COMMON STRUCTURE OF DRAW FRAME MACHINE:
A draw frame machine consists of the following common structure:
1. Creel or sliver feeding system.
2. Drafting system.
3. Suction system for drafting arrangement.
4. Sliver coiling system.
5. Can changing system.
6. Auto levelling system.
1. Creel or sliver feeding system:
An efficient sliver feeding system in draw frame is known as “creel”. The draw frame machine has a positive sliver feeding system. The feeding can diameter ranges between 400 – 1000 mm. The can height varies between 900 to 1100 mm. The cans having carded sliver are put in the creel. The creel ensures the efficient and consistent feeding of slivers to the drafting zone without any interruption in the path. First, the Slivers pass through the condenser and after getting detected by the T&G roll, they are fed into the main drafting zone. The positive feeding of creel helps to avoid the false draft. A pair of rollers above each can is mounted to avoid a false draft.
The creel is also equipped with automatic sliver break stop motion. If sliver breakage occurs, the stop motion of the creel acts immediately and stops the machine. It is designed in such a way that it helps to mend the broken sliver easily and safely. A guiding device leads the rollers into the drafting system.
2 – Drafting system:
The drafting system is the key responsible area for the drafting of sliver in a draw frame machine. It plays a decisive role in drawing process performance. The quality and production rate definitely depends upon the working performance of the drafting system. An effective and efficient drafting system requires the following important characteristics:
• High degree of accuracy in both operation and adjustment make it performance-oriented.
• The design of the drafting system is selected as simple as possible.
• It is designed to work at a very high speed without any quality compromise.
• Easy maintenance of cleanings helps to improve the efficiency of the machine.
• An effective and efficient drafting system has the capability to process any type of raw material.
• Continuous Optimal control system over the movement of the fibres during the drafting operation makes it more efficient.
• Easy and quick setting of roller gap and draft change make it more special.
Common parts of a drafting system:
The common parts for any draw frame machine are given below:
The bottom rollers are made of steel. The bottom rollers are mounted in the roller stands or frames with the help of needles or ball bearings. These rollers are driven by main gears.
One of the following types of flutes are used to improve their ability to carry the fibres:
• Axial flutes
• Spiral flutes
• Knurled flutes
The top rollers are negatively driven. They are fitted with the help of ball bearings in the machine. Top rollers are manufactured by using durable materials. The surface of the top roller is coated with synthetic rubber. The softness of rubber affects the fibre gripping capability directly. If soft rubber is used in roller coating, it helps to grip the fibres more efficiently but it has less durability. The hardness of rubber used for coating on top rollers is measured in terms of degree shore.
Medium coating 70-90 degree shore
Absorb coating Above 90 degrees shore
3 over 3 drafting Arrangement:
This is the most commonly used drafting arrangement. It was first developed by the Platt brothers in 1960. This drafting system works more smoothly with longer rollers. This is applied especially to the front rollers. It is capable to work at lower rpm for a given surface speed also.
In 3 over 3 drafting arrangements, the rollers are made of special alloy steel. The roller’s teeth provide sufficient grip on the fibres. The rollers have required hardness and smoothness to process the fibres precisely and efficiently. The top and bottom rollers are mounted in the roller stand with the help of needle bearings. These needle bearings make the rotational movement smooth and help to achieve a high rotational speed of drafting rollers. Some rank of tension draft is designed between calendar roller and 1st roller to meet the different requirements. Total draft ranges between 5.6 – 8.7.
The standard spring loading system is used in this drafting arrangement. It imparts a constant loading force. The value of the loading force can be adjusted.
This drafting system is capable to process cotton fibres having 22 – 76mm staple length and their blends. It can be used for single doubling some fibres after combing and is widely used for finisher doubling of different kinds of fibres.
4 over 3 drafting arrangement:
The Rieter 4-over-3 drafting system is a very effective and efficient drafting system. The bottom rollers have high-precision fluting which results in the form of perfect fibres guidance.
This system also consists of a pressure bar with a special profile in the main drafting zone which ensures accurate fibre guidance because the smaller size of the bottom roller bearing allows smaller roller gaps in comparison to other draw frames. This characteristic results in the form of good processing of cotton types with short fibre lengths. The fourth top roller gently diverts the fibres and also ensures perfect running properties. A correctly designed web guide nozzle brings the web together especially gently after it leaves the drafting system and prevents unwanted fibre entanglement.
