• The economic consideration should always prevail.
  
• In any case the welder should be convinced that his/her
  selection is the most efficient for the intended use.
  
• Therefore it seems that before committing to any expense
  the welder should make sure that the selection is right.
  
• Ask the supplier where you can see the proposed equipment
  in action. Go there and inquire if it is good for you.
  
• Get permission to practice hands on. Try to obtain it
  for a trial period (say two weeks) before buying.
  Look for used and reconditioned equipment.
  See if you can lease it for a period before purchasing.
  
• Do not let anybody push you before you have proved that
  it meets your requirements.
  
• Purchase only what fits you for the work you need now.

Now to the point

Normally both SMAW and GTAW are operated with a drooping,
constant current power source.

Obviously a larger current capability and wave form manipulation
and control are available with more expensive equipment.
Power sources of the following categories are arranged in order
of increasing price.

• For Home and Hobby work the simplest one phase AC transformer
  with output from 20 to 170 Amps is generally suitable for
  common uses, not too thin, although this type do not include
  wave output control.

• For more demanding light industrial use, a combined power supply
  of AC and DC of about the same output, up to less than
  200 Amps, with constant current characteristic but with adjusted
  wave shape control and fixed balance control between time with
  Electrode Negative (EN) for deeper penetration and Electrode
  Positive for cathodic cleaning action and shallow, wide bead,
  and with High Frequency for easy starts and arc stabilization.

• Industrial use may demand higher current output up to 250 or
  350 or 500 Amps and may offer adjustable balance control.

• Most advanced power supplies are currently those based on
  Inverter technology, that permits to the experienced welder
  to best adapt the output to the application requirements.
  Besides larger range balance control, claimed to increase
  travel speed and deposition rate, inverters offer output
  frequency adjustable in the range 20 to 250 Hz (as opposed
  to fixed 60 or 50 Hz of simple transformers) claimed to
  change the bead shape at will (the lower the frequency
  the wider the bead, the higher the frequency the narrower
  the weld bead).

Accessories

For SMAW only a pair of cables are needed (one connected
to the electrode holder, the other to the ground clamp), apart from the
usual welder's tools like hammer for slag removal and wire brush
and protection gear (hat, helmet, gloves, apron, boots etc.)

Torches for GTAW provide electric current for striking and
keeping the arc and supply the protecting inert gas to the weld.
Air cooling is sufficient for low currents. Above 200 Amp
torches are water cooled. A switch is provided for starting
gas flow and High Frequency current. When switching off the arc,
the gas flow is maintained for a while till the weld cools down.

Conclusion

This presentation comes to an end. It is understood that it
is only a guideline and that other questions may appear.
We would like to suggest that every welder should try to
obtain practical hands on test time before committing to
a purchase, as indicated above.

We will welcome your feedback and suggestions to be published
in next issues if judged of value to other readers.

-----------------------------------------------------------------

3 - How to do it well: Brazing Fittings

Q: During torch brazing of a fitting onto a steel tube, it was found
that the silver alloy filler covered the surface only in part, making the joint unacceptable. How can we improve?
A: First, the clearance between the elements should be correct,
between 0.05 and 0.10 mm (0.002" and 0.004") on the side.
Second, both surfaces must be absolutely clean from dirt, paint,
rust and oil or grease even when a flux is used.
Third, rotating gently one element relative to the other for
a quarter of a turn to the right (or to the left) and back while the braze is still liquid will most probably improve the results.

-----------------------------------------------------------------

4 - Understanding AWS Classification of Welding Electrodes.

The Classification of Electrodes (sticks) for Shielded Metal Arc Welding (SMAW) as established by AWS (American Welding Society) and adopted by industry at large,is used to identify the filler metal required in any given job.
Here we shall present the data for low carbon steel.

Standard diameters of the metal range from 1/16" to 5/16" and lengths are 9" to 18", with a bare length of 3/4" to 1-1/4" protruding from the shield coating, for making contact with the electrode holder.
Electrodes are sold packaged in metal or cardboard boxes.

The letter E indicates electrodes, and is followed by four or five digits the first two or three of which indicate the minimum tensile strength expressed in thousand pounds per square inch (psi) of deposited metal in as welded condition.

