Opening and Cleaning Carding in textile

Purpose of Dust Removal

During the blowroom process, the dust cages and condenser fans draw in a large amount of dust and short fibers. The high-speed components of the carding machine generate significant airflow, which blows out lint, dust, and short fibers from areas such as the doffer–cylinder triangle zone, the taker-in cover, and around the large and small rollers.

If these contaminants are expelled outside the machine, they will severely pollute the workshop air and harm workers’ health. If discharged outdoors, they will not only pollute the surrounding environment but also cause the loss of many short fibers and heat, increasing the air-conditioning load, causing fluctuations in temperature and humidity, and thus affecting production and product quality.

In the blowroom and carding processes, a large amount of undercard waste and flat strips are generated and need to be cleaned and collected in time. This is especially true in carding, where the number of machines is high, and high-speed operation greatly increases the amount of waste generated, thus increasing labor intensity and worsening working conditions. Therefore, dust removal devices must be installed in blowroom and carding processes for the following purposes:

1. Purify workshop air, improve the environmental hygiene around the factory, and protect workers’ health.
2. Improve working conditions and reduce labor intensity.
3. Ensure clean production, stabilize production, and maintain product quality.

The dust concentration in blowroom and carding workshops should be kept below 3 mg/m³. After filtration by dust removal equipment, the dust concentration in the discharged air must not exceed 30% of the allowable workshop air dust concentration, i.e., generally no more than 0.9 mg/m³.

From the perspective of air conditioning, when carding machines use dust suction devices, air is supplied from above and exhausted from below, forming an upward-supply, downward-exhaust airflow pattern. This allows fresh air to pass through the operating area, prevents cotton dust from dispersing, reduces temperature and humidity fluctuations in the workshop, ensures reasonable airflow paths, and improves temperature and humidity regulation.

2. Components of the Dust Removal System

The dust removal system mainly consists of branch ducts from each machine, the main dust collection duct, relay fans, and dust removal equipment.

(1) Dust Removal Pipelines

Dust removal pipelines for blowroom and carding processes can be upward-flow metal duct systems or downward-flow non-metal duct systems, selected according to the location of the suction points.

To prevent dust from settling in the pipelines, a certain airflow speed must be maintained. Based on production experience:

For transporting dust and short fibers: 8–10 m/s

For transporting blowroom waste: about 12 m/s

The pipeline diameter is determined by the total exhaust volume and the airflow speed.

When designing duct layouts, resistance loss should be minimized to reduce fan pressure requirements. This can be achieved by using shorter ducts, more large-diameter pipes and fewer small ones, minimizing unnecessary fittings, and increasing the bend radius of curves to reduce local resistance. Where possible, ducts should be arranged by product type so that stoppages in one line do not affect others. The exact layout depends on the arrangement of the machines.

(2) Selection Basis for Dust Removal Methods and Processes

Main dust removal methods include:

Diffusion and settling

Cyclone separation

Filter media filtration

Electrostatic adsorption

Different combinations of these methods form various dust removal processes. The choice depends on:

1. Residual exhaust pressure at dust removal points– In blowroom, each machine has a dust cage fan and residual exhaust pressure, so design must ensure balance. In carding, since machines have no residual exhaust pressure, dust removal equipment should use high-total-pressure fans or a two-stage suction system.
2. Dust concentration in exhaust air– Higher concentration requires larger filter area for the same airflow and may require two- or three-stage filtration.
3. Pressure drop requirements of dust removal equipment– Different devices require different pressure drops; fan selection should match.
4. Matching with production equipment– Dust removal equipment capacity should match production machine output, and operation should be synchronized (start dust removal before production, stop after production stops).

Raw materials and process – Different raw materials and processes produce wastes with varying density and fiber content. Light, fiber-rich dust is best removed by dust cage filters; heavier, low-fiber waste (e.g., broken seeds) is better suited to cyclone separators; fine dust should be removed by filter media.

System resistance – Fan total pressure must match system resistance, with some reserve to ensure negative pressure in the ducts.

(3) Selection of Dust Removal Equipment Parameters

Key parameters include:

Filtering airflow – Air volume the equipment can handle per hour. Should be 15–20% higher than the total exhaust from all connected machines.

Rated dust collection capacity – Should slightly exceed the amount generated by production equipment to ensure safe, reliable operation.

Filtering load – Air volume filtered per unit area per hour. Higher dust concentrations require lower filter loads to achieve good results.

Dust Removal Equipment

With technological progress, dust removal equipment is developing toward high efficiency, low energy consumption, compact design, reasonable process flow, small footprint, easy maintenance, and trends such as miniaturization, modularization, diversification, and automation.

Examples:

Fiber separator and dust compactor – The fiber separator collects and compresses fibers and impurities from the dust stream. (Structure shown in Figure 3-7-1)

5 – Differential Pressure Control Switch Cabinet

6 – Observation Window
7 – Sealed Door
8 – Reducer

The fiber-laden dust stream enters the fiber separator through inlet 1 and flows downward through the conical mesh drum 3. Short fibers and impurities are trapped on the mesh surface of the conical drum, while the filtered air is discharged through the exhaust outlet 6.

