Oxy-Fuel Cutting Torch

What an Oxy-Fuel Cutting Torch Is

An oxy-fuel cutting torch is a hand or machine tool that combines a fuel gas with oxygen to first preheat steel and then, with a separate jet of pure oxygen, chemically burn through it. The defining insight is that oxy-fuel cutting is an oxidation process, not a melting process. The flame does not melt the plate the way a plasma arc or laser does. Instead, the preheated iron reacts exothermically with pure oxygen to form iron oxide, and the reaction itself releases enough heat to sustain the cut once started. This is why the process is sometimes called "flame cutting" or "burning," and why operators speak of the steel being "burned" rather than melted.

Functionally a cutting torch runs two independent oxygen circuits and one fuel circuit. The preheat circuit mixes fuel gas with oxygen and burns it at a ring of small orifices around the nozzle face to raise the steel to its kindling (ignition) temperature, roughly 870 to 900 degrees Celsius, at which point the surface glows bright cherry red. The cutting circuit delivers a separate, central, high-velocity stream of pure oxygen, released only when the operator presses the cutting lever. That central jet oxidizes the iron and the high-velocity gas physically blows the resulting molten oxide, called dross or slag, out of the cut groove (the kerf). Because the molten iron oxide melts at roughly 1,370 degrees Celsius, well below the 1,500-plus degree melting point of the steel itself, the oxide flows away cleanly while the surrounding parent metal stays solid.

The historical roots run deep. Oxy-acetylene welding was developed by French engineers Edmond Fouche and Charles Picard in 1903, and the cutting variant followed quickly, giving shipyards and steel mills their first portable means of severing thick plate. For most of the twentieth century the oxy-fuel torch was the dominant thermal cutting process in heavy industry. Plasma cutting arrived commercially in the late 1950s and laser cutting in the 1970s, and both took over thin-plate and non-ferrous work. Yet oxy-fuel never disappeared: on thick carbon steel beyond roughly 50 mm, on construction sites, in scrapyards, in shipbreaking, and anywhere a low-cost portable tool must sever structural steel, it remains the practical default.

The reason for that staying power is economics and reach. A complete oxy-fuel outfit (two regulators, hoses, a torch handle, a cutting attachment, and a set of nozzles) costs a fraction of a plasma or laser system, needs no electrical power, and can cut steel plate well beyond 300 mm thick, far past the practical ceiling of portable plasma. The trade-off is a wider kerf, a larger heat-affected zone, slower travel on thin material, and the inability to cut stainless steel, aluminum, copper, or other metals whose oxides do not cooperate with the burning mechanism. Understanding where that boundary lies, and how torch, gas, and nozzle choices move it, is the substance of an informed purchase.

Four engineering factors govern the performance of any oxy-fuel cutting setup: the fuel gas chosen, the cutting-oxygen purity and pressure, the nozzle (tip) size relative to plate thickness, and the mixer design inside the torch. None of these is the torch body alone. A premium torch handle fitted with the wrong nozzle, fed low-purity oxygen, will cut worse than a modest torch correctly configured. The chapters that follow treat each factor in turn.

Torch Types and Mixer Designs

Oxy-fuel cutting torches divide first by how they are operated (hand-held versus machine-mounted) and second by how the fuel and oxygen are blended inside the body (the mixer design). These two axes drive most of the catalog differences between products. The table below summarizes the operating categories.

Combination outfits pair a single handle with interchangeable welding, heating, and cutting attachments. They are the most common purchase for general shops because one handle serves several jobs. The cutting attachment adds the cutting-oxygen lever and the larger nozzle seat. Capacity is modest, generally up to about 150 mm, limited by the handle's gas passages.

Dedicated hand cutting torches are heavier, longer, and built only to cut. Their larger internal passages and bigger nozzle seats let them reach plate well beyond 150 mm. Demolition and shipbreaking crews favor long-barrel versions because the extra length keeps the operator clear of radiant heat and spatter when severing thick sections.

