Conventional Trim Systems
Overhead ductwork systems designed to capture and remove trim, paper scrap and dust have been used for many decades in the box and carton industries. While many of the components of these systems look like they did 30 years ago, the 1990s have rediscovered their importance. Concerns about the environment, recycling, and occupational health and safety have forced plant managers to view these systems as vital and necessary element of their plant operations.
Paper Trim (Scrap) Rotary Valves An alternative method of trim removal that is gaining popularity involves setting the duct in an underground trench. At pick-up points, the trim falls from the diecutter onto the top of the rotating vanes of a rotary valve. The valve rotor is set below grade but above the top of the underground duct. Providing the differential pressure seal is a Neoprene wiper tip running along the entire length of the edge of each blade. The rotation of the rotary valve (usually 9 to 12 rpm) allows the trim to settle between the blades and fall into the underground duct.
A paper trim rotary valve is similar to a material-handling rotary valve (or airlock) found beneath screw conveyors and baghouses. On an airlock the seal provided by the edges of the rotating blades (or wipers) allows materials to fall through the unit without experiencing blowback from the higher pressure area below the airlock outlet. A paper scrap valve operates on the same principle allowing trim to fall from the plant floor into a higher pressure underground conveying line. The main difference lies in the shape. Unlike airlocks, paper scrap valve inlets and outlets are much more rectangular than square because of the length of the rotor is elongated to span the entire length of its diecutter (often 8 feet or more). The widths of the trench and paper scarp vale (usually 24 to 30 inches) are made to accommodate the diameter of the underground duct (usually 16 to 18 inches).
As many as five or six diecutters can be placed in series to feed the same underground trench. Paper scrap rotary valves also can be designed to feed two parallel underground lines for grade separation. A clockwise rotation of the valve would feed one line, while a counterclockwise rotation would drop trim into the other line.
The underground rotary valve concept might be less feasible with existing plants if new underground trenches must be constructed, heavy diecutters must be relocated, and concrete removed and redone. It is more likely to be included in the drawings for new facilities where it can be considered in the initial plant design and layout.
A tremendous advantage of the valves is that they use only a small amount of conditioned air from the plant as trim falls into the rotary valves. The valves are gravity feed, not suction feed as is the case of a conventional overhead duct system. The air needed to convey the material in the underground duct can be completely taken from outside and retuned to outside. The result may be noticeable energy savings for some high-altitude locations during the winter months.
Cyclones
There are two general types of cyclones: (1) high efficiency, and (2) low pressure. High efficiency cyclones are tall, narrow units with a small diameter to elevation ratio. They are generally used in the woodworking industry and in the grain industry, especially in feed mills on pellet coolers. Low pressure cyclones have a much larger diameter-to-diameter ratio, and they are most often used in paper scrap collection systems where high-efficiency is not an overriding concern. While a pressure loss across a low pressure cyclone averages 1.5 inch water column, a high-efficiency cyclone may lose as much as 5 inch water column.
Balers
Balers are usually located directly underneath a low-pressure cyclone. They are necessary for collecting, compressing and creating manageable bales of recyclable paper scrap.
Baghouses
A baghouse is a dust collection devices that filter air by passing it through a cloth or synthetic fiber media (or bag). A bag is a long cylinder-shaped envelope that collects dust on its exposed surface. Baghouses differ not by the method by which dust is removed from the airstream but rather by the method by which dust is removed from the bag.
If used in conjunction with a cyclone, a baghouse is used as an after filter and located downstream. Baghouses are necessary for air filtration, not scrap collection. Unlike the cyclone, the fine paper dust collected from a baghouse has no value in recycling. Baghouses are necessary where moderate to stringent emission control measures are in place. In addition to its environmental value, a baghouse may reduce winter heat loss if conditioned air is passed through the baghouse and recirculated back into the facility. Unlike a cyclone, a baghouse can support the cleaning efficiency necessary to direct its outlet air back into the plant.
Baghouse Types
Baghouses are identified by their method of self-cleaning. A reverse-air baghouse blows air backwards through the bags from the clean-air (plenum) section of the unit. This unit requires a three-phase electrical supply to operate its reverse air blower and the blower outlet turning arm mechanism.
By contrast, a compressed-air (or pulse-jet) baghouse requires not only a single phase 120 VAC supply for the electrical sequence timer operation but also a supply of clean, dry compressed air (usually 90-100 psig). This timer controls the operation of a series of solenoid valves that regulate the access of compressed air to the baghouse. A quick pulse of compressed air sends a rippling shock wave traveling down the length of the bag.
A third type of baghouse is the shaker. This involves a framework of cam mechanisms, seated in the top of the unit. The shaking action may be either manual or motor operated.
Determining the type of baghouse from its trade name may prove difficult since not all manufactures share exactly the same terminology. Furthermore, some baghouses may use a combination of two cleaning methods. Some end-users will prefer only one type of baghouse; others may have preferences governed only by economics.