The next to last digit is either 1, for all position welding or 2, for flat or horizontal position only. The last digit indicates the type of covering and the current to use.
As the next to last digit modifies sometimes the meaning of the last digit, it is customary to present the Table with the last two digits.

Table

Last two digits	Type of covering	Type of current
10	High cellulose, sodium	DCRP
11	High cellulose, potassium	AC or DCRP
12	High titania, sodium	AC or DCSP
13	High titania, potassium	AC or DC
14	Iron powder, titania	AC or DC
15	Low hydrogen, sodium	DCRP
16	Low hydrogen, potassium	AC or DCRP
18	Iron powder, low hydrogen	AC or DCRP
20	High iron oxide	AC or DC (1)
22	High titania, sodium	AC or DCSP
24	Iron powder, titania	AC or DC
27	Iron powder, iron oxide	AC or DC (1)
28	Iron powder, low hydrogen	AC or DCRP
(1) Either polarity for flat welds, DCSP for horizontal welds. DC = Direct Current, Either Polarity DCSP = Direct Current, Straight Polarity (Electrode Negative) DCRP = Direct Current, Reverse Polarity (Electrode Positive) AC = Alternating Current

While Electrodes designated for AC can be used also with DC, the opposite is not true: DC electrodes must be used with DC only.
E6010 and E6011 are popular selections, providing deep penetration and good mechanical properties.
E6012 and E6013 provide medium penetrating arc and permit welding
even with poor fit up.
E6020 can be welded only in flat or horizontal position, provide medium to heavy penetration and permit high deposition rate.
Low Hydrogen electrodes should be always kept free of moisture,
and baked when necessary if exposed to the atmosphere;
they are used to prevent cracking in hard to weld steels.

The document dealing with this matter is:
AWS A5.1 - SPECIFICATION FOR CARBON STEEL ELECTRODES
FOR SHIELDED METAL ARC WELDING

Is this article helpful? Let us have your comments by e- mail. Click here.

-----------------------------------------------------------------

5 - In the news: Recent Welding and Cutting Articles

Reference to articles on welding and cutting subjects.

Notes: - The following links, that were active when this publication was released, are no longer supported by AWS.
You may be able to find the articles through their title and the date of their publication in the Welding Journal of August 2003.

News from AWS:

...precision laser cutting of special steel plates up to 16 mm (0.63 in) thick.

...Lasers and solid wire filler metal repair turbine blades.

...2 kW Laser assisted oxygen system cuts up to 3" (75 mm) and
potentially up to 4" (100 mm) steel plates in a fraction of time.

News from TWI:

...hybrid laser/gas metal arc welding for pipelines.
The article was unfortunately removed.
It may still be available by searching the TWI site.
Note: TWI requests a subscription without charge before opening its articles to the public.

News from Newport News:

...The Welding School of Northrop Grumman Corporation received
an award from the American Society for Training and Development.
Read article by clicking here.

-----------------------------------------------------------------

6 - Terms and Definitions Reminder

Do you remember what is meant by...

Forehand Welding?
It is a term used in oxy-acetylene welding for indicating a technique
consisting in directing the flame away from the deposited weld.
This produces important heating of the base metal and a greater proportion is melted.
This technique is usually preferred for welding thin sheets. Its opposite, called

Backhand welding
means the technique directing the flame against the weld just deposited.
Usually there is less melting of the edges of the joint and better retention
of chemistry and properties of the filler rod. Cooling of weld is slower.
Those preferring this technique affirm that it permits saving of time
and consumables, even for beveled joints.

And what about...

Keyhole technique?

It is a term used to indicate the piercing of a hole
through the thickness of the work by the heat source at joint edges.
Moving the heat source along the joint permits the molten metal to fill the hole.
Used generally for intense heat sources like Plasma Arc, Electron Beam Welding and
Laser Beam Welding, this technique finds an application in a much less
energy intensive process, like oxyacetylene welding in the particular situations of
Vertical Up or overhead welding. Welder's skill is here of utmost importance.

Would you want other terms being presented in next issues?
Let us have your feedback by sending your e-mail. Click here.

