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HOW TO CHOOSE WELDING FUME EXTRACTION SYSTEM?

We have mentioned the damages of welding fumes in detail in our other blog posts.
For both human health and environmental cleanliness, safely filtering welding fumes should be the priority agenda of every company engaged in welded manufacturing. 
Let's not forget that; similar things apply to gas, plasma and laser cutting fumes.
Absorption of welding fumes before they reach the breathing zones of people should be the primary goal. 
Detailed evaluation should be made for the selection of products suitable for this target. 
It is necessary to evaluate different options for this;
a.    Mobile fume extraction units:

These units are practical and safe products that can be easily moved within the workshop and have an acrobatic suction arm with a length of 2, 3 or 4 metres. The filtered air is given back to the working environment. The point to be considered here is to be careful when welding high alloy materials such as stainless steel. Such fumes classified as W3 must be filtered by specially manufactured units. Welding fume extraction systems manufactured in accordance with ISO 21904-4:2020 standard meet W3 requirements. Mobile systems are produced with different filtering technologies:

aa. Mechanical (disposable) filter units: In this type of units, there is a main filter that cannot be cleaned. Optionally, auxiliary filter equipment such as activated carbon filter, coarse filter, mesh filter can also be used. In this type of units, the sucked dirty air is directed directly to the filter.
While the cost of ownership is relatively low, the operating costs of these units can be high. The main filter element, which is generally disposable, has an average lifetime of 200 operating hours. If we calculate over 5 hours of arc time per day, filter replacement may be required at the end of 40 working days.

ab. Cartridge filter units: This type of units have a cleanable cartridge filter. Optionally, auxiliary filter equipment such as activated carbon filter, coarse filter, mesh filter can also be used. The cartridge filter can usually be cleaned with a compressed air gun. Some manufacturers also offer cleaning systems with brushes, vibrators, etc. In manually cleanable units, it is useful to look for the filter cleaning feature without dismantling the machine as much as possible.

 

 

Cartridge filter models are also available with fully automatic cleaning. Such units automatically perform the cleaning process when the filter reaches a pre-set level of fullness. The most commonly used method is the jet-pulse system. These units, which contain a compressed air tank, must be continuously connected to a compressed air source.

Models with cartridge filters may have a slightly higher cost of ownership, but their operating costs are lower. This is because a cleanable cartridge filter can be used for several years, depending on usage, filter material and frequency of cleaning.

ac. Electrostatic filter units: These systems are mostly abandoned today. It keeps the particles in the smoke completely electrostatically on the plates. It does not require the use of a filter. However, the filtration rates of such filters may not be satisfactory. Such filters are mostly preferred for filtering coarse and sticky particles such as oil.

If a mobile unit is to be preferred, the following should be considered:
- The welded parts should be small. Because a suction arm suctions from an average distance of 30-50 cm. If large parts are welded, the mobile unit should not be preferred because it will be difficult for the welder to move the arm continuously.
- If there are many welding stations but the area is not large enough, these units will cause overcrowding.
- If there are many welding stations, it is necessary to control the engine power of the mobile unit. For example; if 20 mobile units are to be purchased and one unit has a 1.1 kW motor, the total power will be 22 kW. If this power can be reduced to 10-15 kW with a centralised system, the mobile unit may not be preferred due to energy saving.
- If a unit with manual cleaning cartridge type filter is preferred, it should be ensured that the filters will be cleaned as often as necessary. Otherwise, the filters can clog very quickly and cause unnecessary costs.

 

b. Central fume extraction system with acrobat arms:

 

This is a much preferred system. Several arms connected to a central fan provide smoke extraction through a pipeline. There are different alternatives in these systems:
ba. Systems installed only with a fan: We definitely do not recommend these systems. Because;
- Since there is no filter system before the fan, the fan will fail very quickly. Particles accumulate on the fan blades and the aerodynamic structure of these blades deteriorates. As a result, the desired air flow rate cannot be obtained after a while. In addition, the fan requires frequent balancing.
- Since there is no filter system, all harmful gases and particles in the smoke are thrown into the atmosphere. It is a very dangerous situation for the environment.
- Since the absorbed air will be thrown directly outside, it increases the heating costs in winter. To give an example; When a system is installed with 15 suction arms (each arm absorbs an average of 1000 m³ / hour of air), an average of 15,000 m³ / hour of air will be absorbed. The heated 15.000 m³ air in the workplace will be discharged within one hour. In an 8-hour shift, this amount will be 120,000 m³. A production area with a total area of 2000 m² and a ceiling height of 10 metres has a total volume of 20,000 m³. Discharging almost all the air of such a work area in one hour will make it very costly to heat this workshop in winter.
- Using the same example, 15,000 m³/hour of outside air must also enter this work area. Otherwise, the negative pressure environment and insufficient air inside will make the employees very uncomfortable. In the past, we have also witnessed that in some enterprises that made similar applications, the entrance doors were very difficult to open due to this negative pressure. For this reason, openings should be provided in the appropriate areas of this work area where at least 15,000 m³ / hour air can easily enter.

