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While the drive to reduce operating costs may seem like a

never-ending road for metalcasting operations, an organi-

zations ability to convert those cost-efficiencies into pow-

erful and immediate market leverage is undeniably a deciding fac-

tor in their long-term survival. What makes this formidable task

even more challenging is the acceptable cost of cost reductions.

Significant capital investment in new production equipment yields

true savings only after the payback period is complete. At the same

time, should a more attractive solution arise later it may be difficult

for a customer to change again. Technical flexibility is an advantage

few organizations actively manage well, but those who do expose

themselves to the least risk.

Cleaning room or casting finishing operations have long been

target areas for increased efficiency and cost-reduction efforts, and

can represent a significant portion of total production cost. Removingrunner systems and risers from a finished casting typically requires

foundry personnel to use cutting saws, abrasive wheels, or cutting

torches. Although effective, these techniques also expose workers to

risk of injury from repetitive vibration, high noise levels, heavy lift-

ing, and respiratory dust.

While some of the largest foundries (mostly captive OEM) have the

financial ability to purchase one or more automated robotic systems

to handle finishing operations, most medium-sized and smaller met-

alcasters continue to search for less costly options simply to remain

competitive. Not surprisingly, innovative foundries that find ways to

squeeze costs or make their cleaning operations more efficient tend

to protect their discoveries, particularly when those methods do not

require large capital expenditures and can be adopted easily.

Internal Best-Practices

One of the most surprising, yet effective techniques that has been

a back-room best practice for many foundries is using standard

silica-mesh fabric in runner systems and in the base of riser sleeves

to create cleavage planes that typically come apart during vibratory

shakeout, or with the minor impact of a shop hammer. For anyone

watching cleaning room personnel spend hours cutting small cast-

ings from runner trees, or witnessing a hydraulic ram violently bash

risers from large castings, the value of low-impact de-gating is nomystery. An additional benefit of using standard silica-mesh material

as a de-gating aid is that it acts as a molten metal filter wherever its

placed. While its not uncommon for foundries to use ceramic foam

filters placed directly in runner systems or in the bottom of riser

sleeves for additional filtration, ceramic foam filters do nothing to

make runner segmentation or riser-removal any easier.

No one-size fits all

Of course, there are certain drawbacks and limitations to using

standard silica-mesh cloth that foundrymen should consider for their

specific application. These considerations include: Molten metal temperature maximum of approximately2,800F/1,534C The application alloy pouring temperature should

2 FOUNDRYMANAGEMENT & TECHNOLOGY JANUARY 2011

2011 Databook Pouring

Improved De-Gating Techniques Yield High Cost Reductionsfor Metalcasting Finishing Operations

not exceed the recommended level as the mesh material can quicklybreak-through. Therefore, casting stainless steel or other high-

temperature alloy applications must be monitored carefully to avoid

temperature variations.

Incompatibility with aluminum and pure copper Typically,standard silica-mesh cloth is treated with a thermal setting phenolic

resin and pre-shrunk to create the rigidity necessary to hold the spe-

cific shapes for foundry applications. This treatment, although nec-

essary, also precludes it from being used with pure copper because

the resin chemicals are attacked by the oxides and slag generated

by melted copper and lead to a rapid structural failure, and the mesh

breaks through. A different problem can occur with aluminum alloysas standard silica-mesh material will off-gas as the molten alumi-

num passes through it, often causing porosity-related defects.

Above: Custom-cut CerraBreakers pre-placed in

a pattern for an aluminum casting, using No-Bake

molding. Below: the resulting flat cleavage plane from

a CerraBreaker used in a ductile iron application. The

runner was knocked away using only a shop hammer.

Standard

silica-mesh cloth

CerraBreaker/

RiserBreaker

Molten alloy

pour temp max: 2,800F

Molten alloy

pour temp max: 3,500F

Incompatible with

copper and aluminum

Compatible with copper,

aluminum, and more

Deflection into body

of casting or riser sleeve

No deflection

flat cleavage plane

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Deflection or flexing of material into casting body Withregard to keeping the molten alloy pouring temperature below maxi-

mum, standard silica-mesh fabric typically deflects or flexes (but

does not break) in the direction of alloy flow. This deflection is usu-

ally an acceptable drawback, as the material remains intact as a filter

and provides the cleavage plane necessary for easier runner segmen-

tation later. However, when placed in the bottom of a riser sleeve,

the silica mesh can deflect downward into the body of the casting or

upward into the riser sleeve, and when knocked off will create a

surface problem that must be machined away later. The best result is a

flat cleavage plane that requires no additional re-work.

Closing the gaps

Considering the wide-ranging benefits that could be realized in

finishing/cleaning room operation by addressing the problems of

standard silica-mesh fabric, Comanche Technologies has developed

two new products the CerraBreaker

and the RiserBreaker

that leverage the technical strengths of CerraFlex, a ceramic-

coated, high-strength silica mesh filter material. Each CerraBreaker

is a custom-cut piece of CerraFlex thats placed directly in the runner

system where the mold designer wants break-points. Because each

CerraBreaker is also a molten metal filter, designers often place ad-

ditional units earlier in the flow stream to capture slag and inclusions

directly in the runner network, as well as directly at the contact area

for each casting.

A RiserBreaker is a CerraBreaker that has been framed within

a core-sand breaker core, attached to the base of any variety of riser-

sleeve. This frame design is critical to ensure there is no deflection

of the CerraFlex material in either direction of molten metal flow,

while the breaker-core itself creates a smaller contact area that makes

knock-off even easier. Each RiserBreaker-Sleeve unit is custom-

calculated according to customer provided, application-specific data

to ensure optimal performance.

Operational cost savings

So the larger (and easily the most important) question for every

foundry should be how much will we save by using CerraBreakers

or RiserBreakers in our finishing operations? The honest answer is

it will depend , because the scale of cleaning or finishing room

operations varies significantly from one foundry to another basedon average size of castings produced, alloys cast, etc. Moreover, as

these techniques are used across the metalcasting process spectrum

(green sand, no-bake, permanent mold, investment casting, etc.),

average cost-savings will vary as well. Ultimately, this question can

be answered by your operations team, as they should be driving the

cost-saving, efficiency-finding initiatives. But, the workers doing the

grinding and sawing will thank you.

2011 Databook Pouring

Jason Hitchings is the general manager of Comanche Technologies.

The author gratefully acknowledges the previous research published

as Use Fabric, Breaker Cores to Cut Ductile Iron Finishing Cost,

(Modern Casting, 1999) as a reference for this article.Contact him at JHitchings@comanchetechnologies.com, or visit

www.comanchetechnologies.com .