What Do the Numbers Mean?

Find out which sand tests you should be doing on a regular basis and what aspects of your sand system the tests are measuring that will help you produce good castings.

Scott Honeyman, Carpenter Brothers Inc., Minneapolis

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What does a minimum green sand testing program look like? What tests need to be done regularly? What tests can be done less frequently? What do the tests actually measure anyway?

Metalcasters have two primary reasons for green sand testing:

To check the consistency of the prepared green sand. 

To determine if the green sand has the physical and chemical properties to produce good castings.

Poor quality sand can lead to a number of casting-related defects. To ensure the properties necessary to avoid casting defects and produce the quality you desire consistently throughout the entire green sand system, metalcasting facilities need to test their green sand daily for:

  • Compactability.
  • Moisture.
  • Specimen weight.
  • Permeability.
  • Green compression strength.
  • Dry compression strength.
  • Methylene blue clay content.
  • In addition, the following tests should be done on a weekly basis:
  • AFS or 25 micron clay content.
  • Screen analysis.
  • Total combustibles (LOI).
  • Volatiles at 900F (482C).
  • Available bond.
  • Working bond.
  • Muller efficiency.

 

This article will review the basic green sand tests, what the tests results tell you about your green sand and why they are necessary to prevent common casting surface defects. (Tests are referenced by the test number and protocol as defined in the AFS Mold and Core Test Handbook).

Everyday Tests

Compactability of Molding Sand Mixtures (Rammer Method)—AFS test 2220-00-S

The purpose of this test is to determine the percentage decrease in the height of a loose mass of sand under the influence of compaction (i.e., how resistant is it to squeeze and compaction?). Compactability is probably the most common green sand test and is usually performed by a 3-Ram compactability tester. Also there are inline automated testing systems such as the “Hartley” sand tester used by many metalcasters. The compactability test tells you how wet or dry the green sand is and helps control the most common green sand defects. It is directly related to the performance of the green sand in the molding operation and reflects the degree of temper of the green sand. It indicates how a fixed volume of green sand will react to a fixed energy input (such as mulling or molding). Metalcasters want to select a compactability level high enough to avoid cuts and washes, friable broken edges, hard-to-lift pockets, cope downs, crushes, penetration, burn on and erosion scabbing. Yet, compactability must be low enough to avoid oversized castings (due to mold wall movement), shrinks, blows, pin holes, super voids, poor finish, expansion defects, gas and rough surfaces, shakeout problems and high ramming resistance.

Moisture Determination (Forced Hot Air Method)—AFS 2218-00S

This test is used to determine the percentage of moisture in the molding sand. Moisture in molding sand affects the plasticity of the clay bond, which controls most sand-related defects.

Moisture content of a green sand molding system is not an arbitrary number. It must be maintained within a narrow range. The moisture content is affected by the hydration of the binder composite, coating of the sand particles and muller efficiency with regard to working and available bond. Moisture affects all other green sand properties and is the most abused ingredient in green sand.

The two major factors that affect moisture requirement are the type and amount of clay and the type and amount of additives in the green sand mix.

Excess moisture will produce an oxidizing atmosphere in the mold, promote excess gas evolution and lower permeability, cause high dry and hot strength, reduce mold hardness and result in poor flowability of the sand.

Insufficient water produces dry friable green sand that is difficult to mold.

The specimen weight in the Forced Hot Air Method is an indicator of the consistency of the green sand and the presence of oolitic materials, referred to as dead clay or ash, which is diluted by new sand additions. It also indicates changes in sand distribution.

The 2 x 2-in. specimen weight called for by the test should be recorded at or near a predetermined compactability. A variation in the specimen weight indicates green sand density changes are taking place in the system.

When the specimen weight drops, it indicates a build-up of oolitic material. This build-up can lead to burn-in, burn-on and penetration defects. A trend of lower specimen weight indicates not enough new sand is entering the mix to dilute the oolitic material.

Compression Strength (Green and Dried)—AFS 5202-00S

The green and dried test determines the compression strength of an AFS 2 x 2-in. specimen. Green compression strength indicates the maximum compression stress the sand mixture is capable of sustaining and is used to control the rate of clay addition to the green sand system.

The degree of mulling, sand to metal ratio, clay content, compactability range and additive type affect green compression strength.

Low green compression strength provides good flowability but can result in broken molds and poor draws. Indicators of low strength are low clay content, dry sand and poor mulling.

High green compression strength means stronger molds but difficulty in shakeout, poor casting dimensions, poor flowability, high ramming resistance and higher cost. High clay content is an indicator of high strength.

The dry compression strength test determines the maximum compression load a dry sand is capable of sustaining. It indicates the resistance of the mold to stresses during pouring and casting cooling and the ease of shakeout. The higher the dry compression strength, the greater the number of hard lumps present at shakeout.

