Harold Wakefield's engineer/fitter course notebook
Title
Harold Wakefield's engineer/fitter course notebook
Description
Contains: notes on physics of force and moments with formulae and calculations. Notes on chemistry of fuels, requirements for carburettor,. Continues with mechanics of stress and properties and chemistry of metals. Continues with geometry and drawing followed by physics of magnetism. Then is included part of a letter to Sheila followed by notes on metal alloys diagrams and graph.
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Type
Format
Multi-page notebook with handwritten entries
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This content is available under a CC BY-NC 4.0 International license (Creative Commons Attribution-NonCommercial 4.0). It has been published ‘as is’ and may contain inaccuracies or culturally inappropriate references that do not necessarily reflect the official policy or position of the University of Lincoln or the International Bomber Command Centre. For more information, visit https://creativecommons.org/licenses/by-nc/4.0/ and https://ibccdigitalarchive.lincoln.ac.uk/omeka/legal.
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Identifier
MWakefieldHE174040-171016-20
Transcription
[front cover of notebook]
1582185 A.C.2 WAKEFIELD, H.E.
123 ENTRY.
Form 714.
ROYAL AIR FORCE.
Rough Notebook for use in Laboratories and Workshops.
T. 9686. Wt. 8930. 350,000 Bks 2/41. E.J. & S. Ltd.
[page break]
[inside front cover]
[underlined] Questions & Answers [/underlined]
1/ Is a compound of iron & carbon called ferric carbide.
2/ is a laminated structure of cementite & ferride [one indecipherable word] it is the eutectoid of steel.
Solid solution is an intimate mixture of one substance dissolved in another in the solid state.
Austerate is a solid solution of cementate [sic] in it is formed when steel is heated where the upper vertical points critical or change points are these temperatures at which structural changes take place in the solid metal. Lower critical points if the temp at which the change from [one indecipherable word] steel to austenite begins (also called A.C. 1)
Upper critical point is the temp. at which the above change is complete (also called A.C. 3)
Decealascent [sic] points are the change points observed on testing the metal which appears to glow less brightly at these temperatures.
Recealascent [sic] points are change points observed on cooling the metal which appears to glow more brightly at these temps.
E is that alloy which changes completely from solid solution to normal perlite [sic] solution (or vice versa) at a temp lower than any other carbon steel it has only one critical point for example 84% carbon steel or perlite. [sic]
[page break]
[underlined] FORCE:- [/underlined] is that which will cause a body to move faster or to move slower.
The unit of force in British engineering practise is the [underlined] pound weight. [/underlined]
The pound weight is the force exerted by gravity on a mass of 1lb.
[underlined] Moment of a force [/underlined]
[sketch]
It is required to find the value of x
Sum of clockwise moments = Sum of anti-clockwise moments.
[calculations]
[sketch]
Where must a 2lb weight be placed between B & C so that the lever is just kept horizontal.
[calculations]
[page break]
[sketch]
The weight of the lever is 5lbs. Find the reaction on each support.
[calculations]
[underlined] Work [/underlined] = force x distance. The unit of work in engineering practice is the foot pound.
A crane raises 650lbs. through 25 ft. How much work has been done?
WORK = FORCE x DISTANCE
= 650 x 25 ft. lbs.
= 16250 ft. lbs.
[underlined] Power:- [/underlined] is the rate of doing work, WORK DONE PER SECOND or WORK DONE/TIME.
An aeroplane weighing 5 tons rises through a vertical distance of 1000 ft. in 5 mins. What [inserted] extra [/inserted] power is the aircraft developing during ascent?
[calculations]
[underlined] Horse power:- [/underlined] is the rate of doing 550 ft. lbs. of work per second.
H.P. = WORK DONE/TIME x 550
1/ A crane raises 55 tons of cement thro’ 66 in 2 mins. What H.P. is developed?
[calculations]
[page break]
2/. A small engine of cyl. bore 3”.8 and stroke 4” has an average pressure 50 [missing word] and makes 1000 revs per min. What H.P. is developed?
[calculations]
3/ A loco. has a mass of 120 tons & maintains a speed of 30 mph. up a slope of 1 in 100. If one slope is 2 miles long what extra h.p. is required to make the ascent?
[calculations]
[page break]
N.B. Mechanical advantage = load/effort
Vel. ratio = distance moved by effort/distance moved by load
Efficiency = work done by load/work done by effort
N.B. The efficiency is always less than 1
Efficiency = Work got out/Work put in
[sketch]
[calculations]
[page break]
Density = Wt. of 1 cu.ft of substance
Specific gravity = wt. of substance/wt. of equal substance of water.
Pressure = Force per unit are (lbs. per sq. inch)
Pressure = Force (lb.)/Area (sq.in.).
Density = Weight (lb)./Volume (Cu.ft.)
Pressure = Ht. x Density (lbs./sq.ft.)
Degree of hotness = Temperature.
