The Hill and Griffith Company's News Blog

Biodegradability Redefined and Volatile Organic Compounds Update

Government regulations are changing the rules for compliance – but what are they?

January/February 2010 | PRECAST INC.

By Bob Waterloo , Technical Sales Manager, Concrete Release Agents, Hill & Griffith Co., Indianapolis

Have you ever played a game with others and in the middle of the game they start changing the rules? Frustrating, isn’t it? Or maybe you played a game and nobody knew what to expect next. You don’t know if the old rules apply, or if they are making the game up as they go along (perhaps so they can win?). On the other side of the coin, perhaps the changes were made so that the playing field is leveled, or perhaps the original “rules” were unreasonable and left everyone confused and in doubt.

    It appears that this is what is happening with the definition of biodegradability. New federal rules, regulations and definitions are now in effect, but there has been little in the way of notification to the players. The purpose of this paper is to provide precasters with current information on this changing environmental landscape to help them make decisions regarding form release agents.

Biodegradability

One thing is for certain: Humans generate a lot of garbage (both personal and industrial), some of which is considered toxic waste and some of which will contaminate our environment. Perhaps we won’t see the impact of this contamination for years to come. Other waste, both personal and industrial, will degrade back to the natural environment over a short period of time and may even be beneficial to our environment. But how do we know what is – and what is not – environmentally acceptable? And what are we using in our plants that is environmentally responsible or detrimental to the environment?

    As outlined in “Form Release and the Law” (Precast Inc., Jan/Feb 2006), the word “biodegradable” has been terribly misused. Given enough time, everything is biodegradable. Unfortunately, in many cases, by the time the degrading process has taken place, the environment is contaminated. For that reason, and many others, I’m sure, the U.S. Environmental Protection Agency (EPA) issued guidelines as to how and when the word “biodegradable” can and should be used. Further, while there is no official organization to verify the use of the claim of biodegradability, the U.S. Federal Trade Commission (FTC) has issued some general guidelines on what type of products qualify as legitimately biodegradable. They have even sued some companies for unsubstantiated, misleading and/or deceptive use of the term on product labels.

    More attention is now being paid to biodegradability, and many agencies, companies and organizations are getting involved. Again, given enough time, anything is biodegradable.

    Because the word “biodegradable” has been inappropriately used in the past, it is important that we understand how it is truly defined and what criteria a product must meet in order to be considered biodegradable. One definition of “biodegradability” can be found in the EPA 1998, “Fate, Transport and Transportation Test Guidelines, Office of Prevention, Pesticides and Toxic Substances (OPPTS) 835.3100, Aerobic Aquatic Biodegradation”; and in EPA 712-C-98-O and ASTM D-5864-00, “Standard Test Methods for Determining Aerobic Aquatic Biodegradation of Lubricants or Their Components.” This reference gives everyone the guidelines to be followed when determining biodegradability and using the word “biodegradable” in claims relating to various products, including concrete form release agents. The U.S. EPA definition includes an allowable “28-day half-life” of materials in order to be considered biodegradable. Half-life is the time required for the decay of one-half of a given component in a system.

    Precast operations that are near free-running water or have relatively shallow aquifers should be especially concerned about contaminants in the soil that may adversely affect the environment. A word of caution: Just because a release agent is “water-based” does not necessarily mean it will meet the EPA requirement to be classified as biodegradable. If you plan to use a form release (or any material, for that matter) that claims to be biodegradable, ask whether the material meets the 28-day half-life criteria that U.S. EPA describes. As there are often misunderstandings on the term “biodegradable,” it is wise to go that extra step in clarifying that the material meets the criteria you require.

    While it appears that there are no federal mandates on biodegradability of concrete form release agents, we can certainly expect new rules and regulations in the future. How soon is anyone’s guess, but we do see more precasters trying to pre-empt the regulations that are expected, or are in some cases already in effect in their local region (wetlands are a good example).

    Based on my research, there is no current legal definition of “biodegradable” or “biodegradability.” The ASTM (American Society for Testing and Materials) defines the term as “degradation caused by biological activity, especially enzymatic action, leading to a significant change in the chemical structure of the material.” The EPA, however, has given more specific guidelines of biodegradability (like the 28-day half-life that have been accepted by industry and governmental agencies.)

