CENTRIFUGAL CASTING METHOD AND APPARATUS
A method and apparatus for centrifugal casting, in which transfer functions are developed relating the fluidity of molten metal, for example iron of varying composition, to casting machine movement for a particular mold in order to cast objects, for example pipe, having desired and uniform characteristics, including wall thickness. Fluidity is calculated for each pour of molten metal based on the measured pour temperature and measured liquidus arrest temperature. A drive system controlled by a programmable logic controller moves the casting machine in accordance with the output of the transfer functions based on the calculated fluidity.
1 . A method of developing control equations to relate the fluidity of molten metal to the volumetric requirements of a rotating mold for centrifugally casting an object from molten metal poured from a container, said molten metal having a liquidus arrest temperature and, when poured, a pour temperature, said method comprising:
(a) recording the liquidus arrest temperature of the molten metal in the container;
(b) pouring the molten metal into a trough to deliver the molten metal to a rotating mold;
(c) recording the pour temperature of the molten metal poured into the trough;
(d) moving the rotating mold relative to the trough to dispose molten metal into the mold, wherein said movement is controlled to deliver a volume of molten metal to said mold to cast said object in accordance with predetermined specifications;
(e) recording a predetermined set of parameters characterizing said movement and actual specifications of said object as cast;
(f) repeating steps (a) through (e) a statistically significant number of times;
(g) performing a regression analysis on said recorded parameters, recorded specifications, and fluidities calculated from said liquidus arrest temperatures and pour temperatures to produce control equations relating said parameters, specifications, and fluidities.
2 . The method of claim 1 , wherein step (f) is performed with molten metal of varying fluidity.
3 . The method of claim 2 , further comprising, prior to performing step (g), selecting a subset of said objects as cast with actual specifications most closely conforming to said predetermined specifications, and wherein in step (g), said recorded parameters, recorded specifications, and fluidities are those of said selected subset.
4 . The method of claim 1 , wherein said predetermined parameters comprise the time elapsed from when molten metal leaves the trough until a predetermined volume of molten metal is disposed in the mold and corresponding movement of said trough relative to said mold.
5 . The method of claim 1 , wherein said predetermined parameters comprise the time elapsed as the volume of molten metal leaving the trough increases per unit time and corresponding movement of said trough relative to said mold.
6 . The method of claim 1 , wherein said predetermined parameters comprise the time elapsed as the volume of molten metal leaving the trough decreases per unit time after molten metal is no longer poured into the trough and corresponding movement of said trough relative to said mold.
7 . The method of claim 1 , wherein said predetermined parameters comprise the time elapsed from a time at which the trough is stopped at the end of the mold until molten metal ceases to pour from the trough into the mold and corresponding position of said trough relative to said mold.
8 . The method of claim 1 , wherein said object is an iron pipe and said predetermined specifications comprise wall thickness.
9 . The method of claim 8 , wherein said predetermined parameters are selected from the group consisting of flag delay time and corresponding movement of said trough relative to said mold; bell acceleration and corresponding movement of said trough relative to said mold; spigot deceleration and corresponding movement of said trough relative to said mold; and spigot check and corresponding movement of said trough relative to said mold.
10 . The method of claim 1 , further comprising centrifugally casting the object in a casting process comprising moving the rotating mold moving the mold relative to the trough to dispose molten metal into the mold, wherein said movement is controlled in accordance with the control equations.
11 . The method of claim 10 , wherein the object is an iron pipe.