Automatic Temperature Control In Vacuum Brazing Furnace Using P.L.C

ABSTRACT
Brazing alloys used for brazing the components of gas turbines and aerospace applications contain nickel as the base material. Nickel has highest affinity for oxygen. Incase if components are brazed using nickel as based filter material in air or atmosphere the braze joint will porous and braze strength is not achievable. To avoid the presence of oxygen while brazing, either inert gas furnace or vacuum furnace can be used. Vacuum furnace is superior to inert gas controlled by furnace as only one ppm of oxygen can be present and hence it is possible to get good braze and strength. Apart from this the surface finishing of the processed components is an additional advantage. In the furnace while processing, it has three phases.
1. Creation of vacuum.
2. Heat treatment
3. Cooling
 In the first phase vacuum is created using mechanical pumps. The range of created in the furnace is less than 10 power of -5 mbar and is sensed using cold cathode gauge.
In the second phase the control variable is temperature. The maximum temperature achievable from this furnace is 1350degree C. In this phase it includes 2 cycles-brazing cycle and post brazing cycle. In the first cycle brazing for process takes place with the temperature developed. In the second cycle uniformity of temperature in component takes place. Molybdenum heating elements are used in this furnace. Thermocouples are used as sensing elements
 In the third phase either gas cooling or water cooling system can be used.  A PID (PROPORTIONAL PLUS INTEGRAL PLUS DERIVATIVE) controller is used to control vacuum and temperature and the desired values are accomplished using PLC (PROGRAMMABLE LOGIC CONTROLLER) using ladder diagram programming. The program is fed into the programmer-UP25 (UNIVERSAL PROGRAMMER) controller. The follower-UT35 (UNIVERSAL TRANSMITTER) controller follows the program written in the programmer.



TABLE OF CONTENTS

CHAPTER ONE
1.0 Introduction
1.1Aims and objectives
1.2 Statement of problem
1.3 Relevance of the project
1.4 Scope and limitation of study
1.5 Methodology

CHAPTER TWO
2.0 Literature review
2.1 Vacuum brazing technology
2.2 Characteristics of vacuum brazing furnaces
2.3 Types of vacuum brazing technology
2.3.1 Aluminum vacuum brazing furnaces
2.3.2 Copper vacuum brazing furnaces
2.3.3 Nickel brazing vacuum furnaces
2.4 Problems with brazing furnaces
2.5 The programmable logic controller
2.5.1 Hardware


CHAPTER THREE
3.0 Equipment design, specification and working principle
3.1 Universal programmer 25
3.1.1 Set point and parameter display
3.2 Universal transmitter 35
3.3 Signal conditioting circuit
3.3.1 Vacuum brazing furnace:
3.3.2 Temperature sensor
3.4 Therrmocouples
3.4.1 Principle:
3.4.2 Resistance thermometer
3.4.3 Vacuum sensor
3.4.4 Recorder
3.4.4.1 Features
3.5 Thyristor control
3.5.1 Specifications:
3.6 Vacuum instruments
3.6.1Mini convectron vacuum gauge:
3.6.2Front panel features:
3.6.3Vacuum adjustment:
3.6.4Atmosphere adjustment:
3.6.5 Set point adjustment:
3.6.6 Monitor common:
3.6.7 Control valves:
3.6.8 The 307vgccontrol unit:
3.6.9 VGC control unit front panel
3.6.9.1 Units of measure: 
3.6.9.2 Ion gauge on /off:
3.6.9.3 Degas on/off 
3.6.9.4 Available remote input/output option
3.7 Process software
3.8 Program pattern


CHAPTER FOUR
4.0 Operating procedures, maintenance and trouble shooting
4.1 The operating procedure
           4.1.2 Close down procedure
           4.2 Maintenance
           4.2.1 Trouble shooting flow diagram
4.2.2 Safety procedure while using the thyristor controller

CHAPTER FIVE
5.0 Conclusion and Recommendation
5.1 Conclusion
5.2 Recommendation

REFERENCES