Advise for Galvanized Steel

[CENTURION]

Originally Posted by yash101

Let's just end this argument about whether zinc fumes are dangerous. Let's just say, zinc oxide can be dangerous, but isn't always, so just make sure to have proper ventilation. Just a fan blowing outside the building from where you are working should probably suffice, I guess!

It's never bad to be overcautious, especially when you can be harmed severely, or maybe even killed. That's why we give safety tests to students before they can use tools!

(Emphasis mine)

Please, if you don't actually know what you're talking about, don't offer safety advice on the subject.

I'm a professional machinist, so I handle safety concerns regarding our machine shop. I'm not a professional electrician or electrical engineer, so it's not a very good idea for me to give out safety advice about electricity besides "Don't touch it". Misinformation can cause accidents.

For this same reason, people will give out the advice; "Don't weld galvinized steel". Even though, as others have pointed out; it can be done. But it can only be done if you really, really know what you're doing. But "Don't do it" is a pretty good rule if you don't know exactly how to do it.

A fan blowing air out of the room to the outside is pretty much the bare minimum for ventilation. It might cut it if you want to get rid of some paint fumes, but when you're dealing with fumes that are actually dangerous, it's not going to be good enough.

[Alan Anderson]

Originally Posted by yash101

Let's just say, zinc oxide can be dangerous, but isn't always, so just make sure to have proper ventilation. Just a fan blowing outside the building from where you are working should probably suffice, I guess!

Please don't guess when health and safety are involved. You don't yet have the experience and expertise to give such advice...

...especially when you can be harmed severely, or maybe even killed. That's why we give safety tests to students before they can use tools!

Have you had any training involving the welding of galvanized steel? If not, I urge you to hold your tongue when you get the urge to answer safety-related questions about it. But please keep asking questions!

[edit]I didn't see Evan's note above when I wrote my reply, and I apologize for the redundant message. I didn't delete it, because I think my final sentence is important.[/edit]

[FrankJ]

Here is a fact sheet from the the American Welding Society on metal fume fever. Google is you friend.

[JamesCH95]

As a welder I prefer to TIG-braze galvanized steel with silicon-bronze filler material. I find it results in a strong weld joint and greatly reduces the amount of noxious fumes emitted by the joining process due to the low heat input of brazing and the fact that the base steel isn't actually melted. Several critical parts on our 2013 climbing mechanism were TIG-brazed with silicon-bronze filler.

Others have done a great job of addressing the safety concerns.

[DELurker]

Originally Posted by jman4747

We recently got a local sheet metal company to donate their scrap metal to us. They have 3003 aluminum but not a large amounts. Most of what they can give us would be galvanized steel and I wanted to know what most people would use it for. I was also wondering about any suggestions on machining it and what other types of tooling to use as well as safety. From looking at the scrap I saw everything from angle to strips to sheets as big as 4'x4'.

Coming back to the original post...

Remember that steel is as strong as aluminum per pound. To accomplish the same task will require the same weight of either metal. With that said, aluminum is usually a better choice because (let's face it), we're building relatively low-weight robots compared to industry. Steel is (mostly) harder to machine than aluminum (slower feed rates, smaller cuts, etc).

For machining it, the machine is as important as the tooling. Although a drill press will work, I'd advise a mill for the improved control and precision. For safety, if you're not cooking it (see previous posts), it's (mostly) just like machining regular steel.

Personally, I'd advise my team against the galvanized steel in large quantities. We'd never go through enough of it to justify the hassle of storing it and machining it. Plus, we're always running close to the weight limits and steel would just make that worse.

[Ether]

Originally Posted by DELurker

Remember that steel is as strong as aluminum per pound.

Not true as a general proposition. Depends on the type of steel, and type of aluminum being compared.

[magnets]

Can you weld galvanized steel?

Yes.

Would I feel comfortable doing it around or with high school students?

No.

[magnets]

Originally Posted by DELurker

Coming back to the original post...

Remember that steel is as strong as aluminum per pound. To accomplish the same task will require the same weight of either metal.

Not true. Aluminum (as a generalization for FRC, you can find exceptions) has a significantly higher strength to weight than steel. In fact, for shafts/gears, your 7075 aluminum is both lighter and stronger that the common stainless steels places like andymark use. In terms of ultimate yield strength, aluminum is roughly 1/3 the weight and almost twice as strong.

[yash101]

I wouldn't say "significantly stronger" but yeah, it can be stronger per unit of weight.

[DampRobot]

Originally Posted by magnets

Not true. Aluminum (as a generalization for FRC, you can find exceptions) has a significantly higher strength to weight than steel. In fact, for shafts/gears, your 7075 aluminum is both lighter and stronger that the common stainless steels places like andymark use. In terms of ultimate yield strength, aluminum is roughly 1/3 the weight and almost twice as strong.

