Share

The Importance of Clean Compressed Air in CNC Machine Shops

For the proper functioning of machine tools, manufacturing companies must implement a compressed air system with an air dryer. Each time an automated tool change takes place, the tool holder shank and the spindle taper are exposed to oil, dirt, chips and other contaminants that are produced during the cutting process. This cleaning process can only be achieved with dry air. The importance of air in CNC Machining entails activating the tool-change mechanism, transporting oil to the spindle bearing, and blowing away chips and contaminants from tools and parts.

For the proper maintenance of machines, it is key that particles produced during cutting do not stick to those exposed surfaces which can reduce machine accuracy and stiffness, and cause permanent damage to the connection. The majority of CNC machine tools use a blast of dry, compressed air to keep exposed surfaces free of debris. When the air is not dry enough, water in the air will condense on the surface causing rust.

 

Relative Humidity in the Shop
As a result of water being present in the air of machine shops through natural humidity, there is water in the compressed air. Many contributing factors determine the amount of water, however, the main contributor is temperature. Warm air holds more moisture than cold air. Generally, the amount of moisture is expressed by the relative humidity (RH); the amount of water in the air compared to the amount of water the air can hold. This can result in complications because the process of developing compressed air changes its temperature.

 

The Compressing process
During the compressing of the air process, heat is formed resulting in releasing air from the compressor that is generally well over 37.8 Celsius. When the air hits a cold surface, for instance, the inside of the compressed air tank and cools, water condenses out of the air as dew. This process can be compared to the wet droplets or “sweat,” which can be seen on the outside of a glass containing a cold beverage, or the fog on a bathroom mirror. The temperature at which the water begins to condense is the dew point.

 

When the air has been compressed to the point of saturation (e.g. 100% relative humidity), the dew point is the same as the air temperature. When less water is found in the air, the relative humidity is lower and the dew point is less than the air temperature. This condensing process is important to note because the point of air drying for machine tools is to rid enough moisture so the dew point of the air will be reduced to considerably less than any temperature the air will encounter during manufacturing.

 

Ways to Remove Moisture
The first step of air drying is to address the compressed air on the inside of the storage tank. The water that condenses during this process is collected at the bottom of the tank, where it should be periodically or automatically drained.

 

Generally, the air will pass through what is called a “separator.” This cylinder-shaped gadget causes the air exiting the tank to spin around in a chamber at high speed. The centrifugal force pushes water droplets, oil and other unwanted particles, down the sides of the chamber, where they gather in the bottom, for regular or automatic drainage. Typically, these steps remove about half of the moisture from the air. For some machines, this process is enough to prevent condensation when the air is used in the machine tool.

 

If necessary, an additional step that can be added to the process is to employ a refrigeration dehumidifier. Here, a separate cooling system, such as a refrigeration system, or chilled water, produces a surface a few degrees above the freezing point of the water. As the air touches this surface, extra moisture condenses out and is collected. This can be compared to the dehumidification process in a residential air conditioner.

Another option of removing water is by utilizing either a membrane air dryer, deliquescent dryer, or desiccant dryer. Each offers a different approach to capture moisture. With a membrane air dryer, the air goes through bundles of hollow, semipermeable tubes. The water vapour can go through the tube walls, but the air cannot. The water is collected on the outside of tube bundles and is released. With a deliquescent dryer, the air goes through a bed consisting of a chemical with an affinity for water, such as salt or calcium chloride. As the air goes through the bed, the chemical dissolves the water vapour and the resulting liquid is released at the bottom of the tank. The chemical must be periodically replenished. Lastly, a desiccant system uses chemicals that are not absorbed, like silica gel that absorbs water on its surface.

Specific Solutions
The materials your machine shop is made out of will dictate the varying degree of moisture problems. Moisture can cause an array of issues and impact the bottom line of a machine shop. Water in metal causes rust, water in walls creates mould, and water in wood causes rotting. Moisture in a machine can damage the compressor, air motors, valve and could contaminate the workpiece.

 

The importance of air in CNC machining with an air compressor and dryer system is the type of preventative maintenance that saves machine shops hundreds of thousands of dollars in repairs or replacement machines. From simple problems with a finished part to a full machine replacement, it is vital to the successful operation of a machine that preventative measures are taken. All machine shops must include an air compressing/drying system to avoid future complications.

You may also like