1. Introduction
Carding is a critical process in the production of yarn. During the process, fiber turfs are separated into paralleled single fibers to remove dust, impurities, and short fibers. The carding performance is strongly influenced by the application of various types of card clothing [
1], especially metallic card clothing installed on the main cylinder and flat-top card clothing installed oppositely in a carding machine. In classical operating experiences, the card clothing types for cotton fibers differ from those for man-made fibers. This phenomenon is a drawback for spinning mills when they want to change the types of yarn repeatedly to quickly adapt to the market demands because of the high cost of changing card clothing due to extended machine downtime and expensive card clothing. The MAGNOTOP system [
2] for the quick change of a flat top developed by Trutzschler can reduce the downtime to several hours to avoid the drawbacks and improve adaptability to fibers. However, the system was not cheap enough and could not be applied to most types of carding machines due to technical problems.
A cheaper method was developing a type of card clothing that could adapt to several different fibers without changing the card clothing. Before designing the unique card clothing, we should know how the card clothing works in the carding process.
A classical theory points out that the carding process was just the fiber transfer competition balance between the flat-top needles and the tooth tips of the cylinder card clothing. In their classical article [
3,
4,
5], Singh and Swani proposed a value of pf to describe the ratio of the fiber load held between the flat-top needles and cylinder teeth in the carding state to the fiber load on the cylinder. The pf was defined as the ratio of the fiber load on the flattop and the fiber load on the surface of the cylinder.
In their opinion, better carding performance needs a higher pf. The experience told us that pf had limitations because too high of a pf could result in the fill-up of the flat top and shut down the machine. Once a type of card clothing was installed, the value of pf would be limited to a narrow range. The value may be suitable for cotton, but for man-made fibers, it could be too small to have good performance or too big to avoid the shut-down of the carding machine. This was why the spinning mill had to change the card clothing to adapt to different fibers.
However, which dimension of the card clothing affected the pf was unclear. A Japanese engineer suggested that the working angle of metallic card clothing was the critical parameter that influenced the balance in the carding process [
6]. So, card clothing with three different working surfaces on one tooth tip was invented. Thus, the range of pf was expanded. The top on the teeth gave a suitable pf range for cotton, and the middle gave another range for man-made fibers. In brief, the card clothing provided at least two different carding positions, one for cotton and one for man-made fiber. However, the truth was that only the fibers held at the top of the teeth would be well carded. The middle of the card clothing was not a good position for any fibers. Not only does the working angle impact the balance but also the carding position from the tips. The main reason for this pity was a lack of a systematic estimation method to describe the card clothing quantitatively.
Fortunately, with the development of simulation methods, the complex airflow between the narrow space of cylinder card clothing and flat-top needles can be well investigated. This will significantly help us understand the balance in the carding process, which could make the adaptable cylinder card clothing compatible with cotton and man-made fibers.
Since the first attempt from RWTH Aachen University by Mahlmann I [
7], computational fluid dynamics have been recommended as one of the essential methods to investigate carding progress. One of the reasons was that the airflow was so strong that it would influence the movement of the fibers, while the spacing between the cylinder and the flat top was too small to easily put any device for measurement [
8]. The airflow drag that could be strong enough to pull a single fiber out of the turfs was then verified according to the simulation by Shanshan He in 2019 [
9]. However, the simulation was needed to improve accuracy further to investigate more carding details because of its abstract and simple flat-top needles and rough mesh grid. The carding area was a complex geometry with too many faces, so the simulation consumption was always a big problem. Thus, our group applied a simplified carding area with a uniform flat-top needle model for simulation in developing double-tooth carding clothing in 2021 [
10]. In that article, the airflow distribution around tooth tips was taken as a physical indicator to describe the carding performance of metallic card clothing. This indicated the development direction of high-output card clothing and was corroborated by several patents from other card clothing providers [
11,
12,
13]. However, the geometry was still not accurate enough to distinguish between any match of the metallic cylinder card clothing and the flat-top needles.
