Method and apparatus for estimating dimensional uniformity of cast object

Abstract

A method and apparatus for providing an estimate of uniformity of wall thickness of a centrifugally cast object, such as a pipe cast from molten iron, substantially immediately after the casting process is complete. The volume of molten metal entering the mold over time is determined and correlated with casting machine position and velocity data to estimate wall thickness along the length of the pipe. Process defects can then be identified promptly and corrective action taken.

Claims

1. An apparatus for determining an estimate of uniformity of wall thickness of an object centrifugally cast by molten metal poured from a ladle into a trough that is positioned relative to a rotating mold for disposing the molten metal from the trough into the mold, the apparatus comprising: an image capture device positioned to capture an image of a stream of molten metal poured from the ladle; a drive system coupled to at least one of the trough or the mold; a controller for controlling the drive system and receiving data indicative of movement of the trough relative to the mold; a processor programmed to measure an area of a sample of the stream from the image, to determine an amount of a volume of molten metal associated with the sample using the measured area, to correlate over time the determined volume of molten metal poured from the ladle with position data of the trough relative to the mold and to calculate using the determined volume and the correlated position an estimate of wall thickness uniformity.

2. The apparatus of claim 1, further comprising a graphical display in operative communication with the processor, wherein the processor is further programmed to provide an indicator of uniformity on the display.

3. The apparatus of claim 1, further comprising a sensor positioned to detect when molten metal exits the trough, the sensor in operative communication with the processor.

4. The apparatus of claim 3, further comprising a scale positioned to weigh the centrifugally cast object, the scale in operative communication with the processor.

5. The apparatus of claim 1, further comprising a scale positioned to weigh the centrifugally cast object, the scale in operative communication with the processor.

6. The apparatus of claim 1, further comprising a tilt system coupled to the ladle, wherein the controller controls the tilt system.

7. An apparatus comprising: a ladle for containing and pouring molten metal, the ladle tiltable from an upright position to a pouring position; a tilt system coupled to the ladle for moving the ladle between the upright position and the pouring position; a trough with an upper end and a spout, the upper end positioned to receive molten metal poured from the ladle; a rotatable mold for receiving molten metal from the spout of the trough and centrifugally casting an object, the mold having a distal end and a proximate end; a drive system coupled to at least one of the trough or the mold, the drive system capable of moving the trough relative to the mold to controllably position the spout from the distal end to the proximate end of the mold; a controller for controlling the drive system and the tilt system and receiving data indicative of movement of the trough relative to the mold and the position of the ladle; an image capture device positioned to capture an image of a stream of molten metal poured from the ladle; a processor programmed to measure an area of a sample of the stream from the image, to determine an amount of a volume of molten metal associated with the sample using the measured area, to correlate over time the determined volume of molten metal poured from the ladle with position data of the trough relative to the mold and to calculate using the determined volume and the correlated position an estimate of wall thickness uniformity of an object centrifugally cast in the mold.

8. The apparatus of claim 7, further comprising a graphical display in operative communication with the processor, wherein the processor is further programmed to provide an indicator of uniformity on the display.

9. The apparatus of claim 7, further comprising a sensor positioned to detect when molten metal exits the trough, the sensor in operative communication with the processor.

10. The apparatus of claim 9, further comprising a scale positioned to weigh the centrifugally cast object, the scale in operative communication with the processor.

11. The apparatus of claim 7, further comprising a scale positioned to weigh the centrifugally cast object, the scale in operative communication with the processor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be explained, by way of example only, with reference to certain embodiments and the attached figures, in which:

(2) FIG. 1 is an exemplary embodiment of a casting machine, which forms part of an embodiment of an apparatus of the present invention;

(3) FIG. 2 is an example of a pipe cast from the embodiment of FIG. 1;

(4) FIG. 3 is a block diagram of an embodiment of the apparatus of the present invention;

(5) FIG. 4 is diagram of an exemplary arrangement of the camera and ladle of the embodiment of FIG. 3;

