How Does the Oxy-fuel Cutting Process Work?

How Does the Oxy-fuel Cutting Process Work?

Oxy-fuel Cutting – Step by Step Process, Characteristics, & Application

ESAB's experience with oxy-fuel cutting dates to 1907. Oxy-fuel cutting is regarded as the most cost-effective process for carbon steel cutting. One of the greatest advantages is that the process can be combined with plasma or waterjet on the same part. In the present article, you will learn how does the oxy-fuel cutting process work.

What Is Oxy-fuel Cutting?

Oxy-fuel cutting is a process where a mixture of fuel gases and oxygen is used to cut metals. Some of the commonly used fuel gases include propane, natural gas, acetylene, and a few other mixed gases. The technique is immensely popular on CNC machines for cutting steel plates.

How Does the Oxy-fuel Cutting Process Work?

Oxy-fuel cutting is a chemical reaction between pure oxygen and steel to form iron oxide. It can be described as rapid, controlled rusting. An oxy-fuel cutting torch with a flame is used to cut shapes out of plate steel.

Here are the basics of how the oxy-fuel cutting process works:

Step1: Preheat

Before cutting the steel, the metal is to be heated up to its kindling temperature, about 1800°F with preheat flames. This makes the steel readily react with oxygen. An oxy-fuel torch is used to provide preheat flames to heat the metal.

Fuel gas is mixed with oxygen inside the torch to form a highly flammable mixture. The torch has a nozzle containing multiple holes designed in a circular pattern to focus the flammable gas mixture into multiple little jets. This fuel-oxygen mixture gets ignited outside the nozzle. The resulting preheat flame forms at the nozzle tip. Adjusting the fuel-to-oxygen ratio enables to adjust the preheat flame to produce the highest possible temperature in the smallest possible flame. This helps to concentrate the heat on a small area on the surface of the steel plate that is to be cut.

Step 2: Piercing

On application of preheat flame, the surface of the plate reaches kindling temperature (approximately 1800°F). Pure oxygen is then directed toward the heated area in a fine, high-pressure stream to pierce through the plate. This is known as ''cutting oxygen''. When the cutting oxygen stream hits the pre-heated steel, a rapid oxidation process begins. The oxidized steel changes into molten slag. The slag needs to be removed to allow the stream of oxygen pierce through the plate. Depending on the plate thickness, the oxygen stream is pushed deeper into the plate. In the process, the molten slag gets blown out of the pierced hole.

Step 3: Cutting

When the oxygen stream pierces through the plate, the torch can be moved at a constant speed to form a continuous cut. The molten slag formed during the process is blown to the bottom of the plate.

The heat generated during the chemical reaction between the oxygen and the steel preheats the surface of the plate but just in front of the cut. However, this heat is inadequate to perform cut without preheat flame. Therefore, preheat flame is used throughout the cut to add heat to the plate as the torch moves.

Does Oxy-fuel Cutting Process Work on All Metals?

Only metals whose oxides have a lower melting point than the base metal itself can be cut with this process. Otherwise, as soon as the metal oxidizes, it terminates the oxidation by forming a protective crust. Only low carbon steel and some low alloys meet the above condition and can be cut effectively with the oxy-fuel process.

Characteristics of High-Quality Oxy-Fuel Cut

A quality oxy-fuel cut has the following characteristics:

  • Square top corner (with minimum radius)
  • Cut face flat top to bottom (no undercut)
  • Cut face square with respect to the top surface
  • Clean smooth surface with near vertical drag lines
  • Little to no slag on the bottom edge (easily removed by scraping)

These are just the basics of oxy-fuel cutting. Some of the factors that affect the quality of the cut edge include cut oxygen pressure, plate temperature, preheat flame adjustment, speed, cutting height, etc.

Various Applications of Oxy-flame Cutting

Oxy-fuel cutting is extensively used to make plate edges for groove and bevel welding. The cutting process also finds its use in:

  • Manual rough severing
  • Scrap cutting
  • Automated precision contour cutting
  • Metalizing
  • Cutting and bending
  • Flame hardening

Oxy-fuel cutting process is cost-effective and workable on metals of varying thicknesses. Therefore, the process finds application in field repair work and construction sites.