Why a anodized mast?

[Delancey]

I have some professional experience designing extrusions for architectural applications. Generally, "mast manufacturers" pay a fee to have an extrusion die produced, which then goes to an extruder, typically one who has won a bid for production, dies can travel around depending.

Shapes are extruded in a press, the diameter of the shape dictates the size of the press. The bigger the press the more you tend to pay per pound of extrusion. Part of the process involves straightening after extrusion.

For something like a mast alloys like 6061 T6 or 6063 H52 are commonly used, as mentioned these are different from the type used for hulls which tend to be 5000 series. Lengths tend to not exceed 40' but I have heard of some out to 60', masts which are longer than this usually have a butt joint. Oftentimes the builder will take a section of the same extrusion and remove a portion of it along the axis reduce the outside diameter and sleeve the butt joint, sometimes a separate sleeve is extruded.

Anodizing is an electrochemical process whereby the surface of aluminum is converted into a stabile oxide coating. The quality of the coating is gauged by its thickness. The process involves an acid bath, a rinse, the anodizing bath, a dye bath if the path is to be colored, and finally a sealer to fill are the micro pores from the acid bath. The longer the time in the anodizing bath, the thicker the coating, the higher the cost.

Keep in mind, even a forty foot anodizing tank is rarely more than about three feet wide or deeper than about four or four and a half feet deep. Because of this you're not likely to see an anodized hulls on anything bigger than a canoes.

Anodizing addresses one of the main problems when it comes to finishing aluminum, the fact that the naturally occurring oxidation on aluminum tends to be rather unstable which means it tends to slough off most coating in time.

Besides anodizing the way around this is to use a zinc chromate base primer, the only way to expect any success with paint. There varieties suitable for brush applications, a spray can version marketed for painting out drives, and primers intended for different LPU or APU paint systems such as Awlgrip, basically airplane or automotive paints that have at best 5 year warranties for exterior applications. Zinc chromate paints are dangerous to work with BTW so be careful.

The best paint system for aluminum is called Kynar which is available from licensed applicators with up to a twenty year warranty but good like finding someone who can handle a part bigger than about twenty feet, the process requires a post-cure in an oven.

[Delancey]

A couple more bits about anodizing - the anodized surface is significantly harder than the base metal. Typically the anodizing process works from the outside in but there is another kind called Hardcoat that actually build up a thickness to your part. This Hardcoat Anodizing also happens to have the greatest hardness of any anodized coating which is why it get used for M-15 rifle magazines, frozen pizza factory crust baking pans, and sailboat winches.

Anodizing Fun Fact - anodized surfaces are electrically NONCONDUCTiVE.

[Helios]

Also because the ano layer is both very hard and thin the base aluminum can't be formed or bent after the anodization process without cracking the oxide layer and ruining the cosmetic finish. This prevents manufacturers from buying pre-anodized sheet aluminum to use in the hull fabrication process.

[Cheechako]

Originally Posted by Delancey

I have some professional experience designing extrusions for architectural applications. Generally, "mast manufacturers" pay a fee to have an extrusion die produced, which then goes to an extruder, typically one who has won a bid for production, dies can travel around depending.

Shapes are extruded in a press, the diameter of the shape dictates the size of the press. The bigger the press the more you tend to pay per pound of extrusion. Part of the process involves straightening after extrusion.

For something like a mast alloys like 6061 T6 or 6063 H52 are commonly used, as mentioned these are different from the type used for hulls which tend to be 5000 series. Lengths tend to not exceed 40' but I have heard of some out to 60', masts which are longer than this usually have a butt joint. Oftentimes the builder will take a section of the same extrusion and remove a portion of it along the axis reduce the outside diameter and sleeve the butt joint, sometimes a separate sleeve is extruded.

Anodizing is an electrochemical process whereby the surface of aluminum is converted into a stabile oxide coating. The quality of the coating is gauged by its thickness. The process involves an acid bath, a rinse, the anodizing bath, a dye bath if the path is to be colored, and finally a sealer to fill are the micro pores from the acid bath. The longer the time in the anodizing bath, the thicker the coating, the higher the cost.