    Based on the Federal Trade Commission (FTC) definition, only products that contain materials that “break down and decompose into elements found in nature within a reasonably short amount of time when they are exposed to air, moisture and bacteria or other organisms” should be marketed as “biodegradable.” Also, the FTC acknowledges that even products appropriately labeled as biodegradable may not break down easily if they are buried in a landfill or are otherwise not exposed to sunlight, air and moisture, the key agents of biodegradation (aerobic vs. anaerobic).

    According to federal regulations (Federal Register Part 260 16 CFR 260 7), the claim of biodegradability must be substantiated using environmental biodegradable testing. As form release agents are subject to both aerobic (with oxygen) and anaerobic (without oxygen) conditions, it is normally necessary to evaluate degradation under both conditions before claiming “biodegradability” to whatever extent.

    The half-life of a material is still the most common definition of whether a material can truly be considered biodegradable. That is still true, but there have been alternative guidelines published that change the wording and allowances of being biodegradable. Originally, concrete form release agents were required to have a half-life of a maximum of 28 days in order to be classified as biodegradable. (EPA 1998 Fate, transport and transportation test guidelines, office of Prevention, Pesticides and Toxic Substances (OPPTS) 835.3100, “Aerobic Aquatic Biodegradation”; and in EPA 712-C-98-O and ASTM D-5864-00, “Standard Test Methods for Determining Aerobic Aquatic Biodegradation of Lubricants or Their Components”)

    The Consumers Union maintains that if a manufacturer has solid scientific evidence demonstrating that the product will break down and decompose into by-products found in nature in a short period of time, then claiming that it is “biodegradable” is not deceptive. Words like “Environmentally Acceptable,” “Environmentally Friendly,” “Environmentally Preferable” and “Environmentally Responsible” are also used to describe items produced with biodegradable materials or, in many cases, part biodegradable material, without knowing if the whole formulation could be rated as biodegradable.

    The California Advertising Statute, amended April 30, 1991, states that a manufacturer cannot claim that a product is biodegradable unless it meets the following definition: “Biodegradable means that a material has the proven capability to decompose in the most common environment where the material is disposed of within three years through natural biological processes into nontoxic carbonaceous soil, water, carbon dioxide or methane.”

    Also, the term “bio-based” is used to describe products from vegetable, plant or animal based materials. However, just because the term “bio-based” is used, it does not necessarily mean the composition is readily biodegradable or ultimately biodegradable. It would depend on the other base oils that may be included in the formulation.

    The EPA and FTC (Federal Trade Commission) have restated the definition of biodegradability into two specific clauses:

1. Readily Biodegradable – Pertaining to the material having a 60 percent or greater degradation in 28 days.

2. Inherently Biodegradable – Pertaining to having a maximum half-life of 60 days or less.

The Degradation Accumulation Expert Group of the Organization Economic Cooperation Development (OECD) Environmental Committees has established a series of tests that classify compounds as:

• Readily Biodegradable – Rapid and compete mineralization

• Inherently biodegradable – 20 percent to 70 percent biodegradable within 28 days

• Non-biodegradable – Negligible removal of material under test conditions

The OECD recommends that degradation rates, or half-lives, are preferably determined in simulation biodegradation tests conducted under conditions that are realistic for the particular environment they are subject to or presented with (surface water, sediment, soil, etc.).

    The OECD’s 301-B CO2 Evaluation Test (Modified Sturm) is probably the most recognized test in the lubricant (petroleum solvent) industry, and is listed in the EPA Guidelines.

    The EPA and FTC now recognize ASTM OECD-301 B Modified Sturm procedures within ASTM-5684-00 and CEC- 33-T-82 as “Standard Test Methods for Determining Aerobic Aquatic Biodegradation of Lubricants.” While these tests may be expensive, they provide reliable and repeatable results for testing of biodegradability. The test method “covers the determination of the degree of aerobic aquatic biodegradation of fully formulated lubricants or their components on exposure to bacterial inoculums under laboratory conditions,” according to the “Renewable Lubricants Manual” (see listing in “References”).

