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Fume Extraction Shrouds: A Detailed Explainer

Posted by Etienne Blouin on Feb 24, 2020 9:30:00 AM
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If you are a welder, weld foreman, or welding engineer using a fume extraction welding gun, the shroud is one of the more unique features you have questions about.

The reason being is:  most people have never seen a shroud before and have no clue what it is.

To review: fume extraction torches have a fume shroud that either envelopes the regular welding nozzle or serves as a bridge piece to the nozzle and the neck. Shrouds that envelope the nozzle can be removed while still welding with the torch because it's slipped on above or around the welding nozzle. Shrouds that thread to the neck and connect to the nozzle cannot be removed while still using the welding gun.

Many of the questions/comments I get from welders, welding foremen, and engineers alike are the following:

  • Can Shrouds be Removed When Welding?

  • What’s the Difference Between Threaded and Slip-on?

  • Why Do the Openings Matter?

  • What are Fume Shrouds Made Of?

  • Why Are These Design Features Important?

  • Welding Engineer Considerations

Without delay, let's dive in on these questions.

Can Fume Shrouds Be Removed When Welding?

I get this question a lot when I show fume extraction torches to the welder. An operator welding with the torch is trying to access a corner and there are access points that are smaller so they you would like to remove the shroud to get to that corner. Or when they get to a corner they have a lot of air velocity and they want to remove the shroud to prevent the shielding gas extraction issue with the shroud.

It is important to know that if you remove any sort of shroud, the effectiveness between the weld and the extraction is completely changed. These tools are not designed to weld without the shroud being utilized.

By removing the shroud in designs where that is possible, you find yourself with a vacuum part of the torch that's too far away to be efficient and does not extract weld fumes properly.

Can you weld without some of these shrouds? Yes.

Can you extract properly? Absolutely not.

What's the Difference Between Threaded and Slip-on?

Slip-on shrouds comes with a few pros and a few downsides in their best use case:

Upsides Downsides
  • Adjustable
  • Close to the weld
  • Well-suited for low powered extraction systems
  • Less visibility
  • Less joint accessibility
  • More prone to spatter
  • More likely to cause porosity

The biggest pro of the slip-on shroud is it's adjustable. If you feel like you're not getting enough suction or getting too much suction, you can adjust the placement of that shroud over the nozzle in order to optimize that for yourself on the job.

The biggest downside of that is that it is bulkier. Your visibility to the weld is compromised for sure. There's also a component in terms of the fume extraction system. A high flow system does not work as well with that slip on shroud design.

Why?

Because even at it's farthest point away from the nozzle, it's still closer to the weld then a threaded design would be, and is prone to removing shielding gas and collecting spatter because of that proximity – especially if the shroud design openings are not very large.

Most of the slip-on shrouds are bulkier and closer to the weld. You can adjust them in a certain zone from being very close to or even further away. But you cannot adjust them to the back of the nozzle because they sit on the nozzle, so there's a limitation on how far you can go.

The other difference between a threaded shroud and a slip-on is the amount of flow that you can use or apply on the torch. If you're very close and you apply too much flow you start compromising shielding gas flow quickly.

If your shroud is more recessed, you can extract a lot more volume without affecting the welding process. So if you have a slip-on by default you have a torch design that allows less flow to go through to avoid welding quality issues.

Fume Shroud Recess Comparison

The advantage of the slip-on is that it works well with lower powered fume extraction systems. If you don't have a powerful enough vacuum to use a threaded should, you need to be closer to the weld, and slip-on shrouds are able to be adjusted to sit closer to the weld arc and capture fumes effectively at low settings.

Threaded shrouds have their own upsides and downsides, including:

Upsides Downsides
  • Less effect on the welding process
  • Better visibility for the welder
  • More suited for high parameters
  • Capable of extracting fumes in vertical positions
  • More design varieties
  • Does not work well with low powered extraction systems
  • Not adjustable along the nozzle

I prefer a threaded design for welding applications where you're further away and have more flow in the vacuum. This allows more room for a different fume extraction scenario – not only does the threaded design give you a better view of weld, it has less effect on the welding process.

Fume extraction does not interfere with the welding process as much when you are further away. With the proper vacuum flow applied, a threaded recessed fume shroud allows room for different angles, different approaches, and you get a lot of fume capture with the right system.

Why Do the Openings Matter?

Whether you utilize a slip-on or threaded shroud, you have different shapes and different sizes.

With a threaded shroud you will have some that are longer, some that are shorter, some that are bulkier, and some that are smaller. All of that allows for some adaptation to your welding process.

If you have a tight access angle you may need a torch with the smaller slip-on shroud. Because they envelope the nozzle, they still are bigger than the regular nozzle, but you can have a range of secondary shroud sizes and styles. Some have more recess than others, but in that situation again you're always around the shielding gas and around the welding arc, so you are always bigger than the welding nozzle. Within the slip-on fume extraction torch family you are afforded some range in options, but they are all close to the weld and bulkier.

