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Sand reclamation = sand savings with proper planning.

While the foundry industry is well known as the original recycler (first metal, then sand), the rest of the world has caught up slowly. Cans, bottles and newspapers (to name a few) have become recycling targets and are bagged separately.

Now, as the money required for recycling catches up with the hype, it seems that wide-scale recycling was just that--hype. According to the Natural Resources Defense Council, effective July 1, 2002, New York City suspended its recycling program for plastic and glass for one and two years, respectively, as a response to the city's budget deficit,

Foundries also seem to have fallen off the sand recycling bandwagon. Like the situation in New York, cost and other factors, such as transport and dumping concerns, have played into the decision on whether to continue a recycling program.

However, as foundries search for cost reduction strategies in this tenuous economy, sand reclamation, particularly green sand to green sand, must be seen as an option. When properly implemented, green sand reclamation is a means to maximize sand performance and additive use to achieve the, largest bang for each buck spent on sand molding.

Breaking It Down

Green sand often is recycled. After several reuses, however, it is contaminated with enough fines, dead clay and silt that it needs refreshing. This signals the time for reclamation.

At its most basic, green sand to green sand reclamation involves cleaning dead or used clay from sand particles, adding new clay and using the sand again for mold making. The high pouring temperatures imposed on most green sand molds kill the bonding ability of some clay particles. Reclaiming the used sand removes the fines and dead clay while leaving as much of the live clay on the sand as possible.

By reclaiming sand, foundries retain the quality level of their sand system without the added expense of 100% new sand, Some new sand always must be added to reclaimed molding sand--the reclaiming process is, after all, a reducing process.

Reclamation works best as a stepping stone process-starting with the simplest method and moving up the ladder of processes as production requirements or capabilities change. Each ensuing process produces higher quality sand than the previous process.

Most foundries recondition their sand by bringing used sand back to the muller, adding more clay, seacoal and water, and mulling it. This treats the sand as a mass, not as individual grains.

Foundries that want to reuse sand more than a few times invest in the next level of reclamation--mechanical. Mechanical sand reclamation uses abrasion, such as a turning wheel, to break up sand lumps and then knock off used binders.

Pneumatic reclamation performs the same task, but uses air rather than physical force. Sand is entered into an air stream and shot at a conical-shaped target. The target collects a layer of sand and other grains sandblast this sand-covered target, creating a sand-on-sand impact and knocking off loose material (dead clay).

Mechanical and pneumatic processes often are used for green sand to green sand reclamation and only can make core sand or high quality facing sand at a slower production rate. The processes can be improved somewhat, however, by adding additional scrubbers to clean the sand as much as possible. Foundries that want to reclaim sand containing multiple binder systems or use reclaimed sand for large numbers of cores need to look beyond these processes.

Beyond basic green sand reclamation is the thermal process. Thermal reclamation uses heat to bum off any organic matter attached to the sand grains and depends on a scrubber to knock off deadened clay and fines. The process is more complex--it requires a heating element and cooling facilities--but it can be used for different types of sand, multiple binder systems and can create core or facing sand.

Optimizing Objectives

Before committing to a sand reclamation program, foundries must perform a self-evaluation (see sidebar, "Self-Evaluate before Reclaiming") to assess their needs and optimize the benefits available through reclamation. Sand reclamation is not a replacement for new sand purchases--it merely keeps the useful material in the sand for the maximum amount of time, reducing both the amount of new sand required and used sand to be dumped. Reclaimed sand doesn't require the same properties as new sand, but it must achieve the required properties for the castings being produced.

For the process to be financially attractive, the total sand cost--reclamation, new sand and any remaining disposal costs--must be less than all of the costs involved (freight, dumping, new sand, etc.) with the purchase of all new sand. If the process is planned thoroughly before implementation, it can result in significant savings for the foundry, both in terms of dumping costs and new sand purchases.

To optimize any sand reclamation process, follow these suggestions:

* eliminate all metal scraps from the sand to be reclaimed. If any metal remains, the catalyst will react with it instead of the binder;

* eliminate all sand lumps and trash material. They create impurities in the sand, leading to problems with the binder and casting surfaces;

* reduce inert and organic material to a low and constant level for sand makeup consistency. The acceptable level depends on the sand, binder and metal used, as well as the sand-to-metal ratio;

* reduce clay to a low and constant level based on the intended use for the reclaimed sand. High residual clay is detrimental with any liquid binder systems;

* reduce fines to a low and constant level to prohibit the collection of impurities;

* reduce sand grain coatings to a low and constant level. The coating level must be consistent on each sand grain because uniform sand surfaces ensure maximum efficiency;

* check that reclaimed sand grain distribution is similar to that of new sand to maintain a consistent casting surface;

* follow the manufacturer's recommendations for operation. A unit that is rated to reclaim 5 tons/hr should not be increased to reclaim 7 tons/hr--the sand quality will diminish;

* examine castings and verify that those made using reclaimed sand plus makeup new sand are as good as or better than castings made with all new sand. Avoid major changes in operation, and if differences occur, test the reclaimed sand to find the discrepancies between it and the new sand;

* check that the foundry has adequate dust collection to handle the reclamation unit. The binder knocked off the sand grains in mechanical and pneumatic processes must be collected and disposed of properly.