(6) FIG. 5 is an exemplary image of a stream of molten iron captured by a machine vision system, such as the camera of FIG. 4;

(7) FIGS. 6A-6C are exemplary graphs plotting molten iron volume and casting machine position (FIGS. 6A-6B) or casting machine velocity (FIG. 6C) over time;

(8) FIG. 7 is an exemplary graph plotting pipe wall uniformity according to an embodiment of a method of the present invention;

(9) FIG. 8 is an exemplary graph plotting casting machine velocity versus iron stream cross sectional area, according to an embodiment of a method of the present invention; and,

(10) FIG. 9 is a flow chart of one embodiment of a method of the present invention.

DETAILED DESCRIPTION

(11) This disclosure will describe certain embodiments of the invention with respect to an exemplary application of centrifugal casting of iron pipe specified to have uniform diameter with a constant wall thickness. Embodiments of the present invention may be readily applied to produce pipe of varying (tapering) diameter or cross-sectional profiles (e.g., hexagonal), with varying wall thickness along the length of the pipe. It should be also understood that embodiments of the present invention may be practiced with respect to the centrifugal casting of any object from molten metal of other alloys, by using known metallurgical relationships for such alloys in place of such relationships as described in this disclosure with respect to iron. Further, a reference to iron should be understood as a reference to an alloy of iron, typically comprising quantities of carbon, silicon, and phosphorous, but which also may comprise quantities of other elements or compounds that may affect its properties. Embodiments of the method and apparatus of the present invention are ideally suited to casting objects within a desired tolerance from iron or other molten metal having varying or unknown composition from batch to batch in the casting process.

(12) FIG. 1 illustrates part of an exemplary embodiment of an apparatus of the present invention. As shown in FIG. 1, a casting machine 5 is a typical centrifugal casting machine as is known in the art, which comprises a conveying system 10 to transport a quantity of molten iron into a mold 20, which is rotated by a motor 60 during the casting process. In a preferred embodiment, the conveying system 10 comprises a machine ladle or other container 25 that contains the molten iron and a U-shaped trough 30. The machine ladle 25 preferably dispenses a constant volume of iron per degree of rotation. It should be noted, however, that embodiments of the present invention can be used with any type of ladle or dispensation container, so long as it provides a consistent pour profile from one pour to the next. The terms “ladle” or “machine ladle” are synonymous and shall refer to any container used for dispensation of molten metal for casting. The trough 30 is angled slightly downward and extends axially into the interior of the mold 20, terminating at a spout 35. When the machine ladle 25 is tilted, molten iron flows in a stream 75 from the lip 27 of the ladle 25 (as shown in FIG. 4), down the trough 30, out the spout 35 and into the mold 20 under the influence of gravity. The mold 20 is mounted to a drive system 40.

(13) The drive system 40 comprises actuators 45 to move the mold back and forth within a fixed range of motion with respect to the fixed end (i.e., spout 35) of the conveying system 10. The actuators 45 may be any type of actuator known in the art to move the mold 20, including hydraulics, electrical motors, a belt or chain-drive mechanical linkage to an engine or motor, any combination thereof, or other means known in the art for moving a mold. In some embodiments, the conveying system 10 is moved longitudinally by a drive system 40 with respect to the mold 20, which remains fixed in position. In this disclosure, the terms casting machine velocity or casting machine movement refer to movement (or the rate thereof) of the mold 20 relative to the trough 30 as driven by drive system 40, and may describe an apparatus in which either or both components move relative to the other.

(14) Similarly, the machine ladle 25 is coupled to a tilt system 42, which includes actuators of any type known in the art, including hydraulics, electrical motors, a screw drive, a belt or chain-drive mechanical linkage to an engine or motor, any combination thereof, or other means known in the art, to controllably rotate or tilt the machine ladle to or from any desired degree, or otherwise to cause a stream 75 of molten iron to pour from its lip 27 (as shown in FIG. 4) at a predetermined pouring rate (typically uniform per degree of tilt), and to return the machine ladle from the pouring position to its initial upright or pouring position.

