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

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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.

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Technische Universität München

Institute for Carbon Composites

Boltzmannstraße 15

85748 Garching

www.lcc.mw.tum.de

Contact

Address

Fax

Email

Tel

Room

+49 89 /

+49 89 /

Institute for Carbon Composites donated by

David Schultheiß

289 - 15066

MW 1441

289 - 15097

schultheiss@lcc.mw.tum.de