-----------------------------------------------------------------

7 - Site Updating

We are continuing to review and add new pages on the Site:
recently we added a page on Magnesium welding, and we are preparing a bunch of new pages where we want to deal in detail with welding of Carbon steels, of High Alloy Steels and of Tool Steels.

We want to add the subject of Braze-Welding as soon as possible.
Other subjects are too far down the line to be mentioned here.
And we plan also to add a page About Us, to come closer to our readers and to let them better know us.

If you would like a particular subject to be presented in the Site just let us know: drop us a line by e-mail: click here.

This is to say that any time you go back to the Site you may find
new information added: click here.

-----------------------------------------------------------------

8 - Work in Progress

We want to pay attention to readers' comments and feedback in future issues of Practical Welding Letter and we will do our best to make it more helpful and interesting.
We will present more articles on Selection of Welders, to cover other processes, and new items as they come to our attention.
We will report on recent updates of the Site.

-----------------------------------------------------------------

9 - Readers' Contributions

We would welcome contributions of our readers with articles of general interest.
In particular, personal experiences may be interesting to a larger public.
We must reserve the right of accepting, editing or rejecting readers' writings, in order to keep control on the level and integrity of the publication but we feel that the voice of the practical welder should be heard and listened to.

So you are invited to contribute with your thoughts and experience, by e-mail: click here.

-----------------------------------------------------------------

10 - Explorations: beyond the Welder.

We would like to recommend a few Sites of general interest that might take you over to new horizons, in unlimited Exploration trips,
for discoveries, learning and pleasure.

The excellent Site of Scientific American can be browsed by clicking here.

To see another very interesting Site, that of NASA, with subjects appealing to many people click here.

For the curious and the adventurous person, see what the Site of SBI has to offer to anyone ready to take the plunge in the Internet. Click here

-----------------------------------------------------------------

11 - Correspondence: a few Comments

We are glad to report that many people use the links provided
in the Site for submitting us the most diverse questions.

It is encouraging to see a growing number of interested browsers
who are ready to check if any good could come to them
from a direct question to somebody hitherto completely unknown.

We welcome all questions and will do our best to provide useful and practical answers.

This said we must stress that we seldom find all the basic data
in the messages we receive.
Either they are considered not important, or they are not known,
or they are simply forgotten.
It must be understood however that we cannot guess
the real situation if we are not given all relevant data on
materials, condition, welding process, parameters etc.

A few questions are clearly school assignments:
nothing wrong with that except that we would like to see a short note to this effect.
It would be easier for us to address the inquirer to pertinent literature to be studied.

Other questions are part of cloudy development projects whose details must be kept secret lest somebody might steel the idea:
it is very difficult to provide practical advice when the purpose of the development is not enounced.

A very frank reader complained that while looking in the Site
for advice on which equipment to buy, he came out more confused then helped. (He did not however clearly state his needs):
I am indebted to this reader for the decision to include in this issue
the article on How to Select Your Welder. I hope this makes clear that a number of decisions must be taken before operating the selection.

We would gladly publish questions and answer of general interest
but it seems that up to now our readers have very specific questions: that may change, though.

Keep on asking, we all are learning.

-----------------------------------------------------------------

12 - Bulletin Board

12.1 - A few readers sent us attachments to their messages.
We must inform you all that, as a matter of policy and of self protection, we will not open attachments at all.
It might be too dangerous.
So you are invited to append your photo or sketch
at the end of your message and avoid sending attachments.

12.2 - We would like to inform you that we will be unable
to respond quickly to all questions submitted during the third week of September 2003 because of a brief absence for personal reasons.
All messages will be answered the following week.

12.3 - We would like to let you know that we know and use an exceptional facility prepared to let anybody with no previous experience, build a successful Site
on the Internet. We recommend it because it works. See for yourself. Click here.

--------------------------------------------------------------

Visit the Welding Advisers Site at
https://www.welding-advisers.com/
and browse the several updated pages
Covering Welding Processes, Equipment, Materials,
Jobs and Careers, Quality, Safety and Related
Processes/Applications.
Free Subscription and Download. Questions welcomed.
Contact us at questions@welding-advisers.com.

--------------------------------------------------------------

Copyright © 2003, by Elia E. Levi and welding-advisers.com, all rights reserved