(15) As shown in the embodiment of FIG. 3, each of the drive system 40 and the tilt system 42 is preferably controlled by a programmable logic controller (PLC) 50 in operative communication with a computer 55 for the transfer of commands and data between them. Computer 55 is used broadly here to refer to any computational system capable of receiving, directly or indirectly, and processing the data and performing the calculations and other steps of the methods described herein, and would include a local standalone general purpose computer programmed with appropriate software, such a general purpose computer in communication with a server over a network dividing tasks or storage between them, a cloud-based processor remote from the casting site and receiving the appropriate data over a communications network, a mobile or handheld device, an application specific computing device, or any combination of the foregoing. The PLC 50 controls and encodes the casting machine movement over time, including position, velocity, and acceleration. Data provided from the PLC 50 to the computer 55 may include positional data of the mold 20 relative to the trough 30 over time, the velocity of the mold 20 relative to the trough 30, and the extent or degree of tilt of the machine ladle 25 over time.

(16) Hence, in an exemplary process, the machine ladle 25 is tilted to a predetermined extent for a predetermined duration to deliver molten iron to the rotating mold 20 via the conveying system 10. The tilt of the machine ladle 25 is reversed, typically in a single continuous movement, to return it to its initial or resting position, in which no molten iron is poured. The mold 20 is moved with respect to the conveying system 10 such that molten iron is disposed along the length of the mold in a volume intended to provide a cast object (as illustrated, a pipe) having predetermined specifications, including for example, wall thickness.

(17) The embodiment 105 further comprises an instrument for measuring the volume of the stream 75 of molten iron poured from the machine ladle 25. In a preferred embodiment, this instrument is a machine vision device, such as an image capture device referred to herein as camera 65, positioned as shown in FIG. 4 to capture data representative of images of the iron stream 75 after it exits the lip 27 of the machine ladle 25 and before it reaches the trough 30. In a still preferred embodiment, the camera 65 may be a Cognex Model 821-10020-IR machine vision system. The camera 65 is configured to capture a series of images of the stream 75 at predetermined intervals of time and provide these images (or more specifically, data representative of them) to the computer 55. An exemplary image of an iron stream as captured by the camera 65 is shown in FIG. 5. The computer 55 includes software, for example Cognex In-Sight Explorer (provided with its machine vision system), that obtains a diameter D of the iron stream from an image captured by the camera 65, as shown in FIG. 5. Alternative embodiments may, for example, provide a continuous or near continuous video feed at a desired frame rate (such as 32 frames/second) to the computer 55, which executes image processing software to compute the volume of the iron stream continuously or at any desired time interval or point in time from the video, such as by determining the diameter or cross sectional area of the stream.

(18) FIG. 2 shows an exemplary iron pipe 500, a typical profile in the industry, cast by a centrifugal casting machine such as shown in FIG. 1. For such a pipe, the casting process can be divided into five main steps. Data indicative of these steps is illustrated in FIGS. 6A-6C. Specifically, FIG. 6A reflects the operation of the machine ladle 25 as shown by the pour curve 100, which plots the diameter of the iron stream 75 poured from the machine ladle 25 as captured by the camera 65 over time, and the operation of the casting machine 5 as shown by position curve 200, which plots the position of the spout 35 from the bell end of the mold 20 over the same time axis. As noted above, there is a time delay from when molten iron is poured from the machine ladle 25 to when it enters the mold 20. In FIG. 6B, the pour curve 100 has been offset on the time axis by this delay; FIG. 6B therefore correlates the volume of iron entering the mold 20 with the position of the mold at that time. In FIG. 6C the velocity of the casting machine shown by curve 300 and the pour curve 100 are plotted over time, again with the pour curve 100 offset by the delay between the molten iron leaving the machine ladle 25 and entering the mold 20.