An increase in moisture content, the type and amount of clay, rammed mold density and excessive moisture significantly affect dry compression strength. Low dry compression strength means easy shakeout by loose friable sand, cuts and washes, burn-in, inclusions and erosion. High dry compression strength leads to stronger molds, but difficulty in shakeout, loss of return sand, cracks and hot tears.

Permeability (Standard 2 x 2 in. Test Specimen)—AFS 5224-00-S

Permeability is a test of the venting characteristics of a rammed green sand mold. Important factors in regulating the degree of permeability include sand grain size, shape, distribution and type, binder composite quantity and the density to which the green sand has been rammed, and moisture content.

Low permeability will lead to a smooth casting surface finish, but also could cause blows, pinholes and expansion defects. High permeability reduces gas pressure but can result in mechanical penetration and a rough surface finish.

Methylene Blue Clay Test (Molding Sand)—AFS 2211-00-S

This test measures the amount of live clay present in a sample of molding sand. The test determines the amount of exchangeable ions present in the active clay by adsorption of the methylene blue dye. Clay that still has ion exchange capability will contribute to green, dry and hot strength properties of the green sand. The methylene blue clay value varies depending on the type of clay in the binder composite.

Weekly Tests

AFS or 25 Micron Clay Content

In this test, the percentage of clay and other particles that settle at a rate of less than one in. per minute of water is determined, which indicates the amount of fines and water-absorbing material in the green sand system.

Any particle that does not settle through 5 in. of water in five minutes may contain active clay, dead clay, silt seacoal, cellulose, cereal, ash, fines and any other materials that float in water. Only active clay gives bonding capacity to the green sand system.

Sieve Analysis (Particle Size Determination of Green Sand)—AFS 1105-00-S

Grain Fineness Number (AFS GFN, Calculation)—AFS 11-6-00-S

The purpose of the sieve anaylsis test is to determine the particle size distribution and estimate the average sieve size of green sand using standard testing sieves. Calculating the grain fineness number gives an estimate of the average sieve size of a sand sample.

The distribution of the green sand has a bearing on the physical properties that can be developed by the sand system. The distribution influences the amount of bond required and the surface finish of the castings.

The screen, or sieve, analysis should be run on the washed system sand and the dried system sand. A comparison of the dried sand screen analysis and the washed screen analysis shows how much agglomeration is taking place in the green sand system.

Loss on Ignition (LOI)—AFS 5100-00-S

Loss on ignition measures the weight change of a sample, consisting of weight losses and weight gains, when a sample is fired at 1,800F (982C). This includes weight loss due to volatization of organics, removal of chemically bound water, dissocation of inorganic compounds (with one or more components given off as a gas), and weight gain due to oxidation reactions.

Loss on ignition determines the total amount of combustible material in the green sand. The green sand sample is fired at 1,800F until it reaches a constant weight. The quantity of gas forming materials in the green sand will affect casting results.

A high LOI may produce gas defects such as pinholes, blows and scabbing. In steel castings, a high LOI could lead to carbon pickup on the casting surface. A low LOI can lead to poor casting peel and a rough casting surface finish.

Volatile Material at 900F (482C)—AFS 2213-00-S

This method is used to determine the amount of material in the system sand or additives that will volatize at a temperature of 900F (482C). Results from this and the LOI test are used hand in hand. Low combustibles (as determined by the LOI test) and volatiles lead to lower cost and less moisture required but also can result in poor casting peel, poor finish and poor shakeout.

High combustibles and volatiles cause lower expansion but can result in pinholes, smoke, blows, brittle sand, higher cost and higher moisture requirements.

Available Bond

Available bond indicates the moisture-absorbing materials in the sand system, including live, latent and dead clay and additives. The value is derived by relating green compression to moisture using a prepared graph, slide rule or the calculation (0.105 x GCS) + (1.316 x MOIST).

The live clay actively bonds the sand, and the latent clay can be activated with further energy input. The dead clay does not add to green tensile or green splitting strength, but does absorb moisture.

Working Bond

The working bond percent indicates the amount of clay that actually is producing bond strength in the sand mix. Working bond (or effective clay) is derived by relating green compression to compactability using a prepared graph, slide rule or the calculation (15.29 x GCS) / (132.1 - COMP).

Higher working bond indicates more efficient use of the clay. Large variation indicates variation in the clay additions or in the effectiveness of the mulling.

Mulling Efficiency

The higher percent mulling efficiency, the greater the clay utilization and the lower the clay content required. The working bond value divided by the available bond value (and multiplied by 100) gives a percent mulling efficiency reading.

