Taking the plunge: selecting the correct plunger type for work holding system design

Machinery and capital equipment are playing an increasingly more important role in today’s engineering industry, as businesses seek faster production methods, which accelerate times to market and improve efficiency. Having access to a stable and reliable workstation is one way that engineering companies can ensure more consistent seamless production times. As a result, engineers are seeking out tools which are more dependable, economical, and easy to use when developing work holding solutions. Marcus Schneck, CEO at norelem UK, looks at the vital role that plungers are playing in making these fixtures and systems more effective and reliable.

In many ways, plungers are an unsung hero of work holding system design, used for locating, stopping, aligning and holding parts in a variety of applications. When fixturing applications where pressure is required for accurate positioning and indexing of components, plungers play an invaluable role. However, given the versatility and breadth of these parts, it is perhaps inevitable that they come in a range of variants, each tailored to the specific requirements of an application. With a huge amount of choice available, selecting the correct plunger type based on an understanding of the individual application requirements and intended operating environment, can ensure that the correct standard component is specified, ensuring sustained reliability.

Springs, indexes, and balls
When it comes to the challenge of joining two or more parts together, few plunger products are as effective as spring plungers with thrust pins. A common but often overlooked fixture of industry, these are used for a wide range of applications and are particularly effective when work holding systems are required to keep components in place for long periods of time. These parts contain a spring which is used to provide force to push either a spigot, bolt, or ball into a corresponding hole, thus locking multiple parts into place securely. This facilitates fast and easy machining of components.

Where a spring plunger with a thrust pin is not used, a spring plunger with a ball is a common alternative. These contain a sprung ball bearing which provides the force. The ball detent forms a bearing surface, which retracts and snaps into the corresponding hole or groove. This force can be exerted very quickly, making spring plungers with balls most effective for applications where the plunger needs to be moved in and out of position very quickly, for example when locating or positioning in drawers, doors, dies, and other fixtures.

Although effective, and popular components, there are occasions when index and spring plungers with thrust pins are unsuitable for an application. For example, a spring plunger with thrust pins is designed to allow slight movement when lateral force is applied, and would be overpowered by a heavy load. Likewise, the ball bearing contained within spring plungers with balls is very shallow, which means that only a small amount of the plunger is inserted into the hole, rendering it ineffective when used with heavy loads.

In this instance, an index plunger would be the more effective choice of component. An indexing plunger has a bolt instead of a ball. This enables it to latch, hold, and align components together very quickly. An important characteristic of index plungers is their rounded or bevelled noses, which allow them to fit comfortably into any indexing receptacle.

Environmental considerations
When selecting the most suitable plunger component for an application, it is also important to consider the working environment in which you want it to perform. For example, sustained vibrational force in any application is a concern for many engineers and has the potential to reduce performance and even cause damage to components over time.

In cases where this poses an issue, it is worth specifying a spring plunger with thrust pin which features an integrated LONG-OK thread lock as this protects the component from becoming loose or dislodged as a result of impact, shock or vibration. By acting as a wedge between the internal and external threads, the nylon locking system pushes the play between the threads to one side, causing surface pressure on the thread flanks. The resulting loosening torque is subsequently higher than that which is offered by most conventional mechanical methods.

Many applications are also characterised by harsh and aggressive operating environments; therefore, it is essential to understand how these might impact on performance. One such concern is corrosion. In harsh and aggressive environments, corrosion-resistant materials can prolong the life of a spring when it is subjected to frequent wear and tear. One solution is to go for the tensile and chemical resistance characteristics of silicon nitride make it the ideal material choice for ball components found in plungers. Notably, these offer significantly better wear over time, ensuring greater reliability over alternative materials.

Choosing the right type of plunger may seem a simple task but it is surprising the number of times that this decision is made incorrectly. There’s often an assumption that all plungers are similar and can be used for any application, which is incorrect. The wrong plunger may not only cause loosening and fall out, particularly during impact shock or vibration, but engineers can lose valuable time refastening and reapplying unsuitable plungers, in an attempt to create a safe and secure work holding system. As engineers continue to face pressure to achieve more in less time, paying attention to the small, standard components which enable seamless and fast production, is often time well spent.

Workholding accessories can be found in THE BIG GREEN BOOK from norelem, which can be ordered at
https://www.norelem.se/se/sv/Service/Katalogbest%C3%A4llning.html

About norelem
norelem is a world-leading manufacturer and supplier of flexible standard parts and components for mechanical engineering. The company supplies 38,000 standard products relating to standard machinery and operating elements, as well as automation components. Ninety-eight per cent of these parts are available from stock, and the business delivers on-site technical support for products. This high level of inventory enables norelem to provide fast and reliable delivery times, with orders placed before 3pm, being dispatched on the same day.

About THE BIG GREEN BOOK
The BIG GREEN BOOK is both norelem’s ideas catalogue and a reference book, and has become the norelem trademark. More than just a standard product catalogue, the BIG GREEN BOOK represents everything norelem stands for, combining product information, specifications, and technical information, with best practice references, advice, and guidance.

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