Heat Treatment basics

1. The beginners guide to
Heat Treatment Control
Beginners Level (Heat Treatment)
© Peter Sherwin | Eurotherm | V2 2014
Introductory Guide

2. Introduction
The purpose of this guide is to introduce the
basics of Heat Treatment control and is aimed
at new Engineers supplying control systems to
the Heat Treatment Industry.
This guide is part of as a series of six separate
publications which cover the following:
1. The Beginners Guide to Heat Treatment
Control
2. Understanding CQI9 (intermediate)
3. Understanding AMS2750E (intermediate)
4. Practical PID for Heat Treaters (intermediate)
5. Advanced Control methods (expert)
6. Business Performance and algorithms (expert)
Guide Overview
These guides have been produced to help answer
some of the common questions asked about Heat
Treatment Control systems.
There are three levels:
Beginners - aimed at recent recruits or Engineers
new to providing control systems into the Heat Treat
Industry and who want to learn more about the role
of control systems in the Heat Treatment process.
Intermediate – specific guides on industry standards
for both suppliers and end users. These guides
have been produced to explain the key points in the
standard and provide an overview of how your
instrument manufacturer can help you meet the
requirements of the standard.
Expert – these guides are a deep dive into the detail
of control and how modern instruments and
associated algorithms can directly help Business
Performance. These guides are for Engineers with
prior knowledge of control systems.
Hyperlinks (links to websites) are included in the
guides to provide quick access to more detailed
information. 2

3. Contents
1. Chef
2. Heat Treater
3. Heat Control
Energy Source
Electric
Gas
Sensor
Program
PID
4. Red Tape – Regulations & AMS2750
Regulations
AMS2750
5. Watch-out
6. Support
Thermocouple management
Calibration of instruments
Record Keeping TUS
Programmers
Appendix – Heat Treat Applications
Useful Links
Further information
C
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3

4. 1
Chef

5. 1. Chef
Think of heat treaters as glorified chefs!
A chef takes raw inedible food and creates a
sumptuous meal through careful mixing of
ingredients and application of a known level of
heat for a defined period of time.
Introduction
Interesting fact - Eurotherm controllers are
used in pizza ovens!
5

6. 2
Heat Treater

7. 2. Heat Treater
The heat treater takes widgets that are pretty
useless in terms of strength properties and
changes the structure through the application
of heat and additives (usually gas mixtures)
for a known time and temperature.
Hardening Treatments
To develop useful engineering properties
such as strength and wear resistance.
• Direct Hardening
• Case Hardening (Carburizing, Nitriding etc.)
Softening Treatments
To facilitate a manufacturing process or to
eliminate stresses remaining at the end of a
manufacturing process.
• Annealing
• Normalizing
• Stress Relieving
7

8. 3
Heat Control

9. 3. Heat Control – Energy Source
Obviously the temperature scale is different than
that of the chef, but the principles remain the same.
If your temperature is too low or time too short you
undercook the food, or for the heat treater the
material properties are not correct. If you burn your
food then you might have to throw it away, it’s the same
principle in heat treat, if the temperature is too high
or your process time is too long then the parts can be
scrap.
The heat applied is either through electric heating
elements or gas fired burners.
9

10. 3. Heat Control – Electric
The electric heater is regulated by devices that can
adjust the electrical supply to the elements.
Common types of Power Control (in order of
increasing precision and speed of control):
1. Contactor
2. Solid State Relay (SSR)
3. Silicon Controlled Rectifier / Thyristor (SCR)
10

11. 3. Heat Control – Gas
Gas Fired systems are controlled by sending
appropriate signals to solenoid valves (for pulse fired
burners) or to actuating devices for conventional gas-
fired burners.
The actuating device controls the valve position of the
supplied combustion air and sometimes the gas lines
as well.
11

12. 3. Heat Control – Sensor
So how do we control the required energy input into
the furnace? We need a sensor to detect the temperature.
This is typically a thermocouple – the construction of this
sensor is based on an assembly of dissimilar metals that
when heated creates an electrical signal. The
thermocouple creates a mV (millivolt) reading and the
magnitude of this reading is related to the temperature
level.
The sensor is connected to a control or indicating device
which can automatically interpret and convert this mV
signal into a well known temperature scale (the
calculation is based on the type of Thermocouple).
The scale used is typically degrees Fahrenheit (°F) for the
United States and degrees Centigrade (°C) for Canada,
Europe, India etc.
12