Volatile Organic Compounds in the United States and Canada
    United States. In September 1999, the Environmental Protection Agency enacted Volatile Organic Compounds (VOC) regulations that affect the concrete industry. These regulations can be found in the Federal Register, Vol. 63, No. 176, Friday, Sept. 11, 1998, under 40 CFR-59, [AD-FRL-6149-7], RIN 2060- AE55, National Volatile Organic Compound Emission Standards for Architectural Coatings, pages 44848-48887. There are 64 materials used in the concrete industry that are subject to VOC regulations and limits. Concrete form release agents are listed (specifically) and allowed a maximum of 450 gallons per liter (g/L). Further, some individual states have passed legislation allowing a maximum of 250 g/L or 2.1 pounds per gallon of VOCs. Fifteen states and the District of Columbia have passed legislation reducing the allowable levels of VOCs in concrete form release agents from 450 g/L (federal allowable levels) to 250 g/L. Keep in mind that any state can have more stringent requirements than the federal levels, but no state can be less stringent than federal levels. As of today, the following states have maximum allowable levels of VOCs of 250 g/L: California, Illinois, Ohio, Virginia, Connecticut, Delaware, Maine, Vermont, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island and the District of Columbia. All of these states are members of the South Coast Air Quality Management District (SCAQMD), the Ozone Transport Commission (OTC) or the Lake Michigan Air Directors Consortium (LADCO). While individual states have taken the initiative to make changes in lower allowable VOC levels, the
EPA has yet to act on making the requirements nationwide. We can, however, expect the bureaucracy to follow suit in the near future based on the number of states that have already taken this step forward.
    The U.S. EPA has been forecasting changes to the VOCs (on form release agents and other products), but has not taken any steps to make these changes. It continues to forecast “in six months,” but has not yet taken any definitive action. Is EPA leaving the individual states to make the changes in anticipation of a federal mandate? Perhaps so, considering the activity of state legislatures to take matters into their own hands without federal government involvement.

Canada. The Canadian Ministry of the Environment – Environment Canada has also become a player on VOCs. Dating back to April 26, 2008, the Ministers of Environment and Health published a Notice of Intent entitled “Federal Agenda on the Reduction of Emissions of Volatile Organic Compounds from Consumer and Commercial Products.” This document outlined a series of measures intended to reduce emissions. The thenproposed “Volatile Organic Compound (VOC) concentration Limits for Architectural Coating Regulations” were published in the Canada Gazette, Part I, on April 26, 2008. The proposed regulations set out specific VOC concentration limits for 49 categories of architectural coatings, including form release compounds. In the case of concrete form release agents, the effective date for a maximum allowable level of VOCs of 250 g/L is Sept. 9, 2012.

Conclusions
• Biodegradable/biodegradability continues to be left to ambiguous interpretation. However, there are now established test methods that give positive indications of the environmentally friendly or responsible attributes of many materials, including form release agents. It behooves you and your supplier to discuss and substantiate claims of biodegradability in order to protect your operation and your environment.
• Biodegradability “redefined” has some benefits to the precast industry as there are some petroleum solvents that are readily and inherently biodegradable. On the negative side, there is a price to be paid for this quality.
• We can expect the U.S. EPA to continue its efforts in reducing VOCs to a federal level of 250 g/L.
• Without specific testing, it is difficult for a supplier to the industry to make claims regarding biodegradability and VOC compliance. As definitions become more specific, and allowable testing procedures are outlined, suppliers must invest in the precast industry by making reliable data available to the precaster.

Bob Waterloo is technical sales manager, Concrete Release Agents, Hill and Griffith Co., based in Indianapolis. He can be reached at (317) 432-2797 or bwaterloo@HillAndGriffith.com. Please visit Hill and Griffith’s Web site at www.HillAndGriffith.com or www.grifcote.com.

Thanks to Randy Ayes, Hill & Griffith’s branch manager, for his invaluable research and support for this paper.

References

“Renewable Lubricants Manual,” Chapter 6, Understanding Biobased & Biodegradable, United Bio Lube, Hartville, Ohio

“Form Release and the Law,” Precast Inc., Jan/Feb 2006

“Volatile Organic Compound (VOC) Concentration Limits for Architectural Coatings Regulations,” Canada Gazette, Part 1, April 26, 2008

ASTM D5864-05, “Standard Test Method for Determining Aerobic Aquatic Biodegradation of Lubricants or Their Compounds”

U.S. Environmental Protection Agency, “Fate, Transport and Transformation Test Guidelines, OPPTS 835.3100 Aerobic Aquatic Biodegradation,” EPA 712-C-98-0, April 1996

OECD Guideline for Testing of Chemicals, April 2005, Proposal for Revised Introduction to the OECB Guidelines for Testing of Chemicals, Section 3; Part 1: Principles and Strategies Related to the Testing of Degradation of Organic Chemicals

“Understanding Biobased and Biodegradable,” United Bio Lube, Palo Alto, Calif.

