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Optimizing Sand control at New Haven Foundry.

Due to a change in its casting mix, this foundry required increased control of its green sand properties to improve casting qualily.

The demands of the automotive sector place a premium on surface finish and dimensional reproducibility for its casting suppliers. Due to these demands, foundries must continuously re-examine re·ex·am·ine also re-ex·am·ine  
tr.v. re·ex·am·ined, re·ex·am·in·ing, re·ex·am·ines
1. To examine again or anew; review.

2. Law To question (a witness) again after cross-examination.
 their existing production practices such as sand control and molding to ensure the required casting properties are being met today and will be met in the future.

For New Haven New Haven, city (1990 pop. 130,474), New Haven co., S Conn., a port of entry where the Quinnipiac and other small rivers enter Long Island Sound; inc. 1784. Firearms and ammunition, clocks and watches, tools, rubber and paper products, and textiles are among the many  Foundry, a gray iron shop located in New Haven, Michigan
Alternate use: There are two New Haven Townships in Michigan.

New Haven is a village in Macomb County in the U.S. state of Michigan. The population was 3,071 at the 2000 census.
, the demands of the future prompted self-evaluation. The foundry produces 160,000 tons/yr of automotive components such as cylinder heads, flywheels and bearing caps via horizontally parted green sand molding. In anticipation of new demands from its automotive customers, including the addition of new brake rotor rotor: see generator; motor, electric.  component production, the foundry decided to begin optimizing its sand system in 1999.

The focus of this optimization was low-cost upgrades. The foundry was looking for Looking for

In the context of general equities, this describing a buy interest in which a dealer is asked to offer stock, often involving a capital commitment. Antithesis of in touch with.
 opportunities for increased control of sand system properties rather than an upgrade of technology. This article takes a look at New Haven's sand system and the optimization it underwent.

Sand System

The sand system at New Haven Foundry consists of two 200-ton/hr mixers equipped with controllers feeding 2 jolt squeeze molding lines. The molding lines are producing 300 molds/hr at a flask flask (flask)
1. a laboratory vessel, usually of glass and with a constricted neck.

2. a metal case in which materials used in making artificial dentures are placed for processing.
 size of 22.5 x 39 x 9 in. The majority of the foundry's cores are hotbox hot·box  
An axle or journal box, as on a railway car, that has become overheated by excessive friction.

Noun 1. hotbox - a journal bearing (as of a railroad car) that has overheated
, but the foundry also produces coldbox cores.

The base aggregate of the sand used by New Haven is a four-screen lake sand at 55 AFS A distributed file system for large, widely dispersed Unix and Windows networks from Transarc Corporation, now part of IBM. It is noted for its ease of administration and expandability and stems from Carnegie-Mellon's Andrew File System.

AFS - Andrew File System
 grain fineness number (GFN GFN Gone for Now
GFN Gay Financial Network
GFN Good For Nothing
GFN Glass Filled Nylon
GFN Group-Forming Network
GFN Grand Forks, North Dakota (border patrol sector)
GFN Goodbye for Now
GFN Global Futures Network
) for molds and 48 AFS GFN for cores. A small quantity of finer bank sand (70 AFS GFN) is added to the system to increase the amount of fines (particularly 140 mesh). This controls the casting surface finish and balances the core sand going into the system to maintain the required AFS GFN. Besides bank sand, new sand is not added to the system other than the large amount of sand entering from core breakdown. A mechanical system was set up to remove core sand from a shakeout Shakeout

A situation in which many investors exit their positions, often at a loss, because of uncertainty or recent bad news circulating around a particular security or industry.

During the dotcom boom and bust, numerous shakeouts occurred.

The bond for the molding sand (Founding) a kind of sand containing clay, used in making molds.

