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INTRO TECHNOLOGY PART 2
TABLE OF CONTENT
1Measuring Current, Voltage
& Power
3. Maintenance
4. Machine
5. Water flow
7. Forging
11. Abrasives
12. Glues
13. Wood work joint
1.0 Measuring Current, Voltage & power
Ability to measure
electrical quantities helps to maximize its usefulness and minimize its
dangers. With the help of measurement, manufacturers have been able to produce
appliances with known voltage, current and power rating.
A simple electric circuit
may consist of a cell connected by copper wires to cell or more resistors and
other components.
An ammeter should disturb
the circuit, into which it is connected, as little as possible. A low resistance, connected in parallel, shunts the metre.
A cell provides an
electromotive force, which sets up potential differences across the various
circuit components and drives the current through them. These components
themselves offer varying degrees of resistance to the flow of the current.
total resistance in circuit = ( 1/R ) =
1/R1 + 1/R2 + 1/R3.
Thus, in any electric
circuit there are three things, which have to be measured:
(a) Current, measured in amperes (A).
(b) Electromotive force and potential
difference both are measured in volts ( V ).
(c) Resistance, measured in Ohms (Ω).
Current is the flows of electrons in
an electric circuit.
Voltage or electromotive force is
that, makes the current to move round the circuit.
Resistance is a measure of the
opposition to the flow of current.
In the year 1826, George Simon Ohm, a
teacher of physics at
The current passing through a wire at
constant temperature is proportional to the potential difference between its
ends.
Ohms (Ω), is the resistance of a conductor
such that, when a potential difference of 1 volt is applied to its ends a
current of 1 ampere flows through it.
It follows that,
volts/ampere = ohms
Or in symbols V/I = R
Whence also V/R = I
And V = IR
A coulomb is the quantity of
electricity, which passes any point in a circuit 1 second when a steady current
of 1 is following
Thus, Coulombs = amperes
x seconds
= It
Power in an electric circuit is equal
to the product of the Voltage and the current. In other words power
Power = voltage x Current.
Power is measured in watt (W) .A
wattmeter is an instrument that is read directly in watts.
The
rate at which heat is produced by, say, an electric fire is the power of the
appliance. It is measured in watts. Thus the fire might be rated at 300watts
(or 3kw, kilo watts). The power of the fire is given by multiplying the
potential differences across it by the current through it.
The total heat produced is found by
multiplying the power of the appliance by the time for which the current flows.
If the power is watts and the time in seconds the energy is given in joules.
Thus, Energy = power x time.
Example: Find (a) the current taken,
(b) the resistance of the filament of a lamp rated at 240υ, 60w
Watt = volts x amperes
: . Amperes = watt
volts
Hence current taken = 60w
240 υ
= 0.25A
Also Ohms = volts
amperes
Hence resistance of lamp = 240 υ
0.25A
= 960Ω
Example: three resistors rated as 4
ohms, 3 ohms, and 5 ohms are connected in series with a 12 volt supply,
calculate the current flowing in the circuit and the total resistance in the
circuit?
Total resistance in circuit = (R) = R1
+ R2 + R3
= 4 + 3 + 5
= 12 ohms
From Ohm’s law I = V/R
= 12v
12ohms
=
1A
: . Total resistance = 12 Ω
Current flowing = 1A
Example: Two resistors 2ohms and 4
ohms are connected in parallel and in series with a third resistor of 3 ohms in
a circuit supplied from 12 volts supply. Calculate the total current flowing in
the circuit and the electrical power consumed.
Total resistance = (1/R) = 1/R1
+ 1/R2
= 1/2ohms + 1/4ohms
= 2 +1
4
: . R
= ¾ or 0.75 ohms
Total
resistance in circuit = 0.75 + 3ohms
= 3.75 Ω
From ohm’s law I = V
R
= 12v
3.75 Ω
= 3.2 Ω
Electrical power = volts x current
= 12 x 3.2 Ω
= 38.4 watt
Or
= 38 w
Consumers of electricity from the
mains pay for the electrical energy they use. The energy used is recorded on a metre, which can be found where the mains supply enters the
house. The total cost is found by multiplying the number of units use by the
cost per unit. For example, one unit cost N 14.
Example: Find the cost of running a 3kw
electric energy for 4 hours?
Cost
= power x time x cost per unit
=
3kw x 4 hours x N14
= N
168.ook.
Anything, which is able
to do work, is said to possess energy, and therefore energy is the capacity to
perform work.
Work and energy are, of
course, both measured in the same unit, namely, joules.
The world we live in
provides energy in many different forms of which the most important has been
chemical.
The law of conservation
of energy stated that energy is never destroyed but, is only transferred from
one form to another.
The forms that energy
exists are heat, chemical mechanical, electrical, light, and nuclear e.t.c.
For example electrical
energy can be changed into heat, light and sound by using the following
electronics appliances; heater, electric iron, Bulb, radio, electric, bell,
electric stove e.t.c.
While, chemical energy to
heat energy can easily take place by wood, coal or charcoal, kerosene and gas.
2.1 Electric to heat energy
The basic principle of
these appliances is that a heating element is built into them. The heating
element is made of a material with high resistance and high melting point.
As current flows through
the current, the immense electrical energy used to overcome the high resistance
is turned into heat energy and the heat thus produced is used in ironing,
cooking or boiling water as the case may be. The high melting point property of
the element enables it to withstand the great heat.
The heat produced is
proportional to the circuit resistance. It is also proportional to the square
of the circuit current.
Heat energy = I2
R t
Example: A heating coil has resistance of 1.5 Ω and is supplied with a current of 5A
for a time to of 10 minutes. Calculate the heat energy produced in joules?
