Showing posts with label Shedding. Show all posts
Showing posts with label Shedding. Show all posts
6 October 2012
Principle of Negative Tappet Shedding Mechanism
Principle
The heald shafts have heald eyes T and U through which
the war p threads pass X is the war p sheet and Y is the cloth. The odd
ends are passed through one heald shaft while the even ends are passed
through the other heald shaft.
Working
When the bottom shaft is rotated in the clockwise direction as shown in the figure, the tappets are also rotated. The tappet will depress the anti-friction bowl and the treadle. Being fulcrumed at one end, the front portion of the treadle moves down. This action is transferred to the lamb rod, the heald shaft and the leather strap. So one heald shaft is lowered and the threads connected to this heald shaft are lowered and form the bottom layer of the shed.
The leather straps attached to the reversing rollers are connected in opposite directions, i.e. when leather strap is pulled down, it is unwound from its roller. The shaft therefore rotates in the clockwise direction and the other leather strap is wound on to its roller. The heald shaft is raised and therefore the lamb rod and treadle lever are also raised. The threads connected to the heald shaft are also raised and form the top layer of the shed.
For the next shed, the other tappet works with the other set of bowl, treadle, lamb rod, heald shaft, strap and roller and the other heald shaft is lowered. The first heald shaft is raised by the top reversing rollers, and the positions of the healds shafts are thus interchanged. Thus, for one rotation of the bottom shaft, two sheds are formed.
In this type of tappet shedding therefore, one tappet depresses the concerned treadle and the corresponding heald shaft is lowered. But the other heald shaft is raised by means of the top reversing rollers. So this type of shedding mechanism is known as “negative tappet shedding mechanism”
Timings and settings
1. Turn the crank to the top centre position.
2. Fix the anti-friction bowls to the treadle levers; they should move freely in the slots.
3. Fix the treadle levers with a bracket to the back rail of the loom.
4. Set the grid and grid bracket to the front rail of the loom in the slots of the grid.
5. Make sure that the tappet with the lower throw is fixed to the bottom shaft at the starting handle side.
6. Fix the top reversing rollers to the top reversing roller shaft to be equidistant from the ends and at the same time ensure that the connecting screws of the rollers are symmetrical about the central axis of the shaft when the heald shafts are at the same level. The roller of smaller diameter is always connected to front heald shaft.
7. The heald shafts are connected to the top reversing rollers by means of cords and leather straps. The leather straps are connected to the rollers, such that when one of them winds on its roller the other strap unwinds from its roller and vice versa.
8. Lamb rods are connected to the heald shafts by cords.
9. Adjust the tappets on the bottom shaft and make sure of the following points :
i. The tappet with a bigger throw should be connected to the back heald shaft.
ii. The bowls should have perfect contact with the tappet surfaces.
iii. The treadles should be at the same level and parallel to each other at the top centre position.
iv. Heald shafts : The hook of the lamb rod of the front heald shaft should be connected to the first notch of the treadle lever while that of the back heald shaft should be connected to the third notch. If the depth of shed is altered, the connections of the hooks to the treadle levers can be changed.
Points to be observed
1. Turn the crank shaft through two revolutions and make sure that the bowls are always in contact with the tappets.
2. The heald shafts should not touch the side frames or the sley.
3. Turn the crank shaft to the bottom centre and check the size of shed. The bottom line of warp sheet or the heald eyes of the lowered heald shaft should have a clearance of 1 mm from the race board and the top.
A
tappet is given a rotary motion so that it depresses a follower and a
lever, known respectively as the anti-friction bowl and the treadle
arrangement, by means of which the heald shaft is operated.
Construction
Figure 2 shows a negative tappet shedding mechanism. A pair of tappets A and B are fixed to the bottom shaft C at 180 degrees to each other. Two treadle levers D and E are connected to the loom back-rail by a bracket F.
The bracket acts as a fulcrum for the levers. The two treadles have teeth to carry the lamb rods G and H respectively. Two heald shafts J and K are connected to the lamb rods. A top reversing roller shaft Q carries two rollers of different diameters. The roller of small diameter N is connected to a leather strap L to which the front heald shaft J is connected. The roller P of large diameter is connected to a leather strap M to which the back heald shaft K is connected. The tappets A and B touch the anti-friction bowls or followers R and S respectively, which are fixed to the treadle levers.