Federal Trade Commission Web site – “What Does ‘Biodegradable’ Claim Really Guarantee?”

Illinois Pollution Control Board; “Proposed New 35 ILL ADM. CODE, Part 223, Standards and Limitations for Organic Material Emission for Area Resources,” May 7, 2009

Hill and Griffith Customer Service

We're known for our hands on approach. Let us visit your plant and recommend concrete release agents, packerhead concrete form releases, concrete form seasoning, potable water concrete form release, non-petroleum concrete form release, biodegradable concrete form release, rust inhibitors and concrete dissolver products that suit your needs.

Product Samples

We are pleased to provide samples in quantities large enough to allow you to "try before you buy."
Contact Us »

Technical Services & Support

On-site casting defect investigations, product testing, machine start-ups and much more. Also, lab facilities are available to provide testing upon request.
Contact Us »

Thanks to the American Foundry Society Newsletter: March 18, 2015

Sixth graders at Oakridge Upper Elementary School, Muskegon Mich., dug their hands in sand to build molds to make castings last week as part of an AFS Foundry in a Box demonstration. Reg Crowe, retired, Jill Koebbe, Air & Water Compliance Group, Jeff Cook, Eagle Alloy Inc., and Rob Kriger, Eagle Alloy Inc., led students in Mrs. Rikki Grave’s 6th grade science class on Friday, March 13, showing them how to make a sand mold, pour molten tin, remove the sand from the solidified casting and clean the casting’s surface. Since its inception, the Foundry in a Box has been utilized at events and schools throughout the country. For more information on Foundry in a Box, click here.

The American Foundry Society is a not-for-profit organization formed in 1896. With its headquarters in Schaumburg, Ill., AFS provides members and consumers with information and services to promote and strengthen the metalcasting industry.

Student participates in Foudnry in a Box demostration.

Hill and Griffith Customer Service

The Hill and Griffith Company's green sand metalcasting foundry supplies help achieve the EPA's M.A.C.T. standards and reduce Benzene emissions. Our variety of environmentally sound release agents, coatings, partings, lubricants, core oils and specialty products will help you meet your metal casting's needs. We're known for our hands on approach. Let us visit your plant and recommend products that suit your needs.

Product Samples

We are pleased to provide samples in quantities large enough to allow you to "try before you buy."
Contact Us »

Technical Services & Support

On-site casting defect investigations, product testing, machine start-ups and much more. Also, lab facilities are available to provide testing upon request.
Contact Us »

Congratulations to Hill and Griffith Logistics for achieving the Cincinnati Business Courier's Book of Lists for Largest Logistics Firms.

October 28, 2016 Cincinnati Business Courier

15/22; HG Logistics; hglogistics.com; Address: 1085 Summer St., Cincinnati, OH 45241; Phone: 513-244-3026; Local full-time employees: 20; Total 2015 revenue: $12 million; Business description: Third-party freight broker; Geography covered: U.S., Canada, Mexico; Top local executive: Doug Bierman.

This is the first time the Courier has complied a list of the region's largest logistics firms.

Hill and Griffith welcomes you to stop by their booth number 215.

The 2016 Die Casting Congress & Tabletop is underway at the Greater Columbus Convention Center in Columbus, OH until September 28th. This event includes three days of Congress sessions given by experts from around the world. The presentations expose metalcasters to the latest technology, ongoing research and successful management tools that assist companies in enhancing their competitiveness.

The Hill and Griffith Company booth theme is "Always Taking The Right Direction" and features Diluco Die Lube, Plunger Lubricants, Water Glycol, Hydraulic Fluids, Start-up Lubricants, Metalworking Fluids and Cleaners. From left to right are Tim Cowell, Technical Director; Angela Cox, Ryan Canfield, Ron Schweyer, Technical Sales Representatives and Mike Lawry, Sales Manager. 

