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CONSIDERATIONS FOR RECLAIMING CHEMICALLY BONDED SAND

Foundry Management & Technology Magazine, January
23, 2012 issue.
Written by Jack Palmer.
Reprinted by permission of Penton Media, Inc.
Considerations for Reclaiming Chemically Bonded Sand
While the initial investment may seem onerous, justification is usually
fast enough to meet even the most aggressive ROI requirements.
|
The factors that justify sand reclamation are changing, and
redefining the planning process. |
Reclamation and reuse of foundry sands has always made economical and
environmental sense, however the recent demands placed on sand by the
oil and gas industries has made sand reclamation a process that no
foundry can afford to overlook. While the initial investment may appear
onerous, justification is usually fast enough to meet even the most
aggressive ROI requirements. There are also new technologies available
to accommodate all foundries, from the large-volume production foundry
to the shop that does small runs, and even those that produce
one-of-something, etc.
Determining ROI — A very simple spreadsheet analysis
can determine ROI. It is essential to include all of costs: freight of
sand both incoming and for disposal, cost of new sand, storage, and
additional handling for disposal, and disposal fees. Also, make sure you
understand how much sand you will be processing versus disposing. The
amount of sand used is usually defined as the amount to keep the LOI
(loss on ignition) percentage at an acceptable level. After totaling all
of these costs, it becomes obvious that it doesn’t take a very large
operation to justify at least a good mechanical sand reclamation system.
Disposal costs — Of the big three costs (sand,
shipping, and disposal) the cost of disposal is the great unknown.
Disposal costs can double, triple, or even rise tenfold with one phone
call. There have even been cases where foundry sand that had been
desirable for use as landfill cover gets reclassified as hazardous
waste, with a huge increase in dumping fees, and still be used for the
same purpose.
Justification — Reclamation system justification must
include all costs: engineering the project, shipping equipment to the
site, site prep, installation, commissioning, floor space, daily
operating costs, annual maintenance costs, and capital costs, etc.
Careful consideration obviously needs to be given to the equipment to
reclaim the sand to a cooled, screened, reusable state but attention
also must be given to the overall system process and how it integrates
into the plant as a whole.
Reclamation planning — No reclamation system should be
designed for current requirements and throughputs. If financial
restraints requires equipment to meet only current needs, the system
should be designed to be as easy and inexpensive as possible to expand
in the future, because many shops experience a gradual increase in mold
size and (hopefully) mold production.
Among the decisions that must be made when planning to install sand
reclamation capability:
- Location: What will be the system’s proximity to incoming molds, and
point of reuse?
- Usage: Will the system be designed for single- or multiple-shift
operation? The likelihood of material surges is a consideration, too:
what will be the rate of throughput?
- Storage silo/day bin capacities: The size and location of all
storage devices need to be carefully considered. A general rule is two
to four hours usage above the mixer, with a bulk silo able to hold all
the mechanically reclaimed sand from all the molds on the floor or in a
system. Obviously, these sizes vary depending on several factors, but it
is good to get the largest silo that is reasonable. As the size of a
silo increases, the cost per ton of available capacity decreases
quickly.
- Thermal reclamation: Will this function be part of the initial
system? If not, where will it be installed/configured later?
- Blending: Reclaimed sand (mechanical and thermal) needs to be
returned to the system in a controlled manner to eliminate variables,
but at acceptable LOI levels. New sand additions (not the same as
thermally reclaimed sand) also need to be consistent and controlled.
- Maintenance accessibility.
Reclamation equipment — Current reclamation equipment
technology also needs to be researched to determine the optimal design
to fit a given requirement. Recent developments in vibratory and rotary
mechanical attrition, low-level combination decks, shakeout decks with
no holes to damage castings, and a number of gas and electric thermal
reclamation concepts need to be thoroughly investigated.
Thermal sand reclamation — Most no-bake shops have some
form of mechanical reclamation; however, frac technology developments
require that current systems be analyzed for adding thermal reclamation.
It is very common for a foundry to outgrow equipment, but this process
is usually so gradual and not noticeable until it becomes financially
obvious. Nowhere is this truer than in no-bake shops where the tendency
is for work to get larger. Mold size increases in a green sand facility
usually take a large financial investment in sand processing equipment,
skill levels, etc., but in no-bake foundries it is fairly
straightforward to make a larger mold as long as it can be handled.
Thermal reclamation equipment is comparatively expensive but can make
economic sense at a certain level of sand usage. This tonnage level is
obviously different in every case but it is trending downward.
Justifying thermal sand reclamation is different than justifying
mechanical reclamation, because there are intangibles or unknowns that
are difficult to quantify, depending on sand type, binder system, etc.
One of the main foundry advantages of thermally reclaimed sand is that
it helps lessen expansion defects. This is especially critical for cast
surfaces with impellors, volutes, etc. It is not uncommon for foundries
to run all new sand through the thermal system for this reason.
Thermally reclaimed sand also require may substantially less binder to
achieve acceptable strengths, compared to new sand.
Jack Palmer is the president of Palmer Manufacturing & Supply, Inc.,
Springfield, OH. Visit
www.palmermfg.com for more information.