Author Archives Bossard

How to Find Your Correct Torque Like a Pro

All design engineers are faced with questions like “What torque is the correct torque?” and “How do I know my assemblers are achieving the correct torque?”. When Bossard engineers hear these questions we typically respond by asking “What clamp load are you trying to achieve?”. When asked, engineers usually reply with confused expressions, or the unveiling of a torque chart from engineering manuals or colleagues.  There is no doubt time and effort went into these torque charts, but how does the testing to create the chart relate to the application the engineer is working on?

Bossard’s biggest piece of advice is to test, test, test! The approach that yields the most success and maximizes the strength of fasteners is to test the application until failure. Until you know the point that the current fastener fails, you are throwing darts at your target clamp load. In some instances, friction varies from lot to lot and can affect the clamp load enough resulting in loose fasteners. Testing until failure helps you achieve a baseline average of total fastener strength. This baseline encompasses friction and is incontestable. The only thing left for the engineer to decide is the percentage of the baseline that is needed for the application. Typically, 75% of the failure torque is used for assembly but there are times in critical applications that fasteners are needed to be pushed further.
When investigating current torque strategies at your company don’t be afraid of torque charts. They can often be used as a great starting point. When a clamp load needs to be met to hold something together, challenge the tightening strategy and test it to prove its validity. You will never regret testing the actual application.

Have more questions about clamp load and proper torque? Reach out to Bossard at ProvenProductivity@bossard.com to receive personalized advice from one of our Application Engineers!

Ben Oostdik
Application Engineer
boostdik@bossard.com

October 20, 2017
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The Importance of Friction in Your Bolted Joint: Part 2

When doing research for your bolted joint it is important to understand the coefficient of friction of the finish of the fastener. There are many different options for coatings that will give you different ranges in values. Typically, those values are tested to a certain specification. Whether it’s an OEM specification, or per the ISO 16047 standard, each one can have minor differences (if you have questions on standards reach out to a Bossard engineer). So what do those values actually mean and how are they relevant to your joint?

Most of the testing that is done to validate the values of the coating is done on M10 surrogate bolts with a standard hex head cap screw. They are tested in lab conditions with either a plain finish washer or nut that is cleaned and degreased or with different variations done in a lab setting. The cause for concern is using those values in your joint. The values can change depending on your bearing surface and your mating threads (material, surface condition, lubrication, bearing surface area, etc.). As stated in previous Proven Productivity blog posts, it’s important to understand the relationship so you prevent costly errors down the road.

That is why we at Bossard always recommend doing bolted joint testing. We have the capability to perform joint testing so we can help you better understand the coefficient of friction and the torque tension relationship in your joints. We can perform testing onsite at your facility or you can visit one of our engineering design centers.

Contact us at ProvenProductivity@bossard.com for more information.

Jon Dabney
Application Engineer
Jdabney@bossard.com

October 13, 2017
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Why You Should Respect Your Fasteners

Take a minute to think of some of the most amazing mechanical marvels we have today: electric vehicles, exo-skeletons, cell phones, wind turbines, and many more. What do most of them have in common? They are all held together with some type of fasteners.

Now think about your product. What happens if the fasteners fail during use? At best, the customer is not happy and may look at other brands for their next purchase. At worst, damage to property or personal injury could result.

So, why are fasteners always the last thing we think about in our design? It’s true that assembly is the last step in the product design process, but fastener selection should be carefully considered in the early product design stages to ensure the best and safest product. Early fastener selection is also associated with time and cost savings making your process more lean and efficient.

Not sure what is the best choice? Have questions about what’s readily available or what’s new in fastener technology? Contact your fastening solutions provider to help you select the best hardware for your project. Don’t wait until two weeks before production starts!

Contact ProvenProductivity@bossard.com for information about the latest and greatest hardware innovations, and get help with your next project!

Doug Jones
Applications Engineer
djones@bossard.com

October 06, 2017
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A Complete Guide to European Standards

Standardization in the fastener industry is a necessity. Without fastener standards, there would be inconsistency and inefficiency. Because of fastener standards, engineers and consumers alike know exactly what to expect.

Because of the consistency that comes along with standards, international business and trade becomes much easier. Companies can purchase products from around the world and can rest easy knowing that the product will fit in their application. There are many organizations that create fastener standards; one of these organizations is the European Committee for Standardization.

In 1991, the European Committee for Standardization, also known as CEN, began working on the standardization of the fastener industry intended to be applicable throughout Europe. International Organization for Standardization (ISO) standards are adopted as European (EN) standards wherever possible. However, new EN standards are established when the ISO standards are not deemed suitable.

German Institute for Standardization (DIN) standards are being replaced by EN or ISO standards. In the future, DIN standards will apply only to products for which no ISO or EN standard exists.

