With the widespread use of plasma cutting machines, the smoke and dust produced during steel plate cutting pose a significant air pollution problem.
As environmental regulations become increasingly stringent, the persistence of smoke and dust in the workshop can result in the temporary closure of a factory for remediation.
It is imperative to implement a smoke and dust treatment method to address these waste gases.
This article provides an overview of the methods for treating smoke and dust generated from plasma cutting and aims to be informative and helpful.
For the treatment of dust generated by plasma cutting machines, there are two methods that can be employed: the dry treatment method and the wet treatment method.
I. Plasma Cutting
Modern industry requires the processing of heavy metals and alloys. The manufacture of tools and transport vehicles necessary for daily activities can’t proceed without metals.
For instance, cranes, cars, skyscrapers, robots, and suspension bridges are all made from precisely processed metal components. The reason is simple: metal materials are very sturdy and durable.
For most manufacturing, particularly when it comes to large and/or sturdy items, metal materials become a logical choice.
Interestingly, the strength of metal materials is also their drawback: because metals are not easily damaged, it’s challenging to process them into specific shapes.
When people need to process a component that has the same size and strength as an airplane wing, how can precise cutting and shaping be achieved? In most cases, this requires the use of a plasma cutting machine.
Sheet & Plate
Steel plates are one of the four major types of steel (plate, tube, profile, wire). In developed countries, the production of steel plates accounts for over 50% of total steel production. With the development of China’s national economy, the production of steel plates is gradually increasing.
Steel plates are flat steel materials with a large width-thickness ratio and surface area. Steel plates are divided into two major specifications based on thickness: thin plates and thick plates.
Thin steel plates are produced using hot-rolled or cold-rolled methods, with a thickness between 0.2-4mm.
Thick steel plates refer to steel plates with a thickness above 4mm. In practical work, steel plates with a thickness less than 20mm are often called medium plates, steel plates with a thickness greater than 20mm and up to 60mm are called thick plates, and steel plates with a thickness greater than 60mm need to be rolled on a special extra-thick plate rolling machine, hence the name extra-thick plate.
The width of thick steel plates ranges from 0.6mm-3.0mm. Thick plates are further divided according to their uses into shipbuilding steel plates, bridge steel plates, boiler steel plates, high-pressure vessel steel plates, checkered steel plates, automotive steel plates, armor steel plates, and composite steel plates, etc.
Plasma Cutting History
During World War II, American factories produced armor, weapons, and aircraft at a rate five times faster than the Axis powers. This was largely thanks to significant innovations made by private industries in the field of mass production.
One part of these technical innovations was the quest for more efficient ways of cutting and assembling aircraft parts. Many factories that produced military aircraft adopted a new welding method that involved the use of inert gas shielded welding.
The groundbreaking discovery was that a barrier could be formed around the welding point by electrolyzing gas through an electric current, preventing oxidation. This new method resulted in tidier welds and stronger bonded structures.
In the early 1960s, engineers made another discovery. They found that accelerating the airflow and reducing the orifice size could enhance the welding temperature. The new system could achieve temperatures higher than any commercial welding machine.
In fact, at such high temperatures, the tool no longer functioned as a welder. Instead, it acted more like a saw, cutting through tough metal as easily as a hot knife through butter.
The introduction of the plasma arc revolutionized the speed, precision, and types of cuts that could be made, and it could be applied to various metals.
The ability of a plasma cutter to easily penetrate metal is due to the unique properties of the plasma state. So, what is the plasma state?
There are four states of matter in the world. Most of the substances we come into contact with in our daily lives are either solid, liquid, or gas. The state of a substance is determined by the interaction between its molecules. Take water as an example:
Solid water is ice. Ice is a solid formed by electrically neutral atoms arranged in a hexagonal crystal lattice. Due to the stable interaction between molecules, it maintains a solid shape.
Liquid water is the state we drink. There is still a force of interaction between the molecules, but they move at a slow speed relative to each other. Liquids have a fixed volume but no fixed shape. The shape of the liquid changes according to the shape of the vessel that holds it.
Gaseous water is water vapor. In water vapor, the molecules move at high speed and have no connection with each other. Since there is no force of interaction between the molecules, the gas has no fixed shape or volume.
The amount of heat (converted to energy) received by water molecules determines their properties and their state. Simply put, more heat (more energy) allows water molecules to reach a critical state where they can break free from the effects of their chemical bonds.
In a low heat state, the molecules bind tightly together, forming a solid. As they absorb more heat, the forces between them weaken, and they become a liquid. When they absorb even more heat, the forces between the molecules are almost completely lost, and they become a gas.
So, what happens if we continue to heat the gas? It reaches a fourth state: the plasma state.
When the gas reaches extremely high temperatures, it enters the plasma state. Energy begins to completely separate the molecules from each other, and atoms start to split.
