You may have heard of "Blue Bolt Coating", its real name is Whitford Xylan(R) Coating... and it isn't always blue. Many of our customers ask for the "Blue Bolt Coating", but what exactly is Xylan and when should it be used?

Xylan is a blend of fluoropolymers, engineering plastics and selected corrosion inhibitors which, when combined, create these characteristics in fasteners:

• Low friction 
• Exceptional adhesion 
• Unusual resistance to wear and abrasion 
• Excellent corrosion resistance 
• Resistance to chipping
• Resistance to the weather, sunlight and salt water

Xylan's versatility is best demonstrated as a coating for stud bolts and nuts, where it provides unparalleled performance in ease of installation, corrosion resistance and ease of removal. It can be used on standard alloy steel nuts and bolts, or can be paired stainless steel fasteners for even more benefits.

Xylan fastener coatings or "Blue Bolt Coatings" are typically specified in oil and waterworks applications. Contact us for more information.

A bolt’s function essentially boils down to applying a high enough clamp force that when external forces are applied, transverse movement and separation cannot occur.

Using calibrated torque tools to tighten fasteners and apply that clamp force is far superior to going by the user’s judgement or feeling.  Or, as one senior technician calls it “The One Grunt or Two Grunts Method”.  Measuring torque alone, however, does not ensure a proper installation.

• Torque is an indirect indicator of Tension.

  • Torque is the measurement of twisting force needed to thread the fasteners together.

• Tension is the force that actually holds an assembly together. Put another way:

  • A bolt can stretch similar to a spring, as it becomes tightened once all the parts of the assembly are brought together.

  • The higher the torque applied to the fastener, the more tension is created as the bolt stretches.

If a bolt is like a spring and more torque equals more tension, why doesn’t a certain amount of torque always result in the same amount of tension?

Though the relationship between torque and tension is linear, many other factors can affect this relationship. Some of these factors include surface texture, rust, oil, debris, material type, locking elements and human error.  Because of these variables, tightening to a specific torque setting can create varied results in the field or on the assembly line. 

The Torque/Tension Equation is a method used to estimate the torque/tension relationship in an assembly. T = (K D P)/12--------------------- can be used to developt a torque value that will achieve a certain tension or clamp load. 

T = Torque (ft.-lbs.)

D = Nominal Diameter (inches)

P = Desired Clamp Load Tension (lbs.)

K = Co-Efficient of Friction

The K factor can vary depending on the condition of the threaded fasteners. 

Commonly used factors range

• Lubricated with wax, oil or other coating = 0.10

• Plain, uncoated = 0.20

• Galvanized = 0.30

• Dirty or Rusty = 0.30+

While most bolt torque charts use this formula, these are only estimates, and since conditions can vary in real world applications, torque charts and this formula should be used only as a guide. 

"
The best way to determine correct torque is through experimentation under actual assembly conditions.
"

There are other methods used to achieve specific Clamp Load, including:

• Turn-of-the-Nut. Specific Tension can be accurately reflected in the number of rotations a fastener needs to bring the parts of an assembly together.

• Direct Tension Indicator. A Direct Tension Indicator washer (DTI washer) has protrusions that compress when the joint is tightened. That compression amount is measured by a feeler gage in some structural applications to correlates to a specific tension. Another type of DTI washer is the Squirter(R) type washer, which contains a small amount of silicone material that is expelled when the proper tension is reached.

Need more info than you see here about torque? Call us at +86-755-27859830.

The short answer is NO.

General commodity commercial fasteners do not fall under the umbrella of products that would require a UL listing or ICC-ES report. There are three main governing bodies that cover specifications for fasteners. ASTM (American Society for Testing and Materials) covers primarily bolts and fasteners for construction applications. SAE (Society of Automotive Engineers) covers fasteners for automotive, machinery, and OEM applications. ASME (American Society of Mechanical Engineers) standards B18.2.1 and B18.2.1 cover dimensional tolerances for square and hex head bolts, screws, and nuts. China Special Fasteners provides fasteners to these three sets of specifications (ASTM, SAE, and ASME). A fourth specification group that is also applicable is AASHTO (American Association of State Highway & Transportation Officials). AASHTO specifications are typically only called out on highway projects and many AASHTO designations can be directly converted to an ASTM equivalent.