1. Heat to raise 1lb. Water through 1 Deg C.
= 1 Centigrade Heat Unit (CHU)
2. Heat to raise 1lb water through 1 deg F
= 1 British Thermal Unit (B. Th. U.)
[underlined] Fuels [/underlined]
Hydrocarbons
[underlined] Mixture Strength [/underlined] - ratio of air / fuel by weight.
A/ [underlined] Chemically correct [/underlined] - ideal, worked out from chemical equation (15 : 1 for petrol).
B/ [underlined] Rich Mixture [/underlined] - contains less air than A/ 12 : 1 = 20% rich.
C/ [underlined] Weak mixture [/underlined] - contains more air than A/ 18 : 1 20% weak.
Density of a gas varies with pressure & varies inversely with temperature.
[page break]
Cylinder temperature:-
Flame rate - 1/ rapid for rich or correct mixture.
2/ slow for weak mixture.
causes high cyl. temp in [circled 2].
[underlined] Detenation [/underlined] [sic] - spontaneous ignition of part of the charge - due to high cyl. temp. & pressure.
[underlined] Over. Rich [/underlined] - 1/ take - off. Extra fuel for cooling, to prevent detonation.
2/ [underlined] Rich [/underlined] (12-1) full power, normal running.
3/ Weak (16-1) cruising under small load. Gives fuel economy.
[underlined] Energy equation: [/underlined] Total energy in a gas is constant.
Pressure energy + kinetic energy = constant.
1/ [underlined] Volatility:- [/underlined] property of vaporising easily.
2/ [underlined] Calorific [deleted] heat [/deleted] [inserted] value [/inserted] :- [/underlined] heat produced in combustion of 1 lb. of fuel.
3/ [underlined] Latent heat of vaporisation:- [/underlined]
4/ [underlined] Freezing point:- [/underlined] should be as low as possible (about -500 C to -600 C)
5/ [underlined] High anti-knock value:- [/underlined] can be raised by
[circled 1] Blending (e.g. benzole)
[circled 2] Doping (with tetra-ethyl-lead)
[page break]
Requirements of A/C carburettor.
1/ the liquid fuel must be broken up as far as possible and thoroughly mixed with the air.
2/ in normal working conditions a constant mixture strenght [sic] must be maintained.
3/ a rich mixture must be supplied for idling.
4/ extra fuel must be supplied during acceleration.
5/ provision must be made for weakening the mixture when cruising at reduced power.
6/ provision must be made for enriching the mixture for max. power & take off.
7/ means must be provided for preventing the mixture from becoming richer with increase in altitude.
8/ ice must be prevented from forming within the carburettor.
9/ as far as possible the carb. should be automatic, simple to adjust, & robust enough to remain in adjustment under service conditions.
[underlined] Idling System:- [/underlined]
[page break]
[underlined] Volumetric Efficiency:- [/underlined] = Wt. of charge drawn in/Wt. of charge filling cyl. at S.T.P.
To increase power, we raise V.E. by increasing [underlined] density [/underlined] of charge by [underlined] supercharging. [/underlined]
[underlined] Reasons for supercharging [/underlined]
1/ To increase the power of an engine of given size & weight.
2/ To maintain the sea-level power up to a high altitude.
[underlined] Acceleration:- [/underlined] Sudden throttle opening causes fuel deposition & the mixture tends to become [underlined] weak. [/underlined] Prevented by small pump discharge of fuel.
[underlined] Rated Altitude - [/underlined] that [deleted] wh [/deleted] at which full power is obtained at full throttle, with climbing boost & standard R.P.M.
[underlined] Supercharger - [/underlined]
1/ Fixed gearing.
2/ Two - speed gearing
3/ Exhaust driven turbine.
[page break]
[blank page]
[page break]
[blank page]
[page break]
[underlined] STRESS [/underlined] When a body is acted upon by a force These forces are called stress.
Stress is measured as internal force per unit [deleted] measure [/deleted] [inserted] area, [/inserted] & so measures the tendency to break.
[underlined] Measurements of stress:- [/underlined] Stress equals applied load/area transmitting load.
[underlined] Strain [/underlined] when a body is acted upon by a force it is deformed. This deformation is called strain.
Measurement of strain, tensile strain = extension/original lenght [sic]
compressive strain = contraction/original length.
[underlined] Elasticity. [/underlined] If strain dissappears [sic] when the force is removed the body is elastic.
[underlined] Relation between stress & strain. [/underlined] [deleted] W [/deleted] within the elastic limit, stress is proportional to strain. (Hookes law) Stress/Strain = Constant (E)
[2 sketches]
[underlined] Proof Stress:- [/underlined] the test piece is subjected to a specified stress for 15 secs. The stress is removed & if there is no permanent deformation the yield point must be higher than the applied stress.
[page break]
Heat treatment normally applies to high carbon steels.
Steel when heated undergoes several changes of internal structure which affect it properties. These changes in the reverse order take place on cooling only if a cooling is slow. The various changes take place at fairly well defined temps. Steel should be heated slowly. Do not insert directly into the furnace.