A typical atom consists of protons and neutrons in the nucleus, surrounded by electrons. In the plasma state, the electrons separate from the atom.
Once the heat energy causes the electrons to leave the atom, they start moving at high speeds. The electrons carry a negative charge, while the remaining atomic nucleus carries a positive charge. These positively charged atomic nuclei are called ions.
When high-speed electrons collide with other electrons or ions, they release a tremendous amount of energy. It is this energy that gives the plasma state its unique properties, resulting in an incredible cutting ability.
In the universe, nearly 99% of matter exists in a plasma state. Due to its extremely high temperature, it is not commonly seen on Earth; however, it is very common on celestial bodies like the sun. On Earth, this state can be found in lightning.
Plasma Cutting Machine
Plasma cutting machines come in a variety of shapes and sizes. There are large plasma cutting machines that use robotic arms for precise cutting, as well as simplified handheld plasma cutting machines used in manual workshops.
Regardless of size, all plasma cutting machines are based on the same principles and have similar structural designs.
During the operation of a plasma cutting machine, compressed gases such as nitrogen, argon, or oxygen are sent through a narrow tube. A negative electrode is placed in the middle of the tube.
When power is supplied to the negative electrode and the nozzle touches the metal, a conductive circuit is formed, and high-energy electric sparks are generated between the electrode and the metal.
As the inert gas flows through the tube, the electric sparks heat the gas until it reaches the fourth state of matter. This reaction process produces a stream of plasma with a temperature of approximately 16,649 degrees Celsius and a velocity of up to 6,096 meters per second, which can quickly melt the metal.
The plasma itself has an electric current flowing through it. As long as power is continuously supplied to the electrode and the plasma remains in contact with the metal, the electric arc production cycle is continuous.
To ensure this contact while avoiding oxidation and damage caused by other unknown characteristics of the plasma, the cutting machine nozzle is equipped with another set of tubes. This set of tubes continuously releases shielding gas to protect the cutting area. The pressure of the shielding gas can effectively control the radius of the columnar plasma.
The thicker the steel plate to be cut, the greater the cutting current required.
Plasma Cutting Dust
During the plasma cutting process of metals, a large amount of smoke and dust is produced, such as acetaldehyde, metal oxides, sulfides, hydrocarbons, etc. These particulates billow into the air, posing hazards to workers’ health and the overall environment.
They could lead to the development of various occupational diseases, and severe complications can even cause death. Therefore, the control of smoke and dust from cutting machines is becoming increasingly urgent.
II. Wet treatment
The wet treatment method involves placing a water bed beneath the plasma cutting machine. During the cutting process, the workpiece is submerged in water, which captures harmful substances produced and prevents them from entering the atmosphere.
While this method is widely used, it has some drawbacks. Firstly, it can lead to water pollution and generate waste water that requires further treatment. Additionally, in colder climates, the water in the bed can freeze, making this method unsuitable for use in these areas.
Furthermore, this method is not recommended for cutting metals that produce explosive dust, such as aluminum and magnesium. Also, the steel plate may become rusted from exposure to water during cutting, and the cutting efficiency is lower when performed underwater.
III. Dry Processing Method
The dry treatment method involves collecting the smoke and dust produced during plasma cutting. There are several collection methods available, including side suction, lower suction, and upper suction. The smoke and dust are drawn into a pipeline by a fan and then purified using dust removal equipment before being discharged into the workshop or outside.
This method is constantly updated with the advancement of cutting machine technology. Previously, a movable suction cover was installed on the cutting head, but in practical applications, it was found that this was not effective in removing smoke and dust due to the narrow gap between the steel plate and the cutting position. Most of the smoke and dust is located in the lower part of the plate, and the upper dust suction cover is unable to effectively remove it.
A dust extraction work platform is installed beneath the cutting machine, equipped with a cutting fume purification system. This system directly transports the dust-laden smoke produced during cutting to the purifier for processing. The purified, up-to-standard gas is then discharged through the purifier’s exhaust vent.
Advantages: This setup prevents secondary pollution; dust cleanup is convenient; after cutting, the workpiece can directly proceed to the next process, thereby improving work efficiency. This system is suitable for non-ferrous metal cutting.
Disadvantages: Dust removal requires an investment, resulting in higher initial investment costs.
Components of Dry Processing Dust Removal System
The dry processing dust removal system is composed of a dry cutting platform, dust removal pipeline, purifier, and fan, among other components. During cutting, the smoke and dust produced are captured by the dry cutting platform.
The platform’s air outlet is connected to the dust removal pipeline’s air inlet. Under the pipeline’s negative pressure, the cutting smoke and dust enter the dust removal pipeline and subsequently the purifier for purification.
Here, the cutting platform is a key component of the dust removal system.
The dust removal system can be categorized based on the method of capturing smoke and dust from the cutting platform into:
- Damper-based cutting platform dust removal system
- Blow-suction cutting platform dust removal system.