Construction
Figure 2 shows a negative tappet shedding mechanism. A pair of tappets A and B are fixed to the bottom shaft C at 180 degrees to each other. Two treadle levers D and E are connected to the loom back-rail by a bracket F.
The bracket acts as a fulcrum for the levers. The two treadles have teeth to carry the lamb rods G and H respectively. Two heald shafts J and K are connected to the lamb rods. A top reversing roller shaft Q carries two rollers of different diameters. The roller of small diameter N is connected to a leather strap L to which the front heald shaft J is connected. The roller P of large diameter is connected to a leather strap M to which the back heald shaft K is connected. The tappets A and B touch the anti-friction bowls or followers R and S respectively, which are fixed to the treadle levers.
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| Figure 2: Negative tappet shedding mechanism |
Working
When the bottom shaft is rotated in the clockwise direction as shown in the figure, the tappets are also rotated. The tappet will depress the anti-friction bowl and the treadle. Being fulcrumed at one end, the front portion of the treadle moves down. This action is transferred to the lamb rod, the heald shaft and the leather strap. So one heald shaft is lowered and the threads connected to this heald shaft are lowered and form the bottom layer of the shed.
The leather straps attached to the reversing rollers are connected in opposite directions, i.e. when leather strap is pulled down, it is unwound from its roller. The shaft therefore rotates in the clockwise direction and the other leather strap is wound on to its roller. The heald shaft is raised and therefore the lamb rod and treadle lever are also raised. The threads connected to the heald shaft are also raised and form the top layer of the shed.
For the next shed, the other tappet works with the other set of bowl, treadle, lamb rod, heald shaft, strap and roller and the other heald shaft is lowered. The first heald shaft is raised by the top reversing rollers, and the positions of the healds shafts are thus interchanged. Thus, for one rotation of the bottom shaft, two sheds are formed.
In this type of tappet shedding therefore, one tappet depresses the concerned treadle and the corresponding heald shaft is lowered. But the other heald shaft is raised by means of the top reversing rollers. So this type of shedding mechanism is known as “negative tappet shedding mechanism”
Timings and settings
1. Turn the crank to the top centre position.
2. Fix the anti-friction bowls to the treadle levers; they should move freely in the slots.
3. Fix the treadle levers with a bracket to the back rail of the loom.
4. Set the grid and grid bracket to the front rail of the loom in the slots of the grid.
5. Make sure that the tappet with the lower throw is fixed to the bottom shaft at the starting handle side.
6. Fix the top reversing rollers to the top reversing roller shaft to be equidistant from the ends and at the same time ensure that the connecting screws of the rollers are symmetrical about the central axis of the shaft when the heald shafts are at the same level. The roller of smaller diameter is always connected to front heald shaft.
7. The heald shafts are connected to the top reversing rollers by means of cords and leather straps. The leather straps are connected to the rollers, such that when one of them winds on its roller the other strap unwinds from its roller and vice versa.
8. Lamb rods are connected to the heald shafts by cords.
9. Adjust the tappets on the bottom shaft and make sure of the following points :
i. The tappet with a bigger throw should be connected to the back heald shaft.
ii. The bowls should have perfect contact with the tappet surfaces.
iii. The treadles should be at the same level and parallel to each other at the top centre position.
iv. Heald shafts : The hook of the lamb rod of the front heald shaft should be connected to the first notch of the treadle lever while that of the back heald shaft should be connected to the third notch. If the depth of shed is altered, the connections of the hooks to the treadle levers can be changed.
Points to be observed
1. Turn the crank shaft through two revolutions and make sure that the bowls are always in contact with the tappets.
2. The heald shafts should not touch the side frames or the sley.
3. Turn the crank shaft to the bottom centre and check the size of shed. The bottom line of warp sheet or the heald eyes of the lowered heald shaft should have a clearance of 1 mm from the race board and the top.
