Effect of Roller Speed and Moisture Content of Cotton on Ginning Rate, Lint Quality and Electric Energy Consumption in Double Roller Gins

Effect of Roller Speed and Moisture Content of Cotton on Ginning Rate, Lint Quality and Electric Energy Consumption in Double Roller Gins

Patil, Prashantkumar Gulabrao

Abstract To optimize the ginning parameters, a study was performed to investigate the influence of leather roller speed, fiber moisture on ginning rate, lint quality and electric energy consumption during ginning on double roller ginning machine. Seed cottons of different staple lengths were ginned at three levels of roller speed and moisture contents and experiments were performed on a specially designed experimental set up, which recorded roller revolutions per minute (RPM) and energy consumption. Duncan’s Multiple Range Test revealed that the highest roller speed of 120 RPM coupled with 7 % moisture content of seed cotton showed the highest ginning rate with maximum saving in electric energy. Further, the highest ginning rate and maximum energy saving were observed for higher staple length of fibers as compared to lower staple length of fibers. Fiber properties of lint obtained from different treatments were measured using High Volume Instrument and Advanced Fiber Instrumentation System and results showed that the important fiber parameters remain unaffected.

Key words roller speed, moisture content, ginning rate, electric energy

Ginning is the first important process to which cotton is subjected on its way from the field to the textile mill, before it is spun into yarn and converted into fabrics. The gin stand is the heart of the ginning plant [1]. In a double roller gin, two spirally grooved leather rollers pressed against a fixed knife with the help of adjustable dead loads, are made to rotate in opposite directions at a definite speed. The three beater arms are inserted in the beater shaft and two knives are then fixed to the beater arms with proper alignment. This is known as beater or moving knife, which oscillates by means of a crank or eccentric shaft, close to the leather roller. When the seed cotton is fed to the machine in action, fibers adhere to the rough surface of the roller and are carried in between the fixed knife and the roller, such that the fibers are partially gripped between them. The oscillating knives beat the seeds from top and separate the fibers, which are gripped from the seed end. This process is repeated a number of times and the fibers are separated from the seeds, carried forward on the roller and dropped out of the machine. The ginned seeds drop down through the slots provided on the seed grid, which is part and parcel of the beater assembly, which also oscillates along with the moving knife. In India, the double roller gins are used for ginning about 80 % of total cotton production (4.15 million tonnes of fiber in the year 2005-2006) [2]. The quality of ginned lint and the production of gin depend upon the type of gin used, moisture content and staple length of seed cotton, operating speeds of roller and moving knife, etc. A technical survey [3] conducted by the Central Institute for Research on Cotton Technology (CIRCOT), Mumbai and Textiles Committee of Government of India revealed that 43585 ginning machines (4245 single roller gin stands, 38286 double roller gin stands and 1054 saw gin stands) are presently working in India.

Leonard and Gillum [4] studied the effect of fiber moisture on roller ginning i.e. rotary knife roller gin having 1016 mm (40 inch) wide and 381 mm (15 inch) diameter of roller. It was observed that the optimum range of fiber moisture content for roller ginning and lint cleaning was from 5.0 to 6.0%. The maximum ginning rates were obtained in the 5.0 to 5.4% range of fiber moisture content. The maximum average energy consumption by the gin stand was associated with low fiber moisture contents. Energy consumption increased substantially with fiber moisture content above 7.0%. Slight trends towards longer fiber length and low grades occurred with increasing fiber moisture contents. After lint cleaning, the nep level tended to progressively lower as the fiber moisture content increased. Johnson et al. [5] studied the ginning performance by varying the crank and roller speeds on Pima and SXP varieties of cotton on 1016 mm (40 inch) roller gin. This study revealed that by increasing the speed of crank from 650 to 840 revolutions per minute {RPM) (29%), the amount of lint ginned per hour increased from 18.2 to 22.0 kg (i.e. 40.0 to 48.3 pounds) (21%). It was further observed that by increasing the speed of the roller from 110 to 150 RPM (36%), the amount of lint ginned per hour was stepped up from 18.8 to 22.5 kg (i.e. 41.5 to 49.5 pounds) (19%). The staple length of cotton was not affected by increasing the roller speed and the indicated differences in grade steps were insignificant. Gillum [6] studied the performance of different roller gin covering materials and found that for walrus leather roller, power in watt per inch (25.4 mm) lengths of roller required to drive the roller while ginning and not ginning were 33.5 and 35.0, respectively.

