As a sales engineer in the precision engineering industry, I have noticed that many business owners and technicians are unaware of the benefits of using expansion plugs for use in mechanical applications. These devices are essential for plugging holes and maintaining high pressures  in safe conditions in mechanical, hydraulic and pneumatic systems. In this article, I’ll walk you through everything you need to know about sealing caps, including the types available, the benefits of using them, and how to choose the right sealing cap for your application.


What are sealing caps and how do they work?

Expanding metal plugs, also known as expanders or sealing plugs, are devices used to hermetically close holes in mechanical components. These plugs can be made in various types of materials according to the application.

Blanking plugs work by creating an airtight seal around the hole or opening in the mechanical component. This prevents liquids, gases or dust from entering the component. In addition, sealing caps can prevent liquids or gases from escaping from the component.


The advantages of using expansion plugs in the world of precision mechanics

The use of expansion plugs has numerous advantages, one of the main ones being that it will be sufficient to have a hole (meticulously following the instructions in the PDF catalogue), insert the plug in the seat with the ball facing outwards and in contact with the shoulder, press the ball into the sleeve so that the top of the ball is slightly below the top level of the sleeve and you’re done! Plugged hole without the need to thread the seat or use sealants.

Furthermore, in terms of safety, we can be sure that if the hole has been carried out in a workmanlike manner, the maximum working pressure can reach up to 500 Bar.

Finally, the use of this technology will allow us to automate assembly using pneumatic hammers.


Types of metal plugs: EXP caps, RS or RL tear caps, CLW screw caps, threaded caps with seal ring

There are different types of expansion plugs available in the market. The four main types are HC EXP plugs, RS or RL tear-off plugs, CLW screw plugs and last but not least ED-PAD or O-Ring threaded plugs.

HC EXP plugs are made of passivated 400 stainless steel with a black oxidation bearing steel ball. Once inserted in the hole, just hit the sphere with a hammer and the appropriate punch which, by inserting it into the plug, will cause a plastic deformation on the body to cling to the hole. These plugs are usually used for applications where a tight seal is required at high pressures.

The RS or RL tear plugs are made of case hardened steel or steel and are used to quickly, securely and cost-effectively plug holes in hydraulic applications, e.g. in clamping fixtures. The installation of the expansion plugs with tie rod is carried out with the appropriate assembly tool and the plug and the tie rod are already pre-assembled and therefore can also be used in automatic processes.

CLW screw plugs are made of low carbon steel or hardened steel, they are threaded and can be used in multiple applications with seals up to 450 Bar.

Finally, threaded plugs with ED-PAD gasket or with O-RING are made of hardened steel with a surface action treatment. Available with metric or gas thread.


How to choose the right expansion plug for your application

To choose the right metal plug for your application, several factors need to be considered. One of the most important factors to consider is the material of the mechanical component and the maximum working pressure.

Another important factor to consider is the size of the hole, finally, it is important to consider the environmental conditions in which the sealing cap will be used. If your application is in a high temperature environment or in contact with chemicals, you will need to choose a cap that is resistant to environmental conditions.

We advise you to enter as much data as possible when quoting.


Plug installation

The installation of expansion plugs depends on the type of plug used.

HC EXP plugs expand to fit the diameter of the hole, so they require you to hit the ball inside the body with a special punch which varies according to the diameter of the plug.

The RS or RL tear-off plugs with tie rod are installed using a pneumatic or manual assembly tool that will pull the tie rod until it breaks.

CLW screw plugs are screwed into the hole or using a hex key the use of a sealant is recommended.

Finally, the screw plugs with ED-PAD seal or with O-RING are simply screwed into the hole using an Allen key.


Maintenance of sealing plugs

Sealing caps require little maintenance, but it’s important to check them regularly to ensure the seal remains airtight. If the sealing plug shows signs of wear or damage, it must be replaced immediately.


Common problems with expansion plugs and how to fix them

One of the most common problems with sealing plugs is leaking. This can be caused by a sealing plug not matching the size of the hole or opening, or damage to the sealing plug.

To fix this, you need to remove the sealing plug and check if it is damaged or if it does not fit properly in the hole or opening. In case of damage, the sealing cap must be replaced with a new one.


Where to buy certified metal plugs

Sealing plugs are available from suppliers who specialize in mechanical, hydraulic or pneumatic components. It is important to purchase this type of product from a reliable reseller to ensure product quality and traceability of the entire production chain.