Machine or straight cutting torches have no hand levers; the preheat and cutting oxygen are valved remotely and the torch is clamped into a rack on a CNC table, a profile cutter, or a beam-coping machine. Running unattended at a fixed standoff and steady travel speed, a well-tuned machine torch produces the cleanest oxy-fuel edges, approaching the perpendicularity and surface quality limits of ISO 9013. Large gantry tables routinely cut carbon steel plate up to 300 mm, and special torches reach far higher.

The second axis is the mixer design, which determines how safely and flexibly the torch handles different fuel gases. The table below contrasts the two classic approaches plus the modern universal mixer.

An equal-pressure (positive-pressure) mixer assumes both oxygen and fuel arrive with meaningful pressure and blends them through turbulence between the handle and the head. It is simple and well suited to acetylene, which is delivered at usable cylinder pressure. A injector (venturi) mixer uses the velocity of the oxygen stream to draw in the fuel gas, so it works even when fuel pressure is low or variable, which is why it suits natural gas or long, restrictive hose runs. The modern universal mixer (Victor markets a combined spiral-plus-injector design) lets one torch run acetylene, propane, propylene, or natural gas with only a nozzle change, which is why universal-mixer torches dominate shops that switch fuels.

Fuel Gases and Their Trade-offs

The fuel gas is the single decision that most changes how an oxy-fuel torch behaves. Each gas burns at a different temperature in oxygen, concentrates its heat differently between the inner cone and outer envelope, demands a different volume of oxygen, and carries different cost and safety constraints. The torch and nozzle must match the fuel. The table below compares the four common fuels by their neutral-flame temperature in oxygen and the oxygen volume each requires.

Acetylene burns hottest, roughly 3,160 to 3,200 degrees Celsius in oxygen, and concentrates that heat in a sharp primary cone. The result is the fastest preheat and the fastest pierce, which makes it the standard for thin plate, frequent starts, bevel cutting, and portable repair where speed of ignition matters. It also needs the least oxygen, around 1.1 to 1.2 volumes per volume of fuel. Its limitations are real: acetylene is chemically unstable and must not be used above 103 kPa (15 psi) gauge pressure, cylinders have a limited safe withdrawal rate (roughly one-seventh of cylinder volume per hour), and it is the most expensive fuel per unit of heat.

Propane burns cooler, near 2,810 degrees Celsius, and delivers more of its heat in the outer envelope rather than a tight cone. This makes piercing slower and preheat broader, but propane is inexpensive, widely available, and stable, so it dominates long production cuts and heavy plate where pierce time is a small fraction of total cut time. The penalty is oxygen consumption: propane needs roughly four to four and a half volumes of oxygen per volume of fuel, so the oxygen bill rises even as the fuel bill falls. Propane requires a two-piece nozzle and propane-rated seals.

Propylene sits between the two, around 2,900 degrees Celsius, with a more concentrated primary flame than propane and easier lighting due to a higher flame speed. Its headline advantage is economy of use: the same volume of fuel lasts roughly five times longer than acetylene, which is why propylene has become the popular middle-ground fuel for shops that want acetylene-like behavior at lower running cost. Natural gas (methane) is the cheapest and safest fuel, often piped directly to machine cutting tables, but it has the lowest flame temperature and the slowest pierce, so it is reserved for fixed installations where a plumbed supply offsets its sluggish starts.

A point often missed by buyers: the fuel choice changes the torch and nozzle hardware, not just the cylinder. A one-piece nozzle is correct for oxy-acetylene; alternate fuels (propane, propylene, natural gas) require a two-piece nozzle that vents their larger fuel volume around the nozzle seat. Switching a shop from acetylene to propane therefore means buying alternate-fuel nozzles and confirming the mixer and seals are rated for the fuel, not merely swapping a regulator.

Nozzles, Cuttable Materials, and Standards

The nozzle (also called the tip or, in European usage, the cutting nozzle) is the consumable that does the work. Its central orifice meters the cutting-oxygen flow, and the ring of small surrounding orifices forms the preheat flames. Nozzle size is matched to plate thickness, because too small an orifice cannot deliver enough cutting oxygen for thick steel, while too large an orifice wastes gas and widens the kerf. Acetylene nozzles to the common ANM / ANME pattern are sized by orifice in fractions of an inch; the table below gives the standard thickness mapping.

