MECHANICAL TECHNOLOGY

GRADE 11

NOVEMBER 2011

MARKING MEMORANDUM

Question / Assessment Standard / Content covered / Marks / Time
1 / 1-9 / Multiple- choice questions / 20 / 18
minutes
2 / 6-8 / Applied Mechanics / 50 / 45
minutes
3 / 2 / Tools and equipment / 20 / 18
minutes
4 / 3 / Materials / 20 / 18
minutes
5 / 1,4 and 5 / Manufacturing Process, Construction Methods and safety / 50 / 45 minutes
6 / 7 and 9 / Pumps and Maintenance / 40 / 36
minutes
TOTAL / 200 / 180 minutes

QUESTION 1: MULTIPLE CHOICE QUESTIONS

( Learning Outcome 3 : Assessment Standard 1-9)

1.1D (1)

1.2B (1)

1.3D (1)

1.4B (1)

1.5C (1)

1.6A (1)

1.7D (1)

1.8C (1)

1.9A (1)

1.10A (1)

1.11C (1)

1.12D (1)

1.13A (1)

1.14C (1)

1.15B (1)

1.16C (1)

1.17B (1)

1.18A (1)

1.19B (1)

1.20C (1)

[20]

QUESTION 2 : APPLIED MECHANICS

( Learning Outcome 3 : Assessment standards 6 and 8 )

2.1.1Clockwise moments = Anti-clockwise moments

(Y x 6.2)+ (40 x 3) = 80 x 3.5√

6.2 Y + 120 = 280 √

6.2 Y = 280 – 120√

Y = 160 √

6.2

= 25.8 N√(5)

2.1.2Load on support = Total of all downward forces

Load = 80+40+ 25.8 √

= 145.8 N √ (2)

2.2.1Take moments about reaction left (RL)

RR x 8 = (1N x 2 m) + (4N x 3 m) + (2N x 6 m)√

RR = (2 + 12 + 12) √

8

RR = 3,25 N√

Take moments about reaction left (RR)

RL x 8 = (2N x 2 m) + (4N x 5 m) + (1N x 6 m)√

RL = (4+ 20 + 6) √

8

RL = 3,75N√(6)

2.2.2Bm A:(3,75 x 2) – (1 x 0)√= 7,5 Nm√

Bm B: (3,75 x 4 ) – (1 x 2) – (4 x 1)= 9 Nm√√

Bm C: (3,75 x 6) – (1 x 4) – (4 x 3) – (2 x 0) = 6,5 Nm√√(6)

2.2.3

2.3

  • Prevents concentrated loads on the tips of the teeth

during initial meshing

  • Contact between the meshing teeth takes place

very gradually

  • Much quieter than spur gears
  • Much stronger than spur gears
  • Can carry heavier loads
  • Can transmit more power
  • Drives are smooth and silent(Any 2)(2)

2.4

  • the area of contact√
  • the tension√
  • the co-efficient of friction√(3)

2.5

  • the speed of the chain√
  • the ratio between the sizes of the sprockets√
  • the centre distance between the shafts√
  • the efficiency of the lubrication√
  • the type of bearings used on the shafts√
  • the nature of the loading√
  • the ratio between the magnitude of the load and the size

of the chain√

(Any 5)(5)

2.6

  • ISO metric screw thread√
  • Acme screw thread√
  • Square screw thread√
  • Buttress screw thread√(Any 3)(3)

2.7

  • Provide a fluid storage tank
  • Promote air separation from the fluid
  • Support the pump and electric motor
  • Promote heat dispersion
  • Acts as a base plate for the mounting of control equipment

(Any 4)(4)

2.8

  • the high cost
  • their servicing must be done by a specialist
  • they are more expensive than multi-barrel carburettor

Installations(Any 2)(2)

[50]

QUESTION 3 :TOOLS AND EQUIPMENT

(Learning Outcome 3 : Assessment Standards 2)

3.1.1Outside Micrometer (1)

3.1.2 measure thickness and for measuring diameters (2)

3.1.3A.Carbide tipped anvil

B.carbide tipped spindle

C.Barrel

D.Thimble

E.Ratchet

F.Spindle lock

G.Frame

(7)

3.2.It prevents bolts or studs from breaking

It prevents bolts and nuts from loosening

It prevents castings from warping(Any 2) (2)

3.3.Taper tap

Second or intermediate tap

Bottoming or plug tap (3)

3.4

Eliminate last decimal place1,05√

Eliminate second decimal place1,90√

Make up whole numbers16,00√

75,00√

100,00 √

193,95 (5)

[20]

QUESTION 4: MATERIALS

(Learning Outcome 3 : Assessment Standards 3)

4.1

  • Work piece size√
  • Quenching rate√
  • Carbon content√(3)

4.2

  • the working area should be well ventilated and provided

withexhaust hoods.

  • goggles must be worn when working with lead, cyanide,

or nitrate pots.

  • no damp or wet is introduced into the heating pot or an

explosion could occur.

  • wear leather apron and gloves.
  • Use correctly shaped tongs when working with hot steel.