Looking at more and more cotton varieties being introduced in India and some of the developments which have occurred in the design of roller gins during the recent past, this research work was carried out to study the effect of roller speed and fiber moisture on lint quality and power requirement in double roller gins.

Materials and Methods

Different levels of fiber moisture content were obtained by moisture conditioning the seed cotton before it was ginned. The fiber moisture content at the time of ginning was intentionally varied to determine its effect upon the roller gin operation and lint quality. seed cottons of different staple lengths (Cotton A: 29.1-31.8 mm, Cotton B: 30.031.0 mm and Cotton C: 23.0-24.0 mm) were subjected to three levels of roller speed (80, 100 and 120 RPM) and three levels of moisture contents (5, 7 and 9%). However, it should be noted that the ratio of roller RPM and beater oscillations per minute (OPM) was maintained constantly at 1:10. The tests were conducted and analyzed as completely randomized design replicated two times. In all, 54 experiments were conducted to ensure an adequate response in ginning rate, power consumption and quality of lint. A lot of 5 kg of seed cotton was used in each ginning trial. The crops were raised in selected farmers’ fields and the seed cotton used in ginning trials was a mixture from the first and second pickings. The seed cotton was not processed through pre-cleaner, but was carefully hand opened and cleaned before ginning.

Double Roller Gin Setting

The gin machine adjustments were made according to the manufacturer’s specifications. The edges of the fixed knife were set to 85 mm from the seat on the knife rail throughout. The moving knife was set parallel to the fixed knife throughout at a distance 1.5 to 2.0 mm. This was effected by adjusting the ratchet. If the gap was more, then packing had to be provided on beater arm to lift the moving knife. Beater shaft was fixed to oscillating head and head pin was inserted and connected to the connecting rod by wrist pin. Moving knife was set in such a way that strokes on both the sides were equal. It was ensured that the moving knife cleared the upper edge of fixed knife by about one-third of the staple length of the cotton being ginned. Slight reduction or increase in overlap was adjusted by adjusting the head pin. By pulling out the head pin from the oscillating head, the overlap was reduced. By pushing the head pin in the oscillating head, the overlap was increased.

Seed Grid Selection

The selection of seed grid is important in double roller gins. The grid slots should be slightly bigger than the seed size. Seed size is calculated by formula [7,8] as seed size = (length × breadth × thickness)^sup 1/3^. The length, breadth and thickness of the randomly selected cottonseeds were measured by Mitutoya Digimatic Caliper (least count 0.025 mm) and averaged. seed size for Cotton A, Cotton B and Cotton C was calculated to be 5.8,6.4 and 5.0 mm, respectively and grid sizes selected as 7.1, 7.1 and 6.3 mm, respectively. Further, there was provision for seed grid adjustment, which was brought towards or away from the knife-rail. When the seed grid was adjusted towards the knife-rail, there was a reduction in unginned droppings because the ginned seeds were retained on the seed grid for a longer time, but there was a decrease in output of the lint per hour.

Roller Pressure

Jadhav [9] reported roller to stationary knife (RSK) force calculated by theoretical equation (1) developed from the line diagram of the forces for the double roller gin when the system was under equilibrium as shown in Figure 1.

where 1. W^sub 1^ = Weight of the long arm = 5.5 kg

2. L^sub 0^ = Length of the long arm = 0.6 m

3. L = Distance from centre of sliding dead load to fulcrum = 0.04 m

4. Wg = Weight of the sliding dead load for Gear side = 34 kg

5. Wo = Weight of the sliding dead load for Off side = 27.1 kg

6. W^sub dl^ = Total weight of the sliding dead load, Wg + Wo = 61.1 kg

7. L^sub r^ = Distance from fulcrum to roller = 0.07 m

8. W^sub r^ = Weight of the roller = 52.9 kg

9. θ^sub 1^ = Angle made by the loading (long) arm with the horizontal = 0°

10. θ^sub 2^ = Angle joining the roller axis to the fulcrum with the horizontal = 30°

11. θ^sub 3^ = Angle made by the knife edge with vertical = 30°

After entering all the values in equation (1), the RSK was calculated as 0.142 kN and the same was kept constant during all the experiments. Area of contact between roller and fixed knife was measured to be 0.0136 m^sup 2^. Therefore, the roller pressure was found to be 10.4 kN/m^sup 2^.

