Λύσεις — Κεφάλαιο 5: Joining Metals (σελ. 104-121) – VOCATIONAL LANGUAGE LEARNING COURSEBOOK FOR MECHANICAL ENGINEERING TECHNICIANS Β ΕΠΑΛ

Λύσεις — Κεφάλαιο 5: Joining Metals

Ενδεικτικές λύσεις των 14 κλειστών TASK της ενότητας (σελ. 104-121): μηχανικές/θερμικές μέθοδοι, soldering/brazing/welding, εξοπλισμός, διαδικασίες ένωσης σωλήνων και ηλεκτροσυγκόλλησης τόξου.

Μέθοδοι ένωσης μετάλλων — συμπλήρωση κειμένου (σελ. 104)

Ερώτηση: TASK 1. Study the diagram and then complete the text that follows. There are two methods of joining metals. The and the . In the mechanical method, metals are joined by using fastening devices such as , and , while in the , by using a heat source. are used for holding pieces permanently. and , on the other hand, for making temporary joints, or if the requires occasional adjustment. According to the temperature of the heat source used, the thermal method is distinguished into , and ___.

Απάντηση:

• Συμπληρωμένο κείμενο: «There are two methods of joining metals. The mechanical and the thermal. In the mechanical method, metals are joined by using fastening devices such as rivets, bolts and screws, while in the thermal, by using a heat source. Rivets are used for holding pieces permanently. Bolts and screws, on the other hand, for making temporary joints, or if the construction requires occasional adjustment. According to the temperature of the heat source used, the thermal method is distinguished into soldering, brazing and welding.»

Σύνοψη: (ενδεικτική) Οι δύο μέθοδοι είναι η μηχανική (rivets, bolts, screws) και η θερμική (soldering, brazing, welding) — όπως στο συμπληρωμένο κείμενο παραπάνω.

Ικανότητες τεχνικού και τεχνικές ένωσης με θερμότητα (σελ. 106)

Ερώτηση: TASK 1. Answer the questions. 1. Which abilities are required from a technician in order to make strong joints? 2. What does the selection of the appropriate technique for a certain joint depend on? 3. What are the base metals and what the filler metals? 4. Is it possible to make a joint without using a filler metal? 5. Which techniques require higher temperatures; those in which a filler metal is used or those in which the base metals are melted at the point of the joint? 6. Which form are the filler metals available in? 7. Whose melting point is higher, the base metals' or the fillers'?

Απάντηση:

• 1. A knowledge of the properties of metals, a steady hand, and skilfulness in using the appropriate equipment.
• 2. It depends on the kind of material to be joined, its thickness, and the nature of the bond.
• 3. Base metals are the pieces to be joined; filler metals are the materials that melt and flow into the joint to bond them.
• 4. Yes — in some techniques the base metals themselves are melted at the joint area and let to flow together, without any filler.
• 5. Those in which the base metals are melted at the point of the joint require higher temperatures.
• 6. In wire form (in rolls), or in the form of rods and electrodes.
• 7. The base metals' melting point is higher than the fillers'.

Σύνοψη: (ενδεικτική) Οι επτά απαντήσεις προκύπτουν αυτούσιες από το κείμενο της σελ. 105, όπως παραπάνω.

Ελληνικοί όροι τεχνικών ένωσης με θερμότητα (σελ. 106)

Ερώτηση: TASK 2. In the spaces provided, write the Greek term for the various techniques of joining metals with a heat source. a. melting both metal pieces at the point to be joined: b. using a filler metal to join the pieces: c. melting both the base metals and the filler: d. heating the base metals at the point to be joined (at a temperature slightly lower than their melting point) and pressing them at that point: e. joining pieces composed of the same metal: f. joining pieces composed of different metals:

Απάντηση:

• a. αυτογενής συγκόλληση (τήξη των τεμαχίων στο σημείο ένωσης, χωρίς υλικό προσθήκης).
• b. συγκόλληση με υλικό προσθήκης (κόλληση: τα τεμάχια ενώνονται με λιωμένο υλικό προσθήκης).
• c. συγκόλληση τήξης με υλικό προσθήκης (λιώνουν και τα μέταλλα βάσης και το υλικό προσθήκης).
• d. συγκόλληση με πίεση (θέρμανση λίγο κάτω από το σημείο τήξης και συμπίεση).
• e. ομογενής (ομοειδής) συγκόλληση — ίδιο μέταλλο και στα δύο τεμάχια.
• f. ανομοιογενής συγκόλληση — ένωση διαφορετικών μετάλλων.

