Media Abrasive

Media Abrasive
volume velocity converted to linear velocity converting. CFM to FPM?

I have a micro abrasive media blaster that uses 1.25 CFM (cubic feet per minute) of 85psi Compressed Air through a nozzle with a .0472" diameter orifice. I need somebody to check my math for the velocity at the nozzle. Let A=area of the orifice, and V=velocity.
(A)in²=Pi(.0236in)²; Then divide by 144 to convert to feet
(A)ft²=(1.2174 x 10e-5)ft², or .000012174ft²
V = 1.25ft³/min x 1/(A)ft²
V = 1.25ft / (A)min
V = 102680 ft/min
This doesn't seem correct. That's over 1160 miles per hour???

You and OilField are both mostly correct.

Compressed air is measured at atmospheric pressure, so at 85psi has much less volume than 1.25ft³. At the pressure side of the orifice, the air has relatively low velocity. As it goes though, it loses pressure and increases velocity. Outside the nozzle, it is back to atmospheric pressure.

You assume the entire pressure drop is across the orifice. This is fine for a first level course, but not entirely representative of what really happens.

Speed of sound is about 760 mph. Unlikely you are over 0.8 times this, due to compressibility effects (speed of sound issue). You are not going to have enough energy in the compressed air to move it to the speed of sound. Thus, speed at center of orifice is probably absolute max of 600 mph, and air is still compressed somewhat when coming through. There is also friction at the orifice that will slow the air near the edge, so the speed across the airstream won't be uniform.

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Sony Introduces High Capacity AIT-5 Data Tape Cartridges

Sony has incorporated the WORM functionality in mid-range backup storage technology. AIT-5 media tape technology is more advantageous than other tape formats as it is more economical and performs multi-functional tasks. Highly durable AIT-5 media tape format supports the WORM tape media and also the rewritable AIT tape cartridges. New durable Sony AIT-5 tape format provides advanced and innovative mechanisms which help the businesses to backup their useful data at a fast rate. Sony has incorporated soft tape loading and automated cleaning technique to its high capacity AIT-5 format that has strengthened its media robustness and efficiency.

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When the data is being read by the AIT-5 tape drive, the position of the MR Head is automatically controlled by the innovative dynamic tracking capability. This new technique introduced in AIT-5 tape media format has helped to heighten the quality of the read-back signals. Data read back recovery and strength is maximized in Sony AIT5 tape technology as the recorded data is automatically tracked by the tape head.

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As the AIT-5 tape drive fills the data cartridge in one pass, therefore this advantageous feature ensures reliable backup storage operations. Media of AIT-5 data tape is based on a highly efficient AME-III technique. AME-III technique assures smooth backup operations, increased efficiency and exceptional areal recording in AIT-5 tape technology. Advanced features have been added to the AME-III technology in which advanced mechanisms have been introduced to apply the magnetic layer along with new highly durable lubricant and media coating layer. Magnetic particle residue has been significantly reduced in AIT-5 tape format by the AME-III technology. Sony AIT-5 tape cartridge features an ultra smooth tape media that produces low noise and increased output characteristics. Minimized spacing loss results in increased output frequency and fast transfer rate. Less abrasive in AIT-5 tape storage technology results in increased head life.

Media blasting is accepted as a means of removing coatings from most any surface. In log home restoration, it works well at removing old stains and finishes to prepare the wood for a new sealer. Like any tool, it has it's place, but sometimes is over used.

 

Media Blasting or Abrasive Blasting is the process of using compressed air to propel abrasive particles from a blast machine or blasting pot, through a hose and onto a surface at a high rate of speed in a way as to remove the existing coating and to be an effective cleaning treatment. Media Blasting for surface preparation removes unwanted coatings and leaves a clean surface ready for re-coating or other types of finishing.

Used in log home restoration, many contractors use it to remove any type of coating, oil or latex or just for cleaning to remove grayed out wood, dirt and mildew. Because of the nature of the process, it is more expensive than the basic chemical strip and requires some specialized equipment. An industrial type Air Compressor capable of producing at least 185 cubic feet per minute of air volume must be used. Some contractors own their own, but most rent one as needed. Also a special "blasting pot" designed to dispense crushed glass, baking soda and ground corn cob media is used. It is similar to a sand blaster, but modified to handle different media. Along with this special equipment, several thousand pounds of the media itself is needed. Three to four thousand pounds in not unusual.

Using Media Blasting for log home restoration does an excellent job of removing whatever is on the logs, however it is really best suited for the harder to remove water based and latex stains and paints. Chemical stripping on the other hand is best suited for oil based stains which is 75% of what is used on log homes in this area.

 

Media Blasting has it's advantages. The biggest being that it is a dry process. When the finish or coating is removed, the stain can be applied immediately. There is no waiting for the logs to dry as with chemical stripping, and no water to contend with inside the home from leaks. Also, the used media can be gathered up, sifted and reused. Once spent, it can be bagged and disposed of or, being biodegradable, it can be spread out and used as a soil amendment.

 

The actual blasting is a fairly fast process once everything is set up and staging and scaffolding is in place. Usually two people can handle the work; one operating the nozzle and one filling the hopper, adjusting air/media mixtures and watching that the machinery and hoses are in good working order and running properly.

 

There are also disadvantages with media blasting. There is more expense involved compared to chemical stripping due to the cost of the blasting pot, compressor rental, the media itself and the large amount that is needed. Also, walk boards, scaffolding and staging are needed where as with chemical stripping, ladders will usually suffice. And although a dry process, it does create massive amounts of heavy dust. This dust gets into anything and everything nearby.

During a log home restoration using chemical stripping, water can get inside the house from between the logs, around the corners and ceilings and other areas you might not expect. Anywhere the water can get in, so can media dust. Unlike water that will trickle through and can easily be wiped up, media dust on the other hand creeps in and can circulate throughout the house covering everything. If you have a good contractor, they will usually line the exterior walls with plastic which helps, but depending on how good of a seal is used, some dust will find it's way onto the kitchen table, cabinets, furniture and any other horizontal surfaces.

 

Another disadvantage is the profile left on the logs. This profile is created when the media hits the grain of the wood. The grain has soft and hard spots, and the softer spots will be removed deeper than the harder spots leaving a profile in the wood. This may or may not be an issue depending on the finish used, the number of coats applied and the look that is wanted. Depending on the wood species and the media blast operator, some grooves created in the logs may have to be sanded out. Be sure to discuss this with your contractor before your log home restoration begins so there will be no surprises after the coating is removed and there are logs left with a deep profile you did not expect to see.

Finally, maybe the biggest disadvantage of media blasting is the fact that it is being used when it may not be needed at all. Log home owners are paying for something they don't need. If your log home has the typical linseed oil based stain on it, media blasting is not needed. A chemical strip will work fine, cost less and much easier to clean up. Media blasting is needed only for latex stains and paints and only necessary on the toughest intact oil/alkyd based stains.

So when it is time to begin your log home restoration, do your homework. Make sure you are aware of what is needed and what is not. It not only could save you some time on the project, it could also save you money, money that could be used on other projects.

Glass media blasting