What is flame cutting?

Flame cutting is the process of cutting a shape from a steel plate using oxygen and fuel gas. It falls under the term steel profiling which encompasses services such as laser cutting, waterjet cutting and plasma cutting. It is also known as profiling, burning or oxy cutting. The process is straight forward and hasn’t changed over the years (although the guidance system has). We are constantly improving efficiencies through material handling, bed design, computer programmes, training and developing our staff.

The Origin of Flame Cutting

In 1899 in the USA, John Harris discovered oxy-acetylene cutting by accident! While he was researching the manufacture of synthetic rubies, he cut the metal plate beneath. Flame cutting was born! He exhibited his torch in 1904 at the World Fair in St Louis. He continued to refine it and also manufactured related accessories including gas pressure regulators.

Early flame cutting machine

Early flame cutting machine

Flame cutting using a hand held torch is still used today, but more accuracy and speedy repeatability was needed! A machine system was required and a hand held roller following a wooden template with a single torch was developed. Known as a U arm machine, this was superseded by a magnetic roller following a metal

template. (See example of a 36 inch machine by Universal in 1925).The size of the template was reduced by half the roller diameter and half the Kerf (the width of the cut) was added. There were often as many template makers as machine operators.

 

 

 

Developments in cutting technology

The 60’s and 70’s saw two further steps forward. Firstly a light incorporating a cruciform was positioned over a black line and guided by the operator who followed the line and cutting head(s) produced the profiles. A steady hand was necessary!

Secondly the Optical Head or ‘’magic eye’’ transformed the accurate guidance of multi-headed machines. (See bank of new magic eye machines at Malthouse Engineering in 1973). An accurate pencil drawing was made and a line half the width of the cut (kerf) was added in black ink. The paper was placed and secured on the tracing table and the magic eye positioned over the black

Bank of Flame Cutting Machines at Malthouse Engineering

line. A powerful light emphasised the black ink line on the white paper. The reflected image was directed by glass prisms onto a light sensitive transducer which converted the image into electrical signals – the x and y axis or in the case of a curve, a combination of both. A signal was returned to ‘’lock’’ the eye to the black line.

The advantages were obvious but one disadvantage was that paper changed size in damp weather!
The beam holding the magic eye could now be extended over the bed supporting the plate and a number of cutting heads (1, 2 and often up to 8) could now cut the steel plate accurately. The table with the drawing could be locked firmly into position and after the cut unlocked and moved for a further blank (or blanks) to be cut.

The Computer Age

Computer guided systems were introduced in the Mid 80’s. Simple shapes were drawn typically on a BBC computer and downloaded to a ‘’Burny’’ controller on the machine. When the computers were enhanced and confidence in them grew the magic eye and table were dispensed with and the machine carrying the cutting torches set as a ‘’gantry’’ giving greater stability and accuracy. The space saved by removing the tracing table now allows wider plates to be cut or a smaller ‘’footprint’’ of the machine. The computers evolved as did the software. Malthouse has standardised on the Procut system which with its many updates and improvements is now quite sophisticated.

The Cutting Process

Commercial cutting uses bulk oxygen from a tank and bulk propane – usually kept as far apart as possible! This is the most common combination and covers the whole thickness range (up to 1000mm and beyond but propane is the most popular gas). The propane is lit and heating oxygen is mixed into a flame until an inner blue core is

Cutting Flame Shapes

Cutting Flame Shapes

seen. This is often called a neutral flame with the mixed gases flowing through an annulus of holes in the copper nozzle. The tip of the inner blue core is 3000°C and is concentrated above the surface of the steel plate.

As the steel starts to melt (at 1450°C – 1500°C) the central cutting stream of high pressure oxygen is concentrated into the molten pool changing the (Ferrous) steel into ferrous oxide. This flows away at 400°C as sparks as the torch is moved (inched) away slightly preventing the ferrous oxide sparks from entering the holes in the nozzle potentially causing a blowback. So the cut is made and continues by a combination of chemical reaction and oxygen pressure and a smooth accurate movement of the torch(s) by the electric motors creates a smooth cut on the plate edge.

The Cutting Bed

The plate to be cut is supported on a bed. This is typically a steel box with open front and back enabling slag and small parts to be removed. At Malthouse this process has been automated and the system patented. Across the top are parallel bars of 10mm thick material 200mm apart supporting the plate whilst allowing small cut parts and ferrous oxide (dross) to fall into the bed. As the flame passes repeatedly over the bars, damage is caused to the top edge. Others use conical supports or bed bars set at an angle. The bed bars have slots in them to secure them to the bed in such a manner that they are reversible doubling the life of the bars.

Other Matters

Thin plate (up to 5mm) tends to buckle during the flame cutting process. If a large quantity of components is required then a pack of plates (say 10) can be bolted together tightly such that no gaps can open up allowing the flame to migrate. Heavy plate and high carbon material (EN8/EN9) benefits from pre heating and gives a smooth cut and in case of high carbon material prevents crackling.

For further information on flame cutting you can go to the oxy fuel welding and cutting page on wikipedia here or if you would like to find out more about how we could help you with your flame cutting requirements please go to our flame cutting page here, email sales@malthouseengineering.com or phone 0121 557 8455.