Experimental Set Up

Laboratory experimental set up was specially designed to conduct the experimentation (Figure 2). The instrumentation specifications are shown in Table 1.

Desired speed of roller was achieved by A.C. drive by varying frequency. The temperature of roller was recorded by temperature sensors. RPM of roller was also measured and recorded. The test envelope, test point and test sequence [10, 11] (Table 2) were decided on the basis of known ranges of variation of the independent variables like roller diameter, roller length, roller speed, beater OPM, moisture content, etc. The energy input of the machine was measured by a specially designed system interface with computer through analog digital card. The required hardware like V potential transformer, current transformer, temperature sensor and software for interfacing were prepared. The experimentation was conducted as per test plan. Measurements were made at 1.4 seconds interval. The measurements made during the first 200 seconds were discarded to avoid non-equilibrium temperature of the roller.

Important fiber properties, such as 2.5% span length, micronaire, fiber tenacity and uniformity ratio were determined using High Volume Instrument HVI-900 of Uster Technologies, and maturity ratio, short fiber content, neps and seed coat neps determined using the Advanced Fiber Instrumentation System (AFIS). All these tests were performed at standard conditions of humidity and temperature (65 ± 2% RH and 27 ± 2 °C). The ginning rate (gm^sup -1^s^sup -1^) was obtained by dividing the quotient of lint weight and roller length by the ginning time [6]. Duncan’s Multiple Range Test (DMRT), a statistical method [12,13], was used to test for differences between more than two groups of treatments.

Results and Discussion

It was observed that the important parameters that influenced the ginning rate and energy consumption in ginning were the speed of rotating roller, moisture content and the staple length of the cotton. The effects of roller speed and staple length with different moisture contents on ginning rate and energy consumption are shown in Figures 3 and 4, respectively.

Effect of Roller Speed and Moisture Content on Ginning Rate

A summary of the results of the experimental tests is shown in Table 3 and the data show that a definite relationship among the roller speed, moisture content and ginning rate existed. For seed cotton moisture content of 7%, our study showed that by increasing the speed of roller from 80 to 120 RPM (50%), the amount of lint ginned in kg per hour increased from 46.3 to 88.8 (92%), 39.3 to 75.1 (78%) and 50.1 to 77.3 (34%) for Cottons A, B and C, respectively. Statistical analysis by DMRT (p > 0.05) as presented in Table 4 revealed that there was a significant difference in lint output with the increase in speed of roller for all types of cottons.

Existing machine worked at a roller speed of 100 RPM; hence, analysis of data was also carried out considering 100 RPM as reference point. For seed cotton moisture content of 7%, our study showed that by increasing the speed of roller from 100 to 120 RPM (20%), the amount of lint ginned in kg per hour increased from 55.0 to 88.8 (61.4%), 47.3 to 75.1 (48%) and 60.8 to 77.3 (15.2%) for Cottons A, B and C, respectively. Maximum ginning rate was observed for higher staple length of fiber (Cottons A and B) as compared to lower staple length of fiber (Cotton C). Statistical analysis by DMRT (p

Effect of Roller Speed on Electric Energy Consumption

Table 3 shows that optimum seed cotton moisture and RPM of roller were found to be 7% and 120, respectively for maximum ginning rate and minimum electrical consumption per unit lint ginned. From Table 3, it is also revealed that electrical units consumed to gin 100 kg lint were lowest and found to be 4.34, 5.39 and 5.10 for Cottons A, B and C, respectively for 7% moisture content and 120 RPM of roller. Further in the case of 120 RPM, there was a saving in electricity of 25.4, 22.2 and 8.7% for Cottons A, B and C, respectively, as compared to roller RPM of 100.

Statistical analysis by DMRT (p

Effect of Roller Speed on Quality of Lint

Seed Cottons A, B and C were ginned with roller speeds of 80,100 and 120 RPM. The lint thus obtained after ginning was tested with HVI for its length, uniformity ratio, fineness and tenacity. Neps, Seed Coat Neps (SCN), Maturity Ration (MR), and Immature Fiber Content (IFC) % were determined by AFIS. Quantitative data showing the influence of roller speeds on quality parameters in ginned lint is reported in Table 5.

DMRT analysis indicated that there were no significant variations of the 2.5% span length, Uniformity Ration (UR) %, Micronaire (MIC), tenacity, MR, IFC % with different roller speeds of 80, 100 and 120 RPM. However, 2.5% span length was of great significance in the present work in the context of increased ginning rate. Thus, it is clear that output per hour can be increased significantly by increasing the speed of the roller at the same time preserving the quality of lint.

