time of the cleaning operation, etc.) that can optimize the results of the cleaning operation, which can be monitored and adjusted in a relatively simple and straightforward manner, merely by watching and monitoring how rapidly and effectively the coating material is being removed from the structure that is being cleaned, and adjusting the flow rate of either or both media types until an apparently optimal blend or ratio is achieved, as shown by optimal removal of the coating material as a wand, gun, or other applicator nozzle is moved across its surface. In dual-bin or dual-hopper systems, maximal flexibility and control can be provided by enabling valve-type adjustment of the flow rates for both of the two different types of media. Alternately, if one type of blasting media is being supplied to an applicator at a relatively constant rate (for example, dry ice pellets generally should be pumped to an applicator through an insulated conduit, without any delays for temporary storage in a bin or hopper), then a single adjustable control over the other media type can allow the operator to conveniently create a desired ratio of the two media types.
Tests to date indicate that blasting mixtures containing about 90% dry ice (by volume) mixed with about 10% of harder particulates can be extremely effective in removing even difficult coatings from surfaces.
These systems also generate much lower quantities of waste, compared to blasting systems that use only a single particulate media with no dry ice. In some cases, when dry ice was combined with a harder grit, waste production levels were reduced to only about 10 to 20% of the waste levels that were created using the harder media type alone.
In addition, the systems disclosed herein will provide an operator with an additional type (or dimension, parameter, etc.) of control that can help an operator efficiently remove a coating from an underlying material, with minimal scarring, pitting, or other damage to or degradation of the underlying material.
One of the advances that renders such systems possible is the creation of new types of hopper systems, as illustrated in FIGS. 4 through 6. If desired, these new designs can be constructed in a way that are compatible with each other, such as by allowing an injection tube (as shown in FIG. 5) to be installed in a dual-media hopper (as shown in FIG. 4) whenever needed, and then removed when not needed.
Referring to FIG. 4, hopper system 400 has a first chamber 404 and a second chamber 406, which are isolated from each other in a manner that is essentially watertight. This is in direct contrast to hopper 100 as shown in FIG. 1, in which a gap 110 exists between diverter tray 102 and hopper floor 108, allowing media to travel directly from chamber 104 to chamber 106 via gap 110.
The isolation of chambers 404 and 406 from each other is accomplished by the design of a chamber (or interior) wall 450, which includes a partial floor component 452. The angled slope of a portion of wall 450 is designed to emulate the slope of a conventional diverter tray in a standard hopper. The exact slope and shape of wall 450 are not essential; in general, the shape of chamber (interior) wall preferably should avoid or minimize the creation of a potential “dead zone” where media would tend to become stationary, especially if the system is designed to handle dry ice.
FIG. 4 also depicts a first type of media 412, a second type of media 414, a travel path 410 provided by a vertical gap between hopper floor 408 and partial floor 452, a vibrator 440, and an outlet 420 coupled to a hose, pipe, or other conduit 422. Typically, a relatively short segment of pipe or large-diameter hose is used as conduit 422, to convey the blasting media from hopper 400 to a mixer, compressor, or other mechanical unit, as shown in FIGS. 2 and 3. A longer flexible hose then conveys the particulate media from the mixer, compressor, or other component, to a “gun” that is held and moved by a human operator, during a blasting operation.
A movable gate or valve component 460 is used, to allow an operator to control whether first media 412 or second media 414 is being supplied to an applicator gun at any point in time. Gate 460 is illustrated in FIG. 4 as a gate-type door or flap affixed to an axle, in a manner that allows rotation about the axle. If this design is used, the axle can extend through both of the side walls of the hopper, and can be connected to lever-type handles mounted outside both walls, allowing operators on both sides of the hopper to exert large amounts of torque and leverage on the gate 460, if such torque is necessary to shut off the flow of some types of particulates through the gate. Various other gate styles and designs can be used, as known to those skilled in the art of handling particulates. If desired, a slot system or other screening mechanism can be affixed to outlet 420, to prevent small pebbles or particle aggregates from entering outlet conduit 422.
Hopper system 400 in FIG. 4 can be designed and built to enable either or both of chambers 404 and 406 to be open and unpressurized, or closed and pressurized. Any or all of the hopper walls can be insulated, to allow dry ice pellets to be handled by either of both of the two chambers. In general, chamber 406 is likely to be preferred for handling dry ice pellets, since it can reduce the travel distance and “dwell time” for such pellets, which must be protected against premature warming and vaporization.