See also: Molding
 is added in the form of a pre-blend containing Western bentonite bentonite (bĕn`tənīt'): see clay. , Southern bentonite and seacoal. The system operates at a methylene blue methylene blue
A basic aniline dye that forms a deep blue solution when dissolved in water and is used as a bacteriological stain and as an antidote for cyanide poisoning.
 clay level of 6-7%. Loss on ignition Loss on Ignition is a test used in inorganic analytical chemistry, particularly in the analysis of minerals. It consists of strongly heating ("igniting") a sample of the material at a specified temperature, allowing volatile substances to escape, until its mass ceases to change.  (LOI LOI Letter of Indemnity (international trade and carriage business)
LOI Letter Of Intent
LOI Loss On Ignition
LOI Letter of Inquiry
LOI Lack Of Information
LOI Lack of Interest
LOI Letter of Invitation
LOI List Of Items
) is maintained between 3.2-4%. The fineness of the washed molding sand is 55 AFS GFN. New Haven maintains the balance of working bond vs. total bond to guard against expansion defects.

In order to expand its product mix to accommodate brake rotor production, New Haven required an upgrade to its sand system that was focused on increasing sand flowability by optimizing sand properties and reducing variations. Brake rotors require high sand flowability for optimal casting quality. The molding sand, when operated at the target levels of 6.6% methylene blue clay and 38% compactability, produces optimum casting quality. When clay level or compactability run above current specifications, the flowability is not optimal for producing molds. With this in mind, New Haven determined that the critical areas to control in its sand system were the water addition, preblend addition (bond and carbon), bank sand addition, core sand influx and the working bond.

Sand Control Program Implementation

The first step in the sand quality improvement program was to ensure collection of the necessary daily (hourly) and weekly sand test data using proper testing procedures. Once the necessary equipment and testing were in place, the foundry's sand technicians were trained to ensure reliability of the data collected. With equipment and operator variations reduced to a minimum, the sand test data then can be relied upon to reflect the true variations in the sand required to control it. While conventional sand testing methods (other than compactability testing) do not allow for optimal real time control of the sand system due to the time required to complete the tests, one must realize that careful analysis of the sand testing data produces useful information to assess overall sand system performance.

With this data collected, any major sources of variation can be identified. Once they are identified, the sand system can be upgraded to eliminate the major sources of variation, and eventually to fine-tune the sand system. While on-line control systems such as those for compactability control and bond addition are necessary, a good sand laboratory is still recommended to verify and complement these systems.

New Haven Foundry began to employ printouts in the lab and developed a computer-based on-line monitoring system for the sand system controller results in house. This PC monitoring is performed in the sand room and in the plant metallurgist's office. The foundry focuses on the following for monitoring:

* control of the water;

* control of the bond and carbons addition;

* control of the new and return sand additions.

Water Control

Inadequate water control is one of the major causes of green sand-related casting defects. New Haven utilizes mullers equipped with controllers that are sometimes unable to timely finetune water additions. The foundry attempted to study and understand the shortcomings A shortcoming is a character flaw.

Shortcomings may also be:
  • Shortcomings (SATC episode), an episode of the television series Sex and the City
 of the control system and set in an offset in one of the controllers to provide consistent sand properties (compactability and strength) from both its mixers. Since the water and bond additions were based on the controller readings, this step was critical to fully understanding the control systems and making the necessary adjustments to suit the individual mixers. This was verified by the sand test data gathered by the sand laboratory. The problem was that the foundry still had a divergence divergence

In mathematics, a differential operator applied to a three-dimensional vector-valued function. The result is a function that describes a rate of change. The divergence of a vector v is given by
 on the controllers. Due to production constraints in the past, the foundry accepted this divergence as common and made adjustments as best as possible even though the laboratory results indicated that the compactability and green strength properties trom eacn mixer mixer, either of two electronic devices in which two or more signals are combined. In the type of mixer used in radio receivers, radar receivers, and similar systems, a signal is translated upward or downward in frequency.  were different.

However, during this sand optimization project, this issue was revisited after comparing additional laboratory tests to the results on the controllers. Compactability of both mixers needed to be verified and controlled based upon laboratory data, and the controllers needed to be offset to produce similar laboratory results. Now, the compactabilities displayed on the two monitors of the controllers are different, but they produce the same laboratory compactabilities and green strengths. The laboratory tests are more accurate and should be the baseline.

Water Cooling Water cooling is a method of heat removal from components. As opposed to air cooling, water is used as the heat transmitter. Water cooling is commonly used for cooling internal combustion engines in automobiles and electrical generators.  PLCs

With any automated controller, certain criteria must be met for the system to function optimally. If the return sand entering the mixer varies greatly in the amount of clay, temperature or moisture level, most controllers are not capable of producing perfect sand on every batch. Depending upon the set up of the controller, multiple batches of the sand may need to be produced to even out the variations and return the sand to a target level.

