by George DiSylvestro
DiSylvestro Videography Service
Abstract
The successful progress in casting metals with silica sand as its basic mold or core molding material, has been continuous and profitable. This has made surviving metal casting plants improve in quality production and growth. Achieving these goals, has been gratifying for those who have committed themselves to a continuous search and implementation of excellence.
Production research and dissemination of information regarding the control of a green sand molding system, has been in separate reports of various areas of the casting process.
Listed here, are the most important testing, control and standardization issues for those who wish to evaluate, compare, improve, or profile their entire existing sand system. This can be used to identify problem areas causing poor production, increased costs and barriers for needed quality improvements.
Auditing and Control
The control and auditing of a green sand system has been on a continuous improvement incline. Progressive foundries confirm the need for correct information from sources that influence quality and ultimately can reduce casting losses.
Using a molding sand form such as per Form #1 confirmed that many foundries have limited auditing and testing, until a serious problem occurs. Then they immediately grope for answers and sometimes find they have no standards for reference, when quality castings had been produced previously.
By using a daily reporting form similar to Form
#2, developed and acted on by experienced production personnel, process abnormalities can be revealed quickly. This information should be reviewed by all who attend daily scrap meetings for analysis of previous casting cycles. This will encourage immediate action to be taken when necessary.
A step further in the search for excellence, would be to combine metallurgy and pouring information with data gained from
Forms #1 and #2. Having a similar surveillance form for metal production to synergize with sand reporting could put all of the valuable current operating information in the hands of the decision makers.
Define the Existing System
To develop a data bank, we use the foundation of current accurate information that characterizes the molding sand. A research study can be very rewarding to deter abnormalities that occur of consequence.
To understand and pinpoint the critical auditing areas for maintenance and engineering, an up-to-date sketch of the entire sand system (including dust collection) should be made available as is. Unfortunately many times changes or improvements, in equipment, processing or transporting, are made and never reported. This has been known to cause major problems, including safety and environmental mishaps.
An article published in the Ductile Iron News, Issue #3, 1998, on
"Prioritizing of Green Sand
Testing," reveals a complete description of primary and secondary tests that can be performed. Reviewing this article is a prerequisite for the following information to standardize and document casting quality when it is at the optimum level, to achieve your goals for excellence.
Profile the Sand System
The following listing of tests, auditing areas, and procedures are suggested as raw material evaluation, material specifications and certification, mulling and molding equipment performance.
- Raw material evaluation
- Material specification and certification
- Mulling and molding equipment performance
- Mulling cycle and consistency
- Compacting characteristics during molding
- Effectiveness, efficiency and control of dust collectors
This review does not coerce the quality control department to run all of these tests and auditing documentation. To know your sand systems limitations, it is suggested consideration to complete a one time testing with accurate documentation of critical areas. Especially at a time of acceptable level of production, quality and low scrap. Be certain of the accuracy and establish ranges of acceptance or tolerance.
Distribute and educate all departments and inspectors so that they have complete knowledge of what these test values are and how they may affect operating conditions, especially, when safety is compromised. When a significant change from normal occurs, it becomes urgent to re-audit and make a complete routine comparison of any one of these six profiles.
Recommended Profiles
The profiles are listed in order of their priority and can be used as a bench mark for introducing a new material or making a major change.
- Base sand and system sand quality.
- Evaluation & characteristics of bentonite
- Evaluation & characteristics of sea coal, carbons and additives.
- Mulling, mixing & effect of water
- Molding sand compaction tests
- Dust collector and controls
Molding Sand Quality Profiles
1. Grain size distribution and base sand quality of system sand.
- Suppliers certificate of analysis as shipped
- Unwashed and washed sand sieve analysis
- Percentage of sand balls, clay balls, core butts and waterproofing test
- "The silica program" sand autopsy.
- Autopsy of fines from dust collector system
See Reference #1
Base Sand Quality
Since approximately 90% of the mold is sand, a major effort should be given to this profile for your database. The standardization and testing of sand is fairly simple. The effects of minor changes can be very influential and affect most all other sand characteristics. Changes can be gradual and not detected easily. Look for changes in casting finish, bond and water requirements, permeability and sand compaction. Cost differences for a quality sand that fits the casting needs, are mostly due to plant geography. The sand fineness and size frequency with uniform compaction, is basic and determines the casting finish and casting dimensions.
