Latest from Issues and Ideas

Pouring Systems: Vision vs. Laser Control

Nov. 25, 2005
Advanced automatic-pouring systems provide interactive control by monitoring and adjusting the flow of metal into the mold.

Early automatic-pouring systems were blind. They were preset by the operator to pour for a fixed amount of time to fill the mold. But a number of factors, including slag build-up in the nozzle and/or changes in metal temperature or metal level, led to over-pours and under-pours. Often, operator intervention was required to stop these systems from pouring metal over the top of the mold, or from only partially filling the mold.

Today’s more advanced automatic-pouring systems provide interactive control of the pour by monitoring and adjusting the flow of metal into the mold. When linked to a responsive stopper-rod pouring mechanism, these systems can:
• Supply metal to the mold at its optimum rate
• Effectively dispense difficult-to-pour metals, such as ductile iron and non-ferrous metals
• Allow more efficient sprue, riser and gating arrangements
• Keep pace with today’s high-speed molding machines
High-precision pouring increases production rates, reduces metal waste, produces fewer scrap castings, and allows the castings themselves to be lighter and have thinner walls.

Early laser systems

The first interactive automatic-pouring systems used a laser-based process to calculate the depth of metal in the sprue cup during the pour. It included a laser generator to provide a laser spot directed at a special channel, or “tail,” extending from the main sprue cup. This tail was required to isolate the laser measuring point from metal turbulence in the sprue. A sensor captured the laser light reflected from the metal in the tail and by triangulation calculated the depth of metal in the sprue cup.

While this system worked well, laser generators were expensive devices and the need to add a tail to all the patterns required extensive retooling. Also, the tail wasted metal, typically using one pound or more per mold; and with ductile iron, under-filling the sprue cup to save metal was not an option since anything less than a full sprue cup could lead to shrink defects.

Vision technology introduced

Soon after the advent of laser-based pouring systems, Inductotherm pioneered vision technology to provide a more cost-effective, precise, and flexible method for real-time control of stopper-rod automatic-pouring systems for all types of flask and flaskless mold lines. These systems were designed for use with all styles of pouring devices, including tundishes, coreless bottom-pour, and induction-heated pressure pour vessels. They were able to pour gray, malleable, and ductile iron, as well as copper-based alloys.

Control systems based on vision technology did not require adding a laser “tail,” nor any change to an existing sprue cup, which saves retooling costs and metal.

Unlike laser-based systems, vision systems monitor the entire opening of the sprue cup throughout pouring with a standard (and less costly) industrial video camera linked to a personal computer controlling the pour. The camera’s image of the sprue cup is digitized, only in black-and-white pixels in real-time, and the data generated is used to calculate the level of molten metal in the sprue accurately. This camera also supplies a video image of the actual pour to the unit’s control panel.

Robert Wright, foundry manager of Vermont Castings, reports that his operators use the video screen on the control panel along with the joystick to establish the ideal pouring profile for a new pattern. “With the camera, it’s easier to see the pour. It eliminates the glare of the molten metal, and we can see the level of metal in the sprue cup better.” Vermont Castings operates a 10,000-lb pressure-pour furnace with vision-based stopper-rod controls pouring gray iron. The foundry casts stove parts and thin-section jobbing work.

Vision systems make it possible to complete precise pours at speeds matching the highest mold production rates of modern molding machines. Most, in fact, are being used today to pour vertically-parted flaskless molds on high-speed lines.

Scott Lakey, production manager of Lodge Manufacturing, a leading producer of high-quality cast-iron cookware, has extensive experience with vision-based automatic-pouring systems with heated pressure vessels. At its foundry in South Pittsburg, TN, Lodge uses this pouring control technology on the two DISA lines it operates.

“Our (vision-based) automatic systems have no trouble pouring with the DISA-recommended sprue cup we use for most of our molds,” Lakey reports. “And, where we reduced that size to save metal or adjust for a difficult or tight pattern, pouring was not effected.”

Lodge’s mold sizes range from 14 to 23 lb, though the average is 17 lb, Lakey notes. “We normally pour 420 to 430 molds per hour, with our highest rate hitting 450 molds per hour. Our Visipour® system easily keeps up with our mold output.”

According to Lakey, Lodge’s vision-based automatic-pouring systems produce a highly accurate pour. “While we might get a slight over-pour or under-pour as the system adapts at the start of a run, or when we start a new pattern, overall performance is excellent,” he notes.

As noted, vision systems do not require any “tails” or other costly changes in sprue size, shape, or location. And, because they monitor the total surface of the sprue cup, vision-based systems can accurately pour sprue cups as small as 2.5 times the size of the pouring nozzle. This is not a limitation of the control system, which can maintain its pouring accuracy with even smaller cup sizes, but rather reflects the inability of a smaller sprue cup to empty into the mold fast enough to accommodate a higher metal flow from the pouring nozzle.

