Fastener Technology

Why are my zinc plated screws stretching and breaking?

For years, zinc electroplating has been the standard finish for fasteners, and hexavalent chromium was used over the zinc to protect against corrosion of the parts. With Restriction of Hazardous Substances, also known as RoHS, gaining traction in the United States, many platers are eliminating hexavalent chromium in favor of trivalent, which meets the restrictions for now, but also has some unwanted side effects.

Trivalent chromate is not self-healing, like hexavalent, so handling damage can degrade the corrosion resistance quickly if something is not added to the finish. Often what is added is some form of sealer, which helps with corrosion resistance but will change the friction coefficient of the joint, in many cases making it lower, especially when high hour corrosion resistance is desired.

So, back to the original question in the title: why are my zinc plated screws stretching and breaking? The easy answer is “lower friction”. The question you should be asking is, what is the friction coefficient of my electroplating? If you do not specify, it’s almost certain that it has changed in the last five years, and as a result, you are getting a different clamp load in your bolted joints.

For more information on how changes to your finish can affect your clamp load, contact us at ProvenProductivity@bossard.com.

Doug Jones
Applications Engineer
djones@bossard.com

July 07, 2017
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Specialty Screw Threads for Direct Assembly

Not all screws thread into nuts. There are many specialty type screws that are designed to thread directly into untapped holes in different types of material.

Wood screws have been around for years, but standard wood screws often don’t work well in particle board or MDF (medium density fiberboard). Standard wood screws have a 60° flank angle, and when threaded into a drilled hole, have to move quite a bit of material to make room for that thread. Specialty screws with a narrower flank angle and a taller thread put less stress on the wood and provide greater pull out force without damaging the material.

Similar specialty screws exist for soft thermoplastics, having very sharp, narrow angled threads that can be successfully assembled into molded or drilled holes or into bosses. Harder thermoset plastics may require a cutting slot on the end of a screw to remove some of the material, acting like a thread tap.

Spaced thread tapping screws work well for sheet metal, but for thicker steel, thread rolling screws with a finer pitch are required. Thread rolling screws have the same pitch and shape as regular screws, and are sometimes hard to tell apart from each other. Thread rolling screws often have a triangular shape to the point and the body of the thread, which you can feel if you roll the threads between your fingers. These screw threads are also generally case hardened to make them harder than the steel that they are threading into.

Similar screws with special thread geometry exist for threading directly into lightweight metals such as aluminum and magnesium.

For more information on specialty screw threads, contact us at ProvenProductivity@bossard.com.

Doug Jones
Applications Engineer
djones@bossard.com

June 30, 2017
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Loose Fasteners: Causes and Solutions

A common headache for engineers and consumers alike is fasteners coming loose and causing problems. So, what are some of the causes of loosening?

Under tightening, which results in low clamp load, is one main cause of loosening fasteners. If a joint does not have enough clamp load to keep the joined parts from slipping against one another, rotational loosening or fatigue failure may occur. It’s important to follow manufacturer’s recommendations for proper tightening.

Using fasteners with a small bearing surface area to join softer materials can lead to embedment of the head into the material. Over time this can cause a loss in clamp load resulting in loose joints. It’s important to understand surface pressure limits of screws and mating materials, and match them accordingly to avoid embedment. Flanged head fasteners or hardened washers are a good way to spread the load out and avoid this problem. It should be noted that many flat washers are not hard enough to support high-strength fastener loads, so choose your washers accordingly!

Vibration is another cause of loose fasteners. In a nut and bolt joint, a good design will actually stretch the bolt slightly to create a rubber band-like effect, which helps to keep the fastener tight. A good rule of thumb for design engineers is to use a clamping length of 5 times the bolt’s diameter to ensure good stretch when torqued properly. For joints subjected to vibration which cannot use this rule, then serrations, locking patches, or specialty lock washers may be needed.

For more information on how to keep fasteners tight, contact us at ProvenProductivity@bossard.com.

Doug Jones
Applications Engineer
djones@bossard.com

June 23, 2017
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Fastener Lead Times

“It’s just nuts and bolts, why does it take 26 weeks to get my parts?” Lead times for fasteners can be frustrating and hard to understand when I can often go to the hardware store and get something that will work. So why does it take so long to get parts?

Standard off-the-shelf parts don’t require much lead time. Depending on the order quantity and the available inventory, parts can normally ship anywhere from one day to three weeks from the receipt of an order. For high volume standard parts or special parts, the lead time can increase substantially.

