No announcement yet.

What is meant by billet aluminum

  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    There's been some talk of "voids" and "particles" I would add "coarse grain structure". These in the sense of physical properties can be good or bad or have little effect depending on the nature and end use of the material.

    Used to be when a casting cracked it was "stop drilled" the drilled hole had a way of preventing the crack from propogating. For the same reason, inclusions and voids in some materials make them a bit more fatigue resistant, some less.

    Any common alloy is a careful balance of dozens of properties not the least of which is cost. Stressed parts in old cars were made form frequently rich and relatively expensive alloys. Makers of traditional hand planes and chisels look for pre '70's automotive leaf springs for re-forge stock. Model "T" Ford driveshafts have been converted to countless uses.

    Castings used in aircraft structure looks crystaline when it fails - like a brittle cast iron fracture - but there's considerable yield before it does. If you look closely at a machined portion near the fracture the deformed metal looks porous and the crystaline nature of the material stands out clearly in the surface. First time I saw this in an piece of aircraft wreckage I was shocked. Then I reflected that aircraft are made of the strongest and lightest materials. There must be some reason that particular alloy is used. Later discussion with an old metallurgist confirmed my conclusions.

    The Navy builds warship structure from a low carbon steel with superb welding and cold water ductility properties. If the ship is grounded (what ship won't be at some time in its career) they want the plates to deform rather than tear or shear. Plastic deformation keeps the plates intact and the water out. Extra thickness is provided as a corrosion allowance.

    The hull could be made of something corrosion resistant but even the lower alloy stainless suffer from chloride stress corrosion, fatigue susceptability.

    While most austinetic stainlesses weld very well, there's the problem of securing the same corrosion properties in the weld as the base metal. Cost is enough to scuttle forever the notion of stainless steel hulls; even low alloy stainless contains significant percentages of nickel and chromium making it maybe ten times as expensive as low carbon steel.

    Material selection for high stressed part continues. High revving racing engines with characteristic strain reversals and middling heat have been very well met with what could be called conventional materials commonly used in the automotive industry.

    My performance car expertise is spotty and now its certainly out of date but here's an example of stuff doesn't have to be expensive to perform well. For a long time, Chevy and Chrysler used closed die forged alloy steel cranks while Ford used cast nodular iron. The manufacturing costs for the forged crank were said to be double the cast crank. I've seen liturature where The Ford cast crank is superior in terms of longevity and catastrophic failure compared to the forged crank. The tensile tests of the cast crank were lower but there were properties inherent in the material that uniquely suited it to requirements of automotive cranks.

    The same was previously true of titanium connecting rods Vs alloy steel but superior design and greater knowledge of the inner mysteries of titanium has resulted in titanium as the preferred choice in the spare-no-cost world of competition.

    One reason why "billet aluminum" is popular for after market automotive parts is that there was mountains of it available in the form of aircraft production remnents in Southern California in the early boom years of hot-rodding. It was also easy to machine and provide with colorful anodizing. What we have here is an economic incentive become tradtion. Here is the only reference to "billet" in this piece.

    Hot-rod magazines are rife with know-it-all writers of shallow experience blathering to an uncritical readership about how adding this pile of (expensive) parts makes 16 (or 162) more HP when no before and after instrumented test data is offered.

    The assumption is their readership is ignorant. The tragedy is the assumption is frequently correct; there is a sucker born every minute.

    I watched as an acquaintance of mine poured tens of thousands of dollars in a racing engine over a period of three years working from magazine ads claims ignoring cautionary tales from the knowledgable (not me, I didn't know him well enough to trash his dreams).

    When he was done the drag racing rules had evolved and most of his work wasted so far as the competitive advantages he'd built into his '69 Pontiac GTO: the racing world went and moved the goal post.

    To add insult to injury, he trailered his car to a famous local competition shop for a dyno tune-up. He assumed from the magazines he read he'd get over 500 HP from his 389. In fact he got less than 400 in spite of the tune-up shop's best efforts. It was porting and pistons, they didn't work together.

    All that time and money and he didn't even have a worthy street rod. His world was crushed. He not only invested a lot of money but his expectations of glory and all for nought. It seems silly to put it this way but its true: he grieved for more than a year. His wife had a hard four years thanks to this debacle but she persevered and their family came out of this obsession intact.

    The fool-and-his-money market seems to be fading from the performance parts scene I'm glad to say, but it's not gone completely.

    While it's a great pleasure to me to work on fine mechanisms and assemble well designed and fitted parts I think there should be some benefit attached to the work. After-market kits and modifications have become much more competitive these days and the manufacturers no longer have an eager uncritical customer base. They're forced to provide some support for their assertions (least their competition leap into the breach) thus the assertions have become more moderate and less comprehensive.

    I love the expressions: "Show me", "Why", and the expression on the saleman's face when you confound him by offering a simple uncontrovertable refutation.

    My point is to love the pretty go-fast stuff (I do) but remain skeptical.

    [This message has been edited by Forrest Addy (edited 02-11-2003).]


    • #17
      Good post, Forrest.



      • #18
        Hey Forrest
        That literature that claimed that nodular iron cranks had better longevity than forged cranks, who wrote that article? In the 60's and early 70's Chev.also used cast cranks but only in their low-reving motors, the high-perf, high reving engines all had forged cranks. Did they do this just to raise their costs or was there an advantage to using the forged cranks? Chevy's connecting rods also followed the same senario. I believe that ford also used forged cranks and rods in their hi-perf engines. I don't think anyone building hi-perf engines uses cast cranks, maybe this literature was in error.



