Industrial Dust Collection & Dry Media Blasting Equipment Blog

VI.    OUTLOOK FOR THE FUTURE AND OTHER CONSIDERATIONS

Initial Applications Slow to Develop

Due to the initiative and leadership of the U.S. military in fostering the PMB technology through experimentation, “real world” application and the awarding of study contracts to independent consulting and research firms, the age of Plastic Media Blasting is upon us: and it is our opinion that the ultimate worldwide market for the PMB technology in terms of equipment, accessories, plastic media, masking supplies and services will run into the hundreds of millions of dollars.  Although there are many who are still skeptical and cautious, the major economic and environmental rewards of the technology far outweigh its few shortcomings for most applications.

In certain cases, our research indicates that many negative reactions to the PMB process were occasioned by the witnessing of improper applications of the technology by untrained personnel or by the inappropriate application of PMB to substrates not amenable to the process, such as very thin aluminum and magnesium surfaces.

At the beginning of the exploration of the PMB technology, the few progressive and pioneering vendors and service firms addressing the marketplace had tunnel vision on aircraft airframe applications.  To a great extent, this is still the case; and the technology continues to be relatively unknown in the private sector.

Both the military and general aviation market have been slow to develop for several reasons.

1.    The initial caution of the military, the aircraft manufacturers and FAA over the application of a new technology to multi-million dollar weapons and aircraft systems.

2.    The initial concern of these same parties over the application of a new process to products where there could be a potential for loss of life and limb; and

3.    The concern of both equipment vendors and service firms over possible product liability exposure.

As a consequence, U.S. vendors, not yet recognizing the ultimate potential of the PMB technology, have been reluctant to expend thousands of dollars in advancing the state-of-the-art.  This seems to be especially true with respect to the manufacturers of media blasting vessels and dust control equipment, who operate in a highly-fragmented market and, by most standards, are relatively small companies.  Also, at the high end of the spectrum may be found the suppliers of requisite compressed air systems.  Many of these firms are divisions of large multi-national concerns which, indeed, do have the resources to modify their equipment to accommodate the high CFM, low PSI demands of PMB.  To date, however, they have not seriously addressed the market.

To some extent, the attitude of many vendors who could participate in this emerging industry has been a “wait and see” or “if it ain’t broke, don’t fix it” approach.  This is very unfortunate, since as has been the case in the past for U.S. industry, there will be offshore companies which may step in and capture a significant share of this new industry.  Let’s all hope that this will not be the case.

Yesterday’s Wall Street Journal did an extensive article on the recent sugar refinery explosion in Georgia. We in are industry are all too aware to the explosive nature of dust in the manufacturing environment. This is the reason that we are in the business of offering dust collection solutions to a wide range of industries.

This article pointed out that the refiner had gone to great lengths to address their dust collection needs. It is believed that dust that had collected in the ceiling rafters was what ignited this deadly explosion.

Those not associated with these industries often find it hard to imagine that sugar could be explosive. When I first worked for this company in the early 90’s I was shocked to learn that dust could be explosive. Dust explosions were so common in the early 70,s in the grain elevator industry. So much so, that the federal government studied the problem at length.

New regulations were put into place in 1987 to address dust control issues. A 2003 report showed that these new regulations showed a 42% drop in explosion and a 70% decrease in fatalities since these regulations where implemented. We who manufacture dust collection equipment are deeply saddened by this loss and our prayers go out to the families of this tragedy.

It at times like this that we again realize that the equipment that we manufacture not only saves the manufacturer money, but it ultimately was the potential to save lives. The need for a safe work environment is why we do what we do.

I. SYSTEM SIZE

The first question that comes to mind is: What size system is needed? The answer to this can be subjective unless you first establish a few basic parameters by answering the following questions:

This white paper will be presented in multiple sections.