DIN EN ISO plus a number (e.g. DIN EN ISO 4027) would indicate that a combination of all three standards are acceptable.

DIN ISO plus a number (e.g. DIN ISO 7049) indicates an ISO standard that is an adopted unchanged DIN standard.

Standards can sometimes be confusing. If you have any questions about fastener standardization, let us know by reaching out to us at ProvenProductivity@bossard.com.

 

Joe Stephan
Application Engineering
jstephan@bossard.com

September 29, 2017
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Why Quality Fasteners are Worth It

You’ve spent months on your design doing careful analysis and selecting the right materials. You are finally getting close to production – but wait, you haven’t selected a fastener supplier yet. You need mostly standard fasteners, except for those few specialty print parts. It’s just fasteners; how hard can it be?

 

The next step is to turn over your fastener list to the buyer and have them find the cheapest hardware they can negotiate to save a few pennies on the product. After all, it doesn’t matter where they come from. All fasteners are the same, right?

This scenario may be a bit harsh, but is all too often true. If manufacturers are making standard fasteners, they should be using the same fastener standards. Unfortunately, some manufacturers take short cuts to keep costs down in this highly competitive market. Some low-cost providers may make perfectly good fasteners 90% of the time, but is 90% good enough for your design? Assembly issues, failures in the field, warranty claims costs, and poor customer satisfaction when a new widget breaks or doesn’t perform as advertised can be very expensive and time consuming.

 

My advice is this: know where your fasteners are coming from. Here are some questions you can ask yourself before selecting a supplier:

  • Does the manufacturer have good process controls?
  • Are they tracking reject rates both internally and externally?
  • Are they subcontracting fastener finishes or heat treatment?
  • Do the subcontractors have good process controls?

 

Contact us through ProvenProductivity@bossard.com and see what steps we take to ensure good quality fasteners.

 

Doug Jones
Applications Engineer
djones@bossard.com

 

September 22, 2017
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6 Types of Bolt Failure and How to Prevent It

Designing fasteners into your application requires a complete analysis of the joints to make sure nothing was missed. Understanding the types of failures that can occur will help with this analysis. Read on to see how to prevent bolt failure.

Failure Type of Failure Solution
  Overloading (stretching)

– Make sure that the appropriate material and grade was used

– Make sure your design is well understood and that the bolts are not overstressed

  Fatigue

– Make sure that the appropriate material and grade was used

– Make sure your design is well understood and that the bolts are not overstressed

– Make sure that the fasteners are well-tightened

  Galling

– Use a lubricant

– Avoid fastener misalignment

– Avoid high speed installation – keep installation speeds low

– Avoid rough surface – smooth finishes

[1] Shearing

– Make sure to re-evaluate tightening strategy

– Threaded section in shear plane – use shank instead

[2] Galvanic corrosion

– Avoid use of dissimilar metals

– Prevent moisture entrapment

– The fastener should be the cathode (more noble)

  Hydrogen Embrittlement

– Eliminate susceptible alloys, hydrogen, stress (service or residual)

– Use non-electrolytic platings

– Increase bake times

– Risk is never eliminated

 

For further information on these or other types of bolt failure, please feel free to contact us at ProvenProductivity@bossard.com

 

Fadi Saliby
Technical Sales Director
FSaliby@bossard.com

 


[1] http://www.learneasy.info/MDME/MEMmods/MEM30006A/Bolted_Joints/Bolted_Joints.html

[2] https://en.wikipedia.org/wiki/Corrosion

September 15, 2017
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What Your Bolts are Telling You

When identifying nuts and bolts, there is some information that can be gathered about them simply by looking at the part. Here is a quick overview of how to identify nuts and bolts by taking a quick glance.

Metric bolts have the class marked on the bolt and the nut. This is identified by two numbers separated with a decimal point. This is an easy way to determine that the bolt thread is metric. A line below the property class is used to indicate if boron was used in the manufacturing of the base material. Common classes are 8.8, 10.9, and 12.9.

Inch bolts are identified by lines on the head of the bolt. If there are no lines but a head marking, that is a Grade 2 bolt. Grade 2 is soft and not heat treated. Three equally spaced lines 120 degrees apart are used with a Grade 5 bolt. Six equally spaced lines are used to identify a Grade 8 bolt. The use of boron steel is identified by equally spacing the identification marks over 180 degrees on the bolt head face.

Metric nuts are identified with a number. This number should be the same as the first number on the bolt. Inch nuts have multiple ways to be identified depending on the standard produced to. If not explicitly stated (number on the face for the grade of the material) the nut will be identified by lines. Grade 2, non-heat treated parts, will have either no line or one line on one of the faces of the nut. Grade 5 nuts will be marked with two lines that are 120 degrees apart. Grade 8 parts will have two lines that are roughly 30 degrees apart (similar grades have 3 equally spaced lines; these are manufactured to alternative standards).