ICC (International Code Council) is the primary governing body responsible for writing and maintaining building, plumbing, mechanical, and fire codes adopted by local and state municipalities, and the federal government. ICC-ES (International Code Council-Evaluation Services, Inc.) is the branch of ICC responsible for performing technical evaluations of building products, components, methods, and materials to ensure that they meet the requirements of the codes. This evaluation process culminates in an ICC-ES report that provides evidence that the evaluated product or system meets code requirements. However, in the case of most anchor bolts and fasteners, the applicable sections of the codes (International Building Code, International Residential Code, International Property Maintenance Code, Etc.) direct you to the ASTM specifications covering said anchor bolts or fasteners. As the ASTM specifications already cover anchor bolts and fasteners in detail, there is no reason for ICC to write their own specifications for these items. For the same reason, ICC-ES does not need to perform evaluation testing of anchor bolts or fasteners. As long as the bolts meet the applicable ASTM specification(s), they will meet the applicable Code section(s).

UL Listings are a service provided by Underwriters Laboratories Inc (UL). Manufacturers submit products to UL for testing and safety certification on a voluntary basis. There are no laws specifying that a product must be tested and given a UL Mark. While there are many municipalities that have laws, codes or regulations which require a product to be tested by a nationally recognized testing laboratory (such as UL) before that product can be used within their jurisdiction, anchor bolts and fasteners are typically not among these products. This is for two reasons; the first being that products required to be tested and receive a UL Listing are typically potentially hazardous products, including marine products, life saving devices, fire suppression and containment products, chemicals, and industrial, mechanical and automotive equipment. The second reason is that, just as with ICC-ES, the ASTM specifications already cover bolts and fasteners in depth, and it would be redundant to re-cover the same information.

In summation, as long as a bolt or fastener is manufactured to the correct ASTM, SAE, ASME, and/or AASHTO specification, there is no need for it to be tested or evaluated by ICC-ES, UL, or other similar listing services. When you purchase from China Special Fasteners, you can request a complete certification package, ensuring that your product meets the applicable specification(s).

Self-tapping screws are one of the most commonly used industrial fasteners. As on of the earliest engineered fastener products, self-tapping screws were manufactured out of hardened steel, and their use powered the Industrial Revolution. Still incredibly common today, self-tapping screws now include many styles and types made for specific fastening functions.

Terminology used in the commercial fastener trade, unlike that used in aerospace or military fasteners, can be imprecise and often cause confusion. A prime example of this impreciseness is the distinction between self-tapping screws and self-drilling screws.

Self-Tapping

Self-Drilling

• A self-tapping screw can accurately be described simply a tapping screw, but is also regularly referred to as a sheet metal screw, since they are used so heavily in the sheet metal trade.

• Whichever name is used, a self-tapping screw (or sheet metal screw), is designated as such because it contains form mating threads (thereby “tapping” the threads) in a pre-drilled hole into which they are driven.

• A self-drilling screw is a type of self-tapping screw that also features a drill point. The sharp drill point will both drill a hole and form the mating threads in a single operation.

• So where does the confusion between terms come in? In many cases, the person specifying a this type of screw will interchange the terms self-tapping screw (or “Self-Tapper”) with self-drilling screw, but a screw is only a self-drilling screw when it will drill its own hole.

Other similar fasteners that could be considered to be self-tapping screws are:

• Thread-Cutting Screws (TCS) - Screws that can be used to cut threads in a pre-drilled hole are known as thread-cutting screws. Thread-cutting screws are classified into different types depending on the thread-form to accomplish the thread cutting.

• Thread Rolling Screws (TRS) - Screws that will roll or extrude threads in a pre-drilled hole in the substrate without removing any material are known as thread rolling screws. These screws create a very tight fit with zero clearance.

To recap, the terms self-tapping and self-drilling are not interchangeable. All self-drilling screws are self-tapping screws, but not all self-tapping screws are self-drilling screws. Both of these screws come in numerous configurations, and are widely used in the commercial, industrial and construction markets.

Have a question you want the Fastener Expert to answer? Contact us and your question and answer may be featured next!

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