Fume Shroud OpeningsIn the family of threaded shrouds there's different designs that allow you to go from the super slim tapered design you can use to reach very tight access spaces. If you have tight corners to weld and you really do not want to affect your shielding gas, using these slim tapered recessed shrouds will give you more access while avoiding porosity.

There are bigger tapered shrouds that are shaped to get a little closer to the weld. With these designs you're still extracting after the regular welding nozzle but come closer and wider. In vertical welds or in a hard to catch welding position, you must have a closer position to the smoke so that your weld fume capture is higher.

The position of the torch is critical here, as well. The welder articulating the torch so the nozzle points upward, for instance, greatly decreases the effectiveness of smoke extraction while welding vertical.

What are Fume Shrouds Made Of?

if we go back into the days of creation of these fume extraction welding guns, the first shrouds that appeared were made of brass. So there were like sheet metal forming to go around the welding nozzle and they were brass material. Now, quickly realizing that the spire and the durability of these shrouds were a problem, makers went through a chrome-plated shroud oftentimes still made of brass.

Other companies came with hybrid shrouds. That meant the shroud was actually attached to the nozzle and you had to change them together. These designs blocked the siding and chrome-plated outside. The primary purpose was surface protection. If you have a plating on top of brass it's easier to clean.

Fume Shroud MaterialIn the latest generation, because of durability and life expectancy of the parts, the in-demand shroud material is steel that is black anodized. With that you have the maximum mechanical strength so that durability is much, much higher. The black coating also has corrosion resistance and spatter resistance as well.

We often with new fume extraction welding users suggest that you protect your shrouds or the front part of your torch with a dry anti-spatter ceramic spray so that it is easier to clean. So in total, you have mechanical durability, corrosion resistance, and spatter resistance all in one.

To differentiate what is a more durable steel compared to a brass material, use a magnet to check, or you can just look and likely tell the difference. The cost of the anodized steel shroud is higher (up to $5 more in most cases), but because their durability is much greater it pays back quickly to have a shroud that is really resistant to daily welding and abuse.

Why Are These Design Features Important?

On threaded fume extraction shrouds, you can expect to see two different shapes. One is, on purpose, extremely tapered and completely slim along the torch line. This type of design does not affect the accessibility at all and it does not affect the vision at all. Typically, this shroud will extract smoke after the nozzle so you need more vacuum power to be effective being that you're positioned farther away.

With this design you have to consider the size of the opening and the proximity to the weld and the shape. Tapered fume extractions shrouds need to have the maximum amount of ingress possible because you want the maximum airflow to compensate for the fact that you're farther away – as much as three inches away from the weld.

Fume Extraction Questionnaire

The other types of treaded shroud design is called reverse section, or an umbrella shroud. These fume shrouds are the shape of a reverse funnel. This design allows you to be wider and closer to the weld, and because you are wider on the opening, you are able to effectively capture weld fumes at a high rate of suction while welding in more difficult positions and areas such as vertical, overhead, or on pipe.

The calculation that you have to make sure of with a reverse suction shroud is that you are not affecting the welding zone and the size and the volume getting through the reverse shroud does not affect movement of the air close to the weld. Because you are closer and wider to the weld, the shroud has better coverage of the smoke with less vacuum.

The reverse shroud allows for more room to play in. If you're welding at an angle that's difficult to access, or if you can't put your torch into the right place for the smoke extraction, the umbrella style allows for some forgiveness in such scenarios.

This style also works well when dealing with different types of fume extraction systems. If you have less vacuum power available, the reverse suction style is less sensitive to lower vacuum power and static pressure. It is more forgiving and gives you a great result. The downside is it's a little bulkier. When I introducing fume extraction torches to new welding plants, my go-to shroud is actually the reverse suction shroud to start. Then if you have any issues you can move on to other types of shrouds to address your specific issues.

Welding Engineer Considerations

The main factors for welding engineers when it comes to fume extraction and fume shrouds include:

  • Joint access
  • Weld quality
  • Effective and proper extraction of weld fumes

If you are a welding engineer evaluating fume extraction torches, and subsequently shrouds, one of the big factors you will weigh is accessibility. If you have a tool that is not allowing your welder to go into certain areas without issues, you have to redesign your parts. Sometimes engineering needs are so specific that redesigning the weld pattern is impossible or prohibitively expensive.

If you are a welding engineer, you want the shroud that is going to be normal for your design and maintains welding quality, because you care about that.  In my opinion, both the characteristics of accessibility and weld quality are key to the process. And a welding engineer most of the time will decide to go for the threaded tapered version of that shroud. You do want to make sure you have thickness and you have the proper vacuum systems to go along.

Fume Shroud Summary

Fume shrouds are critical for smoke extraction. You always want your fume shrouds on the torch, even if you are able to remove it. When you have your shroud on the torch, it is very important to do a proper maintenance on them.

You want to avoid debris or any spatter build up along the opening because any reduction of the holes would quickly bring a reduction of the smoke extraction quality. Fume shrouds need proper maintenance and cleaning.


Ready for more on fume extraction? Our eBook, The Complete Guide to Fume Extraction, walks you through everything you need to know to get started with fume extraction in your plant. And what's better, it's freely available! 

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Topics: Fume Extraction