Evaluation of the bentonite Bond
- List specifications of bentonite(s) used, trade name, description, chemical and physical analyses
- Bond activation time and durability tests, air set, dry, hot and baked retained strengths can be obtained from supplier or performed internally.
Viscosity and gel profiles of bentonites in water separately and in composition of the premixture with water at different solids content.
See Reference #2
Dialogue on Bonding Requirements
The profile for bentonite clay, the second main constituent in molding clay, has much influence on the molding characteristics and determines the thermal properties at casting temperatures. The casting weight or mold weight as poured, pattern configuration or design, usually determines the type of bentonite or blend required. The combination of sodium and calcium bentonites can assist greatly in producing consistent shakeout if the water content is controlled. This is a must to prevent the loss of sand from lumps in the sand system and to keep the hoppers full as much as possible. There can be a great influence on mulling energy and time needed when blending clays. Sodium bentonite requires the most. For these reasons, confirming the clay bond and its consistency is very important in achieving and maintaining best production and casting dimensions.
Evaluation of Carbons and Additives
- Suppliers specifications of carbon or cellulose additives
- Test and record volatile content and loss on ignition
- Ash content of sea coal at 1850oF for 1 hour
- Approximate production of lustrous carbon oxidizing or reducing atmosphere of additives
- Develop calculations for control of an adequate reducing atmosphere.
See Reference #3 and #4
Application of Seacoal Carbons & Additives
The removal of sand from the casting is a great expense in the casting production cycle. The function of carbons such as seacoal, gilsonite or seacoal replacements, play a major role in developing the degree of casting peel, shakeout and casting defects. The distinguishing features in these profiles can produce very favorable economics of operation, especially when they affect the foundry atmosphere and environment. Most cast irons require a consistent carbonaceous volatile at casting temperatures to overcome the oxidizing effect of steam, which results from sand moisture. This control can reduce and prevent burn-on, burn-in, and chemical penetration on the surface of the casting.
See Reference #5
Mulling tests and the Effect of Water
- Bond vs. temper water, bond development during mulling to evaluate bentonite clay or pre-mixtures. Degree of mulling required
- Friability and moldability tests
- Mulling cycle profile and standardization of moldability controller (maintenance)
- Aerator settings and condition of sand at molding station (sand balls)
- System sand temperature profile from shakeout, through muller and a point of use
- Standardization of water used and use of black water for environmental reasons.
See Reference #6
Dialogue on Mixing and Mulling
The Muller or mixing equipment is a key factor for producing sand consistency to approach homogeneity with the returned sand, bonding clay, additives and water. The compactability of the molding sand distinguishes the uniformity achieved in the mold and compliments the molding process and molding machine. The amount of water required is determined by the sand, bentonite and additive profiles. Mulling performance can be monitored automatically, if other profiles are held as constant as possible. The returning sand temperature is the most difficult to control and is influenced greatly by the sand to metal ration, cooling equipment (if any) and the storage inventory and transportation method. The quality and temperature of the water used can change the molding sand characteristics, especially very cold and hard water. Good muller and aerator maintenance should be mandatory and audited.
Molding Sand Compaction Studies
- Three to six rammed standard compaction tests comparing density, permeability, mold hardness, and green compression strength vs. rammed energy at optimum moisture level. Sand should be taken as received at the molding station and graph curves made for documentation of molding sand characteristics.
- Lateral movements tests
- Resistance to compaction tests
See Reference #7
Molding Sand Compaction Tests
Casting to size with a very minimal deviation in casting dimensions can reduce machining, and is welcomed by casting buyers. Casting reproductability is governed mostly by the uniform density of the mold and the casting stresses incurred by the casting geometry and gating or risering restrictions. Conducting compaction profiles can detect changes that may be occurring that otherwise cannot be measured accurately by other methods. The influence of compacted density (especially non-uniform) affects sand expansion, mold permeability, mechanical penetration, run-outs, casting distortion, and the ease of shakeout. These factors can have a great impact on the amount of cleaning and grinding, casting abnormalities and scrap. Mold testing, such as mold hardness, mold strength and mold permeability is now a new dimension in control and is becoming universally accepted.
