Design And Fabrication Of A Foundry Sand Mixer Using Locally Available Materials

ABSTRACT

Most small foundry shops mix their sand manually which is not efficient since homogenous mix cannot be guaranteed and even when foundry mixer are available most of them are imported costing the nation huge foreign exchange. A foundry sand mixer capable of mixing foundry sand has been designed and fabricated using locally available material. The sand mixer components machine frame, mixing pan, motor support, gear box speed reducer, Shaft, discharge door and Mixing blades were designed ,produced and assembled together to produce the mixer. A step-turned shaft of diameters 23mm and 33mm attached to a 2hp, 3 phase electric motor to transmit the torque required to effectively turn and mix the sand in the pan. The mixer test results show that the average mixing time of the sand mixer to mix 20kg of sand was 14minutes and the mixer efficiency was 52%.The fabricated mixer compare favourably with the the imported existing one which has an efficiency of 59%.The application of this sand mixer by foundry shops will eliminate the use manual effort which is cumbersome, time wasting and inefficient.It will also save the the country of huge foreign exchange used in the importation of foundry sand mixers.

NOMENCLETURES

D_p= Diameter of the mixing pan, m F_c = Force acting on the shaft, N H_p= Height of the mixing pan, m M_c = Mass of moulding sand, kg

N₁ = Rotational speed of the electric motor, rpm

N₂ = Rotational speed of the shaft, rpm P = Power required, W

S_c = Allowable sheer stress of shaft material, N/m2 T_c = Torque on shaft, Nm

V_p = Volume of the mixing pan, m3

d_b = Distance from one blade to another through the centre of the shaft

d_c = Diameter of shaft, m

g = Acceleration due to gravity, m/s

r_b = Radius of one blade to the centre of the shaft ε = Efficiency of the machine, %

q_c = Density of moulding sand, kg/m3

TABLE OF CONTENTS

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

TABLE OF CONTENT

CHAPTER ONE

1.0      INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

1.2      OBJECTIVE OF THE PROJECT

1.3      SCOPE OF THE PROJECT

1.4      PURPOSE OF THE PROJECT

1.5     ADVANTAGES OF THE PROJECT

1.6      APPLICATION OF THE PROJECT

1.7      LIMITATION OF THE PROJECT

CHAPTER TWO

2.0     LITERATURE REVIEW

2.1      REVIEW OF THE STUDY

2.2     ORIGIN OF FOUNDRY SAND

2.3      CURRENT MANAGEMENT OPTIONS OF FOUNDRY PROCESS

2.4      HIGHWAY USES AND PROCESSING REQUIREMENTS

2.5      MATERIAL PROPERTIES

CHAPTER THREE

3.0     METHODOLOGY

3.1      SAND MIXERS WORKING PRINCIPLES AND DESIGN

3.2     PARAMETERS OF THE MIXER

3.3     MATERIAL SELECTION AND MACHINE FABRICATION

3.4     EXPLODED, SIDE AND PICTORIAL VIEW OF THE MACHINE

CHAPTER FOUR

RESULT ANALYSIS

4.0      CONSTRUCTION PROCEDURE AND TESTING

4.1      TESTING OF MIXER

4.2      ASSEMBLY PROCEDURE

4.3      OPERATIONAL/SAFETY GUIDE

4.4     OPERATIONAL GUIDE

4.5      GENERAL MAINTENANCE

4.6      COST ANALYSIS

CHAPTER FIVE

5.0      CONCLUSION, RECOMMENDATION AND REFERENCES

5.1      CONCLUSION

5.2      RECOMMENDATION

5.3      REFERENCES

CHAPTER ONE

1.1                                                        INTRODUCTION

Mixing of any material or combination of materials is accomplished by moving the materials together against themselves. The mixer, regardless of design or materials to be blended, exists only to accomplish a uniform distribution of the components. Whether mixing concrete, polymers, liquids, powders, or silica sand with differing chemical system, the purpose of the mixing machine is to move the materials against themselves.

In our industry we are mixing sands with very small amounts of different binding agents, all having different and variable properties. The first sand that exits the chamber is obviously not the same as the sand a few seconds behind it, as there is really nothing for the first sand to move against. Even with today’s technologies (timers, flowmeters, valving), we cannot get away from this basic goal: to make the first sand usable, and exactly the same as the sand right that follows it.

It is a simple process to catch the first 1-2 seconds of sand that exits the mixer and then put it in the molds as soon as the pattern is covered. A properly trained and motivated mixer operator will waste very little sand.

The object of a continuous mixer is to produce sand for quality cores or molds using just enough binder to obtain the desired casting results at the lowest possible cost. Chemicals are a high percentage of the casting cost. Lower resin levels reduce costs, improve the reclamation process, and improve the working environment. In order to keep chemicals levels as low as possible it is important to control the temperature variables.

