For refrigerated air dryers:

1.      The performance of a refrigerated air dryer are based on an inlet temperature of 100 F and pressure of 100 psig.

2.      The air capacity is rated in scfm as usually the same rating as the compressor.

3.      Both, air and water cooling are available. Water cooled units have a slightly higher rating but, are more expensive.

4.      The normal dew point rating is 35 F. This can be lowered by operating below the rated capacity. The humidity of the surrounding air has to be considered. Humid regions will have a higher dew point air output.

5.      The initial cost to purchase a refrigerated air dryer is lower than for desiccant dryers. The installation cost is simpler and less expensive

6.      The refrigerated air dryer uses large amounts of electricity. This makes the operating costs high

One advantage of refrigerated air dryers is that they can operate at higher inlet temperatures and pressure than desiccant air dryers.. Therefore, for plastic molding machines plus in many food and pharmaceutical applications the refrigerated air dryer is used at the output of piston compressors.

Both, the electrostatic and the centrifugal mist collectors are for small volumes of air ( less than 1000cfm)  With both methods, the vapor particles can drain from the surfaces and as such are well suited for continuous operation. The oil or coolant draining from the collector surfaces can be fed back into the coolant container for re use.

The coalescing filters trap the vapor particles but the drain off is slow. Also, since the air passes through the filter, any dirt particles in the air will get trapped and drained off with the oil. These filters have to be cleaned periodically. These filters are relatively inexpensive and it pays to have multiple filters which can be switched back and forth for easy cleaning. To reuse this oil, it will have to be filtered to remove any particulates.

High speed metal cutting machines use a large amount of cooling fluid to keep the cutting tools from overheating. Most of these cooling fluids are water based, but whether water or oil based the vapors they create have to be drawn from the machine and filtered. The liquid portion can be returned to the cooling fluid container and the air released to the atmosphere.  

Industrial tables usually have a metal grating. It may be aluminum or steel. Often it is coated with plastic or rubbery material. Fiberglass, plastic or wood composites may be available as options.

To trap particulates, cartridge filters are the most common filter media because they are available in different porosities. For low volume activity and hobby use, bag filters may be sufficient. This depends on the volume of particles produced and the acceptable throughput from the filter into the air. Bag filters do not have the removal efficiency of cartridge filters, however, they are easily cleaned for repeated use. For this reason, bag filters are also used, often as pre filters for high volume particle removal.

In industry, downdraft tables are used where grinding and welding produce dangerous fumes. Here the trapping of fumes is equally as important as trapping particles. The same is true for soldering electrical components and wires by hand.

The particles created by the grinding of certain metals such as aluminum can cause fires when left collected in filter media in open air. Tables which draw the metal fines into a water bath are used for this application. The postal service uses downdraft tables to handle material that may be contaminated with chemicals dust or bacteria.

Oil free tank mounted piston compressors come in single phase only. The cooling of the compressor can be with water or air.  

Piston compressors can be single or two phase. In the single phase, models having two cylinders, both cylinders work independently drawing in and releasing the compressed air. In the two phase configuration, the output from one cylinder is fed into the input of the second cylinder giving a higher pressure output, but at a lower capacity. For the two phase compressor the output temperature will be very high and most likely will need an after cooler.

With single phase compressors the maximum pressure is about 70 psig (5 atm). With two phase models the maximum pressure is about 175 psig (12 arm). The air capacity depends on the size of the system.

Capacity FAD is the measure of free air delivery which is the air volume drawn into the compressor and psig is psi gage. Gage pressure is zero at sea level.

Most piston compressors on the market today have two pistons with each one feeding into the compressed gas line or tank. The compressor feeds the compressed gas in short intervals causing pressure pulsation of the compressed gas. With two or more pistons feeding the compressed gas line, the pulsation becomes more of a ripple. It is always recommended that single or double pistons feed the compressed gas into a tank. Depending on the size of the tank, the pressure pulsation will be dampened or eliminated.

The storage tank allows the gas to cool down. The compression creates heat in the gas which should be dissipated. Also, the moisture in the gas drawn into the compressor leaves a high moisture level in the compressed gas. This, plus oil vapors from the compressor lubrication all can be turned to liquid and removed when the air cools down.   

Reciprocating compressors can be single stage, two stage, or multi-stage. Single stage compressors compress the gas using only one cylinder. Two stage compressors have two cylinders and take the compressed gas from the first cylinder and feed it into the second to compress it further. Multi-stage compressors have more than two cylinders in series, with each one taking the compressed gas from the cylinder before it and compressing it further

When specifying a compressor, the output pressure and air capacity are the two main parameters. The pressure rating is in either psi or psig for US built rotary screw compressors. European built models would be rated in atm. For the US, the psig (psi gage) is the pressure above sea level and more accurate reading. Many catalogs say psi but actually mean psig. The atmosphere (atm) reading is the pressure above sea level. The capacity rating is stated as cfm, acfm or FAD. Acfm (actual cfm) and FAD (free air delivery) state the volume of air drawn into the compressor and not the volume of compressed air. Compressed air at 73 psig has about 1/5 of the volume of the air that entered the compressor. If the manufacturer rates their compressors in cfm, this point needs clarification.

