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Crankshaft terminology

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  • Steve Antonucci

    Crankshaft terminology

    I have a question regarding crankshaft terminology and I'd
    like to solicit opinions from members here.

    As we all know, originally there were cast & forged crankshafts available
    from the factory. Cast cranks are obviously just that - cast.
    Forged crankshafts start life as a rough casting, then go
    through the forging process to compress the steel and make
    it inherently stronger. So, is it correct to refer to
    forged crankshafts as a casting ( eg. this crankshafts casting
    number is '7115 ), or should that '7115 be the forging number?

    For those that know, are the part numbers on the forged
    cranks ( eg. 6223, or 7115, or 7118 ) originally cast in to
    the rough castings, or added during the forging process?

    I often hear people refer to casting numbers when they refer
    to forged crankshafts. I just want to know if this is correct.

    Steve
  • Duke W.
    Beyond Control Poster
    • January 1, 1993
    • 15610

    #2
    Re: Crankshaft terminology

    Cast cranks are created when molten iron with about 2 percent carbon is poured into a mold that is very close to finished crankshaft dimensions. After cooling the raw casting is finished machined. The term "casting number" is correct for a cast crank.

    A forged crank is formed from a "billet" that is produced at a steel mill. The molten steel (about 0.4 percent carbon for a steel crankshaft) is poured into a mold and then formed into a rough shape after cooling to a plastic state where it is easily formed.

    The raw billet is then delivered to the forging plant that reheats the billet to a plastic state and uses multiple forging dies to hammer the billet to final rough form - similar to what comes out of the casting mold on a cast crank. OE GM cranks are forged "flat" and then "twisted" to form the cruciform crank throws.

    The embedded part number is most likely part of the forging process from the raw billet, not formed into the raw billet at the steel mill, so the term "forging number" is appropriate.

    Duke

    Comment

    • Steve Antonucci

      #3
      Re: Crankshaft terminology

      Thanks Duke! That pretty much puts that to bed.

      Steve

      Comment

      • Steve Antonucci

        #4
        Re: Crankshaft terminology

        Duke,

        When you wrote "formed flat, then twisted", what exactly does that mean?

        Steve

        Comment

        • Duke W.
          Beyond Control Poster
          • January 1, 1993
          • 15610

          #5
          Re: Crankshaft terminology

          The initial forging operations orient two throws at zero degrees and two at 180 degrees, which is "flat". Then final operations "twist" one of the journals to 90 degrees and another to 270 degrees orientation to form the final four throw or "cruciform" crankshaft form.

          Duke

          Comment

          • Christopher R.
            Extremely Frequent Poster
            • March 31, 1975
            • 1599

            #6
            Re: Crankshaft terminology

            Crankshaft forging plants have to be the dirtiest places in the world. The noise and heat (esp. in the Summer) are bad. But the dirt is incredible. They spray powdered graphite on the cranks which permeates the air. Gets on everything. Can't touch or brush against any surfaces in the plant. As a visitor, you wear a Tyvek jumpsuit and 2 pairs of booties. The employees dont'.

            Billets come down a conveyor belt to an induction furnace where they're heated to a few thusand degrees. They plop in front of the operator who sticks them in the die with tongs. 20, 40, or 60 ton forge slams down on the billet. Guy flips it over with the tongs, and the forge hits the other side. Believe it gets hit again on the way out of the forge to trim it. The hot crank is then hung to cool. Machining, heat treating, nitriding, etc. are all done later someplace else. Set up times always take too long, so once they get running, they like to keep going. That means long shifts, nights, and weekend work.

            Feels like Dante's Inferno on the floor. I don't know how they keep employees. They don't pay those guys enough. Thank your parents for making you study in school.

            Comment

            • Steve Antonucci

              #7
              Re: Crankshaft terminology

              Thanks Duke & Chris!

              Hey Chris, a crankshaft forging plant sounds like the perfect place for Mike
              Rowe and his "Dirty Jobs" program. Perhaps you should contact them and give
              them that idea. They're always soliciting viewers for ideas. Maybe you'll
              get a T-shirt or something.......

              Steve

              Comment

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