Alloy Steel Fittings vs. Die Cast AKA “Thin Wall Fittings”


Know the Difference

What’s the Difference?. . . PLENTY!  They’re Called Thin Wall Fittings for a Reason.

View this video to learn more about Die Cast and Steel Fittings

 

Malleable Iron vs Steel vs Die Cast

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Malleable Iron vs Steel vs Die Cast


Todays’ conduit runs not only carry electrical service cables, they contain low voltage data, security, fire alarmCTTV, and even fiber optic. Any disruption to conduit connections places sensitive, expensive equipment, security systems, and assets at risk. Why is the weakest connection of your entire installation the conduit fitting?  It is when you use a thin wall die cast fitting.

FACT: During Contractor Installations, 1 Out of Every 10 DIE CAST ELECTRICAL FITTINGS Is Scrapped Due to Cracking or Damage From Normal Torque!

FACT: 1 Out of Every 4 Fittings, 1″ or Less, Will Semi-Deform During Installation, As a Result of Set Screw or Compression Torque!

FACT: Todays’ Longer Conduit Runs Create GREATER STRESS On Coupling Fittings!

FACT: Die Cast Products Have Natural  Porosity.   View Enlargement of Photo   Porosity and inclusions in a die cast product degrades the quality and integrity of the part. This is especially true, if the porous areas in the die casting are large enough to affect overall shell strength.

Die Cast Fitting ExplosionLR

Now, Look at Our Fully Machined Alloy Steel Fittings View Enlargement

Steel Electrical Fitting Coupling Made in USA

Need to Know More? Here are  the Technical Facts


Steel Fittings vs. Zinc Die Casting Fittings,  Know the Difference

When selecting EMT or Rigid Electrical Conduit fittings contractors will often choose the “least expensive” product regardless of the material or design mainly because it is Underwriters Laboratories (UL) listed and it is considered as “good enough”  (meeting minimum acceptance levels).

However, do you know the wrong fitting material and design could compromise the raceway installation, put personnel and assets at risk? Did you know the right chosen fitting saves costly installation costs?

The “good enough” concept in the wrong environment and or misapplication create an integrated problem for all wiring passing through that just good enough system. Comprised systems to literally save pennies is a foolish cost saver when you consider down time, labor savings in installation, and long term integrity.

Although all UL listed products, regardless of material, have been tested to the same performance specification, a UL listing does not always promise raceway integrity under a variety of conditions.

  • UL compliance is based on testing and meeting minimum performance requirements.
  • UL does not offer categories of fittings such as “Light Duty”, “Heavy Duty”, “Commodity Grade”, “Commercial Grade”, or “Industrial Grade”; these are all subjective marketing nomenclatures assigned by the fitting manufacturer.
  • Selecting the fitting with wrong design and/or material could be damaging.   Example:  What would happen to a fitting in a wastewater treatment facility, salt or fresh water marine installation, or during a seismic incident that can occur in many areas of the United States?
  • What raceway integrity occurs when using thin wall die cast fittings in the longer 20’ pipe runs occurring today? Yes, there are hangers, but force and moment stress affects the fitting in hung pipe. Expansion and contraction are also a key factor for these thin wall die cast products.

Factors that affect fitting performance include materials (such as steel, malleable iron, and zinc die cast), fitting wall thickness, and style of fitting such as setscrew or compression, plus the overall product design.

PRODUCT FACTORS

DESIGN:  Product design is vital to fitting performance AND application of use.

Wall Thickness”- Some fitting manufacturing processes permit the use of thin walls, such as zinc die castings with thicknesses as low as .047” (when reinforced with ribs), thin wall stamped steel .025” thick, and sand cast iron .063” thick.

AMFICO  ½” through 2” steel fittings are machined from solid US steel bar stock with no seam to split and have minimum wall thicknesses of at least .080”, 2-1/2” and larger size malleable iron products have a wall thickness of at least.190”; both material thicknesses are over 3 times the UL requirement.