At New Haven, some variation in bond and carbon level occurred when running jobs without cores vs. high-core jobs. In addition, sand temperature was not always consistent, which also could throw off the controller.

One of the problems with sand temperature arises when the rotary screen of the return sand becomes plugged with wet sand. (This happened at New Haven when one of the molding lines was not running and the sand cooling system cooling system: see air conditioning; internal-combustion engine; refrigeration.
cooling system

Apparatus used to keep the temperature of a structure or device from exceeding limits imposed by needs of safety and efficiency.
 added water to the return sand as if both lines were running.) When this happens, the foundry would alert the sand room that the sand was too wet, and the sand room would reduce or turn off the cooling water. But this results in hot sand entering the mixers, and the controller then would need to readjust re·ad·just  
tr.v. re·ad·just·ed, re·ad·just·ing, re·ad·justs
To adjust or arrange again.

 itself again.

To eliminate this problem, the foundry installed a PLC system on the water cooling system that takes into account the depth of the sand on the belt, upstream sand temperature (before water addition) and downstream sand tempeature (after water addition).Since initial implementation and tweaking tweaking Vox populi Fine-tuning to produce optimal results  of this system, plugging of the rotary screen has been minimized. In addition, significant improvements in compactability control, consistency in bulk density, moisture, permeability permeability /per·me·a·bil·i·ty/ (per?me-ah-bil´i-te) the property or state of being permeable.

1. The property or condition of being permeable.

, green compression and methylene blue clay content of the sand have been realized (Table 1). Comparisons of the 180 sets of data before and after the PLC system show reductions in standard deviations In statistics, the average amount a number varies from the average number in a series of numbers.

(statistics) standard deviation - (SD) A measure of the range of values in a set of numbers.
 up to 40% for these properties. Histograms (Fig. 1) show how the repeatability of the sand system properties (as it relates to compactability) increased dramatically with the addition of the PLC.

Pre-Blend Addition System

As system performance was assessed further at New Haven Foundry, changes also were required on the pre-blend addition system. The system was originally a screw feed mechanism that did not allow for accurate additions. Weigh adders were installed on both mixers to ensure more accurate amounts of bond were added to each batch.

Laboratory testing also discovered that the seacoal level of the pre-blend was too low for a sand system producing iron castings. The result for the foundry was a rougher casting finish then it desired. To compensate, New Haven had to shotblast its castings a second time, increasing cost and reducing throughput time. A simple change in clay/carbon ratio in the pre-blend brought the LOI level up to 3.8% and minimized the need to re-blast castings.

Core Sand Dilution

Early during the development of a sand control program, New Haven also was experiencing problems with drawing deep pockets and mold breakage. The problem with drawing pockets was due to brittle (jargon) brittle - Said of software that is functional but easily broken by changes in operating environment or configuration, or by any minor tweak to the software itself. Also, any system that responds inappropriately and disastrously to abnormal but expected external stimuli; e.  sand from excessive core sand dilution, Friability fri·a·ble  
Readily crumbled; brittle: friable asbestos insulation.

[Latin fri
 and cone jolt toughness tests confirmed this problem.

Initially, when the molding sand was first tested for these properties, friability was 18% and cone jolt toughness was 25 jolts at a methylene blue clay level of 6%. According to according to
1. As stated or indicated by; on the authority of: according to historians.

2. In keeping with: according to instructions.

 past research performed on core sand dilution, more than 10% friability is considered surface brittle for a molding sand and can lead to erosion- and inclusion-related problems. In addition, less than 40 cone jolts is considered a brittle sand from a bulk brittleness Brittleness

That characteristic of a material that is manifested by sudden or abrupt failure without appreciable prior ductile or plastic deformation.
 standpoint, and makes the sand prone to difficulty. Gradually, New Haven increased the methylene blue clay level to its current 6.8%, producing 35 jolts and about 8-9% friability (Fig. 2). The intensive mixing provided by the sand mixers along with additional cumulative mulling mulling (mul´ing),
n the final step of mixing dental amalgam; a kneading of the triturated mass to complete the amalgamation.
 through core sand removal has made this possible.