In addition to the Congress sessions, the show features the winners of the International Die Casting Design Competition and the Die Casting Awards Lunch. 

For more information click here.

Tim Cowell, Technical Director, The Hill and Griffith Company
Published in the Sept. 2014 issue of DIE CASTING ENGINEER, official publication of the North American Die Casting Association

Introduction

In the Die Casting Industry, many of the castings manufactured undergo secondary operations incorporating the use of paints, adhesives and other polymers such as RTV (Room Temperature Vulcanization).  The application of these types of materials requires the polymer to bond to the metal substrate (surface) of the casting.  When this bond fails, it is considered to be an adhesion problem. For the die caster, this can be a very costly problem; therefore, it is imperative that it be solved quickly.

To gain a better understanding of the problem and its potential solution, the following points will be discussed. 

1. What creates Adhesion?
2. What prevents Adhesion?
3. Assessing the Problem
4. Solving the Problem

Please note:  For the purpose of this paper, it will be assumed that all of the coatings and polymers along with their curing processes are performing without problems.

What creates Adhesion?

It is generally agreed that the primary forces creating the adhesion phenomena are chemical bonds and mechanical interlocking. 

Chemical Bonds

An Ionic Bond is a chemical bond formed by the electron attraction between positive and negative ions. An example of this type of bond is NaCl or table salt, where the Na+ (Sodium) ion carries a positive charge and the Cl- (Chloride) ion carries a negative charge.

Van der Waals bonds are forces that result from the interaction of the positive and negative charges between neighboring atoms or molecules. These bonds exhibit themselves in very long chain molecules that make up polymers that are part of our everyday life, such as rubber and plastics.

Although the strength of the Van der Waals bonds is fairly weak, collectively, they represent a significant force within the adhesion bond.

While it is not known which type of chemical bonding is predominate, it is known that a combination of both Van der Waals and Ionic bonding takes place between specific components of the polymer (coating) and the reactive hydroxyl groups/metallic ions that form on the surface of the metallic castings, particularly aluminum alloys. 

Mechanical Interlocking 

With Mechanical Interlocking, good adhesion only occurs when the coating/polymer penetrates into the pores, holes and crevices and other irregularities of the surface of the casting, and locks mechanically to it after curing. The coating/polymer must not only wet the substrate, but also have the right rheological properties to flow into the pores and openings in a reasonable time before the curing process begins to take place.  See Figure 1.1.

What Prevents Adhesion?

Figure 1.1 - Graphic illustrating surface irregularities

Figure 1.2 - Surface contaminants inhibit or prevent proper adhesion

Any material, organic or inorganic, or process that prevents the polymer from having intimate interfacial contact with the metallic substrate will inhibit or prevent the adhesive bond from forming. This could be surface contaminants, such as dirt, wax, oils, moisture and excessive oxide layers. See Figure 2. 

Assessing the Problem 

There are several steps in assessing the specific adhesion problem.

The first step is to determine the chemical make up and physical nature of any contaminants present on the surfaces of the castings where adhesion failed to take place. This can be accomplished through Analytical Chemical Testing.

There are two specific types of analysis that are crucial to the identification of the source of the contaminants; Fourier Transform Infrared Spectroscopy and Energy Dispersive X-ray Spectroscopy:

Fourier Transform Infrared Spectroscopy (FTIR)

This kind of Spectroscopy identifies chemical bonds in a sample by exposing the it to an infrared laser and recording the different wavelengths at which various chemical bonds absorb, thereby producing an infrared absorption / transmission spectrum. The resulting spectrum produces a profile of the sample, a distinctive molecular fingerprint that can be used to easily scan samples for many different components. See Figure 1.3.

Figure 1.3 - A profile of a sample

Energy-Dispersive X-ray Spectroscopy

Energy-dispersive X-ray spectroscopy (EDS, EDX, or XEDS) is an analytical technique used for the elemental analysis and chemical characterization of a sample. It relies on the interaction of a source of X-ray excitation and the sample being evaluated. Its characterization capabilities are due to the fundamental principle that each element has a unique atomic structure allowing unique set of peaks on its X-ray spectrum. Refer to Figure 1.4

Figure 1.4 - Energy-dispersive X-ray spectroscopy

The data from these two analyses will provide the die caster with sufficient chemical information to identify the source or sources of the contaminant(s) responsible for interfering with the adhesion bond.