Due to the primary function of the card clothing being influenced by the shape, the wear resistance of the card clothing was significant. So, the material of the card clothing was an essential issue in designing the new metallic card clothing. Studies investigating the effect of alloying elements on the local microstructure and mechanical behavior have been carried out recently [
14,
15]. The development of steel in card clothing was slow because of the extreme property requirements of high ductility in its annealed state for drawing to wire less than Φ1 mm and extremely high hardness of more than 800 Hv
0.2 after quenching. Tungsten and vanadium alloyed steel, also known as 80 WV in the field of textile equipment, has been chosen as the primary material for card clothing since the 1990s [
16], and it is still applied to most high-end card clothing. This was a big drawback because of the increased wear resistance requirement in modern high-speed and output carding machines. The unclear wear mechanism between fiber and steel mainly caused the difficulty with the development of steel. Fortunately, the attempts at niobium alloying of high carbon steel showed that niobium could generate much finer grain size and increase the eutectoid content in the martensite, which could increase the wear resistance of steel when the fiber was chosen to be the grinding material, similar to the polishing process [
17,
18,
19]. In this article, a first attempt of this method on AISI 1090 steel was carried out with the production and wear test of metallic cylinder card clothing, which showed an evident increase in the wear resistance.
The friction and wear of metallic card clothing is a significant problem in the textile industry. By adopting appropriate design and material manufacturing processes, the wear resistance of metallic card clothing can be effectively improved. Especially when a new design of metallic card clothing is compatible with different fiber materials, the above problems become more urgent. It is necessary to analyze and understand the carding behavior and bearing capacity of a newly developed cylinder card clothing from the perspective of simulation calculation so as to provide basic design parameters for materials and material processes and lay the foundation for explaining the deep mechanism of friction and wear of cylinder card clothing in the next step.
This article employed a novel and precise geometry to analyze a cylinder card clothing compatible with both cotton and terylene fibers through computational fluid dynamics. This approach posed numerous challenges, including mesh generation and fine-tuning the algorithm to ensure convergence. Wall shear stress was chosen as a metric to depict the equilibrium of fiber movement between the cylinder card clothing and the flat-top needles. In the following parts of the article, we demonstrate that the method shows the potential to estimate the carding balance quantitatively, in other words, pf. The wall shear ratio between the flat-top needles and the cylinder teeth show the potential to be a positive correlation quantity of pf.
Consequently, an adaptable cylinder clothing was developed by Nb alloying of AISI 1090 steel, renowned for its exceptional strength and wearability. This innovative cylinder card clothing boasts at least two distinct tooth shapes within a repeat section along the tooth wire, enabling fibers to occupy two positions for optimal carding balance in cotton and synthetic fibers. In the present study, the tooth shape design parameters and wear resistance of the tooth were thoroughly analyzed using this carding simulation method. The cylinder wire made from AISI 1090 steel with Nb alloying and new tooth shapes underwent testing in the spinning mills of Texhong International Group Limited. The findings reveal that this metallic card clothing could be utilized for both cotton and terylene fibers, yielding satisfactory sliver quality through mere adjustments to the carding parameters. This eliminated the need to replace the card clothing or incur excessive downtime.
3. Results Analysis and Discussion
3.1. Material and Wear Testing Results
Figure 6 shows the grain size before and after the addition of niobium. The grain grade was improved to about 13.5, which was fine enough to handle the deformation during the process. The cut edge of the card clothing was also identified with an optical microscope, and the results showed a smaller burr after punching compared with other conventional materials (
Figure 7).
The hardness test results showed a noticeable improvement in the new steel, with at least 20 Hv
0.2. As a result, the wear resistance of Nb alloying of AISI 1090 steel was also improved by about 25% compared with 80 WV, which showed less weight loss in the wear test lasting about 9 h, with five examples for each material (
Figure 8). The 80 WV always had a grain grade of 13 with suitable heat treatment because of the micro alloyed vanadium and tungsten, so the wear resistance increased a lot compared with carbon steel without alloyed elements like AISI 1080. The Nb alloying of AISI 1090 steel had a slightly smaller grain size and a higher hardness, so the wear resistance was also improved. These results show that a suggestion to improve the wear resistance of steel for card clothing is that a higher hardness and a finer grain size could be a better choice for the mechanism of wearability with high strength and toughness.
According to the Hall–Petch effect, the hardness and toughness of the steel would be improved with refinement of the grain. Thus, the wear resistance of the steel would be enhanced. However, the average grain size of the AISI 1090 was about 2–3 μm, approaching the boundary where the Hall–Petch effect could be practical and showing a better wear resistance than expected. This meant there could be an unknown wear mechanism for the AISI 1090 steel. The wear mechanism could have a relationship with the size of soft abrasive particles, for the diameter of the fiber was about 10 μm, much smaller than common abrasive particles. It was still a problem to explain why soft materials could wear down hard materials. Recent research [
23] showed that the detailed arrangement of the metallographic structure and the contact modes could significantly impact the wear resistance. The addition of Nb to AISI 1090 may have a similar mechanism, which should be further studied. Anyhow, Nb alloying AISI 1090 may be a good choice when the fiber is an abrasive particle in the textile industry.
