chemically bonded defects panel - … · chemically bonded defects panel ... • common in sharp...

AFS Sand Casting ConferenceOctober 20-22, 2014 – Indianapolis, IN USA

Chemically Bonded

Defects Panel

Randal Campbell – HA International

Giuseppe Iorio – Naval Surface Warfare Center

Joe Muniza – ASK Chemicals

Mitchell Patterson – HA International

Ayax Rangel – HA International

Ralph Showman – ASK Chemicals


What’s “Special” about

Chemically Bonded Molds/Cores

• Sand coated w/ binder to create a

resin bridge


Chemical Binder Types

• In-organic

– Silicates

• Organic

– Phenolic Urethane

– Furan

– Acrylic / Epoxy

– Ester-cured Phenolic


Production Methods

• Hot / Warm box– Heat cured

• Coldbox– Gas catalyzed

• Nobake– Liquid catalyzed


How does the chemical binder

relate to casting defects?

• Binder cure mechanisms– Production method

• Binder decomposition– Decomposition products

– Decomposition mechanism


Defects Related to Chemical

Binders• Erosion

• Veining

• Scabbing

• Penetration

• Warpage

• Blows

• Gas porosity

• Nitrogen fissures

• Hot tears

• Lustrous carbon

• Flake skin


Erosion

What is it?

• A projection of metal

outside the desired

shape and into the

molding material

where the core sand

was washed away


Erosion

Causes

• Insufficient sand

cohesion

• Poor compaction

• Poor gating design

• Aggregate insufficient


ErosionPotential Solutions

• Increase binder level

• Use binder with higher hot strength

• Improve compaction – harder, more uniform ramming

• Use a refractory coating / more resistant refractory

• Modify aggregate – in total or facing problem area

• Re-design the gating system

• Use ceramic gates or strainer cores


Background• Casting is a process which carries risk of

failure occurrence during all the process of

accomplishment of the finished product

• The correct identification of the casting

defect at the initial stage is essential for

taking remedial actions

• This presentation summarizes casting

defects involved with various casting

processes


Lustrous carbon defects

What is it?

• Lustrous carbon forms

on inert surfaces

through thermal

decomposition of

hydrocarbon-bearing

gases in reducing

atmospheres above

650°C.


Lustrous carbon defects

What is it?

• Lustrous carbon is

deposited as a film on the

silica grains of the mould.

Relatively thick layers of

lustrous carbon film can

result from the gas

pressure which develops,

particularly when

deposited on core

sections


Possible Causes

• Resin-bonded sand

• Lustrous carbon producing capacity of the

core binder too high

• Insufficient venting of core gases.

• Gating and pouring practice

• Too much turbulence, leading to inclusion of

lustrous carbon

• Pouring temperature too low


Metal Penetration

What is it?

• A projection of metal

outside the desired

shape and into the

molding material

• AKA burn-In, fuzz, etc


Metal Penetration

Causes

• Poor sand compaction

• Excessive binder

• Refractory failure

• Low surface tension

alloy


Metal Penetration

Potential Solutions

• Modify compaction method

• Lengthen work time

• Increase bench life, or blow cores within bench life

• Decrease binder

• Choose alternate binder

• Use a refractory coating

• Modify aggregate

• Reduce pouring temperature

• Modify alloy


Veining

What is it?

• An expansion defect

caused by fissures in

the core / mold

• Lines of extra metal

that look like veins

appear on the surface

of the casting


VeiningCauses

• Mainly related to aggregate expansion

• Binder thermal properties play a role in veining

• Expansion exceeding the deformability and ultimately

lessening core strength

• Common in sharp angles and curve shapes

Stress caused by

sand expansion

Sand grains Veining

Damaged section


Veining

Potential Solutions

• Aggregate selection

• Sand additives

• Binder system

• Right level of compaction

• Pouring temperature


Gas Defects

What is it?

• Gases dissolved in

the metal are expelled

during solidification

• External gas pressure

creates a “bubble”

and the metal

solidifies around it.


Gas Defects

Causes

• Moisture / Water

• High LOI

• Lack of Venting

• Low pouring temp

• N2 content of binder


Gas Defects

Potential Solutions

• Control Moisture in sand and in compressed air

• Optimized binder type

• Optimized binder levels

• Titanium additions 0.02 – 0.04%

• Optimized venting practices

• Optimized metal pour temperature

• Desiccant dryers on Part II


Metallurgical Surface Defects

10x

100x 100x


Defect Causes

• The sand mold is very insulating and casting

temperature remains high for an extended time

• Decomposition of the organic binder creates an

atmosphere rich in CO with some N

• This could be described as “heat treatment”

• Shakeout time determines casting temperature

and “quench”


Defect Prevention

• Control gas composition

– Binder type

– Additives

– Venting

• Control “quench”

– Shakeout time & temp


Urethane Acid Cured Alkaline Phenolic Shell

Core Float/Shift in Casting 4 2 2 1

Core Warpage 3 2 4 1

Gas Blow 4 2 1 3

Hot Tears 2 1 3 4

Erosion 3 4 2 1

Burn In (Poor Density) 2 3 3 1

Lustrous Carbon 4 1 1 3

Veining 3 2 1 3

Urethane Acid Cured Alkaline Phenolic Shell

Nitrogen Sulfur Pick-Up

Sintering (salt build-

up) Nitrogen

Blows (uncured

center)

Blows (uncured

center)

1: Least Susceptible - 4: Most Susceptible

Defect Potential by Binder System

Defects Unique to Binder Chemistry


QUESTIONS???


For additional information, please

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chemically bonded defects panel - … · chemically bonded defects panel ... • common in sharp...

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