Σύνοψη: (ενδεικτική) a. αυτογενής συγκόλληση· b. συγκόλληση με υλικό προσθήκης· c. συγκόλληση τήξης με υλικό προσθήκης· d. συγκόλληση με πίεση· e. ομογενής συγκόλληση· f. ανομοιογενής συγκόλληση (διαφορετικών μετάλλων).

Κριτήρια αξιολόγησης:

• Οι όροι (e)/(f) αφορούν το είδος των μετάλλων που ενώνονται (ίδιο/διαφορετικό), όχι τη μέθοδο θέρμανσης — μην τους συγχέεις με τα a-d.
• Ενδεικτικές αποδόσεις· στην ελληνική ορολογία ο όρος «ετερογενής συγκόλληση» χρησιμοποιείται για τις κολλήσεις όπου λιώνει μόνο το υλικό προσθήκης (soldering, brazing).

Αναγνώριση διαδικασίας από ορισμό (σελ. 107)

Ερώτηση: TASK 1. Depending on the temperature and the kind of filler used, thermal methods can be distinguished in soldering, brazing or welding. Read the paragraphs and identify the process defined. 1. It is the process of joining metals at temperatures above 500 °C using alloys of copper and silver, phosphorus or other metal as a filler. 2. It is the process of joining metals at very high temperatures, either by using a filler or by heating (fusing) the base metals to their melting point. 3. It is the process of joining two or more metal pieces by means of a filler (solder) which is an alloy of tin and lead, antimony or other metal having a low melting point (below 500 °C).

Απάντηση:

• 1. Brazing (θερμοκρασία >500°C, filler κράμα χαλκού-ασημιού/φωσφόρου).
• 2. Welding (πολύ υψηλές θερμοκρασίες, filler ή τήξη base metals).
• 3. Soldering (filler solder, κράμα κασσιτέρου-μολύβδου, <500°C).

Σύνοψη: (ενδεικτική) Παράγραφος 1 = Brazing, παράγραφος 2 = Welding, παράγραφος 3 = Soldering, με βάση τα κριτήρια θερμοκρασίας και είδους filler.

Ερωτήσεις γνώσεων για soldering/brazing/welding (σελ. 108)

Ερώτηση: TASK 2. How much do you know about soldering, brazing and welding? Check your knowledge. Find the answer to each of the following questions. 1. Which are the most widely used techniques in the three thermal methods? 2. What kind of filler is used in soldering? 3. Which is the alternative term for gas brazing and welding? 4. What is melted in gas soldering and gas brazing; the filler or the base metals? 5. In which form are the fillers used in gas brazing and gas welding? 6. Which methods are used to make most tubing connections nowadays? 7. Why is electric welding also called arc welding? 8. Which gases are used to create the flame in gas brazing and welding? 9. How are the metal pieces joined in arc welding? 10. What is used to create the flame in gas soldering? 11. Which method produces stronger bonds and is used to join both similar and dissimilar metals; soldering or brazing? 12. Are the filler metals heated or melted directly by the heat source in soldering and brazing? ANSWERS: a. In the form of rods. b. Oxygen and acetylene or oxygen and MAPP gas... c. Brazing. d. No, they aren't. It is the base metals which are heated... e. Liquid propane, air acetylene or MAPP gas. f. Because in this technique, the metals are melted by the heat produced by an electric arc. g. Only the filler is melted. h. The high temperature of the arc melts the base metals... i. They are also called oxyacetylene brazing or welding. j. Those in which the heat is produced by burning gases, and those in which the heat is produced by electric current... k. Soldering or brazing, because the joints made by these methods are strong and don't cost much... l. An alloy of tin and lead, antimony or other metal having a low melting point (below 500 °C), which is called solder.

Απάντηση:

• 1-j (methods: gas ή electric soldering/brazing/welding).
• 2-l (soldering filler: κράμα κασσιτέρου-μολύβδου, solder).
• 3-i (gas brazing/welding = oxyacetylene brazing/welding).
• 4-g (στο gas soldering και gas brazing λιώνει μόνο ο filler).
• 5-a (fillers σε μορφή ράβδων).
• 6-k (soldering ή brazing — ισχυρές, φθηνές ενώσεις).
• 7-f (η θερμότητα παράγεται από ηλεκτρικό τόξο).
• 8-b (oxygen+acetylene ή oxygen+MAPP gas).
• 9-h (το τόξο λιώνει τα base metals, το ηλεκτρόδιο λειτουργεί ως filler).
• 10-e (liquid propane, air acetylene ή MAPP gas).
• 11-c (brazing — ισχυρότερες ενώσεις, όμοια/ανόμοια μέταλλα).
• 12-d (όχι· θερμαίνονται τα base metals και ο filler λιώνει όταν έρθει σε επαφή μαζί τους).

