A: This questions comes up a lot and the answer depends on several variables.

1. What size nozzle is going to be used.

2. What blast pressure will be required.

3. What size the blast hose is.

4. How far is the compressor from the location of the blasting.

The larger the blast nozzle and/or the higher the blast pressure used, the higher the air volume requirement. If the blast nozzle diameter is reduced, the air volume requirement will be reduced since it will take less air to maintain pressure through the smaller nozzle. Likewise, if the blast air pressure is reduced it will reduce the air volume requirement through the same size blast nozzle.

The following chart will provide a general idea of the volume of air required to operate the listed nozzle sizes at the pressures indicated.

CFM CONSUMPTION

NOZZLE VENTURI PSI

NO. SIZE 25 30 35 40 45 50 60 70

________________________________________________________

CFM

4 1/4 in. 28 32 37 41 45 49 56 61

5 5/16 in. 44 50 57 64 70 76 88 101

6 3/8 in. 63 73 82 91 100 109 126 143

7 7/16 in. 85 99 112 124 137 149 172 194

8 1/2 in. 112 129 146 163 179 194 225 252

Q: I was told that I needed a 6,000 CFM fan for my old dust collector and it would need a 15 HP motor. I found a 6,000 CFM fan in my Grainger catalogue that looked just like the one I was quoted and it only needed a 2 HP motor. What’s going on?

A: Fans are rated based on two factors.

1. CFM, which is the volume measured in Cubic Feet per Minute (CFM) of air flow that a particular fan will produce.

2. SP, which is a measure of resistance measured in inches of water gage and referred to as static pressure (SP). This factor will give you the amount of resistance that a particular fan will produce its rated volume against. In the case of a dust collection system, SP refers to a negative pressure (vacuum) that is generated as the fan tries to pull air through a dirty filter. The dirtier the filter, the higher the SP. Once the SP exceeds that for which the fan is rated the CFM will begin to diminish, sometimes drastically.

The fan you were quoted was probably sized for pulling 6,000 CFM of air through a dirty filter media as well as through ducting and various elbows, hoods etc. that make up your particular system. In order to ensure you had the full 6,000 CFM during actual use the SP that was calculated for all this resistance resulted in a motor size of 15HP.

Most system vary with regard to HP requirement since every installation is different unless you are using a product like the Envirosystems AirWall units which do not required ducting and therefore can have the same fan for every installation. The AirWall units already have sufficient HP to provide full volume even when the filters are full and ready to begin pulsing.

The fan you found in Grainger will probably only delivers 6,000 CFM at an SP of between 1 and 1.5 In. S.P. (w.g.). While this would be fine for moving air through a room, it is useless for dust collection since even a clean dust collection filter of any type will have a resistance of almost that much before they even have any dust in them. I can appreciate your concern about fan cost as well as energy cost for the high HP fan, but if your particular system, due to filter type, ducting, etc. requires an S.P. of 6 to 8 inches, then the HP requirement for that fan may very well be 15 HP. While there are slight differences in how much HP is required by various types of fans to achieve the same volume per unit of resistance, the basic concept of HP per CFM at a given SP is fairly constant and are calculated using what are referred to a fan laws.. If you would like to do more research on this you can reference the following universal fan laws. You may find several sources of information regarding them on various web sites.

FAN LAW FORMULA

CFM varies Directly with RPM (CFM 1 / CFM 2 = RPM 1 / RPM 2)
SP varies with the SQUARE of the RPM (SP 1 / SP 2) = (RPM 1 / RPM 2)2
HP varies with the CUBE of the RPM (HP 1 / HP 2 = (RPM 1 / RPM 2)3

Just remember that it is important, any time you are getting quotes for dust collection systems or any other air movement device, which you ask for the SP at which your fan volume is being rated. This will help eliminate the possibility of getting a system that works very well at first but after a few weeks or months doesn’t seem to be moving enough air. All 6,000 CFM fans are not equal.

Q: How do I calculate how large my dust collector needs to be?

A: This is a very good question and one we address several time a day. The first thing you must determine is how fast you want or need the air to move through the area you are collecting dust from. Depending on the type of dust and the size of the room, this could be anywhere from 50 feet per minute (FPM) to over 160 FPM. For the sake of explanation let’s settle on 50 FPM.