Heat energy = I2
R t
= 52 x 1.5 Ω x 10 x 60
= 22500 j
2.2 Chemical
to heat energy
Everything you see is a
substance of some kind or another; for example when you burns candle with a flame; it
gives out light and heat. Some substance when burn changes their form, the
change is a chemical change. The two kinds of chemical changes are:
(a) A substance heated in our in air gains
mass. The substance has combined with some the air. This is called chemical
combination.
(b) A substance heated in hydrogen loses
mass. The hydrogen has split the substance and left a metal. This is called
chemical decomposition.
A chemical reaction between
substances produces a chemical change in which substances are formed.
These changes were
brought about by heating or by using an electric current.
When a substance is
decomposed it forms simpler substances.
If a substance cannot be
decomposed by any chemical means, it is an element (an element is a substance
which cannot by any known chemical process be split into two or more simpler
substances).
Element combine together
to form compounds. When element combine with other elements to form a compound,
there is an increase in mass of the mass of the element to the mass of the
compound. Compound can be decomposed to form elements.
The commonest method of
obtaining heat is by burning fuels. Fuels are group into solid, liquid and gas.
Solid fuels such as wood and charcoal are complex compounds of carbon,
nitrogen, metal and sulphur while; gaseous fuels of
various types are compounds of hydrogen and carbon. The gaseous fuels are
usually referred to as hydrocarbons.
During the combination
process heat is released.
Example: An electronic
appliance was related 25v, 5w, used for 3hrs. Calculate the total heat energy
produced by this appliance in the stated period?
Heat energy produced = I2
R t
P = V x I
From Ohm’s law
: . w = V I
w/v
= v I/V
w/v
= I
Or
I = w/v
I = 5w/25v
=0.2A
I = V/R
From Ohm’s law
: . I R = V
I R / I = V/I
R = v/I
= 25v/0.2A
= 125 Ω
H.E = I2 R t
: . H.E = (0.2) 2 x 125
x 3
=
0.04 x 125 x 3
=
15j.
Ass. For evaluation
1. Heat energy is I2 R t
: . H.E = (0.2) 2 x 125 x
180 x 60
= ?
2. (a) Draw a
simple circuit showing resistors in parallel?
(b) Four resistors rated as 5 Ω, 6 Ω and 2 Ω are connected in parallel and in
series with the fourth resistor of & Ω in circuit supplied with 12 volts.
Calculate the total current flowing the circuit and power consumed.
3. State and explain the law of
conservation of energy?
4. State the three items to be
measured in a given circuit and their units?
Solution
1.
H.E = 54000j.
(b) 1/R = 1 + 1 + 1
5 6 2
= 6 (1) + 5 (1) + 15
30
= 26
30
= 0.67 Ω
Total resistance = 0.67 +
8
=
8.67 Ω
From ohm’s law I =
V/R
=
12/8.67
=
1.38A
: . Power = V I
=
12 x 1.38
=
16.56 w
3. The law of conservation of energy
stated that energy can neither be created nor destroyed, but be changed from a
form to another.
4. (i) Current measured in amperes (A).
(ii) Electromotive force and
potential difference both measured in volts
(V).
(iii) Resistance, measured in Ohms
(Ω).
Maintenance
simply means taken care of goods that are in used, for their value and beauty
to remain.
Two methods are employed in
-
Maintaining
goods in used, these are:
-
Preventive
method.
-
Corrective
method.
Preventive method is
carried out in order to prevent goods in use from breaking down. Preventive
method is the avoidance of breakdown by regular taken care of the goods.
Corrective method is
carried out after goods have been broken down.
3.1
Domestic goods
Domestic goods has classified into
three, these are:
-
Furniture
-
Kitchenware.
-
Electronic
appliances
The materials used are producing
these goods are: wood, metal, plastic etc. in maintaining these goods
consideration must be given to the materials used in producing the goods.
3.2 Mechanical
goods
Mechanical goods are goods that
consist of during arm, fixed pivot and driven arm; anytime you push the driving
arm, the pivot activate the movement and makes the driving arm execute the
good.
The working of the
driven arm against the driven arm, cause wear, tear and heat, all
resulting from friction. If the wearing, tearing and heating, continuous there
will be failure of the goods. Avoiding the failure means maintaining the goods.
In maintaining mechanical goods, one
of the two ways is employed, the two ways are:
-
Oiling
-
Greasing.
The application of any of the two
avoids the occurrence of wear, tear and heat. The application means, one is
lubricating the mechanical goods and lubrication of frictional force.
4.0 Machines
Machine is any device by means of which a force applied at one
point can be used to overcome a force at some other point.
Lever: -
The
simplest form of lever in common use is a steel rod known as a crowbar but the
team lever may be applied to any rigid body, which is pivoted about a point
called the fulcrum. A force called the effort is applied at one point on the
lever and this over comes a force called the load at
some other point.
Mechanical advantage: -
M.A
= load
effort
If a lever can be used to overcome a
load of 50N by applying an effort of 10N, the lever is said to have a
mechanical advantage of 50/10 or 5.
Some
machine are designed to overcome a load much greater
than effort used, for example, a spanner used to undo a tight bolt or a screw
jack to lift a motor car. In such cases the mechanical advantage is greater
than 1.
In
certain other mechanical advantage is less than 1, in these; the effort is
greater than load. It is not generally realize that a bicycle is a machine with
mechanical advantage is less 1. Under ordinary conditions the resistance of the
motion of a bicycle along a level road, is comparatively small and there fore,
a large mechanical advantage is unnecessary. Thus, although a cycle list works
at a mechanical disadvantage.
In
another word, a machine can be best described as a device for doing work. It
receives energy and uses it or converts it to new work. A motor vehicle is a machine in as far as it receive energy of fuel and changes
this in to propelling force at the driven wheel, so that the vehicle can
transport load from one place to another. A spanner is a simple machine.