10 July 2012
Characteristics of Jacquard Mechanisms | Advantages and Disadvantages of Jacquard Mechanisms
General Characteristics of Jacquard Mechanisms:
Advantages:
- For designs that require the reproduction of freely drawn shapes , it is usually necessary for each end in the repeat to be separately controlled.
- Jacquard machines are used for a wide variety of purposes from ties to carpets.
- Their patterning possibilities virtually unlimited.
- The most elaborate designs (reproduction of freely drawn shapes, i.e. floral designs) are woven on an intricately constructed loom called the Jacquard loom, and the weave of these fabrics is called the jacquard weave .
- Elaborate designs could not be made on the regular harness loom. Because intricate designs require many variations in shedding.
- Virtually no limit to the number of picks /repeat (i.e. 5000 picks or more)
- The length of the repeat is limited only by the cost and inconvenience of a very long pattern chain .
- Jacquard machines are made in a wide variety of sizes to control from 100 to 2000 or more ends per repeat.
- In conventional jacquard machine field, the spectrum now ranges from 192 through 3200 to 6144 hooks.
- When a higher no.of independent lift is required two or three jacquard machine is placed side to side.
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| Jacquard mechanism fabric |
Advantages:
- Tremendous design possibilities,
- Simpler in principle than dobbies
- Large scale moving parts makes the machine and its harness relatively costly to install and maintain.
- Jacquard fabrics are much more costly to produce.
- Jacquard machines are even more liable to produce faults in the fabric than dobbies.
- Pattern change is a time consuming process.
- Until recently, the jacquard machine had tended to impose limitations (300 picks/min )
- Jacquard shedding is normally used only when the cloths to be woven are outside the scope of dobby shedding.
3 August 2011
Experiment name: Study on Jacquard shedding mechanism.
Introduction:
In weaving if we want to make any design in our fabric we have to separate the warp yarn according to our weave plan. In tappet or dobby shedding we have some limitations in shedding for a critical design. But in jacquard shedding it can be done easily. Jacquard is a shedding device placed on the top of the loom to produce large no of patterns by using a very large no of warp threads separately by means of harness cords, hooks and needles. The figuring capacity of a jacquard is 1800+. It means it can produce design with more than 1800 warp threads by controlling them individually, which is far beyond the capacity of a dobby or tappet loom.
Main parts:
1. Pattern chain.
2. Motor.
3. Pattern cylinder.
4. Needle.
5. Knife.
6. Harness cord.
7. Neck cord. 8.Comber board.
9. Top board
Introduction:
In weaving if we want to make any design in our fabric we have to separate the warp yarn according to our weave plan. In tappet or dobby shedding we have some limitations in shedding for a critical design. But in jacquard shedding it can be done easily. Jacquard is a shedding device placed on the top of the loom to produce large no of patterns by using a very large no of warp threads separately by means of harness cords, hooks and needles. The figuring capacity of a jacquard is 1800+. It means it can produce design with more than 1800 warp threads by controlling them individually, which is far beyond the capacity of a dobby or tappet loom.
Main parts:
1. Pattern chain.
2. Motor.
3. Pattern cylinder.
4. Needle.
5. Knife.
6. Harness cord.
7. Neck cord. 8.Comber board.
9. Top board
10. Hook.
11. Grid bar
12.Dead weight.
13.Spring board.
14.Needle board.
14.Needle board.
Shedding mechanism:
For shedding mechanism here punched card are used which is made according to design. One pattern card is used for one pick. With these pattern cards pattern chain is made which is placed on the pattern cylinder. On each pick pattern cylinder rotates 1/4th of the full rotation in clockwise direction. At the same time it oscillates to and fro forming an arc.
With every 1/4th rotation a new card comes front of the cylinder in the hook side and for the two and fro movement the needles enter inside the holes of the punch card. This selection of entrance inside the punches of the needles is actually done according to design.
If a needle enters in the hole of the card the needle remains stationary in its position. So the needle crank also remains stationary in its position. So for the upward movement of the knife the hooks also goes upward along with the warp threads to form the top line.