3.2. Simulation Results with Conventional Card Clothing
This study selected wall shear stress as the physical quantity to describe the hold force of the carding elements, an indistinct experienced concept. The reason was that the wall shear stress had the same distribution as the wear on the surface of the containers in some references [
24]. The wall shear stress distribution on card clothing seemed similar to the wear distribution (
Figure 9), and the wall shear stress implied the carding position and changes in carding position in the simulation analysis. The higher the contact friction force between the fibers and tooth surface, the higher the loss of tooth tips because of the wear. This way, wall shear stress can be selected to act as a physical indicator to describe the holding force in the carding process.
Table 5 shows several matches of the card clothing applied in the spinning mills. The rules of the model name of each metallic card clothing can be found in the FZ/T 93038-2018 national standard of China [
25]. MCH55/AC2040 × 01740 is a classical match that was used for decades due to its stable performance. However, this match always has good but not excellent performance with relatively higher neps in the sliver in recent years. MCBH58/AC1745 × 01835 was developed to obtain extremely low neps in the yarn. The wall shear stress ratio was raised between the flat-top and cylinder teeth, which showed that the fibers carried by the cylinder teeth were more likely to be caught by flat-top needles. The mechanism of the carding performance improvement was similar to that in the development of double teeth. The matches in the terylene were identical. Classical AC2520 × 01560 had lower breaking stress of the yarn with higher neps in the sliver, according to the carding result from a spinning mill in China. The carding parameters in
Table 5 were all true and were carefully collected from real and typical spinning mills.
This way, the development direction of the card clothing seemed to be clear. For the carding of cotton, the ratio of shear stress needed to be between 0.9875~1.2010, while for terylene, it needed to be between 0.8450~1.0570. A higher ratio limit in these ranges meant better performance. So, the balance of fiber transfer between the flat top and the cylinder can be described in mathematical values. The ratio of cotton and terylene was different, but they still had overlaps. The excellent performance in MCBH40S/AC1730 × 01550 and the good performance within an acceptable range in MCH 55/AC2040 × 01740 had a similar ratio of around 1. In a sense, this was the physical basis of the invention of the adaptable cylinder card clothing.
3.3. Simulation Result of the Adaptable Cylinder Card Clothing
The results show that the ratios of the wall shear stress between the flat-top needles and the cylinder teeth were not influenced by the cylinder speed. The competition between the flat-top needles and cylinder teeth was changed a little by adjusting the cylinder speed. This meant that the spinning mills could flexibly adjust the cylinder speed depending on their output and the yarn-quality requirement. The increased wall shear stress on the cylinder tooth tips and flat-top needle tips indicated a higher interaction with the fiber turfs, meaning a better opening effect, and could result in a better performance if the breakage of fibers was well controlled. However, as a disadvantage, the tooth and needle would suffer more wear and have a shorter service life at high cylinder speed. These inferences concluded by the simulation results were similar to the operation experiences concluded by engineers. The carding gauge did not affect the ratio of wall shear stress between flat-top needles and cylinder teeth. Consequently, these results imply that once the card clothing was determined, the fiber would be restricted to a limited number of similar types. Therefore, in conventional design, it is necessary to alter the card clothing if the fiber is changed from cotton to terylene.
In
Table 6 and
Table 7, the ratios were around 1 and 1.2, similar to the simulation results in
Table 5, with cotton as the carding fiber. Tooth I in the card clothing yielded the standard carding performance, for its ratio was near 1, while tooth II performed better. For the carding of terylene, the results were different. Tooth I performed well, but tooth II needed to be taken care of. The ratio was a little bigger than the matches mentioned in
Table 5. This meant the breaking of the balance. The cylinder teeth took too small a part in the carding, so the performance was not as good. There was better performance for tooth I and worse performance for tooth II, so the carding performance was still acceptable. As a result, this type of carding clothing could be acceptable in the cotton carding process, with good carding performance.
The design of card clothing is tailored to enhance cotton’s performance due to the varying components of its raw material. Cotton typically contains significantly more impurities compared to synthetic fibers, necessitating meticulous carding.