FIG. 5 illustrates an alternate design for a hopper system 500, which uses an injection tube 550 (rather than an isolated second chamber) to supply a second type of particulate media into hopper outlet 520 and outlet conduit 522. FIG. 5 also depicts diverter tray 502 (which can be shaped to provide a water-tight chamber wall with a floor, as shown in FIG. 4, if desired), first chamber 504, second chamber 506, hopper floor 508, travel gap 510, particulate media 512, vibrator 540, and outlet collar 524 with entry slots 526.
This type of “direct injection” system as shown in FIG. 5 is likely to be preferable when a chemical powder (such as soda, i.e., sodium bicarbonate) is being used as one of two blasting media. This arises from the fact that some powders are sensitive to temperature and moisture, and may require specialized cooling and dehumidifying equipment, as mentioned in the Background section and as described in more detail in sources such as the website of the ProBlast company, which specializes in equipment that uses soda blasting. A “direct injection” system may also be preferable for use with dry ice pellets, since it is generally easier and more efficient to insulate the smaller surface area of a tube, compared to the larger wall surfaces of a chamber or bin.
In addition, outlet collar 524 with outlet slots 526 represents an adjustable control system, which will allow an operator to adjust and control the percentages (or ratios, blends, etc.) of the output mixture, as needed to optimize the results of any particular cleaning operation.
FIG. 6 shows an alternate preferred embodiment, in which two separate hoppers 610 and 620 are both coupled to a combined outlet 630. In that arrangement, hopper 610 is provided with an internal wall 612, a vibrator 614, and an outlet conduit 616, while hopper 620 is provided with its own internal wall 622, vibrator 624, and outlet conduit 626. Both outlet conduits 616 and 626 provide particulates to metering supply device 630, which in turns provides steady but controllable quantities to compressor 640.
In another preferred embodiment, a main hopper can be provided with a “sidecar” hopper, which can be affixed to the main hopper in a secure but detachable manner, such as by using clamps, threaded bolts, etc. This will allow both of the hoppers to use a single vibrator.
By providing gating or valve mechanisms, which are conventional and well-known in this industry, it is possible to operate any of the hopper systems shown in FIGS. 4 through 6 in a manner that will allow a mixture of two different media to enter a gating, mixing, compressor, or similar unit. For example, this approach can be used to blast a surface with a mixture of grit and dry ice, simultaneously. The dry ice in such a mixture can prevent any undesired heating of the surface that is being cleaned, and it also can freeze some types of surface coatings, making them brittle and easier to remove.
As one example of how this system can provide advantages over prior art systems, a prototype unit, having a dual-media design as disclosed herein, was tested and used to clean the surfaces of several oil pipelines in the Prudhoe Bay region of the arctic coast of Alaska, during 2006, after serious corrosion problems were detected on those pipelines. During the 1970's, when that oil production facility was being built, the network of smaller pipelines that handle oilfield operations (as distinct from the much larger pipeline that carries oil south, across the state) were coated with a specialized chemical coating that was designed both to protect the pipeline surfaces, and to help provide thermal insulation while withstanding extremely cold weather and harsh conditions. Roughly thirty years later, the weathered and worn coating had to be removed and replaced.
Neither grit nor dry ice, when used alone, were able to adequately clean those pipeline surfaces. However, a mixture of rice and dry ice, mixed together and blasted out of a single nozzle, rapidly and efficiently removed the coating, enabling the pipelines to be inspected, repaired, and recoated. The rice particles were eaten by birds, so there was no need to clean up grit that otherwise would have been scattered around the area.
In some uses, including dry ice in a blasting media mixture can provide important additional advantages, such as to reduce unwanted heating. Any use of high-velocity blasting media generates high levels of energy transfer, which heats the surface being cleaned. In some settings (such as when airplane surfaces are being blast-cleaned), heat buildup is highly undesirable, since it can cause metal surfaces to warp, which can distort a plane's aerodynamic shape. If dry ice is included in a blasting mixture, it will absorb and dissipate any such heat, thereby preventing any warping.
Similarly, depending on both (i) the surface coating material being removed, and (ii) the blasting media being used, a risk of explosion can arise, in some situations. As one example, if wheat starch is used as a blasting media, the tiny particles of organic material, floating in the air, can literally explode. However, if dry ice is added to a blasting media mixture, it will reduce the temperatures that are involved, and it also will displace the oxygen in the air (which is necessary for combustion) with carbon dioxide, which is inert and nonflammable. Both of those two effects will reduce any risk of explosion.
Accordingly, the addition of dry ice particles to other types of blasting media, to create a blasting media mixture, can provide major advantages in some settings. Therefore, this invention discloses both machinery and methods for carrying out blast-cleaning operations using mixtures of two different blasting media, and an important subclass of such operations involves dry ice particles mixed with other types of blasting media.