The next thing you must determine is the size of the area you wish to ventilate. Again, for the sake of explanation let’s settle on an entire room with dimensions of 20 ft. wide by 10 ft. high by 50 ft. long.

For the purpose of determining air flow there are only two dimensions that are important; the width and the height. The length is relatively un-important unless it is extremely long, in which case there may be some consideration given to that fact. In our case, 50 ft. is not an issue. To calculate how large a system we need we will multiply the width by the height. A 20 ft. width times a 10 ft. height will give us a 200 Sq. Ft. cross section.
We now multiply this cross section by the air movement we want in FPM. Our 200 Sq. Ft. cross section multiplied by 50 FPM will give us a required air volume of 10,000 Cubic Feet per Minute (CFM). Once you understand how this works it is quite simple. We simply take the cross section area and move it through the room the number of feet we want it to move each minute and then total the volume of space that took up.

FOR APPLICATIONS

OTHER THAN AIRCRAFT AIRFRAMES

As Presented at the:

DEPARTMENT OF DEFENSE

TRI-SERVICE

ADVANCED COATINGS REVOMAL CONFERENCE

Orlando, Florida

March 1, 2 & 3, 1988

By Kenneth E. Abbott, Mgr. Member
Envirosystems Manufacturing, LLC
2555 N. Coyote Dr.
Tucson, Arizona 85745, USA

Founder and Former President
Stripping Technologies, Inc. (STI)
Tucson, AZ
I. INTRODUCTION

Overview

Envirosystems Manufacturing, LLC (ESLLC) formerly STRIPPING TECHNOLOGIES, INC. (“STI”) is involved in virtually every aspect of Plastic Media Blasting (“PMB”), ranging from the extensive use of PMB for the removal of coatings to its development and marketing of advanced, state-of-the-art PMB turnkey systems. These turnkey systems include plastic media blasting and reclamation systems, compressed air equipment, dust control systems, blast rooms, cabinets, accessories, masking supplies and plastic blast media.

Prior to forming STI, the principals of STI had in-depth experience in the application of PMB to aircraft airframes, including the stripping of the UH-60A Blackhawk helicopter, Gates Learjets, Sabreliners, Bell JetRangers and scores of small aircraft.

Although there continues to be a pressing need for the PMB process to replace the toxic chemicals used for stripping airframes, we recognized other applications that we believe, ultimately, will dwarf the aviation market. These applications include both the military and private-sector marketplace and encompass military ground support equipment, motor vehicles, marine vessels, machinery and equipment and a vast range of commercial and industrial components and structures.

As is evident from the papers presented at this Conference in the last few days, there are still many factors to be considered before there is a consensus on the application of PMB to aircraft airframes, especially where the process is to be applied to advanced composites and thin aluminum and magnesium substrates.

It was felt, therefore, that a presentation on some of the non-controversial applications for PMB might be a welcome change.

For many years STI employed PMB to strip a broad range of products other than whole aircraft airframes. These products included aerospace ground support equipment for the 355th Equipment Maintenance Squadron stationed at Davis Monthan Air Force Base in Tucson, Arizona; Maverick Missile airframes for Hughes Aircraft Company; aerospace and aircraft parts; metal and fiberglass automobiles and boats; large aluminum trailers; and a host of commercial and industrial components and structures. In short, they found the application of PMB to be limited only by the imagination. All of our applications have been performed rapidly and economically and without any damage to substrates.

The major economic and environmental rewards associated with the application of PMB to aircraft airframes have been advertised and discussed extensively in technical reports and in aircraft publications. Often overlooked, however, are advantages inherent in the technology that relate to non-aircraft applications. These include:

1. The ability, often, to remove coatings one layer at a time, leaving primer and surface fillers intact if desired.

2. The ability to remove coatings from most metal substrates without pitting, etching, stretching, warping or metal loss.

3. The ability to remove coatings from both flexible and rigid urethane and engineered plastic parts without laborious hand or mechanical sanding.

One has only to talk to an experience re-finisher of ground transportation equipment to appreciate these advantages.

If there is one facet of the PMB technology which most impresses the layman, it is the appearance of substrates after stripping. Steel substrates, for example, appear brand new and the look on a customer’s face when he picks up his parts often borders on disbelief.