See References #4, #6, #8,
#9, #10
Dust Collector Profile and Controls
- Maintain a detailed and up to date sketch of the present dust collector system and settings.
- Audit dust collector fines for wet and dry dust collector for bonding clay and carbons.
- Ultimate responsibility for dust collector performance can benefit environmentally and be cost effective.
- Develop an inspection and reporting schedule for possible OSHA inspections.
Dialogue on Dust Collection Systems
More than ever, the foundry environment and any pollution to the atmosphere is becoming increasingly important and costly. Reduction and compliance can be monitored by the surrounding community and OSHA. All of the previous profiles discussed here, can be changed substantially by the dust collection system. This compulsory equipment that detracts from profitability, can significantly alter the consistency and performance of the molding sand, casting finish and quality. This profile, or "silica program" should be the responsibility of management to maintain a clean and healthy working environment for its personnel. Training is necessary for the maintenance department to know the importance for auditing and documenting the tests made in the laboratory. This team effort can also keep replacement and repair costs at a bare minimum.
Conclusions
Metalcasting plants that cannot confirm from their operation where they were, when good production and quality occurred, will find it difficult to make correct decisions to bring the and system into compliance when problems develop. It takes days or weeks to bring some systems back to an acceptable level, depending upon cycling time and the degree of change(s) made. Having a detailed accurate database from your research of the profiles listed is like an insurance policy against costly problems before they become serious. If the foundry engages and develops a daily auditing and quality surveillance procedure that synchronizes with maintenance, engineering, molding, metal production, and training, wide variations in scrap rates can be improved and reduced.
The Search for Excellence
The important questions for growth of a profitable operation are; where were we? where are we now? and where do we want to be? The incentive for answering and taking correct action on these questions can reduce costly breakdowns that retard production, and improve safety and morale of the dedicated personnel. It encourages training in achieving continual excellence through communications.
Determine an approved second source of raw materials that meet your general specifications. This could prevent shut downs or production slow downs in case of strikes, shipping problems, weather conditions, suppliers problems or acts of God. It can also be used incase of the cost increases that are not justifiable. Be sure the change has been production tested to confirm its acceptance.
Training personnel by sending them to the Ductile Iron Society's Metalcasting Seminars, Technical and Operating Meeting, and reviewed video training tapes listed in the report, where made live, at previous DIS Training Seminars. If you are in the know, confidence and success in managing can be very rewarding.
See Reference #11
The significance of these recommendations of profiling and the molding sand system research, can document the operating conditions of present castings produced. It is as important as the database and records kept by the melting and processing of metal that is required by high quality castings buyers for insurance against failures in the field.
References
For those who wish to enhance any of these suggested profiles for greater understanding or for training purposes, the following are complete videotapes presented at Ductile Iron Society T&O Meetings, Training Seminars or in previous "Hot Topics" publications.
No. 1 - Training - DIS Video #6 on raw materials, Part 1, Sand
No. 2 - Video - same as above, Part 2, "Bentonite Bonds"
No. 3 - Video - same as above, Part 3, "Seacoal and Carbons"
No. 4 - "Controlling Green Sand Finish" DIS Hot Topics, Issue #1, 2002
No. 5 - "Experiences in Defect Diagnosis - Metal Penetration", DIS Video #1
No. 6 - "Mixing and Mulling Molding Sand", DIS Video #17
No. 7 - "Critical Molding Factors Affecting the Production of Ductile Iron Castings", DIS Video #3
No. 8 - "High Density Molding Technology", DIS Video #5
No. 9 - "Prioritizing Green Sand Testing" by George DiSylvestro, Ductile Iron News,
Issue #3, 1998
No. 10 - "Factors That Affect Compactability and Consistency in Green Sand",
Ductile Iron News, Issue #3, 2002
No. 11 - "Reproducing Casting Dimensions in Green Sand, DIS Video #18", 2002 T&O Conference
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George DiSylvestro
Disylvestro Videography Service
717 No. Florence Drive
Park Ridge, IL 60068-2103
Phone 847-825-5620
Fax 847-825-2512
Email: disylvestrovideo@attbi.com
Daily Quality Surveillance Report
Molding Sand Survey Form 1
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