How can water cut through steel?

A waterjet is a tool used in machine shops to cut metal parts with a (very) high-pressure stream of water. As amazing as it sounds, if you get water flowing fast enough it can actually cut metal.

Think of a waterjet as something with about 30 times the pressure of the power washer wand at your local car wash. Power washing at car washes is an everyday example of a dirt film being "cut" off the body, wheels and tires of an automobile.

The key to cutting metal with water is to keep the spray coherent. Waterjets are able to cut because the spray is channeled through a very narrow jeweled nozzle at a very high pressure to keep the spray coherent. Unlike metal cutters, a waterjet never gets dull and it cannot overheat.

Low pressure waterjets were first used for mining gold in California in 1852. Steam and hot water jets were used in the early 1900s for cleaning. High pressure waterjets were used for mining in the 1960s, and about 10 years ago industry began using waterjets for cutting. Abrasive water jets (abrasivejets) were first used in industry in about 1980.

In the past, only one piece of metal could be cut at a time with a saw or other metal cutting mechanical process. It was time intensive and expensive. Computer-controlled waterjet and abrasivejet cutting are used today in industry to cut many soft and hard materials. The plain water-abrasive mixture leaves the nozzle at more than 900 mph. The latest machines can cut to within two thousandths of an inch, and have jet speeds around Mach 3.

Waterjets can cut:

  • Marble
  • Granite
  • Stone
  • Metal
  • Plastic
  • Wood
  • Stainless steel

A water jet can cut a "sandwich" of different materials up to four inches thick. This odorless, dust-free and relatively heat-free process can also cut something as thin as five thousandths of an inch. The tiny jet stream permits the first cut to also be the final finished surface. This single cutting process saves material costs and machining costs. For example, the engineer merely gives a gear drawing to the cutting shop via a diskette or e-mail and gets the finished gear back.

Abrasivejet machine with a 26-inch square cutting area. Note the reservoir of reddish garnet sand abrasive.

Courtesy of OMAX Corporation

Waterjets cut softer materials, while abrasive jets are used for harder materials. The actual cutting is often done under water to reduce splash and noise. Faster feed rates are used to prevent the jet from cutting all the way through.

The water pressure is typically between 20,000 and 55,000 pounds per square inch (PSI). The water is forced through a 0.010" to 0.015" in diameter orifice (hole) in a jewel.

A waterjet can remove the bark from a tree at a distance of 40 feet if one alters the chemistry of plain water by adding SUPER-WATER®, available from Berkeley Chemical Research. The SUPER-WATER® is a soluble polymeric chemical that acts like a series of molecular spinal columns or concrete reinforcement bars that tie the individual water molecules together in a more structured way to form a coherent jet. Imagine the potential for cutting down roadside weeds.

Abrasivejet-cut parts.

Courtesy of OMAX Corporation

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How fast does a waterjet cut?

An abrasive jet can cut half-inch thick titanium at the rate of 7 inches per minute when a 30 HP pump is used. The abrasive jet moves in a manner very similar to a slowed-down pen plotter.

Abrasive jets have been used to:

  • Remove materials inside train tunnels
  • Help rescue "Baby Jessica" from the well in Midland, Texas
  • Cut virtually any shape in bullet-proof glass
  • Cut out the parts for the F-22 and Stealth bomber, and other aircraft and spacecraft
  • Cut into the hull, using diamond powder abrasive, of the submarine Kursk to recover the bodies of the Russian crew
  • Remove highway marking strips
  • Carve wooden signs
  • Create sculpture
  • Cut logs in a sawmill

Industries that can use abrasive waterjet and abrasivejet technologies:

  • Building: Patterns in stone material for floors can be cut. Matching parts of a lettered sign, made from stone and metal can be cut. Special shapes for metal and tile roofs can be cut.
  • Manufacturing: Precise gears and other intricate parts such as parts made of foam and rubber can be cut without use of any heat, like a laser would produce.
  • Designers: Intricate shapes can be cut for jewelry, sculptures, and mirrors.
  • Other: Waterjets are used to cut candy bars and diapers, too. There is a special drilling bit for oil exploration that has waterjets on the bottom to speed the drilling process. When used with a directional jets, a waterjet can bore under a road to route fiber optic cable.

Click the pressure reading to see and hear 5-second movie clip of a Flow Corporation abrasivejet. A 50 HP pump creates 52,400 PSI pressure for a jet of water and garnet abrasive mixture to cut 1/16-inch steel. This abrasivejet has an internal .013" ruby orifice to produce a .040" diameter jet of water. Look for a few sparks to fly!

Special thanks to ADR Hydro-Cut, Morrisville, N.C., Carl Olsen at WaterJets.org and W. Glenn Howells at Berkeley Chemical Research, Inc. for technical help with this article.