Core Sand Removal

Although the friability of the sand was satisfactory, cone jolt toughness was still less than 40 jolts at times (especially when methylene blue clay was too low), indicating a brittle molding sand. To combat this problem without raising the clay level too high (and reducing flowability), the foundry worked to remove core sand from the system at shakeout.

Core sand dilution is a major problem for many foundries as today's core binders break down rapidly and thoroughly at shakeout. Depending on the binder binder: see combine.

An earlier Microsoft Office workbook file that let users combine related documents from different Office applications. The documents could be viewed, saved, opened, e-mailed and printed as a group.
 system, degree of burnout Burnout

Depletion of a tax shelter's benefits. In the context of mortgage backed securities it refers to the percentage of the pool that has prepaid their mortgage.
 and mold atmosphere, the core sand grains can be coated with a layer of residual binder and/or lustrous lus·trous  
1. Having a sheen or glow.

2. Gleaming with or as if with brilliant light; radiant. See Synonyms at bright.

 carbon. Residual binder on the core sand grains is not always a problem, but if the coating is lustrous carbon, the clay may have difficulty adhering to the grain when this core sand cycles back into the mixer. The lustrous carbon acts as a lubricant Lubricant

A gas, liquid, or solid used to prevent contact of parts in relative motion, and thereby reduce friction and wear. In many machines, cooling by the lubricant is equally important.
 making it difficult to bond the sand with the bentonite. In addition, decomposition decomposition /de·com·po·si·tion/ (de-kom?pah-zish´un) the separation of compound bodies into their constituent principles.

 of the core binder when exposed to heat in the casting process causes lustrous carbon and other organics to be absorbed into the clay interlayers, causing a "waterproofing" of the bentonite that interferes with normal hydration hydration /hy·dra·tion/ (hi-dra´shun) the absorption of or combination with water.

1. The addition of water to a chemical molecule without hydrolysis.

 and dehydration dehydration

Method of food preservation in which moisture (primarily water) is removed. Dehydration inhibits the growth of microorganisms and often reduces the bulk of food.
 in the molding/casting process. Even in the case of core sand grains with no residual coating or a residual coating that does not interfere with bonding, if the a mount of core sand input is excessive, brittle sand results simply from too much new material input into the system, which results in less cumulative mulling.

At the start of the optimization, the core sand dilution into the molding sand system was estimated at 600 lb/ton or double the recommended level (300 lb/ton of metal poured for iron sand systems) of new material (as new or core sand). To combat this, perforations were made in the shakeout deck to selectively remove residual core sand. The particular spot chosen was determined by taking samples from the beginning of the shakeout deck to the end and testing methylene blue clay level. At the first point in the shakeout deck, the methylene blue clay level closely matched that of the molding sand, but further down the length of the deck, methylene blue clay was less than 0.2%, and the sand grains appeared coated with a black/silvery layer of lustrous carbon. Perforations then were made in the shakeout deck at this point to remove this sand from the system into a bin that is weighed and emptied routinely.

Although these perforations are helping to reduce core sand dilution; the system must be continuously maintained by cleaning the perforations when they become clogged. Future plans involve placing a perforated per·fo·ra·ted
Pierced with one or more holes.
 slide gate on the deck to vary the level of core sand removal depending on the level of cored jobs being run.

Beyond sand system performance, the success of removing core sand from the sand system also has had a positive affect on the foundry's bottom line. Molding sand is no longer removed at shakeout with core sand (reducing disposal costs), so the green sand will receive the benefits of cumulative mulling. As a result, the foundry has been able to reduce its new bank sand additions to the sand system, which were used to adjust the AFS GFN to the required level. The bank sand now is added primarily to control the permeability and to help the sand flow into deep pockets.

Dust Collector Cleaning

New Haven also began regular monitoring of its dust collector system (on the sand system) and buildup build·up also build-up  
1. The act or process of amassing or increasing: a military buildup; a buildup of tension during the strike.

 in its tubes.