A motor drives the cotton-squeezing screw 2 through a reducer, rotating it slowly to gradually press the fibers and impurities downward. This action forces the spring-loaded discharge door 4 to open, allowing the fibers and impurities to be expelled through the waste outlet 5.

The dust compactor functions to separate and compress dust. Its collection capacity is 40 kg/h, and the compressed dust volume is about one-fifth of the original. Its working principle is essentially the same as that of the fiber separator.

(2) Disc Filter
The disc filter is mainly used for filtering short fibers and coarse dust, i.e., for handling dust-laden air with relatively low dust content. Typical applications include filtering the exhaust air from the carding machine dust box, the dust stream after fiber separator filtration, and the dust-laden air discharged from the condenser fan in the blowroom process. The structure of the disc filter is shown in Figure 3-7-2.

Under the suction of the main fan, short fibers and impurities in the dust stream are trapped on the stainless steel mesh screen 4. Driven by a motor, the rotating suction nozzle 2 turns at a speed of about 3 r/min, removing the short fibers and impurities from the mesh via the nozzle outlet 3 and delivering them to the fiber separator for collection. The filtered airflow then enters the next-stage dust filter.

(3) Plate Filter
The plate filter is mainly used to filter fine dust and generally serves as a secondary filtration device. It can be combined with a fiber separator or disc filter to form a two-stage filtration system. When used together with a dust collector, it can also be directly applied for return-air filtration. The structure of the plate filter is shown in Figure 3-7-3.

To achieve a large filtering area within a limited space, multiple filter media panels are arranged in parallel, forming vertical filter slots 2. When dust-laden air enters the slots, the airflow passes through the filter media and exits from the back-side slots, while short fibers and dust blocked by the filter media are removed slot-by-slot by a mechanical suction arm 1 and sent into the dust collector.

The dust collector is an auxiliary device for the plate filter. The top section is a sheet-metal dust chamber, the middle section consists of fabric filter bags, and the bottom section holds plastic collection bags. The fine dust drawn in through the suction nozzles adheres to the inner walls of the fabric filter bags. The air pressure inside the bags alternates between positive and negative as the high-pressure fan starts and stops, causing the bags to oscillate periodically. This shaking dislodges the dust from the inner surfaces, which then falls into the plastic bags. The maximum handling capacity of the dust collection bags is no more than 1000 m³/h.

(4) Honeycomb Filter
The honeycomb filter is also used for filtering fine dust. It consists of cylindrical mini dust cages made from flame-retardant, long-pile filter material. Each row contains six cages arranged in a honeycomb pattern, allowing for a large filtering area in a small space. As dust-laden air passes through the mini dust cages, dust is trapped on the inner surfaces, and the air is purified. Six small suction nozzles, driven by a mechanical suction arm, sequentially remove dust from each row of cages according to a set program, ensuring continuous operation. The structure is shown in Figure 3-7-4. Honeycomb filters can be used as secondary dust filtration devices or as primary filters for return air.

(5) Ring-Type Filter

As shown in Figure 3-7-5, the ring-type filter is also a secondary filter. It is assembled from four sets of eight cylindrical filter units of varying diameters, arranged concentrically. Dust-laden air from the primary filter enters the cylindrical filter units 3 of different sizes. As the air passes through the inner and outer filter cages, dust is trapped on the long-pile filter material, and purified air is discharged. Driven by a long-shaft lead screw, the comb-like suction nozzle 2 both rotates and reciprocates to remove dust adhering to the filter media. The dust is then compacted into blocks by the dust compactor and collected. The separated air is recirculated back into the dust filter housing for further filtration.

4 – Transmission Device
5 – Flexible Rubber Hose
6 – Central Rotating Shaft
7 – Plastic Hose
8 – Purified Air Discharge Ring
9 – Dust-Laden Air Inlet Ring

Dust Filtration Units

According to the characteristics of the dust source, dust filtration equipment can be combined into dust filtration units based on the functions and performance of each individual machine.

For example, in the blowroom and carding processes, because the dust source contains a higher proportion of fibers and impurities, a two-stage dust filtration unit is commonly used. The first-stage filtration unit filters, separates, and collects the fibers and impurities from the processed air. The second-stage filtration unit then filters, separates, and collects the fine dust particles remaining after first-stage filtration, purifying the air to a standard suitable for recirculation or discharge.

(1) Flat-Plate Dust Filtration Unit
The configuration of a flat-plate dust filtration unit is shown in Figure 3-7-6. The first-stage filtration unit consists of a disc filter 3, a fiber separator 1, and an exhaust fan 2. The rotating suction nozzle removes fibers and impurities trapped on the disc mesh and sends them to the fiber separator for separation. The separated fibers and impurities are compressed and discharged, while the dust-laden air is drawn by the exhaust fan back into the first-stage housing.

The second-stage dust filtration unit consists of a plate filter 4, an exhaust fan 6, and a dust collector 7 (or dust compactor). A moving suction nozzle removes dust trapped in the filter slots, which is then drawn by the exhaust fan into the dust collector or dust compactor for collection.