As stated earlier, the age of Plastic Media Blasting has arrived and we agree with those who are of the opinion that PMB will be the Best Available Technology for most paint removal tasks for at least the next decade.  Aircraft from the large C5 Galaxy to the exotic B2 Stealth Bomber are now stripped using one form or another of PMB, with many more applications waiting to benefit from the unique features of this remarkable technology.

I. MILITARY APPLICATIONS OF PMB, OTHER THAN AIRCRAFT AIRFRAMES

We still believe that the PMB process offers major advantages to the military, not only for the stripping of airframes but also for the depainting of thousands of pieces of ground support equipment, motor vehicles, marine vessels, missiles, tanks, machinery and equipment and many commercial-type products procures by the armed forces.

Of particular significance will be the removal of Chemical Agent Resistant Coatings (CARC), a program initiated by the Department of the Army. CARC is the polyurethane system and the solvents used as a resin vehicle are very aggressive. In order for the system to be properly applied, the old topcoats must be completely removed. If this is not done, there is a high probability of paint failure occasioned by the “lifting” of old coatings and the breaking of the paint film integrity.

There is almost a natural union between the CARC program and the PMB process. Not only will the PMB process successfully remove the thick, multi-layered coatings found on equipment in the field, but it will remove it rapidly and without damage to hoses, brake lines, bearings, or seals. Nuts, bolts and screw heads, which have become almost buried in paint, will look as if they had been replaced with brand new hardware. Sheet metal panels on vehicles and equipment will be left without any etch whatsoever and will appear to have been newly fabricated. Since the PMB process does not remove metal, the longevity of equipment will be greatly extended and will be left without the dry and battered look occasioned by sandblasting,.

Finally, where PMB might otherwise compete with pneumatically-conveyed hard abrasive, such a silica sand, or walnut shells, the reduction in the amount of masking of sensitive accessories and the reduction in contaminated waste will be major cost offset.

III. SELECTIVE STRIPPING

The operator control which is possible with the PMB process reduces masking requirements and affords an operator discretion in the determination of the number of coatings to be removed, including primer and surface fillers. Although this claim has been made almost from the beginning of the PMB technology, to a painter the ability to remove one layer of paint at a time borders on alchemy.

Examples of the degree of control possible for selective paint layer removal include a 1949 Willys Overland which was being restored by a Tucson, Arizona paint shop. STI removed approximately 8 separate paint systems from this vehicle, and somewhere between the 5^th and 6^th paint layer discovered an old advertisement. Thinking that the new owner might find this interesting for his restoration documents, STI completely remove the paint from around the sign and, subsequently, removed only the paint layers covering the sign. You could still read the old hand-lettered sign, “Homaid Bread Co., Treatype Products, 1406 Lily St., Tucson.” Needless to say, the owner was delighted.

II. POWDER COATINGS

Another potentially large market for PMB is the removal of powder coats, especially from sensitive substrates, such as aluminum and magnesium. Powder coat systems are being used increasingly in the aerospace and high-tech industries. In the case of powder coated magnesium castings used in the manufacture of compound archery bows, the PMB process eliminated the heat stress problem associated with burn off ovens and left a superior surface finish for re coating.

III. OTHER EXAMPLES

Another great example of the virtues of PMB include the stripping of old paint and hull coating from a line of bolts attaching the hull of a Grumman Widgeon to its airframe. STI completed the stripping work on this airframe for the Pima Air Museum in Tucson, Arizona. The previous owner had begun chemically stripping the airframe and found that the chemicals would not remove the hull coating, even with wire brushes. There were literally thousands of these bolts surrounding the entire airframe. Imagine the time it would have taken to wire brush these seams clean, and the resulting painting surface with which you would be left. The complete cleaning of these bolts was accomplished in only a few hours using PMB technology. Keep in mid that the hardware on this aircraft was over 40 years old but when completed it almost looked as if it had just been replaced.

Besides the many component and vehicle applications, there are a number of small tools and machinery ideally suited to the PMB technology. A common, 15-ton aircraft axle jack can be stripped clean in 2.5 minutes. There is virtually no making required.

The possible uses for PMB in the military are endless. Everything from weapons systems to motor vehicles, marine vessels, tools and machinery and even office furniture can utilize the process for the rapid and safe removal of paint or other coatings.