The purpose of all of the above self-cleaning methods is to loosen excessive dust from the outside of the bags. The dust particles are then free to fall toward the bottom of the baghouse into a hopper or drum. Dust buildup in a hopper can be removed by either a rotary valve (airlock) or a screw conveyor.
Baghouse Selection
Given an air capacity, a baghouse often may be selected based on a set air-to-cloth ratio. The air-to-cloth is not actually a dimensionless "ratio". In the U.S. system of units it equals the average filtration velocity (feet per minute or fpm) which is the system capacity (cubic feet per minute or cfm) divided by the cloth area (square feet). Although air-to-cloth ratio standards differ from user to user, their usual range is from 5:1 to 10:1, with 8:1 as the most common.
Although the air-to-cloth ratio is an essential design parameter, it is not more important that a manageable interstitial velocity. The interstitial velocity is the velocity of the unfiltered air traveling upward in between the bags. This velocity is greatest near the base of the bags, before any air is absorbed through the media. The maximum interstitial velocity can be calculated by dividing the cfm filter capacity by the horizontal cross sectional area of the unit, counting only the area outside of the bags. If this value is too large (over 400 fpm), it will prevent dust from falling below the elevation of the baghouse air inlet. The dust particles that have been blown (or pulsed) away from the dust layer on the bags will become entrained in the upward moving airstream and forced back toward the surface of the bags. Fine paper dust is especially susceptible to this, even at low interstitial velocities (over 200 fpm).
Baghouse Bag Types
Most fabric dust collectors in the paper industry are equipped with either 12 ounce or 16 ounce, singed polyester, non-woven (felt) bags. The weight of the filter media (12 ounce versus 16 ounce) is based upon one square yard of clean fabric. The slightly heavier 16 ounce media is preferred by customers who launder their bags often. Although a 16 ounce media is more durable that a 12 ounce media, it is not necessarily more efficient. Singed polyester is good for all grain, paper, woodworking and most medium-temperature non-toxic duct environments. For heavily acidic or alkali dusts, PTFE (Teflon®) or polypropylene bags should be considered. An upper temperature limit for singed polyester media is 275 degrees F for continuous operation and 300 degrees F surge (for only brief periods of use).
Although they are used to a much lesser extent that singed polyester, a pare-pleated bag has an advantage over a conventional flat-surfaced polyester bag since it and squeeze more filter media area in the same volume. However, price works to its disadvantage. A paper-pleated bag may cost more than 10 times that of a polyester bag of the same diameter and length, while providing only four to five times the filtering area.
Baghouse Efficiency
The efficiency of any baghouse depends much more on the dust-loading conditions that the weight of the filter media. Laboratory test performed on either 12 or 16 ounce singed polyester bags usually result in an efficiency of 99.9% (by weight) when silica dust was used as the containment. A standard silica test would be conducted within the following parameters: A. The incoming airstream has a dust concentration that does not exceed 10 grains per dry standard cubic foot of air. (7000 grains = 1 lb.) B. The median dust particle diameter is 0.6 microns, and the particle size distribution is such that 50% of the particles were 0.5 microns or less (1,000,000 microns = 1 meter) C. The average filtration velocity (or air-to-cloth ratio) is no greater than 5 fpm.
Some filtering applications are designed to fall within the above guidelines. However, because of either spacial or economic constraints, a baghouse large enough to hold the filtration velocity below 5 fpm may not be available. As a result, a majority of actual filtration velocities climb into the 8 to 9 fpm range. According to some bag manufactures, operating the baghouse in this range will diminish the efficiency slightly, but not below 99.7%. Other factors may further hinder bag efficiency, such as torn bags resulting from improper bag installation as well as poorly designed or partially blocked baghouse air inlets.
Assuming that the incoming dust concentration does not exceed 10 grains/cu.ft., a 99.7% efficient filter would allow no more that (10)(1-0.997) or 0.03 grains/cu.ft. of dust concentration in the outlet stream. A 99.9% efficient filter would allow no more that (10)(1-0.999) or 0.01 grains/cu.ft. through the outlet.
The concentration and median particle size of dust generated by the product that becomes trapped in the incoming air stream depends on many factors. Some of these factors include the type and density of the product, the method of conveying the product, the moisture content of the product, and the amount of entrained air in the product. This dust concentration may vary from as little as 2 grains/cu.ft. in metalworking facilities to more than 15 grains/cu.ft. in some woodworking operations. There is no substitute for actual on-site testing if this number is critical to obtaining an air permit. Without knowing the incoming air dust concentration, the outlet dust concentration cannot be approximated with any reliable accuracy.