There is no industry-wide standard for orifice diameter, so a size number on a Victor tip does not equal the same number on a Harris or Smith tip. This is why every reputable maker publishes a tip chart that ties each tip part number to a plate thickness, a cutting-oxygen pressure, a fuel pressure, a drill size, and an expected travel speed. Buyers should treat the maker tip chart, not the size number alone, as the authoritative selection document, and should stock genuine nozzles matched to the torch family rather than mixing brands.

Equally important is knowing what oxy-fuel cannot cut. The process only works on metals whose oxide melts below the metal itself, so the molten oxide can be blown clear. Carbon steel and low-alloy steel satisfy this and cut cleanly. Stainless steel cannot be oxy-fuel cut with a plain torch, because its chromium forms a refractory chromium oxide skin that melts near 2,435 degrees Celsius, far higher than the steel, so the cut self-seals; stainless requires plasma, laser, or a powder/flux-injection variant. Aluminum, copper, brass, and other non-ferrous metals cannot be cut for the same reason (aluminum oxide melts near 2,050 degrees Celsius) and because their high thermal conductivity carries heat away faster than the flame can build it. High-carbon and high-alloy steels cut poorly because the slag does not eject cleanly. For these materials buyers should look at plasma or laser instead.

Several standards frame quality and safety. ISO 9013 classifies thermal cuts and sets geometrical tolerances (perpendicularity tolerance u and mean profile height Rz5), applying to oxyfuel flame cuts from 3 mm to 300 mm thick; it is the document a fabricator cites when specifying edge quality. ISO 17916 covers the safety of thermal cutting machines. Gas safety devices follow ISO 5175 / EN ISO 5175 for flashback arrestors, with ISO 5172 for blowpipes and ISO 3821 for rubber welding hoses. A flashback arrestor stops a flame or reverse gas flow from travelling back into the hose and regulator; modern practice fits dry arrestors with at least two safety elements, often with a thermal cut-off valve that shuts the gas before the mixture reaches its ignition temperature. These devices are not optional accessories but core safety hardware on any oxy-fuel outfit.

Key Specification Parameters

Reading an oxy-fuel torch and tip specification is a core procurement skill. A torch data sheet and the matching tip chart together expose the parameters that determine whether a setup will cut your plate at acceptable speed and quality. The parameters below are the ones that actually drive selection.

Cutting capacity (maximum plate thickness) is the headline figure: the thickest carbon steel the torch and its largest nozzle can sever. Combination outfits typically reach about 150 mm, dedicated hand cutting torches about 250 to 300 mm, and machine straight torches 300 mm and well beyond with special nozzles. Always read the capacity against a specific fuel gas, because acetylene and propane reach different limits on the same torch.

Cutting-oxygen pressure rises with thickness and nozzle size. As a representative acetylene hand-torch chart, thin plate near 6 mm uses roughly 25 to 30 psi (1.7 to 2.1 bar) cutting oxygen, 25 mm (1 inch) plate uses about 40 to 45 psi (2.8 to 3.1 bar), and 75 to 150 mm plate uses 50 to 75 psi (3.4 to 5.2 bar). The corresponding fuel (acetylene) pressure runs about 3 to 5 psi for thin plate and 10 to 15 psi for heavy plate, but must never exceed the 103 kPa (15 psi) acetylene safety ceiling. Alternate fuels can run higher fuel pressures. These figures are starting points only; the governing values come from the specific torch tip chart.

Cutting-oxygen purity is decisive and often overlooked. Industrial cutting oxygen should be 99.5 percent or higher, because each one percent drop in purity can cut speed by roughly 10 to 15 percent and raise oxygen consumption, since the inert fraction does not oxidize iron and instead dilutes and cools the reaction. High-volume plants therefore feed machine torches from high-purity pipeline or bulk liquid oxygen rather than low-grade cylinders.