It's also a more expensive. Something else to note is that steel generally is more stiff than aluminum per unit weight. When you're building something like a bridge, those two factors can be important.

The real reason aluminum is thought of as lighter (for FRC purposes) is that we rarely design on weight, we usually design on size. There's a lot of arbitrary standards in FRC (1/4" thick bearings, 20 DP gears, 2x1 tubing, etc) where stuff just needs to be that big to conform to a standard. Your WCD will be a ton harder to design if you choose .75x.75 steel tubing vs alu 2x1, for example. Also, for stuff like shafts, aluminum (especially 7075) usually has an adequate total yield strength, and since the shaft needs to be 1/2" hex, the alu will be a lot lighter than steel. In other places, we need certain plate thickenesses to get the right number of threads in a tapped hope. Again, steel will be heavier because we just care about overall thickness, not strength. Of course, if we designed all our parts to just be a certain strength, steel and aluminum would be a lot more comparable in terms of weight.

Sure, we could crazily pocket steel or change our FRC wide standards to conform to steel robots. But until then, the lower density of aluminum and comparable strength will make it seen lighter for FRC purposes.

[Ether]

Originally Posted by yash101

I wouldn't say "significantly stronger"

The difference is large enough to be noticed, for purposes of FRC use.

[DonRotolo]

Originally Posted by yash101

I don't get why not to put copper with steel. I connect copper to steel, once in a while!
By you saying "electrolysis," do you mean that it will break up water when you electrolyze it and place it inside water?

Um, we are talking about galvanized steel, so the copper would be coming into contact with zinc. Go look up what happens when copper and zinc are in contact with each other. Can you say... "battery"?

You can perform electrolysis with many materials, not just water.

Originally Posted by MrBasse

I always cringe when new people are jumped on for spreading misinformation... but I feel that this is a time for learning as well.

You can weld galvanized steel with no issues as long as you use proper equipment. You do not get zinc poisoning from the fumes.

Thank you MrBasse for the elaboration.

My concern was not the zinc fumes, but weld spatter. Glavanized spits out molten globs of metal a LOT more than other materials.

I did not say it couldn't be welded, just that this particular person should not try it.

I stand corrected.

[DELurker]

Originally Posted by magnets

Not true. Aluminum (as a generalization for FRC, you can find exceptions) has a significantly higher strength to weight than steel. In fact, for shafts/gears, your 7075 aluminum is both lighter and stronger that the common stainless steels places like andymark use. In terms of ultimate yield strength, aluminum is roughly 1/3 the weight and almost twice as strong.

I disagree, although I will point out that stainless steel (302, 303, 304, 316) is a specific and (typically) less durable subset of steels (without getting into hardenable stainless such as 440C). The 3x price differential on stainless makes it less than desirable for teams to work with in the raw, aside from the additional tooling needed to properly work it. However, I will support my original contention with the following links and tables...

Reference #1
Reference #2

from reference #2...
........................................Aluminium. ................Steel
Density, ρ kg m−3...............2,700......................7 ,800
Young modulus, E N mm−2....70,000....................210,000
Shear modulus, G N mm−2.....27,000....................81,000
Poisson ratio, ν.....................0.33........................ 0.3

from matweb.com...
1018 steel versus 6061-T6 aluminum versus ASTM A526 galvanized steel

I could never bring myself to use aluminum for a shaft. It is too weak (comparably) to take that shock and torsion loads, as well as being more prone to unannounced catastrophic failure over steel (steel bends and then breaks ... aluminum has a much smaller deformation period before it snaps under the same loads). I'd rather use a steel shaft so that I could press-fit it into a bearing. The surface properties of aluminum just aren't good enough (at least for me) for rotating or direct-contact sliding.

[jman4747]

So if I have the tooling and can keep the weight down why not save the money? And if I get 3 times as much free sheet steel wouldn't it just be better to save the money and be smart about its use?

Basically what I'm getting at is it isn't as simple as Steel is denser or aluminum is less rigid. For instance at the beginning of last build I found that a welded steel version of the kit-bot frame we used would be several times more rigid and cheaper. It would only have been about 2-5lbs heavier and that robot was 98lbs at inspection. We didn't posses the tooling to work it quick enough yet so we scraped it.

Witch metal to use has to do with the circumstances surrounding the team and the build.

[Oblarg]

Originally Posted by jman4747

Witch metal to use has to do with the circumstances surrounding the team and the build.

This statement can be generalized to "material choices are context-dependent," or "design choices are context-dependent," or even "essentially all utility calculations are context-dependent." It is good to keep in mind the difference between a heuristic rule and a fundamental principal - general statements about "optimal materials for FRC" are quite clearly of the former sort, and you should thus interpret them as such.