In
all machine a certain amount of power is lost in over coming friction. The lower the frictional losses the higher the efficiency of the
machine.
Work done by a machine is given as:
Work done =
load x distance
Work put in to machine is given as:
Work
in put = force x distance
Efficiency =
work done by machine
|
Efficiency = |
work put in to machine
Efficiency maybe expressed as a
percentage.
The ratio of the load moved to the
corresponding effort required is called the force ration or mechanical
advantage.
Force ratio =
weight = mechanical advantage
effort
The movement rations or velocity ration is the relationship that the movement of the driving force bears to the movement of the output or load.
Movement
ratio (V.R) = distance input
istance output
Efficiency can be calculated for the
force ratio and the movement ration.
Thus:
Efficiency = force ratio
Movement
ratio
= Force ratio
x 100
Movement ratio
1
=
M.A x 100%
V.R
Example
A
lifting tackle requires a pull of 250N to left a mass of 600kg. A movement of
1m at the handle produces a lift of 0.005m at the load. Find:
(a) Velocity ratio
(b) Mechanical advantage
(c) Efficiency.
Solution:
(a) V.R = Movement of pull
Movement of load
= 1
0.005m
= 200
(b) M.A = load
Effort
= 600
x 9.81
150
=
39.24
(c) Efficiency = M.A x 100
V.R
1
= 39.24 x 100
200
1
= 19.62%
Flow simple means run: water flow means how water run
from one point to another. It is important to know the water flow for purpose
of designing or selecting a practical, efficient and economical piping system
for water supply.
The water engineer needs a good
understanding of all these phenomena in order to design a pipeline system that
will deliver water to our houses satisfactorily.
Types of flow
The
manner of flow of water could be classified into two main types;
(a)
An
almost free and peaceful flow called “laminar flow”.
(b)
A
force flow which lead to what is called “Tinbalent
flow”
Laminar:
- in this flow all, portion of the water more in paths parallel to the
confining surface; of a drain channel like the steel gutter or ever the
ordinary flood track in the community is observed immediately rain begins to
falls, it will be seen that the first course of the flood is usually slow and
smooth, especially if rain is not a very heavy one. If object is carried, `it
would not strik the walls of the channel, instead it
would more at the same low velocity as the water carrying it and always moving
parallel to the sides of the channel in which the water is flowing .
Turbalent:- During a rainfall the
velocity of the flood either in the drain channel or in the flood –tract
is initially low. Gradually the flood begin to gather
speed until we begin to hear the noise made by the flood as it flows down the
drain. By this time, the flood has acquired a very and a greater force capable
of moving hearly objects. This type of flow is said
to be turbalant.
The water particles are unable to flow in straight lines.
Instead, cross each other and move from side tom side within the wall of the
gutter or drain.
When water flows at high velocity in large main supply
pipes, the flow is usually, turbulent, it also occurs ate high speed in narrow
pipes. Therefore when water supply lines are designed and built, the jointing
cycles of pipes are not at high angle but at an cycle
to the main.
This is done in order to reduce the effect of the force of
the turbulent water flow in the pipes as this force may be sufficient to burst
the pipes.
5.2
VISCOSITY
When fluids flows in a pipe
line the velocity of the fluid at the center of the pipe is greater than that
of the fluid adjacent to the pipeline walls or boundary surface. This
difference is velocity occurs partially as a result of friction between the
fluid and the boundary surface or wall of the pipe. This (friction) resistance
to flow is called viscosity. This viscosity is that property of a fluid which
determine it ability to resist the shearing force (or frictional force) between
fluid layers.
Velocity at point x are less
than that of point A. all real fluid possessed velocity. Viscosity result
fundamentally from cohesion and molecular momentum exchange between fluid layer and as flow occurs there effects appear as tangential
or shearing stresses between the moving layers.
Viscosity varies widely with
temperature in liquid; viscosity decreases with rising temperature and in gases
viscosity increases with increase in temperature.
ASSESSMENT FOR EVALUATION
1. Define
velocity?
2. Define
viscosity in liquid flow?
3. State
the two methods of maintenance?
4. What
are mechanical goods?
5. What is
machine?
6. Define
movement ratio or velocity ratio and give it mathematical expression?
SOLUTION
1. Velocity
is defined as the rate of change of distance moved with time in a specified
direction (or rate of change of displacement).
2. Viscosity
is that property of a fluid, which determine it ability to resist the shearing
forces (frictional force) between fluid layers.
3. –
Preventive method.
- Corrective method.
4. Mechanical
goods are goods that consist of driving arm, fixed pivot, and driven arm;
anything you push the driving arm, the pivot actuate the movement and makes the
driven arm execute work.
5. Machine is any device by means of
which a force applied at one point can be used to overcome a force at some
other point.
6. Movement
ratio or velocity ratio is the relationship that the movement of the driving
force bears to the movement of the output or load.
M.R or V.R = distance input
distance output.
6.0 PRELIMINARY SITE OPERATIONS
6.1 SITE
INVESTIGATION : -In
major building operations, the investigation of the side involving the soil,
the type of terrain, topography
obstructions, subsoil installation proximity to existing properties etc. is
carried out at the design stage by the designing group. For the purpose of
tendering for such a contract, the contractors, in his own
interest, also carries out these aspects of site investigation.
It is however, essential and
advisable on the part of the builder to examine the proposed site before
building operations start in order to ensure that some
statutory regulations are not countermarked.
6.2
ADVANTAGES OF SITE INVESTIGATION
a. Saves the contractor from future
legal tussles with the legal authorities and / her occupancies of adjacent
property.
b. Gore-Warms the contract of the types
of problems to be expected during the operation and enables him to take steps
in advance to solve them.
c. Presents unnecessary danger to
workers, through proper planning of the operations.