But if needle gets no perforation to enter, the hook is pushed to the right and as result the needle crank takes away the hook along with it. So when the corresponding knife goes upward it cannot lift the hook with it. Thus the warp ends of those hook remains fixed in its position and form the bottom line.
After certain time the knife releases two hooks which is lifted to form the top line and due to wrap tension and dead weight the heald eye comes down. Its downward movement is controlled by grid bar. Each needle has a spring push at its right and that spring pushes back the needle when the next card comes.
Conclusion:
By this experiment we learned about the jacquard shedding and how it works. It is the finest of all machines for making the designed woven fabrics that have been invented and far superior in capacity to a dobby or tappet loom.
21 March 2009
Tappet Shedding | Tappet Shedding Mechanism | Scope of Tappet Shedding | Driving of Shedding Tappet
Experiment name: Study on Tappet shedding mechanism.
Objectives:
1. To know about the different parts formed this shedding.
2. To learn the mechanism of tappet shedding.
Scope of tappet shedding:
Tappets are generally used for heald shedding. Tappet, cam and wipers are names given indiscriminately to those irregular pieces of mechanism to which a rotary motion is given for the purpose of producing, by sliding contact, reciprocating motion in rods and levers. When the rod is to receive a series of lifts, with intervals of rest, the piece is generally called tappet.
Types of tappet:
Various kinds of shedding tappets are used in industries.
Objectives:
1. To know about the different parts formed this shedding.
2. To learn the mechanism of tappet shedding.
Scope of tappet shedding:
Tappets are generally used for heald shedding. Tappet, cam and wipers are names given indiscriminately to those irregular pieces of mechanism to which a rotary motion is given for the purpose of producing, by sliding contact, reciprocating motion in rods and levers. When the rod is to receive a series of lifts, with intervals of rest, the piece is generally called tappet.
Types of tappet:
Various kinds of shedding tappets are used in industries.
They are of two main types:
1. Negative shedding tappet
2. Positive shedding tappet
Main parts:
1. Motor
2. Motor pulley
3. M/C pulley
4. Crank shaft
5. Crank shaft gear
6. Bottom shaft gear
7. Bottom shaft
8. Tappet
9. Connecting rod
10. Heald shaft
11. Top arm
Position of fixation of shedding tappet:
The shedding tappets are may be fixed in different parts of a loom.
Namely-
In our loom tappet gets motion in the following way. At first machine pulley gets drive by belt from motor pulley. Then machine pulley, which is directly joined with the crank shaft, gives motion to bottom shaft. This crank shaft gives motion to bottom shaft via gearing. Two tappets are joined with the bottom shaft. So when bottom shaft moves then the tappets also rotate. When it gets contact with tradle bowl it lifts the tradle levers and the heald shafts are lifted by tradle levers via links. As this is a negative shedding tappet the heald shafts are lowered by their own weight.
Conclusion:
Tappet shedding mechanism is important for driving loom. It is also important for fabric design. By this experiment I learn this mechanism. This would be very helpful in my future life.
1. Negative shedding tappet
2. Positive shedding tappet
Main parts:
1. Motor
2. Motor pulley
3. M/C pulley
4. Crank shaft
5. Crank shaft gear
6. Bottom shaft gear
7. Bottom shaft
8. Tappet
9. Connecting rod
10. Heald shaft
11. Top arm
Position of fixation of shedding tappet:
The shedding tappets are may be fixed in different parts of a loom.
Namely-
- Under and over the centre of heald shaft.
- Under and over one end of heald shaft.
- Out side the loom framing.
In our loom tappet gets motion in the following way. At first machine pulley gets drive by belt from motor pulley. Then machine pulley, which is directly joined with the crank shaft, gives motion to bottom shaft. This crank shaft gives motion to bottom shaft via gearing. Two tappets are joined with the bottom shaft. So when bottom shaft moves then the tappets also rotate. When it gets contact with tradle bowl it lifts the tradle levers and the heald shafts are lifted by tradle levers via links. As this is a negative shedding tappet the heald shafts are lowered by their own weight.
