What Is a Cutting Torch?

The role of the cutting torch is to mix oxygen and acetylene in proportion to form a preheated flame, and spray high-pressure pure oxygen onto the workpiece to be cut, so that the cut metal is burned in an oxygen jet, and the oxygen jet and the melt generated by the combustion Slag (oxide) is blown away to form a slit. The torch is the main tool for gas cutting workpieces.

The cutting torch is divided into two types of injection suction and isobaric according to the mixing method of oxygen and acetylene in the preheated flame. The use of the injection torch is the most common. The cutting torch is divided into ordinary cutting torch, heavy cutting torch and welding and cutting torch according to its purpose. ^[1]

The jet-suction torch is a mixture of fuel and oxygen that is combusted by the jet-injection action of the jet of oxygen. The fuel used in this type of torch is divided into two types: gas and liquid. Base fuel, etc. Taking the country's overall requirements for restricting the development of acetylene gas and seeking new energy to replace acetylene as a starting point, a liquid-fuel-based jet suction torch is studied to eliminate the disadvantages of acetylene torch.

First, the working principle of shooting and cutting

The key structure of the jet suction liquid fuel cutting torch is a jet pump. A jet pump is a pump without moving parts. It is a pump that uses the energy of one fluid to pump another fluid. When the jet pump is working, high-pressure oxygen is ejected from the jet pump nozzle at a high velocity of V1, continuously taking away the air in the suction chamber, forming a low-pressure zone in the suction chamber, and the pumped liquid fuel enters the suction at the velocity of V2 under the effect of atmospheric pressure. In the room, the two fluids transfer and exchange energy in the throat, the speed of the working fluid decreases, and the speed of the sucked fluid increases until the throat exit, so that the flow velocity and pressure of the two tend to be the same, and then the diffusion tube makes After part of the kinetic energy is converted into pressure energy, it is transported to the nozzle of the cutting torch through the pipeline, and mixed with the cutting oxygen at the cutting nozzle to burn and achieve the purpose of cutting metal.

The designed torch uses liquid fuel, which generates a high-temperature flame at the nozzle, so that the torch has a certain temperature and is transmitted to the throat of the torch, so that it has the appropriate heat to heat and atomize the liquid fuel in order to obtain more Good gasification effect, improve combustion efficiency.

Second, the factors affecting the performance of injection and cutting data

1.Design parameters and assembly factors

1) Design parameters.

The main parameters of the jet pump are: pressure ratio h, flow ratio q, throat area ratio m, and density ratio of the two fluids. The above parameters can be used to represent the basic equation of the jet pump pressure ratio: h = f (m, q, From the basic performance curve of the jet pump, it can be known that when is constant, under a certain throat area ratio, the pressure ratio and the flow ratio are approximately linear. As the value of m increases, the straight line changes from a steep drop to a gentle one. When the area ratio is fixed, the flow rate and pressure ratio with the highest jet pump efficiency become the optimal flow rate and pressure ratio.

2) Assembly quality.

When assembling the ejection structure, attention should be paid to the coaxiality of the nozzle and the throat to ensure that it has sufficient ejection capacity, and the tightness of the ejection structure should also be ensured to ensure that there is no air leakage. When assembling the cutting torch's cutting nozzle, the inner core and outer sleeve of the cutting nozzle must be kept concentric so that the cutting oxygen jet is located in the center of the preheated flame. When installing the cutting nozzle, pay attention to tighten the cutting nozzle nut to prevent fuel leakage.

2.Operating factors

1) Processing before cutting.

The paint, rust and dirt on the workpiece should be cleaned before cutting. If cutting on hardened ground, it is necessary to raise the workpiece to prevent the ground from being heated and the slag will be splashed to ensure the safe and effective operation.

2) Cutting oxygen pressure.

Select the oxygen pressure according to the thickness of the workpiece, the type of the cutting tip and the purity of the oxygen. Too much or too little cutting oxygen pressure will result in poor cutting results. In actual cutting, the optimal cutting oxygen pressure can be determined by testing the air line. For the selected cutting nozzle, when the air line is the clearest and the longest, the pressure is an appropriate value.

3) Preheat flame power.

When cutting, the power of the preheating flame should be neutral flame or slightly oxidized flame to ensure its intensity is moderate. In practice, it should be selected according to the thickness of the workpiece, the type of the cutting nozzle and the quality requirements. The preheating time of the cutting is determined according to the thickness of the workpiece.