Σύνοψη: (ενδεικτική) 1-j, 2-l, 3-i, 4-g, 5-a, 6-k, 7-f, 8-b, 9-h, 10-e, 11-c, 12-d.

Διάγραμμα θερμικών μεθόδων ένωσης (σελ. 109)

Ερώτηση: TASK 3. Complete the diagram below with the various techniques used to join metals with a heat source. THERMAL METHODS FOR JOINING METALS (three boxes, each divided into two smaller boxes).

Απάντηση:

• Οι τρεις θερμικές μέθοδοι είναι soldering, brazing και welding (σελ. 104, 107).
• Κάθε μέθοδος χωρίζεται σε δύο τεχνικές, ανάλογα με το πώς παράγεται η θερμότητα: με καύση αερίων (gas) ή με ηλεκτρικό ρεύμα (electric) — απάντηση j, σελ. 109: «a) gas soldering, brazing and welding, and b) electric soldering, brazing and welding».

Σύνοψη: (ενδεικτική) THERMAL METHODS FOR JOINING METALS → SOLDERING (gas soldering, electric soldering) · BRAZING (gas brazing, electric brazing) · WELDING (gas welding, electric/arc welding).

Διόρθωση λανθασμένων προτάσεων (σελ. 109)

Ερώτηση: TASK 4. The following sentences are wrong. Correct them. 1. To join two metal pieces by soldering, we heat the base metals at a temperature above 500 °C and when they melt, we let them flow in the joint. 2. In arc welding, the heat needed to join the metals is produced by a flame created by oxygen and acetylene or MAPP gas. 3. The appropriate temperature for joining two metals by brazing is below 500 °C. 4. In soldering, the heat used to join the metals is produced by burning propane and oxygene or MAPP gas. 5. In soldering and brazing, the melting point of the base metals is lower than the melting point of the filler used. 6. In gas welding, the gases used to produce the flame are acetylene and MAPP gas. 7. In gas welding, the base metals are never melted. 8. In soldering, we don't heat the base metals directly. We heat only the filler.

Απάντηση:

• 1. To join two metal pieces by soldering, we heat the base metals at a temperature below 500 °C; the base metals do not melt — only the filler (solder) melts and flows in the joint.
• 2. In arc welding, the heat needed to join the metals is produced by an electric arc.
• 3. The appropriate temperature for joining two metals by brazing is above 500 °C.
• 4. In soldering, the heat used to join the metals is produced by burning liquid propane, air acetylene or MAPP gas (without oxygen).
• 5. In soldering and brazing, the melting point of the base metals is higher than the melting point of the filler used.
• 6. In gas welding, the gases used to produce the flame are oxygen and acetylene or oxygen and MAPP gas.
• 7. In gas welding, the base metals are melted (fused) at the point of the joint.
• 8. In soldering, we don't heat the filler directly. We heat only the base metals, and the filler melts when it comes in contact with them.

Σύνοψη: (ενδεικτική) Οι οκτώ προτάσεις διορθώνονται με βάση τις σελ. 105-109 (θερμοκρασία, είδος filler, πηγή θερμότητας), όπως παραπάνω.

Κριτήρια αξιολόγησης:

• Στην πρόταση 8 έχουν αντιστραφεί οι ρόλοι: σύμφωνα με την απάντηση d (σελ. 108) θερμαίνονται τα base metals και όχι ο filler, ο οποίος λιώνει όταν ακουμπήσει τα θερμά μέταλλα.

Πίνακας συγκόλλησης — fillers/gases/equipment (σελ. 112)

Ερώτηση: TASK 1. Complete the table. Columns: SOLDERING – BRAZING – WELDING. Rows: FILLERS (given for welding: • welding rods • ___ (alloys of various metals)), GASES, EQUIPMENT – GAS, EQUIPMENT – ELECTRIC (given for brazing: electric brazing machine).