The second step is to identify which of the products that come in contact with the casting could be the source(s) of the contaminant(s).  The chemical characterization of the contaminant(s) should very helpful in narrowing down the search.  For instance, die release agents can contain wax and siloxane components and their presence is easily detected through the FTIR analysis.  While excessive an amount of aluminum hydroxide is detected through the EDS analysis.

Following is a list of possible sources of contaminants: Table 1.1 

Each of these should be evaluated as possible contributors to the problem.

The third step is to evaluate the pretreatment process.

The pretreatment process is a system designed to remove contaminants, modify the casting surface to be adhesion friendly, and seal the surface for protection against corrosion. Although, there are several different designs of pretreatment systems, the most effective systems incorporate 5 stages or more.  See Figure 1.5.

Figure 1.5 - The most effective systems incorporate five or more stages

All of the possible sources of the contaminants listed above come in contact with the casting before it is submitted to the pretreatment process.  If there is organic / inorganic contaminant(s) remaining, then the pretreatment system is either not working effectively or it is incapable to address the full range of contaminant(s) being introduced to the system.

Evaluating the Pretreatment Process 

Chemistry

Cleaner

The most popular and most used aqueous cleaners used today are the high alkaline cleaners (pH >10.0). Although they are very effective against stubborn soils, most of the alloys used in the casting process (aluminum, zinc and magnesium) are attacked by these high alkaline cleaners and often create a process called smutting. Smutting is where the Caustic of the Cleaner reacts with the surface of the metal forming a layer of metallic oxides and hydroxides on the surface of the casting.  This condition is detrimental to adhesion.

Therefore, mild alkaline cleaners containing inhibitors are usually the product of choice.  

Concentration of the cleaner should be checked at least 2 times a shift to make sure that it is within the process specifications. Also, system should be periodically dumped and recharged to eliminate excessive build up of soils.

Conversion Coating

Once a casting has gone through the cleaner stage and been rinsed it is subjected to an acid bath of some type to remove any oxides on the surfaces that may have formed in storage or transportation.

Often an Iron Phosphate Treatment is used to etch the surface of the alloys as well put on a conversion coating in preparation of the polymer. While this is effective when preparing steel parts to be coated; with aluminum, the normal acids do not etch the casting and the reaction between the phosphate and aluminum never takes place. Therefore, the majority of the pretreatment processes have incorporated an ammonium bifluoride, which creates a weak solution of hydrofluoric acid. This acid readily etches the aluminum surface creating fresh sites for the Mechanical Interlocking mechanism of adhesion to take place.

The amount of iron phosphate and hydrogen fluoride (when present) should be checked at least once per shift to assure that there is sufficient material to properly etch/coat the surface.

Sealer

After a metal surface receives a conversion coating, the surface is water rinsed to remove unreacted chemicals, and a sealer is usually applied. The sealer increases the corrosion and humidity resistance as compared with conversion coatings without final sealers. In the case of electrocoat applications, final deionized (DI) or reverse osmosis (RO) water rinse is required to minimize contamination of high-conductivity water on the substrate surface from the post rinse. In these cases, it is imperative to have a reactive final rinse that maintains its properties after the DI or RO rinsing rather than a dry-in-place rinse.

Sealers historically have been based on chromic acid, however, with increasingly strict effluent limitations, most finishers have converted to either trivalent-chrome or non-chrome post-treatments.

Water

The chemistry of the water can impact the overall coating process, by leaving hard water deposits on the casting surface. Reverse Osmosis water is the most ideal source of water to be used in the system; however, many finishers’ choose to use either city or well water. In those cases, the Pretreatment Tanks need to be monitored for excessive hard water salts build up at least once per day.

Temperature

A die lubricant’s chemical components (waxes, silicones, oils) are designed to withstand the heat of the die casting process. Therefore it should not be a surprise that heat would be used in the removal process of its decomposition products.

Heat enhances the cleaning by:

• Synergistically increasing the chemical activity of the cleaner

The chemical reactivity of a cleaner is directly proportional to increases in temperature. This increase in activity allows the surfactants to penetrate the surface crevices and lift out the contaminants as well as etch the surface in preparation for the coating /polymer. 

