Some of the most long-standing and trusted manufacturing and engineering processes are as relevant today as they were when they were first invented!

This is certainly true of the important production functions performed by hydraulic presses, which have been around for hundreds of years.

So, what are hydraulic presses, and how do they work?

Equipment powered by hydraulic energy

The basic definition of a hydraulic press is a piece of equipment that straightens, compresses or moulds some form of material – for example metal plates or rolls – using a constant force created by a liquid component.

The actual process is based on a scientific formula called Pascal’s theory. This dictates that certain fluids in a confined space exert pressure that is constant, and strong.

This is known as ‘Hydraulics’ and it’s a principle used throughout science, engineering and manufacturing. (An alternative technique is using enclosed gases to exert pressure, which is called pneumatics.)

One of the reasons that hydraulics has gained such a firm foothold in processes, is that the pressurised liquids can be used to generate and transmit power in a very controlled way.

Incidentally, hydraulics is also a natural function that occurs in the human body, in the form of blood pressure!

The first person to apply the principle to a mechanical process for engineering is believed to Joseph Bramah who patented a hydraulic press design in 1795.

Using hydraulics to change shapes

The size and calibration of a hydraulic press dictate how it converts this scientific principle into a practical application.

For example, the plates used to compress, mould or straighten the metal can be altered, as can the level of force used in the process.

Though presses relying on hydraulic power can vary in their application, their basic structure is usually the same.

They consist of two cylinders containing the liquid (often oil). When the liquid passes into what’s known as the ‘slave cylinder’, it is transported along a narrow space where it is then pushed by a piston.

The pressurised liquid flows through a pipe into the ‘master cylinder’ where the energy gained can be used to push the press into action.

Typical uses of a hydraulic press

The most common uses for hydraulic presses are straightening, crushing or punching holes in metal.

For example, car compactors are often large hydraulic presses containing a hydraulic motor to create a substantial force.

Hydraulic presses can also be used to thin glass, to manufacture cosmetic packaging, for instance.

Large scale lamination machines can also include a type of hydraulic press, and they are used to process everything from cocoa beans to raw steel thinned into blades.

Their versatility – and ability to provide important functions with a relatively small footprint – is often key to their timeless nature and commonality in manufacturing and engineering.

Names given to types of hydraulic presses

As they do vary in their structure and purpose, you will see this equipment referred to in various ways.

For example, arbour presses work on the same principles to carry out such functions as piercing, stamping, inscribing, ripping and flattening metals.

In an assembly line, a C-frame press in various sizes and pressure gauges could be used to carry out a single press motion within the production cycle.

Larger, heavier and more hazardous versions are known as power presses and are generally associated with heavy industry and large scale equipment.