High volume standards may not be in stock, so a manufacturer will have to make them to order. Fastener manufacturers schedule their work to keep their machines busy and running as efficiently as possible, so when they receive an order to make a certain size, it may not fit into their schedule for several weeks. The same is true for specialty parts. Normal lead times for domestic manufacturers is 12 to 14 weeks on a first-time order. For overseas suppliers, transit time is added which can easily reach 24 to 26 weeks. Expediting an order is often possible, but break in fees and/or increased shipping fees may apply which raise the cost of the parts.

The best way to combat long lead times is to give plenty of notice for first-time orders, and then provide accurate forecasting for future orders.

For more information on fastener lead times, contact us at ProvenProductivity@bossard.com.

Doug Jones
Applications Engineer
djones@bossard.com

June 16, 2017
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Fastener Cost Drivers

Why do some fasteners cost so much more than others? This is a question many purchasing professionals and engineers struggle to understand. Many factors contribute to the cost of a fastener.

Fasteners which conform to a standard and are readily available will always come with a lower price tag. Any slight change that deviates from the standard, whether it’s thread length, a special finish, or a slightly different dimension will require costly modifications or parts that need to be made special to order. This can easily double or triple your part cost.

Volume is another key factor to better pricing. Generally, there are three prices for a part depending on if they are considered low, medium or high volume. In general for screws from M5 – M12 (1/4″ – 1/2″) high volume is greater than 250,000 pieces, low volume is under 1000 pieces and medium volume is in between. Many manufacturers also have MOQs or minimum order quantities for non-standard parts which are based on weight. It is not uncommon to see MOQs of 2,000 pounds on special fasteners.

Fastener finish, or the plating or coating of the fastener, is often what forces us to purchase non-standard fasteners. Most standard, off-the-shelf fasteners will come with commercial zinc plating, which may be fine for interior applications which never see moisture. However, if your application requires more corrosion resistance, then the finish becomes a key factor and you are no longer buying standard fasteners. Many specialty finishes exist to meet the customer’s needs, but without high volume requirements, they can be quite costly.

For more information on the fastener cost drivers, contact us at ProvenProductivity@bossard.com.

 

Doug Jones
Applications Engineer
djones@bossard.com

June 09, 2017
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Length of Engaged Thread

Length of Engaged Thread

Length of engagement is important to understand. The required minimum length of engagement changes for different materials and hardness of said materials. This is something that needs to be determined during the design process.

When screws need to be fully loaded in tensile, it is important to note the strength of the material that the ‘nut’, or female threaded component, is made of. The minimum length of the engaged thread will depend on it. Ultimately, it is important to achieve the required minimum length to give the joint the durability it needs.

Below are some examples of recommended minimum lengths of engaged thread in internal threads based on the material of the nut component for heat-treated steel bolts. These have been determined from practical trials:

Recommended minimum lengths of engaged thread in internal threads.

Make sure the toolbox of information needed to determine the proper length of engagement is readily available. Reach out to us at ProvenProductivity@bossard.com if there is any questions regarding this!

June 02, 2017
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Fatigue Resistance in Fasteners

Fatigue Resistance in Fasteners

Simply put, you want your fasteners to hold up under many situations including conditions of changing load. However, some fasteners cannot hold up to the challenge. One of the most common forms of fastener failure is fatigue. That is why fatigue resistance and strength is something to look for in your fasteners.

A fastener can experience fatigue for a variety of reasons including assembly parameters, fastener material, geometry, and stress on the fastener. Fatigue often occurs in the first load-bearing part of the thread, and it can be detrimental to your project. This means your design must allow for screws to increase its fatigue strength. However, the fatigue strength of fine threads decreases with increased rigidity and fineness of thread, so there are some things to keep in mind with fatigue strength in your fasteners.

There are ways to increase the fatigue strength of your screws. These would include measures that reduce the effective peak stresses or prevent combined loading.

Check out some options for increasing your fatigue strength:

  • Use longer screws rather than shorter screws
  • Use screws with waisted shanks
  • Use pins or fitted shoulder screws to absorb lateral forces
  • Adequate and controlled pre-stressing of the screws

Reach out to us at ProvenProductivity@bossard.com to learn more about fatigue resistance and to find the fastener with the perfect fatigue strength for you.

May 26, 2017
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bigHead® for Wind Turbines

bigHead® for Wind Turbines

Solving your fastening problems is what bigHead does. Whether it is a difficult project or an extreme environment, we can come up with fastening solutions tailored to your needs. That is what bigHead did for offshore wind turbine maintenance hatches.

Siemens nacelle suppliers approached bigHead with a fastening problem. They recently came up with a composite hatch to replace a steel panel for covering a maintenance hatch. The only problem with the composite hatch was fastening it with traditional bolt fixings. This was a challenge because two people were required to perform the operation—one inside and one outside the nacelle. That made the operation not only less safe, but more challenging and time consuming to perform.