Kerf width and heat-affected zone follow from nozzle size and thickness. Oxy-fuel kerf is wider than plasma or laser, growing from a few millimeters on thin plate to over ten millimeters on very thick sections, and the heat-affected zone is correspondingly larger. Parts must be nested with this kerf allowance, and tight-tolerance parts may need machining after cutting.

Travel (cutting) speed falls as thickness rises. Thin plate cuts at hundreds of millimeters per minute, while very thick plate may cut at only tens of millimeters per minute. Speed also depends on fuel choice and oxygen purity, so makers publish speed against thickness for each tip.

Connection and consumable parameters round out the sheet:

• Inlet connections: standard oxygen and fuel hose fittings (commonly 9/16 inch or 3/8 inch threads), with fuel fittings left-hand threaded and notched per safety convention.
• Mixer type: equal-pressure, injector, or universal, which sets fuel flexibility (see Chapter 2).
• Nozzle family and seat: ANM/ANME, Victor, Harris, or proprietary; determines which genuine tips fit and whether one-piece (acetylene) or two-piece (alternate fuel) nozzles are required.
• Head angle: 75-degree, 90-degree, or straight, chosen for the cutting geometry and operator clearance.
• Safety devices: integrated or in-line flashback arrestors and check valves to ISO 5175, fitted at both torch and regulator ends.

Selection Decision Factors

To turn the preceding chapters into a specific purchase, follow the decision sequence below. Most selection mistakes are not a single wrong number but a decision made at the wrong level, for example choosing a torch body before confirming the material can even be oxy-fuel cut. These steps double as an RFQ template.

1. Confirm the material first: oxy-fuel cuts only carbon and low-alloy steel. If the work includes stainless steel, aluminum, copper, or other non-ferrous metal, the process is wrong and you need plasma or laser. Settle this before any torch comparison.
2. Define plate thickness range: the thickest plate sets the required cutting capacity and the largest nozzle size; the thinnest sets the smallest practical nozzle. A single torch with a nozzle set should span the full range.
3. Choose the fuel gas: acetylene for fast piercing, thin plate, and portable repair; propane or propylene for economical heavy and long cuts; natural gas for plumbed machine tables. This decision drives mixer type, nozzle type (one-piece versus two-piece), and seal rating.
4. Select hand versus machine: hand torch for site work, demolition, and maintenance; machine straight torch for CNC tables and repeatable production edges to ISO 9013. Portable motorized carriages bridge the two for straight and bevel field cuts.
5. Specify the mixer: equal-pressure for dedicated acetylene work, injector for low or variable fuel supply, universal mixer if the shop switches fuels and wants one torch to do everything.
6. Lock the nozzle family and tip chart: commit to one nozzle pattern (ANM/ANME, Victor, or Harris) and source genuine tips, because orifice sizing is not standardized across brands and mixing tips degrades cut quality.
7. Fit safety devices: flashback arrestors and check valves to ISO 5175 at both torch and regulator ends are mandatory, not optional, and many specifications add thermal cut-off valves.
8. Validate oxygen supply: confirm 99.5 percent or higher cutting-oxygen purity and adequate flow; for high-volume cutting, plan pipeline or bulk liquid oxygen rather than low-grade cylinders, since purity drives both speed and cost.

One last commonly overlooked dimension is manufacturer serviceability: local availability of genuine nozzles, seals, valves, and flashback arrestors, plus repair parts for the torch handle and cutting attachment. A torch is a long-lived tool, and the consumables (nozzles wear and the preheat orifices clog) determine running cost and downtime more than the initial purchase. For manual cutting, Victor (an ESAB family brand), Harris Products Group (Lincoln Electric), Smith (Miller), and GCE maintain broad distribution and genuine consumable supply. For machine and portable mechanized cutting, Koike Aronson (IK-12 Beetle profile cutter, Handy Auto motorized torches), Messer Cutting Systems (Turbo Flame torches, CNC gantry tables), and ESAB/Victor machine torches are the established choices. Confirm the chosen brand stocks matched nozzles and arrestors in your region before committing to a large fleet.