6.3
SITE CLEARANCE.
Site clearance is necessary for all
types of buildings. It the new building is to be built on an area where a
building already exist the old building has to be demolished, the debits
cleared away and existing service discounted and removed. Demolition does not
come within our present level. Origin site have to be cleared of grasses,
trees, rocks and old vehicles. The disposal of this rubbish may constitute a
problem to the contractor in heavily populated and congested city sites.
In terms, some, trees have
preservation orders on them. It is an offence to destroy such trees and the contractor
can be heavily denied for the offence. Enquiries should to the town planning
office to ascertain that trees with preservation orders do not exist within the
proposed site before clearance is started.
6.4 SITE LEVELING : - After the clearance of the site it has to be
leveled, many building site were originally parcels of land used for
cultivation of farm crops, and often certain moulds and ridges. These has to be leveled to assume a certain surface before
the setting out of the building can be accomplished. Nowadays
mechanical are
invisibly used for the purpose, except where the building is in small domestic
type. This stage
of leveling the site is usually refered to as
“reduced level” and it involve cutting high area of the soil and
fitting up the lower area within the site.
6.5 SETTING OUT: - in building contract, the planning
of the project and its design are often done before the builder or the
contractor is selected. This means the contractors will have the task of
interpreting the design provided by the designer. This is the setting out of
the of the building demands careful consideration right from the earliest
stages of the contract. Setting deserves the attention of an expert as mistake
may prove too costly for the contractor to amend at a later stage.
Correct setting out should ensure
that:
a. The building faces the right
direction.
b. The building is erected on the
correct plots of land.
c. The overall sizes (Length and breath)
are according to these shown on the drawing.
d. Regard is paid to the local building
line.
6.6 METHODS OF SETTING OUT.
In setting out simple building use
may use one of
these methods. Theses are :-
a. The 3:4:5 methods.
b. The builders square methods.
c. Leveling instrument.
A. 3:4:5 Method:-
1. Marked out the building line the road
by measuring the required distance from the center of the road, or by stretching a
line along the existing building to the proposed site. The building is then
represented by a line known as the ranging line, which also marks the front
wall of he building as shown in GG
2. Marked out overall length of the
building by
driving in pegs at A
and B, along the ranging lines.
3. Procure two steel tape measures and
mark out four equal distances on the ranging line starting from the corner peg
at B. the distance may be in any unit of measurement, i.e. mm, cm, m e.t.c.
4. Pull a tape measure from B to C and
ask assistance to hold it it readily with a hammer
and a peg.
5. Pull the second tape from the fourth
market D ton the ranging line to point E on the first tape.
6. The distance 5m, if using meters, on
tape DE should concile with the point 3m, on tape
BEC, to prove that the angle B is 900. if this does
not happen , th tape BC is either 5m, on the outwards
or inwards until 5m, on the second tape coincile with
the 3,mark on the first tape.
7. Report of the same procedures to
obtained the right angle for BAF, and marked out the overall bidths of the building.
8. Establish cover pages and erect profiles.
9. Marks the position of partition walls
on the profiles with either nails or saw cuts, ranging lines are stretched
through this wall and the cover pegs to mark the ground to indicate the line of
excavation for the foundation trenchers
B. The building squares methods:-
1. Set out the from or the building in the usual manner with pegs or
mark at the required distance.
2. Place the builders square so that the
front line touches on side of the square right through the lengths as
3. Stretch a line from
the corner pg so that it is parallel to the second side of the square and
establish the third peg. A corner with an angle of 900 is there by obtained.
4. With the aid of a tape measure, mark
out the length and breath of the proposed building.
5. Transferring the builders square to
the remaining corner and repeating the above operations a simple rectangular
building can be set out.
6. After establishing the corner pegs
profiles (separate or continuous) may be erected in the same way as described
earlier.
C. Leveling
instrument.
1. The front or the
building line is set out in the usually manner with pegs or marks at the
required distance shown.
Peg (1) Front line Peg (2)
_____ _____ ___ ______ ____ ____ ____ ____ ____
2. Set up the tripod at
no. 2 peg so that the datum rod is directly over the peg or mark, which
represents the corner point. Make sure that the legs are firm on the ground.
3. Release the spike
screw and extend the spike so that it site firmly on the nail or mark. Tighten
the screw.
4. Before mounting the
instrument on to the tripod head, ensure that the locking screw is tightened.
Screw on the site square. Release the locking screw. By rotating the site
square, the lower telescope along the front or building line. Tighten locking
screw.
5. Check the circular
bubble over the top of the instrument. This will probably be found to be
“off – centre”. To correct this, release tripod leg screws
and adjust the instrument until the bubble comes into the centre of the block
circle. When this is achieved, tighten the tripod leg screw. The instrument is
now ready for use.
6. Sight on to peg no.
1.through the lower telescope to obtain the “ dead on “ position by
means of the fine setting screw which moves the left and by tilting the
telescope up or down.
7. When this position is
obtained, measure the distance required to peg no.3
now by sighting through the top telescope, taking care not to rotate the
instrument to the right or left signal an assistant to move the peg side ways
until it is “dead o”. Peg no.3 is now positioned at an angle of 90o.
8. By moving the site
square to peg no.3 and “lining up” on peg no.2 the remaining corner
peg no.4 can be set out using the procedures already given.
9.
Profiles can be marked easily by tilting the telescope upwards, having sighted
on to the peg, and placing a nail in the “dead on” position on the
profile board.
6.7 Trench excavations:
After setting out the
building and fixing the profiles, the next operation will be the excavation
takes in various forms depending on pun the types of foundation to be laid.
