Λύσεις — Κεφάλαιο 5: Joining Metals – VOCATIONAL LANGUAGE LEARNING COURSEBOOK FOR MECHANICAL ENGINEERING TECHNICIANS Β ΕΠΑΛ

VOCATIONAL LANGUAGE LEARNING COURSEBOOK FOR MECHANICAL ENGINEERING TECHNICIANS Β ΕΠΑΛ VOCATIONAL LANGUAGE LEARNING COURSEBOOK FOR MECHANICAL ENGINEERING TECHNICIANS Β ΕΠΑΛ – ΛΥΣΕΙΣ – ΑΠΑΝΤΗΣΕΙΣ Ασκήσεων Σχολικού Βιβλίου Λύσεις — Κεφάλαιο 5: Joining Metals – 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

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.

Κριτήρια αξιολόγησης:

Ικανότητες τεχνικού και τεχνικές ένωσης με θερμότητα

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.
1. It depends on the kind of material to be joined, its thickness, and the nature of the bond.
1. Base metals are the pieces to be joined; filler metals are the materials that melt and flow into the joint to bond them.
1. Yes — in some techniques the base metals themselves are melted at the joint area and let to flow together, without any filler.
1. Those in which the base metals are melted at the point of the joint require higher temperatures.
1. In wire form (in rolls), or in the form of rods and electrodes.
1. 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.

Κριτήρια αξιολόγησης:

Ελληνικοί όροι τεχνικών ένωσης με θερμότητα

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. τήξη (fusion/welding χωρίς filler).
b. συγκόλληση με προσθήκη υλικού πλήρωσης (brazing/soldering με filler).
c. τήξη και βασικού μετάλλου και υλικού πλήρωσης (fusion welding με filler rod).
d. σφυροσυγκόλληση/συγκόλληση με πίεση (forge/pressure welding).
e. ομοιογενής συγκόλληση (ίδιο μέταλλο και στα δύο τεμάχια).
f. ετερογενής συγκόλληση (διαφορετικά μέταλλα).

Σύνοψη: (ενδεικτική) Κάθε τεχνική περιγράφεται με τον αντίστοιχο ελληνικό τεχνικό όρο, όπως παραπάνω.

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.

Αναγνώριση διαδικασίας από ορισμό

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).
1. Welding (πολύ υψηλές θερμοκρασίες, filler ή τήξη base metals).
1. 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.

Κριτήρια αξιολόγησης:

Ερωτήσεις γνώσεων για soldering/brazing/welding

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-d (μόνο ο filler λιώνει, όχι τα base metals).
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-g (μόνο ο filler λιώνει, όχι απευθείας από την πηγή θερμότητας).

Σύνοψη: (ενδεικτική) Πλήρης αντιστοίχιση ερωτήσεων 1-12 με τις δοσμένες απαντήσεις a-l, όπως παραπάνω.

Κριτήρια αξιολόγησης:

Διάγραμμα θερμικών μεθόδων ένωσης

Ερώτηση: TASK 3. Complete the diagram below with the various techniques used to join metals with a heat source. THERMAL METHODS FOR JOINING METALS

Απάντηση:

Το διάγραμμα συμπληρώνεται ως εξής: THERMAL METHODS FOR JOINING METALS → κλάδος «below 500 °C»: Soldering — κλάδος «above 500 °C»: Brazing και Welding (όπως στο εισαγωγικό διάγραμμα του TASK 1, σελ. 104).

Σύνοψη: (ενδεικτική) Οι θερμικές μέθοδοι κατατάσσονται σε Soldering (κάτω από 500°C) και Brazing/Welding (πάνω από 500°C).

Κριτήρια αξιολόγησης:

Διόρθωση λανθασμένων προτάσεων

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 filler (not the base metals) at a temperature below 500 °C, and when it melts, we let it flow in the joint.
1. In arc welding, the heat needed to join the metals is produced by an electric arc, not a gas flame.
1. The appropriate temperature for joining two metals by brazing is above 500 °C.
1. In soldering, the heat is produced by burning propane (or acetylene) and it is used to melt only the filler, not to join the metals directly by burning gas — soldering does not require oxygen/MAPP gas necessarily; it is typically done with propane alone.
1. In soldering and brazing, the melting point of the base metals is higher than the melting point of the filler used.
1. In gas welding, the gases used to produce the flame are oxygen and acetylene (or oxygen and MAPP gas), not acetylene and MAPP gas together.
1. In gas welding, the base metals are (can be) melted — welding may involve fusing the base metals themselves.
1. This sentence is actually correct as stated for soldering: we heat the filler, which melts on contact with the heated base metals — the base metals are heated but not melted.