bb. Centralised systems with filters: Systems that filter the absorbed smoke and then return it to the working environment will prevent the above-mentioned negativities. 
If a central suction system with acrobat arms is to be preferred, the following should be taken into consideration:
- The welded parts must be small. Because a suction arm suctions from an average distance of 30-50 cm. If large parts are welded, it should not be preferred because it will be difficult for the welder to move the arm continuously.
- The system must be designed by a professional company. Factors such as pipe diameter calculation, fan selection, filter selection are necessary for proper operation of the system.
- High efficiency fan/motor should be selected as much as possible. It is possible to do the same work with lower energy consumption. The investment cost may be higher at first, but this difference will be recovered in a very short time.
- A flap system should be foreseen for each arm. When the welder, who is not working at that moment, keeps the flap of the suction arm closed, systems that can reduce the motor rotation speed according to the number of open arms should be used. There are also systems with flaps that close automatically when there is no more welding process. These systems are equipped with special particle sensors.

 

 

c. Downdraft tables: Downdraft welding tables can be mobile or with central connection. Downdraft tables can absorb welding fumes and grinding dust before they rise. They are ideal for operations where relatively small parts are welded.
However, these tables also have disadvantages:
- In gas-shielded (MIG, MAG, TIG, etc.) welding processes, there is a risk of suction of the shielding gas.
- If the central system is installed and the sucked air is discharged directly, it increases the heating costs in winter months.
- Fresh air must enter this working area from outside as much as the air sucked in. Otherwise, the negative pressure environment and insufficient air inside will make the employees very uncomfortable. In the past, we have witnessed that in some enterprises that made similar applications, the entrance doors were very difficult to open due to this negative pressure. For this reason, openings should be provided in the appropriate areas of this work area where at least as much air as the absorbed air can easily enter.
- Mobile tables must have a fire prevention system. Sparks arising during the welding process must be extinguished before reaching the filter.

 

Image from Teka

 

d. Fume extraction systems on-torch:  In these systems, a special MIG or TIG torch is connected to a high vacuum unit to absorb the fumes before they spread around. Some companies are also developing suction equipment that can be mounted on conventional torches.  Torch mounted suction systems are not limited to manual welding torches. It can also be applied with automation torches and welding robot torches. In fact, applications with automation and robot torches can be more efficient than manual torches.
The disadvantages of this system can be listed as follows:
- If the gas flow rate is high, the smoke is pushed away from the suction port. In this case, suction efficiency decreases.
- If there is too much spot welding, i.e. if there is too frequent triggering, the fume extraction efficiency decreases because there is a higher pressure gas outlet at the start of the arc. It is necessary to use special equipment to regulate this pressure change. Again, in applications such as spot welding, fume extraction may not be possible because the welder will move fast.

- The angle between the welding pool and the torch is very important. If the torch is not held at an appropriate angle, the suction efficiency decreases.
- Welding position and method affect the efficiency. The most efficient area is corner welding. It can also be said to be a little efficient in the PA position. Suction efficiency can be very poor in PC, PD and PE positions.

 

- Anti-spatter sprays and pastes affect suction efficiency.
- Each torch manufacturer may recommend different air flow rates for their products. For this reason, suction units with adjustable air flow rate should be preferred whenever possible. It is useful to check the air flow rate frequently with the air flow measurement apparatus supplied with the torches. 
- Since the suction units used for this system are designed in a small size, the filter surface may be small. In this case, there is a risk of frequent filter replacement. For professional use, we recommend systems with automatically cleanable cartridge filters. 
- Smoke suction torches are slightly heavier than conventional torches. They can be a problem for welders during long shifts. In addition, the cost of these torches can be high as their consumables are different.

 

 

e.    Hall ventilation systems: They are efficient systems. They should be preferred for all production areas where local suction is not possible. It is preferred for filtering all volatile particles in the working environment.
If we examine the welding fume in particular; When the welding fume particles, which rise very rapidly due to the thermal effect, reach a certain height, they are suspended first. This height will form a cloud-like cloud in the range of 2.5-5 metres on average, depending on many different factors such as season, ambient air currents. Most of these particles, which cool down thoroughly, are directed downwards by the effect of gravity. But since these particles are very light, they can move up to 40 metres. In other words, they are scattered all over the production area and even inside the office.
The priority of hall ventilation systems is to absorb and filter these volatile particles without allowing them to spread and to provide filtered air to the environment again. Since these systems do not take air from outside and do not give air to outside, they save up to 70% in heating costs in winter months. Some manufacturers add cooling and heating features to these systems.
The ACH (air cycles per hour) required for the ambient air to reach a particle exposure in accordance with legal limits must be calculated correctly. The exposure rate is applied differently in each country. Germany reduced the exposure rate from 3 mg/m³ to 1.25 mg/m³ in 2012. In Türkiye, the level of 3 mg/m³ is applied. In order to calculate the number of towers, a lot of information is needed such as the amount of welding machines in the working area and the projected future numbers, the operating amperes of the machines, arc times, shift numbers, other pollutants in the environment. The expert team that will design the system should calculate the total amount of pollutants in this environment by taking this information and make the necessary design calculations to reduce the target exposure rate.
It should not be forgotten that; trying to remove such volatile particles from the environment with ceiling type fans is not an efficient solution. There are of course areas where it can be applied, for which a specialised team should be asked for help.

