Mechanical Technology Grade 12 IEB 2019 Memo

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE EXAMINATION NOVEMBER 2019 MECHANICAL TECHNOLOGY: WELDING AND METALWORK MARKING GUIDELINES Time: 3 hours 200 marks These marking guidelines are prepared for use by examiners and sub-examiners, all of whom are required to attend a standardisation meeting to ensure that the guidelines are consistently interpreted and applied in the marking of candidates' scripts. The IEB will not enter into any discussions or correspondence about any marking guidelines. It is acknowledged that there may be different views about some matters of emphasis or detail in the guidelines. It is also recognised that, without the benefit of attendance at a standardisation meeting, there may be different interpretations of the application of the marking guidelines. IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: MECHANICAL TECHNOLOGY WELDING AND METALWORK – Page 2 of 13 MARKING GUIDELINES QUESTION 1 MULTIPLE-CHOICE QUESTIONS (Generic) 1.1 A 1.2 C 1.3 D 1.4 A 1.5 B 1.6 D QUESTION 2 SAFETY (Generic) 2.1 Name THREE safety rules to be remembered when using a manual guillotine  Keep hands clear of blade.  Don't cut material that is thicker than machine can handle.  Do not adjust or service during operation.  Blade guard or back of machine to catch material. 2.2 Explain the difference between an act and a condition  An act is something that workers do that could cause unsafe conditions in a workshop leading to injury.  A condition is something created by the act or the unsafe conditions of the building or equipment where workers are working. 2.3 Name TWO advantages of a process layout  High machine utilisation.  Better supervision.  Less interruption.  Lower equipment cost.  Better control of total manufacturing cost.  Greater flexibility in the production process. 2.4 What is the maximum distance that the tool rest should be set from the grinding wheel of a bench grinder?  3 mm IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: MECHANICAL TECHNOLOGY WELDING AND METALWORK – Page 3 of 13 MARKING GUIDELINES QUESTION 3 MATERIALS (Generic) 3.1 List THREE factors that must be considered when hardening steel through heat treatment.  Workpiece size  Quenching rate  Carbon content 3.2 Name TWO testing machines used to check the resistance to bending, scratching and abrasion.  Vickers  Rockwell  Brinell 3.3 What is the reason for doing the following heat-treatment processes? 3.3.1 Tempering Tempering is a process used to relieve strains induced during the hardening process. 3.3.2 Annealing Metal is annealed to relieve internal stresses that may have been set up during previous workings and to soften the material. 3.3.3 Normalising Normalising is done to relieve internal stress produced by machining, welding or forging. 3.4 What sound do the following materials make when tapped with a hammer? 3.4.1 Cast iron Very dull sound 3.4.2 Cast steel High ringing sound 3.4.3 Mild steel Medium metallic sound IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: MECHANICAL TECHNOLOGY WELDING AND METALWORK – Page 4 of 13 MARKING GUIDELINES QUESTION 4 MULTIPLE-CHOICE QUESTIONS (Specific) 4.1 B 4.2 D 4.3 D 4.4 D 4.5 C 4.6 B 4.7 C 4.8 C 4.9 B 4.10 C 4.11 A 4.12 B 4.13 B 4.14 C IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: MECHANICAL TECHNOLOGY WELDING AND METALWORK – Page 5 of 13 MARKING GUIDELINES QUESTION 5 TERMINOLOGY (Templates) (Specific) 5.1 What is a flange template used for? A flange template is used to mark angle cleats and is fitted over the edge of the angle iron. 5.2 What is a lattice girder and what is it used for? A lattice girder is called a truss and is used over long spans of a structure. 