Tuesday, February 25, 2020

STRUCTURE OF SIMPLEX ( ROVING ); FRAME AND WORKING PROCEDURE OF SIMPLEX OR ROVING FRAME MACHINE


STRUCTURE AND WORKING PROCEDURE OF SIMPLEX OR ROVING FRAME MACHINE:

The common systems of a simplex or roving frame are given below:

Creel:

Creel is a very important system of a simplex machine. The slivers are fed to the machine through a positive mechanism called creel. A creel of simplex consists of many rollers driven positively. These rollers carry forward the sliver into the drafting system.

The separators are used to keep slivers away from each other in the creel. The guide rollers help to assure the movement of slivers toward the drafting system. The creel is equipped with sliver break stop motion. The stop motion acts immediately and stops the machine in case of a sliver break in the operation of a simplex machine. A very little amount of draft gets employed between creel and drafting system to maintain the tension of sliver fed and to avoid the slackening of sliver during operation. Group creel loading and changing result in the form of improved yarn quality. Since every piecing of sliver causes a thick or thin place in the yarn so that 30 – 60 cans are changed together to minimise the effect of sliver piecing in the roving.


Sliver support system:

When drafting force acts on the sliver, the chances of variation in the material increase. Therefore the sliver necessitates extra support during drafting action in the simplex machine. This extra support helps to maintain the uniformity of material and improves the evenness of roving to be produced. Since in the drafting region, the number of fibres is less and they are passed through the drafting system so that any floating fibre content occurs fabric defects and it has to be avoided. These two aprons are used to provide support to the material during drafting action. The upper aprons are short and are made of 1.0 mm. thick synthetic rubber. The lower aprons are larger in size and are made of the same synthetic rubber as upper aprons. In the main drafting region, aprons are used to further control further the drawing sliver.

Drafting system:

The drafting arrangement to be used in the simplex or roving frame mainly consists of the following parts:



Bottom steel fluted rollers

The bottom rollers are mounted in the stand. These rollers are made of good quality steel. The bottom rollers of the drafting system rotate by means of a positive mechanism. These rollers are driven by the main gear transmission system. These rollers are fluted to obtain improved material carrying capacity in the forward direction. Mainly axial fluted, spiral or inclined fluted or knurled fluted bottom rollers are used in the drafting system in the simplex machine. In today’s simplex frame fluted rollers are used to achieve improved gripping of fibres during drafting. The use of inclined fluted rollers also results in the form of less wear and tear of top rollers.

Top rollers:

These are twin rollers. The top rollers are made of steel and the surface is coated with synthetic rubber. The rubber coating provides improved fibre gripping capacity to the top drafting rollers during drafting action. The degree of hardness of coated rubber to be used varies according to the material to be processed. These rollers necessitate grinding to obtain better fibre gripping after a certain quantity of production. The diameter of the top drafting roller decreases after every grinding. After a certain number of grindings, it needs to change from the new one. The top rollers are replaced after 15 – 20 years of use.

Type of drafting arrangements:

In 4 over 4 drafting arrangements, the maximum total draft can be employed up to 13. The thickness and hairiness of roving resulted in this drafting arrangement is less. Since the fully drafted fibres are just condensed in a front zone in this system so the lapping tendency on the second top or bottom roller is increased highly if the stickiness of material in case of cotton and static charges in case of synthetic materials are processed. But in the case of the front roller, since the twist is penetrating up to the nip, lapping on the front bottom or top roller is less.



In 3 over 3 drafting arrangements, the maximum total draft can be employed up to 11. The thickness and hairiness of roving resulted in this drafting arrangement being more than 4 over 4 drafting systems.
`3 over 3 drafting system is suitable for fibres longer than 51 mm. The bottom rollers having diameters of 30 – 32 mm. are used in this arrangement.

Drafting roller pressure system:

When the material (sliver) passes between the nip of drafting rollers, it is attenuated by drafting rollers. Fibre slippage occurs between rollers during drafting. A certain amount of pressure is required to achieve better nip gripping of drafting rollers. The pressure is applied to the main drafting roller. Thus an improved and higher nip contact is obtained between them. In a pressure system, a pressure arm is used in which a spring is fitted to it. A pneumatic pressure system is also in use. The pressure on the top rollers is maintained over the bottom rollers consistently with the help of the pressure arm. The amount of pressure varies according to the type of material to be processed. The amount of pressure may be kept equal in all rollers or it may be different for various drafting rollers. The amount of pressure is set precisely to get optimum performance of the simplex machine. Pressure more than required causes damaging the fibres while less pressure affects the uniformity of roving and increases the unevenness percentage of roving.

Roving condensing system:

When the sliver is drafted between the drafting rollers, the fibres try to spread out and cause unevenness in the roving. When widely spread fibres strand leaves the drafting region, it leads to an increased high fly level and hairiness in the roving to be produced. Thus a device is used to prevent the spreading of fibres in the roving after drafting. This device is called a condenser. The main objective of the condenser is to bring the fibres strand together. In the Simplex machine, two condensers are used in the drafting system. The size of condensers is selected according to the hank of the sliver to be processed in the machine.

Drafting rollers cleaning system:

Cleaning plays a very important role in the performance of any drafting arrangement. Since the high draft is employed to the sliver to be processed, the short fibres present in the sliver may leave the main flow of fibres. These fibres are wound onto the drafting rollers themselves.  These wound fibres affect the gripping of drafting rollers. Thus the quality of roving to be obtained is also lowered. Tow aprons are used in simplex machines to clean every roller during drafting operation. Two top and bottom cleaners are also used for the cleaning objectives in the simplex machine.

