Welding Techniques and Equipment Overview

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Questions and Answers

List the equipment required to outfit a SMAW station.

AC or DC welding machine, electrode and work piece leads, electrode holder and work table, ventilation and welding booth.

What welding processes use constant current arc welding machines?

SMAW and GTAW.

What minimum information should be provided when describing an arc welding machine?

Type of the power source, whether constant current or constant voltage, and whether AC, DC, or AC/DC.

What is a typical open circuit (no load) voltage for an arc welding machine?

60-80 volts. Signup and view all the answers

What are the advantages of using a constant current arc welding machine?

Large % change in voltage will result in small % change in current. Signup and view all the answers

Explain how SCRs are used to control the welding current from the transformer.

SCRs can be turned on at different times in the AC half cycle and control the amount of current from the transformer. Signup and view all the answers

How is DC created in an AC alternator or transformer type welding machine?

The AC passes through a rectifier which uses diodes to cause the current to travel in only one direction. Signup and view all the answers

What direct current polarity flows from the electrode, across the arc, to the work?

Direct current electrode negative (DCEN) or direct current straight polarity (DCSP). Signup and view all the answers

Briefly explain the steps taken in an inverter machine to turn AC input into DC welding current output.

The AC is rectified to DC. This DC goes through an inverter circuit which creates high frequency AC. It goes through a transformer and then another rectifier and an inductor. Lower voltage, high amperage DC is used for welding. Signup and view all the answers

Why is an inverter transformer so much smaller in size than a regular transformer?

Transformer size is inversely proportional to the frequency used. An inverter uses high frequency current and thus is smaller. Signup and view all the answers

When a welding machine is used at a higher current setting, does the duty cycle increase or decrease?

Decreases. Signup and view all the answers

What is used to grip the electrode while welding?

An electrode holder. Signup and view all the answers

What size welding leads are required to carry 300A a distance of 90' (27.4 m)?

1/0. Signup and view all the answers

What are the 5 functions of the flux covering on the SMAW electrode?

Produce shielding gas to protect the metal from oxidation; provide fluxing agents, scavengers, and deodorizers; produce slag covering over the weld bead to protect it while it cools; the slag permits metal to cool slowly and establish the polarity and electrical characteristics of the electrode. Signup and view all the answers

What information is obtained from the first and second (possibly third) number in the AWS electrode classification?

Tensile strength of the electrode wire in thousands of pounds (psi) or kilo-pounds (ksi) per square inch. Signup and view all the answers

What is in an EXX24 electrode covering?

Iron powder and titania. Signup and view all the answers

List 4 electrode numbers which contain low hydrogen.

E7015, E7016, E7018, E7028. 5, 6, and 8. Signup and view all the answers

List 3 AWS electrodes that contain iron powder.

E6027, E7014, E7018. Signup and view all the answers

What does the electrode classification E316-16 tell the welder?

The electrode is a low chromium or chromium/nickel, low hydrogen electrode used with AC or DCEP. Signup and view all the answers

What number filter lens is recommended for SMAW?

#10 and #14. Signup and view all the answers

Study Notes

Equipment for SMAW Station

Necessary items include AC or DC welding machine, electrode and work piece leads, electrode holder, and work table.
Proper ventilation and a welding booth are crucial for safety.

Welding Processes with Constant Current Machines

Shielded Metal Arc Welding (SMAW) and Gas Tungsten Arc Welding (GTAW) utilize constant current arc welding machines.

Information for Arc Welding Machine Description

Essential details comprise the type of power source, designation as constant current or constant voltage, and the form of current (AC, DC, or AC/DC).

Open Circuit Voltage

Typical no-load voltage for an arc welding machine ranges from 60 to 80 volts.

Advantages of Constant Current Machines

Significant voltage changes result in minor current fluctuations, providing better control over the welding process.

SCRs Control in Welding

Silicon Controlled Rectifiers (SCRs) operate by switching on at various points in the AC half cycle to manage the current supplied by the transformer.

DC Creation in Welding Machines

Alternating current (AC) is rectified by diodes to produce direct current (DC), ensuring that the current flows in one direction.

Direct Current Polarity

The current flows as Direct Current Electrode Negative (DCEN) or Direct Current Straight Polarity (DCSP) from the electrode to the work.

Inverter Machine Process

AC input is rectified to DC, passed through an inverter circuit creating high-frequency AC, which is then transformed and rectified again, resulting in lower voltage, high amperage DC suitable for welding.

Inverter Transformer Size

The size of an inverter transformer is smaller than regular transformers due to its operation at high frequency, which inversely affects the transformer size.

Welding Machine Duty Cycle

Using a welding machine at higher current settings results in a decreased duty cycle, limiting the duration of welding operations.

Electrode Holder Function

An electrode holder is employed to securely grip the electrode during the welding process.

Welding Lead Specifications

Welding leads rated for 300A over a distance of 90 feet should be sized at 1/0.

Flux Functions in SMAW Electrodes

The flux covering serves multiple purposes: creates shielding gas, provides fluxing agents, forms slag for cooling protection, allows slow cooling of weld beads, and establishes electrode electrical characteristics.

AWS Electrode Classification

The initial numerical classification provides information about the tensile strength of the electrode wire in psi or ksi.

Composition of EXX24 Electrode Covering

The EXX24 electrode contains iron powder and titania in its covering composition.

Low Hydrogen Electrode Designation

Electrodes designated as E7015, E7016, E7018, and E7028 contain low hydrogen, indicated by the last digits 5, 6, and 8.

AWS Electrodes with Iron Powder

Examples of AWS electrodes that contain iron powder include E6027, E7014, and E7018.

E316-16 Electrode Classification

The E316-16 classification indicates a low chromium or chromium/nickel, low hydrogen electrode compatible with AC or Direct Current Electrode Positive (DCEP).

Recommended Filter Lens for SMAW

For Shielded Metal Arc Welding, filter lens numbers #10 and #14 are recommended for eye protection.

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Description

This quiz covers essential equipment and processes utilized in Shielded Metal Arc Welding (SMAW) with a focus on constant current machines. It includes information on necessary items, safety considerations, and the advantages of using certain welding technologies. Test your knowledge on arc welding machines and their operational details.