Water jet cutting exertise offered

Offering over 50 years' experience in developing waterjet cutting equipment, Ingersoll-Rand is able to offer help on any cutting application.

Ingersoll-Rand, the leading specialists in high pressure technology promotes its products under brands such as Streamline SL-IV, Active Autoline and Aqualine.

The company has over 50 years' experience in designing and developing waterjet cutting equipment and is able to offer help on any cutting application, manufacturing cutting systems of the highest quality for reliability and efficiency.

Here, UK Area sales and service manager, Peter Longman discusses the history of principles of waterjet cutting technology.

The waterjet cutting process is relatively new when compared with more traditional methods, the first commercial application not being put into use until 1971 when it became an instant success.

Since then, continuous development has meant that waterjet cutting hasbeen applied to virtually all industries including glass, wood and food production.

More and more companies have come to realise the benefits of the highly accurate, fast, environmentally compatible cutting method.

Waterjet is able to cut a broad spectrum of materials with no heat-affected zone, no hardening or material stresses, without producing any dust or smoke, leaving a smooth cut edge with no burrs.

Before looking at the principles of the technology it is worth looking at the history of waterjet cutting.

Back in the 1870's when Californian gold miners needed to remove layers of sand and rock they used pressurised water to great effect.

By the 1920's waterjets were beginning to be used for the removal of stones and sand in construction work.

These jets had characteristically large flow rates at pressure levels of a few hundred bar and were only suitable for removing large volumes of material, with no precise cutting being possible at the time.

It was not until the 1950's that the first ultra-high pressure pumps were developed by McCartney Manufacturing of Kansas USA for catalyst injection in low-density polyethylene production.

In 1963 Ingersoll-Rand acquired McCartney and in 1968 the concept of a waterjet cutting machine with a pressure of 700 bar was patented.

As mentioned previously, the first commercial application came in 1971 when a system devised by Ingersoll-Rand's McCartney Manufacturing was used for cutting paper tubes.

Further applications quickly followed including the cutting of paper nappies and honeycomb materials used in the aerospace industry that were difficult to process using traditional methods.

Since the early 1970's Ingersoll-Rand has been manufacturing pumps that generate a continuous output pressure of 3,800 bar (55,000 psi) and nowadays pure water cutting continues to be used for soft, hard and sensitive materials in a very precise manner, whilst the injection of hard abrasive materials into the jet - a development of the early 1980's - makes it possible to cut very hard materials such as ceramics, glass, stone and steel.

So how is waterjet cutting able to achieve such impressive results? Every cutting method relies on the input of energy into the material in order to overcome the chemical bindings present in its structure.

For example, thermal cutting methods utilise the energy of chemical reactions, electricity or light to produce high temperatures in order to melt the material at the cutting kerf, whilst mechanical methods utilise the kinetic energy of the moving tool, or form ductile materials through the application of pressure.

When looking at the operating principles of waterjet cutting it can be classified as a mechanical method.

The energy of the rapidly moving jet - either of pure water or an abrasive mixture - is applied to the workpiece, causing microerosion of the material.

During the operation the cutting water also works as a cooling agent which also contributes to the very high quality cut.

The Streamline pump develops a pressure in the primary oil circuit - achieved through the use of a variable displacement pump - which is then multiplied by a factor of 20 in the reciprocating intensifier assembly.

Today intensifier units with power ratings between 11 and 75kW (15-100HP) that generate output pressures of over 4000bar (60,000 psi) with flow rates between 1.2 and 7.6 litres/min can be supplied.

Pumps can also be connected together to create higher flow rates.

From the intensifier, the water passes through special high-pressure tubing, which is partially flexible to allow movements of the cutting head.

The head itself consists of a pneumatically controlled needle valve and a nozzle tube, the end of which has a diamond or sapphire orifice, sealed in a cone.

The orifice effectively converts energy again from pressure to velocity to produce an outgoing stream of water travelling at over twice the speed of sound.

In most cases the cutting medium consists of nothing more than conventional tap water which normally meets specification requirements.

In other cases a conventional water softener may be added to meet the specification.

During the cutting process, the workpiece is placed on a lattice above a water tank that is usually about one metre deep to help capture and disperse the energy of the waterjet as it exits the workpiece.

When cutting harder materials that require the hydro abrasive method, an abrasive cutting head is used.

This is mounted below the orifice (0.1 - 0.35mm) and consists of a mixing chamber where the high velocity jet causes a vacuum that draws in air and abrasive sand (either garnet or olivine) through an entry port.

In order to bring the mixture into alignment, a focusing tube (0.5 - 1.1mm) of three times the diameter of the water orifice is required, out of which passes the sharp jet of water and abrasive mixture.

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