[underlined] Normalising:- [/underlined] object,
1/ To relieve the stresses set up by previous work, such as forging & bending &
2/ To produce a good internal structure.
[underlined] Method:- [/underlined] Heat to cherry red heat & allow to cool freely in air.
[underlined] Annealing:- [/underlined] object,
1/ To produce softest possible state when cold.
[underlined] Method:- [/underlined] heat to a cherry red heat & cool as slowly as possible N.B. The best way is to allow steel & fire to cool together, or to bury steel in the hot ashes.
[underlined] Hardening:- [/underlined] object:-
1/ To produce a maximum hardness.
[underlined] Method:- [/underlined] heat to a cherry red & cool very rapidly by quenching in water, or oil, which is less drastic.
The rapid quenching prevents the usual change of structure & traps the steel in a hard intermediate form. This form is only stable providing
[page break]
that the steel is not heated above 2000 C in use.
Tempering:- Object
1/ To relieve excessive brittleness consequent on hardening while retaining sufficient hardness.
[underlined] Method:- [/underlined] Reheat to the temp. appropriate to the purpose of the two & quench.
[underlined] Equilibrium Diagram of C-Steel. [/underlined]
[sketch]
If more than 1.8% carbon then you get cast iron. Cast iron used for piston rings, because of its high elasticity, good wearing, self-lubricating.
1/ Up to .25% carbon is always called low carbon or mild steel
2/ .25 to .7% carbon is always called medium carbon or mild steel
3/ .7 - 1.5% carbon is always called high carbon or mild steel
All known as straight steels as there is no alloy present in them.
[page break]
As the percentage of carbon increases the hardness & tensile strenght [sic] increases but the material becomes more & more brittle.
Impurities of carbon steel:- all classes of carbon steel contain small quantities of silicon sulphur & phosphorus. Sulphur causes brittleness & tensile strength. The ill-effects of sulphur eliminated by adding .5 to .7% manganese, which combines with the sulphur to form anon injurious product.
Phosphorous causes softness
[underlined] Silicon [/underlined] gives fatigue resisting properties
Silicon manganese [inserted] steel [/inserted] used for laminated springs.
Silicon chrome steels heat resisting.
[underlined] Alloy Steels [/underlined] Their strength depends more on their structure & composition than on the hardness produced by special heat treatments as in the case of carbon steels.
1/ Increased tensile strength (40 - 110 tons per [symbol] “ combined with greater ductility.
2/ Increased impact volume & greater resistance to fatigue
3/ Minimised mass effect giving increased uniformity in strength & toughness throughout large masses
4/ Anti-corrosive properties
5/ Large reduction in weight.
6/ Greater strength at high temps
7/ Less rapid quenching necessary, owing to slower critical changes consequently less risk of cracking.
8/ More difficult to produce needs special care & treatment
[page break]
during manufacture, thus more expensive.
[underlined] Alloying elements used:- [/underlined]
Nickel Ni Molybdenum Mb Vanadium V Cobalt Co Tungsten W Chromium Cr Manganese Mn Silicon Si
[underlined] Ni [/underlined] Increases tensile strenght. [sic] Lowers critical points & percentage carbon in the eutectoid. Anti-corrosive, reduces the crystal size increases the depth of hardening, gives a fine grain, no scaling (3.15% nickel gives .75% carbon in eutectoid.
[underlined] Invar [/underlined] Contains 36% nickel & is an austenitic steel i.e. critical points are below room temp. It has a low coefficient of expansion & is thus used for precision instruments.
[underlined] Non-magnetic steel [/underlined] contains 25% nickel. Is used for shafts of polar inductor magnetos.
[underlined] Perlitic Nickel Steels [/underlined] 3 to 4% nickel & .2 to .5% carbon used for core hardening (tough core, hard case)
[underlined] Chromium [/underlined] gives great strenght & hardness slows up the critical changes gives greater depth of hardness in large masses. Raises critical points & produces fine grain i.e. added strenght without loss of ductility
Chromium Steels.
1/ Less than 2% chromium if strenght & hardness & toughness required
2/ 2 to 4% chromium - for permanent magnets.
3/ 10 to 20% chromium - stainless steel.
[underlined] Nickel Chrome Steels [/underlined] When alloyed together they give increased strength & hardness combined with greater toughness & ductility. These steels must be quenched to avoid brittleness.