Much of what has been said above, applies to any compressor. The characteristics of rotary screw compressors are first of all their high air capacity. The two screws meshing and continuously moving in one direction draw a lot of air into the screw cavities. As the air moves along, the cavities get smaller compressing the air.  Second, the screws have a long edge in contact with the outside walls which permits air leakage. Therefore the pressure rating of rotary screw compressors does not go much above 250 psig.

The ovens have a maximum temperature of 300 C. The thermal insulation is usually rock wool or fiberglass. It is light weight, but makes a good insulator giving the ovens fast heat up and recovery times. To have uniform temperature throughout the oven the use of circulating fans is recommended.  Where a convection oven may have a temperature uniformity of +/- 3 C, with a circulating fan, the uniformity in the same chamber will be +/- 1 C.

The standard temperature controller is a temperature set point on/off control. This will give a temperature fluctuation of about 3 % of set point. Using a PID temperature controller reduces the fluctuation to ½ % of set point.

The inside of the ovens is stainless steel and for vacuum and inert atmosphere ovens is tightly sealed, but has tubes with fitting for external connections. These ovens have tight seals around the door.  

The normal laboratory ovens have a single door and room for 2 to 10 shelves depending on the oven volume. Most models only come with 1 or 2 shelves standard. More shelves are extra

Four mechanical structures of coordinate measuring machines are available for holding the measuring probe. The bridge system holds the CMM probe vertically downward on a horizontal beam which is supported on both ends by posts in a bridge fashion and is located on a granite table. This is the most common design for metrology labs and manufacturing. Gantry systems are very big bridge shapes where the horizontal beam holding the CMM probe moves in a gantry form on top of the uprights. The horizontal or cantilevered probe is held by an arm on a single fixed vertical support. The probe can move in the X direction and up and down in the Z direction. The gantry and the horizontal measuring methods are used for very large products. The fourth method is the articulated arm. Here the CMM probe is held by a 4 or 5 axis arm and all measurement are in reference to the base of the arm.

Today’s software and inexpensive computing power permit measuring systems such as a coordinate measuring machine to obtain temperature signals and other data to correct the measurements for errors due to thermal expansion or flexing parts

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The “eye” of the vision inspection system is the CCD camera. In recent years the CMOS camera has made progress for certain applications. The CCD pixels send an analog signal to the frame grabber, which then converts it to a digital format. This requires complex electronics. The CMOS pixels have part of the electronics in each pixel and it sends a digital signal to the frame grabber. This simplifies the electronics of the vision system.

The CCD camera is still preferred for its higher resolution and speed. Either camera can be black & white or color. For high precision and resolution, the B&W camera is preferred.

The vision inspection system has a stage or platform on which the object is placed. The stage can move in the X and Y direction. It can be moved by hand, servo motors or be programmed by a CNC control. Height or Z axis measurements are possible by a laser probe coming through the camera lens.

 All vision inspection systems can with a dedicated computer and the required software plus a screen for visual observation

In an optical comparator, the item to be inspected is placed in a path of light in such a manner that it passes by an edge of the object. The light path may be horizontal or vertical. Horizontal light paths are to inspect small, light weight objects The light source is in front of the operator shining horizontally toward an optical sensor away from the operator. The object being inspected is held in place by a fixture mounted on a stage located between the light source and sensor. Vertical light paths are for larger, heavier, objects. Here the light source is in the inspection stage or platform, shining upward. The light sensor is mounted above the source. Objects being inspected are laid on the stage

The stage or platform of an optical comparator can move in the X and Y direction. This may be done manually, by servo drives or, on the newer models, by CNC programming.

The optical “sensor” is actually a lens which captures the light and passes it on through a series of lenses to a matted round screen where the image (shadow) is displayed. The optical comparators are divided into two styles, bench mount and floor mount depending on the size of the screen. Comparators with screen diameters up to 16” are bench mounted. Everything larger, up to 70”, is floor mounted.

When an object is viewed through a lens, it appears upside down and the left turned to the right. When viewing complex shapes on an optical comparator, it may be difficult to interpret the images on the screen. Therefore, corrective lenses are used in most comparator models. The most common correction is to turn the image around from left to right, but leave it upside down with corrected side-to-side view. Optical comparators with completely corrected images are available, but at a premium cost.