Analysis and Elimination of Common Fault
Ⅰ. Method of Check
The key to the elimination of the faults is to make a wise diagnosis. The wise diagnosis lies in careful check and analysis. When meeting with the faults of thread skipping, broken thread, broken needle, sewing material crinkle or heavy operation, check will first be carried out to find out what is wrong according to the condition and features of the faults. Then begin to repair to eliminate the faults. Otherwise, the faults can’t be correctly solved. Now we introduce four methods of repair to the repair workers as follows:
1. Mechanism checking method:
The canvas sewing machine is made up of four main mechanisms as cloth pricking, thread picking, thread hooking and feeding. The four mechanisms have their own tasks but cooperate with one another. When faults occur, we should find out the faults according to their tasks, and then you do less and get more. The common faults of sewing machines can mostly adopt this checking method.
1). The cloth-pricking and thread-hooking mechanisms are responsible for forming thread trace. When faults such as needle skipping, broken thread or broken needles, we should first check the two mechanisms. The key is to check if the cooperation between needle and the swing shuttle and the position of the hooking thread is correct and then consider the other mechanisms.
2). The thread-picking mechanism is to ensure the clearness, beauty and firmness of the thread trace. When facing faults like disordered, ugly and loose trace, the thread-picking mechanism and its thread shall be first checked.
3). The cloth feeding mechanism can directly affect the speed of sewing materials advancing and the length of trace. When feeding is not smooth, the sewing materials crinkles or runs sideways, the feeding mechanism shall be first checked. The height and speed of cloth feeding tooth shall be first checked.
The mechanism checking method can find out the cause of the majority of faults. But the operation of mechanisms is connected. If one of the mechanisms suffers, the work of others can also be affected. So when you
Can’t find out the causes using the mechanism checking method, you should also check other connected mechanisms.
2.Feature checking method
When or after happening, some faults have some strange performance. For example, the moving of the sewing materials is mainly due to the too high assembly position or unevenness of the cloth feeding tooth. The back of the sewing material being bitten broken results from the fact that the pressure of the presser is too big or the feeding tooth is too sharp. According to the strange performance in the course of sewing to find out the causes. Using this method, you can find out the causes as fast as possible.
3.Cause and effect checking method
When a fault occurs due to a certain obvious cause (e.g. changing parts, sewing materials, needles or threads), we can try to find out the faults by focusing on this certain cause. This method is called cause and effect checking method.
Cause and effect checking method is a relative labor-saving method. For example, the machine is formerly very smooth, but it runs heavily after changing a conic screw. The main cause is the screw is assembled too tightly. So loosen the screw properly, and the fault disappears. Take another example. The canvas sewing machine runs properly when sewing double-layer sewing materials and the thread trace is proper in length. But when sewing multi-layer materials, its operating speed as trace is slow. Using this method, you can find out this is caused by low presser pressure, low feeding tooth and too narrow needle space. Thus the presser pressure shall be adjusted, the cloth-feeding tooth shall be raised and the needle space shall be widened. When necessary, it is better to change needles or thread and loosen the sewing thread.
4). Completely- listing checking method
When a fault occurs and the three methods mentioned above fail, we can turn to the complete listing checking method, that is, list all the possible faulty causes or parts until the final fault is found out. For example, when the machine runs with difficulty, if you doubt if there is something wrong with the lower shaft running mechanism, you can disassembly the large connecting rod cover. This can make the lower shaft running mechanism and the upper shaft separate, then run the upper wheel. If the upper wheel runs smoothly, there must be something wrong with the lower shaft running mechanism. Then check all the sectors of the cloth feeding mechanism until the fault is found out. Although this method is relatively labor-consuming, it is a practical method for those difficult faults without features or cause and effect.
Only by experiencing can you master the inner connection among the parts and use wisely the four methods mentioned above.
Ⅱ. Analysis and Elimination of Common Fault
1. Thread skipping
|
Fault features |
Causes |
Countermeasures |
|
1.The under-thread can’t be guided |
1. The shuttle thread is too short
2. The shuttle thread is caught in the shuttle gate
3. The needle is too high and the shuttle can’t hook the thread ring |
1. Lengthen the shuttle thread
2. Check if the under-thread is caught. If so, eliminate it.
3. The needle space connecting shaft tightening screw is loose and the needle lever has gone up. So adjust the needle lever lower and collate the needle and tighten the tightening screw |
|
2. Needle bar floating up and down |
1. The needle bar or the needle bar wear and tear
2. The needle bar connecting shaft screw is loose and the bar moves sideways |
1. Change the needle bar sleeve or choose new needle bar
2. Check the needle again and tighten the fixing screw |
|
3. Skipping needle after several stitches |
1. The swing shuttle is worn out or the shuttle tip is too blunt
2. The position of the needle is too high or too low. |
1. Change the shuttle.
2. Adjust the height of the needle bar or the needle and check the needle again. |
|
4. Continuous skipping or sewing failure |
1. The needle is bad in quality or curve and cannot form thread ring
2. The position of the needle is too high and cannot hook the thread. The material, thread and needle don’t cooperate well.