Kenneth E. Abbott

Managing Member

Envirosystems Manufacturing, LLC

2555 N. Coyote Dr., Ste. 114

Tucson, Arizona 85745, USA

I. INTRODUCTION

Dust collection is a necessary requirement in many industries and the Composite industry is no exception. Air borne dust, even that regarded only as nuisance dust, is not only a housekeeping expense but will also reduce worker productivity and contaminate product.
Unfortunately, unlike high tech manufacturing equipment such as CNC Routers or Mills which reduce labor, increase productivity and increase profit; dust collection equipment is generally considered just a cost of doing business. The fact is nothing could be further from the truth. Proper dust collection equipment can add to the bottom line by reducing housekeeping and equipment maintenance costs while at the same time boosting worker productivity, not to mention the pride that comes from working in a clean manufacturing environment. Additionally, as we all know, the business of manufacturing with Composites, whether it be basic raw material manufacture or final fabrication, is very sensitive to both air borne and surface contamination. A small amount of contamination on a faying surface can easily ruin a complex assembly and sometimes this damage is not detected until very late in the process, resulting in the complete loss of many hours of labor not to mention scraped materials. The vast majority of these types of problems can be easily eliminated with the proper dust collection system. The question is: “what is the proper dust collection system?”
To be continued…

1. What is generating the dust?

2. How big is the generating area?

3. Can the generating functions be grouped and/or isolated?

The answers to these questions will help to determine the size and type of equipment needed to do a proper job of collecting air borne contamination in your facility.

Whenever possible, all the dust generating activities should be grouped in one area. This is not always possible, and there are ways to deal with this problem if it exists, but to the extent possible, the most cost effective method of eliminating air borne contamination is to confine it to one area where it can be isolated and filtered using the least possible amount of air.

All air borne contamination is removed by directing it into a controlled air flow generated by a fan. This flow of air will pull the contamination through a filtration system made up of various types of filter media. The filter media type will be determined by the type of contamination involved, but the amount of air is solely determined by the size of the area that is being controlled. The larger the area, the more air required. The actual calculation used to determine the amount of air volume required for a particular application is very simple. The width of the room is multiplied by the height resulting in a room cross section value expressed in sq. ft. As an example a room that measures 40 ft. wide by 60 ft. long by 10 ft. high has a cross section of 400 sq. ft. (40 ft. wide x 10 ft. high), the length being unimportant for air flow volume calculations.

By multiplying this cross section by the required speed of the air movement through the room in feet per minute (FPM) a value will result expressed as cubic feet per minute (CFM). In our example room, if airflow of 50 FPM is desired we would multiply the cross section of 400 sq. ft. by the desired flow of 50 FPM to arrive at the fan volume size of 20,000 CFM.

It is now easy to see why we would want to use the 40 ft. dimension of the room as our cross section and not the 60 ft. dimension. Had we decided to move the air across the width of the room instead of down the length, we would have been multiplying the 10 ft. height by 60 ft. with a resulting cross section of 600 sq. ft. and a fan volume requirement of 30,000 CFM, a 50% increase for the same room size.

There are times when the room size is so large that providing dust collection for the entire space is not practical. In these cases there are some alternatives. If the dust generating activities can be grouped in one area, a simple three sided enclosure can be erected around the generating activities consisting of two side walls, a ceiling with lighting (an additional perk to this type of approach) and a dust collection unit in the rear wall. The front is left open with the dust isolation resulting from a relatively high air flow, typically in the 140 to 160 FPM range, flowing into the open front of the enclosure as the dust collection unit is pulling it out through the back wall. While this type of dust isolation requires a higher air flow, which consequently increases the fan volume requirement, the cross section reduction achieved more than off sets the additional air flow requirement. Additionally, the open and well lighted work area is very conducive to worker productivity.

As far as results are concerned, this approach, if sized properly, is 100% effective with absolutely no escape of transient dust into the adjoining work areas. We refer to these enclosures as Contamination Control Booths or CCB’s. They are typically fabricated of light sheet metal and can be quickly set up. A typical interior height would be 8 ft. but they can be easily fabricated in any size. The result is that now the ventilation requirement is sized based on the cross section of the CCB not the building itself.
As an example, lets assume that the dust generating activities in the room above only took up an area of 20 ft. long by 10 ft. wide and was being generated by hand sanding of product surfaces on individual work tables. A CCB could be erected with floor dimensions of 10 ft. wide by 20 ft. long with an overall height of 8 ft. The cross section to be ventilated is now only 10ft. x 8 ft., or a cross section of only 80 sq. ft. Since the front of this CCB is open we would need to generate an airflow of 140 FPM to provide isolation of the dust inside the CCB, but even at this higher air flow rate, the CFM requirement is now only 11,200 CFM or roughly half the amount needed to accomplish the same task in the entire room.

I. SYSTEM TYPE

Now that we have a handle on sizing the system, the next question is; what type of system will be the most cost effective for a given operation? There are two variables which ultimately determine the cost of any dust collection system.

