Methods Of Bolts Tightening

While bolt tightening might often feel simple and straightforward forward the reality is that there is a lot of science that goes behind tightening your bolts properly. If bolts are not tightened properly then chances are you might find them unwinding on their own or loosening up over time. This is something that should always be avoided as it could lead to bigger problems in your constructions and projects. This guide will help guide you through everything you need to know regarding bold tightening including the best methods for tightening your bolts.

What is bolt tightening?

Bolt tightening is a process of tightening bolts by turning them with torque. The entire process depends on the friction created by the bolt and torque. However, one of the main challenges of this process comes from the fact that it is nearly impossible to predict what the exact amount of friction applied to your bolt is going to be. As a result, you might find that during the tightening process your bolts or threads get damaged. This is not the only challenge that you might encounter through.

Another common problem is known as settling. Essentially, settling is the result of irregularities in the bolts. These surface irregularities and coating can lead to bolts not clamping in the way that you might have expected. With settling the most common solution is to simply retighten the bolt. However, while this might be a simple enough solution, it can become quite a tiresome procedure if you are working with high volumes of production.

Is there anything to remember before you start tightening?

While tightening might seem simple, it actually all starts from the moment you assemble your product by using a bolt and nut. Proper preloading is often considered a simple task, but its simplicity should not be used as an excuse for not taking the proper case when you are setting everything together. Insufficient preload can often be one of the key reasons why the tightening of the nut is not going smoothly. This could lead to a bolted joint failure.

How many methods are there for tightening bolts?

There are six key methods currently used for tightening bolts. These are:

1. Toque tightening

2. Angle control tightening

3. Yield control tightening

4. Bolt stretch method

5. Heat tightening

6. Tension indicating methods

What tools are necessary for tightening bolts?

There are many different types of tools that you might require depending on the method you opt for. The most common of these tools include manual wrenches, clicker wrenches, pneumatic and electric torque tools, and angle tightening tools. The one type of tool that is not recommended for bolt tightening is any type of high-impact tool. While these impact tools may essentially look like they are completing the task at hand, in most cases the bolts will actually become looser over time. That is if the tension caused by the impact does not lead to the bolts being completely destroyed.

What are the differences between each bolt-tightening method?

1. Torque tightening

Torque is the term used to describe the rotation stress that a certain bolt head is going to feel. Torque is normally used to twist a bolt, and lets its threads rotate into the nut. This will result in the plates compressing and the bolt being elongated. In general, the higher the stress, the higher the torque. For this process, it is usual to use a clicker tool as it allows you to apply torque that falls right in the threshold of 40 to 50% of applied torque which needs to be used in order for underhead fiction to be overcome. However, clicker wrenches are not the only tools that you can use, and with time it can become a lot easier to know how much pressure and torque you will need to apply in order for the bolt to tighten and stay in position well.

2. Angle control tightening

The angle control method requires that instead of twisting the bolt you are going to be focusing on twisting the nut. This became a more prevalent method of bolt-tightening after the Second World War. This is also a common method to use if you are using electric wrenches for your production. In this particular method, the preload becomes increasingly important as it can lead to variations in the tightness level. However, if you achieve a consistent preload then this type of method can be one of the most accurate ways for tightening structural bolts with consistency. This is why it is commonly used in the automotive industry. One of the negative aspects of the angle is also the fact that it is unusual for it to be able to be reapplied effectively a number of times before it actually loosens up and falls.

3. Yield Controlled Tightening or Joint Control Method

Yield Controlled Tightening, or as it was previously known Joint Control method, is a method that allows for consistent and accurate preload that helps reduce friction. This method requires a certain level of expertise as it used to require feeling with a wrench the yield points in order to tighten the bolt with greater precision. Currently, there are also some electronic tools that are able to replicate this process and determine based on the bolt being used what the bolt's torque gradient sensitivities are in order to determine how the bolts should be tightened.

While this method has the lowest amount of preload scatter, there is still some scatter that can result from this process. Despite its effectiveness, the inaccessibility of the tools necessary to electronically replicate this process often leaves manufacturers opting for more traditional methods.

4. Bolt Stretch Method

The bolt stretch method is predominantly used for tightening large bolts. In order for this method to be applied the use of hydraulic torque wrenches is necessary. This is commonly the case for those bolts that are over 20mm in diameter. As part of the process, a small hydraulic ram is fitted on top of the nut. With the use of hydraulic oil and a small pump the ram is turned and acts on the threaded puller that is attached.

Due to the entire process being controlled by hydraulic pressure, this entire process can actually be beneficial for bolts with small amounts of preload. However, in the case of bolts being damaged due to corrosion, this method can make those bolts hard to remove.

5. Heat Tightening

Much like the use of electric and hydraulic tools is an option, heat can also be used in order to expand the thermal characteristics of the bolt. The way in which this method works is that the bolt is heated which leads to it expanding and fitting into the nut. The nut needs to have been indexed with the use of the angle method. Once the two have been tightened, then the bolt should be allowed to cool down.

There are many different methods and ways the necessary heat can be achieved. These include using direct flame, sheathed heating coil, or other electronic tools that produce heat. One of the negatives of this process is that it usually will take a lot longer than all of the other methods mentioned on this list. This method is also not easily applicable to large bolts.

6. Tension Indicating Method

In order for this method to be used you will need to have special load-indicating bolts, as well as load-indicating washers. For finding the right types of bolts for your project you can always head to ayafasteners.com to find high-quality bolts that will work for your products.

In order to apply this method, it is important to understand that there is a number of different ways in which bolt tension can indirectly be measured. Finding the way that works best for you can be one of the key aspects of this method. These special bolts that you are using for this project should usually provide you with an indication of the force. Similarly, the load-indicating washers will usually have raised pips on the surface, which can greatly deform when a load is applied to them. This allows you to determine whether you are using the correct preload.

Ultrasonics, micrometers, and other tools can also be useful in measuring the tension of the bolts and then adjusting your tightening based on that information.

Conclusion

When it comes to bolt tightening it is important to understand that all the different methods tend to have a better application in specific situations. This means that depending on the project that you are constructing and the tools and bolts you have on hand you might find that one of these methods works better for you than the others.

AYA FASTENERS is one of the most reputable leading fasteners manufacturers and suppliers in China, we focus on assembly and fastening materials, supplying global customers with high-quality screws, bolts, washers, and nuts products over 20 years.

AYA has been deeply involved in the Fastener industry with a single-minded and dedicated attitude, devoted itself to providing our customers with more industry-specific, professional, standardized, and precise Fastener solutions. If you want more information, please contact AYA FASTENERS for the details.