Exercise 7. Answer the following questions. Use the information of the previous text.
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What metals can be forge welded?

What should be metal thickness in forge welding?

What is required in furnaces to heat objects to the plastic state?

What kind of heating is necessary in furnaces?

How are surfaces of metal peaces prepared?

 

Exercise 8. Agree or disagree with the statements.

1) The parts are placed on the anvil after heating up to over l000°C until they are plastic.  
2) Parts are hammered together until the solid state.  
3) If made correctly, a forge welded joint is soft.  
4) Forge welding requires considerable skill on the part of the operator  
5) Forge welding is a rapid process as compared to arc and gas welding  
6) There is no danger pickup by the metal from the coke of the furnace.  
7) Fire welding in which pieces to be joined are heated in the fire by the blacksmith.  
8) Edges of the plate are heated by furnace.  

Exercise 9. Give English equivalents to:

наковальня, доменная печь, прокатка, толщина металла, соединение, плавка, давление, шов, кромка, пластина, окисление, ковка

значительный, медленный, низкий, пластичный, ковкий, хрупкий, прочный, прокатанный, твердый, быстрый, вытянутый, сжатый, постоянный

предотвращать, сваривать, преобразовывать, применять, защищать, нагревать, выполнять, получать, образовывать

Exercise 10. Watch the video about MIG welding www.youtube.com/watch?v=IpBFUrpUGZg . Discuss the following questions:

1. What is MIG welding?

2. What does the MIG welding process consist of?

3. Why do we use the inert gas?

4. What are the characteristics of MIG welding?

5. What is the thin copper layer on the steel wire used for?

6. Name the types of wires that can be utilized for MIG welding?

Exercise 11 . Fill in the WORKSHEET 2.

 

A. WHAT “MIG” STANDS FOR: M_______________________________ I________________________________ G________________________________
B. THE CHARACTERISTICS OF MIG WELDING ARE:   · _______________________________   · ________________________________  
C. ITS COMPONENTS ARE:   · HIGH-_________________ STEEL WIRE COILED IN A __________________ · SET OF DRIVE __________________ · _________________ SUPPLY · MIG __________________ · SUPPLY OF ___________ ____________  

 

D. THE INERT GAS IS FED ________________ THE GUN TO ________________ THE WELD FROM ___________________ AND __________________ IN THE ATMOSPHERE.

 

 

E. THIN COPPER ____________________ IS USED FOR GETTING THE _________________________ ONTO THE __________________ AS IT GOES INTO CONTACT.

 

F. TYPES OF WIRES USED: · CARBON _______________ WIRE · _______________________ STEEL WIRE · ____________________ WIRE · ALUMINIUM ______________.

Higher Level:

 

Text3. ARC-welding (1)

Technique of arc welding.

Metal-arc welding is a process of joining two pieces of metal by heating, melting and fusing the edges or surfaces under the temperature of 5,400-6,0000 F. In arc welding, the intense heat, required to reduce metal to a liquid state, is created by an electric arc. The arc is formed between the work to be welded and a metal wire called an electrode. The electrode, held in a suitable holder, is brought close to metal to be welded, forming an arc between the tip of the electrode and the work.

The arc is a means for transforming electrical energy into heat. The tremendous heat, highly concentrated at the tip of the electrode, molten a small pool of metal. The pieces to be joined thus become liquid and fuse together in this molten pool called the crater. At the same time, the end of the electrode at the arc metals, and this molten metal is carried over by the arc to the molten pool on work piece. With a consumable electrode, once the arc is obtained, it is necessary to move the electrode uniformly toward the work piece, thus compensating for the loss of metal at its end. As the areas solidify, the metals are joined into one solid, homogeneous piece. Metal-arc welding is a normally a manual rather than mechanized operation. If the pieces to be joined are relatively thick, it may be necessary to make two or more passes in order to complete the weld.

The arc welding process requires a continuous supply of electric current, sufficient in amount (amperes) and of proper voltage to maintain an arc. This current may be either alternating (AC) or direct (DC). The source of energy must provide a range of voltage across the arc from 17, which in the minimum for starting an arc, to approximately 45 volts. Welding current may vary from 10 amperes to as high as 1,500 and over for automatic welding.

If DC is used, the polarity of the welding circuit is important to correct procedure. DC welding machines have positive and negative terminals. When the electrode is connected to the negative terminal, «straight» or standard polarity is used. This means that the current is flowing from the work to the electrode. By changing the lead or polarity switch the current will flow in the opposite direction, from electrode to work. This is known as «reveres» polarity. Most welding machines are equipped with a polarity switch for reversing the flow of current without changing the lead cables at the terminals.