5.3 Calculate the dimensions of an 10 mm × 10 mm steel square bar that is to be rolled into a cylindrical form with an external diameter of 700 mm. Mean dia = ED – Plate thickness Mean dia = 700 – 10 Mean dia = 690 mm Circumference = π × Mean dia Circumference = π × 690 Circumference = 2167,70 mm 5.4 Resistance welding refers to a group of processes and uses symbols to indicate the type of weld to be used on the joint. Name FIVE resistance symbols used.  Spot  Seam  Projection  Foil seam  Flash or resistance butt 5.5 What is the purpose of supplementary symbols? Give THREE examples. The purpose of supplementary symbols is to provide extra (supplementary) information regarding a welded joint Contour Finish Site weld Weld all round IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: MECHANICAL TECHNOLOGY WELDING AND METALWORK – Page 6 of 13 MARKING GUIDELINES QUESTION 6 TOOLS AND EQUIPMENT (Specific) 6.1 Explain the principle of operation of the following equipment utilised in a welding workshop: 6.1.1 Spot Welder Spot welders do not use a consumable electrode like conventional welders. It utilises a heating effect when the current occurs and flows through the plates fusing them together. 6.1.2 Plasma cutter Plasma cutting is done by an electrically charged accelerated jet of hot plasma. It creates an electrical channel of ionised gas that is plasma through the workpiece that is clamped via a grounding clamp. The plasma provides sufficient heat to melt the workpiece. 6.2 What is the primary task of the regulators? They are primarily used to change cylinder pressure to operating pressure. 6.3 A Major diameter/ Outside diameter/ Nominal diameter B Effective diameter C Minor diameter/ Core diameter D Crest E Helix angle F Pitch G Thread width (thickness) H Thread angle IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: MECHANICAL TECHNOLOGY WELDING AND METALWORK – Page 7 of 13 MARKING GUIDELINES QUESTION 7 FORCES (Specific) 7.1 NOTE: Use a tolerance of 2 mm "+" and "–" on the vector diagram. = a tolerance of 10 N "+" and "–" on the answer. IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: MECHANICAL TECHNOLOGY WELDING AND METALWORK – Page 8 of 13 MARKING GUIDELINES 7.2 7.2.1 RL × 5 m = (4 kN × 3 m) + (4 kN × 2 m) + (6 kN × 1 m) RL × 5 m = 26 kN.m 26 RL = 5 RL = 5,2 kN RR × 5 m = (6 kN × 4 m) + (4 kN × 3 m) + (4 kN × 2 m) RR × 5 m = 44 kN.m 44 RR = 5 RR = 8,8 kN 7.2.2 Bending moments: BMA: (5,2 kN × 2 m) – (4 kN × 0 m) = 10,4 Nm BMB: (5,2 kN × 4 m) – (4 kN × 2 m) – (4 kN × 1 m) – (6 kN × 0 m) = 8,8 Nm IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: MECHANICAL TECHNOLOGY WELDING AND METALWORK – Page 9 of 13 MARKING GUIDELINES 7.2.3 + 7.2.4 7.3 Calculations 7.3.1 The strain in the metal Change in length Strain = Original length 0,005 Strain = 400 Strain = 0,0000125 IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: MECHANICAL TECHNOLOGY WELDING AND METALWORK – Page 10 of 13 MARKING GUIDELINES 7.3.2 Young's modulus of elasticity for the metal Stress YM = Strain 20000000 YM = 0,0000125 YM = 1600Mpa OR 1,6 × 1012 = 1,6 Tpa 7.3.3 The diameter of the round bar in mm 4𝑥𝐴 D=√ 𝜋 4𝑥 D = √ 𝜋 0.0009621127 D = 0,034999 m D = 35 mm QUESTION 8 JOINING METHODS (Inspection of Weld) (Specific) 8.1 It is important to observe the weld whilst welding; observation can improve the standard and ensure that the settings and material are correct. Name TWO inspections for each of the following: 8.1.1 Inspection during arc welding. Rate of rod-burning Amount of penetration Flow of weld metal Sound of the arc 8.1.2 Inspection during oxy-acetylene welding. Correct flame Correct angle of blowpipe Depth of fusion and penetration Rate of progress along the joint 8.2 Weld gauges can be used to rapidly check a welded joint for quality. Figure 