Striping foundation requires the excavation of steps trenches, pod or isolated
foundation require holes dug where the foundations are to come only, unless
connected by ground beans, while drafts and basements need the excavation of
the whole areas of the building referred to as bulk excavation.
Excavation work may be done by
hand or machine. For ordinary house building, hand excavations are most
commonly used, while larger excavations are done with the aid of mechanical
excavations.
When
trenchers are being excavated to depth likely to cause the caving in of the
sides they must either be given some from of temporary support or the sides
sloped to provides self support. The
support given to the sides of the trench and the soil condition. Weak
soils will require more elaborate temporary supports most temporary supports
take the form of time baring the sides. As timbering the sides is only meant to
support the sides of the trash until all foundation work is complete, over
– timbering should always be avoided so that progress of the work is not
hampered in anyway.
To lay the foundation concrete the
following procedures are a followed:
(a) Bottoming:- this is achieved by cutting high portions of the bad of
the excavations, filling low places and compacting the loose earth. This
operation is necessary in order to ensure that the concrete rest on a flat,
solid bed, thus minimizing the possibility of differential settlement.
(b) Pegging:
- to maintain an even thickness through out the foundation page are driven in
to the bad of the tranch, learing
them projection, to a depth equal to the despaired thickness of the concreate. During the laying, the concrete is tamoed down to the level of the page.
(c) Wetting:
- during the dry hot season foundation trenches must be thoroughly wetted
before powering in the mixed concrete. If this is not done, the water in the
concrete will be quickly absorbed by the dry soil of the trench with the result
that the concrete will develop false setting, producing a weak foundation.
(d) Pouring the concrete:- Concrete must not be poured from a height that will allow
the segregation of the consituent aggregations. If
the trench is deep and laying is being done manually,
the concrete should lowered in buckets and not poured direct from the wheel
barrow at ground level. After pouring, the concrete is spread with a spade and
roughly tamped down to the required level. The foundation is then allowed to
curve and again strength before starting work on the walls that rest upon it.
6.8 FOUNDATIONS:
Is
the lowest parts of the walls of a building. They may be formed of
stone, concrete e.t.c.
Although the most common material is
modern construction is concrete. The pressure imposed by the foundations of a
large building is considerable and where there are weak portios
of substrata, the foundations may fail during the process of eventual
settlement.
The purpose of a foundation is to
support the building transmitting the weight of the building, both live and
dead weight to the subsoil without failing as long as the building lasts. A good
foundation should not:
(a) Break under a load.
(b) Be destroyed by roots of trees.
(c) Be affected by the presence of water.
There are many types of foundation,
each one being selected according to the type of condition and the load
expected to be carried. For our purposed, it will suffice to limit our
discussion to the common ones with which we are bound to deal. These are:
1. Strip foundation.
2. Pad foundation.
3. Raft foundation.
4. Pile foundation.
Strip foundations, as the name
implies, are continuous strips of mass concrete or reinforced concrete or
stones laid at a pre – determined depth below ground level and a long the
positions of the load bearing walls only. These types of foundations are
suitable for boundary walls, retaining walls and domestic building of not more
that three storeys.
Footings, which are then enlargements
of the bottom courses of the wall, may be used in conjunction with strip
foundation with the aim of spreading the imposed loads rarely used nowadays,
probably because of the cost and the fact that strong and better concrete is
now produced.
Pad foundations, may be circular
rectangular or square in section. The most common are square. The May but
reinforced concrete pads are generally used to support isolated loads such as
those in columns, piers, and heavy machinery in factories.
Raft foundations, the name for this
foundation is derived from the raft, which is used to cross a river. The
foundation consists of a continuous reinforced concrete slab under the whole
building. The foundation uses the principles of a floating raft and the weight
of the building is evenly distributed over a large area so that no particular
area is made to receive hearier loads.
Pile foundations,
the construction of pile foundations is beyond the scope of this syllabus.
6.9 WALL CONSTRUCTION:
Bonding:
Walls built with stones, blocks and bricks consist of individual units. For
such walls to fulfill the functions expected of them, i.e. to be strong and
durable, the unit blocks or stone must be arranged in a pre – determined
pattern which must present a pleasant surface appearance and at the same time
eliminate, as far as possible, straight joints.
Load – bearing walls must
always be bonded. Several bonds are in use which give
quite pleasant elevational appearances. Bonding is
not only applied to the individual units in the course, but the entire courses
in the wall. Other there is more than on solution to a bonding problem. The
craftsman will select the one, which is most appropriate.
TYPES OF BOND:
There are many types of bond in use
by the bricklayer but for our purpose we shall be concerned only with the most
important. These are as follows:
(a) English bond: This consists of
alternate courses of headers and stretchers. The bond has no straight joints
internally or externally and it is considered one of the strongest bonds. It is
suitable for the construction of load – bearing walls and for places
where straight is of utmost importance.
(b) Flemish bond: This consist of alternate hearders
and stretchers in the same course. Flemish bond is said to give more attraction
face appearance than English bond as it appears less monotonous. It affords a
saving in facing bricks because of the headers.
(c) Stretcher bond: As the name implies this consists
of only stretchers on the face elevation except at corners ends. The lapof bricks in one course is half
the length of the brick in the preceding course. This is the bond most commonly
adopted in the construction of block walls.
TYPES OF WALL
1. Partition wall.
2. Load – bearing wall.
3. Gable wall.
4. Earth – retaining wall.
6.10 DAMP PROOF COURSE:
This
refers to the incorporation of damp resistant materials in a solid concrete
floor.
The membrane is laid on top of the
structural concrete floor and the screed topping as then laid over it.
Materials used include sheets of polyvinyl chloride, polythene, building paper
and bitumen between two sheets paper. Membrane D.P.C in the
walls.