IV. Dry Cutting Dust Extraction System
Damper Style Cutting Platform Dust Extraction System
- Single-Side Down-draft Damper Style Dust Extraction System (For Cutting Platform Width <4m)
- Double-Side Down-draft Damper Style Dust Extraction System (For Cutting Platform Width ≥4m)
Blowing and Suction Type Cutting Platform Dust Extraction System
- Single Sliding Duct Blowing and Suction Dust Extraction System (For Cutting Platform Width ≤4.5m)
- Double Sliding Duct Blowing and Suction Dust Extraction System (For Cutting Platform Width >4.5m)
V. Louvered Cutting Platform Dust Removal System
Working Principle: A louvered suction work platform is installed under the cutting machine, dividing the platform into several suction chambers of equal width along the length of the platform. Each suction chamber is fitted with a dust hopper with a suction port.
On both sides of the platform length, there are air ducts, each equipped with a louver and cylinder corresponding to each suction chamber on the side of the air duct. When the cutting head of the cutting machine moves over each suction chamber, the cylinder is controlled by the sensor switch to open the louver of the corresponding suction chamber on the air duct.
This process sucks in the smoke and dust produced during cutting into the dust removal air duct, before finally entering the main purifier for purification.
Structure of wind door cutting platform
- Grating Plate
- Material Rack
- Material Hopper
- Material Box
- Air Door/Cylinder/Inductive Switch
Features of the Louver-Type Cutting Platform Dust Removal System
The suction of the cutting platform effectively concentrates in the region where the cutting head is located (with a width equal to that of the cutting platform and a length of approximately 1m). This region moves with the cutting head, significantly saving the amount of suction.
- The structure is relatively complex, consumes a lot of steel, and requires high manufacturing precision.
- There are numerous cylinder and louver components, resulting in multiple points of failure and making maintenance inconvenient.
- If a single louver does not close tightly or fails, it affects the suction effect.
- Removing slag is inconvenient.
- The required suction volume for equal cutting platform width is high, leading to higher dust removal investment.
- Under equivalent track spacing, the effective cutting width is large.
- The suction is uniform, the effect is good, and it is not affected by the steel plate’s coverage rate on the cutting platform.
The louver-type cutting platform is more suitable for dust removal applications where the platform width is less than 4m.
Calculation of the Suction Volume of the Louver-Type Cutting Platform Dust Removal System
The required suction volume of the louver-type cutting platform is greatly related to the cutting platform’s width. The calculation formula for the suction volume is as follows:
Q = W × 2 × 0.667 × υ × 3600
- Q – Dust removal system suction volume m3/h
- υ – Suction speed of the platform cross-section m/s (Generally taken as 0.8 – 1m/s)
- W – Effective cutting width of the cutting platform
- 3600 – Unit conversion
Affected by the structure of the cutting platform, for cutting platforms with an effective cutting width of less than 4m, a single-sided suction structure is generally adopted. For cutting platforms wider than 4m, a double-sided suction structure is used.
Single-sided/Double-sided Exhaust Cutting Platform CAD Structural Diagram and Exhaust Volume Calculation
Based on the equation above, if the width of the cutting platform is between 2m and 4m, the required exhaust volume Q = (2~4) × (0.8~1) × 3600 = 6000~12000 m 3/h.
If the cutting platform width is 4m~6m, then the required exhaust volume Q = (4~6) × (0.8~1) × 3600 = 12000~22000 cubic meters per hour.
Single-Sided / Double-Sided Exhaust Cutting Dust Removal System – Selection Table for Kaitian Dust Collector
|Cutting Platform Structure||Cutting Platform Width||Exhaust Volume（m3/h）||Dust Collector Model|
|Single-sided Exhaust Platform||2000||6000||KTJZ-6.OKQ|
|Double-sided Exhaust Platform||4000||12000||KTJZ-12KQ|
Note: The above model selection is for reference only. Factors such as the length of the cutting platform, the number of plasma cutting heads, and the distance from the dust collector installation position to the cutting platform may affect the model of the dust collector. For specific model selection, please consult a Kaitian Environmental Protection sales representative.
Application Examples of Louver-style Dust Removal Systems
- Cutting Platform Size: 2600×14000
- Cutting Platform Structure: Single-sided Wind Gate Style
- Dust Collector Model: KTJZ-12KD
- Usage Time: Since 2006
- Cutting Platform Size: 4000×18000
- Cutting Platform Structure: Double-sided Wind Door Style
- Dust Collector Model: KTJZ-18KH
- Usage Time: Since 2004
- Cutting Platform Size: 5000×18000
- Cutting Platform Structure: Double-sided Wind Door Style
- Dust Collector Model: KTJZ-25KH
- Usage Time: Since 2005
- Cutting platform dimensions: 5200×17000
- Cutting platform structure: Double-sided louver style
- Dust collector model: KTJZ-25KH
- Usage time: Since 2006
VI. Blow-Suction Cutting Platform Dust Removal System
Working Principle: A square air intake duct is installed on one side of the cutting platform. Above the duct, there is a sliding air intake trolley that can move along with the cutting machine. On the other side of the cutting platform, an air blower is installed.
