Cost Reductions through Direct Pouring on Automatic Horizontal Molding Machines

T. Tackaberry
Foseco Metallurgical Inc., Cleveland, Ohio

ABSTRACT
The yield improvements and cost reduction advantages of direct pouring combined with the quality and scrap reduction benefits of ceramic foam filtration are widely recognized and accepted by ductile iron foundries. However, mold accessibility and space limitations on some automatic molding equipment can complicate and limit the application of direct pour units.

This paper describes a direct pouring system for iron that brings the quality improvements of reticulated ceramic foam filtration and the cost-reduction benefits of direct pouring to users of automatic horizontal molding lines. Application of this system is illustrated in examples of ductile iron castings produced at Grede Foundries, Inc., Liberty Division, Milwaukee, WI.

Each of the castings was originally produced using a conventional gating, risering and in-line filtration system. After redesigning the patterns to incorporate direct pouring, castings were subjected to destructive and non-destructive testing and found to be 100% sound. Substantial casting yield improvements, scrap reductions, reduced shakeout and despruing times, as well as metal utilization improvements were noted.

INTRODUCTION
The effectiveness of conventional gating systems, designed to allow inclusions to float out of the molten metal stream and attach to runner walls, can be improved by the addition of in-line ceramic foam filters. However, these traditional gating, risering and filtration systems consume valuable space on the production pattern plate that might otherwise be devoted to producing additional castings.

Direct pouring utilizing a specially designed feeder sleeve containing a ceramic foam filter can eliminate conventional gating system components, leading to yield improvements, increased productivity and cost reduction. Direct pour units designed for use with horizontal automatic molding equipment can overcome pattern plate accessibility limitations that have, in the past, restricted the use of direct pouring on automatic molding equipment.

DIRECT POURING
In direct pouring, the mold cavity is filled with molten metal without the use of a conventional sprue, runner or ingate system. Liquid metal is poured directly though a riser at the top or side of the casting cavity. In fact, the direct pouring unit replaces the pouring cup, down sprue, runner, ingate, contact and riser. As a result, substantial yield improvements can be attainable, as well as improved directional solidification characteristics.

KALPUR direct pouring units have been developed that consist of a specially designed insulating sleeve containing a reticulated ceramic foam filter.

Filtration Effectiveness
The reticulated foam filter presents a tortuous path through which the metal must pass. Oxides and other suspended non-metallics are trapped on the surface of the filter or become entrained within the filter body pores. The fluid flow pattern developed in each pore results in the entrained particles becoming trapped within these circulating currents. Should a random particle find its way out of one pore, it travels into another pore and so on, thus preventing the particle from escaping the filter. As a result, the reticulated foam filter is capable of trapping oxide particles significantly smaller than the open area of the pores.

The second predominate characteristic of the ceramic foam filter is that it efficiently reduces metal turbulence, thus eliminating the reoxidation of the metal stream. As water models and metal radiographs demonstrate, when liquid iron passes through a Pressed or Extruded Filter, considerable metal splash is generated, resulting in reoxidation of the metal stream. In contrast, the ceramic foam filter (Figure #3) encourages smooth laminar metal flow on exiting the filter, without generating excessive splash or air entrainment.

Pressed Filter	Extruded Filter Ceramic
	Fig. 3 Water modeling shows the degree to which various iron filtration media reduce turbulence in aerated water.
Foam Filter

Insulating Sleeve
The insulating sleeve allows the metal contained in the riser to remain in a molten state longer, thus increasing the modulus and volumetric feed characteristics of the riser. Moreover, the direct pouring unit becomes the pouring cup, down sprue, riser, and filter support.

Two basic types of direct pouring units
The conventional direct pouring unit (Figure 1) is tapered from top to bottom and is designed for use in casting operations where there is access to the top of the cope. The direct pouring unit can be inserted in a molded cavity after the mold is formed or may it be rammed up in position when reinforced with a removable plug.