[page break]
[underlined] MARKING OUT EXS. [/underlined]
1/ [underlined] To disect an angle. [/underlined]
[2 sketches]
2/ [underlined] To draw a perpendicular to a line. [/underlined]
[sketch]
3/ [underlined] To disect a line. [/underlined]
[sketch]
b. [underlined] Quick method [/underlined]
[sketch]
[page break]
4/ [underlined] To draw a parallel to a given line [/underlined] (1 1/2” from it)
[sketch]
5/ [underlined] Bisection of angle - lines not meeting [/underlined]
[sketch]
6./ [underlined] Perp. [deleted] at [/deleted] [inserted] near [/inserted] end of line. [/underlined]
[sketch]
[page break]
7/ [underlined] To divide a line into 7 equal parts [/underlined]
[sketch]
8/ [underlined] To draw a square on given base line. [/underlined]
[sketch]
9/ [underlined] To contruct [sic] a regular hexagon. [/underlined] (2” across corners)
[sketch]
[page break]
10/ [underlined] Chamfer. [/underlined] Radius of chamfer 1/2”
[sketch]
11/ Draw circle of radius 3/4” In centre of circle, draw 1” [symbol]
[sketch]
[calculations]
[page break]
[calculations]
[underlined] Magnetism:- [/underlined] Natural magnet - lodestone
Artificial magnet - cobalt Steel, Nico & Alnico.
[underlined] Rule:- [/underlined] Like poles repel
Unlike poles attract each other.
A magnet is surrounded by
A [underlined] magnetic [deleted] flux [/deleted] field [/underlined]
A magnetic field is made up of a number of [underlined] lines [/underlined] of [underlined] magnetic force [/underlined] The closer together these lines of force lie the stronger is the magnetic field or flux.
Soft iron is easily magnetised & demagnetised & is more permeable to magnetic lines of force than air.
This means that when a piece of soft iron is placed in a magnetic field, the lines of force crowd into the iron increases the magnetic flux & the iron becomes a temporary magnet. The iron loses its magnetic properties on being removed from the field.
[underlined] Electricity [/underlined] An electric current is a flow of electrons.
All [inserted] material is [/inserted] made up of small particles called [underlined] atoms [/underlined]
Atoms have equal amounts of positive electricity (protons) & negative electricity (electrons)
Conductors of electricity e.g. metals.
Will lose electrons when a force is applied. This is called an Electro Motive Force (EMF) & is measured in volts.
[page break]
There must be a [underlined] potential difference [/underlined] or pressure difference between the terminals of a battery or a storage cell, before a current flows through a circuit.
This P.D. is also measured in volts.
Electric current is measured in [underlined] amperes [/underlined] (amps)
[underlined] Ohm’s Law [/underlined] EMF/current = constant
E/I = R (Resistance)
[underlined] Resistance is measured in Ohm’s. [/underlined]
If a current of 1 amp. flows through a conductor under a force of 1 volt the resistance of the resistance of the conductor is one Ohm.
[underlined] Resistance depends on [/underlined]
(1) The kind of metal
(2) Secondly on the lenght [sic] of conductor.
(3) on the thickness of conductor.
[sketch]
[page break]
[2 sketches]
[page break]
[blank page]
[page break]
1582185 A.C.2 Wakefield, H.E.
Hut No1, A Line,
A Squadron, IT.T. Wing,
R.A.F. Cosford.
Nr. Wolverhampton.
Staffs.
Tuesday.
Dear Sheila,
Many thanks for your last letter. You’re nearly as bad as Den, it took him two weeks to reply to my letter it took you ten days. I thought you weren’t going to write back. Not that it worried me!
At the moment a Flt. Lieut. is giving us a lecture on something or other, I don’t know what because I’m not listening.
[page break]
[blank page]
[page break]
Two Score Steel High Cr non-corrodable [sic] steel.
Staybright (High chromium, high nickel steel) 188 Steel 18% chrome 8% nickel This is more resistant to corrosion, is austenetic [sic] & so can’t be hardened by quenching. Hardened by cold working. Non-magnetic. Very tough & difficult to machine. Resistant to sealing at high temperature & no tendency to harden on cooling. Is used for aero-engine valves. Chromium is key element in valve steels
Molydenum [sic] - small quantities .15 to .65% produce fine grain, it also induces a uniformly fine grain or structure in steel. Thus it increases impact value greatly, gives a tougher steel which is more resistant to vibration
Tungsten is the base of all high speed tool steels (i.e. steels which retain their cutting edge to a dull red heat & also permit of heavy rapid machining operations in which a straight carbon steel would be completely softened. Tungsten raises the critical points (almost double)
2% tungsten to straight carbon tool steel gives a finer grain, a tougher material & a much more durable cutting edge. 6% tungsten used for permanent magnet steels. 14% tungsten gives normal qualities of tungsten 22% tungsten gives better qualities
Silicon is not a metal but behaves as one in steel alloys. It is present in all steels up to .33% as an impurity, gives fatigue resisting properties This good quality is increased if alloyed with manganese Silver. manganese steels are used for laminated springs.
[page break]
Silico Chrome gives great heat resisting properties Nickel Molybdenum Chrome Steel. High expansion steel used for steel inserts for valve seats The valve seats are hardened by facing with
1/ [underlined] Stellite [/underlined] Co 65% — Cr 27% — W 4% — Si 2.75% — C 1.25%
2/ [underlined] Brightray [/underlined] 80% Ni 20% Chrome.
3/ Duro-chrome Si Cr Mb
These are also used for facing rockers, valves, [inserted] stems [/inserted] tappets, cams, etc.