However, bigHead and Siemens came up with a solution through prototyping and extreme testing to make sure the fastening solution could hold up under the harsh conditions that the offshore wind turbines endured.

The solution for these offshore wind turbines was surface bonding the 316 marine grade stainless steel bigHead to the outer skin of the nacelle and passing the threaded stud section through its composite structure. This means the panel can easily be secured or removed by one person from the interior of the structure. The bigHead’s large perforated head allows a generous flow of adhesive to firmly secure it in position and its outer surface includes an over-moulded insulation layer that safeguards the nacelle against lightning strikes.

bigHead and Siemens worked together to create the perfect fastening solution for a tough problem. bigHead has been manufacturing its distinctive and leading brand of discrete bonding fasteners for over 50 years and has extensive experience across a wide range of industries where formed and molded composite products require discrete and completely secure fixing. Applications range from carbon fiber panel fixing in specialist and luxury car production to building and construction, railway carriage construction, marine and boat building, and more.

Do you have a tough problem that needs a fastening solution? Reach out to us at ProvenProductivity@bossard.com and we can find your perfect solution or even develop one for you.

May 19, 2017
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Fastening Solutions for the Rail Industry: bigHead® and FRP materials

Fastening Solutions for the Rail Industry bigHead® and FRP materials

Improving efficiency and reducing costs are two focuses of any industry or any business and mass transit is certainly not an exception. The rail industry is always looking at embracing new materials and new production techniques to improve their processes. bigHead® is a fastening solution that will help do just that.

FRP Materials and the Rail Industry

One of these new materials that has become popular recently in the rail industry is the use of fiber-reinforced polymer composite (FRP) materials. The FRP materials help to create lightweight but high-strength structures, and they are also good for design flexibility.

bigHead® Fastening Solutions

However, to use these materials successfully, you need a fastener that is safe, secure and discrete. This is where bigHead® comes in. Fastening solutions from bigHead® offer you advantages over many other fasteners. Check out the reasons to look into bigHead® below:

  1. bigHead® fits your project perfectly – You can receive a wide range of standard or customized product solutions, which means bigHead® will be a perfect fit.
  2. bigHead® can save you time – With bigHead® you can fasten without drilling, which offers you many advantages. You will save time by not drilling, and you will also preserve your materials and keep them strong because you don’t have to create holes in your materials. You can use bigHeads to complete and assemble pods into the vehicle structure. Also, bigHeads can be used on the inside of your pods and structures to fix internal panels, flooring, signage and even trim into place.
  3. bigHead® can reduce your assembly costs – When you use bigHead® fasteners, they can be embedded in composite materials during the lay-up process or they can be surface bonded with adhesive. This means you don’t need a secondary assembly process which can reduce your manufacturing costs.

Every company and industry is looking for innovative ways to make their products and services more successful. At Bossard, with our bigHead® fastening solutions, we are providing the solutions to make your products more successful. You can save time and money with bigHead®, and you can rest assured that these solutions work.

If you have any questions, contact us at ProvenProductivity@bossard.com.


April 28, 2017
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5 Benefits of Metric Dimensioning Fasteners

Metric Fasteners

When looking at fasteners, you have to decide whether you want imperial fasteners or metric fasteners. When designing new products metric dimensioning should be considered as a low cost solution to fastener assembling.

Metric fasteners most often win out over imperial fasteners and here’s why:

  1. It is a simple form of measurement with a base of whole numbers. This can help reduce the number of fasteners in a bill of materials.
  2. They are interchangeable in a global market. Parts can be assembled globally because of the availability of tools. Replacement fasteners can be purchased from local sources. Interchangeability was the key reason the automotive industry has moved to the metric form of fasteners.
  3. The metric system is the most precise form of measurement. It has been adopted by the medical industry as well as the aerospace and electronics industries.
  4. Metric thread falls between an inch course and fine thread. This allows the designer to take advantage of both thread types. It’s a better choice for vibration resistance as well as providing a larger stress area in the cross section of the screw. A commercial finish can be applied without gaging issues.
  5. Standard metric fasteners are manufactured in accordance to the ISO 4759 standard. This is a global base hole system that uses a letters and numbers system to determine a standard plus/minus tolerance for threaded fasteners.

These benefits will aid long term cost savings in design, manufacturing, and assembly, as well as product longevity in the market. If you are interested in other ways of making your business more productive, check out our product solutions and our Smart Factory Logistics.

As always, if you have any questions or concerns, let us know how we can help you by contacting us at ProvenProductivity@bossard.com.


April 21, 2017
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