The Design And Construction Of Electrical Centrifuge

Project and Seminar Material for Science Laboratory Technolofgy (SLT)

Abstract

A laboratory centrifuge is a piece of equipment generally driven by an electric motor and some older ones usually spun with hand, that puts an object in a rotation around a fixed axis, applying a force perpendicular to the axis. It spun liquid samples at a high speeds and thus creates a strong centripetal force causing the denser materials to travel towards the bottom of the centrifuge tube more rapidly that they would under the force of normal gravity.

The present high cost of imported centrifuges necessitate the design and construction of an electrical centrifuge using local raw materials. The use of steel for the construction of the body, aluminum for the centrifuge head, rotor and buckets, made the centrifuge cheaper and more adaptable to the local environment.

The inner chamber which consists of four rotors could accommodate four test tubes at a centrifugation cycle. The average speed of a centrifuge is 100RPM (100 rotation per minutes) and the average time is five minutes while the maximum time is 10 minutes. The duration of successful centrifugation is 5 minutes.

Table Of Content

Preliminary Page(s)

Title page
Approval page
Dedication
Acknowledgement
Abstract
Table of content

Chapter One

1.0 Introduction

Chapter Two

2.0 Literature review

2.1 History of centrifuge
2.2 Types of centrifugal separation
2.3 Design of centrifuge

Chapter Three

3.0 Description of the centrifuge

3.1 Mechanical aspects
3.2 Electrical aspects
3.3 Working principle of a centrifuge
3.4 Tubes that can be used for centrifugation
3.5 Operating hints

Chapter Four

4.0 Test and results

4.1 Cost analysis

Chapter Five

5.0 Conclusion and Recommendation

5.1 Conclusion
5.2 Recommendations
References

Chapter One

1.0 Introduction

In a typical laboratory, there exists three different sizes of centrifuges. The smallest are the microfuge centrifuges. These are made for spinning 1 to 2ml plastic centrifuge tubes at sped up to 12 or 13 thousand rounds per minutes. They have very small, light rotors in them (the rotor is the part of the centrifuge that contains the holes for the sample tubes) which speed up and slow down rapidly. They are convenient for low to medium speed centrifugation of small quantities of materials.

The next common size centrifuge is the large super speed centrifuge that have up to about 20,000 rpm and can take tubes of various sizes, depending on the rotors (the larger the rotor, the slower the maximum speed). Finally, the third size is an ultracentrifuge; speeds up to 70,000 rpm are available on typical modern versions. Its size of tube and maximum speed vary from rotor to rotor.

Before centrifuging, the sample is a tube, a mixture of solutions of differing specific gravities with no clear separation. This makes it impossible to determine how much of each solution is present. After spinning, the samples in a centrifuge, the different solutions in the sample are separated into layers with the heaviest at the bottom of the tube. The quantity of each solution can now be readily determined.

Types Of Laboratory Centrifuge

Micro Centrifuges:

They are usually used to spin micro tubes e.g. 1.5/2.0ml, 0.5ml, 0.4ml, and 0.2ml tubes. They have fixed angle rotors (i.e. holes for sample tubes) and have variable speed up to around 15, 000rpm. The rotors can accommodate up to 30 x 1.5ml/2.0ml tubes with the most common being 24 x 1.5/2.0ml tubes rotor.

Refrigerated Micro Centrifuges:

They have a cooling system with adjustable temperature in the range -10oC to +40oC and are usually run at 40C.

Mini Micro Centrifuges:

They usually have a fixed speed (around 600rpm/200xg) and integral rotor for 0.2/2.0ml tubes with adaptors for 0.5ml, 0.4ml and 0.2ml tubes or adaptor to hold 2 times strips of 8 x 0.2ml tubes. Another model can hold 2 times micro array slides for removing excess liquid.

Benchtop Centrifuges:

They are deigned for use on benchtop as opposed to ultra laboratory centrifuges which have to be floor standing. Some benchtop centrifuges are capable of fairly high speeds and rcf as well as large total sample volumes.

Haematocrit Centrifuges:

They are specially designed for blood sedimentation tests in hematology laboratories, etc. and have a rotor specially designed to hold very narrow bore micro haematocrit tubes. The rotor can have a built-in reading for the sedimentation or a separate card can be used to measure the results.

Cytospin Centrifuges:

They are specifically used in cytology laboratory and have special holes for sample tubes and sample holders.

Ultracentrifuges:

They are designed as very high speed (rpm and rcf) centrifuges which have to be floor monitored. They are very expensive and have very expensive holes for sample tubes.

Centrifugal Evaporators:

They are designed to evaporate multiple samples down using a combination of centrifuge/rotor, vacuum pump and solvent trap. The centrifuge chamber can have the option of heating (to speed sample evaporation) and/or teflon coating (if using samples with aggressive solvents).

Chapter Five

5.0 Conclusion and Recommendation

5.1 Conclusion

At the end of the work, the desired result was achieved. A centrifuge of 23cm height made of steel with four rotors and four buckets that can accommodate four test tubes at a centrifugation cycle was constructed. The centrifuge was used in centrifuging different samples of liquid and accurate centrifugation was achieved.

5.2 Recommendations

Since accurate centrifugation is achieved with the use of electrical constructed centrifuge, I therefore recommend it for the spinning of different sample of liquids.

I also recommend the construction of electrical centrifuges because of its numerous advantages. One of such advantage is its long life span. Electrical constructed centrifuges last longer than foreign made ones.

Also, it is cheaper and saves the cost of importation. As a result of this, I recommend that some of our local materials should be utilized in construction of electrical centrifuge than importing expensive centrifuges manufactured in other countries.

Finally, I would like to recommend the use of electrical constructed centrifuges for technologists and medical laboratories for the spinning of blood samples, urine sample’s and other liquid samples.