Previously, no set frequency to monitoring the dust collector existed. The collector tubes would become clogged after extensive use and fines would not be pulled from the sand system. As a result, the permeability of the green sand would decrease.

New Haven has set up regular monitoring of the dust collector system to coincide with its 140 screen for determining bank sand additions. This has provided further freedom to control permeability.

Control of Incoming Material at New Haven

Another way New Haven Foundry is ensuring a controlled molding sand system is by verifying the properties of incoming raw materials. For incoming sand, the tests include 25-micron clay content, AFS grain fineness number and distribution, acid demand value (ADV ADV Advertisement
ADV Adverb
ADV Advance/Advanced
ADV Advantage (tennis)
ADV Advise
ADV Advocate
ADV Advancement
ADV Advent
ADV Arbeitsgemeinschaft für Datenverarbeitung
ADV Adversus (Latin: Against) 
) and pH. For the base Western and Southern bentonites and a sample of the pre-blend, tests are performed for soluble and leachable calcium and magnesium magnesium (măgnē`zēəm, –zhəm), metallic chemical element; symbol Mg; at. no. 12; at. wt. 24.305; m.p. about 648.8°C;; b.p. about 1,090°C;; sp. gr. 1.738 at 20°C;; valence +2. . These tests determine whether the pre-blend is being properly prepared. Most foundries neglect these tests on incoming bentonite and/or pre-blend. Some may check methylene blue requirement/ion exchange capacity, but ion exchange ion exchange
A reversible chemical reaction occurring between an insoluble solid and a solution during which ions may be interchanged, used in the separation of radioactive isotopes.
 capacity and/ or clay level checks on a pre-blend are not adequate indicators of consistency.

Many bentonites have similar ion exchange capacities as measured by methylene blue, yet they perform quite differently in the molding system. For example, while a Western and Southern bentonite can have the exact same methylene blue requirement, the Southern bentonite will develop faster green strength (less mulling energy required) and will produce lower hot strength and durability than the Western bentonite. This is due to a difference in exchangeable ions, which are measured with the calcium and magnesium tests. The important point is that by measuring soluble calcium and magnesium and leachable calcium, bentonites and pre-blends can be checked in a manner significant to the properties they will produce in the molding sand system. If these values are constant, the bentonite or pre-blend can be considered consistent, and can be expected to perform consistently in the sand system. This control is useful when adjustments to the pre-blend composition become necessary with the changing sand to metal ratio brought about by the changing product mix.
Table 1. Comparison of Properties Before and After PLC Was
Installed on the Water Cooling System
Properties                               Before PLC
Permeability (AFS permeability)            108.97
Green Compressive Strength (psi)           20.85
Moisture (%)                                2.89
Methylene Blue Clay (%)                     6.59
Compactability (%)                         38.96
Weight of Compactability Sample (lb)       222.96
                                      Standard Deviation
Permeability (AFS permeability)              7.18
Green Compressive Strength (psi)             1.5
Moisture (%)                                 0.23
Methylene Blue Clay (%)                      0.37
Compactability (%)                           4.75
Weight of Compactability Sample (lb)        17.32
Properties                                After PLC
Permeability (AFS permeability)            109.31
Green Compressive Strength (psi)            20.93
Moisture (%)                                2.81
Methylene Blue Clay (%)                     6.57
Compactability (%)                          38.05
Weight of Compactability Sample (lb)       227.23
                                      Standard Deviation
Permeability (AFS permeability)              5.59
Green Compressive Strength (psi)             1.22
Moisture (%)                                 0.16
Methylene Blue Clay (%)                      0.32
Compactability (%)                           2.82
Weight of Compactability Sample (lb)        10.87
Properties                            Change in Standard
                                        Deviation (%)
Permeability (AFS permeability)             -22.14
Green Compressive Strength (psi)            -18.67
Moisture (%)                                -30.43
Methylene Blue Clay (%)                     -13.51
Compactability (%)                          -40.63
Weight of Compactability Sample (lb)        -37.24

[Graph omitted]

[Graph omitted]
COPYRIGHT 2001 American Foundry Society, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2001, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Comment:Optimizing Sand control at New Haven Foundry.
Author:Raman, Vijay
Publication:Modern Casting
Geographic Code:1USA
Date:Aug 1, 2001
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