Many times, the bolt head will have a manufacturer’s mark as well. The manufacturer’s mark can be very telling when processing issues with problem parts. If the head markings between two parts are different, they would not be from the same manufacturer, let alone the same manufacturing lot.

More information about identifying nuts and bolts can be found on Bossard’s Website or by contacting us at ProvenProductivity@bossard.com with any questions.

 

Brandon Bouska
Application Engineer
bbouska@bossard.com

September 08, 2017
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Quick Guide to Serrated Flange Nuts

A hex flange nut with serration is a nut that is formed with an enlarged circular base that flairs out from the bottom of the nut. When the nut is torqued into place, the bearing surface of the serrated base displaces the material of the mating surface. This forms a locking effect which resists vibrational loosening.

Because of the seated surface, the nut will require a greater amount of torque to loosen adding to the locking feature. The flanged surface will span an oversized or a poorly aligned hole and provides a more uniform bearing stress to clamp force ratio than a finished hex nut.

Serrated hex flange nuts are available in Grade 5 and Grade 8.

When using serrated hex flange nuts, the bearing surface will be damaged as the serrations dig, which can cause concerns for engineers. A painted surface will become chipped exposing the material. This may cause accelerated corrosion of the assembled parts.

Contact us at ProvenProductivity@bossard.com for more information on multi-functional fasteners.

Joe Stephan
Application Engineer
jstephan@bossard.com

September 01, 2017
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4 Essential Steps to Choosing a Fastener Finish

Choosing a Fastener Finish

When choosing a fastener finish, there are many factors to be considered. But if you follow these four essential steps, finding the perfect fastener finish becomes much easier.

  1. Corrosion resistance
    The necessary corrosion resistance depends on the operating environment of your product. Is the product protected from the elements, or is it exposed to moisture or weather changes? Industrial or agricultural environments where dirt, debris, or chemicals encounter fasteners can also be a factor.

 

  1. Friction control
    Friction control is often overlooked when choosing a fastener finish, but it is a key component. If you don’t know the friction of your fastener finish, then you don’t know how much torque to apply to the joint to achieve your desired clamp load. Using torque values from a chart can be dangerous and lead to premature joint failure.

 

  1. Current regulations
    Recent regulations on chemicals such as hexavalent chromium have also dramatically changed the composition of fastener finishes over the past five to ten years. Your industry may not require compliance to RoHS or WEEE regulations, but there is a good chance that your fastener finish is different than it was ten years ago. Know the difference and how it affects your end product.

 

  1. Cost
    Finally, cost is always a factor. A lot of designer finishes exist out there to address all of your concerns, but you will pay for the technology. Educate yourself on the actual needs of your design and what is available. Then, you should be able to arrive at the proper finish for your product.

Contact us at ProvenProductivity@bossard.com for more information on fastener finishes.

 

Doug Jones
Applications Engineer
djones@bossard.com

August 25, 2017
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Why Do Bolts Break?

Have you ever broken a bolt? How do you determine why the bolt failed?

One of the most common types of failure is overloading. All bolts have a maximum load that they can bear before they begin to yield, and generally this load is applied in the form of torque. If friction is lower than expected, the bolts may yield before reaching the prescribed torque. When a bolt yields, it will stretch, causing a “necking down” in the threaded area of the clamping zone that is not engaged into the mating threads. Assemblers can usually feel the bolt stretching as it will take many more rotations of the wrench before either breaking or stalling the wrench. If the bolt breaks, you will see an obvious reduction in surface area at the break where the bolt has necked down.

If a bolt breaks after it has been assembled, there a couple of failure modes that should be considered.

How does fatigue failure occur? Fatigue failure happens when the bolts have not been tightened properly, or have loosened up during its service life. If enough force is acting on the loosened joint during use of the product, bending stresses can weaken the fastener, eventually causing it to fail. This can normally be diagnosed by a fastener expert by close examination of the broken fastener and the mating components.

A third, less common type of failure is caused by hydrogen embrittlement. This type of failure is considered a delayed failure and will always happen after assembly. The hydrogen embrittlement time to failure is typically within 48 hours. The break will almost always be directly under the head of the fastener and not in the threads. The head may break off completely, or it may simply crack enough to relieve clamp load, and remain attached. Either way, the joint has failed and is not safe. This type of failure, while not common, almost always occurs in very high strength fasteners, or case hardened fasteners that are electroplated.

Contact us at ProvenProductivity@bossard.com for more information on failure analysis of bolted joints.

 

Doug Jones
Applications Engineer
djones@bossard.com

 

August 18, 2017
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