Efficient Dust Extraction from Laser Cutting

The key to protecting both workers and equipment.


Laser technology over the years has seen a continuous growth in technology and performance in cutting technologies.  This growth in technology includes advancements in both CO2 to Fiber lasers.  Companies are well aware of the advantages provided by the wider range of laser power available that cut a spectrum of potential materials (more potential applications of stainless, aluminum, brass, and copper) and thicknesses at faster speeds.

However, the resultant increase in precision and productivity is also associated with an increased emission of dust, sometimes in the submicroscopic range. The more you cut, the more dust is generated.  This increase further emphasizes the importance of sufficient dust collection to protect the health of the operator from the emission hazard and the ensure the functioning of the laser system. 

While conventional dust collectors can be used for metallic and non-metallic dust, special separation processes are necessary for organic material.

Laser Cutting Challenges:

One health risk that has become of increased awareness is the hazard of hexavalent chromium, toxic form of chromium.  Chromium (VI) can be generated and present in the fumes from hot work on stainless steel and other metals containing chrome alloy.  There are numourous health risks associated with Chromium (VI) exposure including lung cancer, respritory damage, and skin/eye irritation.  Due to these concerns, OSHA has issued standards for general industry, shipyards, and construction to limit the exposure of workers to an 8-hour TWA permissible exposure limit (PEL) of 5 µg/m3 and an Action Level of 2.5 µg/m3.  Therefore, over the course of any 8-hour work shift, employees cannot have an average exposure to Cr(VI) exceed 5 µg/m3 with 2.5 µg/m3 triggering specific requirements. >

Potential control measures include providing adequate dust collection to the production process in order to capture any fumes and dust generated.  The dust collection should include stage of a high-efficiency particulate air (HEPA) filter that filters at least 99.97% efficiency of 0.3 micrometers and larger particles.

 

Laser cutting of organic materials, such as plastics, rubber, and wood, provide a challenge for traditional cartridge dust collectors due to the sticky aerosols generated in the process.  These sticky fumes clog quickly clog the pores of the filter element causing premature failure of the dust collector.  However, Keller’s solution to dust collection of organic material provides a long filter life alternative that relies on (3) critical characteristics:

  1. Automatic Dosing Supply: The automatic online dosing of an inert powder (limestone or clay) into the dust collector dirty air plenum.  This powder coats the filter elements and acts as a sacrificial barrier by absorbing the adhesive and humid particulates and preventing from penetrating the filter pores 

  2. KLR Filter Plate: Keller’s KLR-bran filter plate with PTFE membrane ensures that the combination of pre-coating powder and process emissions can easily disperse off the filter plate by automatic self-cleaning compressed air pulses.  The wide pleats of the KLR-bran filter plate, in comparison to the deep pleats of traditional round cartridges, provide continuously active filter surface area without trapping the particulates

  3. Bin Dosing: When the KLR-bran filter plates are cleaned off additive agent is dosed from the disposal bucket providing an additional protective layer on the filter surface until new material is fed by the automatic dosing unit

This combination not only provides long filter life with constant 24-hour airflow but has additional ancillary benefits of reduced fire risk due to the addition of inert powder into the mixture of dirty air emissions and potential smell reduction (absorption of hydrocarbons).  Additional optional post-filtration measures include activated charcoal filter for additional gas phase and further smell reduction.

Fires in dust collector systems rely on two factors: fire load (the fuel for the fire) and ignition source (the source for the fire).

The fire load can exist due one of more of the following fuels:

  1. Filter Elements: Filter elements consist of natural, synthetic or organic material (paper, cotton, needle felt and plastic granulate) and are therefore classified as combustible. Basically, a fire risk exists. For example, the thermal value for polyester is 6.3 kWh/kg.

  2. Secondary Sources: Secondary flammable sources such as oily air from sheet metal sheets, aerosols, or other foreign matter that can be easily ignited

  3. Dust: The fire risk increases by the dust accumulation in the filter if the material separated is also flammable

 

The source of the fire can come from internal or external sources:

1. Internal Ignition Source (Inside the Dust Collector)

  • Hot Surfaces
  • Static Electricity

2. External Ignition Source

  • Operational ignition sources (ie. sparks)
  • Exothermic reactions including spontaneous ignition of dusts 

 

Some potential solutions to reduce the risk for fires include:

  • Spark Preseparation: The threat of introducing ignition source from the operation is reduced by using a spark preseparator to divert and minimize their energy.  However, no spark preseparator is 100% effective and a residual risk remains.  

  • Solid Matter Inertization: Solid matter inertization offers the possibility to generate a non-combustible dust mixture from combustible dust by adding limestone powder via a dosing device.  This reduces the threat of combustion and provides an auxiliary protective layer on the filter elements to extend filter life.

  • Monitoring Fire Detection: Sensors to monitor for different fire sensors including sparks entering (infrared spark detector) and smoldering fires (temperature sensors in hopper and clean air side).  The detection can be used to either alert the operator of the fire hazard or initiate automatic fire suppression system.

  • Automatic Fire Suppression: After alert of a fire event an automatic fire suppression system can be initiated with a return valve preventing the flame from escaping and a shut-off valve preventing the exhaust of the suppression agent.  An extinguishing agent such as Argon is dispensed into the isolated filter housing to remove the fire risk.

Keller's Laser Cutting Dust Solution

Dust Collectors in the VARIO, PT-filters or L-CUT series are ideal for the very fine particulates and fumes generated in laser cutting processes. The required airflows can vary depending on the process, material, and table or enclosure size. 

 

L-CUT Series - Laser Dust Collector

The L-Cut is, as it's name describes, designed specifically around the requirements for dust collection from laser cutting applications. To meet the needs of a wide range of laser sizes and airflow requirements, the L-Cut series comes in four models. For technical specification, please refer to Keller's L-Cut Technical Data.

This plug-and-play unit offers the following features:

The L-CUT series is designed for quick installation and with the ablity to be placed in tight spaces, near the machine tool. For additional convenience, all critical elements (disposal buckets, electrical control, solenoid valves, fan motor / impeller, etc.) are accessible from the operator side. 

The integrated spark pre-separator protects the filter elements from damage that could be caused by coarse, potentially glowing particles entering the dust collector.

The L-CUT units have built-in radial fans that operate at very low sound levels.  Futhermore, the cleaned air is directed upward through an integrated silencer allowing for quiet operation.  

The collector's housing is of welded design with an adjustable baffle at the dirty air inlet. All relevant components (i.e. disposal bin filter elements, motor-impeller section, solenoid valves, electrical switch and control system) are accessible for servicing from the front.

Keller's L-Cut 2 and L-Cut 4 collectors come in designs for either dry cartridge or KLR plate filters. Both filter elements are designed for high efficiency and easy maintenance, with the KLR-Filter® rated for 20,000 operating hours (over three year filter life even for 3-shift operations!).