Segregation in transport, loss or buildup of fines due to a lack of dust collection, bond quality, temperature and muller or mixer condition all may affect mulling efficiency.

This article is based on a presentation originally given at the AFS 2014 Sand Casting Conference.

W

ith gridlock in the 113th Congress and continued to resistance to the administration’s legislative agenda, President Obama is utilizing federal agencies to achieve his policy agenda. Dozens of federal regulations, directives and policies are being pushed through via government agencies such as the U.S. Environmental Protection Agency (EPA), National Labor Relations Board, U.S. Department of Labor and the Occupational Safety and Health Administration (OSHA). The wave of regulations is reflected by the fact that over the last five years, 157 new major regulations have been released, many of which have direct impact on U.S. manufacturing and the metalcasting industry.
A major regulation is defined as a rule with $100 million or more in expected economic impact. Since President Obama was elected, a record 3,659 final rules and 2,594 proposed rules have been issued. Those that are not deemed significant are not required to include a cost-benefit analysis, even as their layered implementation has a cumulative economic impact on businesses. More regulations are on the docket for 2014, 2015 and 2016 addressing issues like health care, crystalline silica, power plant emissions and ozone protection.
EPA Regulations
Among the several EPA regulations recently introduced, the power plant rule, ozone legislation and the proposed waters of the U.S. rule may have the most impact on metalcasters.
Power Plant Regulation
EPA’s Clean Power Plan Rule, released June 2, proposes emission guidelines for states to follow in developing plans to address greenhouse gas emissions from existing fossil fuel-fired electric generating units. Specifically, EPA is proposing state-specific rate-based goals for carbon dioxide emissions from the power sector, as well as guidelines for states to follow in developing plans to achieve the state-specific goals.  
Manufacturers will be hit twice by greenhouse gas regulations, both as users of the energy being regulated and as industries considered next in line to receive similar regulations from EPA.
The current proposed power plant rule would substantially increase electricity and natural gas costs and create reliability problems, all for a relatively small global climate impact. For example, EPA says the proposed rule would eliminate 730 million metric tons of carbon by 2030. From 2010 to 2011, China’s carbon dioxide emissions rose by 705 million tons. The rule would substantially reduce use of coal-fired generation. Coal-fired power is a low cost and reliable source of electricity. Importantly, coal competes with natural gas on a Btu basis and helps keep electricity prices from rising. Many in the business community believe the EPA power plant rule would increase dependency on natural gas for power generation.
A lawsuit against EPA challenging the agency’s failure to assess the job-loss impact of its power plant rules has been allowed into federal court (Murray Energy Corporation v. U.S. Environmental Protection Agency, No. 14-1112). A three-judge panel was expected to hear the case this month.
In September, EPA extended the comment period for its “Clean Power Plan Rule” 45 days, until December 1. The American Foundry Society (AFS) is in the process of receiving input from its members and drafting comments.  Based on comments from EPA staff, the agency still intends to finalize the rule by June 2015.
Ozone Regulation
This summer EPA’s Advisory Panel and staff recommended to the EPA Administrator that the national air standards for ozone be lowered to 60-70 parts per billion (ppb) from the current 75-ppb standard, which was set in 2008. The agency cites scientific data and exposure information that “provide strong support” for revising the health-based national ambient air quality standard for ozone of 75 ppb.
The EPA Office of Air Quality Planning and Standards, which prepared the assessment, said a revised standard set within that range “could reasonably be judged to provide an appropriate degree of public health protection, including for at-risk populations and life stages.”  
The regulation could become the most costly in U.S. history if the new standard is implemented. In 2010, EPA estimated the annual compliance costs for a 60-ppb standard would be $90 billion in 2020. The National Association of Manufacturers (NAM) released a report in July that estimated a revised ozone standard of 60 ppb could cost the U.S. economy up to $270 billion per year and result in the closure of one-third of the nation’s coal-fired power plants. The lower standard will require large reductions in NOx and volatile organic compound (VOC) emissions from power plants, manufacturing facilities and mobile sources such as cars, trucks and off-road vehicles. Requiring a reduction to 60 ppb would leave nearly all of the U.S. in a so-called “nonattainment zone.” Metalcasting facilities of all sizes in nonattainment areas would not be able to make investments and expand operations without other businesses reducing their emissions or, worse yet, shuttering their operations. EPA has until December 1 to decide whether to keep or change current national air quality standards for ozone. President Obama delayed EPA’s previous attempt to promulgate a lower ozone air quality standard in 2011. A final rule is expected to be made by October 2015.
Waters of the U.S. Rule