(19) First, the machine ladle 25 is tilted to a predetermined position to obtain a desired pour flow rate. The mold 20 is brought into position with the spout 35 of trough 30 in the bell portion of the mold. For efficiency in process time, this may be done as the iron stream begins pouring from the machine ladle 25 and travels down the trough. Preferably, a sensor such as a photoelectric sensor detects when molten iron exits the spout 35 of the trough 30. As the molten iron exits the spout 35 of the trough 30, the mold 20 remains stationary until the bell of the pipe mold is nearly filled, as shown in the portions of the curves labeled 110, 210, and 310, respectively, on FIGS. 6A-6C. This time period is referred to as the flag delay time. In this exemplary process, as known in the art, a sand core having dimensions in accordance with a desired pipe specification is held in place at the end of the mold by a core setter, which is a mechanical arm attached the casting machine. (The core setter may also serve as a mount for the sensor that detects molten iron exiting the spout 35 of the trough 30.) The bell of the pipe is cast in a precisely defined cavity formed between the sand core and the pipe mold. For a given sand core specification, the cavity defining the bell has a predetermined and constant volume from one casting cycle to the next. Therefore the bell weight is likewise constant and referred to as the standard bell weight. During this phase, as shown by the pour curve 100, the volume of molten iron increases as the stream of molten iron first exits the ladle until it reaches a more constant volume.

(20) Next, at the point labeled “flag,” the casting machine enters the bell acceleration phase labeled 120, 220, and 320, respectively, and accelerates to a constant velocity. Next, with the iron stream having reached a near constant volume, the casting machine moves the mold at a near constant velocity during phase labeled 130, 230, and 330, such that molten iron is disposed substantially evenly along the length of the mold corresponding to the barrel of the pipe. Towards the end of this phase, as shown near the point 135, 235, 335, the machine ladle is tilted back, which is usually referred to as “the machine ladle cutback position,” and the diameter of the iron stream (and its resultant volume) quickly diminish; however, molten iron continues to flow out of the trough 30 into the mold 20. As the machine approaches the end of the barrel, referred to as the spigot, the machine decelerates in the spigot deceleration phase 140, 240, and 340, to a stop. This corresponds to the filling of a portion of the barrel near the spigot end of the pipe. Finally, during the spigot check phase labeled as 150, 250, and 350, a delay transpires corresponding to the time at which the casting machine is stopped near the end of the mold 20 until molten metal ceases to pour from the spout 35 of the trough 30 into the mold 20. This time period, 150, 250, 350, is referred to as the spigot check time or dwell time. The casting machine then moves to the end point of the mold.

(21) The actual iron delivery flow curve for a given pour of molten iron, especially sourced from recycled materials, is difficult to predict and varies from batch to batch of molten iron. As a result, casting an object within close tolerances of a given set of specifications can be difficult. In one embodiment, the object to be cast is a pipe of uniform wall thickness through its barrel and spigot. Wall thickness is a function of iron delivery to the mold, and therefore the volume of iron delivered per unit distance should be constant over the length of the mold to provide pipe of uniform wall thickness. The uniformity wall thickness (or other desired specification) can be controlled by the movement of the conveying system 10 relative to the mold 20 according to a transfer function that accurately relates the required acceleration, deceleration, and velocity of the relative motion of the casting machine 5 to the volumetric delivery requirements of the mold 20 to achieve the desired specifications. This is described in the patents referenced above owned by the applicant. Wall thickness also is affected by the pour rate from the machine ladle, flag delay time, the machine ladle cutback position, and the spigot check or dwell time, all of which may be influenced by non-linearities in pouring.

(22) In an embodiment of the method of the present invention, data corresponding to the position of the casting machine over time (and hence its velocity) and the volume of the iron stream 75 are recorded. In the embodiment of the apparatus described above, data representative of the casting machine over time is captured by the PLC 50 (which also controls its movement), and of the iron stream is recorded by the camera 65. In this embodiment, software in the computer 55 extracts the diameter of the iron stream from image data captured by the camera and reports it upon predetermined intervals, for example, every 0.1 seconds. Further, upon completion of the casting of the object (such as the exemplary iron pipe), the object is ejected from the mold and its weight is captured by a scale 70.