Απάντηση:

• Fillers: Soldering — solder (alloy of tin and lead, antimony or other metal with a low melting point)· Brazing — alloys of copper and silver, phosphorus or other metal (brazing filler rods)· Welding — welding rods, electrodes (alloys of various metals).
• Gases: Soldering — liquid propane, air acetylene or MAPP gas· Brazing — oxygen and acetylene or oxygen and MAPP gas (sometimes only acetylene or MAPP gas)· Welding — oxygen and acetylene or oxygen and MAPP gas.
• Equipment (gas): Soldering — torch used with propane, bottle with propane / portable propane bottle, gauge and propane pressure regulator, portable MAPP gas bottles· Brazing and Welding — cylinders with oxygen and acetylene (or portable set with MAPP gas), gauges and pressure regulators, hoses, torch.
• Equipment (electric): Soldering — soldering iron, soldering gun· Brazing — electric brazing machine· Welding — machine for electric (arc) welding, electrode holder, ground cable and clamp.

Σύνοψη: (ενδεικτική) Ο πίνακας συμπληρώνεται με βάση τις πληροφορίες και τις λεζάντες εξοπλισμού των σελ. 105-111, όπως παραπάνω.

Μέθοδος/τεχνική ανά χαρακτηριστικό (σελ. 112)

Ερώτηση: TASK 2 Write the method(s) or technique(s) related to the following: Tempe- (1) below 500 °C: rature (2) above 500 °C: (1) melting of the base metals: Method (2) an alloy of tin and lead as a filler: (3) alloys of copper as a filler: (4) an electrode as a filler: (1) an electric machine: Equipment (2) a gas torch: (3) an electric iron or gun: (4) cylinder(s) with gas: (1) air acetylene: Heat Source (2) liquid propane: (3) mixture of oxygen and acetylene: (4) MAPP gas (alone): (5) mixture of oxygen and MAPP gas:

Απάντηση:

• Temperature: (1) below 500°C → soldering. (2) above 500°C → brazing, welding.
• Method: (1) melting base metals → welding. (2) tin-lead filler → soldering. (3) copper alloys filler → brazing. (4) electrode filler → (arc) welding.
• Equipment: (1) electric machine → electric brazing, electric (arc) welding. (2) gas torch → gas soldering/brazing/welding. (3) electric iron/gun → electric soldering. (4) gas cylinders → gas soldering/brazing/welding.
• Heat Source: (1) air acetylene → gas soldering. (2) liquid propane → gas soldering. (3) oxygen+acetylene → gas brazing/welding (oxyacetylene brazing/welding). (4) MAPP gas alone → gas soldering (and sometimes gas brazing). (5) oxygen+MAPP gas → gas brazing/welding.

Σύνοψη: (ενδεικτική) Κάθε χαρακτηριστικό αντιστοιχίζεται στην τεχνική/μέθοδο/εξοπλισμό που περιγράφηκε στις σελ. 105-111, όπως παραπάνω.

Προτάσεις από τον πίνακα εξοπλισμού (σελ. 114)

Ερώτηση: FOLLOW UP. Use the table to make meaningful sentences. 1. Two regulators, 2. Two manometers, 3. The hoses, 4. Screws and bolts, 5. Rivets, 6. A heat source, 7. The gas valves on the torch, 8. Welding rods, 9. Acetylene and oxygen — is/are needed in order to / used for: a. regulate the proportion of oxygen and acetylene in the torch, b. carrying the gases from the cylinders to the torch, c. control the pressure of the gas flow in the hoses, d. make temporary joints, e. carry out soldering, brazing and welding, f. making strong joints, g. produce the flame in gas welding, h. indicate the amount of pressure in the hoses and cylinders, i. holding metal pieces together permanently.

Απάντηση:

• 1-c: Two regulators are needed in order to control the pressure of the gas flow in the hoses.
• 2-h: Two manometers are used for indicating the amount of pressure in the hoses and cylinders.
• 3-b: The hoses are needed for carrying the gases from the cylinders to the torch.
• 4-d: Screws and bolts are used to make temporary joints.
• 5-i: Rivets are used for holding metal pieces together permanently.
• 6-e: A heat source is needed in order to carry out soldering, brazing and welding.
• 7-a: The gas valves on the torch are used to regulate the proportion of oxygen and acetylene in the torch.
• 8-f: Welding rods are needed for making strong joints.
• 9-g: Acetylene and oxygen are used to produce the flame in gas welding.

Σύνοψη: (ενδεικτική) Πλήρης αντιστοίχιση 1-9 → a-i με ολοκληρωμένες προτάσεις, όπως παραπάνω.