1. How much air volume is required?

2. How much energy (horsepower) will it take to achieve it?

The first step is to do everything possible to minimize the volume of air required to control the dust. This is where the grouping and, perhaps, the use of CCB type enclosures can dramatically reduce the ultimate cost of the system required. The next step is to configure the dust collection components to minimize the amount of energy required to provide the established air volume.

The cost of horsepower is significant. Assuming an average cost for industrial power is approximately 8 cents per kilowatt hour (KwH) and your facility operates a single shift, 5 days a week for 52 weeks, a 5 HP fan will cost $805 per year to operate. If that fan needs to be 30 HP to provide the same volume because of ducting or other installation considerations, the cost to move the same volume of air will be $4,238. It is easy to see how important it is to understand your particular dust collection problem and find the best way to control it.

Locating the dust collector as close as possible to the area it is filtering is one way to reduce the ducting required and, consequently, the fan horsepower. Ducting produces friction or resistance to flow for any fan system and the only way to overcome that is to use a bigger motor. The more ducting needed for your fan, the more horsepower will be required.

Minimizing the area to be filtered is another great way to reduce fan size requirements. If the entire area can’t be located inside a CCB type enclosure, the use of a dropped ceiling is the best method of greatly reducing the fan volume requirement since it reduces the cross section and therefore the total volume of air required. This is one of the easiest and best value facility modifications you can make to maximize dust collection efficiency and minimize energy consumption.

There are many types of basic and hybrid systems available for removal of air borne contamination, but for the purpose of this paper we will address four of the most common:

1. Simple Exhaust Units

2. Source Point Capture

3. Push-Pull Re-circulating

4. Negative Pressure Re-circulating

II. SYSTEM SIZE

The first question that comes to mind is: What size system is needed? The answer to this can be subjective unless you first establish a few basic parameters by answering the following questions:

1. What is generating the dust?
2. How big is the generating area?
3. Can the generating functions be grouped and/or isolated?

The answers to these questions will help to determine the size and type of equipment needed to do a proper job of collecting air borne contamination in your facility.

Whenever possible, all the dust generating activities should be grouped in one area. This is not always possible, and there are ways to deal with this problem if it exists, but to the extent possible, the most cost effective method of eliminating air borne contamination is to confine it to one area where it can be isolated and filtered using the least possible amount of air.

All air borne contamination is removed by directing it into a controlled air flow generated by a fan. This flow of air will pull the contamination through a filtration system made up of various types of filter media. The filter media type will be determined by the type of contamination involved, but the amount of air is solely determined by the size of the area that is being controlled. The larger the area, the more air required. The actual calculation used to determine the amount of air volume required for a particular application is very simple. The width of the room is multiplied by the height resulting in a room cross section value expressed in sq. ft. As an example a room that measures 40 ft. wide by 60 ft. long by 10 ft. high has a cross section of 400 sq. ft. (40 ft. wide x 10 ft. high), the length being unimportant for air flow volume calculations.

By multiplying this cross section by the required speed of the air movement through the room in feet per minute (FPM) a value will result expressed as cubic feet per minute (CFM). In our example room, if airflow of 50 FPM is desired we would multiply the cross section of 400 sq. ft. by the desired flow of 50 FPM to arrive at the fan volume size of 20,000 CFM.

It is now easy to see why we would want to use the 40 ft. dimension of the room as our cross section and not the 60 ft. dimension. Had we decided to move the air across the width of the room instead of down the length, we would have been multiplying the 10 ft. height by 60 ft. with a resulting cross section of 600 sq. ft. and a fan volume requirement of 30,000 CFM, a 50% increase for the same room size.

There are times when the room size is so large that providing dust collection for the entire space is not practical. In these cases there are some alternatives. If the dust generating activities can be grouped in one area, a simple three sided enclosure can be erected around the generating activities consisting of two side walls, a ceiling with lighting (an additional perk to this type of approach) and a dust collection unit in the rear wall. The front is left open with the dust isolation resulting from a relatively high air flow, typically in the 140 to 160 FPM range, flowing into the open front of the enclosure as the dust collection unit is pulling it out through the back wall. While this type of dust isolation requires a higher air flow, which consequently increases the fan volume requirement, the cross section reduction achieved more than off sets the additional air flow requirement. Additionally, the open and well lighted work area is very conducive to worker productivity.