Keep in mind, even a forty foot anodizing tank is rarely more than about three feet wide or deeper than about four or four and a half feet deep. Because of this you're not likely to see an anodized hulls on anything bigger than a canoes.

Anodizing addresses one of the main problems when it comes to finishing aluminum, the fact that the naturally occurring oxidation on aluminum tends to be rather unstable which means it tends to slough off most coating in time.

Besides anodizing the way around this is to use a zinc chromate base primer, the only way to expect any success with paint. There varieties suitable for brush applications, a spray can version marketed for painting out drives, and primers intended for different LPU or APU paint systems such as Awlgrip, basically airplane or automotive paints that have at best 5 year warranties for exterior applications. Zinc chromate paints are dangerous to work with BTW so be careful.

The best paint system for aluminum is called Kynar which is available from licensed applicators with up to a twenty year warranty but good like finding someone who can handle a part bigger than about twenty feet, the process requires a post-cure in an oven.

Great post. Most of the longer masts Ihave seen have been spliced. I dont know that I've ever seen an anodized mast over 40 feet or so...? Even if there were tanks long enough, one reason might be that the acid would get trapped into the spliced/sleeved area and that would not be good.
I have looked into purchasing extrusion dies and they are surprisingly not as expensive as I would have thought. 40 feet is the normal trucking length, maybe that's one reason they dont commonly extrude longer? One also has to wonder how straight they can keep the extrusion beyond 40 feet. Also, Arent they heat treated after extrusion? I cant imagine they are being extruded in T4 or T6 condition...

[HappyMdRSailor]

Originally Posted by Delancey

A couple more bits about anodizing - the anodized surface is significantly harder than the base metal. Typically the anodizing process works from the outside in but there is another kind called Hardcoat that actually build up a thickness to your part. This Hardcoat Anodizing also happens to have the greatest hardness of any anodized coating which is why it get used for M-15 rifle magazines, frozen pizza factory crust baking pans, and sailboat winches.

Anodizing Fun Fact - anodized surfaces are electrically NONCONDUCTiVE.

I've had my hands on thousands of anodized parts and never knew this.... Indeed a FUN FACT!

Originally Posted by Cheechako

Great post. Most of the longer masts Ihave seen have been spliced. I dont know that I've ever seen an anodized mast over 40 feet or so...? Even if there were tanks long enough, one reason might be that the acid would get trapped into the spliced/sleeved area and that would not be good.
I have looked into purchasing extrusion dies and they are surprisingly not as expensive as I would have thought. 40 feet is the normal trucking length, maybe that's one reason they dont commonly extrude longer? One also has to wonder how straight they can keep the extrusion beyond 40 feet. Also, Arent they heat treated after extrusion? I cant imagine they are being extruded in T4 or T6 condition...

Cheech... I have heard the same thing about extrusion lengths doing research for sticks... Everything over 40' being spliced... Now that I think about it, can't recall a big stick anodized?

[Delancey]

Splicing extrusions usually involves mechanical fasteners and after the parts are anodized. But when designing connections with anodized parts allowances have to be made for reducing or building up the part thickness depending on anodizing type.

As far as I can tell the max length thing is more a function of demand balanced by practical necessity. Most metal stock tends to not be supplied in lengths greater that about twenty feet which is fine for most people making most things.

The anodizers with the long tanks that I am aware of tend to be located near industry that has a specific need for those long lengths. An example would be a company called Pioneer Metal Finishing in Greenbay, Wisconsin does anodizing for the paper production industry based there, big long paper rollers and whatnot.

Regarding alloy types and temper, confess I don't know all the ins and outs as I haven't needed to learn them but the first four digits are the actual alloy type and the subsequent letters and numbers (the T-6 part or the H-32) are the tempers and in general the aluminum is extruded from its molten state and tempering happens after the fact either deliberately or naturally in the case of the air hardening types.