Please note: It is important to make sure the temperature and chemical concentration are controlled to avoid excessive etching (smutting) especially with aluminum alloys. This smutting can and will cause adhesion problems as well.

• Liquefying and emulsifying stubborn contaminants such as waxes or high molecular esters that exist in a solid state when not emulsified.

Low to medium melt point waxes and siloxane (paintable) polymers can sometimes be removed with a mild alkaline cleaner running at temperatures of about 130 - 150º F , however high molecular polyethylene (synthetic) waxes do not begin to soften until a much higher temperature range (160 – 180 º F). These types of waxes require that the casting substrate be heated sufficiently to the point that the wax begins to soften and allows the cleaner’s surfactants to get under the contaminant and lift it to the surface where it can be removed by the washer spray or agitation. 

The heat should be held between 160 – 170˚ F.  If the temperature is much lower than this, some of the residues will not soften and resist removal.

Pressure

Too many times, people forget that cleaning is not only a chemical process but also a physical one. 

Chemical cleaning requires the surfactants to be able to interact with the soils. However due the stubbornness of many soils (high temperature waxes), mechanical energy is required to perform the actual removal of the soil from the substrate. Spraying is a more effective means of removal than immersion or submersing. 

The higher the pressure, the more efficient the cleaning process. Recommended pressure is between 15 – 20 psi, but is often determined by the geometry and size of the part. Too high of pressure will result in parts being blown out of their baskets or hangers.

It should also be noted that the spray pattern associated with pressure should be check to make sure that the spray is making proper contact with the part.

Time

You can have all the proper components in the Pretreatment System, but if the process does not allow enough contact time between the part and the treatments, the parts will not be properly cleaned and prepared for the polymer.  Also if there is too much time, exposure to the cleaner and conversion coating stages will have adverse effects on metal surface. 

Solving the Problem

Once the source of the contaminant(s) has been identified and the pretreatment process has been reviewed, the solution is found in the answers to the following two questions?

1. Are the process variables in specified ranges?

If the process variables are outside the specified ranges, then the appropriate adjustments need to be made and castings tested after the adjustments to verify that the problem as been resolved.

2. If process variables were within specified ranges, then what needs to be changed in order to solve the adhesion problem?

Depending on the nature and source of the contaminant, adjustments such as cleaner concentration, temperature, location of spray, and time are all variables within the system that are adjustable.  One variable needs to be adjusted at a time and parts evaluated.

There are also some post treatment operations that are being incorporated after pretreatment to assist with the adhesion process;        

Post Treatment Alternatives 

• Baking Ovens

The castings are raised to a temperature of 400 F for periods ranging from 15 minutes to 60 minutes.  This is to eliminate any remaining organic contaminants that might create out gassing (raised deformities) or prevent proper adhesion. 

• Plasma Treatments 

Within this process, a plasma field is formed when flammable gas and air are combined and combusted to form an intense blue flame. Brief exposure to the energized particles within the flame affects the distribution and density of electrons on the substrate’s surface and polarizes surface molecules through oxidation. This method also deposits other functional chemical groups that further promote adhesion.

The Flame plasma process generates more heat than other treating processes, but materials treated through this method tend to have a longer shelf-life. These plasma systems are different from air plasma systems because flame plasma occurs when flammable gas and surrounding air are combusted into an intense blue flame. Objects’ surfaces are polarized from the flame plasma affecting the distribution of the surface’s electrons in an oxidation form. (www.plasmatreating.com)

Summary

It is the author’s desire that the information shared in this paper will be helpful to the die caster regarding specific steps to take in troubleshooting and resolving future adhesion problems.

The keys are to know what contaminants are contributing to the adhesion failure and are the pretreatment stage variables operating with the specified limits?  Until those two evaluations are performed, all adjustments to the process are shots in the dark.

About the Author 

Tim Cowell is the Technical Director for The Hill and Griffith Company. He has over 28 years of experience in the Metalworking Industry. He is responsible for new product development, working with die casting and machining manufacturers on special projects and providing technical support to the technical and sales teams.

Tim has a BS degree in Chemistry from Cedarville University. He has authored several articles on paint adhesion problems, die casting continuous improvement initiatives and scrap reduction projects. Tim also assists as an instructor for several North American Die Casting Association courses.