        • #19
          Early '70's. Maybe I was in error. I do remember a short fuss about which was superior and the Ford cast cranks won by a nose. There was an article in one of the engineering trade magazines of the time; "Design" maybe. The exact truth is lost in the mists of time.

          The llustration was intended to emphasize a point on materials not a particular manufacturer's superiority.


          There's many reasons for selecting a particular material for service in mass production goods; not the least of these is marketing advantage. "Forged steel" always has the feeling of rugged durability whereas "cast iron" even with "nodular" attached evokes parlor stoves and frying pans regardless of sophisticated metallurgy and proven performance in the manfufactured article.

          Golfers and fishermen are always marks for exotic claims. Take a 22 handicap golfer or a dry fly fisherman with nary a fish scale in his creel and you can always snare his attention with a titanium anything if it suntracts one stroke or adds one fish to the tally.

          People are crows I keep telling you. They flock to the glittering promise. They'll accept sizzle instead of steak and pay more money besides. Make up a trendy name, add some plastic and decals and drape a scrawny model over an otherwise reliable but lackluster car and you have the year's best seller.

          Sad to say, scientific method and every-day life are contradictory and sometimes antithetical. That African tribal elder was right: Americans are consumers first and reasonable and wise last.

          [This message has been edited by Forrest Addy (edited 02-11-2003).]


          • #20
            I see your point. As a chemist scientific method was drilled into my head in school,however, it rarely is practiced anymore. Today we run on conjecture, junk science, opinions, and B.S.---hey, don't confuse me with facts, remember if it's said, read, or heard it's true!!!



            • #21
              Forrest could be nicer with his words, but its hard to tell the king he has no clothes on.

              Its not only the magazines for the kids that pass out bum info, its trade magazines some sponsered by the the re-builders association. Good info is hard to come by. And if you get some, hold on to it and be sceptical of of info that can not be confirmed with a stop watch.

              Gonna try to make the motorcycles at Daytona this year. Those are machines that are real!!!!
              edit comment: just so there is little doubt- i agree with with forrest in the main but forrest you took away their joy and gave little in return.

              [This message has been edited by docsteve66 (edited 02-11-2003).]


              • #22
                Geeze you guys are sensitive. The places where I was seeming the most outrageous was where I was funnin' ya the most. If polititians aren't venal, women aren't unpredictable, and hotrodder and bikers aren't gullible this wouldn't be America wwhere we celebrate out foolishness.

                No wonder the people who make the cell phone stick-on that acts like an antenna four feet long made a fortune.

                See, there I did it again.


                • #23
                  The following is a quick explanation on how aluminum is process.

                  Aluminum is produced in reduction cells called pots. The aluminum is siphoned from the pot and then can be pored into sows, 2000 lb chunks in cast iron molds, pigs which are approximately 50 pounds. The sows and pigs are just cooled in air and will be used later when they are put in furnaces and melted. This is where alloying of the aluminum takes place. Anytime aluminum is remelted about 2% of it weight is lost.

                  Aluminum is also taken for the pots and put directly in furnaces. The metal is then alloyed to whatever spec is called for. The metal is then cast in open pit using the DC (direct chill) casting technique. The metal is allowed to flow into a mold at a controlled rate. When the mold is about filled a platen moves a bottom block out of the bottom of the mold. The mold has a water jacket in it that starts to chill and solidity the outside of the aluminum in the mold. As the aluminum leaves the bottom of the mold water is sprayed on it to continue the solidification process. All sizes and shapes (rounds, square, rectangular, and large "T" shapes) are produced this way. These aluminum shapes can weigh up to about 40,000 pounds. The big rectangular shapes are called rolling ingots. The round shapes are called logs. During the cooling process some of the alloying components will freeze out preferentially and freeze in the skin of the shape. All of these DC castings are then put into a homogenizing furnace and brought up to it critical temperature (about 900 degrees) and held there for several hours. This help control the grain structure and will make the metal the same throughout except for the outside surface of skin. The logs (round shape) are then sawed into smaller lengths 12 to 24 inches long and are called billets. These are normally sent to extrudes where they are processed in extrusion presses to make the shapes we are all familiar with, angle, flats, etc. That is first time that the aluminum is refered to as billet.

                  The big 40,000 pound and smaller big casting are refered to as ingots. Rolling ingots are the biggest. They are scalped, removing the outer surface of the ingot, on a big milling machine called a scalper. These are big machines. they will remove .250 depth and better 72" wide in one pass. These are then processed through soaking pit or other big furnaces to homogenize them. The rolling ingots are processed hot on a hot line which rolls them into thinner long pieces or plate. The mills on a hot line will process a 24" thick ingot into a .250" thick sheet that is coiled at the end of the line. The coils are all annelled before being processed in cold rolling mills to produce thinner sheet. There is a lot more to this but it would take too long.

                  Just trying to help with the understanding of how aluminum is processed.


                  [This message has been edited by WJHartson (edited 02-12-2003).]


                  • #24
                    Thanks Joe for that insightful description.



                    • #25
                      I see what you are getting at, and are reminded of a little old lady in the eighties proclaiming "Where's the beef!"

                      In this day and age it can be difficult to separate the sheep **** from the cherry stones...

                      [This message has been edited by Thrud (edited 02-11-2003).]


                      • #26
                        22 replies and we finally get a good answer to the original question. THANKYOU. Not that I didn't enjoy the banter but I believe the group could have answered the question sooner.