Vanadium in small quantities up to .25% increases fatigue resistance usually alloyed with tungsten, cobalt & mb. are sometimes added. used in valve springs.
[underlined] Cobalt [/underlined] gives powerful magnetic properties
Alnico, 15 25 & 10%
Mn gives greater depth of hardness in large masses a tough non magnetic steel used for steel helmet.
[page break]
[blank page]
[page break]
[3 sketches]
[page break]
[3 sketches]
[page break]
[line graph]
[page break]
[line graph]
[page break]
[inside back cover]
[missing words] is third alloy which completely solidifies or melts at a [missing words] lower than any of metals of which the alloy is [missing words] used & lower than any other alloy of these metals.
1582185 A.C.2 WAKEFIELD, H.E.
123 ENTRY.
Form 714.
ROYAL AIR FORCE.
Rough Notebook for use in Laboratories and Workshops.
T. 9686. Wt. 8930. 350,000 Bks 2/41. E.J. & S. Ltd.
[page break]
[inside front cover]
[underlined] Questions & Answers [/underlined]
1/ Is a compound of iron & carbon called ferric carbide.
2/ is a laminated structure of cementite & ferride [one indecipherable word] it is the eutectoid of steel.
Solid solution is an intimate mixture of one substance dissolved in another in the solid state.
Austerate is a solid solution of cementate [sic] in it is formed when steel is heated where the upper vertical points critical or change points are these temperatures at which structural changes take place in the solid metal. Lower critical points if the temp at which the change from [one indecipherable word] steel to austenite begins (also called A.C. 1)
Upper critical point is the temp. at which the above change is complete (also called A.C. 3)
Decealascent [sic] points are the change points observed on testing the metal which appears to glow less brightly at these temperatures.
Recealascent [sic] points are change points observed on cooling the metal which appears to glow more brightly at these temps.
E is that alloy which changes completely from solid solution to normal perlite [sic] solution (or vice versa) at a temp lower than any other carbon steel it has only one critical point for example 84% carbon steel or perlite. [sic]
[page break]
[underlined] FORCE:- [/underlined] is that which will cause a body to move faster or to move slower.
The unit of force in British engineering practise is the [underlined] pound weight. [/underlined]
The pound weight is the force exerted by gravity on a mass of 1lb.
[underlined] Moment of a force [/underlined]
[sketch]
It is required to find the value of x
Sum of clockwise moments = Sum of anti-clockwise moments.
[calculations]
[sketch]
Where must a 2lb weight be placed between B & C so that the lever is just kept horizontal.
[calculations]
[page break]
[sketch]
The weight of the lever is 5lbs. Find the reaction on each support.
[calculations]
[underlined] Work [/underlined] = force x distance. The unit of work in engineering practice is the foot pound.
A crane raises 650lbs. through 25 ft. How much work has been done?
WORK = FORCE x DISTANCE
= 650 x 25 ft. lbs.
= 16250 ft. lbs.
[underlined] Power:- [/underlined] is the rate of doing work, WORK DONE PER SECOND or WORK DONE/TIME.
An aeroplane weighing 5 tons rises through a vertical distance of 1000 ft. in 5 mins. What [inserted] extra [/inserted] power is the aircraft developing during ascent?
[calculations]
[underlined] Horse power:- [/underlined] is the rate of doing 550 ft. lbs. of work per second.
H.P. = WORK DONE/TIME x 550
1/ A crane raises 55 tons of cement thro’ 66 in 2 mins. What H.P. is developed?
[calculations]
[page break]
2/. A small engine of cyl. bore 3”.8 and stroke 4” has an average pressure 50 [missing word] and makes 1000 revs per min. What H.P. is developed?
[calculations]
3/ A loco. has a mass of 120 tons & maintains a speed of 30 mph. up a slope of 1 in 100. If one slope is 2 miles long what extra h.p. is required to make the ascent?
[calculations]
[page break]
N.B. Mechanical advantage = load/effort
Vel. ratio = distance moved by effort/distance moved by load
Efficiency = work done by load/work done by effort
N.B. The efficiency is always less than 1
Efficiency = Work got out/Work put in
[sketch]
[calculations]
[page break]
Density = Wt. of 1 cu.ft of substance
Specific gravity = wt. of substance/wt. of equal substance of water.
Pressure = Force per unit are (lbs. per sq. inch)
Pressure = Force (lb.)/Area (sq.in.).
Density = Weight (lb)./Volume (Cu.ft.)
Pressure = Ht. x Density (lbs./sq.ft.)
Degree of hotness = Temperature.
1. Heat to raise 1lb. Water through 1 Deg C.
= 1 Centigrade Heat Unit (CHU)
2. Heat to raise 1lb water through 1 deg F
= 1 British Thermal Unit (B. Th. U.)
[underlined] Fuels [/underlined]
Hydrocarbons
[underlined] Mixture Strength [/underlined] - ratio of air / fuel by weight.
A/ [underlined] Chemically correct [/underlined] - ideal, worked out from chemical equation (15 : 1 for petrol).