(23) Further steps of a preferred embodiment of the method of the present invention, to estimate the uniformity of wall thickness of a centrifugally cast object, are shown in FIG. 9. These steps are preferably programmed into software that is executed by computer 55. In step 400, the casting data is acquired. Specifically, in step 410, the outer diameter of the pipe being cast and, for an exemplary pipe having a profile shown in FIG. 2, the standard bell weight are retrieved from a memory (which may be any memory or storage medium known in the art accessible to computer 55). In step 420, casting machine position data and pipe weight are received from the PLC 50. Alternatively, in some embodiments, the scale 70 may communicate the weight directly to the computer 55 via a data link, or the weight may be entered manually into the computer 55 by an operator observing a visual readout on the scale 70. In yet other embodiments, a standard weight for the pipe is retrieved from a memory and used in the calculations described in the steps below. After an actual weight of the pipe is measured, the calculated thickness of the pipe wall is adjusted by the actual-to-standard ratio.

(24) In step 430, data representative of the volume of the iron stream over time is received from camera 65. In a preferred embodiment, this data comprises images of the stream over time, which is processed by software in the computer 55 to return the diameter of samples of the stream upon desired or predetermined intervals, for example, ten samples per second. In other embodiments, the data may be a continuous video feed of the iron stream, which is further processed by computer 55 to determine relevant dimension(s) of the stream over time. In still further embodiments, the camera 65 processes each image and communicates data representative of any one of diameter, area, or volume of the iron stream over time.

(25) In step 440, the weight of the pipe as measured by the scale 70 is converted to volume in accordance with the following equation:

(26) $V=\frac{W}{d}$
where V is volume, W is the measured weight of object as cast, and d is the density of the material from which it is cast, in this case, molten iron (0.238 lbs/in.sup.3).

(27) Next, in step 450, the iron stream sample data is correlated with the casting machine position data. As described above, with respect to any sample of the iron stream, there is a delay from when the stream leaves the ladle (when the image is captured) to when it exits the trough. Accordingly, each sample S is associated with the longitudinal position P of the pipe where that sample was cast by correlating the sample with the position of the trough 30 (relative to the mold 20) when the sample left the trough 30 and entered the mold 20. In a preferred embodiment, casting machine position data P and iron stream image data S are sampled simultaneously on the same interval, for example, ten samples per second. Further, as noted above, a sensor records the point in time that molten iron leaves the spout 35 of the trough 30, and the point in time at which the casting machine 5 first moves, referred to as the flag, also is known and obtained from the PLC 50. The time period from the when the molten iron leaves the spout 35 of the trough 30 to when the casting machine 5 first moves is referred to as the flag delay time. The iron stream sample taken nearest the flag time and the casting machine position P at the flag time are associated with one another to align the iron stream samples with casting machine position. Stream sample data and casting machine position data after the flag, which are preferably taken on the same time interval, are associated accordingly. Stream samples taken before the flag, when the casting machine is stationary, are associated with the bell of the pipe. For example, if the flag delay time was two seconds in an exemplary process, and samples are taken every 0.1 seconds, then the first twenty samples represent the volume of iron poured between the sand core and mold to form the bell and likewise correspond to the standard bell weight.

(28) In step 460, the volume of molten iron for each stream sample is calculated. In a preferred embodiment, the cross sectional area of the stream of each sample is determined. For example, the diameter of each stream sample may be measured or determined from the image data of the stream. The area then is calculated as follows:

(29) $A={\pi \left(\frac{D}{2}\right)}^2$
where A is cross sectional area of the iron stream for a sample, and D is the diameter of stream for that sample. Next, the calculated cross sectional areas for all samples are summed. The length of the iron stream is determined by dividing the pipe's volume by this sum:

(30) $L=\frac{V}{{.Math.}_{S=1}^n{A}_S}$
where L is the length of the iron stream, V is the volume of the pipe, n is the number of samples S, and A is the area for each sample S from 1 to n. The volume of molten iron for each sample can then be determined:
ΔV.sub.S=L×A.sub.S
where ΔV.sub.S is the volume of a sample S for samples 1 to n, L is the length of the iron stream, and A is the cross sectional area of that sample.