The second type (Figure 2) is a reverse-taper unit designed for use in automatic horizontal molding applications, where normally no cope access is allowed. The reverse-taper (RT) unit can be inserted into the cope mold; or, with molding machinery where the cope mold is not accessible, the direct pour unit can be placed on the drag mold half, or on a cover core package, and is closed over like a core.

Fig. 2 Direct pour unit for horizontal automatic molding.

REVERSE-TAPER APPLICATION METHODS
The reverse-taper direct pouring unit contains a ceramic foam filter that is located in the top of the riser sleeve and held in place by heat-shrink tape. This eliminates the need to handle loose filters, and the tape volatilizes upon contact with the molten metal. The riser sleeve is made of a highly insulating material. This allows the metal contained in the sleeve to remain in a molten state longer, thus increasing the modulus and volumetric feed characteristics of the riser.

Reverse-taper units may be positioned at the base of the downsprue as side risers or positioned directly above the casting as top risers. Reverse-taper units can be easily inserted into rotated cope molds, inserted into cope molds using an insertion tool, or placed on the drag half of the mold and closed over.

Fig. 4 A special riser bob creates a cavity for insertion of the reverse-taper unit.

Insert Technique
If the cope is accessible (as is the case with certain molding machines that rotate the cope 90 degrees after squeezing), the unit can be manually inserted into a special riser bob cavity.

The riser bob (Figure 4) is combined with a sprue to produce the mold cavity needed for insert application of the reverse-taper direct pour unit into the cope mold. Crush strips, molded into the cavity formed by the riser bob, may be used to retain the unit while the mold is rotated and closed. (Figure 5).

Fig. 5 The reverse-taper unit may be manually inserted into a rotated cope for top feeder applications.

Close-over Technique
In close-over applications, multiple positions for the pouring basin/cup are available across the squeeze plate (head board) to accommodate various pattern plate layout configurations. During molding, the cope frame is filled with green sand and the squeeze cycle compresses the green sand, forming the pouring cup, sprue and reverse-taper direct pour unit cavity. After the mold is made, the direct pour unit can be set into a slight recess print that is created in the drag pattern. The cope can then be closed over the unit (Figure 6).

FEEDING AND MODULUS
The "geometric modulus" or feeding capacity of the reverse-taper unit sleeve is equal to the feeding capacity of an exothermic/insulating feeder of the same size. The ceramic filter does not affect the unit's feeding efficiency.

However, the "system modulus" or feeding capacity of the reverse-taper-sleeve/sprue/basin combination is increased since the sprue and pouring basin metal function as part of the feeding system (See Figure 4). During solidification, the metal in the pouring basin and sprue freeze off first, and the balance of the feeding is done by molten metal contained in the insulating sleeve.

If the filtration capacity and flow rate of the unit are suitable for the application, the system modulus will normally be more than adequate to feed the casting. The only possible exception being heavy-section, cube-like shapes.

For side-gated applications that may be used to pour/feed single or multiple castings, the unit should be mounted on a suitable riser base, close to the casting cavity or cavities. (See Figure 7)

Connecting feeder necks/gates should be sized to promote efficient feeding. Proper sizing of the feeder neck/gate is a function of the casting or section modulus and is unaffected by the application of the reverse-taper direct pour system. As the foundry gains experience in the application of reverse-taper units, the advantage of a "live" neck/gate condition can reduce neck contacts.

In a correctly sized runner system, the sprue itself functions as the choke, thus producing an unpressurized system that prevents the metal from spraying into the casting cavity. This also allows for faster pouring since the foam filter controls head pressure and dampens the metal velocity causing it to enter the casting with minimal turbulence.

UNIT SIZE SELECTION
In most applications, the size of the reverse-taper unit selected is determined by the filtration capacity (total weight of metal that can pass through the filter before blockage occurs) and flow rate (weight of metal it will pass per second) of the filter attached to the sleeve. Consideration must also be given to the feed volume requirements of the casting - keeping in mind that the pouring cup/sprue will be part of the feeder for the early stages of feeding.