Baghouse Pressure Drop
The pressure differential (or pressure drop) across the bags is most easily measured by taking the pressure difference across the tube sheet. This is possible because all of the air inside the bags is at the same pressure as the air in the clean-air plenum above the tube sheet.
A newly installed baghouse will initially show a pressure drop of only 0.5 to 1.5-inch water column. This pressure differential will slowly and steadily increase to level at about 3-inch water column after one to two months. A properly functioning self-cleaning baghouse will not allow this pressure differential to continue to increase much beyond this point. Usually the baghouse pressure drop will range from a minimum of 3-inch to a maximum of 5-inch, averaging 4-inch water column. A pressure drop of over five usually indicates that the bag are blinded. This occurs when dust particles have so thoroughly saturated every microscopic void between the bag fibers that airflow is noticeably restricted. This is most often caused by a high air-to-cloth ratio (or filtration velocity).
Baghouse pressure differentials are not necessarily a direct indication of filter efficiency. The building up of a dust cake on the exterior surface of the bags may actually increase efficiency, but too thick of a layer will diminish the ability of the bags to handle their designed quantity of air.
Bag Life Expectancy
Depending on whether a baghouse operates under a continuous or intermediate duty cycle, the average life expectancy of a 12 ounce or 16 ounce singed polyester bag ranges from four to eight years. While some companies may to elect to replace bags every year or every other year, a bag typically should not show any noticeable decline in efficiency until after at least three years. Improper laundering, high-filtration velocities (over 12 fpm), high temperatures (over 120 degrees F), continuous saturation under high humidity, or a combination of these adverse factors may abbreviate bag life. On the other hand, nags that show little or no wear after ten years should indicate to the user that perhaps the baghouse was initially oversized for the system; therefore, neither the bag nor the baghouse was ever used to develop its fullest potential.
Advancements,Biotechnology,Cell Phones,Communication,Electronics,Gadgets and Gizmos,GPS,Information Technology ,Video Conferencing ,VoIP
Thursday, November 13, 2008
A Short History of VoIP
Voice over Internet Protocol, or VoIP, has only been around for a relatively short period of time when you look at the big picture of human history. In the roughly six thousand or so years of recorded history, VoIP has only been around for a very short time, a small blip or dot in the timeline of man. That said, in the time it's been around, it has grown by leaps and bounds.
The beginnings of VoIP can be found with the introduction of the telegraph and the first telephones - that desire to be able to communicate over vast distances easily, cheaply, and in real time. When Alexander Graham Bell invented the telephone in 1876, he started a ball rolling, a ball of information that would build up over the years.
For many years after the invention of the telephone, use skyrocketed and phones became commonplace and found in everyone's homes. During these initial decades, though, the technology progressed slowly. Slow evolution is still evolution, though.
By the mid 20th century, man was becoming good at transmitting all sorts of data over wires and eventually wireless toward the close of the century. Also during this time, computers became smaller and more powerful, allowing the transmission of data, of ones and zeros, to be able to be translated into other things - like a voice.
The first VoIP devices were found back in 1995, when the Internet was still a long way off from what it is today (and what it's going to become when it eventually reaches its potential.) Even in those early days, though, a lot of people became early adopters because they believed in the technology and could see the benefits would only increase as time went on.
At this point, things really began to move. As it was shown that there was a market for VoIP technology, a lot of people entered the game and started offering service - real time communication via the same "wire" that feeds your Internet connection. And with a lot of people entering the ring, competition led to innovation - smaller devices, better reception, more features, and even a lower price.
All of these things will drive more and more people to look into VoIP and how it can help better their lives. And that will only keep the ball rolling with innovations and improvements to VoIP. And if the cycle does continue for even a generation or two, there's no telling where the technology might lead.
However far it goes in innovation, VoIP is bound to play a bigger role in more people's lives as time progresses. It's not a perfect technology or one that will solve all the world's problems, but it's something that can help you in a lot of different and positive ways.
The beginnings of VoIP can be found with the introduction of the telegraph and the first telephones - that desire to be able to communicate over vast distances easily, cheaply, and in real time. When Alexander Graham Bell invented the telephone in 1876, he started a ball rolling, a ball of information that would build up over the years.
For many years after the invention of the telephone, use skyrocketed and phones became commonplace and found in everyone's homes. During these initial decades, though, the technology progressed slowly. Slow evolution is still evolution, though.
By the mid 20th century, man was becoming good at transmitting all sorts of data over wires and eventually wireless toward the close of the century. Also during this time, computers became smaller and more powerful, allowing the transmission of data, of ones and zeros, to be able to be translated into other things - like a voice.
The first VoIP devices were found back in 1995, when the Internet was still a long way off from what it is today (and what it's going to become when it eventually reaches its potential.) Even in those early days, though, a lot of people became early adopters because they believed in the technology and could see the benefits would only increase as time went on.