4) Cutting speed.

The cutting speed is related to the thickness of the workpiece and the type of the cutting nozzle. The thicker the workpiece, the slower the cutting speed, and the faster the cutting speed. The cutting speed must be compatible with the oxidation speed of the metal in the cut. If the cutting speed is too slow, the edges of the cut will be uneven, and even the local melting phenomenon will occur. If the cutting speed is too fast, the amount of drag will be too large, and it will not even cut through. During the cutting operation, the cutting speed can be determined according to the direction of the slag sparks falling in the cut, and the normal speed is when the spark is discharged vertically or slightly forward. When cutting in a straight line, a faster speed of discharging the spark slightly backward is adopted.

5) Inclination between cutting tip and workpiece.

The inclination is related to the thickness of the workpiece, and its size affects the cutting speed and back drag. When the cutting nozzle is inclined at a certain angle in the cutting forward direction, the slag can be blown to the leading edge of the cutting line, reducing the amount of back drag, thereby improving the cutting speed. If the inclination angle is not selected properly, it will increase the oxygen consumption and even cause cutting difficulties if the cutting efficiency is impaired.

6) The distance from the cutting tip to the workpiece.

The distance from the cutting nozzle to the surface of the workpiece should be determined according to the preheating flame power and the thickness of the workpiece. Generally, the distance between the flame center and the workpiece surface is in the range of 3 ~ 5 mm. If the height of the cutting nozzle is too low, the cooling effect of oxygen on the cutting seam increases; if the distance is too large, the flame temperature is insufficient, the cutting seam burns badly, and the cutting oxygen flow force is reduced, making slag discharge difficult and affecting the cutting quality.

Analysis of common problems

1) The torch shooting ability is reduced.

Long-term use of dust and impurities enter the cutting torch, causing the oxygen channel to be blocked and the oxygen pressure of the jet to be reduced. At this time, the oxygen regulating valve can be opened to reverse the oxygen flow and blow out the impurities. If the cutting nozzle is blocked, the needle can be used to remove the impurities; The nozzle and the throat are caused by different axes, and should be straightened and aligned in time.

2) The cutting flame is partial and the working condition is unstable.

Liquid fuel has a poor atomization effect, poor mixing uniformity with oxygen, and insufficient gasification performance after mixing. The leak-tightness of the injection and suction structure can be checked to ensure the atomization effect; or due to the thread wear of the oxygen valve needle, matching The gap is too large, causing air leakage and other phenomena. The oxygen valve needle must be replaced.

3) Fire extinguishing occurred during welding.

One of the reasons is that the cutting nozzle is loose, and the cutting nozzle and the torch body should be reconnected in time to ensure tightness; or because the temperature of the cutting nozzle and the mixed gas pipe is too high, the fuel gas pipe should be closed at this time and the cutting nozzle should be immersed in water to cool.

There are many factors that affect the jet suction liquid fuel cutting torch, including design parameters, assembly quality, and operating methods. In order to achieve the best results of the jet-suction torch, it is necessary to combine theory with practice to obtain the best design parameters and operating methods to improve work efficiency and safety in the production process. In the process of cutting with a torch, other unexpected problems may also occur, which need to be specially treated by the design and users and summarized in time to achieve the best results. ^[1]

EXA-6000 6m × 18m underwater plasma CNC cutting machine, the system used is NCE2000, the model of plasma cutting power supply is MAX200, 200A, oxygen plasma air protection. It offers high cutting speed and good economy.

The main parameters

Plasma gas type is oxygen, plasma gas pressure, test 3 4kg, running 3.5 4.8kg, protective gas type is air, protective gas pressure is 5kg, the distance between cutting torch and workpiece is different according to material and thickness, it can be adjusted within 3 6mm The arc current is set to 200A, the arc voltage is set to 125 to 145V, the operating speed is 3700 to 680mm / min, the plasma gas inlet pressure is 8.5kg, and the protective gas inlet pressure is 6.5kg. ^[2]

Cutting torches and welding torches are important tools for gas welders. If used incorrectly, they may cause flame out, tempering, and even combustion and explosion accidents. Therefore, the following matters should be noted during use:

1. Equipped with the pressure and volume of oxygen and acetylene according to the welding torch and cutting torch size.

2. The nozzle and the metal plate must not touch each other.

3. Carefully check the gaskets and valves at all stages for leaks.

4. The nozzle is clogged. When using a needle to pierce the nozzle, remove the nozzle and clear it from the inside out.

5. Before use, the air in the rubber tube should be exhausted, and then the oxygen and acetylene valves should be opened respectively, and the test welding can be ignited after being cleared.