Σειρά βημάτων — ένωση σωλήνων με brazing (σελ. 118)

Ερώτηση: TASK [1]. The instructions below describe the steps followed to join two tubes of the same diameter by gas brazing. They are given in jumbled order. Write numbers in the space provided in front of each step to show their correct order in the procedure: Cool the joint with water. / Fit the joint securely and support all its parts... / Use a swaging tool to expand the edge of one of the tubes... / Apply the brazing filler rod to the heated parts... / Remove burrs with a file or reamer. / Clean the joint thoroughly using warm water and a brush. / Apply clean flux as recommended... / Heat the joint evenly to the recommended temperature... / Clean the surfaces to be joined thoroughly with stainless steel wool or wire. / Cut the tubes to the desired length. / Watch carefully for a poor adhesion...

Απάντηση:

• Σωστή σειρά: 1. Cut the tubes to the desired length. 2. Remove burrs with a file or reamer. 3. Use a swaging tool to expand the edge of one of the tubes to be joined. 4. Clean the surfaces to be joined thoroughly with stainless steel wool or wire. 5. Apply clean flux as recommended for the brazing alloy to be used. 6. Fit the joint securely and support all its parts, so that they will not move. 7. Heat the joint evenly to the recommended temperature, keeping the torch moving in a «figure eight» motion (heat the copper first on a copper-to-steel joint). 8. Apply the brazing filler rod to the heated parts (do not heat it with the torch). 9. Watch carefully for a poor adhesion (dark, cup-shaped areas) and make the necessary corrections during the brazing operation. 10. Cool the joint with water. 11. Clean the joint thoroughly using warm water and a brush.

Σύνοψη: (ενδεικτική) Αριθμοί με τη σειρά που δίνονται τα βήματα στο βιβλίο: 10 (Cool), 6 (Fit), 3 (Swaging tool), 8 (Apply filler rod), 2 (Remove burrs), 11 (Clean with warm water), 5 (Apply flux), 7 (Heat), 4 (Clean surfaces), 1 (Cut), 9 (Watch for poor adhesion).

Σύγκριση διαδικασιών soldering και brazing (σελ. 118)

Ερώτηση: TASK 2. Compare the two procedures of joining metals (by soldering and by brazing) described. Spot their main similarities and differences.

Απάντηση:

• Ενδεικτική σύγκριση των δύο διαδικασιών (soldering σελ. 115-116, brazing σελ. 118): In both procedures, we cut the tubes to the desired length, remove the burrs with a reamer or a file, clean the surfaces to be joined, apply flux, fit the pieces firmly so that they will not move, heat the joint with a torch and apply the filler to the heated parts, not to the flame. In both soldering and brazing, we finally wash off the flux with water and a brush. When soldering, we join the tube to a fitting, while in brazing we expand the end of one tube with a swaging tool so that the other tube fits into it. In soldering we clean the surfaces with a wire brush or sandpaper, whereas in brazing we use stainless steel wool or wire. In brazing, unlike in soldering, we keep the torch moving in a «figure eight» motion and heat the joint to a higher temperature (above 500 °C). Finally, in soldering we allow the joint to cool, while in brazing we cool it with water.

Σύνοψη: (ενδεικτική) Ομοιότητες: κοπή, αφαίρεση γρεζιών, καθαρισμός, flux, σταθερή συναρμολόγηση, θέρμανση με φλόγα, filler στα θερμά μέρη, τελικό πλύσιμο του flux. Διαφορές: σύνδεσμος (fitting) έναντι διεύρυνσης με swaging tool, μέσο καθαρισμού, θερμοκρασία (κάτω/πάνω από 500 °C), κίνηση φλόγας «figure eight», ψύξη (φυσική έναντι με νερό).

Σειρά βημάτων και ταξινόμηση — arc welding (σελ. 120)