Filtration capacity and flow rate of the ceramic foam filter are affected by the porosity of the filter, metal temperature, metal cleanliness, melting and inoculation practices, alloy composition and pouring method. Reverse-taper units with 10 ppi (pores per linear inch) filters are recommended for ductile iron applications and units with 20 ppi filters, for gray iron applications.

As mentioned above (See FEEDING AND MODULUS), if the filtration capability of the unit is satisfactory for the casting, the "system" modulus/feeding capability will normally be large enough to support the casting solidification requirements.

GREDE FOUNDRIES, INC. LIBERTY DIVISION

FOUNDRY HISTORY:

Grede Foundries, Inc., Liberty Division is located at 6432 West State Street, Wauwatosa Wisconsin. It was purchased by Grede Foundries in 1920 and specializes in producing ductile iron castings that have complex internal shapes, and require close dimensional tolerances. The foundry produces approximately 3000 tons of ductile iron and high-silicon moly iron castings per month. The iron is melted in three 5-ton Brown-Boveri electric furnaces and transferred into a 1600-lb. capacity tundish ladle where an addition of 5% magnesium ferrosilicon with a 75% silicon cover nodularizes the iron. The iron is manually poured using 700-lb. teapot pouring ladles, equipped with ladle harnesses and gearboxes.

Grede Liberty produces castings on two molding lines. A 20" x 24" 8" over 8" flaskless Robert Sinto automatic molding machine produces castings with pour weights to 115 lbs. and a production rate up to 125 molds per hour. The second molding line is a 20" x 20" to 36" x 36" pin-lift, cope-and-drag flask molding machine and produces castings with pour weights up to 160 lbs. with a production rate up to 20 molds per hour. Isocyanate cold-box cores and shell cores are used. The sand system for both molding lines targets a green sand compactability of 40, permeability of 90, moisture of 3.5% and a methylene blue of 8.5-9.5. Internal casting cores are produced from Isocyanate cold-box using various core blowers and from shell sand.

Grede Liberty has employed conventional runner systems with in-line filtration for many years. While casting quality has been satisfactory, the desire to increase casting yield, reduce shakeout and cleaning room time, as well as metal utilization led to the consideration to experiment with direct pouring units. However, because of the configuration of the Robert Sinto Molding Machine, it was difficult to employ conventional direct pouring units, thus the reverse-taper direct pouring units were selected for trial.

CASE STUDY #1
This planetary gear carrier is produced in 65-45-12 ductile iron and has a cast weighing 9.88 lbs. The production pattern contains four casting impressions and is produced on the Robert Sinto Molding Machine. The target pouring temperature is 2550ºF and the target pouring time is 6.0 seconds. This casting was originally produced using a conventional, non- pressurized gating and filtration system. The filter was located horizontally at the base of the sprue and the short drag runner connected the gating system to a greensand riser. Ingates contained in the core package connect the castings to the common green sand riser.

The pour weight of the original system was 79 lbs., producing a yield of 50%. The pouring time for this system averaged 7.5 seconds. Using the 700-lb. teapot ladles, it was possible to pour eight castings per ladle, leaving a 68-lb. heel.

Original Cope

Original Drag

To achieve the desired yield improvement, the pattern was re-engineered to replace the conventional filtered runner system with a 5/8 L10 reverse-taper direct pour unit. The modified pattern plate layout centrally located the reverse-tapered direct pour unit as a side riser between the core packages. The drag pattern was modified to create a riser basin and a print into which the reverse-taper direct pour unit could be set. Attached to the cope pattern was the riser bob required to form the cavity for closing over the direct pouring unit. The pouring basin / pouring cup was positioned on the plate to match the location of the sprue. Ingates contained in the core packages connect the four castings to the direct pouring unit.