13. 3. Heat Control – Program
The sensor is connected to an indicator or a
controller device to indicate the actual temperature.
If the unit is a controller then the information from the
sensors PV (Process Value) can be compared to the
required SP (Setpoint value) and the controller will
then send an output signal to the heating device to
raise or lower the temperature.
Programmers are enhanced control devices which
can
offer automatic profiling of the Setpoint over a time
period. This might be just to ramp up to temperature
and soak or dwell at the temperature for a defined
time (electronic timer), or, ramp to intermediate
temperature, preheat, raise again, soak, and perform
end of cycle actions.
Sophisticated programmers can turn on and off
events during each stage (or segment) of the Process
cycle.
13

14. 3. Heat Control – PID
How do we ensure that the temperature required is
achieved in minimum time (to avoid wasted energy)
and maintained to fine tolerances so Heat Treat
specifications can be adhered to?
It is common to use PID control. PID controllers are
sophisticated instruments that automatically adjust
the heat input to ensure the process stays at the
desired Setpoint.
PID stands for:
1. Proportional
2. Integral
3. Derivative
Basically this type of control reacts when the Process
Value (PV) is close to the desired Setpoint (SP) and
through a set of calculations adjusts the energy input
into the process. The idea is that you can achieve
stable control with correctly set PID constants.
14

15. 4
Red Tape

16. 4. Red tape – Regulations
So is it that simple for heat treaters - just time,
temperature and right additives / atmosphere mix and
an advanced Programmer?
Well… yes and no. The process is fairly
straightforward
and each material has a set defined process cycle,
but
there are local authority laws, regional legislative
requirements, government regulations
and industry standards that all apply to heat treat.
Two key industries that drive Heat Treatment
improvements are Aerospace and Automotive. They
both have heat treat standards (Nadcap Aerospace &
CQI9 Automotive) - at the core of both specifications
is the AMS2750 Pyrometry (or Thermal) Control
specification.
16

17. 4. Red tape – AMS2750
What is AMS2750E? It is the latest issue of an SAE
specification that covers pyrometric (temperature
measurement) requirements for thermal processing
equipment.
The standard covers:
• Temperature Sensors – e.g. Thermocouples
• Instrumentation – e.g. PID Controllers / Programmers
• Thermal Processing Equipment – e.g. Furnace work zone uniformity
• System Accuracy tests (SAT)
• Temperature Uniformity Surveys (TUS)
Basically the standard prescribes both initial and
ongoing accuracy and calibration requirements of
thermocouples, accuracy, calibration and makeup of
instrumentation as well as requirements for furnace
work zone uniformity.
Furnaces are classified based on Temperature Uniformity of the workzone.
The higher class furnaces (e.g. Class 1; +/-5°F) have the best temperature
uniformity and smallest spread of temperature throughout the workzone.
Instrumentation types vary from A through to E. The A instrumentation
provides more information about the temperature within the furnace by
including thermocouples in a number of locations – conversely the E
instrumentation only has one thermocouple.
17

18. 5
Watch Out

19. 5. Watch out
So what are the key issues to watch out for in AMS2750E to
avoid heat treaters falling foul of the standard.
Thermocouple Management
If a heat treater has multiple furnaces each with its own
thermocouple setup, this presents an issue of managing the
calibration and replacement periods for each
thermocouple type.
Calibration of Instruments
Multiple instruments across many furnaces require a
comprehensive Calibration plan.
Record keeping
Not only do you have to make sure you ensure you keep to
your calibration periods and ensure that TUS, SAT’s are all
done on time, the tests all need to be documented to specific
requirements.. This is in addition to running batches to the
correct Process parameters and securely recording that data.
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20. 6
Support

21. 6. Thermocouple Management
21
Ad-hoc
Thermocouples are
changed infrequently
and generally when
there is a process
problem. Sometimes the
thermocouple will be in
the furnace for a number
of years. This would not
meet the AMS2750
requirements.
Manual
Manual thermocouple
management adheres to
the AMS2750
requirements for
calibration and
replacement of
thermocouples. Requires
a lot of faith in manual
record keeping to ensure
you continue to meet the
requirements.
Automated
The furnace control/data
system has some
intelligence that can
track and alert on
calibration and
replacement periods
for thermocouples. The
Aerodaq is a Paperless
Chart Recorder and
Thermocouple
Management system
that provides auto-
tracking of periodic
inspections.