3. The long-used shuttle and shuttle bed and other parts wear and tear. |
1. Change a qualified needle or straighten the old one.
2. Adjust the height of the needle bar or needle according to Chart.2
3. Change the shuttle or shuttle bed. Make a thorough repair when necessary. |
|
5. Skip when sewing thick materials while no skipping when sewing thin materials |
1. The presser pressure is not enough.
2. The needle is too thin.
3. The hooking mechanism and other parts wear and tear seriously. |
1. Adjust the presser pressure.
2. Change the needle.
3. Change parts and make repairs |
|
6. Skip when sewing thin materials while no skipping when sewing thick materials |
1. The needle hole on the needle plate wears too seriously.
2. The needle is too thick.
3. The bottom of the presser wears or the presser pressure is too small. |
1. Change the needle plate.
2. Change thin needles.
3. Change the presser or adjust the presser pressure. |
2.Broken thread
|
Fault features |
Causes |
Countermeasures |
|
1. The first stitch and the thread is broken with the cut-shape |
1. The needle is backward or the needle is not assembled enough firmly so that the needle is too low.
2. The material is too hard, the needle is relatively thin or the presser pressure is too big. |
1. Check the assembly of the needle and if the needle bar connecting shaft screw is loose.
2. Change the needle or adjust the presser pressure. |
|
2. The two broken ends of sewing thread show the curve-shape with short hair |
1. The clipping thread is too tight or the sewing threads wind together.
2. The sewing thread is pushed into the shuttle bed guide groove.
3. The sewing thread breaks and winds easily. The quality is bad and burr occurs at the thread-passing part. |
1. Adjust the pressure of the clipping flake, check the passing thread and eliminate the winding.
2. Check the condition of shuttle wearing. When necessary, change the shuttle.
3. Polish the passing thread with sand paper. Change the sewing thread. |
|
3. The lower part of the sewing material accumulate too much thread and the stitches can form. The thread broken part looks like a horse tail. |
1. The cloth-feeding tooth is too low and the material stops. There is too much accumulated thread and broken thread occurs.
2. The cloth-feeding and the thread-picking don’t coordinate and the thread breaks.
3. The presser and the needle are too loose to block the material. |
1. Raise the cloth feeding tooth.
2. Adjust the fixing position of the feeding cam.
3. Tighten the presser and the needle screw. |
|
4. Broken thread happens suddenly when sewing and the surface thread fluctuates with curves. |
1. The position of shuttle bed is not assembled well and the surface thread is caught in the shuttle bed.
2. The shuttle sleeve is not locked tight or moves sideways suddenly in operation.
3. The shuttle is bad in quality, the bobbin spring is too long or the bobbin sleeve is elliptical. |
1. Readjust the position of the shuttle bed.
2. Reassembly the bobbin sleeve.
3. Change the shuttle. |
|
5. The under-thread breaks suddenly when sewing. |
1. The bobbin sleeve is not qualified. The inner diameter is elliptical so that the bobbin can’t run normally.
2. The bobbin spring screw is too tight and the pressure of the shuttle surface is too small.
3. The winding of the bobbin is too full or too loose and disorderly. |
1. Change the bobbin sleeve.
2. Loosen the bobbin spring screw.
3. Rewind the bobbin thread.
4. Change the under thread. |
3. Broken needle
|
Fault features |
Causes |
Countermeasures |
|
1 Broken thread occurs when sewing thick materials |
1. The needle is too thin or bent.
2. The sewing material is not evenly thick.
3. The needle bar moves up and down too hard. |
1. Change new thick needle.
2. Properly lower the sewing speed and use your hands to help feed
3. Change new needle bar or needle bar sleeve. |
|
2. Broken needle with long needle space while no broken needle with short needle space |
1. The cloth-feeding tooth lags.
2. The cloth-feeding tooth is not proper. The needle breaks after touching the end of the cloth-feeding tooth |
3. The position fixing of the cloth-feeding cam shall be adjusted.
4. Properly shorten the needle space or change a new cloth-feeding tooth. |
|
3. The needle breaks beneath the needle plate. |
1. The needle position is too low and the needle touches the shuttle.
2. The shuttle bed is not properly assembled and the tip of the shuttle touches the needle.
3. The space between the shuttle bracket and the needle end surface is too small or too big and the shuttle bracket touches the needle or has lost the function of protecting the needle |
4. Adjust the position of the needle bar or the needle.
5. Reassembly the swing shuttle.
6. Adjust the space between the shuttle bracket and the needle end surface |
|
The needle breaks over the needle plate. |
1. The sewing material is pulled too hard and causes curving needles.
2. The presser screw is loose so that the presser is defective and touches the needle
3. The cloth-feeding cam moves sideways, making the material pull the needle broken.
4. There are some things hidden in the sewing materials to make the needle break. |
5. Strengthen operation practice.
6. Adjust the presser tightening screw.
7. Adjust the position of the cloth-feeding cam screw |
4.Faults about feeding
|
Fault features |
Causes |
Countermeasures |
|
1. The sewing material crinkles. |
1. The needle tip is broken.
2. The strain of the under-thread is too big.
3. The differential mechanism is not properly adjusted. |
1. Change the needle.
2. Turn loose the shuttle bobbin spring screw.
3. Readjust the differential mechanism. |
|
2. The lower part of material is bitten broken, forming case and tooth trace. |
1. The cloth-feeding tooth tip is too sharp.
2. The presser pressure is too big |
1. Grind the tooth tip with an oilstone.
2. Turn loose the screw in charge of adjusting pressure |
|
3. There is hair beneath the material and sound of fiber breaking can be heard. |
The needle tip is broken or too blunt. |
Change the needle. |
|
4. The sewing material stops. |
1. The cloth-feeding tooth is too low.
2. The presser pressure is too big. |
1. Raise the cloth-feeding tooth.
2. Tighten the screw in charge of adjusting pressure |
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