5 shows a sketch of a welded joint. Name labels A–E. A Penetration B Width C Height D Weld bead E Base metal IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: MECHANICAL TECHNOLOGY WELDING AND METALWORK – Page 11 of 13 MARKING GUIDELINES 8.3 List the steps to be taken to do a liquid-dye penetrant test Clean weld to be inspected Spray dye on the clean surface Allow dye to penetrate the weld surface Clean excess dye away with a cleaning agent Allow surface to dry thoroughly Spray developer on surface to bring out faults in weld cracks Dye shows on surface defects 8.4 The diagrams 8.4.1 and 8.4.2 shows TWO defects in welded joints. Name the defect, the cause of the defect and the remedy. (Tabulate your answers.) Defect Cause Remedy 8.4.1 incomplete  Opposing beads do Increase welding penetration not penetrate current  Weld bead not penetrating full depth  Welding current too low (Any 1) 8.4.2 Undercutting  Improper welding Decrease travel arc parameters speed  Travel speed too Reduce voltage fast  Arc voltage too high (Any 1) 8.5 What test is done with high-frequency sound waves? Ultrasonic QUESTION 9 JOINING METHODS (Stresses and Distortion) (Specific) 9.1 Which FOUR factors affect shrinkage whilst welding? Electrode type Electrode size Welding current and flame size Welding speed The rate of cooling while and after welding 9.2 Name FOUR methods that can be applied to reduce distortion. Do not over-weld Intermittent welding Placing welds close to neutral axis Use as few passes as possible Use backstep welding IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: MECHANICAL TECHNOLOGY WELDING AND METALWORK – Page 12 of 13 MARKING GUIDELINES 9.3 Name the THREE classes of carbon steel and each class's percentage carbon Low-carbon steel 0,15% – 0,3% Medium-carbon steel 0,31% – 0,7% High-carbon steel 0,71% – 1,5% 9.4 Name FOUR factors that affect the grain size of steel when it is cold worked. Prior amount of cold work Composition of alloying elements The annealing time and temperature The melting point QUESTION 10 MAINTENANCE (Specific) 10.1 After routine service maintenance of machinery is complete, a final inspection of the machinery must be done. Name FOUR conditions that should be observed before starting up machines. Technicians confirm the machine is safe Check all safety guards are fitted and secure Area around machine is clear Inform workers machine is going to be powered on 10.2 What will overloading of the hydraulic guillotine do to the machine? Overloading of the machine will cause damage to the blade and possible failure of the hydraulic system. 10.3 List TWO factors to be considered when choosing the cutting speed of a drilling machine. Type of material Diameter of drill bit Material Condition of machine Rate of feed Use of cutting fluid Firmness with which the work is clamped QUESTION 11 TERMINOLOGY (Development) (Specific) 11.1 Conical hopper: 11.1.1 Angle E 70 – 40 30 mm 60 Tan θ = 30 Tan θ = 2 E = 63,43° IEB Copyright © 2019 PLEASE TURN OVER

Downloaded from hlayiso.com NATIONAL SENIOR CERTIFICATE: MECHANICAL TECHNOLOGY WELDING AND METALWORK – Page 13 of 13 MARKING GUIDELINES 11.1.2 Length AC: 30 60 AC = Cos 63,43° OR AC = Sin 63,43° AC = 67,08 mm 11.1.3 Circumference AB: Circ = π x 40 Circ = 125,66 mm 11.1.4 Circumference CD: Circ = π × 70 Circ = 219,91 mm 11.2 Square-to-square transition: 11.2.1 The true length A1 A1 = √150² + 150² + 550² = √22 500 + 22 500 + 302 500 = 589,49 mm 11.2.2 True length X1–X2 X1–X2 = √150² + 550² = √22 500 + 302 500 = 570,09 mm 11.2.3 True length A2 A2 = √150² + 450² + 550² = √22 500 + 202 500 + 302 500 = 726,29 mm 11.2.4 True length of A–X2 A–X2 = √150² + 300² + 550² = √22 500 + 90 000 + 302 500 = 644,21 mm Total: 200 marks IEB Copyright © 2019