At this point, things really began to move. As it was shown that there was a market for VoIP technology, a lot of people entered the game and started offering service - real time communication via the same "wire" that feeds your Internet connection. And with a lot of people entering the ring, competition led to innovation - smaller devices, better reception, more features, and even a lower price.
All of these things will drive more and more people to look into VoIP and how it can help better their lives. And that will only keep the ball rolling with innovations and improvements to VoIP. And if the cycle does continue for even a generation or two, there's no telling where the technology might lead.
However far it goes in innovation, VoIP is bound to play a bigger role in more people's lives as time progresses. It's not a perfect technology or one that will solve all the world's problems, but it's something that can help you in a lot of different and positive ways.
Precision Tone Generators Inside Look
In our latest article on tone generators, we've hit the mack daddy of them all. The Precision Tone Generator made by none other than the good old folks at Greenlee are one of the best at what it does. This particular tone generator packs a wallop and it has no shame in showing why it's on of the best of its kind. This is one of the high end tone generators on the market and in the arsenal of Greenlee. So what exactly makes it tick? Worry not dear reader we have all that information loaded up for you and we're going to let you in on the what the whole buzz regarding The Precision Tone Generator is about.
For the longest time we know how good Greenlee's tone generators our and the precision model was no different. There's no doubt that for those that have the extra money and are serious about having the most efficient piece of machinery possible then The Precision Tone Generator is something that you just can't afford to be without. This tone generator boasts some of the most powerful features on the market today and let's not keep you in suspense anymore let's let you in on what this tone generator exactly offers.
Its power requirements include a 6V lantern battery which will normally last you forty hours. The frequency on its transmitter is pulsed at 1Hz and it runs up to 577.5Hz it's also crystal controlled. It reaches 0.1 to 80Vp-p level of output voltage. Its output signal level reaches 0 to +30dBm. The precision tone generator is made out of a very strong ABS plastic and it comes with a case made out of woven polyester. The unit itself weight in around three pounds after adding in the battery.
Now what are its exact capabilities? Well, you are about to find out dear reader, let's hop right to that. It's adjustable level of output lets users tweak the strength of the signal so it'll adapt to certain circumstances and allow for the best possible efficiency.
It's intended to be compatible with any ordinary device such as common amplifiers and exploring coils. Each of its different test leads which total in at three comes with bent nose piercing clips and piercing pins that will insulate. In the telecom business this device is best used for determining pairings and fault locating. Greenlee also throws in a one year warranty with the item.
Well that pretty much tells you how awesome of a device this is. Greenlee as always stays confident in their product and guarantee the absolute best to their customers. You can't ask for much more in a piece of machinery can you? This one year warranty is best explained by Greenlee themselves so we'll leave that part to them but we definitely feel we had to let you in on its existence.
After all what kind of people would we be if we didn't? So dear reader there's the plain and simple on the Precision Tone Generator from Greenlee and we have to say that if that's what you're looking for you can't go wrong. It has many features that will assist you greatly in the work environment and even after the first use the item will definitely pay for itself.
For the longest time we know how good Greenlee's tone generators our and the precision model was no different. There's no doubt that for those that have the extra money and are serious about having the most efficient piece of machinery possible then The Precision Tone Generator is something that you just can't afford to be without. This tone generator boasts some of the most powerful features on the market today and let's not keep you in suspense anymore let's let you in on what this tone generator exactly offers.
Its power requirements include a 6V lantern battery which will normally last you forty hours. The frequency on its transmitter is pulsed at 1Hz and it runs up to 577.5Hz it's also crystal controlled. It reaches 0.1 to 80Vp-p level of output voltage. Its output signal level reaches 0 to +30dBm. The precision tone generator is made out of a very strong ABS plastic and it comes with a case made out of woven polyester. The unit itself weight in around three pounds after adding in the battery.
Now what are its exact capabilities? Well, you are about to find out dear reader, let's hop right to that. It's adjustable level of output lets users tweak the strength of the signal so it'll adapt to certain circumstances and allow for the best possible efficiency.
It's intended to be compatible with any ordinary device such as common amplifiers and exploring coils. Each of its different test leads which total in at three comes with bent nose piercing clips and piercing pins that will insulate. In the telecom business this device is best used for determining pairings and fault locating. Greenlee also throws in a one year warranty with the item.
Well that pretty much tells you how awesome of a device this is. Greenlee as always stays confident in their product and guarantee the absolute best to their customers. You can't ask for much more in a piece of machinery can you? This one year warranty is best explained by Greenlee themselves so we'll leave that part to them but we definitely feel we had to let you in on its existence.
After all what kind of people would we be if we didn't? So dear reader there's the plain and simple on the Precision Tone Generator from Greenlee and we have to say that if that's what you're looking for you can't go wrong. It has many features that will assist you greatly in the work environment and even after the first use the item will definitely pay for itself.