Forging
is the process of shaping metals by hammering them. To do this the metals are
made plastic by heating them and the shaping process takes place whilst they
are hot. Forging is the craft of the blacksmith and it is the oldest method of
metal.
7.1 MATERIALS USED IN FORGING:
|
Metal |
Forging temp. range oc. |
Remarks |
|
Wrought iron |
860 – 1340 |
Easily forged since it possesses
ductility and malleability. |
|
Mild steel |
820 – 1290 |
Readily forged. Stronger than
wrought iron. |
|
Medium - carbon steel |
760 – 1250 |
Reasonably easy to forge but, not
so easy as mild steel. |
|
High – carbon steel. |
760 – 1130 |
More different to forge than any of the preceding
metals. Because of small range forging temperatures any easily be burnt and
spoiled. |
|
Aluminum alloy |
380 – 450 |
Wrought alloys are very suitable
for forging used in the aircraft industry. |
|
Brass |
600 – 800 |
Readily forged. |
7.2 NON – FORGING MATERIALS:
Some
metals are apt to break and crumble when hammered at red heat. Such metals are
called “red short” and are unsuitable for forging. Cast iron is
such a metal and cannot be used for any forging.
The effect of forging:
When steel is forged the original
crystal structure is deformed in effect the crystals are drawn out into threads
and the resemblance to the grain of wood is most marked. The forged metal is
very strong in the direction of the grain flow but, it is weaker in a direction
at right angles to the grain floe.
Many chemical substances are
naturally crystalline.
(a)
By
cooling a substance, which has been molten, until it solidifies.
(b)
By
allowing a substance, which has been dissolved in some other substance, to come
out of solution (e.g. evaporating salt solution).
7.3 RECRYSTALLIZATION
When
a piece of lead is squeezed between a pair of rolls, the act of squeezing it
causes the originals crystal structure to break down and be replaced by fresh
one. The lead has recrystalized itself. For this
reason lead remains soft after squeezing, rolling or bending it. There is no
need to heat the lead, it will recrystallise when
worked in cold place or state.
Steel and other metals however will
not recrystallize in the cold state. The action of
rolling them causes the crystals to elongate. An elongated and distorted
crystal structure of this kind makes the metal harder stronger so that it is
more resistant to further cold work. We say that the metal has been “ work hardened”.
When steel is
heated it recrytallizes. If the steel is heated to two high
temperature the crystal size will increase and go on increasing ( until it becomes too large ) as the steel cools down. At
too low a temperature the steel will not recrystallize
properly. Therefore, when heating the steel we must pay particular attention to
the temperature used.
A large grain or (crystal) size gives
a soft, weak steel whilst a small ( or fine) grain
size gives a harder, stronger metal.
It is the rate of which the steel is
cooled which determines the final crystalline structure of the steel. A very
slow cooling rate produces large crystals and hence a soft, weak metal. A fast
cooling rate produces small crystal and hence a hard, strong metal.
7.4 HEAT TREATMENT OF STEEL
Sometimes
we need to soften steel so that it becomes easier to work. After other times we
may need to harden steel so that it resist wear or so
that it can cut other metals. These properties can be given to a steel by suitable heat treatment. The heat treatment
takes:
1. Annealing.
2. Normalizing.
3. Hardening.
4. Tempering.
Annealing:
This is done to soften the steel so thaty it becomes easier to work. The steel is heated to the
required temperature and it is held at this temperature for a short time. It is
then cooled very slowly. If the heat treatment takes place in a furnance, the cooling may be done by leaving the work in
the furnance and cooling both furnance
and work together. If this is not possible, the work may be cooled in sand or
ashes, as these materials prevent them from escaping too quickly. The
temperature to which the work is heated varies with the carbon content of the
steel.
Normalizing:
After steel has been worked it may
not be as strong and as hard as it should be and it may also be strained ( i.e. have distorted crystal ). To bring the metal to its
original and best condition for use in service, it is normalized. The steel is
heated to the annealing temperature and held at this temperature for a short
time. It is then cooled in air. Thus the cooling rate is much quicker for
normalizing than when annealing. The effect is to make the crystal size
smaller, thus increasing the hardness and toughness of the steel.
Hardening:
To harden steel we heat it to the
annealing temperature and quench it in water or oil. Thus, the cooling rate is
very quick and a very fine grain structure is obtained. Water causes the steel
to be harder than does oil, but with some jobs, quenching
in water may cause the work to distort and crack. Steel containing less than
0.3% carbon are seldom hardened because the amount of hardening obtained is too
small to be of any account.
Tempering:
A steel which has been hardened is
very brittle and it will crack and chip when used. This is particularly true of
cutting tools. Tempering, that is reheating the steel and the quenching it,
takes away some of this brittleness and makes the tool tougher. The temperature
to which the steel is heated depends upon the use to which the article is to be
put. This temperature is always lower than the annealing temperature. It should
be noted that the tempering causes the hardened steel to become softer,
the higher the tempering
temperature, the softer the steel will be. The tempering temperature is
sometimes judges by the temper colour which appears on the fleshly polished
surface of steel when heated. This temper colour appears because the tin oxide
film on the surface of the steel changes colour. It is not a heat colour in the
true sense.
7.5 SIMPLE FORGING TOOLS
A. Hearth forge:
This is popularly known as the
blacksmith forge. It is mainly used for its main purpose; it is to produce the
fire or heat for heating metal so that it can be formed to the desired shape.
The forge may be built of bricks or cashing or mild steel. It may also be built
with a combination of all these materials. It is provided with a small bore
called the hearth which hold the fire.
Coal or charcoal could be used as the
fuel.
B. Anvil:
Services as a
workbench to the blacksmith where all metals to be beaten are placed. It should
be strong to withstand blows and shocks arising from the hammer blows.
