Compressed air pipes

The impact of compressed air on pneumatic tools and abrasive performance

Figure 1: Two controlled evaluations were conducted on 1018 carbon steel plate to show the direct impact of pneumatic air on abrasive performance.

A compressed air system must be able to deliver adequate air volume in standard increments of cubic feet per minute (SCFM) and maintain the proper operating pressure in pounds per square inch (PSI) to meet any application. compressed air of an installation and its applications. Knowing the proper requirements to optimize the compressed air system is essential to meet all air needs.

There is a common misconception that if the line pressure (PSI) is high, all air requirements will be met. This is wrong – in fact it is a combination of PSI and SCFM. Not only does the size or power of the compressor have an impact, but several other critical factors have a direct effect. These include air receiver tank capacity, main pipe diameter, downpipe diameter to manifold, plug/torque type, inside diameter (ID) and pipe length to the tool, and if the installation has a loop system.

A proper air system is important to provide optimum abrasive performance when using an air tool for grinding or sanding. Air tools need air to operate at maximum efficiency under load, which is 90 PSI with the appropriate SCFM for the tool being used. If one or both criteria are not met, either grind cycle/takt time will increase, removal rates will decrease, or both will occur, resulting in lower performance and higher costs.

To prove that PSI has a direct impact on abrasive performance, two controlled evaluations were conducted on 1018 carbon steel flat using the parameters given in Figure 1. (All images are available in the slideshow.)

The test results in Figure 2 show a significant difference in elimination between air pressures. This is further demonstrated by the sparks visible in picture 3, which are directly correlated to the elimination rate; for example, more sparks indicate a better elimination result. Figure 4 shows the percentage improvements and the percentage difference in savings per PSI, which are significant.

To demonstrate that PSI is not the only factor that directly impacts airflow and abrasive performance, a controlled evaluation was conducted with two different coupler/cap assemblies – maximum flow and standard/taper on a weld in 304 stainless steel using the parameters given in Figure 5.

Three weld removal evaluations were conducted with each type of coupler/plug assembly (full flow and standard/tapered) at 90 PSI/43 SCFM to determine the impact of orifice diameter on cycle time/ takt time The results are presented in Figure 6.

Note that the orifice diameter of the standard/tapered plug is approximately 35+ percent smaller than that of the maximum flow rate, as shown in Picture 7. This difference has a direct impact on tool and abrasive performance, as seen in stainless steel welding (Figure 8) delete ratings. Maximum flow assembly removed the weld in less than half the cycle/takt time.

Providing maximum airflow to the tool optimizes the performance of abrasives on the tool. Depending on the material to be ground, the grit size used and the type of abrasive, the productivity improvement achieved by switching from a standard conical pad to a maximum rate pad can exceed 100%. If you use a standard taper plug, productivity could be reduced by more than 50%.

The following suggestions and recommendations can help maintain peak performance of an air tool and abrasive.

Figure 2: Test results show a significant difference in elimination between air pressures.

Maintain adequate airflow

Prevent and eliminate air supply restrictions
Common causes of restrictions:

  • Air supply hose is too long (>20 feet) or there is more than one coupler.
  • The inside diameter of the pipe is too small for the PSI/SCFM requirements of the tool.
  • Air fittings or fittings have an ID that is too small.
  • Too many connections or air fittings are used.
  • When an inline filter is used, the unit may be too small or the filter element may be clogged.
  • When an in-line regulator is used, the unit may be too small, improperly adjusted, or defective.
  • Air supply hose, air fitting, air tool inlet or air tool exhaust may be clogged.
  • If the pneumatic tool is equipped with a speed regulator, this can be closed.
  • Insufficient air supply or drop line diameter (ID) may be too small for the air tool’s PSI/SCFM requirements.
  • The coupler/plug must have maximum flow to eliminate air restriction to the tool.