(2) Honeycomb Dust Filtration Unit
The honeycomb dust filtration unit, as shown in Figure 3-7-7, has its first-stage filtration unit arranged and functioning the same as that of the plate filter unit—comprising a disc filter, a fiber separator, and an exhaust fan.

The second-stage filtration unit consists of a honeycomb filter, a dust compactor, and an exhaust fan. Six small suction nozzles, operating in sequence according to a set program, remove dust from each row of dust cages. The dust is then conveyed to the dust compactor, where it is separated, compressed, and collected. The separated air can be returned directly to the filter housing for further filtration. After purification, the clean air can be recirculated back into the workshop.

• Dust Removal in the Blowroom Process
  The main dust sources in the blowroom process come from the condenser fans, cotton conveying fans, dust cage fans, and droppings under the machines in the blowroom line. Since the dust-laden air from the on-machine fans and the droppings under the machines differ in impurity content and composition, they should be treated separately.

 On-machine dust sources
During normal production in the blowroom process, the dust sources from the on-machine fans of the blowroom line are generally treated using a two-stage filtration system. To ensure synchronization with the main machine’s start/stop operation, and to avoid interference between different main machines in case of a malfunction, each blowroom line is typically equipped with one set of dust filtration units, as shown in Figure 3-7-8. The filter area and filtration load of the dust removal equipment should be selected reasonably according to the type of raw material processed and the concentration of dust-laden air discharged. All parts of the dust removal equipment should maintain appropriate pressure and pressure differences.

1 – Bale plucker
2 – Metal removal device
3 – Automatic cotton mixer
4 – Six-cylinder opener
5 – Multi-bin cotton mixer
6 – Porcupine opener
7 – Double-chamber cotton feeder
8 – Single beater lap former
9 – Disc filter
10 – Flat-plate filter
11 – Single-suction centrifugal fan
12, 14 – Fan
13 – Fiber separator
15 – Dust collecton

2. Under-machine droppings
   The air discharged from under-machine cotton droppings in the blowroom process has a high dust concentration but low fiber content. It is suitable to use a three-stage dust filtration unit for purification. In this setup, a cyclone separator using centrifugal force is employed as the first-stage dust–air separation device to first remove heavier particulate impurities. A screen-type pre-separator is then used to collect fibrous impurities, and finally, a filter media-type filter is used to remove fine dust.
3. Processing waste cotton
   When processing waste cotton in the blowroom process, the discharged air has a higher dust concentration and greater specific weight than when processing regular raw cotton, but a lower fiber content. However, its dust concentration is lower compared to under-machine droppings. Therefore, a two-stage dust filtration unit or specialized dust removal equipment and process can also be used. Since waste cotton processing lines operate for fewer hours, in order to save energy, simplify management, and avoid contaminating the dust removal equipment and filtered air used for normal raw cotton, the dust removal equipment for waste cotton should be kept separate from that for normal raw cotton.

 

4. Dust Removal in the Carding Process
   Dust sources from carding machines come from two main areas:

 

On-machine lint fly escape points – As shown in Figure 3-7-9, due to the high-speed rotation of the licker-in and cylinder, surrounding airflow is driven. At the point where the cylinder and licker-in are spaced apart, the airflows converge, creating a high-pressure zone.

One part of the airflow enters the rear cover with the cylinder and escapes through gaps in the fixed cover plate and the upper edge of the rear cover plate (2), carrying a large amount of short fibers and dust.

Another part enters the licker-in cover (1) with the licker-in. Because the clearance between the licker-in and feed plate is very small, the airflow cannot easily pass through, forming a high-pressure zone under the licker-in cover. This results in lint being ejected through gaps or blown downward from the clearance point, affecting the under-machine droppings behind the machine.

• The airflow driven by the cylinder escapes from the working area outlet (3)and the front fixed cover plate (4). At the cylinder–doffer clearance point (5), most of the airflow is blocked, causing it to be blown forward from under the doffer cover toward the front of the machine. In addition, the high-speed rotation of the doffer cleaning roller increases the dust content in front of the machine, affecting sliver quality.
• As the sliver moves at high speed and is compressed, lint fly escapes from the large and small trumpet mouths (7)and (8).
• On-machine dust sources are mostly composed of short fibers and dust particles.
• Carding machine droppings– These include droppings from under the machine and flats waste. Since there are significant differences between them, they are often handled separately to improve their reuse value.

On the new type of carding machine, suction ports are installed at both the flying lint overflow points and the lint falling positions. The flying lint, dust, and fallen fibers are drawn through branch air ducts and the main air duct into the dust filter chamber by the relay fan. There are two methods of lint suction for carding machines: continuous and intermittent.

When the continuous lint suction method is adopted, all carding machines’ exhaust ducts are connected together and linked to the central dust filter chamber, with the exhaust ducts installed either underground or overhead. This method ensures high efficiency and continuous operation of the entire system.

When the intermittent lint suction method is used, each carding machine is equipped with its own fan and dust filter collection box. The impurities are first blown into the box by the fan, and after filtering, they are intermittently and sequentially drawn into the central dust filter chamber. The FA224 carding machine adopts the continuous lint suction method, with a machine exhaust volume of 3,500 m³/h.