An ounce of prevention

High-quality gas purification and delivery ensure that laser systems perform efficiently and reliably

Th 110917

For new technology to be readily adopted, it needs to be reliable and cost effective. In industrial CO2 laser cutting and welding, the purity of the gas needed to generate the laser beam directly correlates to machine reliability and cost effectiveness.

Most manufacturers specify, in detail, the type and quality of gas to be used with their particular system. Yet, time and time again, the laser manufacturer needs to send a service technician to an installation site to troubleshoot a problem, which in many cases, is isolated to the quality of the gas reaching the resonator.

What really happened? An expensive piece of equipment, a large capital investment, is not generating value. The fabricator cannot effectively service his customer, incurs downtime costs and delays the assembly operation, which produces a ripple effect on the ultimate customer. This is a lose-lose situation for everybody.

Additionally, the laser manufacturer incurs the cost of a service technician's salary and travel expense and may also incur the cost of gas to trouble shoot the system. It may take days to get the gas on site, adding additional costs to the entire supply chain as well as lowering the productivity of the service technician.

There is a way out of this conundrum. It is a final purification system for the lasing gas prior to its entry into the laser. There are basically two different ways to configure this final purification step.

Inlet gas purification

Th 110917
Figure 1. LGP series purification panel.
Click here to enlarge image

Figure 1 shows a single-unit purification panel designed for premixed gas supply. It contains a 2-micron particle filter, an indicating moisture trap and a hydrocarbon trap. A three-unit purification panel is available for pure gas supply, whereby the three most common lasing gases, He, N2 and CO2, can be individually purified.

Moisture and hydrocarbon impurities cause most of the problems in a CO2 laser. Typically, moisture levels less than 5ppm and hydrocarbon levels less than 1ppm are specified by the manufacturer. The glass-encased, high purity moisture trap in the purification panel will reduce moisture levels to <50ppb with inlet levels of 30ppm or less. It has a water capacity of 11 grams, which will provide suitable operational longevity with a high-quality inlet gas stream.

A hydrocarbon trap is designed to remove trace levels of a broad range of organic materials. It is packed with baked coconut-shell-based activated carbon and has a capacity of 600 ft3 (2–3 cylinders) of gas.

A 2-micron filter is mounted last in the flow sequence for final point-of-use filtration. It has a pleated wire mesh element and can be cleaned by flushing with gas in the opposite direction to normal flow.

This purification panel is modular, so that it can be configured to meet a wide variety of application needs. The purifier elements can be easily replaced because they are assembled with compression fittings and the individual panels can be easily removed or installed through quick-connect fasteners. They are mounted to a frame called a tube chase that can provide permanent inlet gas connections on all four sides. The tube chase can be mounted to a wall or the laser itself if so desired.

The inlet pressure to the purification panel is restricted to a maximum of 120 psi and there will be a 10-psi pressure drop across the system. The maximum flow rate is 30 slpm, which far exceeds the requirements of most industrial CO2 lasers.

Inlet gas Pressure control

Th 110929
Figure 2. LP series point of use panel.
Click here to enlarge image

1A point-of-use panel (see Figure 2) provides a convenient way to regulate pressure at the laser location, depending on need. The panels can be configured for multiple pressure regulators and on/off valves. A beam purge regulator can also be mounted on this panel for convenience and ease of use. The back entry feature of the regulators allows unsightly inlet tubing and connections to be concealed. The panel uses a model AGR3800 series line regulator with 1/4 inch tube connections installed through the panel. The beam purge regulator is used to provide purge gas to ventilate the beam path of the laser. It can be piped to the assist gas supply from the point-of-use panel. An optional diaphragm outlet seal valve can be installed to provide flow shut-off while maintaining gas purity.

Continuous gas supply

Th 110928
Figure 3. LPR series rack mounted changeover system.
Click here to enlarge image

The point-of-use panel can be supplied by an automatic changeover system that provides single-stage pressure regulation for a gas supply that is not adjacent to the laser itself. They can be conveniently wall mounted because they are supplied on stainless-steel panels drilled with keyholes. If gas supply is desired in proximity to the laser, automatic changeovers mounted on a process rack can be used as shown in Figure 3.

In this option, automatic changeovers with line regulators are used, eliminating the need for a point-of-use panel. The system utilizes a multi-point alarm that indicates when the back-up cylinder is in use.

The racks are constructed of 11-gauge steel and finished in chemical-resistant epoxy. These made-to-order systems can be configured with 2, 4 or 6 pre-mix or pure component laser gas cylinders. They are free standing and can be floor mounted, eliminating any wall space requirements.

Th 110931
Figure 4. DL series dome loaded regulator.
Click here to enlarge image

For the assist gas, a new dome-loaded regulator has been developed and is shown in Figure 4. This regulator has a unique unibody design that allows it to deliver 15,000 scf at 500 psi inlet pressure. This extraordinarily high flow allows the fabricator to cut thicker steel faster, increasing productivity and throughput.

Summary

The high quality gas purification and delivery systems discussed above will ensure that lasers operate effectively and reliably. The additional costs of a purification panel and high-quality gas delivery systems are more than offset by all the associated costs of a machine performance failure.

Tom Rozek is the VP/GM of Advanced Specialty Gas Equipment. Contact the company at Tel. (888) 999-2743, via laserlink@.asgemail.com or on the web at www.asge-online.com. A comprehensive laser gas delivery brochure is available upon request.

More in Cutting