The anvil is made up of mild steel.
The flat top has two holes. The wide one is called the hardie
hole. The hardie hole is used for fitting square
shank of the hardie, while the smaller one is used
for clearance when punching holes in hot metals.
C. Chisels:
Is of two
types namely cold chisel and hot chisel.the cold chisel
is used for cutting cold metals while, hot chisels are for cutting metals when
hot. Therefore non should be used in place of the
other. Chisels are usually made from high carbon steel whose cross-section is
an octagon.
D. Tongs:
They are used by the blacksmith for
holding hot metals securely. The mouths are made in various shapes of hot
metals. The common types are: Open mouth, Close mouth, Hollow bit, Square mouth
and Pick up tong.
E. Fullers:
Forming tools
of different shapes used in making groovees or
hollows are called fuller. They are often used in pairs. The bottom has shank
which fits into the hardie hole in the anvil. The
process of using these fullers to do work is called fullering.
The work is placed on the bottom fuller and the top fuller is placed on the
work and struck with hammer.
These
are four ways of joining metal piece together. They are: soldering, riveting,
mechanical fastening and welding.
8.1 SOLDERING
Soldering
is a method of joining metals by uniting them by means of an alloy.
There are two types of soldering:
(a) Soft soldering.
(b) Hard soldering.
When solder melts below red heat, it
is called soft soldering but, when it melts at or above red heat it is called
hard soldering.
1. Soft soldering: This type of soldering makes use of
low temperature solder. Soft soldering is applied to small parts where strength
is not important e.g. soldering of wire terminals in radio, television work.
Soft soldering is also applied on article made of tin-plate materials and some
other kinds of metal having low melting point.
There are three major kinds of soft solder:
(i) Tinsmith’s solder.
(ii)
Blow – pipe solder.
(iii)
Plumber’s solder.
These
solders have varying mixture proportions of tin and lead, varying melting
points and varying uses.
2. Hard soldering: Hard soldering is used where a
strong joint is required. There are two types of hard soldering:
(i) Silver Soldering: sometimes called
the metals is silver solder. Silver solder is an alloy
of silver, copper and zinc and is obtained in various lengths. It is obtainable
in three grades, easy flow, medium flow, and hard flow. Easy flow has the
lowest melting point and hard flow the highest (360o).
(ii) Brezing: The uniting alloy is speller. Spelter
is an alloy of copper and zinc and is obtainable in stick, ribbon, and
granulated form. Spelter is available with different
melting points, 850o – 950o .
where ease of brazing is required a low melting point spelter is used.
8.2 COMPOSITION
OF SOFT SOLDER
Basically,
soft solders are alloy of tin and lead in varying proportions sometimes, little
percentages or a proportion of a metal called antimony
is added to provide strength and hardness.
The higher the proportin
of tin a solder has, the softer it is and the lolwer
its melting point. On the other hand, the higher the proportion of lead in the
mixture, the harder the solder and the higher its melting point.
Flux – Flux is very necessary
in soldering. When metal is heated the oxygen in the air attacks the metal.
This oxide, when formed, becomes an enemy to soldering because it prevents the
metal. It has to be got rid of. Therefore flux is applied to do the
following:
(i)
To
dissolve the oxides which form on the bit and on the joint when heat is applied.
(ii)
To
dissolve the oxides on the solder so as to allow it to sun freely into the
joint.
(iii)
To
present formation of more oxide during the soldering.
Soldering bits – Are made of
copper because, is a good conductor of heat, copper retains heat and it is no
very expressive, when compared with other good conductor of heat. Lastly copper
has an affinity with solder.
Tools (bit).
(i)
Electric
Soldering: Iron (has the advantage of maintaining its heat while, switching
on).
(ii)
Hatched
bit Soldering: Iron (used for seams).
(iii)
Solder
store.
(iv)
Straight
bit Soldering: Iron (used for small work).
(v)
Brazing
hearth.
Sheet
of metal simply mean flat piece of metal. Sheet metal work is the process of
making articles with this sheet of metal whose thickness is about 5mm or less.
The type of sheet metal commonly used in sheet metal work is called tinplate.
Tinplate is made from mild steel with low carbon content, which has been rolled
into thin sheet and coated with liquid tin. Most of the tinned foods we buy
from the market are stored in tinplate container.
9.1 SHAPE
DEVELOPMENT
Is
the making of patterns of various shape. A sheet metal
worker must know how to make patterns of any articles he wants to produce.
There are two methods of carrying out
shape development:
(a) By drawing the shape of the articles on
paper and then transferring it to the sheet metal by using cardboard paper.
(b) By drawing the shape directly on the
sheet metal. This method involves measuring and scribing the lines, circles e.t.c. directly on the sheet metal.
9.2 BENDING/FOLDING
SHEET METAL
Bending
in sheet metal work means causing the flat metal sheet to have curves or angles
there by forming various shapes.
Folding is bending of metal edges,
usually done to provide an edge that is smooth and free from injuring the users
of the article.
Procedure: -
Insert the vice jaw caps or thick
paper on both jaws of the vice. This will prevent the hardened jaws of the vice
form scratching the metal surface. Then insert the metal piece to be bent
between the vice jaws already protected with caps. A mallet may be used to
knock at the mlight gauge metal while,
a hammer may be used on the thicker gauges. Remember that the thicker outline
for the bend should correspond with the top edge of the vice on the wooden
pieces, if wood is used between the vice jaws.
Folding bar is used for folding or
bending sheet metal, usually at right angles.
Insert the work between the blades
which, when released, spring tightly together and hold the metal firmly. Then
apply pressure to bend the sheet metal. In order to produce a good job, the
folding bar should be gripped in bench work.