The following case studies are just the tip of the iceberg, and we think you will agree after seeing these examples that there is a broad new horizon for PMB, which is worthy of immediate consideration by the military, other government agencies and the private sector.

AGE Equipment

STI successfully de-painted 216 pieces of ground support equipment for the 355th Equipment Maintenance Squadron stationed at Davis Monthan Air Force Base in Tucson, Arizona. Representative examples are shown in the following Exhibits.

EXHIBIT ITEM BLAST TIME
15 15 Ton Wing Jack 20 minutes
16 “
17 Hi-Pack Air Compressor 90 minutes
18 “
19 “
20 Linkage detail (Hi-Pack)
21 MJ-1A Bomblift (3000 lb.) 150 minutes
22 “
23 MHU-83B Bomblift (7000 lb.) 135 minutes
24 “
25 MHU-83B front break assembly
26 MHU-83B loading platform assembly
27 “
28 Drop Tank Loader 150 minutes
29 “
30 Drop Tank Loader (aft detail)
31 Drop Tank Loader (forward detail)
32 LOX Cart 50 minutes

There is a large requirement for the PMB technology in the stripping of aerospace components. The process has the potential to save many thousands of dollars over current stripping methods and, in fact, can sometimes mean the difference between salvaging a part or scrapping it.

For example, the Missile Systems Division of Hughes Aircraft Company (now Raytheon) uses a coating on the wire spool for the TOW missile which resists chemical stripping. Due to production process requirements, there are times when it becomes necessary to strip and re-coat the surface of these spools. In an effort to avoid having to scrap many of these parts, STI took part in a test program to use the PMB process to strip this coating using 3.5 mohs material in a 30/40 sieve size. Using PMB, STI successfully stripped the epoxy coating, leaving the anodized surface intact.

After proving the potential on the TOW program, the next logical step was to provide the process to the Maverick missile program. Hughes allowed a PMB test on 2 missile airframes. After de-painting, a Hughes process engineer inspected the surface and was satisfied that the surface chemical film (Alodine) was intact. Since this test, STI de-painted several hundred of these airframes, providing the ability to economically re-configure the standard airframe for various branches of the military.

One very unusual application for PMB is the removal, through sacrifice, of phenolic based components from high value structures. STI has performed a test on a MK. 70 booster assembly to evaluate the effectiveness of PMB for the removal of the phenolic, approach cone insulator, when bonding anomalies are found. Due to the location of this component within the structure, removal after bonding is almost impossible without incurring damage to the casing. PMB proved capable of completely removing the phenolic material without marking the casing surface. This process is expected to be a very valuable adjunct to the company involved in the production of this component, with the savings on the first 11 units projected to exceed $400,000.

Our Firm, Envirosystems Manufacturing, LLC, continues to be on the leading edge of the PMB technology, both in application of the process and in the perception of new, worldwide markets.  Further, as a former user of PMB systems we recognized the need for certain equipment modifications required to advance the state-of-the art.
Over the years ESLLC has worked with other equipment suppliers, including former competitors, to help further the use of this amazing technology. Among the needed improvements we have recognized and addressed are the following:

1.    Remote Controls:  The ability of a PMB operator to remotely measure and control, at the blast nozzle, the blast air pressure and the mixture of air and media emanating from the pressure vessels.  This ability to rapidly adjust air pressures and media flow to accommodate transitions from one substrate to another will become increasingly important, not only on aircraft airframes but also on motor vehicles where, increasingly, steel and aluminum substrates are being replaced by urethane and plastic components and advanced composites.

2.    Media Reclamation Equipment:  Equipment to more thoroughly clean the plastic media and, in certain cases, to remove high-density contaminants.  Improvements include more efficient cyclone separators, aspirators, fluidized bed systems and the rapid classification of media by mesh size.  These systems can be both on-line and off-line.

3.    Blast Rooms:  Economical blast rooms, both permanent and portable, especially designed for PMB applications and incorporating the latest in ventilation and dust removal technology.

4.    Dust Control Equipment:  Our Patented AirWall Dust Collection units are the industry standard in high volume, energy efficient, cost effective dust collection for all abrasive blast environments.