(Any 4) (4)

4.3Hardening is achieved by heating the work piece to slightly

higher than the critical temperature and then rapidly cooling it

by quenching the work piece in brine, water or oil.(2)

Tempering is a follow on process from hardening. It is a

process applied to steel to relieve the strains induced during

the hardening process and to reduce brittleness.(2)

4.4

  • Carburising√
  • Nitriding√
  • Cyaniding√(3)

4.5

  • Water and salt (brine)
  • Tap water
  • Fused or liquid salts
  • Molten lead
  • Soluble oil and water
  • Oil
  • Air(Any 4)(4)

4.6

  • Rockwell hardness test√
  • Brinell hardness test√(2)

[20]

QUESTION 5: MANUFACTURING PROCESS, CONSTRUCTION

AND SAFETY

(Learning Outcome 3: Assessment Standards 1,4,and 5)

5.1Safety on millingmachine

  • all guards in place
  • no loose clothing
  • no oil or grease on floor in front of machine
  • clamp work pieces safely and firmly
  • do not use hands to remove cuttings –use wire hook
  • never adjust the cutting tool while machine is running
  • do not lean on machine
  • do not attempt to stop machine by placing hand on the

chuckwhile the machine is slowing down(Any 5)(5)

5.2Arc or spot weldingSafety

  • Wear personal protective clothing
  • Wear correctly shaded welding helmet
  • Wear rubber-soled shoes
  • Ensure that equipment and cable are in good condition
  • Floors must be dry and rubber mats must be provided
  • Adequate ventilation to remove harmful fumes
  • All electrodes must be kept dry(Any 5)(5)

5.3 Pressure process-Resistance or spot welding(2)

Non pressure process-Arc and gas welding(2)

Casting (Thermite) process- Fusion with liquid metal(2)

Any 2 process: 1 per process

1 per example(4)

5.4Welding elements

reference line√

arrow√

weld symbol√

supplementary symbol√

dimension√

tail√

specification, process, or other references√ (Any 5)(5)

5.5.1 Flared bevel butt joint

√√

(2)

5.5.2J- Butt Joint

(2)

5.5.3Corner Flange

√ √

One mark per line(2)

5.6Leftward gas welding

Leftward gas welding involves holding the blowtorch nozzle at

60° – 70° to the joint surface and heating the joint in small circular movements until the parents metal starts to form a molten pool or keyhole. The filler rod in turn should be held in the other hand at

30°-40° to the joint surface and fed into the molten pool as it is consumed. The movement and heat of the welding flame causes the molten pool to progress along the welded joint, forming a welding

bead as it cools and solidifies. In leftward gas welding the rod

precedes the flame (from right to left if you are right handed). This method is most suitable for thin plate and general gas welding applications. (3)

Rightward gas welding

Rightward gas welding or backward gas welding is usually used for welding material 4 mm thick and thicker. Here the rod follows the flame, which tends to anneal the welded joint as the welding progresses. The rod is held at 30° -40°, with the base metal and

flame at 40°- 50°(3)

5.7.1Direction of hydraulic flow(1)

5.7.2Adjustable output flow(1)

5.7.3Pressure gauge(1)

5.7.4Shut off valve (1)

5.8

  • Facing
  • Parallel turning
  • Drilling
  • Boring
  • Taper-turning
  • Screw-thread cutting
  • Parting
  • Knurling(Any 5)(5)

5.9

  • The cutting tool must be sharp
  • The profile of the tool must be correct
  • The tool must be clamped rigidly in the tool holder
  • The centre lathe must be rigid
  • The tool must be set at the correct height
  • The cutting tool must not have too much overhang (Any 5)(5)

5.10M indicates that it is metric√

14 is the diameter of the bolt√

2.5 mm is the pitch of the screw-thread√(3)

5.11Advantages

  • Can hold a wide range of hexagonal and cylindrical work pieces √
  • There are jaws available for external and internal work √
  • You can do work on the end face of the workpiece √
  • You can easily mount the workpiece (self centering) √

(Any 2)(2)

[50]

QUESTION 6: PUMPS AND MAINTENANCE

( Learning Outcomes 3 : Assessment Standards 7 and 9 )

6.1Pump slip

  • worn external packing
  • worn internal packing
  • a strainer exposes above the fluid level
  • a faulty foot value
  • faulty or loose flanges and joints
  • a weak or faulty seat or spring valve(Any 5)(5)

6.2.1Rotor type Pump (1)

6.2.2

  1. Inlet port
  2. Housing
  3. Outer distributor
  4. Inner distributor
  5. Outlet port(5)

6.2.3

  • There are no valves or springs
  • All movements are rotational movements
  • Wear is minimal
  • Operation of the pump is silent
  • Large inlet and outlet parts ensure a steady flow without

pulsation

  • Efficiency is very high, even at low revolution(Any 5)(5)

6.3

  • Gear pump
  • Plunger/piston pump
  • Vane pump(Any 2)(2)

6.4

  • Plunger pressure-relief valve
  • Ball pressure-relief valve(2)

6.5Advantages of CentrifugalPumps over ReciprocatingPumps

  • centrifugal pumps are more compact
  • cost is relatively low
  • maintenance cost is low
  • can pump sandy, muddy and dirty fluids with ease
  • construction is simple and reliable
  • works in high speed
  • water hammer and shocks do not occur(Any 5)(5)

6.6.1Sliding Friction

√

It is the force that resists the motion of an object as it moves

along a surface.√(2)

6.6.2Static Friction

√

It is the force that prevents an object from moving.√(2)

6.6.3Fluid Friction

Objects moving through fluid experiences fluid friction or drag.√

Drag hinders the motion of an object. √(2)

6.7F = µ x N

F = 0,8√ x (5 x 10)√

F = 40 N√(3)

6.8When objects revolve at speed they cause vibration.

Balancing reduces vibration.√

Vibration causes excessive wear√

I t reduces noise√

It increases the lifespan of the component√(Any 2)(2)

6.9Owner knowaboutwheel alignment

  • Start and end with a test drive.
  • The front end and steering linkage should be checked for

wear before wheel alignment.

  • The tyres should be in good shape with wear patterns.
  • Pulling problems are not always related to wheel alignment. Problems with tyres (especially unequal air pressure),

brakes and power steering can also be responsible. (4)

[40]

TOTAL : 200