BENTELER Mechanical Engineering

BENTELER Mechanical Engineering
Advanced Design of Continuous Furnace
for Hot Stamping Line
Agenda

Introduction BENTELER Group

Furnace design

Heating concept

Dew point regulation
 Contact
Agenda

Introduction BENTELER Group

Furnace design

Heating concept

Dew point regulation
 Contact
Global Engineering Expertise
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•
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Bielefeld, Germany
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Agenda

Introduction BENTELER Group

Furnace design

Heating concept

Dew point regulation
 Contact
Hot Forming Technology – Furnace Design
LOADING
HEATING
Z1
INPUT-CONVEYOR
Z2
Z3
Z4
Z5
STAMPING
Z6
Z7
Z8
FURNACE
General layout example for a Hot Forming Line
OUTPUT-CONVEYOR
Hot Forming Technology – Furnace Design
Homogenous furnace
Partial furnace
Hot Forming Technology – Furnace Design
Special features:
•
Modular Concept
•
Expandable
•
Easy installation
•
Easy maintenance
•
Easy usage
• Modular design
• Comfortable access
• Effective safety concept
• All process parameters in recordable prescriptions
(recipes)
Hot Forming Technology – Furnace Design
• Easy Installation
― Pre assembled and installed modular
design
― Insulation installed inclusive rollers
― Cable connections are provided with
connectors
― Transport by standard containers or
trucks
― Without welding during installation
― Installation / assembly to first heating
up: 30 days
― SOP: 10 days after first heating up
Agenda

Introduction BENTELER Group

Furnace design

Heating concept

Dew point regulation
 Contact
Hot Forming Technology – Heating Concept
Example of burner efficiency
Hot Forming Technology – Heating Concept
Radiation heat transfer – Basic equations
• Calculation of radiation energy flux using Stefan-Boltzmann law
• Equation if energy flux for non-black bodies
e(T)= 𝝈𝜺(𝑻𝟒 )
𝝈 = 5.6707e-8 (W∙m-2ˑK-4) - Stefan-Boltzmann constant
𝜺 - Emissivity
T(K) - thermodynamic temperature
• Total net heat flux between bodies (1) and (2) that are non-black (simplified)
𝑸𝟏−𝟐 = 𝑨𝟏 𝝈𝑭𝟏−𝟐 (𝑻𝟏𝟒 − 𝑻𝟐𝟒 )
𝑨 𝒎2 - Surface
𝑭𝟏−𝟐 - Transfer factor
Hot Forming Technology – Heating Concept
Stefan - Boltzmann equation
Blank
930°C
Simplified for gray object in a large
isothermal environment.
900°C
𝑸𝟏−𝟐 = 𝑨𝟏 𝝈𝜺𝟏 (𝑻𝟏𝟒 − 𝑻𝟐𝟒 )
600°C
Radiation
Radiation vs. Convection
Temperature of furnace [°C]
870
900
920
930,0
Temperature of blank [°C]
25
600
900
920,0
Emissivity
0,38
0,12
0,54
0,7
Convection coefficient[W/m2K]
9,0
9,0
9,0
9,0
Heat flux radiation [kW/m2]
36,6
8,9
4,1
2,7
Heat flux convection [kW/m2]
7,6
2,7
0,18
0,09
Ratio between
4,8
13,3
22,8
29,4
Conduction
Convection
0%
50%
50°C
100% Ratio
Temperature of 930°C inside the furnace
Hot Forming Technology – Heating Concept
Radiation heat transfer – FEM Analysis
Hot Forming Technology – Furnace Design
Radiation heat transfer into the blank
Hot Forming Technology – Furnace Design
Furnace Design – thermal simulation of furnace openings
(input and output)
Hot Forming Technology – Furnace Design
Temperature distribution inside the furnace input
Agenda

Introduction BENTELER Group

Furnace design

Heating concept

Dew point regulation
 Contact
Hot Forming Technology – Dew Point Regulation
• Hydrogen embrittlement
― Hydrogen embrittlement is the process by which various metals,
most importantly high-strength steel, become brittle and
fracture following exposure to hydrogen
― Basic chemical reactions during embrittlement process for
uncoated blanks are:
3Fe + 4H2 O → Fe3 O4 + 8H
Fe + H2 O → FeO + 2H (from 570°C)
― Elemental hydrogen diffuses along the grain boundaries inside
the steel structure.
― Formed molecular hydrogen and methane gas builds up
enormous pressures that initiate cracks.
― This is quite important in case of hot formed parts which have
martensitic structure and also contains rest strain from the
forming process.
Hot Forming Technology – Dew Point Regulation
• Hydrogen embrittlement
―
Situation is dangerous especially for coated materials (eg. AlSi) from two reasons.
―
First: the hydrogen can be easily locked under the coating.
―
Second: Al – Si coating also react with water by high
temperature.
―
Basic chemical reactions for Al – Si coated blanks are:
2Al+6H_2 O→2Al(OH)+6H
2Al+4H_2 O→2AlO (OH)+6H
2Al+3H_2 O→Al_2 O_3+6H
Si+〖2H〗_2 O→SiO_2+4H
―
Described processes are running above 200°C, but really
dangerous from 550°C – 650°C due to short d-well time
inside the furnace.
Hot Forming Technology – Dew Point Regulation
• Possible sources causing Hydrogen embrittlement inside the furnace
―
Endo – Exo gas protective atmosphere inside the furnace (H2, CO, N2, CO2, H2O)
―
Nitrogen + natural gas mixture inside the furnace (CH4, CO, N2, CO2, H2O)
―
Open flame inside the furnace (N2, CO2, H2O, CO)
―
Missing controlled atmosphere (N2, CO2, H2O)
• Nowadays, only the parts produced under the controlled atmosphere with
reduced dew point temperature to -10°C level and lower are accepted by
most of the OEM’s.
• BENTELER furnaces have the dew point regulation system in standard basic
configuration.
Hot Forming Technology – Dew Point Regulation
• Key features
― Avoiding the water vapor inside the furnace –
prevent hydrogen embrittlement on the parts
― Based on using of dried air or pure nitrogen
― Process automatically controlled via PLC
― Fits all CQI9 requirements
― Possible system operation with coated and also
uncoated blanks.
― Dew point after air dryer is approx. - 40°C
― Implementation of 2 - 6 measurement points, 2 –
4 regulation zones
― Using of high reliable polymer dew point sensors or
laser moisture analyzer like high end solution
Hot Forming Technology – Dew Point Regulation
BENTELER has developed and patented the Dew Point Regulation in 2011
Agenda

Introduction BENTELER Group

Furnace design

Heating concept

Dew point regulation
 Contact
CONTACT DETAILS
Jad John Tawk
Global Sales Manager
Dr.-Ing. Borek Dvorak
Engineering Manager
AT Design
BENTELER Maschinenbau GmbH
Frachtstrasse 10–16
33602 Bielefeld
Germany
Benteler Maschinenbau CZ s.r.o.
Hodkovicka 981/42
460 06 Liberec
Czech Republic
Phone: +49 521 542-170
Phone: +420.482 465 327
jad.tawk@benteler.com
www.benteler-maschinenbau.de
Borek.Dvorak@benteler.com
www.benteler.cz