Medical Device Link.

Originally Published PMPN November 2004

Laser Fume Extraction

by Jon Young
Purex International

Marking or coding lasers are used in a variety of applications to add traceable information, such as expiration dates and batch codes, to packaging and products. Both laser engraving and laser marking systems (excluding UV photochemical marking) burn away layers of material to cut or mark a product. This process generates fumes that may contain a mix of toxic particles, gases, and vapors. Examples include benzene and toluene released from certain plastics, and chromium and nickel dust produced when processing certain alloys. Laser processing of most materials will emit some hazardous fumes; even cardboard and paper labels can produce breathable dust and formaldehyde.

It is vital that these fumes are dealt with effectively. They may cause serious long-term medical conditions, such as occupational asthma, and lead to expensive compensation claims.

Particulate generated by laser processing can also contaminate expensive laser optics and can attenuate and distort the laser beam, leading to blurred or incomplete marks. It can also contaminate products and coat the laser enclosure and associated machinery, leading to increased downtime for cleaning. A failure in fume extraction is usually a line stopper. In high-volume production, improperly coded products and the resulting downtime due to fume-extraction failure can be costly.

Buying a Laser

It is now widely accepted that some form of fume extractor will be required when purchasing a laser. Customers can purchase both the laser and a fume extractor from the laser OEM, or they can purchase the laser only and source an extractor from elsewhere.

The first option is preferable for several reasons. If the customer does not receive a quote for an extractor from the laser salesperson, he or she may end up with an unsuitable extractor from another source. The extractor may then cause problems with the laser process, such as causing the laser to produce blurred marks. This can leave the customer unhappy and cause him or her to wonder if the laser is at fault. By receiving a quote for the whole package, the customer can benefit from the laser manufacturer’s knowledge of the correct extractor. Sometimes the quality of the fume extractor is the deciding factor for the customer when comparing two laser brands.

Budgets are a consideration for the customer; however, very-low-cost fume extractors available on the market can trade performance, filter life, and even safety for cost. Simple fans that vent to the outside may seem an economical solution at first, but they have significant drawbacks:

• Holes need to be cut in walls/ceilings.
• Planning permission may be required.
• Environmental officers may demand that the fumes be treated.
• Bulky, fixed pipework is required.
• The laser may need to be moved.

If the laser is moved, the fan, holes, pipework, fixings, etc. will need to be reinstalled in the new position and the old ones filled and sealed. In some locations, such as a cleanroom, an external venting point may be prohibited.

What to Consider

A diagram of the Laserex Alpha illustrates the laser fume extraction process.

What does a budget-conscious customer need to be happy with the laser/extractor package? Answer: an extractor that is compact, affordable, quiet, mobile, and delivers excellent extraction rates and filter life.

Filters. A major benefit of buying lasers is that they have few consumables when compared with other methods of marking such as ink-jets. Therefore, the last thing the customer wants is to have to buy many replacement filters for their fume-extraction system. Several design features can help to ensure filters have a long life-span and therefore costs are low for the customer.

One such feature is reverse airflow. Large particles within the laser fumes will prematurely block a filter over time. To prevent this, the speed of the air is slowed when entering the machine, and the direction is changed from horizontal to vertical, forcing larger particles out of the airstream in an action similar to a centrifuge. These particles are deposited in the base of a prefilter, thus prolonging its life.

The prefilter is used to protect the main HEPA filter from premature blockage. It does this by removing 1-micron particles from the airstream. This quick-change, patented filter technology is designed to overcome inherent weaknesses in pleated-paper and bag filter design. The filter’s shape, dust-holding capacity, and deep-graded filter media mean that more particles can be captured. As a result, the main HEPA filter lasts much longer.

A reinforced, submicronic HEPA media is used in main filters to remove small hazardous particles from the air stream. Purex filters are proven in independent tests to capture 99.997% of particles at 0.3 µm and 95% at 0.01 µm in size. A high-performance deep chemical layer in the filter then adsorbs toxic gas before clean air is returned to the workplace.

Additional features. The customer may require additional control of a fume extractor, depending on the individual application. In their most basic form, most fume extractors simply turn on or off without the option to raise or lower their extraction rate. This fixed-speed method of operation is not as energy efficient as a variable-speed drive, and having too high an extraction rate can cause drag marks on the product during engraving.

Filters will last longer if the speed at which the particles pass through the filter media is controlled and maintained. A speed control system allows customers to set the airflow to the optimum level on site (particularly useful for engraving lasers). To prevent the extraction rate falling as the filter becomes blocked, a fully automatic closed-loop flow control system maintains the airflow at precisely the level set by the operator by automatically adjusting the motor speed.

Closed-loop flow control ensures:

• Filter life is maximized.
• Consumable costs are lowered.
• No manual intervention is required to maintain extraction rate.
• Personnel are constantly protected.
• Airflow is constant throughout the life of the filter.

For added safety and control, customers might consider an upgrade that allows interfacing with the laser, providing a closed-loop automatic solution in which operator intervention is kept to an absolute minimum. This allows the extractor to start automatically when the laser is switched on, preventing any damage to the laser optics or any hazardous fumes entering the workplace.

Health and safety legislation, and the need to protect the product and laser optics, make the need for a fume extraction system undeniable. Customers should determine how and where the fume extractor will be used before deciding whether recirculating air or venting fumes to the outside is the best solution. They should also consult a laser OEM when making the decision to purchase a fume extractor.

Jon Young is marketing manager for Purex International based in South Yorkshire, UK.

Copyright ©2004 Pharmaceutical & Medical Packaging News