In a nutshell here are the 6 main things to remember when TIG welding 4130 chromoly tubing:

1. Preheat is not necessary for tubing under .120" thick. however it sure won’t hurt anything. If the ambient temperature is less than 60 F, I would say preheat to at least 100F. You can easily do this with a small propane torch from Home Depot.

2. Weld a little slower than normal. This just makes sense. Think about it. If there is an ongoing argument about GAS welding being superior than TIG welding for Chromoly tubing, then it makes sense to go just a little slower when TIG welding. This will slow the cooling rate and negate any chance of the welded area cooling too fast.

3. Don’t allow any Breeze or drafts in the room and do not speed cool the welds.

4. Use a TIG machine with high frequency starting to eliminate arc strikes. I had a "German Eye" pocket knife once that someone had used to cut a live wire. The small arc on the blade stuck out like a diamond and would not wear down with a file or sharpening stone. The same thing happens but to a lesser extent when you get an arc strike on 4130 chromoly. You get a hard brittle spot and a crack will definitely start there.

5. Do not use 4130 rod. Using a slightly under matched filler metal gives better overall properties and just plain works a lot better . Use E70S2 Tig rod and call it a day.

6. Taper off amperage slowly to avoid crater holes that will turn into cracks later on.

Have you ever tried to bend a piece of 4130 Chromoly tubing? OMG! This stuff is harder than Japanese arithmetic. Compare it to 1010 steel as far as how hard it is to bend and there really is no comparison. Just get a piece of 1/2 inch tubing and try it. You will strain your left testicle trying to bend chromoly tubing.

There are other chromium molybdenum steels like 4140 and 4340 but one of the most common chromoly steels is 4130 chromoly steel.

Back in the day, chromoly tubing was welded with oxy-acetylene. Why?

Because it worked... and because that is what most shops had available. And then years later I am sure some old timer said "because that’s the way we have always done it" .

But research has been done to prove that Tig welding can be the fastest, cleanest and best way to weld 4130 chromoly tubing without risk of compromising material properties(provided the thickness does not exceed .120").
Wyatt Swaim (also known as Mister Tig or "Mr. Tig")
Wyatt Swaim (also known as Mister Tig or "Mr. Tig") has been promoting Tig welding of 4130 chromoly tubing for several years now and even holds seminars and workshops for EAA (experimental aircraft association) enthusiasts to get them acquainted with the TIG welding process. But what does the number 4130 mean? What does the term "chromoly" signify? What is it most used for and why? And what is so difficult about welding 4130?

Chromoly refers to a steel alloy which contains chromium and molybdenum among otherelements. The word ‘Chromoly’ is a short term for “Chromium-Molybdenum" steel. Thenumber ‘4130’ is a code of the American Iron & Steel Institute (AISI 4-digit codesystem) and defines the approximate chemical composition of the steel. The ‘41’indicates a low alloy steel containing chromium and molybdenum and the ‘30’ indicates acarbon content of 0.30 percent.(that’s 3/10ths or 30 one hundredths of a percent) 4130 is often used for high end bicycle frames and race-car roll cages due to its high tensile strength, malleability and easy weldability. In addition, it is considerably stronger and more durable than standard 1020 steel tubing, which is also known as "plain carbon steel".
More details on AISI numbering system for alloy steels
Alloy steels differ from carbon steels in that they have compositions that extend beyond the limits set for carbon steels. Usually this refers to constituents such as boron, carbon, chromium, manganese, molybdenum, silicon and vanadium. They also have chromium contents less than 4%. Steels with chromium contents of greater than 4% become classified as stainless or tool steels. As a general guide, an alloy steel will have:

• Manganese content >1.65%

• Silicon content >0.5%

• Copper content >0.6%

The American Iron and Steel Institute (AISI) naming system is one of the most widely accepted systems.

Designations usually consist of a four digit number, but sometimes this extends to five. The first two digits indicate what the major alloying element is, while the last 2 or three indicate the carbon content in hundredths of a percent.

Example: AISI 4340 is a Nickel,Chromium,Molybdenum containing alloy steel with a 0.40% average carbon content.there also something called a "carbon equivalent formula" that basically calculates the effect that elements like chromium and vanadium etc. have on the hardenability of a steel. In other words, because aisi 4340 has 0.4% carbon but also has around 0.8% chromium, the hardenability might be the equivalent of a plain carbon steel having 0.5% Carbon.