Optional Water Spray, for Dust Control and Power-Washing

If desired, injection tube 550 (shown in FIG. 5) can be coupled to a water supply, using a conventional connector and valve. When in use, this allows a water spray to emerge from an applicator gun that is coupled to outlet hose 522. This can provide a controllable intermittent water spray, which can be used to control airborne particulates generated by a blasting operation, which in many cases will tend to act like a thick load of dust in the air.
In addition, high-pressure water spray can be very effective in cleaning some types of surfaces. When water is involved, that type of pressurized spraying is usually called power-washing, rather than blast-cleaning. Accordingly, it is disclosed herein that it is possible to create a “merged” or “integrated” system that provides both blast-cleaning capability (which requires an air compressor), and power-washing capability (which normally requires water-pumping equipment).
Because both water and air have fluid-flow characteristics, certain types of pumps and compressors are known that can handle either air or water, and such multi-function pumps can be evaluated for use as disclosed herein, if desired. However, blast-cleaning systems use specialized compressors and mixers that have been optimized for handling mixtures of air and particulates; and, high-pressure water systems can be handled more efficiently and less expensively by using high-pressure hoses or pipes, rather than high-pressure bins. Therefore, to extend the operating life of such a system, and to reduce the costs of maintenance, repair, and replacement parts over a span of months or years, an integrated system preferably should keep the “upstream” components of the air-compressing and water-pumping systems separate and distinct from each other.
As mentioned in the Summary section, if a single-hose applicator gun is used, it preferably should be provided with a quick-connect attachment. Such attachment devices are well-known, and are commercially available from numerous suppliers. This will allow an applicator gun to be quickly and easily disconnected from its supply hose, whenever clogging occurs. The clogged applicator gun can be quickly replaced by another applicator gun that has been cleaned out. This will allow an operator to quickly resume a blasting operation, while a support person cleans out a clogged gun (such as by using a surge or pulse of reverse-flow air), to unclog the gun and get it ready it for the next rapid exchange of guns.
Thus, there has been shown and described a new and useful system that can enable a blast-cleaning system to handle multiple types of blasting media, including grit, powder, and dry ice. Although this invention has been exemplified for purposes of illustration and description by reference to certain specific embodiments, it will be apparent to those skilled in the art that various modifications, alterations, and equivalents of the illustrated examples are possible. Any such changes which derive directly from the teachings herein, and which do not depart from the spirit and scope of the invention, are deemed to be covered by this invention.

Claims

1. A mechanical system suited for use in blast-cleaning of structural surfaces, comprising a hopper assembly designed to provide at least two different types of particulate blasting media to an outlet hose, wherein said hopper assembly comprises:

a. a first media chamber, designed to hold a supply of a first particulate blasting media, and provided with a first chamber outlet for conveying said particulate blasting media to a metering supply device;

b. a second media supply subassembly, designed and suited for providing a supply of a second and different type of particulate blasting media to the outlet conduit; and,

c. an outlet conduit designed to accept and transport, simultaneously, two different types of particulate blasting media, in a manner suited for supplying both types of particulate blasting media to a metering supply device,

and wherein the mechanical system also provides an operator with means for adjusting the ratio of the two different types of particulate blasting media, during a blast-cleaning operation.

2. The mechanical of claim 1, wherein the second media supply subassembly is designed to provide dry ice particles to a metering supply device, and wherein the device is designed to enable a blast-cleaning operation that uses a mixture of a first particulate blasting media, and a second particulate blasting media comprising dry ice particles.

3. The device of claim 1, wherein the second media supply subassembly comprises a second media chamber that is positioned adjacent to said first media chamber, within said hopper assembly.

4. The device of claim 1, wherein the second media supply subassembly comprises a conduit that passes through said first media chamber.

5. The device of claim 4, wherein the conduit is thermally insulated.

6. The device of claim 1, wherein the second media supply subassembly comprises a second hopper assembly having an outlet conduit that is coupled to said first chamber outlet.

7. A method for blast-cleaning of structural surfaces, comprising the step of using a particulate blasting media mixture, wherein a first constituent of said particulate blasting media mixture comprises dry ice particles, and wherein a second constituent of particulate blasting media mixture is selected from the group consisting of powdered and grit blasting media other than water ice, and wherein the method utilizes a blast-cleaning system that enables an operator to adjust relative volumes of said first and second constituents of said particulate blasting media mixture.