Design And Construction Of Gas Fired Heat Treatment Muffle Furnace

ABSTRACT

This wok is on the design of a Gas fired heat-treatment muffle furnace using locally sourced materials. The design philosophy is to eliminate the use of heating elements requiring electric power which is poorly supplied in the country. In the design, mild steel was used for the fabrication of the furnace casing, while the other components needed for the design were selected based on functionality, durability, cost and local availability. The furnace was assembled by lining the inner wall of the casing with refractory blocks made from heated mixture of kaolin, clay, sawdust and water after which the inner pot and electro technical devices (temperature controller, light indicator etc) were positioned. Testing was subsequently performed to evaluate the performance of the furnace. It was observed that the furnace has a fast heating rate (61.24⁰C/min to attain a pre-set temperature of 900⁰C); and a fuel consumption rate less than 1.41litres/hr. It was also observed that the furnace has good heat retaining capacity; can be easily maintained and safe for use.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

• INTRODUCTION
• BACKGROUND OF THE PROJECT
• PROBLEM STATEMENT
• AIM AND OBJECTIVE OF THE PROJECT
• SCOPE OF THE PROJECT
• SIGNIFICANCE OF THE PROJECT
• PROJECT MOTIVATION
• APPLICATION OF THE PROJECT
• PROJECT ORGANISATION

CHAPTER TWO

LITERATURE REVIEW

• OVERVIEW OF FURNACE
• DEFINITION OF A FURNACE
• BRIEF REVIEW OF CURRENT FURNACE APPLICATIONS AND TECHNOLOGY
• FUELS FOR FURNACE
• CHOICE OF FUEL
• REVIEW OF PREVIOUS WORKS
• HEAT TREATING PROCESS OVERVIEW
• BASIC REQUIREMENTS OF HEAT TREATMENT PROCESS
• BASIC REQUIREMENTS OF FURNACES
• TYPES OF FURNACES

CHAPTER THREE

                       METHODOLOGY AND MATERIALS SELECTION

• DESIGN CONSIDERATIONS AND CALCULATIONS
• MATERIALS USED
• DESIGN
• FABRICATION PROCEDURE
• DESIGN CONSTANTS AND CALCULATION

CHAPTER FOUR

• RESULT ANALYSIS
• PERFORMANCE EVALUATION
• SAFETY AND MAINTENANCE
• COST ANALYSIS

CHAPTER FIVE

• CONCLUSION
• REFERENCES

CHAPTER ONE

1.0                                                        INTRODUCTION

The modification of microstructures to achieve desired properties is a fundamental approach in metallic materials development. Heat-treatment which is one of the primary routes of developing microstructures requires the use of furnaces to be able to attain desired temperatures, heating and cooling rates; and holding environments required to induce phase transformations [Rose J.W, 1997]. Heat- treatment furnaces with effective temperature sensing, heat retaining capacity and controlled environment are necessary for heat-treatment operations to be successfully performed. Some of the processes require heating cycles for durations spanning a few minutes to several hours depending of the material and the properties desired [Dossee, T. and Boyer, H, 1997]. The absence of constant power supply in the country has made it difficult for a wide range of heat-treatment operations to be effectively performed. In the Universities and research institutes this situation has affected research output for many research scholars who are interested in microstructure development through heat-treatment. This challenge is the motivation for this research aimed at the development of a portable heat-treating furnace that relies on gas (LPG) to fire and generate the heat needed to raise the temperature of the furnace to the desired level. The elimination of the use of heating elements which requires electric power to function is the fundamental design principle justifying the research work. A good number of research works have been reported on the design of furnaces to meet the needs of the Nigerian scientific and technological environment [George, E. Totten, 1998]; but very little literature is available on the design of gas fired heat-treatment furnaces. The design on completion will significantly reduce the dependence on electric furnaces and guarantee uninterrupted experimental heat-treatment research work.

1.1                                         BACKGROUND OF THE PROJECT

Heat treating furnaces are essentially heating chambers, i.e., a refractory vessel which holds the steel stock as well the heat. The furnace chamber is heated with some source of heat. The supply of heat has to be regulated depending on the requirement. More heat is needed during the heating period, but almost a constant heat is required when the furnace has attained the required temperature and is to be maintained at that temperature.