The American Iron and Steel Institute has a numbering system for steels and the 4100 series indicates a chromium molybdenum steel. The "30" in 4130 indicates 0.3% carbon. 4130 also contains 0.4 to 0.6% manganese, 0.8 to 1.1% chromium, 0.15 to 0.25% molybdenum, 0.04% phosphorus, 0.04% sulfur, and 0.2 to 0.35% silicon, but like all steels, it is mostly iron. 4130 chromoly is an ideal material for BMX bicycle frames, roll cages for race cars, and for fuselages on small aircraft because of its high tensile strength and high strength-to-weight ratio.

Welding 4130 is not that much different than welding steel or stainless steel as far as technique is concerned. There are just additional considerations to keep in mind.

Remember...

watch your arc strikes,

dont speed cool,

use E70S2 tig welding rod,

pay attention to good fit ups,

weld a little slower,

use a little preheat if it is chilly in the shop,

taper off your amperage to avoid crater cracks.

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Spherical Pressure Vessel

Consider a spherical pressure vessel with radius r and wall thickness t subjected to an internal gage pressure p.
For reasons of symmetry, all four normal stresses on a small stress element in the wall must be identical. Furthermore, there can be no shear stress.

The normal stresses s can be related to the pressure p by inspecting a free body diagram of the pressure vessel. To simplify the analysis, we cut the vessel in half as illustrated.



Since the vessel is under static equilibrium, it must satisfy Newton's first law of motion. In other words, the stress around the wall must have a net resultant to balance the internal pressure across the cross-section.







Cylindrical Pressure Vessel

Consider a cylindrical pressure vessel with radius r and wall thickness t subjected to an internal gage pressure p.

The coordinates used to describe the cylindrical vessel can take advantage of its axial symmetry. It is natural to align one coordinate along the axis of the vessel (i.e. in the longitudinal direction). To analyze the stress state in the vessel wall, a second coordinate is then aligned along the hoop direction.

With this choice of axisymmetric coordinates, there is no shear stress. The hoop stress sh and the longitudinal stress sl are the principal stresses.
To determine the longitudinal stress sl, we make a cut across the cylinder similar to analyzing the spherical pressure vessel. The free body, illustrated on the left, is in static equilibrium. This implies that the stress around the wall must have a resultant to balance the internal pressure across the cross-section.

Applying Newton's first law of motion, we have,

To determine the hoop stress sh, we make a cut along the longitudinal axis and construct a small slice as illustrated on the right.

The free body is in static equilibrium. According to Newton's first law of motion, the hoop stress yields,


Remarks
• The above formulas are good for thin-walled pressure vessels. Generally, a pressure vessel is considered to be "thin-walled" if its radius r is larger than 5 times its wall thickness t (r > 5 · t).
• When a pressure vessel is subjected to external pressure, the above formulas are still valid. However, the stresses are now negative since the wall is now in compression instead of tension.
• The hoop stress is twice as much as the longitudinal stress for the cylindrical pressure vessel. This is why an overcooked hotdog usually cracks along the longitudinal direction first (i.e. its skin fails from hoop stress, generated by internal steam pressure).

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The majority of the electric cars on the streets today are home-made conversion cars. It is very possible to easily do an electric car conversion right in your own garage. There are many online communities where you will find recommendation and complete instructions on doing an electric car conversion yourself for a comparatively reduced cost. If you're concerned about your emission output and the environmental damage caused by carbon dioxide, then an electric automobile could be just the choice for you.
DC controllers and DC motors are the usual base parts of an electric car conversion. The first step is to select the voltage you would like the motor to run on.

96-192 volts is the normal range. Forklift providers often carry the perfect motors and controllers for electric conversion cars. Most folks use manual transmission vehicles as the donor car. You may need to choose a donor automobile with a fair unimpaired body. You need to also choose a fairly common model auto or the donor, as you will need to find spare parts with small difficulty and cost. there are many kinds of battery technology you can select from. The subsequent choice is to decide on the kind of electrolyte. The good thing about a flooded battery is that it is minimal cost, but the top power of them is low as well .
If you select a pre-packaged conversion kit you are able to save plenty of time. These kits are compiled with the best components you will need by folks who have great experience building electric conversions. They have been tested and proven to be effective .
when you have the kit, you will need to get a roomy and clean work area to start the project. You must also be sure that you have all the parts ordered and that they will be shipped inside a fair time period. To prepare the donor vehicle, you need to steam clean the engine compartment to clear away any residual grease. If you're using a kit, then it will come with an instruction book which you need to study and follow fastidiously throughout .

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