For what it's worth there is general correlation between the alloy series number and it's physical qualities. For example 5000 series tend to be softer and more ductile than a 6000 series which tend to have higher tensile strength and hardness. Hence people tend to weld hulls with 5000 and extrude masts with 6000. Alloys series range I think from 1,000 out to 7,000 but have never used anything other than 5 or 6.

Then there are the casting alloys which are a whole other ball of wax. I have experience making molds and casting with aluminum but nothing structural so don't really know much about the casting alloys.

One thing that always sort of blew my mind was that when we had leftover aluminum in the crucible we would pour it into ingot molds which were sort of like how a chocolate bar is segmented. We would come back with a sledge to break the ingot into smaller pieces.

Surprise, you could break a 2" thick by 3" wide section of cast aluminum with a surprising little amount of effort. Again, we were making sculptures and not structural components and there was very rapid cooling of the ingot mold, but still, I was shocked.

As it is I happen to have an old Isomat rig which has a very high quality clear anodized finish. That is except for the cast aluminum spreader bases which are welded onto the mast before anodizing. This is because of a reaction that occurs involving the cast alloy, the filler rod used in welding, and the extruded alloy which turns the welded filler and cast base black that I learned about the hard way on a job once.

With the correct filler you can avoid having your welds turn black during anodizing when you are welding extrusion or plate, but as far as I know it's a problem with anodizing the cast alloys. Take a look at your neighbors rig once if he has an older Isomat and you will see what I am talking about.

+1 on the earlier comment about cracking that can occur when post forming anodized parts. Due to the relative increase in hardness of the anodized layer compared to the base, anodized parts suffer fatigue related cracking when post formed which can lead to crevice corrosion where you want it the least, an area that has already been deformed.

[HappyMdRSailor]

Originally Posted by Delancey

For what it's worth there is general correlation between the alloy series number and it's physical qualities. For example 5000 series tend to be softer and more ductile than a 6000 series which tend to have higher tensile strength and hardness. Hence people tend to weld hulls with 5000 and extrude masts with 6000. Alloys series range I think from 1,000 out to 7,000 but have never used anything other than 5 or 6.

I've done a ton of stuff outta aluminum, as I fabbed a bunch of gadgets and fixtures over the years... Even welded and anodized stuff myself...

2000 series Al is fun to work with, as it cuts like soft cheese!

[Delancey]

Aluminum is a great material and one of my favs. Its usefulness is evidenced by how widely it is used, and yet I see a lot to steel used where aluminum would be more appropriate I think people tend to be caution by their lack of familiarity with it.

Very much yes to carving, which I have done on 6000 series and now that I think of it some 2000 a long time ago. Wood working chisels can be used but I might not use my finest bevel or risk breaking a tip. This can come in supper handy if you have a clearance issue with mating parts but can't get at it with a grinder or other tool.

A pro tip is to have a stick of parafin handy for coating your cutting tools. Aluminum suffers from smearing during cutting and grinding operations which can clog abrasive pads, drill bits, and router blades so a little wax will go a long way to make your job easier. Include in this files and rasps as well.

One suggestion I have for anyone contemplating a project in aluminum like a radar arch or whatever is to check out your local sign fabricator. Most large metropolitan areas usually have at least a couple custom electrical sign shops and at least one of them has a CNC router table that can be used to quickly and precisely cut parts, all of them will have sheet metal breaks and shears which a more common fab shop that just does welding will likely not. All of them routinely make goofy stuff out of sheet and extruded aluminum using MIG and TIG wleding.

Plus, the sign guys are almost universally highly creative people with great problem solving skills will more likely take an interest in your crazy project than laugh at you. These guys also do fabric awnings and will often have overstock Sunbrella lying around you can get for cheap sometimes.

Happy Building!

Aluminum Fun Fact - Aluminum Oxide is harder than steel! Hence it is widely used as an abrasive for sandpaper, grinding disks, and cut-off wheels.