Σύνοψη: (ενδεικτική) Κάθε λανθασμένη πρόταση διορθώνεται με βάση τα στοιχεία που δόθηκαν στις σελ. 104-109 (θερμοκρασία, είδος filler, πηγή θερμότητας), όπως παραπάνω.

Κριτήρια αξιολόγησης:

Η πρόταση 8 είναι η μόνη «παγίδα»: μοιάζει λανθασμένη αλλά περιγράφει σωστά τη διαδικασία soldering (θερμαίνουμε τα base metals, όχι όμως ως σημείο τήξης τους, και ο filler λιώνει μόνο όταν έρθει σε επαφή μαζί τους) — επιβεβαιώνεται από τη σελ. 108, απάντηση d.

Πίνακας συγκόλλησης — fillers/gases/equipment

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

Απάντηση:

Fillers: Soldering — solder (κράμα κασσιτέρου-μολύβδου)· Brazing — κράματα χαλκού-ασημιού/φωσφόρου· Welding — welding rods (ηλεκτρόδια).
Gases: Soldering — propane· Brazing/Welding — oxygen+acetylene, ή oxygen/acetylene+MAPP gas.
Equipment (gas): torch, gauges/pressure regulators, gas cylinders/bottles, hoses.
Equipment (electric): Soldering — soldering iron/gun· Welding — electric brazing/welding machine.

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

Κριτήρια αξιολόγησης:

Μέθοδος/τεχνική ανά χαρακτηριστικό

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 → arc welding machine. (2) gas torch → soldering/brazing/gas welding. (3) electric iron/gun → soldering. (4) gas cylinders → gas soldering/brazing/welding.
Heat Source: (1) air acetylene → gas soldering/brazing. (2) liquid propane → gas soldering. (3) oxygen+acetylene → gas brazing/welding. (4) MAPP gas alone → gas soldering/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.

Κριτήρια αξιολόγησης:

Προτάσεις από τον πίνακα εξοπλισμού

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.

Κριτήρια αξιολόγησης:

Σειρά βημάτων — ένωση σωλήνων με brazing

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. Watch carefully for a poor adhesion and make necessary corrections. 9. Apply the brazing filler rod to the heated parts (do not heat it directly with the torch). 10. Cool the joint with water. 11. Clean the joint thoroughly using warm water and a brush.

Σύνοψη: (ενδεικτική) Η λογική σειρά ακολουθεί: κοπή → καθαρισμός/προετοιμασία → συναρμολόγηση → θέρμανση → εφαρμογή filler → ψύξη → τελικός καθαρισμός, όπως παραπάνω.

Κριτήρια αξιολόγησης:

Σύγκριση διαδικασιών soldering και brazing

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: In both procedures, we must clean the surfaces to be joined and apply flux before heating. In both soldering and brazing, we use a filler that melts and flows into the joint, while the base metals are not melted. Unlike in soldering, in brazing we heat the joint to a much higher temperature (above 500°C instead of below 500°C) and we use a copper-based filler instead of a tin-lead solder. Also, while in soldering we usually work with a simpler torch/iron, in brazing the joint often needs to be heated more evenly and for longer, moving the torch in a «figure eight» motion.

Σύνοψη: (ενδεικτική) Ομοιότητες: καθαρισμός επιφανειών, χρήση flux, χρήση filler χωρίς τήξη των base metals. Διαφορές: θερμοκρασία (<500°C vs >500°C) και είδος filler (κασσιτερο-μόλυβδος vs χαλκός-ασήμι).

Κριτήρια αξιολόγησης:

Σειρά βημάτων και ταξινόμηση — arc welding

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... TASK 2. Arrange the numbered instructions under the following headings: 1. Preparation for welding, 2. Welding the joint, 3. Finishing the joint. TASK 3. A. Read the additional instructions and say if they refer to: a) the safety of the welder, or b) the quality of the job: 1. Use clamps... 2. Wear arc welding gloves... 3. Keep the electrode moving while starting the arc... 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.

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-a (safety: clamps hold pieces securely), 2-a (safety: protective gear), 3-b (quality: prevent electrode sticking), 4-b (quality: correct speed), 5-b (quality: deepest penetration).
TASK 3.B: Instructions 1-2 belong to the preparation phase (before/while arranging and clamping the pieces); instructions 3-5 belong to the welding phase (while striking the arc and welding the joint).

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.

Κριτήρια αξιολόγησης:

Σύγκριση διαδικασιών gas brazing και arc welding

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.

Κριτήρια αξιολόγησης:

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