“Set Screws and Compression Nuts”- Smaller setscrews limit the amount of engagement with the conduit, while fittings with thinner walls and softer materials can also crack or strip when tightened.  Compression nuts with thin walls can deform during tightening with a wrench or channel locks.

RIGIDITY:  Material properties vary greatly amongst fittings; the obvious selection of steel as being the strongest of all fitting materials is unchallengeable.

Typical Mechanical Properties

  • “Tensile Strength”- Zinc die cast (alloy #7) 41000 psi, malleable iron 52000 psi, thin wall steel (Fe1018) 64000 psi, AMFICO select steel 78000 psi.
  • “Yield Strength”- Zinc die cast 32000 psi, malleable iron 33000 psi, thin wall steel 54000, AMFICO select steel 70000 psi.
  • Hardness (BHN)”- Zinc die cast 80, malleable iron 130, thin wall steel 126, AMFICO select steel 163.
  • “Creep”Only zinc die castings are subjected to this inherent phenomenon, which is described by one zinc alloyer as deformation when subjected to elevated temperatures and stresses.  Simply stated, zinc dies cast fittings may deform over time and/or at elevated temperatures.

CORROSION PROTECTION: UL listed conduit fittings comply with the following requirements:

  • Zinc die cast fittings do not require any corrosion protection; they are sold a cast or after receiving a ball burnish polishing.
  • Malleable iron needs only visible zinc plating because the surface roughness is too coarse to accurately measure plating thickness.
  • AMFICO select steel  have a quality controlled .0005” average zinc plating thickness.
  • AMFICO products can be further enhanced for corrosion protection by galvanizing, a process  not available on zinc die cast and not practical to add to imported thin wall stamped steel and malleable iron products because of shipping lead time.
  •  Harsh environments would normally specify the need for galvanized products- since many manufacturers cannot offer galvanized fitting, contractor and specifiers do not know it is available.

INSTALLATION: Fitting installation is critical to maintain proper securing of conduit, bonding, and ability to carry possible ground fault current.  Improper assembly of fitting to conduit can occur many ways such as:

  • Setscrew tightening is at the resolve of the installer.  Someone who in the past may have had a zinc die cast fitting crack because of over-tightening is more likely to not tighten as much as the UL test value of 35 In-Lbs, likewise thin wall steel fitting could have screw strip with over-tightening.  Both malleable iron and AMFICO steel products are less likely to fracture the casting or strip the threads because of strength and hardness, in fact AMFICO 2-1/2” and larger fittings are provided with case hardened bolts to be tightened with a wrench at UL test value of 160 In. -Lbs  that’s 4-1/2 times that of screwdriver slotted set screws.
  • Screw design and location is also important since fittings with screws spaced too far apart or in-line with each other will not penetrate the conduit enough or will slide easier off the conduit with excessive movements, screw length is also important.  Loosening of the fitting on the conduit could cause inadequate bonding.
  • To avoid being the weakest link in the raceway system the wall thickness of the fitting should as closely as possible match that of the conduit wall thickness.  Samples of rigid coupling were sectioned to reveal wall thicknesses: 2-1/2” zinc die cast, stamped steel, and AMFICO malleable iron; the zinc die cast product with set screws measured .062” thick, stamped steel fitting with set screws .115” thick, and AMFICO malleable iron with bolts.193” thick; the 2-1/2” rigid nominal wall thickness is .203”. See photo below for sample sectioned view.

KEY TAKEAWAY:

Other than, for use on flexible cables and light duty application material selection and design can have significant impact on the raceway system.  Avoid being the weakest link in the raceway system by matching fitting thickness as closely as possible to that of the EMT, IMC, or Rigid conduit.

A Final Point

Considering the issues you may encounter with using thin wall residential fittings in industrial applications, you should also consider the added impact when these fittings come from offshore facilities. Although you may be buying from a domestic major manufacturer or distributor source – ASK THE COUNTRY OF ORIGIN BEFORE YOU BUY! 


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