In March, EPA and the Army Corps of Engineers proposed a new rule to redefine the term “waters of the United States” and the agencies’ jurisdiction over waters they can regulate under the Clean Water Act. The rule extends federal jurisdiction well beyond traditional navigable waters to tributaries, adjacent waters (such as ponds) and vaguely defined “other waters.” EPA’s proposal exposes new facilities and expansion projects to additional federal permitting, triggering new upfront costs, project delays and threats of litigation. Permitting requirements could cost metalcasters nearly $200,000 in some cases.
On September 10, the U.S. House of Representatives passed the Waters of the United States Regulatory Overreach Protection Act (H.R. 5078), which requires EPA and the Corps to revisit the proposed rule with direct consultation with state and local officials to determine which bodies of water should be covered under the Clean Water Act. The White House has issued a veto threat against this legislation, and the Senate is unlikely to take up the Overreach Protection Act this year.
EPA has received more than 500,000 comments to date on the proposal, and the comment period was extended to Nov. 14. The AFS Environmental Health and Safety 10-F Committee assembled comments from the industry on how the new permitting requirements will impact metalcasters. Information about the proposed rule can be found at www.epa.gov/uswaters.
OSHA Initiatives
OSHA’s top priorities in President Obama’s second term have included increased injury reporting requirements, crystalline silica, combustible dust and increased enforcement. 2014 has shown a continued focus on high hazard industries such as metalcasting through the use of national and local emphasis programs, such as the silica and primary metals national emphasis programs.
Crystalline Silica Standard
Of perhaps largest concern to the metalcasting industry is the proposed standard on occupational exposure to respirable crystalline silica. OSHA formally unveiled the comprehensive regulation to control crystalline silica in September 2013. It is one of the safety agency’s most far-reaching regulatory initiatives ever proposed for the metalcasting industry and a number of other key sectors. In addition to the 50% reduction in the permissible exposure limit (PEL), OSHA is proposing requirements including, but not limited to, medical surveillance, record keeping and prohibitions on certain work practices, including compressed air and dry sweeping.
AFS believes the current PEL is adequate to protect the health of exposed workers from silica-related disease when it is fully complied with and enforced. OSHA estimates the rule will result in approximately $44 million in annual costs to the industry. This stands in sharp contrast to the industry analyses whereby AFS estimates a conservative cost to the industry of $2.2 billion per year, or 276% of profits. OSHA expects to issue a final rule by 2016.
For the past year, AFS has been working on gathering and submitting detailed comments and background materials for OSHA, including: prehearing comments submitted Feb. 11; testimony at a March 28 public hearing in Washington, D.C.; post-hearing comments responsive to OSHA’s request for additional information June 3; and the post-hearing brief filed on August 18.
With the docket closed, metalcasters can continue to educate their lawmakers about the impact that rule will have on their metalcasting facility and our industry. The metalcasting association in its meetings with lawmakers is focusing on the regulatory overreach, feasibility and cost of the proposed standard.
Temporary Workers
Metalcasters also should be aware of an initiative launched last year to better train and protect the safety of temporary workers. The OSHA Temporary Worker Initiative includes outreach, training and enforcement.
At least 14 temp workers died during their first day at a new worksite in 2013 across all industries. In recent months, OSHA has investigated reports of temporary workers suffering serious or fatal injuries and cited a number of businesses. The agency and the National Institute for Occupational Safety and Health (NIOSH) has released recommended practices for staffing agencies and host employers to protect temporary workers from hazards on the job. The new publication highlights the joint responsibility of the staffing agency and host employer to ensure temporary workers are provided a safe work environment.
The new guidance recommends that staff agency/host employer contracts clearly define the temporary worker’s tasks and the safety and health responsibilities of each employer.  The new Recommended Practices publication is available at: www.osha.gov/Publications/OSHA3735.pdf.
Injury and Illness Reporting
Two proposals on injury and illness reporting were reclassified as long-term action in May, including the Injury and Illness Prevention Program (I2P2), which would require employers to establish formal written plans to find and fix real and potential workplace hazards, and the MSD Column to OSHA’s Form 300 Injury and Illness Log, which would be used to enforce ergonomics.
Combustible Dust Standard
The Chemical Safety Board documented hundreds of fatalities and serious injuries resulting from combustible dust explosions in a 2006 study. As a result, OSHA began working on a potential rule in 2009 that would require industries, including metalcasting, to better control combustible dust hazards. A number of OSHA standards address aspects of this hazard, but the agency does not have a comprehensive standard. According to the agency’s current regulatory agenda, OSHA intends to initiate a review panel on the proposed rule in December, as required under the Small Business Regulatory Enforcement Fairness Act (SBREFA).  If OSHA does commence a review panel, AFS plans to have a member company be part of the discussions. While a proposed standard is not expected soon, OSHA is gathering information and currently regulating combustible dust through a national emphasis program.