Loading of the top rollers is adjusted by using spring elements. This system is equipped with automatic load relief motion from top rollers.
When the sliver gets wrapped on the rollers, this load relief motion acts immediately and releases a load of top rollers thus it prevents deformation of the covers during machine stoppages which assures the quality of the sliver produced. The large diameter of the top rollers compared to competing products guarantees superior running properties with low roller temperature and long service life.
The central setting of roller gaps quick blend changes. Break draft and main draft distances can be set independently of each other for the first time. The roller gaps can be read off a scale, which makes setting gauges unnecessary. The belts can remain tense during the setting. All mechanical settings can be performed with a single key. The top rollers are swivel-mounted on the loading arm. This permits optimum accessibility. The sliver is threaded-in with the help of compressed air. The mounting bracket of the web guide nozzle is pivoted, which makes access to the take-off discs considerably easier.
3 – Suction system for drafting arrangement:
The vacuum dust cleaning system commonly is an assembly of a motor, blade wheel, hopper and air duct. This cleaning device is driven by an individual motor which assures to working reliability of the cleaning system. The suction system is located outside the machine. The winding rate of the two deliveries keeps identical and can be regulated. The positive auto-stripping unit with hopper is adopted to reduce the labour intensity.
4 – Sliver coiling system:
When the drawn sliver comes out from the drafting zone it goes into the sliver can. A sliver coiling system consists of a pair of rollers and a rotating disc. The sliver passes through rollers and then a rotating disc which helps to make the coil sliver. These coils drop into the sliver can.
5 – Can changing system:
When the cans get fulfilled with the sliver. It needs to change with an empty can. Therefore the draw frame is equipped with an efficient can changing system which helps to change full can within the minimum possible time. Thus downtime of the machine gets reduced.
6 – Auto levelling system:
Without auto levellers, we do not correct errors but avoid them. Auto leveller may be off 3 types.
1. Short term auto levelling system (for lengths of product from 10-12 cm)
2. Medium-term auto levelling system (for length above 3m)
3. Long term Auto levelling system (for length above 20m)
Whatever be the system, the design of an auto leveller falls into two groups.
1. Open-loop auto leveller
2. Closed-loop auto leveller
Open-loop auto leveller:
In an open-loop auto leveller, sliver weight is measured from input material. Here the measurement of sliver irregularity is expressed in terms of voltage and is compared with the desired value (DV). The resulting error signal is amplified (A) and after a suitable time delay (TD) its signal is used to vary the speed of the variable speed device (S). A taco generator (TG) ensures that the variable speed device accurately follows the signal.
Closed-loop Auto leveller:
In a closed-loop auto leveller system, sliver weight is measured (M) from the output material and the resulting signal is integrated (I). Then the signal is compared with the desired level. After amplification (A), the variable speed devices (S) vary the speed of the drafting rollers. Because of the absence of any averaging device, this would cause irregularities in output.
WORKING PRINCIPLE OF DRAW FRAME:
A draw frame mainly performs the following actions:
In the process of doubling, two or more carded slivers are taken and they are fed together. After the drawing process, a combined sliver of the same linear density is obtained. Mostly 6 or 8 slivers are combined together in the doubling process and a single sliver is produced. The resulting sliver has improved uniformity and linear density.
The weight per unit length of the input sliver is reduced in the process of drafting. The hooked and curled fibres are straightened and fibre arrangement in the sliver is improved by making fibres parallel along the sliver length. Fibres are blended together in the drafting process. Drafting also helps to eliminate dust from the sliver. The drafting action is performed with the help of pairs of drafting rollers. In the drafting process, the rollers rotate higher than the previous one.
Improvement of fibre arrangement:
The drafting action reduces the weight per unit length of the carded sliver. During drafting the arrangement of fibre also improves. The fibres are made maximum parallel along the sliver length to achieve good strength and hairiness properties.
Homogeneous mixture of sliver components:
When doubling of slivers is carried out in the draw frame. It also results in the form of a homogeneous mixture of sliver components. The equal effect of sliver components in the sliver is obtained throughout the drawn sliver.
Removal of dust and remaining impurities from sliver:
The drawing is the last process that provides the last chance to eliminate dust and impurities present in the sliver. The draw frame consists of an efficient dust removal system that eliminates the dust and other impurities present in the sliver. More than 80% of the incoming dust is extracted during the draw frame process.