1. Fastener size and grade: choose the right combination of bolt size and grade 

In bolting, bigger does not necessarily mean better. Similarly, a higher-grade bolt is not automatically an improvement to a lower grade bolt. What is important is the combination of these two factors.  

The bolt size and the strength grade can positively or negatively affect the load in the bolt. Once you have the right combination, and you correctly tighten the joint, it is this load that is the crucial factor for your bolted joint to remain secure. 

2. Slackening: create elasticity in the joint to compensate for slackening 

Slackening is one of the main reasons why bolts come loose. There are three primary causes: settlement of rough or irregular surfaces; relaxation, when materials such as polymers or composites become more compact; creep, which is the tendency of materials to move or deform plastically under stress and elevated temperatures. All three of these cause loss of preload and can lead to bolted joint failures. 

Slackening is a growing problem today as bolted joints are exposed to even higher temperatures and loads, while components are increasingly made from composites, plastics, and aluminium. The solution is two-fold: To compensate for slackening you need smooth and hard surfaces, and you need to introduce elasticity into the bolted connection. Think of the bolt as a spring being stretched and you will get the idea. 

3. Thread lubrication: Choose the right lubrication for your application

It’s hard to overstate the importance of lubrication regarding bolted joints. Lubrication minimizes friction scatter and reduces the torque required to achieve a specific preload. It also eases installation and removal and extends the life of the bolt.

4. Design/maintenance: Focus on the lifecycle costs

A frequent dilemma is whether to keep costs down in the present by using more economical solutions or make savings in the long term by investing in higher-quality solutions. Designing or maintaining down to a cost is invariably false economy in the medium- to long-term. 

The best engineering solutions will provide cost-savings during assembly and result in significant savings on maintenance time and costs over the lifecycle of the equipment. 

5. Coatings: Consider coatings to improve your bolted joint

Coatings may be only a few microns thick, but they can improve a fastener’s performance in several ways: protecting against corrosion; reducing friction; enhancing the aesthetic value. There are many coatings available, so which one should you choose for your application? 

Choose your coating based firstly on the level of corrosion protection it offers; then on what friction characteristics you need; and finally on aesthetic properties.

6. Choose genuine products: Invest in the real thing, or you’ll pay later

From clothing to smartphones, cheap copies and counterfeit goods are everywhere, and bolting products are no exception. 

The benefit of investing in genuine products is that you get a product that has proven performance and quality. As with most things in life, when choosing bolting solutions, you get what you pay for. Smart engineers know that buying cheap now gets more expensive in the medium- to long-term. This applies to tools, consumables and of course fasteners. 

7. Quality: Work with partners known for their expertise

Achieving high quality is about working with partners known for their expertise, who will prioritize quality over making a quick profit. 

Nord-Lock Group is recognized for the quality and reliability of its products, and its ability to provide a high level of technical support. The Group holds many industry specific Type Approval Certificates and accreditations for the most demanding applications. 

8. Corrosion: Consider corrosion from the beginning in bolted joint design

They say that the only certainties in life are death and taxes, but a third can be added: corrosion. Any metal product derived from iron or steel will eventually rust and disintegrate when it comes into contact with oxygen and water. Yet there are ways to arrest this process. 

One method is cathodic protection — where a less noble material, such as zinc, sacrifices itself. There are also many corrosion-resistant materials and protective coatings to choose from. The most important aspect is to choose the best option for the specific application. 

9. Reuse: If you have to reuse, lubricate the threads

To reuse or not to reuse, that is often the question. Reusing fasteners – particularly in the field – is more convenient than carrying around replacements of various sizes and grades, and this option is cheaper. 

However, it is hard to know if used fasteners are damaged and might therefore fail. To check if a bolt you are planning to reuse is up to the task, first carry out a visual inspection. If you see signs of corrosion or thread damage, avoid reuse if possible. 

10. Preload and tightening: Choose the right tool and the right tightening procedure

The preload level determines the capacity of a bolted joint. Therefore, it is crucial to determine the preload level required in a joint and then to achieve it through a suitable tightening method and a proper tightening procedure. 

Preload must be sufficient to prevent movement between, or separation of, clamped parts, but still within the yield limit of the material to avoid embedment of mating surfaces and thread stripping.