EBAA Iron Inc. manufactures joint-restraint products for ductile iron and PVC pipe. Its foundries include the most modern ductile-iron casting facilities in the U.S. EBAA operates several vision-based automatic-pouring systems, including two state-of-the-art vision systems at its Eastland, TX, foundry.

Danny Norris, EBAA’s general manager of foundries, reports that EBAA’s new automatic-pouring systems are the latest generation of vision-based pouring control technology. “The guys really like the new systems. They run really smooth in automatic mode. We hardly ever run them using manual control: just when we’re setting up a new pattern or dealing with some problem on the mold line,” he notes.

“Most of our molds have 3.533.5-in. square sprue cups, and I would not call that big,” Norris observes. “But, we have several molds with even smaller sprue cups, and our Visipour system has no difficulty with these cups at all. In fact, we are considering reducing the sprue size on even more patterns.”

At Eastland, EBAA normally pours 300 molds per hour with molds in the 35-100-lb range, but has poured as many as 350 of the 35- to 45-lb molds per hour, Norris says. “But, we are getting ready to challenge the automatic-pouring system. When our new core-setting robot is installed, we’ll be running 400 to 500 molds per hour. I’m sure our automatic-pouring system will be able to maintain that pace.”

Laser loses its tail

The introduction of an improved laser system addressed some of the problems associated with laser-based pouring control, but it did not prove superior to vision technology. The redesigned laser system replaced the point laser with a line of laser light projected across the sprue cup to determine metal level. This line-laser system does not require a “tail” to reflect the light to the system’s “complementary metal oxide semiconductor” (CMOS) video camera.

In theory, this should produce greater accuracy than the older, point measurement laser systems. However, metal turbulence in the pouring cup creates waves that, together with wandering or fanning pouring streams, often cut the line into small non-contiguous parts, potentially reducing the accuracy of data collection. Moreover, as the line is generated on one side of the pouring stream and the system’s sensor camera is on the other, it is possible to have the entire line obscured by the fanning metal from the pouring nozzle.

At its best, the line-laser system still cannot match the resolution of a vision system. Based on the maximum resolution of a typical CMOS camera, the single line of laser illumination used to measure the metal level in the sprue cup would produce 1,024 pixels of data per sample. This compares to the more than 250,000 data points per sample generated by the 5123512 pixels used by the CCD (charge-coupled device) video camera in vision systems. With the vision system’s camera operating at 30 frames/second, that represents 7,864,320 pixels of information per second — almost 500 times more than the reported 16,000 pixels per second used by a point laser system, and still many magnitudes greater than the bits of information captured by the line-laser system. This makes vision technology the clear leader in data feedback to the control system.

Selecting an automatic-pouring system

The important thing to note is that while a vision-based monitoring device provides the most data on metal levels in the sprue, it is just part of a complete automatic-pouring system. Before deciding if your first or next automatic-pouring system should include laser-based control or vision control technology, look at the entire package. Begin by asking these questions:

1. Is the system suitable for the metals it will pour? Does the manufacturer have customers pouring these metals?
2. Is the system compatible with the molding machine and mold line? Is it in use on such lines?
3. Will the system be large enough to pour all of the patterns to be used?
4. Will the system be fast enough to keep pace with current or planned mold production?
5. Do the system’s pouring control computer, operating programs, and stopper-rod mechanism produce accurate pours without over-pours or under-pours?
6. Will the system pour mold-after-mold without operator intervention? Will it support scrap reduction, yield increases, and lower labor costs?
7. Will the system require changes to the size or shape of the sprue cups?
8. Are both unheated tundish and heated pressure vessel systems available?
9. Will the manufacturer take responsibility for all parts of the system, including the pouring mechanism and holding vessel?
10. Are parts and service locally available?

Inductotherm’s Visipour vision-based automatic-pouring control systems are in use worldwide pouring gray, ductile, and malleable iron as well as copper-based metals. They are installed on vertically and horizontally parted flask and flaskless mold lines, including indexing lines and continuously moving lines. Inductotherm has built systems with usable holding capacities ranging from one ton in unheated tundishes, to 30 tons in inductively heated pressure vessels. It will build any special sizes, as well.

According to Inductotherm, its lines are operating with pouring rates capable of exceeding 500 molds per hour. With its highly responsive stopper-rod mechanism and intelligent control systems, Visipour is able to follow its programmed pouring profile accurately, and even to improve upon that profile and adapt the pour to changes in metal level and nozzle diameter. It pours mold-after-mold without operator intervention.

As a vision-based system, Visipour requires no changes in the size or shape of the sprue cup.

Inductotherm provides all parts of its automatic-pouring systems, from holding vessels to pouring controls, and is the single source of responsibility for the system’s operating integrity. The company maintains its own manufacturing facilities in 16 nations and provides worldwide service.