Several different types of welding machines are available for satisfactory welding current. Direct current. Direct current is produced in either electric motorgenerator sets or engine-driven generator sets. Practically all AC arc-welding machines are transformers which take current from an outside source and convert into welding current. Combination welders, producing both AC and DC current, are the most versatile of all types of welders. They are basically a transformer and rectifier with means provided for tapping into the either AC or DC output.

 

Exercise 12. Answer the questions:

1) What was welding in its original meaning?

2) When does the history of electric arc-welding begin?

3) What did Petrov and Davy investigate?

4)Who was a founder of metal-arc welding?

5) When did he develop metal-arc welding?

6) What is metal-arc welding?

7) How is the welding heat created?

8) Describe briefly the metal-arc welding process?

9) What current is used in the metal-arc?

10) What factors are required for maintaining the arc?

11) How do the voltage and amperes of the welding current used?

12) What machines is direct current produced in?

13) What does «straight polarity» mean?

14) How is «reverse» polarity obtained?

15) What is the A.-C. arc-welding machine?

16) What welding machines are the most versatile types of machines?

17) What metal-arc equipment is there in your laboratory?

18) Did you work as a welding operator?

 

Exercise 13 . Watch the video HOW TO BECOME AN ELECTRIC ARC WELDER www.youtube.com/watch?v=WaDsmeB5ywM and discuss the following questions:

 

1. What are the tools for arc welding?

2. How to assemble the welding tool?

3. What is “alive wire”?

4. How to create an electric arc?

5. What happens to a wire when the electric arc is created?

6. What is flux? What is it used for?

7. Tell about the first exercises of an electric arc welder?

8. What is the “rows of neat little dots”?

 

Exercise 14 . Fill in the Worksheet 3.

 

  A. TO CLAMP MEANS   · TO FIX   · TO PLACE   · TO MAKE  
  B. ELECRICALLY CHARGED ELECTRODE IS     ___________________________________  
  C. TO CREATE AN ELECTRIC ARC YOU NEED AND     ELECTRIC ARC     · ____________________ DOWN A PIECE OF STEEL WITH AN ________________     · BEGINS TO _____________________ WIRE.    
    D. WIRE IS COVERED WITH   _____________________________ THAT   PREVENTS ______________ AND    NITROGEN TO GET IN THE    ___________________ .   AND __________________ THE WELD FROM    THE ATMOSPHERE.  

 

Individual Work:

Text 4. Arc welding (2).

Arc welding. In arc welding, the heat required to metal the parts being joined is obtained by striking an arc between an electrode and these parts. Both direct and alternating currents are used but direct current is the common. Two kinds of electrode are used: (a) carbon, and (b) metal, and the latter may be (1) bare, (2) coated, or (3) cored. The metal electrode is by far the most widely used, the carbon arc process being now chiefly confined to certain automatic welding machines and for welds that require no filler metal. In direct current welding the electrode is usually made the negative pole and the work positive, because with a carbon electrode the electrode consumption is less and with a metal electrode the heat developed at the anode (the positive pole) is greater than at the cathode (the negative pole). The choice of polarity, however, depends on many factors most coated electrodes weld better when connected to the positive pole rods containing more than about 0,9 per cent of manganese also generally behave better when the rod is made positive. Reversed polarity (rod positive) is also best for aluminum because it gives better control of the penetration on account of the lower temperature of the plate. The voltage applied across the arc ranges from 18 to 30 with metal electrodes and from 80 to 100 with carbon electrodes: it varies with length of arc, and the current and the rate of deposition will vary accordingly. Some of the acquired skill of a good operator is directed to maintaining the arc length constant. The current employed from 20 to 900 amperes with hand-operated arcs but may be as high as 15.000 amperes in automatic welding machines. With metal electrodes the rate of deposition is roughly proportional to the current employed. Metal electrodes vary between 1/16 and 3/8 in. diameter and are usually from 12 to 18 in. long. The reminder of this section is restricted to metal arc welding.

The current used must be related to the size of electrode and the nature of the work being done. Too low a current is likely to result in poor penetration, the electrode being melted and merely dropped on the job, which is not properly fused. Too high a current results in overheating of the electrode and a poor weld; it also causes excessive spattering and waste of electrode. Nevertheless it is better to use too high than too low a current. With coated electrodes too high a current tends to prevent the slag from covering and protecting the weld deposit, while too low a current produces a viscous slag and increases the risk of slag inclusions in the weld metal. Some idea of the currents used is given by the following table:

 

Gauge of electrode Current, amps
12 80-110
10 110-140
8 130-170
6 160-240
4 180-280

Дата: 2019-07-24, просмотров: 167.