The results also showed the possibility of a single-tooth shape card clothing design with a ratio of nearly 1. Therefore, the performance of cotton would be common and terylene would be better. However, as mentioned above, the spinning mill is always more concerned about the quality of the cotton yarn, whether ring spinning or rotor spinning, because the quality of cotton yarn has an essential impact on the trading value. As a result, this design method is particularly suitable for specific target applications and unique environments and may not be widespread in the present climate.
3.4. Results of the Wear Resistance
Figure 11 shows an approximate anticorrelation between the average wall shear stress and the fiber throughput. After gathering the information from several spinning mills producing similar cotton yarn with similar raw material and the same yarn-forming process, the average wall shear stress calculated from the simulation showed an approximate anticorrelation between the life span of the card clothing measured by the fiber throughput. The higher the wall shear stress was, the lower the life span the card clothing could acquire. However, the quantity relationship was never built because too many factors could have an impact on the life span of card clothing. This anti-relationship is just a glance at the wear mechanism in the carding process. Still, the dominant role of soft materials in the shear stress of hard materials provides theoretical support for this. In the article, the wall shear stress was considered the holding force of the teeth tips, and it was also an essential factor that influenced the carding performance. In general, a higher carding force could yield better carding performance. It was interesting to find that the life span of the card clothing and the carding performance were contradictory, and this is a common phenomenon in most industrial processes.
3.5. Results in Spinning Mills
The test results of the yarn quality in spinning mills are shown in
Table 8. In the first two types of fibers, including cotton 40S and terylene 16S, the adaptable cylinder card clothing showed better results than the average level in the spinning mill, regardless of CV%, neps, and A1 yarn defects. However, the neps increased when the fiber was changed to terylene 40S. This spinning mill was more concerned with A1 yarn defects, so the results were still acceptable. In conclusion, the better performance for cotton and the acceptable performance for terylene are consistent with the simulation results.
The reason for the excellent performance of the card clothing is that it yielded two ratios of wall shear stress, meaning two platforms for exchanging fibers between flat top needles and the cylinder teeth. Conventional card clothing has only one ratio, which is only suitable for several fibers. What is good for cotton is bad for terylene.
The parameters for any fiber were almost the same between the conventional and adaptable card clothing listed in
Table 8. However, the carding process parameters were quite different between cotton and terylene, including the carding gauge and the speed of the cylinder, and they were all within the scope of simulation calculations and design considerations.
Another factor that needed to be considered was whether the types of flat tops were the same. If the types were the same, according to the beginning of this article, the problem of changing fibers without changing the card clothing could be solved. However, this test was imperfect because of a minor difference in the flat-top types for about 3% PPSI with the same needle arrangements. If the yarn quality was not so strict, the problem seemed to be solved by this newly designed cylinder card clothing.
However, the reason for the relative medium difference between terylene 16S and 40S was unclear. Perhaps the carding parameters should be further investigated with the help of the simulation method and more experiments in the spinning mills, and these will be carried out in subsequent work. The adaptable cylinder card clothing is now being utilized in spinning mills in Vietnam, with a scale of hundreds, for robustness testing.
3.6. Discussion about the Carding Simulation
The simulation of the carding process still has three critical problems worth considering. The first problem is the accuracy of the simulation. The airflow around the teeth and needles has a Reynolds number of 1000–3000, where the transition from laminar to turbulence may happen. The transition simulation is still a complex problem in CFD because of too many unexpected flow behaviors. The shape of the airflow domain infinitely influenced the transition model, so the applied standard k-ω SST model in this article had the risk of being inaccurate.
The second problem is the simulation of fibers for too much consumption in the calculation. The discrete element method could be used to describe the fiber behavior in the airflow coupled by CFD [
26,
27,
28]. However, it was still too complex to simulate the carding process in the research of industrial application orientation at the enterprise level.
The third problem was how to analyze the results even better. How to create a correspondence between the calculated physical quantity and the carding performance is a crucial problem. In this article, the calculated results were associated with the carding performance by extending traditional carding theory [
3] using the so-called carding balance as the bridge. As discussed in this article, the wall shear stress of needles and teeth offers a promising avenue for soft materials in the shear stress of worn hard materials. Additionally, the velocity distribution provides another example of the development of double teeth [
10]. More and more related physical quantities would be found to describe the carding process if we continue to focus on improving the simulation model. Then, only by obtaining accurate simulation results can we provide a basis for explaining the deep mechanism of the friction and wear of cylinder card clothing made of Nb alloying of AISI 1090 steel in the next step.