For bolt applications, bigger is not always better. Similarly, a higher grade bolt does not necessarily mean improved performance over a lower grade bolt.
1: Size and Grade
When it comes to bolting, bigger is not always better. Similarly, a higher grade bolt does not necessarily provide improved performance over a lower grade bolt. It’s the combination of the two that’s key.
“If everyone could choose the right bolt size and material, there would be no need for additional bolt safety solutions,” said Bill Eccles, founder of boltscience.com.
Bolt size and strength grade can have both positive and negative effects on bolt load, Eccles explained. If you find the ideal combination and the bolt joint is tightened correctly, this load becomes an important factor in ensuring a secure bolted joint. “You can choose a larger bolt with a lower strength grade, or a smaller bolt with a higher strength grade. Both options may be appropriate,” he said. When you have questions about these critical design choices, Nord-Lock engineers can provide helpful assistance.
2: Bolt Loosening
Thread loosening is one of the main causes of bolt loosening. There are three main causes of thread loosening: surface settling of rough or irregular surfaces; relaxation, which is when materials such as polymers or composites become compact; and creep, which is when materials move or deform under stress and high temperature. All three of these reasons can cause a loss of preload, which can lead to problems with bolted joints.
Bolted joints today are subject to higher temperatures and loads, while more and more equipment components are made of synthetic materials, plastics and aluminum, which is why thread loosening is an increasing problem.
Robin Senn, sales engineer at Nord-Lock Switzerland, believes that the solution to this problem requires two aspects: “To avoid thread loosening, the screw surface needs to be smooth and hard, and the elasticity of the bolted joint should be increased, such as using Nord-Lock X-series washers or Superbolt multi-thrust pretensioners.”
Superbolt multi-thrust pretensioners and Nord-Lock’s versatile wedge locking technology can increase the elasticity of the joint and minimize the effects of thread loosening.
3: Bolt lubrication
For bolted joints, the role of lubrication cannot be overstated. Lubrication minimizes uneven friction. It also reduces the torque-to-tightness ratio. Lubrication also makes installation and removal operations easier and extends the life of the bolts.
Hidenori Araki, field application engineer at Nord-Lock USA, recommends applying lubricant to the bolt head or nut and the screw part of the bolt.
“For bolt lubrication, it is critical to choose the right lubrication for the application,” he said. “Some of the parameters that should be considered are: chemical composition, health and environmental impact, operating temperature range and friction coefficient, and the lubricant manufacturer should be consulted for recommended usage.”
4: Design/Maintenance
A common dilemma during the design phase of a project is whether to choose a low-cost solution to keep current costs as low as possible, or a high-quality solution to achieve long-term cost savings?
“Initial costs should not be the only consideration. Making a smart investment at the beginning of a project can bring significant cost savings later. This approach also helps improve customer satisfaction.”
When Siemens selected a bolt security solution for its multi-million euro gas turbine, it adopted a strategy that focused on long-term cost savings and utilized Nord-Lock’s locking washers and Superbolt tensioners. In the end, not only did costs save during the installation phase, but maintenance costs were also significantly saved during the life of the turbine.
5: Coatings
Coatings may be only a few microns thick, but they can improve fastener performance in many ways, including protecting against corrosion, reducing friction, and enhancing appearance. There are a variety of coating solutions available, with galvanizing being the most cost-effective and simplest. If that doesn’t work, zinc alloys can be used. If more protection is needed, multiple layers of zinc chips are recommended.
Which coating should you choose for your application? Csaba Madru, Global Application Engineer for Oil and Gas at Nord-Lock, believes that some coating properties should take precedence: “The coating should be chosen first based on the corrosion protection level, then based on the required friction properties, as the lubricant can compensate for the lack of friction properties, and finally on the appearance.”
6: Authenticity
Cheap knockoffs are everywhere, from sneakers to smartphones. Bolts are no exception.
If you choose an authentic product, such as a Nord-Lock lock washer, you are getting a product that has been tested on the market for a long time, ensuring excellent performance and quality.
You can identify authentic Nord-Lock products by their laser label. If you are unsure whether the product you purchased is genuine, please contact your local registered sales office and one of our staff will help you verify the product.
“As with many products, with bolting solutions, you get what you pay for. The higher the price of the genuine product, the longer term savings will be due to the reliable performance and reduced maintenance/repair costs,” says Frida Cullin, Technical Center Manager at Nord-Lock.
7: Quality
There are countless fastening solutions. Even some solutions that are widely used may not meet the requirements within a certain temperature or pressure range. Therefore, it is important to choose a partner that can help you achieve high material stability and select the ideal fastening solution.
“Product recalls or damaged brand image can have a huge impact,” says Peter Fjordman of Bolt Securing. “For example, when we see reports of incidents due to leaks in ventilation systems, I wonder if the company has chosen the wrong fastening solution.”
“To achieve high quality standards, you need to work with companies that have deep industry experience and are more interested in quality than quick profits,” says Fjordman.
Nord-Lock is a trusted player in the industry with multiple quality certifications and high-standard application technology certifications, such as offshore, energy and transportation applications.
8: Corrosion
It is said that there are only two certainties in life: death and taxes. Actually, you can add a third: corrosion. Any metal product made of steel will eventually rust and break down when it comes into contact with oxygen and water. “Corrosion is inevitable over a period of time, but there are ways to slow down the progression of corrosion,” says Christian Rabe of DÖRKEN MKS-Systeme, which develops micro-coating anti-corrosion systems.
One of these methods is cathodic protection, which slows down corrosion at the expense of secondary metals such as zinc, and another is non-cathodic protection.
Rabe points out that there are no easy answers to combating corrosion, joking that “the only way is to keep corrosion-prone equipment in an extremely dry desert climate.”
Nord-Lock offers a variety of protective coatings and surface treatments, as well as multiple grades of stainless steel and nickel alloys.
9: Reuse
Whether to reuse bolts is a common question. Reusing fasteners is especially convenient when working in the field, rather than carrying spare parts of various sizes and grades. Plus, it costs less to reuse.
However, it can be difficult to determine if a used fastener is damaged, which could cause problems. Deciding whether a bolt can be reused depends on the situation, and Lena Kalmykova, an application engineer at Nord-Lock, recommends a visual inspection: “If you see signs of corrosion, avoid reuse if possible. If you can see thread damage, avoid reuse.”
“But in some cases, there may be no choice but to reuse a damaged bolt as a temporary solution. If you must reuse it, always use a lubricant. Lubricants will provide some protection against corrosion. If the threads are damaged, lubricants will also help achieve the necessary clamp preload before you have a chance to install a new bolt.”
10: Preload and tightening
The level of preload determines the load-bearing capacity of the bolted joint. Therefore, it is important to determine the level of preload required in the bolted joint and then achieve that preload through the appropriate tightening method and tightening sequence.
The preload must be at an appropriate level to avoid movement or separation of the clamped parts, but should be within the modulus limits of the material to avoid digging into the mating surfaces and thread stripping.
Zouhair Chaib, Senior Technical Specialist at Nord-Lock France, believes that it is also important to distinguish between the static and dynamic load capacity of screws; screws can withstand high static loads, but low dynamic loads. Therefore, the preload level should be kept high to reduce the impact of dynamic loads on the joint.
When tightening, “the ideal tool should be selected and the tightening operations should be completed in a reasonable sequence to ensure that the preload level required by the design engineer is achieved,” said Chaib.
Nord-Lock engineers are industry experts and can provide comprehensive solutions related to bolted connections, including design, product selection and field support.
