Thursday, May 24, 2007

Maintain Those Air Compressors And Air Dryers

With the cost to purchase new drilling and routing machines at hundreds of thousands of dollars, it makes economical sense to provide oil free, and dry air to the equipment.

With the new synthetic oils being used to lubricate the internal mechanical parts of compressor systems today, many overlook the fact that these oils that help compressors run efficiently are the same oils that contaminate and destroy the rubber "O" rings, seals, and solenoids used throughout the entire manufacturing facility when compressors are not functioning at top performance. Many times, years later, equipment that has been run with contaminated compressed air will have a life long list of problems that seems to never go away.

"O" rings and seals are not the only items that can become damaged with poor air quality. The air hoses themselves can become rotten from the inside out. Many of the synthetic oils actually breakdown the rubber hoses to the point where they become super soft in which blowouts are common. These blowouts can occur in the most difficult to reach areas on a machine and can cost the owner thousands of dollars to repair.

Contaminated air can also affect the surfaces of the machines. Many of the drilling and routing machines function with the moving parts floating on a very thin cushion of air. The X Y tables float on air bearings, very similar to how an air hockey puck floats on an air table. The table on many of the PCB drilling and routing machines are made of solid granite, with air shoes mounted on the carriage or overheads. Micro-holes are drilled into the air shoes to allow the air to come out in a small stream, causing the air bearing or air shoe to float away and lift from the surface at a fraction of an inch lift. This type of lift provides very little resistance, and allows the machines to quickly accelerate and operate at very high inches per minute surface feed rates. As little as ten years ago the maximum feed rate speed for the machine movements was 400 inches per minute. Now, it is not unusual to be moving the X Y tables at over 2000 I.P.M. With that type of high velocity movements, air shoes that are contaminated by poor air will result in a very expensive mechanical crash that can destroy both the air bearing and the granite surfaces. In extreme cases, air contamination has resulted in an early death of cnc PCB machines. In the best of cases, where problems are spotted early enough, granite repairs are required to fix the machine surfaces. If the air shoe is only replaced, and the surfaces are not repaired, the new air shoe will fail quickly, because of lack of lift over the damaged areas.

Oil in the air is not the only problem that can have devastating affects to facility equipment. Water is the other contaminate that is not good for any of the equipment. We can't tell you how many times we have seen compressor people come out to work on the compressors, but haven't a clue about the air dryers. First off, an air dryer works on the chilling down of the air to a dew point. It's at this dew point that the water in the air condenses, and turns from a gas to a liquid. If an air dryer is not chilling the air, then the water does not condense at the dryer, but condenses in the air lines leading to the machines and in the machines. Here is a very easy test that anyone can do to quickly determine if an air dryer appears to be functioning properly. Simply feel the incoming air line at the dryer and then feel the outgoing line at the dryer. The outgoing air should be significantly colder than the incoming. If both the incoming and outgoing are the same temperature, it is likely that the air dryer is not function properly. Potential reasons are that the freon compressor system is not working or the cooling fans are faulty.

The following is an example of the amount of moisture content of saturated air.
1000 Cu, ft. of saturated compressed air at 100 psi and 120° F. contains 10.9 fluid ounces of water in the form of water vapor. This same quantity of air when cooled to 60° F. at 100 psi contains 1.58 fluid ounces of water vapor. The difference between the two figures, or 9.32 fluid ounces, is released from the air in the form of liquid water and must be removed from the system with a suitable filter to prevent its passage into air tools, bearings, cylinders or other pneumatically serviced devices. The quantity of water which must be removed from the compressed air system is directly proportional to the amount of compressed air passing through the system. Therefore, in a system supplying 500 cfm, the quantity of liquid water to be removed would be 500/1000 x 9.32 or 4.66 fluid ounces per minute. If the system handled 500 cfh, the quantity of moisture to be removed would be 4.66 fluid ounces per hour.

Lack of proper air pressure and volume can also affect the machines. Many customers over the years have had misconceptions of what the actual air pressure and air flow (measured in scfm) are required in printed circuit board, CNC machining, manufacturing, and fabrication production facilities. Instead of viewing the pressure at the machines, customers are making the mistake of only monitoring the pressure at the compressor itself. There are significant line losses to contend with. Depending on the pipe diameter, it is not unusual to see a change of 5 to 10% air pressure reduction per 100 feet of straight pipe. Add to that, 90 degree and 45 degree elbows, valves, filters, and air dryers, the loss of pressure and flow volume can be even more pronounced. Additionally, the maximum amount of flow through any pipe size is topped out at a certain pressure. This means that a pipe that is too small can only handle a certain amount of flow volume. If you have three machines in your drill room that use 30 SCFM each, and only have a 3/4 inch air line from the compressor to the drill room supplying 100 lbs pressure, the maximum flow volume is only 80 SCFM through the pipe. Add to this the loss of 5 to 10% from the pipe and fittings and you can quickly see that you will not have the volume and pressure to maintain the operation of your equipment. Refer to chart below. Click to expand and open in new window.

Air Pressure Chart
With new equipment being able to drill smaller holes, at higher RPMs, with tighter tolerances, and using air bearing spindles, the quality and quantity of the air supply will be of paramount importance for keeping those machines running for a long time in the future. Protect your equipment investments and invest in a quality, dry, oil free, compressor system today.

If you need help with down machines, preventative maintenance programs, and equipment analysis give us a call today. We are available to travel anywhere in the world.

Contact Probe Industries today.

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