raw mtl - inspection

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Sewing ThreadsDuring sewing process in a high speed lock stitch machine, the thread is subjected to complex kinematic and dynamitic conditions. The speed at which it passes through the needle eye can reach 140-165 km / hour and at the moment at which the thread is caught by the sewing hook, the speed reaches 2000m/sec.

While moving at such high speeds, the thread is subjected to friction from a number of guides, from the needle eye, from the fabric being sewn, from the bobbin case assembly, and from the bottom thread.At the same time, the thread is subjected to many stresses, all of which take place very quickly and at high speed. Such a severe working condition with the heat generated in the needle can reduce the initial strength of a thread by as much as 60% and this is one of the causes of increased breakage in the needle thread during high speed sewing.


ConstructionYarn count, yarn ply, number of twists, twist balance, yarn strength (tenacity), yarn elongation.


PROPERTIES OF SEWING THREADImperfections Sewing threads should be free from slubs, knots or any such defects.

Otherwise, there will be excessive stoppage on the sewing machine, resulting in the lower sewing efficiency.


Finish Thread finish is basically a lubricant applied to a sewing thread so that the thread will slip easily and smooth through the eye of the sewing machine needle and through various thread handling parts of a sewing machine. This finish varies from 3 to 15% of the weight of the thread. The amount of finish must be consistent from package to package and from lot to lot; otherwise, sewing quality and efficiency will be lost completely.

ColorColor of a sewing thread (including white) should match that of either he original or the standard sample and should not vary too much within a lot or shipment of sewing thread.

Also, the color should not bleed in washing and or dry cleaning and fade in sunlight.

Package DensityPackage density of the sewing thread should be consistent from package to package within a shipment or lot and from shipment to shipment. If package density varies too much, sewing machine operators will have to adjust the tension frequently, resulting in lower productivity.

Winding Winding of the sewing thread on packages should be uniform; otherwise, it may result in excessive thread breakages, again causing lower efficiency. Yardage Length of the sewing thread on each package should be at least the specified amount or within certain tolerance, such as + 2% of the labeled length.

ZippersZippers should be checked for the following.

Dimensions Check for the correct width of the tape. If it isnt correct, the machine will run off. Measure overall length with the zipper closed from extreme ends of metal. Tape extensions should be as specified Top and bottom stops be fastened securely Zipper tape should be of uniform in color if that is important

Zipper should not cause wrinkling or puckering after it is sewn in to the garment Can a zipper be washed or dry cleaned? Will it fade? Will the slide deform under pressing or ironing?Check the force it takes to pull open the zipper (sideways)

Pull tab should be affixed firmly to the slider body Slider should ride freely but must not be so free that it is loose on the chain Check also to be sure the slider locks securely

Avoiding Zipper ProblemsMost zipper failures in garments are the result of 1.Improper installation methods in the sewing 2. Questionable garment design or construction 3. Incorrect product application 4. Factory and / or retail customer abuse.

Slider DirectionThe slider direction must run in a specific direction. On metal chain, the points of the teeth face towards the open end of the zipper. Correct direction is more difficult to determine with the plastic chain, but in both cases, arrows are usually printed on the tapes that point towards top, open end

Right Side Up On plastic coil and extruded tooth chain, the slider should be mounted, with the pull tab on the same side as the printing on the tapes. Some of coil zipper is not symmetrical, therefore making slider mounting obvious. Side to side orientation is not critical with metal or molded chain.


Most zippers tapes contain some percentage of cotton, or cotton blend yarns in order to provide a dense anti-sleazy construction. A resin treatment option is available for permanent press or low shrink applications, which are commonly referred to as stabilization. The process consists of applying a material to the chain which, when cured with a specified temperature/time relationship, will impart synthetic qualities to the cotton, at some sacrifice of strength.

Slider and Chain Combinations

Every zipper manufacturer has a large stable of slider and chain available for most applications. Materials vary from light weight plastic through the family of metals such as Zinc, steel, brass, and nickel-silver. Slider action covers a spectrum from nonlock, pinlock, camlock, flangelock, fliplock and atuolock. Selecting the proper combination is best left to application lab of the zipper supplier.

Handling and Processing ZipperZipper chain should be stored at a moderate temperature and humidity. Long term storage at elevated temperatures can cause some tape yarn deterioration, especially with resin treatment. Excessive tension or shock loading of zipper chain during processing can affect dimensions and cause latent shrinkage Running more than one manufacturers chain simultaneously can result in accidental mixing of components.

Ratcheting This is the act of forcing the slider down the chain by pulling the two open halves apart. Although some sliders are designed to ratchet, this action does the damage, degrade the teeth, and with positive locking sliders the chain is destroyed. Ratcheting occurs in the sewing room, finishing, and at industrial laundries when operator wants to open the garments fast.Retail users can ratchet a slider by not fully opening the zipper when putting on or removing the garment, or as deliberate act to allow return of an unwanted item.

Shear This is the act of attempting to shift one half of the chain with respect to the other half after the slider is mounted. It occurs when an operator tries to adjust the waistband alignment without first removing the slider, and usually results in permanent damage.Slider Distortion A slider is clam shelled when the top and bottom have been spread apart, as in opening a clam. This condition can be caused by sticking slider holder or by an overzealous consumer trying to move a stuck slider with a pair of pliers. A crushed slider usually occurs in the pressing buck of the garment factory or in industry laundering.

Slider holder This device holds the slider by the pull tab, and lifts the lock out of the path of the chain during slider threading. A misadjusted holder can cause ratcheting if the lock release malfunction or clam shelled sliders and chain damage if the pull clamp does not release after threading.Bottom Stop The primary function of the bottom stop is to prevent accidental opening of the closed end of the chain. A stop that is not tightly clinched over the zipper teeth, or is totally missing will allow the chain to open behind the slider. This condition can sometimes be repaired in the factory by pulling the slider down thus rehealing the chain, and applying a new stop.

Sewing The major cause of zipper failure is poor sewing. A garment panel attached too close to teeth will interfere with the slider and get caught inside. Attempting to free the slider can cause garment and chain damage, or clam shelled sliders. A sew line that is not parallel to the chain or wanders, causes localized high stresses and curvature which can eventually lead to erratic slider action and tape failure. Low stitch count can lead to tape sleaziness, and using blunt, large diameter needles will cause heating and melting during sewing because of the high density tight weave inherent in zipper tapes. Improper thread trimming will cause interference with slider action when the loose ends become caught.