Fastener Technology

Quick Guide: Austenitic Stainless Steel Fasteners

Stainless Steel Fasteners

Are you thinking about using stainless steel fasteners in your next application but aren’t sure if it’s the right fit? Read on to see if it’s the right fit for your product.

Austenitic Stainless Steel

Austenitic stainless steel is by far the most common material used to manufacture stainless steel fasteners. It has a chromium content between 15 and 20 percent and a nickel content between 5 and 19 percent. It offers the highest corrosion resistance than martensitic stainless steel and ferritic stainless steel. It is also considered to be non-magnetic. The tensile strength may vary between 72,000 psi and 115,000 psi. Austenitic stainless steel is not heat treatable however the strength of this material may be improved by cold working or strain hardening.

18-8

The material that is commonly referred to as 18-8, is a type of austenitic stainless steel that contains approximately 18% chromium and 8% nickel. Austenitic stainless steel includes AISI grades 302, 303, 304, 304L, 316, 32, 347, & 348.

For more information about stainless steel fasteners and how you can use them in your applications, contact us at ProvenProductivity@Bossard.com.

May 18, 2018
Read More

Why Your Fastener is Loose and How to Fix It

Keeping Fastened Joints Tight

Do you have a fastened joint that keeps coming loose? Before proposing a solution, we first need to understand why it’s coming loose.

Reasons for a Fastened Joint Being Loose

  1. Is there visible damage to the surfaces under the head of the bolt or nut? If so, you may have an embedment issue where the surface of the clamped material is not hard enough to support the load of the joint. The best way to address this is to increase the surface area of the fastener by using hardened washers or flanged hardware.
  2. If embedment is not your issue, but you have loose hardware, then rotational loosening is occurring. Some things to check for:
  • What is the clamping length of your joint? 5 times the diameter of the bolt is recommended to ensure proper bolt stretch.
  • Is the proper clamp load being applied? See your hardware supplier to help with bolted joint calculations or a joint study to determine the proper torque to achieve your desired clamp load.

Fixing the Loose Fastened Joint

 Sometimes it is not possible to employ the 5 times the diameter rule, and we still have loosening. Several strategies may be used to help combat this issue.

  1. Thread locking
    • Thread forming screws
    • Pre-applied locking adhesive
    • Liquid thread lockers applied during assembly
    • Lock nuts
  2. Locking at the bearing surface
    • Serrated hardware – make sure to use serrated nuts AND bolts
    • Locking washers
      • Rip-Lock™ – good for up to and including 8.8 property class
      • Ribbed lock washers – good for 10.9
      • Nord-Lock® – good for up to and including 12.9 property class

For more information on keeping joints tight, check out www.bossard.com or contact our engineering department at ProvenProductivity@bossard.com.

Doug Jones
Applications Engineer
Email: djones@bossard.com

May 04, 2018
Read More

Want to Convert to Metric Fasteners?

Converting to Metric Fasteners

Many companies that have been designing with inch (imperial) fasteners for years are very hesitant to switch over to metric. Why would anyone ever use metric hardware? Where we have seen the most interest is from companies who are expanding into global markets. Most countries other than the US are using metric fasteners and for them, imperial fasteners are a mystery.

Metric is simple once you get the hang of it, and some things even make more sense, such as the marking of property classes (grades) on nuts and bolts. The metric system uses numbers stamped into the head or face of the nut rather than symbols that we use for inch hardware. For bolts, the first number indicates the strength in MPa while the second number tells us the percentage of yield strength.

For example:

Property class 10.9 – 10 indicates a tensile strength of 1000MPa, 9 indicates that the yield strength is 90% of tensile.

Property class 8.8 – 8 indicates a tensile strength of 800MPa, 8 indicates that the yield strength is 80% of tensile.

Metric Fasteners Chart

A quick comparison of grades and property classes is shown below:

Grade (inch) Property Class (metric)
5 8.8
8 10.9
Alloy Steel 12.9

If you are considering a conversion to metric hardware, contact Bossard at ProvenProductivity@Bossard.com, or check our technical resources at www.bossard.com including an inch to metric calculator that is also available as an iPhone app.

Doug Jones
Applications Engineer
Email: djones@bossard.com

April 20, 2018
Read More

3 Types of Joint Studies

Joint Study

The purpose of a joint study is to understand the forces acting on the assembly during tightening. A joint study may be necessary if you have a critical joint or if you are having warranty claims that can be linked back to joint failure.  When is a joint considered critical? If the failure of the joint may cause injury or have a serious monetary impact, it should be considered critical.

Typical Types of Joint Studies

1.Torque Tension Analysis

This study is used to make sure that your prescribed torque is achieving your intended clamp load. Low clamp load may lead to loosening through embedment, rotational loosening and/or fatigue which all can result in failure of the joint. High clamp load may yield the fasteners or the mating joint components, lowering their clamping force which can also result in failure of the joint.