22. 6. Calibration of instruments
22
Ad-hoc
Calibration of
instruments may be on
an infrequent basis,
usually annually.
Typically issues occur at
these annual checks and
either recalibration of
units or replacement is
necessary. Cannot meet
the AMS2750 standard
with this practice.
Manual
Manual system that
conform to AMS2750.
Intervals are set with an
internal department or
external supplier.
Typically there is a
delay from calibration of
instruments to receipt of
calibration certificates.
Automated
Using cloud based
software your
maintenance periods
are aligned either with
your internal group or
with an external
calibration services
supplier.
Records are updated in
real-time and available
for review at any time,
Online tracking systems
are available to provide
this information, please

23. 6. Record Keeping – TUS (Temperature Uniformity Surveys)
23
Paper Charts
Accuracy is maintained
on paper recording
systems to conform to
AMS2750.
The individual channel
data is printed on a
paper chart at intervals
of 2 minutes or less.
Significant time is taken
to manually judge max
and min levels from a list
of numbers and then
apply correction factors.
Digital Records
Accuracy is maintained
to conform to AMS2750
requirements with data
recorded in a secure
format. Electronic
Paperless chart
recorders capture the
information, this is
usually exported to a
spreadsheet for analysis
which makes it easier to
apply correction factors
but this data is not
always secure.
Reporting Software
Provides secure links
with digital/paperless
chart recorders so no
extraneous manipulation
of base data is possible.
The report is setup to
guide the user through
creating the TUS report
to meet all the
requirements of
AMS2750. Reduces
time to prepare an
accurate report.

24. 6. Process Performance - Programmers
24
Manual Timer (Clock)
The contract review
process will dictate the
processing parameters
(time @temperature
etc.).
If you rely on a manual
timer to control the
process dwell/soak
period then you can
have variability in
process time that might
not meet the desired
specification.
Timer
For simple single
setpoint time and
temperature setups then
an electronic timer can
reduce the variability
that a manual timer
introduces. You can be
certain that the dwell
time is consistent.
Programmer
More complicated
processes (requiring
preheats etc.) require a
more sophisticated timer
system – this is where
the programmer is
appropriate. Consistent
results are achieved with
the ability to hold a
number of prewritten
programs in a single
device.

25. Appendix – Heat Treat Applications
25
Common Materials
Steel
Glass
Copper and Brass
Ceramic
Aluminum
Composite Materials
Precious Metals
Typical Processes Common Product Areas
Annealing
Normalizing
Stress Relieving
Aging
Quenching
Tempering
Flame Hardening
Induction Hardening
Neutral Hardening
Case Hardening
Carburizing
Carbonitriding
Nitrocaburizing
Nitriding
Cold and Cryogenic
Treatment
For general information:
en.wikipedia.org/wiki/Heat_treating
Automotive Parts
Appliances
Specialty Steels
Pipe & Tube
Fasteners
Machinery
Tools
Powdered Metals
Weapons &
Armaments
Farm & Heavy
Equipment
Foundry
Defence Equipment
Forging
Construction
Materials
Aerospace
Components
Can & Container
Wire
Medical Products
Marine and
Shipbuilding

26. Useful Links
Carbon (Oxygen Probes)
Carbon Probe Sensors
Simple Electronic Timers
Electronic Timer
Cycle (Setpoint) Programmers
Programmer (3504 Programmer)
Temperature and Process Controllers
2-Loop Controllers (3500 series)
Process Recorder
Paperless chart (6000 series chart recorders)
Controller and Recorder Instrument
PID Controller / Recorder (nanodac)
AMS2750E Information
Regulatory Compliance (AMS2750E)
Calibration Services
Eurotherm Calibration Services
Thermocouples, SAT and TUS Management
Aerodaq (thermocouple management)
Data Management
eos (data storage solutions)
Field Test Instrument / Survey Recorder
6100A TUS Portable Temperature Survey Recorder
TUS Auto Report Generator
AMS2750E TUS report software
Further information
SAE AMS2750E Standard
standards.sae.org/ams2750e
NADCAP Audits
www.pri-network.org
AIAG CQI9 Standard
www.aiag.org
© Peter Sherwin | Eurotherm | 2014