Welding veins in fan ?

[danny gabbard]

Whats your ideas ? I am not really sold on welding every one soild. Maybe every other row and stager inner and outer? All your trying to do is keep disk on fan from pushing apart. Less weight and less hard spots from welds heating and cooling down,  Just one of them things I wonder about before I go do something.

[rick m]

Danny,

Most of us just tig the tangs to the fan without rod.  Then you are not adding material. Also. get the fan blade balanced.  It makes a difference. The factory ones were balanced.  If you look close at a factory one, you will find a little washer or weight somewhere on the fan for balancing.

Rick M

[Bruce]

..... and less hard spots from welds heating and cooling down,

That can't happen.  The fan is simple low carbon steel. It doesn't matter how much you heat it and quench it, it's hardness can't be changed.

I once had a welded fan explode.  IMO there's no need to skip welding any of the blades.

[danny gabbard]

Bruce where did that fan break first? Next to the weld probably! And thinks do get harder after they have been welded and the quicker you bring the heat down from after welding also can make welds harder! Thats why things are heat treated or stress relieved after welding. Weld something and run a file over it and run a file over the same material not welded and tell me whats harder ! Plus weld ever other row of veins and just try to pry one of the none welded ones out.

[Bruce]

And thinks do get harder after they have been welded and the quicker you bring the heat down from after welding also can make welds harder! Thats why things are heat treated or stress relieved after welding. Weld something and run a file over it and run a file over the same material not welded and tell me whats harder !

You're absolutely wrong.  Mild steel can NOT be heat treated in any way.  This is basic metalurgy 101.

[Dougy Dee]

I usually weld all the vanes. I'm not convinced the air pressure on the vanes doesn't distort the vanes and pull the tabs form the round housing causing the failure.

[danny gabbard]

And thinks do get harder after they have been welded and the quicker you bring the heat down from after welding also can make welds harder! Thats why things are heat treated or stress relieved after welding. Weld something and run a file over it and run a file over the same material not welded and tell me whats harder !

You're absolutely wrong.  Mild steel can NOT be heat treated in any way.  This is basic metalurgy 101.

Why cant it ! So what your saying, Is that after a part is welded , It can not be heated to almost red and then heat drawn down VERY slow Will not relieve stress in welded area?

[danny gabbard]

Another problem with even the vw fans is that all the holes are punched and not drilled. Punching holes create's stress and small cracks.

[danny gabbard]

Bruce, Your right about heat treating carbon steel ! I just got off phone with phil remmington at dan gurneys. I meant to say that you can aneil after welding ! What I mean by aneiling is heat part back up and cover in lime and draw heat down slow. Sorry if I sturred anything up bruce !!  Sorry about spelling to

[rick m]

Funny threads.  I've not blown up a welded fan...even after sitting in the waterbox at 7,000rpm for quite a long time.  Annealing does help.   :-)

RM

[Bruce]

..... you can aneil after welding ! What I mean by aneiling is heat part back up and cover in lime and draw heat down slow....

You can try to anneal it, but it does nothing.

In order to heat treat steel, there must be a certain minimum amount of carbon present.  A very commonly used cheap steel is AISI 1020.  This is steel with 0.2% carbon.  Because of this low carbon content, heating, quenching, cooling, all have no effect on any of it's properties.

My memory has the transition at 0.4% carbon content.  That means any steel higher than AISI 1040 can be heat treated. 

Here are some of the things you can do to this higher carbon steel:
Quenching:
This is where the steel part is heated in an oven until it is glowing red, around 800ºC.  Then you take it out and dunk it in oil to rapidly cool it.  You can quench it in water, but it doesn't work well since the water in contact with the metal instantly boils, forming a gaseous barrier between the water and the part.  This leads to inconsistent cooling rates.  Oil doesn't suffer this effect.
The result of quenching is that the part becomes as hard as it can possibly be, and very brittle.  This is what you are wanting to avoid when you weld your fan.  However, in order for quenching to alter the properties of the steel part, there has to be at least 0.4% C.  The fan doesn't have that.