Ερώτηση: Arc welding. TASK 1. The instructions below describe the steps followed to join two metal pieces by arc welding. They are given in jumbled order. Write numbers in the space provided in front of each instruction to show their correct order in the procedure. • Turn the machine on and bring the electrode within a few centimetres from the workpiece. • After you have obtained the arc, keep the electrode within 1.5 to 3.2 mm from the metal being welded moving it in a straight direction, smoothly and evenly. As the electrode burns shorter, keep feeding it to the workpiece to maintain the correct arc length. • Adjust the welding machine to the appropriate amperage. • Clean the surfaces to be welded with an abrasive cloth. • Place the proper electrode in the holder and clamp the ground cable to the metal to be welded or to the metal table where the workpiece is placed. • Holding the hot metal with a pair of tongs, clean the joint with a special hammer and a steel brush to remove chips. • Arrange the surfaces to be joined close together. • Start an arc by striking the work piece with the electrode as you strike a match. Then, raise the electrode slightly to form and maintain the arc. TASK 2. Arrange the numbered instructions under the following headings: 1. Preparation for welding: e.g. Instructions 1, ... 2. Welding the joint: 3. Finishing the joint: TASK 3. Below are some additional instructions closely related to the arc welding procedure described above. A. Read them and say if they refer to: a) the safety of the welder, or b) the quality of the job. 1. Use clamps, if necessary, to hold the pieces in place securely. 2. Wear arc welding gloves, an apron, sleeves and a face shield to protect you from the intense light and heat and prevent burning your eyes, skin and clothes. 3. Keep the electrode moving while starting the arc, to prevent it from sticking to the workpiece. 4. Be careful. The correct welding speed is most important. 5. While welding, make sure you get the deepest penetration possible in the joint. B. Find which step of the procedure the above instructions are related to and insert them in the appropriate place in the procedure.

Απάντηση:

• TASK 1 — σωστή σειρά: 1. Clean the surfaces to be welded with an abrasive cloth. 2. Arrange the surfaces to be joined close together. 3. Adjust the welding machine to the appropriate amperage. 4. Place the proper electrode in the holder and clamp the ground cable to the metal to be welded (or to the metal table). 5. Turn the machine on and bring the electrode within a few centimetres from the workpiece. 6. Start an arc by striking the workpiece with the electrode as you strike a match, then raise the electrode slightly to form and maintain the arc. 7. After obtaining the arc, keep the electrode within 1.5-3.2 mm from the metal, moving it smoothly and evenly, feeding it as it burns shorter. 8. Holding the hot metal with a pair of tongs, clean the joint with a special hammer and a steel brush to remove chips.
• TASK 2: 1. Preparation for welding — steps 1-4 (clean surfaces, arrange them, adjust machine, place electrode/clamp cable). 2. Welding the joint — steps 5-7 (turn on machine, start the arc, weld moving the electrode). 3. Finishing the joint — step 8 (clean the joint with hammer/brush).
• TASK 3.A: 1-b (quality: τα τεμάχια μένουν σταθερά στη θέση τους), 2-a (safety: προστατευτικός εξοπλισμός), 3-b (quality: το ηλεκτρόδιο δεν κολλά στο τεμάχιο), 4-b (quality: σωστή ταχύτητα συγκόλλησης), 5-b (quality: βαθιά διείσδυση).
• TASK 3.B: 1 → μαζί με το βήμα 2 (Arrange the surfaces to be joined close together). 2 → πριν από το βήμα 5 (Turn the machine on...). 3 → στο βήμα 6 (Start an arc...). 4 και 5 → στο βήμα 7 (keep the electrode ... moving it smoothly and evenly).

Σύνοψη: (ενδεικτική) Η σωστή σειρά των 8 βημάτων, η κατάταξή τους σε 3 φάσεις (προετοιμασία/συγκόλληση/τελείωμα) και η ταξινόμηση των πρόσθετων οδηγιών σε ασφάλεια/ποιότητα δίνονται παραπάνω.

Σύγκριση διαδικασιών gas brazing και arc welding (σελ. 121)

Ερώτηση: TASK 4. Compare the two procedures of joining metal pieces (by gas brazing and by arc welding) described. Spot their main similarities and differences.

Απάντηση:

• Ενδεικτική σύγκριση: In both procedures, we must clean and prepare the surfaces before joining them, and we need a heat source intense enough to melt a filler (or the base metals). In both gas brazing and arc welding, the pieces are cleaned again after the joint has cooled, to remove any residue. Unlike in gas brazing, where the heat is produced by burning gases (oxygen and acetylene) and a filler rod is applied separately, in arc welding the heat is produced by an electric arc and the electrode itself melts and serves as the filler. Also, arc welding requires special protective equipment (gloves, apron, face shield) because of the intense light and heat of the arc, while gas brazing mainly requires care with the flame and the gas cylinders.

Σύνοψη: (ενδεικτική) Ομοιότητες: καθαρισμός/προετοιμασία επιφανειών, ανάγκη πηγής θερμότητας, τελικός καθαρισμός. Διαφορές: πηγή θερμότητας (φλόγα αερίων vs ηλεκτρικό τόξο), ρόλος filler (ξεχωριστή ράβδος vs το ίδιο το ηλεκτρόδιο), εξοπλισμός προστασίας.