The heat has to be supplied to the whole of the properly designed furnace in a way that the temperature is constant everywhere, or at the places where the charge is being kept otherwise some parts may get under heated, or overheated. The doors, or openings are kept as small sized as possible to reduce the heat losses. Tempering and low temperature furnaces may require provisions for forced air or atmosphere circulation. The carburised parts may be quenched inside the furnace itself.

The heat treatment furnaces play a very important role in imparting reproducible useful properties to the steel components. The design of the furnace is determined by the stock which is to be treated and the particular treatment which has to be carried out at the special temperature. When parts are required to be heat treated at different temperatures, several furnaces may be required as a furnace which may be suitable for use at 1300°C, may be unsuitable for use at 300°C, although the latter temperature is within its maximum temperature range. There are different types of furnace for heat treatment with different types of fueling, but in this work we are going to focus on gas fired muffle furnace for heat treatment.

A muffle is a hollow cuboid or cylindrical retort made of special refractory material, or non-scaling steel. A furnace, in which the heat source does not directly make contact with the material being heat-treated, is described as a muffle furnace. The components are charged in a muffle, and gas firing, or electrical energy can be used to heat the muffle from outside.

The gas is burnt outside the muffle, and the heating is affected by the hot gases which are made to circulate through the ring like space between the interior-wall and the exterior-muffle wall.

1.2                                                  PROBLEM STATEMENT

This work is aimed at the development of a portable heat-treating furnace that relies on gas (LPG) to fire and generate the heat needed to raise the temperature of the furnace to the desired level. The elimination of the use of heating elements which requires electric power to function is the fundamental design principle justifying the research work.

The design philosophy is to eliminate the use of heating elements requiring electric power which is poorly supplied in the country.

1.3                                                   AIM OF THE PROJECT

The aim of the work is to develop a heat treatment muffle furnace capable of heat treating ferrous, non – ferrous and their alloys which uses gas as the firing source.

1.4                                                  PROJECT MOTIVATION

The main motivation for the work is to make available low heat furnace that can be used to heat treat ferrous, non-ferrous and their alloy with ease with high degree of safety and affordable cost and with little or no skilled-personnel maintenance that doesn’t rely on electricity supply to operate instead it uses liquid petroleum gas as the source of energy.

1.5                                                 SCOPE OF THE PROJECT

The heat treatment furnace is a heating chamber that is a refractory or lagged enclosure, which contains the charge and retains heat that should be measurable as well as controllable (Rajan et.al., 1988)

According to the literature given by International Electric Equipment (IEE) regulations, basic standard parameter for the construction and design of a furnace comprises the following: the casing design, the insulating system, the electrotechnicals, and the safety/ controls system.

The products of combustion of the gas do not enter the heating chamber (the muffle), and thus, the atmosphere of the furnace can be controlled, and thus, scaling of the components can be prevented. Also, such a furnace gives reasonable uniformity of temperature distribution.

The muffle is a welded box or cylinder made out of heat resistant steel, a water cooled frame for the door sealing, and a door with a combined insulation of radiation sheets and encapsulated ceramic fibre. The wall thickness and the material depend on size, maximum temperature, and further process parameters.

The most important challenge for the muffle design is to avoid thermal stress. Especially during fast heating and cooling cycles thermal stress can damage the muffle. Rounded corners reduce thermal stress. In addition, the temperature gradient along the section of the water cooled door sealing must be minimized. The design of the door with several radiation sheets diminish the thermal stress inside the muffle mouth because the temperature gradient is distributed over a longer distance.

The maximum temperature for continuous operation of the silicone door sealing is 220°C. Therefore the flat face of the rectangular frame must be water cooled. With additional cooling in the door, the sealing is located in a cold labyrinth passage and perfectly protected.

1.6                                                SIGNIFICANCE OF THE STUDY

Gas firing heat treatment muffle furnace has low capital cost and simplicity of operation is normally preferred for intermittent and cyclic duties. Gaseous fuels tend to provide longer refractory life than other fuels.

1.7                                          APPLICATION OF THE PROJECT

Today, an electric muffle furnace is usually a front-loading box or tube design used for high-temperature applications such as melting glass, creating enamel coatings, technical ceramics or soldering and brazing. They are also used in many research facilities to determine what proportion of a sample is non-combustible and non-volatile.

1.8                                                         PROJECT ORGANISATION

The work is organized as follows: chapter one discuses the introductory part of the work, chapter two presents the literature review of the study, chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.