Tempering:
If you started with the alloy that is used for springs, then you heat it as described above, quenched it in oil, it would be a useless product.  You need to restore some of it's former ductility so it won't break if loaded.  By re-heating the part after quenching, up to the point where a shiny part of the steel turns blue, then slowly cooling, you've now created a spring.

Annealing:
Heat it up, again to around 800ºC, then insulate it as best as you can to allow it to cool as slow as possible.  A common practice is to turn the oven off and let it cool overnight.  This is done to relieve any stresses or localized hardening that may exist in the part. 

All three of the above processes can only be done to steel with a certain minimum carbon content. (AISI 1040)  This is not the stock cooling fan.

Every auto enthusiast has heard of the use of cro-moly steels for making a chassis.  These steels have chromium and molybdenum as well as carbon.  The Cr and Mo have what is called a carbon equivalent that is used to determine it's heat treating properties.  As you've guessed, this carbon equivalent is way over the magical 0.4% that's needed to heat treat.  This means when you weld two pieces together, if the weld is allowed to cool too fast, the joint will be very brittle.  When this happens, the metal has "air quenched".  Also important is to use the right welding rod, so you don't get dissimilar alloys in the weld joint.  At the end of the fab of a frame, the better shop will anneal the entire chassis to eliminate all brittle parts.  The advanced welder can minimize this effect, but the absolute best is to anneal the chassis.

Here's an experiment you can do to demonstrate what I'm talking about. 
One thing most Cal-Lookers have done is to bend a pushrod at least once.  If you have one of these bent pushrods, it's the perfect candidate because it's likely cro-moly steel.  Also get yourself a wire coat hanger.  Cut the coat hanger so you've got the long bottom part.  Change the oil in your car, saving the oil, preferably in a metal container big enough to throw the pushrod in.  Now get your torches out and heat most of the pushrod until it's glowing orange.  Then toss it in the oil.  Do the same with the coat hanger.  Once you fish it out of the oil, clamp one end of the pushrod in the vise and start pulling on the other end.  It won't bend, it will almost shatter.  You may need a bit of a pipe extension.  Do the same with the coat hanger, it will be just as flexy after the quenching as it was before.  That's because the coat hanger does not have enough carbon content.
Another test you can do is to run a file on the pushrod before the quenching, then again after.  Afterwards it will be so hard, the file won't bite, whereas before, the file will cut easily.


http://en.wikipedia.org/wiki/Carbon_steel

[Jeff68]

Thanks for the information Bruce. In my younger days I worked in a Tool and Die Shop and spent some time heat treating different steels when makinging inspection type tooling and machiing fixtures.  Your post brings back many memories of time I spent learning proper heat treating to get specific hardness and properties in certain steels.  I never did try and heat treat low carbon steel, didn't know why at first but learned later. What Bruce has written is correct, I experienced it first hand.   I never knew or considered what a VW was made of, never thought about it until now.  I use a late Berg welded and balanced fan in my 2110.  Jeff

[danny gabbard]

How about useing silicon bronze for welding fan together? Or even panel adhesives that the autobody industry is useing to glue panels on cars? Thanks bruce for info, When I worked at gurneys most of the stuff I built and annealed was cro-moly, And I just figured carbon still annealed the same. One things for sure carbon steel and heat, play hell on how hard it gets Quick question , We use to cover parts in lime powder while parts were cooling down from the 800-900 degree area, never new why we used lime? But if phil remmington told me to do it I did it. rem also told me if I could find a real maulable or soft alloy rod would help. Something That I do see 80-90 percent of people welding is overcook or use to much heat while welding and something else I noticed is that mig welding verse tig welding that the mig welds are alot harder, Maybe rod or wire or maybe even how quick mig cools.