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Welcome to Signature Metal Fab Racing
We know there are a lot of you guys out there building cars at home, whether a seasoned veteran or a complete beginner. This section is for us to be able to share some of our knowledge and industry standards with all of you, in an effort to maintain the level of safety and performance that is required in high level motorsports!
The importance of a good Seat
Some simple philosophies and facts about motorsport crashes:
- If you support the human body well enough in the right places and keep all parts of the body in the same relationship to each other, a body can withstand enormous decelerations with minimal or no injuries. 100G is quite survivable.
- The four parts of the body which need this support are the head, shoulders, pelvis and thighs.
- Lateral/side impacts cause more serious injuries than frontal impacts.
- The body should be stopped as close to the chassis deceleration as possible.
- Only 20% of body movement in a frontal deceleration is in belt stretch; the balance is body reconfiguration.
- Using a crash recorder in the field, we have measured an 81G lateral impact during use of a Racetech seat in a New Zealand motorsport class. The driver had no injury ... and the seat had no damage.
Proper Seat Belt Mounting
Important Installation Guidelines for Harnesses:
1. Shoulder Belts: The optimum location for the shoulder belt anchor is level with the shoulder line. Anchor shoulder belts a MAXIMUM of 5 degrees below and 5 degrees above the shoulder line. When installing shoulder belts in conjunction with a head and neck restraint system the anchor point for the shoulder belt must be in accordance with the head and neck restraint system manufacturer's recommendations.
2. Lap Belt: Lap Belt anchors should be located in a position that is slightly wider than the seat allowing the webbing to pull in a straight line to the mounting anchors. Do not allow the webbing to come in contact with any sharp edges that could cause abrasion. The angle formed by the Lap Belt and the vehicle floor, when the belt is being worn, should be approximately 45 degrees.
3. Anti-submarine Belts: 5-way or 6-way anti-sub belt(s) should be anchored behind the extended Chest Line. The extended Chest Line is a line drawn from the chest to the Lap Belt buckle continuing to the floor. On 7-way systems the outside anti-sub belts wrap around the inner to under thigh and exit the bottom seat. Anchor in the same position as the Lap Belt.
4. Webbing Installation: see diagram for proper installation.
5. Anchor Installation: Anchor hardware must be installed at an angle that is compatible with the load direction of the webbing.
UNDER NO CIRCUMSTANCES ARE BOLTS INSTALLED THROUGH WEBBING ACCEPTABLE FOR INSTALLATION!!
Always use a Restraint Systems that are adjusted correctly. Users should NEVER run a loosely adjusted harness! Installed webbing lengths should be kept as short as possible for best performance.
Tungsten Shape for TIG Welding
Tungsten electrode sharpening is a critical process to produce the required electrode shape, which affects arc starting, weld penetration, arc shape, and electrode life.
In AC welding, pure or Zirconiated tungsten electrodes are usually used. You need to create balled shape of the tungsten electrode tip.
To produce a ‘balled’ end, initiate an arc with the electrode connected to the positive side of the welder, Increase the current until it melts the tip of the electrode.
For DC welding, Ceriated, Lanthanated, or Thoriated tungsten electrodes are typically used. You need to sharpen the tungsten electrodes to a specific angle.
As a general rule, the length of the angle of the electrode tip is equal to approximately 2 to 2.5 times the electrode diameter.
*Always grind tungsten electrode in the lengthwise direction, following the direction of the tungsten. Never grind across or swirl around, This will cause arc wander*
Chromoly Welding Practices
Best Practices for Welding 4130 Chromoly
* Set argon flow to 18 - 25 cfh and check the flow rate every day. More is not always better, as turbulence could suck oxygen into the weld.
* Set gas pre-flow at .3 to .5 seconds; set post-flow to 9 to 12 seconds. Hold the torch in place at the end of the weld for the entire duration of the post-flow.
* Whenever joint access permits, use a gas lens to improve gas coverage. Keep the screen free of debris and spatter.
* For the majority of thin tabs and brackets, use a 1/16-in. tungsten and .045-in. filler rod.
* For welding tube joints, use a 1/16-in. tungsten and 1/16-in. filler rod.
* For welding roll cages (larger, thicker tubes), use 3/32-in. tungsten and 1/16-in. filler rod.
* Most chrome-moly welding is on tubing and parts .035- to .090-in. thick. Set the maximum amperage output to 120 to 130 amps, DC electrode negative, HF start only.
* A dirty-looking grey colored weld may indicate poor argon coverage or too much heat.
* Keep tack welds small and ideally longer in length than width. A good tack has root penetration.
* Keep welds to within their specified size. A weld needs to be no larger than its thinnest section, which will be the “weakest link” in the chain. Larger welds may add excess heat and waste gas, filler rod and time.
* Avoid pinholes by tapering off heat input at the end of the weld and maintaining a constant distance between the tungsten and the weldment.
* Weld in one continuous motion, “pulsing” the foot control and adding filler rod to create the “stack of dimes” appearance. Never Pulse far enough to where the weld puddle cools or goes away between pulses, this may lead to incomplete fusion.
4130 Chromoly vs. Mild Steels
Chassis Tubing: 1020 DOM vs. 4130 Chromoly
- 4130 is an Alloy steel which contains chromium and molybdenum as alloying elements
- 1020 Mild steel is a low-carbon steel that does not contain any alloying elements.
-Mild Steel and Chromoly are the same weight for a given cross sectional area
-Chromoly generally offers 25% higher tensile strength than Mild Steel for the same given cross sectional area.
-Generally speaking, anything that can be successfully made out of mild steel can be made thinner and lighter with
Chromoly because of it’s increased strength.
-1020 DOM, Yield 70 Ksi, Tensile 80 Ksi, Elongation 15%
-4130 NORM, Yield 95 Ksi, Tensile 105 Ksi, Elongation 15%
Yield Strength: The maximum stress that can be applied before it begins to change shape permanently.
Tensile Strength: The resistance of steel to breaking under tensile tension.
Elongation: The percentage of stretch from the original length of the steel to the point of failure
Welding Wire for Chromoly
The best filler material to use for 4130 Chromoly (Normalized condition) is American Welding Society (AWS) ER70S-2 specification.
- The main objective is always to produce porosity and crack free welds This welding filler alloy has a very low carbon content, nominally 0.06, which can handle dilution into the relatively high (in terms of weld metal), 0.30 carbon in the 4130. The resulting weld has a tensile strength of approximately 590 to 620 MPa ( 85,000 to 90,000 psi.) The actual strength will depend on the amount of dilution with the 4130, weld bead size and material thickness.
- With only small additions of filler alloy to the weld puddle there is a high percentage admixture of 4130. In these very small welds this can create a crack sensitive metallurgical structure. The use of ER70S-2 becomes even more of a preferred suggestion because ER70S-2 with its low carbon and leaner Manganese and Silicon alloy creates less of a dilution problem.
- Use larger flat fillets to assure less dilution with the 4130 and a less crack sensitive shape.
TIG Weld, ER70S-2, Tensile 82ksi, Elongation 31%