The preferred temperature for sand and resin is in the 85-95°F range. The set time of PUNB is either doubled or halved for every 18°F change in sand temperature. Unless sand temperature is well controlled, production rates will suffer. Even if the strip time is reduced with additional catalyst (expensive) the evaporation of solvents remains retarded due to the low sand temperature resulting in a higher potential for gas defects.

Heating sand with a traditional fluidized resistance element design can be costly because compressed air is cool and therefore uses a lot of power to raise the sand temperature 20-30° at the flow rates required.

This high kW requirement can add to the monthly electric bill if it is a demand-based system. Fluidized bed heaters with hot water require substantially less energy and are more accurate because the residence time in the comparatively larger chambers is longer, but capital costs are usually double the cost of resistance element designs. While the end temperature is important, the consistency and repeatability of temperature is equally important. The capital and operating costs of correctly sized sand heaters are high, but usually can be justified by lowered resin requirements, greater production levels, fewer scrap molds/cores, and more consistent production.

Resin temperatures should be as close as possible to the correctly heated sand. The normal response to cold resins is to install a drum heater or heat lamps. While these are helpful, they can be problematic; if left on too long or at too high a temperature, the characteristics of the resin can be dramatically changed.

As the solvent evaporates or resin advances, the performance, viscosity, and metering characteristics will change.

These vessel heating techniques usually only heat a couple inches into the drum or tote. The majority of the liquid’s temperature is unchanged – and this difference in temperature within a single drum is another variable that needs to be eliminated.

The correct technique is to have a dedicated recirculation pump that takes the chemical from the bottom of the container, runs it through an in-line heating device, and returns it to the top of the container. This system keeps the chemical throughout the container at the same temperature at all times. Additions to this container should never be more than 25% of the container size to allow the heating system to recover as quickly as possible while still in production.

1.2                                             OBJECTIVE OF THE PROJECT

This objective of this work is to fabricate a locally made foundry sand mixing equipment and more particularly to a means and method for demand responsive custom mixing and blending core sand, resin and catalyst in accord with the particular requirements of one or adjacent machines, in close proximity, to provide high quality cores with the fast curing time for high\production rates.

1.3                                              PURPOSE OF THE PROJECT

The mixer, regardless of design or materials to be blended, exists only to accomplish a uniform distribution of the components. Whether mixing concrete, polymers, liquids, powders, or silica sand with differing chemical system, the purpose of the mixing machine is to move the materials against themselves.

1.4                                          ADVANTAGES OF THE PROJECT

• Large openings in the mixing pan provide easy access for maintenance
• All of the major assemblies (drives and gear units) are located outside the mixing pan
• Wear parts are easy to replace
• A fully loaded mixer can easily be restarted
• Using a frequency inverter for motor control permits the energy input to be adjusted variably over the whole mixing cycle for shorter processing time, better molding sand properties and the potential for energy savings.

1.5                                          APPLICATION OF THE PROJECT

Small, medium-sized sand preparation systems and the most difficult mixing applications.

1.6                                                 SCOPE OF THE PROJECT

This Sand Mixer quickly, uniformly and mechanically manipulate a heterogeneous mass of sand materials, of varying aggregate sizes, into uniformly blended and bonded homogenous product. It consists of cylindrical pan, four heavy blades, which rotate in a circular path about a vertical shaft. A discharge door is provided at the bottom of the pan. The four blades are divided into two sets of two blades each (one set on top the other) and they are slightly off the true radius to allow for free rotation as well as eliminate any wear due to friction which may arise from contact between the blades and the pan.   The design theory of the sand Mixer considers the geometrical parameters of the Mixer, which includes the frame mixing pan, blades, shaft and driving mechanisms.

1.7                                           LIMITATION OF THE PROJECT

1. When mixing sand, you need to coat thick clay slurry on the surface of the sand, and you need to use high-power devices with rubbing function, otherwise, it is impossible to get good quality sand.
2. Since after mixture, the sand has very high strength, when molding, the sand is not easy to flow, and it is difficult to pound, and hand molding is not only laborious but also needs certain skills, while machine molding needs complex and large device.
3. The stiffness of the mold is not high, and the dimensional accuracy of mixings is relatively poor.

CHAPTER TWO

2.0                                                    LITERATURE REVIEW

2.1                                                  REVIEW OF THE STUDY

The increasing demand for castings in the growing car and machine building industry during and after World War I and World War II, stimulated new inventions in casting process technology. Foundry sand is high- quality uniform silica sand that is used to make moulds and cores for ferrous and nonferrous metal castings [1]. The metal casting industry annually uses an estimated 100 million tons of foundry sand for production [2]. The proper blending of these materials enhances desirable properties for moulding. Therefore, Sand mixing is a process of kneading and working sand for the purpose of distributing the ingredients (additives) into a homogenous mixture [3]…