6. All parts of the welding torch and cutting torch must not be contaminated with grease.

7. The nozzle of the welding torch and cutting torch must not be too hot. If it is too high, water cooling is required.

8. When ignition, open the acetylene valve first, and then open the oxygen. The purpose is to release acetylene-air mixture to facilitate ignition and check whether acetylene is unblocked.

9. Leakage of acetylene and oxygen valves should be repaired in time.

10. Do not lay the nozzle of a burning torch or welding torch on the workpiece or on the ground.

11. When leaving the work site, do not place lighted welding torches and cutting torches on the operating table.

12. When switching over or stopping welding, close the oxygen and tempering arrester valves.

13. The rubber tube must be dedicated and marked to distinguish it. The acetylene tube and the oxygen tube cannot be used interchangeably.

14. When the rubber tube is found to be frozen, it should be thawed with warm water or hot steam. It is forbidden to bake with fire, and it is not allowed to use oxygen to blow the acetylene pipe.

15. Rubber hoses for oxygen and acetylene should not be placed randomly, and the nozzles should not stick to the ground, so as to prevent soil and impurities from filling up and blocking. ^[3]

(1) Selecting a suitable cutting nozzle should select a suitable cutting nozzle according to the thickness of the workpiece to be cut. When assembling the cutting nozzle, the inner and outer nozzles must be kept concentric to ensure that the cutting oxygen jet is located in the center of the preheated flame. Pay attention to tighten the cutting nozzle nut when installing the cutting nozzle.

(2) Checking the shooting condition The shooting suction type torch can be connected to the acetylene leather tube only after the shooting condition is checked normally, as long as it is airtight and easy to insert and remove. When using an isobaric cutting torch, acetylene should have a certain working pressure.

(3) After the flame is extinguished, when the preheated oxygen regulating valve is turned to adjust the flame after the ignition, if the flame immediately goes out, the reason is that there is dirt in each gas channel or the contact of the mouthpiece of the ejection pipe and the mouth of the nozzle is not tight, and Inner mouth fits incorrectly. At this time, the ejector tube nut should be tightened; when it is not effective, the ejector tube should be removed, the dirt in each gas channel should be removed, and the gap between the outer sleeve and the inner sleeve of the cutting nozzle should be adjusted and tightened.

(4) Treatment of air leakage in the core of the cutting nozzle After the preheating flame is adjusted normally, the cutting nozzle hair emits a rhythmic sound, but the flame does not extinguish. If the cutting oxygen is turned on, the flame will immediately extinguish. The cause was a leak at the core of the cutting tip. At this moment, the cutting nozzle jacket should be removed, and the nozzle core should be tightened lightly. If the nozzle core still fails, you can remove the jacket and pad it with asbestos rope.

(5) The cutting head and cutting torch are not cooperating closely. Although the flame is normal after ignition, when the cutting oxygen regulating valve is opened, the flame will be extinguished immediately. The reason is that the cutting head is matched with the cutting torch, and the joint is not strict. At this time, the cutting nozzle should be tightened. When it is invalid, the cutting nozzle should be removed and lightly sanded with fine sandpaper. Grind the mating surface of the cutting tip until the fit is tight.

(6) Treatment of tempering When tempering occurs, the cutting oxygen regulating valve should be closed immediately, and then the acetylene regulating valve and the preheating oxygen regulating valve should be closed. When the normal work stops, the cutting oxygen regulating valve should be closed first, and then the acetylene and preheating oxygen regulating valve should be closed.

(7) Keep the cutting nozzle channel clean The cutting nozzle channel should always be kept clean and smooth, and the dirt in the hole should be cleaned with a through needle at any time.

(8) Cleaning the workpiece surface Thick rust, oily water and dirt on the workpiece surface must be removed. When cutting on the cement floor, the workpiece should be elevated to prevent rust and slag from splattering on the cement floor and hurting people. ^[2]