Air supply hose

  • Use the air supply hose with the correct ID diameter recommended by the air tool manufacturer.
  • Use the shortest air supply hose possible for the task at hand.
  • Longer air supply hoses (>20 feet) require larger inside diameters to compensate for line pressure drop.
  • Coiled air supply hoses appear much shorter than they actually are. When using coiled tubing, make sure the inside diameter is large enough to compensate for the length (see Figure 9).

Air Tool Startup Checklist

  1. Examine the air tool before attaching the air hose.
    • The air tool should not be used if parts, such as the muffler and guards, are missing; this will cause the tool to malfunction.
  2. Check the air pressure at the regulator/filter if there is one:
    • The tool will not operate efficiently unless the air pressure at the tool is 90 PSI at the proper SCFM when under load.
    • Never operate the tool at a higher PSI than recommended by the manufacturer. This will cause premature wear of the tool and can be dangerous for the operator.
  3. Examine the air hose:
    • If there are any tears or loose connections, the hose should be replaced. if the hose is damaged or broken, serious injury could result.
    • The length of the pipe should be as short as possible and not exceed 20 feet. For every additional 20 feet of hose, the air pressure drops approximately 50%.
    • Do not use a coupler to increase the length of the hose; each coupler equals an additional 15 feet of hose, reducing air pressure and SCFM.
    • When the tool is connected to the air line, check for air leaks in the hose and coupler/plug.

The air supply is critical to tool performance. Without proper PSI and SCFM, the tool will not work effectively.

Information provided by Saint-Gobain Abrasives, Dynabrade Inc. and US Dept. of Energy.

Preventive maintenance of pneumatic tools

Provide a good air supply:

  1. Reduce or eliminate condensation (moisture) from the air supply by using:
    • Water traps and drains
    • After-coolers
    • Refrigerated air dryers
  2. Prevent debris from entering the air motor:
    • Filter the air.
    • Keep air inlet fittings, plugs and couplers clean, free of dust and debris.
    • Keep mufflers and exhaust components in place. The muffler elements provide a barrier that prevents dust from being drawn into the air motor.
    • Do not use compressed air to blow the tool; this could force debris into the bearings.
    • Do not remove mufflers/exhaust elements to use as blow-out tools.
  3. Lubricate the air motor:
    • Use an automatic lubricator to supply the correct weight and amount of air motor oil if the environment permits. If not, manually lubricate the tool (two to three drops throughout the day) directly into the air inlet, for example, at start-up, morning break, lunch, at the afternoon break and at the end of the shift. Note: The entire muffler should be removed during this process so oil does not clog it. This must be done in an enclosed space so that exhaust air does not recirculate through the plant and cause finish problems.
  4. Remove any airflow blockages, inside or out:
    • Keep tool air inlet clear of debris.
    • Clean or replace exhaust muffler components as needed. Never remove or use the tool without one.
  5. Lubricate gears, sleeves, bearings and sliders:
    • Use the lubricant specified by the manufacturer and apply the suggested amount at the recommended interval. Note: This is usually found in technical support documentation, such as tool manuals and parts pages.
  6. Use the tool, accessory or related product as specified by the tool manufacturer:
    • Observe the specified maximum operating air pressure.
    • Observe the specified maximum operating speed for all tools and accessories, such as grinding wheels, mounted points, cut-off wheels, abrasive sanding discs and backing pads.

Information provided by Saint-Gobain Abrasives, Dynabrade Inc. and US Dept. of Energy.

The perfect air hose

  • The ideal inside diameter of the pipe is ⅜”.
  • The air hose should be as short as possible and no longer than 20 feet in length. For every additional 20 feet of hose, the air pressure drops approximately 50%.
  • Never use couplers to extend the length of the hose, each coupler is equivalent to adding 15 feet of hose length.
  • The air hose can be rubber or synthetic, the attributes are:
    • Rubber
    • Synthetic
      • Lightweight
      • Soft
      • Ergonomic
    • Connections on a hose should be full flow couplers and plugs which will eliminate air flow restrictions.

    Information provided by Saint-Gobain Abrasives, Dynabrade Inc. and US Dept. of Energy.