Twisting system:

When the fibres strand comes out after drafting, it has very low strength because of less number of fibres present in it. It needs to strengthen before winding it onto the bobbin. This problem of poor strength needs to insert a little amount of twist into the fibre strand. A flyer is used to impart the twist into the roving. The flyer revolves around the roving bobbin at 700 – 1300 rpm. One revolution of flyer inserts one turn in the roving. The turns per unit length in the roving depends upon the delivery rate of the simplex machine.

High turns per in the roving decrease production performance of a simplex machine and it causes draft problems during ring frame operation too. If the turns per unit length in the roving is lower than required it causes problems of false draft and roving breakage during operation of the simplex machine. The false twister is used on the flyer when the twist is imparted to between front roller and flyer. This extra amount of twist improves the strength of roving and minimise the breakage rate of roving. The production rate does not affect due to this extra twist. The roving becomes compact due to the extra twist. Because of the compactness of the roving extra length is wound onto the roving bobbin.

Package building system:

The main objectives of the building motion are:

To shift the belt over cone drum mechanism as the bobbin diameter increases.

To change the direction of bobbin rail at top and bottom in the reverse direction.

To reduce the lift of the bobbin rail after insertion of each layer onto the bobbin to obtain the conical shape of both ends (tapered ends) of the roving bobbin.

This system plays a very important role in roving package formation in the simplex machine. This system is also called building motion. During this motion, the bobbin rail travels upward and downward direction consequently. After each cycle of bobbin rail, the travel distance of the bobbin rail decreases regularly. This regular decrease in the distance travelled by bobbin rail helps to make a conical shape of the roving bobbin on both sides.



The system in which bobbin rail reverse earlier after each successive layer is called reversal motion. Each additional layer needs a slow speed of bobbin rail. The speed of the bobbin rail is regulated by using a cone drum mechanism in the simplex machine. Since the bobbin rail moves up and down continuously so that the coils of roving are wound parallel and very close to one another to ensure maximum material length on the bobbin. As the diameter of the roving bobbin increases after each layer, the surface speed of the bobbin also increases in the same ratio. Thus roving tension increases. This tension causes roving breakage.
The bobbin rail is moving up and down continuously so that the coils must be wound closely and parallel to one another to ensure that as much as the material is wound on the bobbin. Since the diameter of the packages increases with each layer, the length of the roving per coil also will increase. Therefore the speed of movement of the bobbin rail must be reduced by a small amount after each completed layer.

Cone drum mechanism:

This mechanism keeps the surface speed of the roving bobbin constant during the operation of the simplex machine. Two cone drums are used in this mechanism. The diameter of the cone drum at the bottom end is kept 7.0 inches and at the top end is kept 3.5 inches. The top cone drum has a positive drive. This is driven through a shaft. The motion from the top cone drum is transmitted to the bottom cone with the help of a transmission belt. This belt is kept on a bigger diameter side on a positively driven cone drum. This belt is connected to the negatively driven cone driven and is kept at a smaller diameter side of the cone drum. 

The diameter of the roving bobbin increases regularly after completing each layer, thus the surface speed of the bobbin increases. At the same time, the transmission belt starts to shift from bigger diameter to smaller diameter and the rotational speed of the bobbin’s spindle is reduced. This reduction of the rotational speed of the spindle keeps the surface speed of the bobbin constant throughout the process. Thus this mechanism also helps to maintain constant roving tension throughout the process.

Shifting of the transmission belt is carried out with the help of a ratchet wheel. The ratchet wheel moves a half tooth.  The diameter of the bobbin increases slowly or rapidly as per hank of roving. The correct distance of belt shifting is ensured by selecting the proper ratchet wheel or replacing other gears. The belt must be shifted through corresponding steps.


Differential motion:

Winding can be achieved by maintaining bobbin speed differential with flyer same as in the case of roller drafting speed differential is maintained between two successive pair of rollers. At each instant, this difference should be maintained to wind the delivered length of roving. So, for this objective bobbin speed must be continuously reduced in a precisely controlled manner after insertion of each layer. So, cone drum speed-reducing drive pass through a compound gearbox which reduce the preciseness speed of the bobbin and maintained the required speed differential. So, it is called a differential box.

Bobbin winding system:

When the twist is inserted into the roving by flyer, at the same time roving needs to wind onto the bobbin. Package formation of bobbin ensures the easy handling of material and makes the roving easy to creel on the next machine. Roving bobbin winding system performs the job of package formation in the simplex machine. 
There two types of winding systems are used in the simplex machine.

Flyer lead system:

In this system, the flyer rotates at a higher speed than the bobbin. This difference in speed helps to wind the roving onto the bobbin.

Bobbin lead system:

In this winding system, the bobbin rotates at a higher speed than the flyer. This speed difference of bobbin helps to wind the roving around itself. Today’s simplex frames are equipped with a bobbin lead winding system because of the advantages over a flyer lead system. The bobbin lead system has the following advantages:

The speed of the flyer remains constant in this system.

The speed of the roller remains constant in the bobbin lead winding system.

In this system, the rotational speed of the bobbin reduces with the winding of each layer of roving but the surface speed of the bobbin remains constant throughout the package. Thus wining tension remains constant throughout the package.

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