B/ [underlined] Rich Mixture [/underlined] - contains less air than A/ 12 : 1 = 20% rich.
C/ [underlined] Weak mixture [/underlined] - contains more air than A/ 18 : 1 20% weak.
Density of a gas varies with pressure & varies inversely with temperature.
[page break]
Cylinder temperature:-
Flame rate - 1/ rapid for rich or correct mixture.
2/ slow for weak mixture.
causes high cyl. temp in [circled 2].
[underlined] Detenation [/underlined] [sic] - spontaneous ignition of part of the charge - due to high cyl. temp. & pressure.
[underlined] Over. Rich [/underlined] - 1/ take - off. Extra fuel for cooling, to prevent detonation.
2/ [underlined] Rich [/underlined] (12-1) full power, normal running.
3/ Weak (16-1) cruising under small load. Gives fuel economy.
[underlined] Energy equation: [/underlined] Total energy in a gas is constant.
Pressure energy + kinetic energy = constant.
1/ [underlined] Volatility:- [/underlined] property of vaporising easily.
2/ [underlined] Calorific [deleted] heat [/deleted] [inserted] value [/inserted] :- [/underlined] heat produced in combustion of 1 lb. of fuel.
3/ [underlined] Latent heat of vaporisation:- [/underlined]
4/ [underlined] Freezing point:- [/underlined] should be as low as possible (about -500 C to -600 C)
5/ [underlined] High anti-knock value:- [/underlined] can be raised by
[circled 1] Blending (e.g. benzole)
[circled 2] Doping (with tetra-ethyl-lead)
[page break]
Requirements of A/C carburettor.
1/ the liquid fuel must be broken up as far as possible and thoroughly mixed with the air.
2/ in normal working conditions a constant mixture strenght [sic] must be maintained.
3/ a rich mixture must be supplied for idling.
4/ extra fuel must be supplied during acceleration.
5/ provision must be made for weakening the mixture when cruising at reduced power.
6/ provision must be made for enriching the mixture for max. power & take off.
7/ means must be provided for preventing the mixture from becoming richer with increase in altitude.
8/ ice must be prevented from forming within the carburettor.
9/ as far as possible the carb. should be automatic, simple to adjust, & robust enough to remain in adjustment under service conditions.
[underlined] Idling System:- [/underlined]
[page break]
[underlined] Volumetric Efficiency:- [/underlined] = Wt. of charge drawn in/Wt. of charge filling cyl. at S.T.P.
To increase power, we raise V.E. by increasing [underlined] density [/underlined] of charge by [underlined] supercharging. [/underlined]
[underlined] Reasons for supercharging [/underlined]
1/ To increase the power of an engine of given size & weight.
2/ To maintain the sea-level power up to a high altitude.
[underlined] Acceleration:- [/underlined] Sudden throttle opening causes fuel deposition & the mixture tends to become [underlined] weak. [/underlined] Prevented by small pump discharge of fuel.
[underlined] Rated Altitude - [/underlined] that [deleted] wh [/deleted] at which full power is obtained at full throttle, with climbing boost & standard R.P.M.
[underlined] Supercharger - [/underlined]
1/ Fixed gearing.
2/ Two - speed gearing
3/ Exhaust driven turbine.
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[underlined] STRESS [/underlined] When a body is acted upon by a force These forces are called stress.
Stress is measured as internal force per unit [deleted] measure [/deleted] [inserted] area, [/inserted] & so measures the tendency to break.
[underlined] Measurements of stress:- [/underlined] Stress equals applied load/area transmitting load.
[underlined] Strain [/underlined] when a body is acted upon by a force it is deformed. This deformation is called strain.
Measurement of strain, tensile strain = extension/original lenght [sic]
compressive strain = contraction/original length.
[underlined] Elasticity. [/underlined] If strain dissappears [sic] when the force is removed the body is elastic.
[underlined] Relation between stress & strain. [/underlined] [deleted] W [/deleted] within the elastic limit, stress is proportional to strain. (Hookes law) Stress/Strain = Constant (E)
[2 sketches]
[underlined] Proof Stress:- [/underlined] the test piece is subjected to a specified stress for 15 secs. The stress is removed & if there is no permanent deformation the yield point must be higher than the applied stress.
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Heat treatment normally applies to high carbon steels.
Steel when heated undergoes several changes of internal structure which affect it properties. These changes in the reverse order take place on cooling only if a cooling is slow. The various changes take place at fairly well defined temps. Steel should be heated slowly. Do not insert directly into the furnace.
[underlined] Normalising:- [/underlined] object,
1/ To relieve the stresses set up by previous work, such as forging & bending &
2/ To produce a good internal structure.
[underlined] Method:- [/underlined] Heat to cherry red heat & allow to cool freely in air.
[underlined] Annealing:- [/underlined] object,
1/ To produce softest possible state when cold.
[underlined] Method:- [/underlined] heat to a cherry red heat & cool as slowly as possible N.B. The best way is to allow steel & fire to cool together, or to bury steel in the hot ashes.