The sliding air intake trolley, the cutting head, and the air blower are all installed in a straight line along the direction of the transverse beam of the cutting machine.
The grid plate on the cutting platform and the steel plate being cut form a “smoke channel”. When cutting the steel plate, the air blower blows the cutting dust generated into the air intake of the air intake trolley via this “smoke channel”, into the square air duct, and finally into the purifier host for purification treatment.
VII. Cutting Platform Structure
Structure of blow suction cutting platform
The structure of the blow-suction cutting platform involves a square suction duct and a sliding suction cart, which are crucial components. During operation, under the effect of negative pressure in the pipeline, the sealing belt closely adheres to the top of the square suction duct, serving a sealing function.
At the sliding suction cart, there are two rollers within the cart. The sealing belt is lifted when it passes through the cart. In this manner, the dust and smoke enter the square suction duct through the cart’s suction opening, and then proceed to the purifier for cleaning.
- Grille Plate
- Square Air Intake Duct
- Sliding Air Intake Trolley / Blower Fan / Sealed Belt
Features of the Blowing-Suction Cutting Platform Dust Removal System
The blowing-suction cutting platform has been widely used in recent years, with noticeable dust removal effects on cutting platforms over 4 meters.
- It has a simple structure and requires less steel material. The production precision requirements are not high.
- There are fewer components, less potential for failure, and maintenance is simple.
- It’s easy to remove slag.
- For the same width of the cutting platform, it requires less ventilation, thereby reducing dust removal investment.
- Under the same rail spacing, the effective cutting width is slightly reduced compared to the air door cutting platform.
- The ventilation effect is greatly affected by the coverage rate of the steel plate on the cutting platform – the higher the coverage rate, the better the effect.
Calculation of Exhaust Volume for Blow-Suction Cutting Platform Dust Removal System
The required exhaust volume for a blow-suction cutting platform is largely related to the coverage rate of the steel plate on the platform, thus the effect of coverage rate on exhaust volume should be comprehensively considered.
For a typical single slide duct blow-suction dust removal system:
Q = 6000~12000m3/h
For a double slide duct blow-suction dust removal system:
Q = 14000~24000m3/h
Due to the influence of cutting platform structure and suction duct size, single slide duct blow-suction dust removal systems are generally used for cutting platforms with effective cutting widths less than or equal to 5m; for those greater than 5m, double slide duct blow-suction dust removal systems are used.
Single/Double Sliding Air Duct Cutting Platform CAD Structural Diagram and Exhaust Volume Calculation
Based on the equation above:
For a cutting platform width ≤4.5m with a single sliding air duct, the required exhaust volume is Q = 6000~12000 m3/h.
The cutting platform width is greater than 4.5m, and it has dual sliding air ducts. Therefore, the required exhaust air volume is Q = 18000~24000m3/h.
Blow-Suction Schematic Diagram
Double Suction Schematic Diagram
VIII. Dust Removal Case Study
Application Examples of Blow-Suction Dust Removal System
- Cutting Platform Size: 5000×48000
- Cutting Platform Structure: Double Wind Channel Double Suction
- Dust Collector Model: KTJZ-20KQ
- Installation Location: Shandong
- Usage Time: Since 2006
- Cutting Platform Size: 4000×16000
- Cutting Platform Structure: Single-side Blow Suction Type
- Dust Collector Model: KTQG-6.0KH
- Usage Time: Since 2007
- Cutting platform dimensions: 4000×28000
- Cutting platform structure: Single-side suction type
- Dust collector model: KTJZ-12KQ
- Year of use: 2008
- Cutting platform size: 4000×48000
- Cutting platform structure: Single-sided blowing and sucking type (Four-in-one)
- Dust collector model: KTJZ-48KQ
- Usage time: Since 2007
XCMG Site Video (Before the Dust Collector is Turned On)
XCMG On-site Video (After Dust Collector is Turned On)
Drag Chain Platform
1. Application of Drag Chain Platform:
- The cutter is used for thin sheet cutting.
- The span of the cutter platform does not exceed 6 meters.
2. Advantages of the Drag Chain Platform
The drag chain platform is sequentially divided into the roller conveyor feeding area, cutting area, and collection cleaning area. These three sections can operate simultaneously, thereby effectively improving the processing efficiency. The cutting slag can automatically fall off during the rolling process of the platform, avoiding manual shutdown for slag removal.
3. Use Case of Plate Chain Platform