 

Important note: Hall ventilation systems cannot be used alone. Workers must use appropriate PPE (e.g. PAPR system).
There are different types of ambient ventilation systems.

e.a. Push-Pull systems: These systems are also known as push-pull or push-pull systems. One of the two pipelines placed opposite each other pushes the contaminated air, while the other absorbs this air and transmits it to the filter system. The filtered air is sent back to the blowing line. Our recommendations for these systems are that the ceiling height should be lower than 7-8 metres and the thermal load should not be high, that is, the annual consumption of welding wire/electrode should be less than 10 tonnes/year.
The design of these systems must be done by specialised teams. Mostly due to miscalculations, in the areas where these systems are installed, the particles above are pushed downwards and cause harm instead of benefit. 
These systems are designed and installed for a specific area. Moving it to an area with other dimensions will cause negative effects. When there is an excessive increase in the number of welding machines during the installation period, the system will again become inoperable. For this reason, the increase in the number of sliding machines that may occur in the following years should also be foreseen during the ordering phase.

 

e.b. Layered systems: These systems are much more efficient. Pipelines placed above suck in the dirty air and send it to the filter system. The filtered air is transported by pipelines and reintroduced to the environment at low speed through diffusers placed at ground level. In some applications, this fresh air is cooled a little more and its effect is increased. These systems, which are installed with the principle of displacement ventilation, always keep the polluted air above the breathing zone. Ideal for halls with high ceilings and high thermal loads. The biggest disadvantage is the cost of ownership. These systems are designed and installed for a specific area. Moving it to an area with other dimensions will cause negative effects. If there is an excessive increase in the number of welding machines during the installation period, the system will again become inoperable. For this reason, the increase in the number of sliding machines that may occur in the following years should also be foreseen during the ordering phase.

 

e.c. Tower systems: These systems are completely pipe-free. They work with the logic of the air purifiers we use in our homes. Four systems are generally used.

e.c.1. Top blowing towers: These towers suck the polluted air from below and the filtered air is blown back to the environment with the jet nozzles on the top. They are usually designed to be more than 5 metres high. Thus, they quickly disperse the particle cloud formed over the production area. 
Disadvantages of this system:
- Depending on the manufacturer, there must be an obstacle 20-30 metres away from the tower. For this reason, installation problems occur in wide halls with open spaces.
- Since they suck the dirty air from the bottom, a continuous mixture of air passes through the breathing zone. So it is difficult to talk about complete clean air in the breathing zone.
- As they are quite large systems, transport and installation processes are costly and long.
e.c.2. Bottom blowing towers: These towers suck the polluted air from the upper side with the displacement ventilation principle and return the filtered air to the environment at low speed at ground level.  They usually have a height of about 4-5 metres and are plug/play. For this reason, transport and installation costs are low and commissioning time is short. 
They always provide clean air in the breathing zone. The clean air blown from the bottom side spreads to quite far areas and prevents harmful particles from coming down as it heats up and goes up.

The disadvantage of this system is;
- The particle cloud accumulated above dissipates more slowly or sometimes not at all. This creates a psychological belief that the tower is useless. Because these towers move the particles above at a much slower speed.
e.c.3. Double-sided blowing towers: This tower system was first developed and patented in Türkiye. It has the same features as the bottom blowing towers. In addition, thanks to the jet nozzles placed on the upper side, the user can disperse the particle cloud at any time. These towers have 5 different fresh air blowing modes.
- Completely bottom blowing
- Completely top blowing
- 30% bottom and 70% top blowing
- 50% bottom and 50% top blowing
- 70% bottom and 30% top blowing
Thanks to this choice of modes, very different installations can be realised.

 

   

e.d. Swarm type systems: These systems are also developed in Türkiye. They offer the advantages of much less energy consumption, much less space occupation, much easier installation and maintenance. A swarm member suspended about 4-5 metres above the floor absorbs and filters the polluted air and releases a large proportion of the filtered air to the environment at low speed with the diffuser on the floor, while a part of the air is blown horizontally with a jet nozzle and pushes the polluted air towards the other swarm member. These air ratios can be adjusted.

 

f. Fume extraction with hoods: If suction hoods are to be used for manual welding operations, appropriate PPE is required. Hoods are mostly preferred in robotic welding systems. The size and height of the hood should be calculated very well.

Image source from VDMA

You can consult our expert team to determine the most suitable system for your needs: info(at)hivent.com

 

HiVent Technology, 16/09/2024, Ankara