[underlined] Hardening:- [/underlined] object:-
1/ To produce a maximum hardness.
[underlined] Method:- [/underlined] heat to a cherry red & cool very rapidly by quenching in water, or oil, which is less drastic.
The rapid quenching prevents the usual change of structure & traps the steel in a hard intermediate form. This form is only stable providing
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that the steel is not heated above 2000 C in use.
Tempering:- Object
1/ To relieve excessive brittleness consequent on hardening while retaining sufficient hardness.
[underlined] Method:- [/underlined] Reheat to the temp. appropriate to the purpose of the two & quench.
[underlined] Equilibrium Diagram of C-Steel. [/underlined]
[sketch]
If more than 1.8% carbon then you get cast iron. Cast iron used for piston rings, because of its high elasticity, good wearing, self-lubricating.
1/ Up to .25% carbon is always called low carbon or mild steel
2/ .25 to .7% carbon is always called medium carbon or mild steel
3/ .7 - 1.5% carbon is always called high carbon or mild steel
All known as straight steels as there is no alloy present in them.
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As the percentage of carbon increases the hardness & tensile strenght [sic] increases but the material becomes more & more brittle.
Impurities of carbon steel:- all classes of carbon steel contain small quantities of silicon sulphur & phosphorus. Sulphur causes brittleness & tensile strength. The ill-effects of sulphur eliminated by adding .5 to .7% manganese, which combines with the sulphur to form anon injurious product.
Phosphorous causes softness
[underlined] Silicon [/underlined] gives fatigue resisting properties
Silicon manganese [inserted] steel [/inserted] used for laminated springs.
Silicon chrome steels heat resisting.
[underlined] Alloy Steels [/underlined] Their strength depends more on their structure & composition than on the hardness produced by special heat treatments as in the case of carbon steels.
1/ Increased tensile strength (40 - 110 tons per [symbol] “ combined with greater ductility.
2/ Increased impact volume & greater resistance to fatigue
3/ Minimised mass effect giving increased uniformity in strength & toughness throughout large masses
4/ Anti-corrosive properties
5/ Large reduction in weight.
6/ Greater strength at high temps
7/ Less rapid quenching necessary, owing to slower critical changes consequently less risk of cracking.
8/ More difficult to produce needs special care & treatment
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during manufacture, thus more expensive.
[underlined] Alloying elements used:- [/underlined]
Nickel Ni Molybdenum Mb Vanadium V Cobalt Co Tungsten W Chromium Cr Manganese Mn Silicon Si
[underlined] Ni [/underlined] Increases tensile strenght. [sic] Lowers critical points & percentage carbon in the eutectoid. Anti-corrosive, reduces the crystal size increases the depth of hardening, gives a fine grain, no scaling (3.15% nickel gives .75% carbon in eutectoid.
[underlined] Invar [/underlined] Contains 36% nickel & is an austenitic steel i.e. critical points are below room temp. It has a low coefficient of expansion & is thus used for precision instruments.
[underlined] Non-magnetic steel [/underlined] contains 25% nickel. Is used for shafts of polar inductor magnetos.
[underlined] Perlitic Nickel Steels [/underlined] 3 to 4% nickel & .2 to .5% carbon used for core hardening (tough core, hard case)
[underlined] Chromium [/underlined] gives great strenght & hardness slows up the critical changes gives greater depth of hardness in large masses. Raises critical points & produces fine grain i.e. added strenght without loss of ductility
Chromium Steels.
1/ Less than 2% chromium if strenght & hardness & toughness required
2/ 2 to 4% chromium - for permanent magnets.
3/ 10 to 20% chromium - stainless steel.
[underlined] Nickel Chrome Steels [/underlined] When alloyed together they give increased strength & hardness combined with greater toughness & ductility. These steels must be quenched to avoid brittleness.
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[underlined] MARKING OUT EXS. [/underlined]
1/ [underlined] To disect an angle. [/underlined]
[2 sketches]
2/ [underlined] To draw a perpendicular to a line. [/underlined]
[sketch]
3/ [underlined] To disect a line. [/underlined]
[sketch]
b. [underlined] Quick method [/underlined]
[sketch]
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4/ [underlined] To draw a parallel to a given line [/underlined] (1 1/2” from it)
[sketch]
5/ [underlined] Bisection of angle - lines not meeting [/underlined]
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6./ [underlined] Perp. [deleted] at [/deleted] [inserted] near [/inserted] end of line. [/underlined]
[sketch]
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7/ [underlined] To divide a line into 7 equal parts [/underlined]
[sketch]
8/ [underlined] To draw a square on given base line. [/underlined]
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9/ [underlined] To contruct [sic] a regular hexagon. [/underlined] (2” across corners)
[sketch]
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10/ [underlined] Chamfer. [/underlined] Radius of chamfer 1/2”
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11/ Draw circle of radius 3/4” In centre of circle, draw 1” [symbol]
[sketch]
[calculations]
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[calculations]
[underlined] Magnetism:- [/underlined] Natural magnet - lodestone
Artificial magnet - cobalt Steel, Nico & Alnico.