2.Drive & Strip Torque Analysis for Thread Forming Screws

Performance of thread forming screws in both metal and plastic are greatly dependent on the hole size and preparation. The correct hole size should offer a good balance between low drive torque and high strip torque which can be determined through testing. These types of joints aren’t often as sensitive to the amount of clamp load they retain, but choosing the proper hole size and assembly torque will greatly affect the joint’s performance.

3.Vibration Analysis

Joints subjected to vibrational forces may experience loosening and eventual failure if not designed properly. Different types of fasteners and locking features are often utilized to address vibrational loosening. Performing a vibration study helps to select the proper hardware for your specific situation.

To learn more about joint studies and to talk to an engineer about your project, contact us through ProvenProductivity@bossard.com.

 

Doug Jones
Applications Engineer
djones@bossard.com

April 13, 2018
Read More

Fine Threads vs. Coarse Threads: Which One is Right for Your Application?

Threads

Coarse threads have become the standard for most fastener applications, but when should fine threads be considered?

Fine Thread Strengths

Fine threads are technically stronger under static loading, because they have a larger minor diameter which translates into a larger cross-sectional area As. If using fine threads to increase strength, it is important to make sure that the mating thread – the nut or tapped hole – can support the additional load. This may require a thicker nut or more thread engagement in a tapped hole. Remember the cardinal rule that the nut member must always be stronger than the bolt!

Fatigue Resistance of Fine Threads

In joints with high cyclical loading, fatigue failure becomes a concern. Repeated cyclical stress can create cracks which typically occur in the first loaded thread of the joint. Studies have shown that fine threads increase the percentage of load on the first thread, which can lead to a shorter fatigue life. In this scenario, fine threads should not be a first choice.

Fine Thread Vibration Resistance

In the past, vibration resistance was thought to be a benefit of fine threads. The smaller helix angle, at least in theory, slows down the loosening process. A tradeoff of this benefit is the slower assembly time of fine threads; the smaller helix angle requires more angle of rotation to advance, slowing down the assembly process. A better solution to vibrational loosening can often be found in some sort of locking mechanism which can be recommended by your fastener source.

In conclusion, fine threads should not be used for load bearing joints unless there is a very specific reason and testing is done to validate the joint. Some exceptions could be hard to tap materials or thin wall materials. For non-load bearing joints that require adjustment, fine threads may be your best option.

For more help on choosing the proper fasteners for your project, contact us through ProvenProductivity@bossard.com.

 

Doug Jones
Applications Engineer
djones@bossard.com

March 30, 2018
Read More

How To Improve Your BOM

BOM

What is one of the most asked questions we receive from a new potential customer? “How hard is it for me to get the right fastener in my bins?” There are a lot of things that go into making sure this process runs smoothly.

Good communication about what is needed for a quote is crucial. A good quote process begins with a Bill of Materials (BOM), the Estimated Average Usage (EAU), quality understanding, and an estimated deadline. The BOM should be clean and detailed with dimensions, head styles, drive styles, product types, materials, and finishes.

Every customer has their own way of abbreviating the information to a short description, so paying attention to the details is key. Some fasteners may also be used in a variety of applications. Understanding the business and having a grasp of the BOM will help make sure the right fastener is in the production line. As mentioned earlier, estimated usage, quality requirements, and a reasonable deadline will help with getting the most accurate quote back for review.

What will it take for you to win business, save the company money, and prevent line down situations when switching fastener vendors? Ordering AND receiving the correct parts the first time! Let the experts at Bossard help you review and translate the terminology of a sloppy BOM and get you the correct fastener the first time around. Contact us at ProvenProductivity@bossard.com for more information.

 

John Syharath
Technical Sales
jsyharath@bossard.com

March 23, 2018
Read More

An Introduction to Hydrogen Embrittlement

Hydrogen Embrittlement

Hydrogen embrittlement is a permanent loss in ductility caused by introducing hydrogen into a metal fastener in combination with stress. A typical hydrogen embrittlement (HE) failure is a delayed failure and happens after assembly. An HE failure is caused when three requirements are fulfilled. These areas are (1) hydrogen induced, (2) stress applied, and (3) high hardness. Continue reading for more information about each area.

Hydrogen Induced

Hydrogen needs to be induced for an HE failure. This is most commonly induced in the electroplating process, but can also be introduced into the material through corrosion of the bolt.

Stress Applied

Once stress is applied to a bolt that has a significant amount of hydrogen trapped inside the molecular structure, it is a matter of time when the hydrogen collects in molecular void and that void will grow bigger until the fastener fails.

High Hardness

This is the easiest pillar of an HE failure to control in the HE failure spectrum. Industry standards dictate that anything 320 Vickers Hardness or higher needs stress relief and possible further special attention.

HE failures can be very dangerous because the failure is delayed after installation and is very sudden. Before a bolt with HE is installed, there is not a visual way to identify if HE is present.

Any fastener that meets the hardness criteria need special attention and care to avoid HE failures. Contact us at ProvenProductvity@bossard.com if you have any questions about HE and its causes.