As far as results are concerned, this approach, if sized properly, is 100% effective with absolutely no escape of transient dust into the adjoining work areas. We refer to these enclosures as Contamination Control Booths or CCB’s. They are typically fabricated of light sheet metal and can be quickly set up. A typical interior height would be 8 ft. but they can be easily fabricated in any size. The result is that now the ventilation requirement is sized based on the cross section of the CCB not the building itself.

As an example, lets assume that the dust generating activities in the room above only took up an area of 20 ft. long by 10 ft. wide and was being generated by hand sanding of product surfaces on individual work tables. A CCB could be erected with floor dimensions of 10 ft. wide by 20 ft. long with an overall height of 8 ft. The cross section to be ventilated is now only 10ft. x 8 ft., or a cross section of only 80 sq. ft. Since the front of this CCB is open we would need to generate an airflow of 140 FPM to provide isolation of the dust inside the CCB, but even at this higher air flow rate, the CFM requirement is now only 11,200 CFM or roughly half the amount needed to accomplish the same task in the entire room.

III. SYSTEM TYPE

Now that we have a handle on sizing the system, the next question is; what type of system will be the most cost effective for a given operation? There are two variables which ultimately determine the cost of any dust collection system.

1. How much air volume is required?
2. How much energy (horsepower) will it take to achieve it?

The first step is to do everything possible to minimize the volume of air required to control the dust. This is where the grouping and, perhaps, the use of CCB type enclosures can dramatically reduce the ultimate cost of the system required. The next step is to configure the dust collection components to minimize the amount of energy required to provide the established air volume.

The cost of horsepower is significant. Assuming an average cost for industrial power is approximately 8 cents per kilowatt hour (KwH) and your facility operates a single shift, 5 days a week for 52 weeks, a 5 HP fan will cost $805 per year to operate. If that fan needs to be 30 HP to provide the same volume because of ducting or other installation considerations, the cost to move the same volume of air will be $4,238. It is easy to see how important it is to understand your particular dust collection problem and find the best way to control it.

Locating the dust collector as close as possible to the area it is filtering is one way to reduce the ducting required and, consequently, the fan horsepower. Ducting produces friction or resistance to flow for any fan system and the only way to overcome that is to use a bigger motor. The more ducting needed for your fan, the more horsepower will be required.

Minimizing the area to be filtered is another great way to reduce fan size requirements. If the entire area can’t be located inside a CCB type enclosure, the use of a dropped ceiling is the best method of greatly reducing the fan volume requirement since it reduces the cross section and therefore the total volume of air required. This is one of the easiest and best value facility modifications you can make to maximize dust collection efficiency and minimize energy consumption.
There are many types of basic and hybrid systems available for removal of air borne contamination, but for the purpose of this paper we will address four of the most common:

1. Simple Exhaust Units
2. Source Point Capture
3. Push-Pull Re-circulating
4. Negative Pressure Re-circulating

SIMPLE EXHAUST SYSTEM

Simple Exhaust Unit: The simplest and by far the least expensive, from an equipment standpoint, is a simple exhaust system. This type of system provides only the very lowest of filtration efficiencies if it provides any at all and is not a viable option in many parts of the Country due to State and Federal air pollution regulations. When it is a viable option, its use will be restricted to those applications where only a small amount of non-listed dust is generated and only in areas where the exhausted contamination will not affect surrounding neighbors. These types of situations are very rare. This type of collection only makes use of very course filtration media and is utilized more for air movement in the workplace than actual dust collection. The course nature of the filtration media, if any is used at all, results in the ability to generate relatively high CFM volumes with very low horsepower, but the lack of proper filtration leaves the operator open to possible litigation if other than non-restricted dust is passed through the system. The fact that the equipment is relatively low cost is usually negated by the fact that this type of system must exhaust all the air outside the building, resulting in loss of heated or cooled air. Exacerbating this situation is the further fact that the air exhausted must be replaced from outside air which must then again be heated or cooled. This type of system has limited applications and is not recommended as a method for serious consideration but is only mentioned for the purpose of explanation.

SOURCE POINT CAPTURE SYSTEM

Source Point Capture: A very common type of dust collection uses what is termed source point capture. This type of system can take several forms, but usually consists of a central dust collection unit which is connected through a series of ducting to various remote locations. The ducting can be attached to stationary dust generating equipment such as saws, grinders, routers or mills or it can simply be connected to a collection hood mounted on a work table. The dust generating point on a piece of equipment is usually enclosed by some form of hood which connects to the duct. As the machine operates and dust is generated, the dust collector pulls air through the hood, capturing the dust before it can be dispersed into the air around the equipment. It then filters the dust and exhausts the filtered air, either back into the workspace or outside the building depending on the installation type.