(31) In step 470, the samples are associated with each section of the pipe of interest so that the wall thickness of each section can be calculated. The exemplary pipe 500 as shown in FIG. 2 has three distinct sections: the bell 510, the barrel 530, and the spigot 550. With the samples having been correlated to casting machine position data (and therefore to longitudinal position P of the pipe) in step 450, the samples associated with each section are identified and segregated. For example, assume that in a set of n samples, the first x samples are associated with longitudinal positions for the bell 510, the samples from sample y to sample n are associated with longitudinal positions on the pipe 500 for the spigot 550, and then the samples in between are associated with longitudinal positions on the pipe 500 for the barrel 530, that is, from x+1 to y−1.

(32) As described above, the trough 30 does not move relative to the mold 20 for at least part of the time that the bell 510 and spigot 550 are cast. For the barrel section 530, the trough 30 moves continuously relative to the mold 20. Using the casting machine position data, the incremental length dl that casting machine moves in time increment dt while the barrel 550 is cast is determined. Because in a preferred embodiment the stream volume data is sampled at the same interval as the position data, dt also represents the time increment associated with each stream sample.

(33) Next, in step 480, the wall thickness of each section of the pipe is computed. The estimated wall thickness of the bell 510 of the pipe 500 is calculated in accordance with the following equation:

(34) $\begin{array}{cc}{\mathrm{th}}_{\mathrm{bell}}=\frac{\mathrm{OD}}{2}-{\left(\frac{{\mathrm{OD}}^2}{4}-\left(\frac{{.Math.}_{i=1}^{x+1}{\mathrm{dV}}_i-V_{{\mathrm{std}}_{\mathrm{bell}}}}{\pi \times \left(P_1-P_{x+1}\right)}\right)\right)}^{0.5}& \left(1\right)\end{array}$
where th.sub.bell is the thickness of the bell, OD is the standard outside diameter of the pipe (as controlled by the mold 20), x is the number of samples associated with the bell, dV.sub.i is volume for each sample from the first to the xth+1 sample, V.sub.std_bell is the standard bell volume, P.sub.1 is the position of the first sample, and P.sub.x is the position of the xth sample. Because equation (1) relates to the period when the bell is filled, during which the casting machine is stationary, the position of the machine P.sub.x+1 upon its first movement after the flag is used in equation (1) to avoid dividing by zero, and the volume corresponding to this time increment is likewise included in the volume summation.

(35) The estimated wall thickness of the barrel 530 of the pipe 500 is calculated in accordance with the following equation:

(36) $\begin{array}{cc}{\mathrm{th}}_{\mathrm{barrel}}={\int }_0^t\frac{\mathrm{OD}}{2}-{\left(\frac{{\mathrm{OD}}^2}{4}-\frac{\frac{\mathrm{dV}}{\mathrm{dt}}}{\pi \frac{\mathrm{dl}}{\mathrm{dt}}}\right)}^{0.5}& \left(2\right)\end{array}$
where th.sub.barrel is the thickness of the barrel, OD is the standard outside diameter of the pipe (as controlled by the mold 20), t is the time during which the barrel is cast (that is, the time period spanned by the samples associated with the barrel (that is, the samples not included in equations (1) or (3)), dV is volume of iron flow during each time increment dt, and dl is the incremental length that casting machine moves in time increment dt.