Conclusion:
Tappet shedding mechanism is important for driving loom. It is also important for fabric design. By this experiment I learn this mechanism. This would be very helpful in my future life.
12 February 2008
Study on Dobby shedding mechanism.
Experiment name: Study on Dobby shedding mechanism.
Objectives:
1. To know about the different parts formed this shedding.
2. To learn the mechanism of dobby shedding.
Introduction:
Dobby is a shedding mechanism placed on the top of the loom in order to produce figured patterns by using large number of healds than the capacity of a tappet. Dobby is also known as a “witch or “wizard”.
Scope of a dobby:
The scope of dobby is limited between a tappet and a jacquard. The number of shafts that can be actuated by a dobby varies between 6 and 40. Theoretically dobby can control 48 shafts (maximum). However, practically it can control 36 shafts in case of wool and allied fibres. Again, for cotton and allied fibers, it can control maximum 24 heald shafts. In these case healds are operated by jacks and levers.
Main parts:
1.Bottom shaft
2.L-lever
3.Upright shaft
4.T-lever
5.Upper draw knife
6.Lower draw knife 7.Upper hook
8.Lower hook
9.S-lever
Dobby shedding mechanism:
Here a climax dobby is described to explain the dobby shedding mechanism. Climax dobby is a double lift double jack-lever negative dobby. Here two jack levers are operated by a single bulk lever. They are joined with the bulk lever by a timber lever and a link. The double lever is fulcrum med at a point and is connected with S-lever.
The S-lever controls two hooks, one upper hook and one lower hook. The hooks are controlled by feelers. One hook is controlled by hooked feeler and other by a connecting needle. The two hooks control two knives that are joined with a T-lever.
The T-lever is fulcrum med and is controlled by an upright shaft and an L-lever. They get motion from motor and machine pulley. When the feeler comes in contact with a peg and when it is not in the contact it goes down.
Conclusion:
Dobby loom is important for its use. We can use 8-12 heald frame in tappet loom but if we want to use more heald frame for more decorative design then we should use dobby loom. This practical helps me to know about the dobby loom and its mechanism. I think this will help me in my future life.
Objectives:
1. To know about the different parts formed this shedding.
2. To learn the mechanism of dobby shedding.
Introduction:
Dobby is a shedding mechanism placed on the top of the loom in order to produce figured patterns by using large number of healds than the capacity of a tappet. Dobby is also known as a “witch or “wizard”.
Scope of a dobby:
The scope of dobby is limited between a tappet and a jacquard. The number of shafts that can be actuated by a dobby varies between 6 and 40. Theoretically dobby can control 48 shafts (maximum). However, practically it can control 36 shafts in case of wool and allied fibres. Again, for cotton and allied fibers, it can control maximum 24 heald shafts. In these case healds are operated by jacks and levers.
Main parts:
1.Bottom shaft
2.L-lever
3.Upright shaft
4.T-lever
5.Upper draw knife
6.Lower draw knife 7.Upper hook
8.Lower hook
9.S-lever
10.Bulk lever
11.Thumb lever
12.Jack lever
13.Healdshaft
14.Returning spring
15.Motor
16.Crank shaft
17.Pattern cylinder
18.Pattern chain
Dobby shedding mechanism:
Here a climax dobby is described to explain the dobby shedding mechanism. Climax dobby is a double lift double jack-lever negative dobby. Here two jack levers are operated by a single bulk lever. They are joined with the bulk lever by a timber lever and a link. The double lever is fulcrum med at a point and is connected with S-lever.
The S-lever controls two hooks, one upper hook and one lower hook. The hooks are controlled by feelers. One hook is controlled by hooked feeler and other by a connecting needle. The two hooks control two knives that are joined with a T-lever.
The T-lever is fulcrum med and is controlled by an upright shaft and an L-lever. They get motion from motor and machine pulley. When the feeler comes in contact with a peg and when it is not in the contact it goes down.
Conclusion:
Dobby loom is important for its use. We can use 8-12 heald frame in tappet loom but if we want to use more heald frame for more decorative design then we should use dobby loom. This practical helps me to know about the dobby loom and its mechanism. I think this will help me in my future life.
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