9.3 FOLDED
AND WIRED
The
edges of sheet metal articles are thin and weak. They are also sharp and
dangerous to handle. To make them safe, the edges are folded or wired.
Procedure: -
(i)
Mark
out the folding or hammering line with a scriber and steel rule on with odd
– leg calipers or dividers.
(ii)
Bend
at right angles on the marked out folding line, isung
folding bar and mallet.
(iii)
Mallet
down the edge.
Wired: -
A wired edge is metal edge which has
been folded round with a thin wire inside the fold. At times, the folding is
done without any wire inside the fold, and it is made in such a way that one
would think that it has wire inside. When it is done, it is called false
– wired edge. As mentioned earlier, the purpose is to give entire
strength, safer and good appearance to the metal edge.
Procedure: -
(i) Mark
out the allowance for wiring. The wiring allowance is usually two and halftime
the diametre of the wire to be used. E.g. if the wire diametre is equal to 3mm
x 2½ = 7.5mm.
(ii) Band over at right angles in
either the bend vice or folding bar.
(iii) Place wire in position and
mallet the metal over it.
(v) Using a tucking hammer, bring
them to the final shape on a flat stake. The edges can also be closed by
passing the metal through a wiring machine, where it is available.
(1) Painting – The metal is cleaned of
all rust or scale and a priming coat applied. This is followed by an undercoat
of flat lead or aluminium paint. Finally a top coat
of either eggshell or gloss is applied.
(2) Lacquering – The finish of
decorative articles made from copper, gilding metal and brass can be preserved
by applying a coating of lacquer or vanish.
(3) Plating – Ferrow
metals can be given a protective coating of tin, zinc, mickel
or chromium.
(4) Lubrication – When working parts
rub together (called friction) wear takes place. Friction is greatly reduced by
the use of oil and grease. Slow moving parts are usually grease and rapidly
moving ones oiled.
Oil and grease also afford a
protection against rust.
Abrasives
are materials used for removing roughness from word surfaces. Abrasives are
used for smooth wood. This process is called sanding. Jobs should not be sanded
before planning as particles of abresive breaking
off, may clog into wood pores and damage the blade of the place.
There are three types of abresive: rough, medium, smooth.
Before having abrasive material, paper or
cloth is coated with hard minerals. These minerals include glass, flint, emery,
garment, silicon, carbide, aluminium oxide e.t.c.
Glue
is any substance capable of bonding two or more materials together.
The following are kinds of glue are
their uses:
(a) P.V.A. Glue:
The glue is a white colour and is
wildly used in wood work. It is supplied ready for use direct from its
container and has an unlimited store life. It is non
– staining and allows about ½ hour for gluing work before
beginning to harden. Work should be left under pressure for a minimum of 2
hours before it is worked. P.V.A glue is not water proof but, gives a strong
joint. It is classified as a synthetic glue.
(b) Resin glue:
Resin glue has advantages over the
other glues. It is water proof, and for this reason is used for boat building.
It is also heat resistant and does not stain. But it is available, ready for
used, in handy plastic container.
(c) Casein glue:
Casein glue is in the form of a white
powder and requires to be mixed with cold water to a thick consistency for use.
It is liable to stain ahrd wood. It is resistant to
heat and damp, but is not water proof. The glue is made from the curds of
soured milk. It is classified as an animals glue.
(d) Scotch glue:
It is an animal
glue, being made from the bones and hide of animals. It is obtained in slab
from or the more favoured pearl beads and is more
easily prepared. The slab form requires to be covered with water and left to
soak for 8 hours while, the pearl form can be covered with water and
immediately brought to simmering heat ready for use. It gives a strong joint
but, is not heat or water proof. Its greatest disadvantage is not heat or water
proof. Its requires to be used very quickly to prevent
the glue from chilling and becoming useless work pressure before being work.
The glue – pot consists of a
small container holding the glue (with the necessary water), which is placed in
ad outer pot of the water to heat the glue. The glue should not be heated above
simmering heat or it will burn.
(e) Impact glue:
They are supplied in liquid form
ready for uses. The glue is spread on both surfaces and allowed to become tacky
before bringing them together. Impact glues are heat and water-resistant.
Useful for bonding laminated plastics glues hard board to wood. Once the two
surfaces of glued are brought into contact they cannot be separated without
causing damages.
The
point at which two or more bodies meet is called joint. The art and skill
joining pieces together is called joinery.
Joint used in woodwork construction
are:
(a) Widening joints – Joining edge to
edge to produce wide boards.
(b) Angle or box joint – To fix
together pieces with faces to form right angles.
(c) Framing joint – Used for frame
construction member jointed end to edge.
13.1 TYPES
IN SUMMARIZED FORM
(1) Halving joint.
(2) Butt joint:
(a)
plain butt joint.
(b) Rebated butt joint.
(3) Baiddle
joint.
(4) Tennon
and mortise joint.
(5) Doretail
joint.
-
Butt
joint is the sunplest and the easiest to use. It is
commonly found in all roof and pre – fabricated house construction work
and simple box construction
-
Dowels
can be used to strengthen butt joint at each joint. Many table tops, chair legs
and benches have this kind of joint, sometimes with corner glued blocks.
-
Halving
joint is given to joints, where the pieces of wood to be jointed meet or cross
each other are to be halved in their thickness or widths so that the faces of
the assembled members are flush. These members jointed end to edge usually meet
at a slope or right angles. Several examples of halving joint can be seen e.g.
corner, cross, and tee joints are frequently used for p
Doors, tables, chairs, picture frames.
- Briddle
joints are simplified forms of mortise and tenon
joints with increase bearing surfaces. The joints are sometimes used in place
of mortise and tenon joints where a stronger joint
than halving joint is required e.g. the tee bridle joint are used for bracing
nails of skeleton framing, gallons, brackets e.t.c.