Test, Test and Test Again

To guarantee that a sand reclaimer is scrubbing sand adequately, several tests must be performed regularly:

1. Screen analysis and AFS grain fineness tests measure the grain size. Results should be similar to those of new sand.

2. The methylene blue clay test determines the amount of active clay present in the sand so that the foundry knows how much new sand to add.

3. The AFS clay and the 25 micron clay tests detect the presence of fines left in the sand.

4. Loss on ignition (LOI) testing determines the amount of material that will bum off a reclaimed sand sample at 1800F fired for at least 2 hr. A high LOI may cause gas defects in castings.

For More Information

"Sand Reclamation Economics for Small & Medium Size Foundries," AFS International Sand "Reduce, Reuse, Reclaim" Conference Proceedings (1994).

RELATED ARTICLE: Tell Me Again Why I Should Reclaim?

Having been out of the spotlight for several years, sand reclamation is due for a little positive public relations. The top three reasons to reclaim spent foundry sand are:

Economics. Foundries want to reduce the total sand cost, including purchase, freight, handling within the foundry and disposal. Sand rates have increased, but more importantly, freight and disposal costs have sky-rocketed. Everyone has garbage to dump, but no one wants garbage dumped near them. In addition, many foundries have to pay a clumping fee for long distance hauls in addition to fees for loading and unloading discarded sand.

Environment. It is becoming more and more difficult to dispose of great quantities of material into the ground. Environmental agencies want to know what chemicals are in all refuse and what amounts might be leached from the sand (see "Managing Environmental Liabilities for Beneficial Reuse," MODERN CASTING, April 2002). The interest generated focuses not only on public dumps, but on the foundry's own property as well. Wastes dumped on foundry property can infiltrate the water table and affect the neighborhood. In addition to the environmental benefits, the reclamation process is of value from the conservation viewpoint. Reclamation means less new sand is being used, and deposits of high-grade sand will last, longer if they are used more efficiently.

Casting Quality. Binder and catalyst usage levels may be reduced with reclaimed sand because the sand has less surface area, requiring less binder to cover the grains. Some new sands have considerable variations in impurity levels. During screen analysis these variations are reduced in an enclosed sand loop. In many reclaimed sand trials, when the sand has been cleaned properly, the casting quality is as good, if not better, than new sand.

One explanation for this is the idea of "survival of the fittest." On each cycle, some of the grains are given a thermal shock from the metal and then they receive mechanical shocks in shakeout, lump breaking and scrubbing. Sands with poor chemical structure or poor cleavage planes will fracture and be removed, leaving the strongest and best structured sand grains to be reused.

Self-Evaluate Before Reclaiming

Before purchasing or installing a new sand reclamation system you must be able to answer the following questions:

* What kind of sand am I using and where will I use the reclaimed sand?

Knowing the sand type and purpose helps to determine the optimal system for your needs. For example, if you're not planning to reclaim sand for coremaking purposes, you don't need a thermal system.

* How much sand am I currently discarding each week/month?

This helps to identify the size system you need and calculate the financial of reclamation. Record where this sand comes from to aid in answering the first question.

* How much does it cost to dispose of my used sand?

These costs often are for gotten. While they won't disappear completely, you can estimate any money that will be saved because of reduced disposal needs.

* How will I get rid of my remaining waste?

With less sand to dispose of, a less expensive or more convenient option for waste disposal may exist. On the other hand, keep in mind that the concentrated waste may be considered hazardous and require special dumping sites and premits.

* How much space do I have to install a unit?

The available space in the foundry coupled with reclamation capacity requirements determine the size system you need. Remember to factor in room for dust collection equipment. In addition, thermal systems require extra square footage for the heating and cooling units.

* How much does it cost run the system, including maintenance and labor?

Compare these numbers, plus disposal new sand costs, to the current cost of disposing of all used sand and buying all new sand to determine the investment and payback time required.

About the Author

Matt Granlund has worked in the foundry industry for 48 yr, including the last l8 yr as an independent sand consultant.
COPYRIGHT 2002 American Foundry Society, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2002, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Comment:Sand reclamation = sand savings with proper planning.
Author:Swenson, Lisa
Publication:Modern Casting
Geographic Code:1USA
Date:Aug 1, 2002
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