The original feeder was eliminated, along with the sprue, sprue basin, filter and runner bar. The reverse taper direct pour unit was sized to provide adequate modulus and volumetric feed capacity for all four casting cavities.

New Direct Pour Cope

New Direct Pour Drag

The reverse-tapered pouring unit reduced the pouring weight from the original system of 79 lbs. to 55 lbs. and increased the yield from 50% to 71.8%. The pouring time was also decreased from an average of 7.5 seconds to 6.0 seconds. With the original system the 700 lb. teapot ladles were only able to pour eight molds (32 castings) per ladle, leaving a 68 lb. heel. However, with the reverse direct pouring system it is now possible to pour twelve molds (48 castings) from each 700-lb ladle, leaving a 40 lb. heel. X-ray examination of the direct poured castings indicated no internal defect, confirmed by quarter-sectioning and visual examination of the pilot run.

Four carrier castings from the direct pour pilot run were sectioned and found to be 100 percent sound.

CASE STUDY #2
This gear blank casting is produced in 70-50-03 ductile iron and has a cast weight of 27.24 lbs. The production pattern contains two casting impressions and is produced on the Robert Sinto Molding Machine. The target pouring temperature is 2550ºF and the target pouring time is 8.0 seconds. This casting was originally produced using a conventional non-pressurized gating and filtration system. The filter was positioned horizontally in the runner bar between the sprue basin and the casting ingates. The short curved runner connected the gating system to the to a green sand riser. Ingates contained in the core package connect the castings to the common green sand riser. The original pour weight was 84 lbs., for a yield of 65.8%.

Original Cope

Original Drag

To increase the yield on this casting, the pattern was re-engineered to replace the conventional filtered gating system with a 6/9 L10 reverse-taper direct pour unit. The reverse-tapered direct pour unit was positioned as a side riser adjoining both casting cavities. The riser bob used to create the close-over mold cavity for the direct pouring unit was positioned onto the cope pattern. The pouring basin was positioned on the plate to match the sprue/riser bob pattern. The drag pattern was modified to create a riser basin and a print into which the reverse-taper direct pour unit could be set at the same time the cores were being set.

The original feeder was eliminated, along with the sprue, the two-section runner bar, the filter and the filter print. The direct pour unit was sized to provide adequate feeding capacity for both casting cavities.

New Direct Pour Cope

New Direct Pour Drag

The reverse direct pour system reduced the pour weight from 84 lbs. to 70 lbs., for a new yield of 79 %. Also, the average pouring time was reduced from 8.0 seconds to 6.5 seconds. In addition to increasing the yield of the 2-on configuration, the new direct pour system reduced the amount of pattern plate area consumed, to the point that a third casting cavity could, and in several cases has been added.

The overall productivity of the foundry's casting operation was also increased without any modification to melting or molding capacity. The melt shop is limited to tapping 1600 lbs. of metal every eight minutes, or 12,800 lbs. per hour. With the new reduced pour weight of 70 lbs. and running at 120 molds per hour, this leaves 4,400 lbs. of metal for the other (flask) molding line. At the original pour weight of 84 lbs., this would only leave 2,270 lbs. for the flask line, often not enough to run the flask line at full capacity (20 molds/hr. x 160 lb./mold = 3,200 lb./hr.).

SUMMARY AND FOUNDRY EVALUATION
The reverse-taper direct pouring system which contains a ceramic foam filter, allows users of automatic horizontal molding lines to experience the production savings of high-volume molding, yield improvements, increased pattern productivity and reduced cleaning expenses of direct pouring. Thus, the result is an overall increase in productivity, and improved foundry profitability.

ACKNOWLEDGEMENTS
The authors wish to thank Grede Foundries Inc., Liberty Division, and Foseco Metallurgical Inc. for their cooperation in the development, testing and application of the reverse-taper direct pouring system and for their support in the preparation of this paper.

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