(37) The estimated wall thickness of the spigot 550 of the pipe 500 is calculated in accordance with the following equation:

(38) $\begin{array}{cc}{\mathrm{th}}_{\mathrm{spigot}}=\frac{\mathrm{OD}}{2}-{\left(\frac{{\mathrm{OD}}^2}{4}-\left(\frac{{.Math.}_{i=y-1}^n{\mathrm{dV}}_i}{\pi \times \left(P_{y-1}-P_n\right)}\right)\right)}^{0.5}& \left(3\right)\end{array}$
where th.sub.spigot is the thickness of the spigot, OD is the standard outside diameter of the pipe (as controlled by the mold 20), n is the total number of samples (which is also the number of the last sample associated with the spigot), y is the number of the first sample associated with the spigot, dV is volume for each sample from the yth−1 to the nth sample, P.sub.y is the position of the yth sample, and P.sub.n is the position of the nth sample. Because equation (3) relates to the period when the spigot is filled, during which the casting machine is stationary, the position of the machine P.sub.y−1 upon its last movement before the spigot check position is used in equation (3) to avoid dividing by zero, and the volume corresponding to this time increment is likewise included in the volume summation.

(39) Advantageously, in step 490, data resulting from the above calculations can be used or displayed in various ways to provide feedback regarding pipe wall thickness uniformity immediately after the pipe is cast, rather than having to wait up to several hours after the cooling and annealing process when the pipe is physically measured. For example, a plot of the thicknesses calculated from equations (1), (2), and (3) provides a graphical illustration of the uniformity of the pipe wall thickness. FIG. 7 is an exemplary plot of uniformity of wall thickness. Upper and lower bounds of acceptable thickness can be added to show if and where the pipe wall does not meet specifications, and other visual indicators can alert the operator and any persons monitoring the process whether a pipe does not meet specification. Alarms can be programmed into the system itself (e.g., the software running on computer 55) with or without graphical displays of thickness when wall thickness is determined to be out of specification.

(40) Also, variability in wall thickness can be consistently shown and predicted by plotting diameter or area of the iron stream over time and velocity of the casting machine over time, as shown in FIG. 6C or FIG. 8. When the pour curve 100 and the velocity curve 300 are aligned in time, as shown in these figures, a difference in the slopes of the pour curve 100 and velocity curve 300 during the constant velocity phase 330 indicates lack of uniformity in wall thickness of the resulting pipe as cast.

(41) With uniformity of pipe wall thickness quantified and preferably graphically displayed at the casting stage, adjustments to controls for machine ladle pouring can be made on one or more successive casting cycles to restore uniformity. These adjustments include changing the speed of rotation of the machine ladle to adjust the pour rate and the time that the machine ladle is in its pouring position. In addition, casting machine (mold) movement, including velocity, bell acceleration, spigot deceleration, and spigot check time, also can be adjusted to restore pipe wall uniformity. For example, if the pipe wall is thinner near the beginning of the barrel, the bell acceleration curve can be adjusted accordingly. Similarly, if some non-linear modality resulting from alteration of the teapot portion of the ladle consistently caused a thickening followed by a thinning of the pipe wall over a certain length of the barrel, then the casting machine velocity could be increased and then decreased to offset the non-linearity in the pour. Whatever adjustments are made to attempt to correct the error, the estimated uniformity of pipe wall thickness provided by embodiments of the present invention provide feedback on the efficacy of the adjustment in the next casting cycle, which may be merely seconds or minutes later, rather than having to wait potentially hours after annealing and traditional measurement techniques.

(42) In addition, examination of the pipe wall thickness data over repeated casting cycles can allow early detection of non-linearity in pouring and identification of the particular condition causing the non-linearity. This in turn can allow the non-linearity to be corrected before numerous out-of-spec pipe are cast. Analyzing aggregate data over time can reveal changes and trends in ladle conditions that ordinarily are not detectable until they are so advanced as to cause defects.

(43) Although the present invention has been described and shown with reference to certain preferred embodiments thereof, other embodiments are possible. The foregoing description is therefore considered in all respects to be illustrative and not restrictive. Therefore, the present invention should be defined with reference to the claims and their equivalents, and the spirit and scope of the claims should not be limited to the description of the preferred embodiments contained herein.