laser fume extraction

A report in the Reedsburg Times, Wisconsin, published on 6th December 2007 reads of  a filtration device catching fire on a laser cutting machine at Seats inc.  The laser machine was being used to cut sheets of steel that were seperated by pieces of paper, when the laser passed over the paper it ignited, the burning paper was immediately sucked through the filtration device causing 10 filters to perish in flames!  A rare occurance no doubt, but which deserved a mention.

Creating enough vacuum around the source of the laser can be achieved via a range of methods, commonly, tip extraction, extract cowlings, downwards vacuum (flat bed) and full enclosures.  Each technique greatly affects the amount of air volume required to meet the minimum 0.5 m/s as set out by COSHH (LEV guidance notes)

Cutting example:

A 120cm x 120cm flat bed laser cutter will probably come with built in extract connections for the entire flat bed area.  This will have a recommended volume extract rate of say 350 m3 per hour (estimate).  This enables 0.5m/s of vacuum to be created across the entire flat bed.  However for a system of this size it is feasible to fit an extract inlet direct to the laser head, thus significantly reducing the required airflow (40-50%).  Allowing a smaller system to be specified, saving capital costs, energy costs and dramtically improving fume containment.  This is not to say the volumetric rate is not applicable, but if the correct flow rate is acheived, naturally the volumetric rate will be also.  We are expanding the issue and invite discussion.

When laser marking, cutting or engraving PVC, attention needs to be made with regards to the Hydrogen Chloride gas which is released in the subsequent plume of laser fumes.  The gas has an occupational exposure limit of just 1ppm (part per million) over an 8 hour period.  It is also highly corrosive and can eat away at not only the laser itself but the internal electronics of any purification system.

So how should a fume extraction system be built to cope with such a fume?

Many companies have designed a system based upon reverse airflow, instead of fume entering from the top down, it is sucked upwards through the filters.  This immediately stops any HCL from dripping onto components from above.  A pre filter must be installed, an option to have this coated in a neutralising chemical (strong alkali) would be idea; although generally a chemical media is applied after the HEPA, which is sufficient.  The acid will also react to the bare metal surfaces of the extraction unit housing, and so must be coated in an epoxy or paint that is resistant to the HCL effects.  If any part of the system fails through HCL corrosion, there needs to be a fool proof mechanism that alerts the users that HCL gas is being released back into the atmosphere.  Most laser purification systems have a VOC sensor but this is inadequate for HCL, which requires a seperate device.  Ideally the sensor should be linked with a shut off to the laser itself so production of any harmful fumes is immediately stopped.

Energy costs are a major factor in the equation for fume extraction systems, attention to key area of design and operations, can guarantee reduction in wasted energy.

“More than 40% of the energy consumed in most manufacturing plants is used to power fans, pumps and ventilators.” Garry Lanham. KBD.

 Within many installations the capital costs of equipment are superseded by there inherent running costs within 2 years.  However by ensuring certain technical elements are featured within the design as well as constant monitoring during operation energy/cost savings can achieved through the 3 factors below:

1) Volumetric Flow Rate

2) Total Pressure

3) Efficiency of the fan

With regards to fume extraction, flow rate is relatively inelastic in order to maintain containment, therefore adjustements to system pressures and fan efficiency are a better place to affect reductions.  A Systems pressure is directly related to the state of filters and to some extent the cleanliness of the hoses, a blocked filter and partially clogged extract hose, increases pressure and such resistance on the fan.  Where fans have a variable motor speed as pressure increases so does the fan speed, so that the flow rate is constant.  Ideal for fume containment, but a point will be reached prior to the filter light flashing when the cost of the increased energy out weighs the cost of changing the filter sooner.  Simply sucking more air through a system when resistance increases is detrimental to energy savings.   A need for further research is certainly required, it would be interesting to hear comments on this matter.

It is now widely accepted that some form of fume extractor will be required when purchasing a laser. On the one hand the customer has to consider their budget and performance requirements and on the other hand the laser sales person wants to clinch the sale of the laser. There are two ways to go in this situation. (1) The customer can purchase both the laser and a fume extractor from the Laser OEM or (2) they can only purchase the laser and source an extractor from elsewhere. Option (1) is the better method for several reasons.  The laser sales person may think that quoting a laser with an extractor will put the customer off because of the additional cost, but this is usually not the case as the customer knows they will have to buy an extractor from somewhere anyway.