[underlined] Rule:- [/underlined] Like poles repel
Unlike poles attract each other.
A magnet is surrounded by
A [underlined] magnetic [deleted] flux [/deleted] field [/underlined]
A magnetic field is made up of a number of [underlined] lines [/underlined] of [underlined] magnetic force [/underlined] The closer together these lines of force lie the stronger is the magnetic field or flux.
Soft iron is easily magnetised & demagnetised & is more permeable to magnetic lines of force than air.
This means that when a piece of soft iron is placed in a magnetic field, the lines of force crowd into the iron increases the magnetic flux & the iron becomes a temporary magnet. The iron loses its magnetic properties on being removed from the field.
[underlined] Electricity [/underlined] An electric current is a flow of electrons.
All [inserted] material is [/inserted] made up of small particles called [underlined] atoms [/underlined]
Atoms have equal amounts of positive electricity (protons) & negative electricity (electrons)
Conductors of electricity e.g. metals.
Will lose electrons when a force is applied. This is called an Electro Motive Force (EMF) & is measured in volts.
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There must be a [underlined] potential difference [/underlined] or pressure difference between the terminals of a battery or a storage cell, before a current flows through a circuit.
This P.D. is also measured in volts.
Electric current is measured in [underlined] amperes [/underlined] (amps)
[underlined] Ohm’s Law [/underlined] EMF/current = constant
E/I = R (Resistance)
[underlined] Resistance is measured in Ohm’s. [/underlined]
If a current of 1 amp. flows through a conductor under a force of 1 volt the resistance of the resistance of the conductor is one Ohm.
[underlined] Resistance depends on [/underlined]
(1) The kind of metal
(2) Secondly on the lenght [sic] of conductor.
(3) on the thickness of conductor.
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1582185 A.C.2 Wakefield, H.E.
Hut No1, A Line,
A Squadron, IT.T. Wing,
R.A.F. Cosford.
Nr. Wolverhampton.
Staffs.
Tuesday.
Dear Sheila,
Many thanks for your last letter. You’re nearly as bad as Den, it took him two weeks to reply to my letter it took you ten days. I thought you weren’t going to write back. Not that it worried me!
At the moment a Flt. Lieut. is giving us a lecture on something or other, I don’t know what because I’m not listening.
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Two Score Steel High Cr non-corrodable [sic] steel.
Staybright (High chromium, high nickel steel) 188 Steel 18% chrome 8% nickel This is more resistant to corrosion, is austenetic [sic] & so can’t be hardened by quenching. Hardened by cold working. Non-magnetic. Very tough & difficult to machine. Resistant to sealing at high temperature & no tendency to harden on cooling. Is used for aero-engine valves. Chromium is key element in valve steels
Molydenum [sic] - small quantities .15 to .65% produce fine grain, it also induces a uniformly fine grain or structure in steel. Thus it increases impact value greatly, gives a tougher steel which is more resistant to vibration
Tungsten is the base of all high speed tool steels (i.e. steels which retain their cutting edge to a dull red heat & also permit of heavy rapid machining operations in which a straight carbon steel would be completely softened. Tungsten raises the critical points (almost double)
2% tungsten to straight carbon tool steel gives a finer grain, a tougher material & a much more durable cutting edge. 6% tungsten used for permanent magnet steels. 14% tungsten gives normal qualities of tungsten 22% tungsten gives better qualities
Silicon is not a metal but behaves as one in steel alloys. It is present in all steels up to .33% as an impurity, gives fatigue resisting properties This good quality is increased if alloyed with manganese Silver. manganese steels are used for laminated springs.
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Silico Chrome gives great heat resisting properties Nickel Molybdenum Chrome Steel. High expansion steel used for steel inserts for valve seats The valve seats are hardened by facing with
1/ [underlined] Stellite [/underlined] Co 65% — Cr 27% — W 4% — Si 2.75% — C 1.25%
2/ [underlined] Brightray [/underlined] 80% Ni 20% Chrome.
3/ Duro-chrome Si Cr Mb
These are also used for facing rockers, valves, [inserted] stems [/inserted] tappets, cams, etc.
Vanadium in small quantities up to .25% increases fatigue resistance usually alloyed with tungsten, cobalt & mb. are sometimes added. used in valve springs.
[underlined] Cobalt [/underlined] gives powerful magnetic properties
Alnico, 15 25 & 10%
Mn gives greater depth of hardness in large masses a tough non magnetic steel used for steel helmet.
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[line graph]
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[inside back cover]
[missing words] is third alloy which completely solidifies or melts at a [missing words] lower than any of metals of which the alloy is [missing words] used & lower than any other alloy of these metals.
Collection
Citation
H E Wakefield, “Harold Wakefield's engineer/fitter course notebook,” IBCC Digital Archive, accessed April 18, 2024, https://ibccdigitalarchive.lincoln.ac.uk/omeka/collections/document/33723.
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