Seed-coat Neps (SCN)

For separation of fibers it is necessary that a force pulling the fibers is at least equal to the force with which it is attached to the seed coat. Normally, the seed coat remains intact as the epidermal cells in which the fiber base is embedded have adequate cohesion amongst themselves. Thus, the ginning action tends to remove the fiber alone. However, at the chalazal cap where the fiber density is high, the total pulling force per unit area of the seed coat is several times higher [14]. This force, effective as it is at the periphery of the chalazal cap, tends to separate the fibers from the remaining part of the epidermal tissue. The process would result in the generation of seed coat fragments. Further reason for the removal of seed coats from chalazal cap could be the excessive force of the attachment of the fibers to the seed coat at this location as compared to other regions. Therefore, it would be quite logical then to expect that those fibers will pull out portions of seed coat.

Leather roller speed primarily seems to influence the incidence of seed coat fragments during ginning. Generally, the higher the speed of the roller, the higher the pulling force exerted on seed surface during ginning will be. Hence, the resultant lint could be expected to have higher number of seed coat neps. However, in the range of investigation (80 to 120 RPM of roller) it was found that occurrence of SCN was more variety specific than due to change in machine parameters. The SCN (cnt/g) was observed in the range of 25 to 44, 30 to 64 and 11 to 14 for Cottons A, B and C, respectively. Further, no specific trend was noticed in incidence of SCN with increase in roller speed from 80 to 120 RPM and with different levels of moisture contents within the variety. Statistical analysis by DMRT (p > 0.05) on SCN (Table 5) showed no significant difference among the three roller speeds for all three cottons.

DMRT on HVI and AFIS data showed that the cotton quality was not affected by increasing the roller speed and indicated differences in the quality parameter were found to be not significant.

Conclusions

Ginning is the first important process to which cotton is subjected on its way from the field to the textile mills, before it is spun into yarn and converted into fabrics. About 3.32 million tonnes of fibers are ginned on double roller gin machines in India. Previous research works [4-6] revealed that by increasing the speed of leather roller and crank (moving knife), the amount of lint ginned per hour was also increased at the same time, while the staple length of cotton was not affected. The present study was performed to investigate and establish the effect of roller speed, fiber moisture on lint quality and electric energy consumption per unit of lint produced in presently used double roller gins. The laboratory experimental set up was specially designed to conduct the experimentation and software for interfacing was prepared. The effects of various parameters on ginning rate and electric energy consumption were quantitatively obtained. DMRT for lint output showed that there was a significant increase in output with an increase in speed of the roller. Power requirement varied significantly with roller speed for long staple (30 mm) cotton like Cottons A and B. DMRT showed, for short staple (24 mm) Cotton C, power requirement did not vary much with roller speed. DMRT (p > 0.05) for lint quality parameters showed that quality was not affected by increasing the roller (120 RPM) and beater speed (1200 OPM) to attain higher ginning rate. Hence, it is concluded that both maximum ginning rate and maximum energy saving were observed for higher staple length of fibers as compared to lower staple length of fibers, and highest roller speed of 120 RPM coupled with 7% moisture content of seed cotton yielded the highest ginning rate and highest electric energy saving, without compromising the quality of lint.

Acknowledgements

The authors would like to acknowledge Dr. S. Sreenivasan, Director and Dr. K. M. Paralikar, Central Institute for Research on Cotton Technology for providing the facilities for our experiments. The authors would also like to acknowledge Bajaj Steel Industries Ltd., Nagpur 440018, India for their help with the experimentation.

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Prashantkumar Gulabrao Patil1

Central Institute for Research on Cotton Technology,

Nagpur 440023, India

Pramod Madhukar Padole

Visveswaraya National Institute of Technology, Nagpur,

India

Jugalkishar Fulchand Agrawal

Yeshwantrao Chavan College of Engineering, Nagpur,

India

Arun Bhimrao Dahake

Central Institute for Research on Cotton Technology,

Nagpur, India

1 Corresponding author: Central Institute for Research on Cotton Technology (Indian Council of Agricultural Research, DARE, Gout. of India), Nagpur 440 023, India. Tel: 91 712 2500592; fax: 91 712 2500592; e-mail: pgpatil_ngp@yahoo.co.in

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