 

Brandon Bouska
Application Engineer
bbouska@bossard.com

March 16, 2018
Read More

Should I Use Weld Nuts, Self-Clinching Nuts, or Blind Rivet Nuts?

assorted nuts & screws

The use of captive nuts is a great design opportunity for a variety of applications. These differing styles of nuts are captive because once installed, they become an integrated part of the assembly. Examples of captive nuts are weld nuts, self-clinching nuts and riveting nuts. For more information on the specific designs consider the technology of each one.

Weld Nuts

Weld nuts are welded to another piece of metal. These can be used instead of sheet metal screws in thin sheet metal applications. Weld nuts come in different sizes and shapes and require equipment to install. These types of nuts form the strongest bonds. They are not plated for corrosion protection as this would hinder the welding process; a subsequent plating process or painting would be required to protect the assembly from corrosion after welding is complete.

Weld Nut

Self-Clinching Nuts (swage nuts or insert nuts)

Self-clinching nuts are clinched or pressed into soft sheet metal. They come with several types of plating options and can be heat treated to provide more thread strength unlike its counterparts. Self-clinching nuts also require equipment to install.

Slef-Clinching Nut

Riveting Nuts (blind rivet nuts)

Riveting nuts are the quickest to install. The necessary tools to implement this nut design are also relatively less expensive. They are installed much like a blind rivet and can be fixed into blind holes unlike self-clinching nuts or weld nuts.

Riveting Nut

Captive Nuts Comparison Chart

Type Application Advantages Disadvantages Special Tool Required
Quick installation Inexpensive piece price Different plating options Different strength options Other Need access to both sides No plating options  Precise pre-drilling required Need special tooling to install Other
Weld Nut General X Strongest bond  X X X Yes → Welding machine $$
Sheet metal
Self-Clinching Nut Sheet metal X X X Strongest threads X X X Yes → Press $$$
Circuit boards
Blind Rivet Nut Sheet metal X X X X X Grip range limited Yes → Pneumatic tool $
Laminated materials

**Advantages and disadvantages are accurate for most catalog offerings of these nuts, exceptions may apply

 

Picking the right captive nut for your design can be difficult. Luckily, Bossard has an engineering team with decades of experience, ready to help you. Contact us at ProvenProductivity@Bossard.com for more information.

Fadi Saliby
Technical Sales Director
FSaliby@bossard.com

March 02, 2018
Read More

How to Use Lighting Industry Fasteners the Right Way

Lighting Industry Fasteners

The lighting industry benefits from modern advancements in the smallest details of engineered lighting components. Rivets and fasteners, as well as wire management products, help everyone with their lighting needs. Whether the requests are for residential electrical jobs or those industrial and institutional lighting projects, the industry is thriving with several options for each scenario.

Rivets and fasteners are a few components that offer creative solutions to many lighting necessities. Drive fasteners, mounting buttons, fastener plugs and push-in fasteners are all a part of successful lighting installations. They can ensure a successful installment of light fixtures with convenience in mind.

Wire management is another concept to be appreciated when stringing it all together. Cable clamps will be a beneficial factor in keeping wires and cables neat and organized. A variety of clips and clamps exist in the markets today that are customized for those very specific jobs at hand.

The lighting industry has come a long way in making the little things matter more. The technological benefits and enhanced features that have been implemented in the smaller aspects of lighting are making more lighting preferences possible.

Reach out to us at ProvenProductivity@Bossard.com to see how Bossard can help you with your lighting fastener needs.

February 23, 2018
Read More

Joining CFRP: Attachment Methods for bigHead® Fasteners

bigHead® Fasteners

Choosing the right method of attachment for bigHead® fasteners can literally make or break your application. With innovations in materials and processes daily, in a continuously growing industry, choosing the right technique is imperative. It all comes down to details.

When it comes to Carbon Fiber Reinforced Polymer (CFRP) and attaching fasteners there are a few methods to consider. Today, traditional adhesive bonding methods are still effectively used in many production environments.  However, we have new techniques currently in development which include lean bonding and pre-form mechanical fixing prior to molding.

The lean bonding solution utilizes a pre-applied dry film adhesive, induction heating and pressure to reduce bonding time dramatically. Bonding times well under a minute can be expected. As an alternative to the adhesive bonding methods, bigHead® fasteners can be attached to CFRP by stitching, tufting, over-laminating or clinching into the pre-formed material.

For a more practical application, outlined below are techniques for attaching fasteners into dry fiber pre-forms:

  • Over-laminated: Either with ply-drops/localized or overlay holes to accommodate for stud
  • Stitching/tufting: Fastener retained in place by stitching into pre-form
  • Pocket stitched: Like over-laminated, but with stitching around the fastener to secure inside “pocket”
  • Pre-coupled patch: Fiber patch pre-applied to fastener and incorporated into molding (can be attached by adhesive or stitching/tufting)
  • Clinched: Fastener with spiked protrusions that embed into the pre-form

If you have any questions about bigHead® fastener attachment techniques into preformed CFRP please contact us through ProvenProductivity@bossard.com.

February 16, 2018
Read More