It is much better then to quote a whole package to the customer who can benefit from the laser manufacturer’s knowledge of specifying the correct extractor. The laser OEM also gets the long-term benefit of supplying the customer with replacement filters and the customer gets a problem free laser process.

Budgets are of course 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 which vent to the outside may seem an economical solution at first but they have significant drawbacks, i ) holes need to be cut in walls / ceilings. ii ) planning permission may be required. iii ) environmental legislation comes into play iiii ) bulky, fixed pipework is required and iv ) what happens if the laser moves? The fan, holes, pipework, fixings etc need to be reinstalled in the new position and the old ones filled and sealed which will be expensive. Also an external venting point may not be available; for example in a shopping mall or school.

A cheap extractor may also cost much more in terms of replacement filters. Worse still if the extractor is inadequate then the health and safety of the operator will be at risk.

Courtesy of Purex Ltd.

Fume extraction systems are inherently noisy apparatus, therefore most companies employ some sort of silencing device to combat the problem.  However when reading through the ‘brochure’ it is worth considering the real life comparison in noise levels.  Bearing in mind the quietest system runs at 45 db, with most running between 55 - 70 db.  See below for examples:

150db - Rock music at its peak                140db - Firearms, jet engine

130db- Jackhammer                                 120db - Jet plane taking off

110db- rock music                                    100db-chainsaw, pnuematic drill

90db - Lawn mower, subway                      80db- Busy main street,

70db - busy traffic                                      60db- loud conversation, dishwasher

50db-moderate rainfall on a tin roof           40db- Quiet room

30db - Library

LEV testing is applicable to laser fume extraction.  Why?  A system is defined as Local Exhaust Ventilation if it is used to contain, control or capture airborn particulate on or near to the point of emmision and then convey it to a point whereby they are released back in to the local atmosphere.  An effective laser fume system must be constructed in order to comply to the testing requirements under COSHH, in addition all LEV systems must tested every 14 months and results recorded and held for 5 years from the date of manufacture.

Regulation 9 - Requires all control measures to be properly maintained and regularly examined and tested. The employer should ensure all control measures are maintained in an efficient state, good working order and in good repair.

Many fume extraction manufacturers offer this as a part of an ongoing maintenance program.  LFE guidance is currently having engineers examined under the BOHS accreditation so that we can supply this service to you as a third party, un biased and easy.  Our full reports comply with COSHH guidelines and are valid for 14 months as required.

As the world’s leading exhibition for optical technologies, LASER. World of Photonics is the most important international information and networking platform for the industrial, research and scientific community where business is initiated and advanced. It is where market leaders and innovative startups present the entire range of solutions related to the key technology of photonics.

With this in mind Laser Fumex have created an industry forum for debate where the most important subjects can be discussed and argued over in the time between the next exhibition.  We hoping to put forward topics for further discussion at the event. 

The international Trade Fair for system solutions in laser processing debuting in Stuggart, Germany.  Lasys will present systems and processes covering the entire spectrum of laser processing: laser welding, laser cutting, laser drilling, laser labeling and much more besides. Lasys will also be a marketplace, a forum for visions and an inter-industry communication platform.  We will keep you upto date as the event gets nearer.

Many processes where dust and fume extraction is necessary take place in an environment where electrostatic discharge can cause problems.

The actual process of air passing through an extraction system can create a static charge. This charge can damage sensitive electronic components, resulting in expensive reject rates. In applications where powder or dust is mixed with the airflow, for example in the chemical handling and pharmaceutical industries, a build-up of static electricity can pose a potential explosion hazard.

It is an interesting discussion point because in laser fume systems electrostatic fibres have been tested in a range of filter media for improving performance.  The theory that particles would ‘stick’ to the filters allowing a more open matrix of fibers was proved in the end to adversely affect the efficiency of a laser fume extraction system:  With particles traveling through to the ‘clean air’ stream when dislodge through vibration.  The issue has now gone full circle from a possible advance in technology to a proven nuisance in particular laser processes!