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Institute for Carbon Composites donated by
Gypsum based tooling system for hollow structures
„A Comprehensive Approach to Carbon Composites Technology“
Symposium on the occasion of the 5 th anniversary of the Institute for Carbon Composites
Research Campus Garching, September 11th - 12th 2014
David Schultheiß
2
Concluding Remarks 6
Demonstrator Component 5
Properties of the Material Mixture 4
Processing of the Material Mixture 3
Principle of the Material Mixture 2
Overview of Existing Tooling Material 1.2
Requriements for Inner Tooling 1.1
Introduction 1
Agenda
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
3
Derivation of tool requirements from component and process demands:
Requirements for Core Materials
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
Surface roughness
Temperature stability
Costs
Flexural stiffness Compressive stiffness
Easy removability
Etc…
Chemical resistance
Surface hardness
Tolerances
Resin tightness Density
CTE
4
Overview of Existing Core Material
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
A Selection
Core Materials
Wax
Metal
Filler and binder
combination
Gypsum Thermoplastic
Fiber reinforced
silicon tubes
Low melting temperature
alloy
5
Principle of the Material Mixture
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
Desired Requirements
hard Desired core behavior weak
Preforming and Infiltration Part demolding
Trigger
Realization
[US2014/0167319A1]
6
Principle of the Material Mixture
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
Functional Verification
7
Principle of the Material Mixture
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
Gypsum
Gypsum …
… is inexpensive and easy to handle
… has different phases (hemihydrate, dihydrate,
anhydrate)
… has a temperature stability up to 700°C
Investigations regarding:
Optimal process parameters
Material properties (mechanical and physical)
depended on material parameters
Investigated gypsum plaster grades:
Calcium sulfate β-hemihydrate (Krone AG)
Calcium sulfate α-hemihydrate (Knauf AG)
Compressive testing of gypsum samples
Comparison of the compressive strength for different water-
powder ratios (r=0.4, 0.5, 0.6)
0
5
10
15
20
Co
mp
ressiv
e L
oad
[kN
]
Gypsum (r = 0.4) Gypsum (r = 0.5) Gypsum (r = 0.6)
8
Expandable graphite …
… is natural graphite with intercalated acid (H2SO4 (sulfuric acid)
… has a free expansion up to a volume 200x the initial volume
… starts expanding between 150°C and 280°C depending on
the intercalation agent
Investigation of material properties
Expansion behavior of the bulk material
Elution of the intercalated acid in water
Investigated expandable graphite grades:
Grades with threshold temperature of 160°C, 200°C and 225°C
(Luh GmbH)
Grade with threshold temperature of 160°C (Kopfmühl AG)
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
Expanded graphite flake
Schematic depiction of the structure of
expandable graphite
[Kro
pfm
ühl A
G]
[Kro
pfm
ühl A
G]
Principle of the Material Mixture Expandable Graphite
9
Principle of the Material Mixture
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
Process Chain
10
Investigations regarding duration of castability and hardening time
Knowledge of process window
Processing of the Material Mixture
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
Rheological Investigations
Viscosity is in the same magnitude
Double process time for the alpha-
hemihydrate
Distribution of the viscosity of beta- and alpha-hemihydrate suspension
with altering water plaster powder fraction at a shear rate of 150s-1
11
Processing of the Material Mixture
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
Rheological Investigations - Casting Process Window
Expandable graphite reduces process time and increases viscosity
Distribution of the viscosity of alpha- and beta-hemihydrate suspension
(αWP=35; βWP=50) with altering expandable graphite fraction (EG=0,10,20)
at a shear rate of 150s-1
Distribution of the viscosity of alpha- and beta-hemihydrate suspension
(αWP=45; βWP=70) with altering expandable graphite fraction
(EG=0,10,20) at a shear rate of 150s-1
12
Processing of the Material Mixture
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
Sealing
Tested sealing agents:
Spray foil (rubber-based foil)
Paints (Thermo paint, High temperature paint)
Mikro-Isolat (based on alginic acid)
PVA paint
Heat-shrinkable tube Most promising systems
Schematic depiction of a porous material with (right) and without (left) sealing
while infiltration
Challenge: No stable sealing agent
known for temperatures above
120°C
Comparison of saturated (left) with non-
saturated (right) gypsum sample
13
Properties of the Material Mixture
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
Mechanical Properties:
Flexural and compressive strength
Surface hardness
Physical Properties:
Thermal conductivity and capacity
Thermal expansion (CTE)
Density and porosity
Surface roughness
14
Properties of the Material Mixture
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
Coefficient of Thermal Expansion
Alpha-hemihydrate:
CTE of W/P=35 sample is not
dependent on expandable graphite ratio
water-plaster ratio = CTE
Investigation of the behavior of the material under temperature load
Knowledge of geometry throughout the temperature cycle
Development of CTE of alpha-hemihydrate core material with altering expandable
graphite fraction (EG=0, 20)
Acknowledgement: The Author likes to thank Montanuniversität Leoben and Polymer Competence Center Leoben GmbH (PCCL) for the execution of the TMA experiments
15
Properties of the Material Mixture
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
Coefficient of Thermal Expansion
Beta-hemihydrate:
No influence by the expandable
graphite on the CTE
water-plaster ratio = CTE
CTE of W/P=60 samples is not
explainable
Range of CTE between 15 and 18*10^-6/K for the core material
CTE values vary due to mineral composition of the plaster and sample production
Development of CTE of beta-hemihydrate core material with altering expandable
graphite fraction (EG=0, 10, 20)
16
Demonstrator Component
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
• Verify the function of the sealing
• Demonstrate the successful removal of the core material
• Defined surface roughness is achievable
17
Concluding Remarks
09/12/2014 | Schultheiß | Gypsum based tooling system for hollow structures
All process steps of the core production chain are evaluated
Rheological investigations
Evaluation of sealing agents
Selected material properties are investigated
Coefficient of thermal expansion are presented
Gypsum dominated property
Verification on demonstrator level
Acknowledgement: The Author likes to thank GE-Global Research for the funding of this project.
18
Technische Universität München
Institute for Carbon Composites
Boltzmannstraße 15
85748 Garching
www.lcc.mw.tum.de
Contact
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Fax
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Room
+49 89 /
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Institute for Carbon Composites donated by
David Schultheiß
289 - 15066
MW 1441
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