Robot cabin

Exhaust of weld smoke from robot welding cabins with a central filter system

Info

Weld smokes are complex substance mixtures including metal oxides, silicates and fluorides, which are generated during machining processes such as welding, thermal cutting and related processes, such as soldering, thermal spraying and flame hardening. These smokes are generated if metallic materials are heated above the boiling temperature and the gases subsequently cool down in the air and condensate to ultra-fine particles. These particles, whose diameter is almost exclusively smaller than 1µm (< 0.001mm!) are severely hazardous to the health because these particles can penetrate the pulmonary alveoli of the body when inhaled. At high concentrations or frequent exposure, these hazardous substances can result in immediate symptoms (feeling of dizziness, headache, metal fever) to even chronic obstructive respiratory tract diseases (chronic bronchitis, asthma, lung cancer) and damage to the central nervous system (Parkinson).

Information about the state of technology in Germany:

TRGS 528 provides information about “Weld smoke” and TRGS 560 provides information about “Air return when handling cancer generating hazardous materials”.

We would be glad to provide consultations about this subject.

John Deere, the manufacturer of agricultural machines such as tractors and harvester threshers, has commissioned a new production line, which executes automatic welding processes through three robots provided by an international reputable supplier. The welding robot in each robot system works alternating in two stations. While the welding process runs in one of the stations, the completed workpiece will be removed from the “free” station using lifting gears and the feeding will prepare the station for the next process cycle. These automated welding processes for unalloyed steel release a large amount of hazardous substances.

Therefore a new, sustainable solution was pursued for a turn-key central system to filter weld smoke at the production system whose exhaust is technically combined.
Each robot was already equipped with a mobile capture hood. The hoods are designed to automatically follow the station change of the robot to be on one hand positioned above the welding process and on the other hand to not hinder the crane work in the feed area.
This requires an active, side-wise motion of the hoods.
During the robot welding process, the weld smoke is collected underneath the exhaust hood supported by the thermal ascending force. A circumferential lamella curtain ensures that the collection is not influenced by cross flows in the production hall..

Due to the partially rather large surfaces of the exhaust hoods (up to 6 x 2.5 m), a significant minimum volume flow of exhaust air must be available for an adequate function and it must then of course be routed to the filter system. This required a sophisticated solution, which addresses the existing limited available space, the free space required for the crane work as well as the required air volume at the accompanying pressure conditions.
This project was assigned to the engineering department of UAS, which had to find an economic solution for the connection of the mobile collection hoods to the planned stationary pipe system. However, the use of flexible hoses was not possible in this case.
The reasons included mainly the vacuum resistance, the space requirements (relative large diameters) as well as the failure and maintenance vulnerability. UAS therefore emphasized a significantly more robust option that was mainly based on stationary piping using an operationally reliable, wear resistant and trendsetting solution.
For this purpose, the collection hoods in each work stations must establish one or two “docking points”, which create a connection between the hood and the pipe system. Motor driven shut-off valves, which are actuated by the robot system, only release those docking points under which the hoods are located. The other pipes will be shut-off to ensure that no additional room air is suctioned in. This limits the air volume demand for the efficient weld smoke collection to a minimum and it provides an economic solution, without the need to compromise the quality of the smoke collection.

A positive side benefit of the solution is that the exhaust power is lower than for conventional approaches by a factor of approx. 2 and it therefore results, in combination with energy efficient fans (ERP 2015 conform), in lower investment and operating costs. The energy consumption must, for example, be approximately 30% lower. In addition, the fan and the IE2 electrical motor are placed in a sound insulation enclosure with an active cooling system to reduce the local noise level.
As described in the information box, the particles in the weld smoke are almost all smaller than 1 µm (approx. 99%). These fine particles (smoke) present severe challenges for the filter medium. On one hand the filter must provide a reliable separation of the ultra-fine hazardous substances to guarantee that the work place and clean air concentrations are at least below the existing limit values and on the other hand the filter should create only moderate pressure losses and provide long durability of the filter cartridges to save costs.

ProTura® filter cartridges with nano fiber technology, which satisfy these requirements, were selected. The advantage of the filter cartridges with respect to the separation power is based on an ultra-thin, synthetic fiber, which is placed on the surface of the conventional filter substrate during the production process by using a jet spinning process and which establishes itself as a fine fiber layer on the substrate. The diameter of this nano fiber is approx. 70 - 150 nanometers, which is equivalent to approx. 0.000100 mm. The particles are separated on this fine pored layer and they create a filter cake on the surface, which can be cleaned and therefore this approach provides a longer durability than conventional filter media at which the particles are settled irreversible in the substrate.
The concept provides several benefits with respect to a high separation performance for hazardous substances, long durability, lower pressure losses and therefore improved energy efficiency. For additional savings, the filtered air can be returned to the hall through a recirculating air operation.

Decision facts:

  • Complete and turn-key total solution
  • Trendsetting collection process
  • Very energy efficient
  • High effective suction output
  • Low air volumes
  • Highest separation performance due to nano fiber technology
  • Long durability due to in-situ jet pulse cleaning system
  • Air return in recirculating air operation

Technical key data

  • Product: Cartridge filter SFC 16-4
  • Suction power under operating conditions: 15,000 m³/h
  • Suction power of the fan: max. 20,000 m³/h
  • Power consumption of the fan: 18.5 kW
  • Power supply: 400 V / 50 Hz (3 phase N PE)
  • Filter weight: approx. 1310 kg
  • Filter surface: approx. 375 m²
  • Pressure loss of the filters: 300 – max. 1,200 Pa
  • Free pressing of the fan: app. 2,000 Pa
  • Paint coating RAL 7037

Legend of figures

Figure 1: Side view welding cabin and exhaust hoods
Figure 2: Side view cartridge filter SFC 16-4 and fan in sound insulation cabin
Figure 3: Top view exhaust hoods and pipe line
Figure 4: Front view cartridge filter SFC 16-4
Figure 5: Scanning electron microscope image of the nano fibers

Our thanks go to John Deere for the release of the article.

Go back