When this type of system is connected to a hood on a work table, a worker will generally be performing some type of hand work in front of the collection hood or capture zone, allowing the contaminate generated to be pulled into the hood and into the dust collector. These are commonly used for such things as soldering or light cleaning of dust generating products. Capture zones, or the area within which the capture velocity exists, is usually very small. A typical capture zone will lose over 90% of its capture velocity within the distance of one conveying duct diameter from the face of the hood. This greatly limits the effectiveness of this type of system, especially when they are utilized for operations where an operator is moving parts back and forth in front of the hood. Once outside the capture zone, dust will simply migrate throughout a room.

A typical effective capture velocity for a soldering operation, where smoke is simply drifting from the tip of the soldering iron, is in the 200 to 300 FPM range. When grinding or sanding however, the contamination is being thrown off the tool head at such a high speed that a capture velocity of up to 2,000 FPM may be required. This greatly increases the volume and, consequently, the size of the fan required to generate this flow. Of even more concern is the resistance to flow this type of system encounters due to the friction of air flow through the ducting. This equates directly to the horsepower required for the fan.

The source point capture system offers advantages for operations where there are many different machines operating in a large space with no way to effectively group and enclose them for effective dust control. While they are not 100% effective, they can greatly reduce the amount of contaminate thrown into the air which, in the case of high speed automated tooling, can be significant. A secondary dust collection system for surrounding air is generally also required but can be significantly reduced in size with volumes calculated on air changes in a room per hour rather than on air flow velocities in FPM.

Another form of source point capture system is known as a down draft table. In this system, the dust collector and inlet hood are built into the work table with the table top being the inlet hood opening. The table is usually covered with a grating or mesh material which allows the air to be pulled through the table surface where it is directed into the filter system with the filtered air being exhausted back into the work area.

Down draft tables, while very effective for operations such as soldering or light sanding, are not commonly used for heavy grinding or sanding operations. This is due to the need for relatively high capture velocities or the velocity of the air as it enters the capture hood or table top opening, when dealing with grinding or sanding operations. A down draft table system can be very effective for a variety of applications but, as with other types of source point capture systems, it will not capture 100% of the transient dust. If the purpose is to significantly reduce air borne dust contamination they will be of value but if absolute control is necessary this type of system will require a secondary dust collection system to collect dust which will inevitably escape the table capture zone.

Re-Circulating:

The most cost effective dust collection system for areas that can be enclosed is what is known as a re-circulating system. In this type of system the dust collector, whether located outside the building or inside, will pull air from a work area into an inlet device where the air will then be directed through filter media. The contamination will be trapped in the filter media and the clean air will be exhausted back into the work area. This results in no pressure balance issues within the room and does not result in the loss of heated or cooled air. The contaminated air is simply circulated through a filter system and then back into the room. The re-circulating method of dust collection generally take one of two forms:

PUSH-PULL RE-CIRCULATING

Push-Pull:  A method where the air is pulled into the dust collector at one end of a room or enclosure and the filtered air is channeled through ducting to the far end of the room or enclosure where it is then exhausted.  This results in a Push Pull effect since the air is being pushed by the clean exhausted air toward the dust collector inlet while it is at the same time being pulled out of the work area and through the filters.  This type of system is best suited to large rooms where it is not cost effective to erect smaller enclosures or CCB’s  and the room size makes it un-economical to ventilate in its entirety.  Let’s use for an example a large room with dimensions of 200 ft. long by 100 ft. wide and a ceiling height of 25 ft.  Let’s further state postulate that a conveyer system is moving parts along a route and at various points some activity is taking place that will create some sort of air borne contamination.  While the contamination may not be heavy in any one location, if left uncontrolled a dust film would soon form over everything in the building.  In this situation the most economically solution might be to try to keep the contamination in the air until such time as it eventually drifts into the capture zone of one the dust collectors space along one wall.  The exhausts from these dust collectors is ducted to the far side of the building where the exhaust streams will essentially blow the contaminated air toward the back wall where the dust collectors are located.  While this is not a strictly controlled air flow, it would be quite effective and, assuming the total dust load is not too great, it will prove to me much more economical than attempting to move the air across this distance at a velocity that would ensure capture without the push effect.