UT4-04-Spectrogram
Contents
4 Mass Spectrogram (1)
4.1 Normal Spectrogram shapes according to different fiber types (1)
4.2 Periodic faults (chimneys) (2)
4.2.1 Distinguishing disturbing periodic faults from tolerable faults (3)
4.2.2 Multiple Periods (4)
4.2.3Examples of common periodic fault types in textile practice (5)
4.2.4 Spectrogram calculations / Finding the source of periodic faults (6)
4.2.5 Calculation examples of periodic faults originating in drafting systems (8)
4.2.6 Calculation example of a periodi c fault caused in the machine’s gear sector10 4.3 Drafting Faults (11)
4.3.1 Examples of drafting faults originating in different process stages (12)
4.4 Special Spectrogram faults (14)
4.4.1 Coiler periodicity (14)
4.4.2 Protection twist periodicity (14)
4.4.3 Faults caused by Autolevellers (15)
4.4.4 Comber periodicity (16)
4.4.5 Card faults (17)
Mass Spectrogram [物]光谱图, 光谱照片, 声谱图
The mass spectrogram graphically illustrates the amount and intensity of linear mass variations of the test material according to the wavelength of the variations.
In most cases, the spectrogram results should be regular shapes with minor deviations. For each type of material, depending on the fiber length and length distribution, different basic spectrogram shapes will result after testing.
4.1 Normal Spectrogram shapes according to different fiber types:
Combed Cotton yarn, main crest at ~7cm
OE Cotton yarn, main crest at ~5cm
Wool yarn, main crest at ~22cm
Cut staple yarn, main crest at ~9cm, dip at ~3.5cm (dip at the actual fiber length) The main crest, i.e. the top of the main …hill“ of th e spectrogram is approximately
2.8 times the average fiber length in mm.
Among the natural random variations present in the test material, there can be undesired systematic variations, which make the spectrogram appear different than normal. They appea r as “chimney” peaks or “hill” crests in the spectrogram.
4.2 Periodic faults (chimneys)
Example of a chimney:
Spectrogram with a 20m chimney, i.e. 20m periodic fault (combed cotton,16Tex)
Cut-length mass diagram of the same material than the above spectrogram, showing the 20m periodic mass variation
The idealized base wave (=sine wave) of the periodicity and an amplified illustration of how the test material’s corresponding mass variation would look are drawn alongside the diagram.
The use of the Spectrogram is to check the test material for any abnormally high periodic or systematic mass variations. In most cases, those variations are due to dirty, defective or wrongly set preparation and spinning machinery.
The source of the periodic fault can be located in a previous material processing stage, i.e. in a machine of an earlier passage than the one the samples were taken from. In that case, the fault will be in a longer wavelength range, such as in the above example.
4.2.1 Distinguishing disturbing periodic faults from tolerable faults
Generally, the end use of a yarn or fiber compound has to be known in order to determine which sizes and wavelengths of periodic yarn faults will be noticable or disturbing.
Nevertheless, there are some commonly used rules for distinguishing severe or disturbing material faults from tolerable faults:
1) For wavelengths shorter than ~ 2m: A period (chimney) 50% higher or more
than its surroundings can be regarded as disturbing.
2) For wavelengths longer than ~ 2m: A period (chimney) double as high or
more than its surroundings can be regarded as disturbing
Examples:
Disturbing periodic faults
UT4-SX will automatically mark disturbing chimneys as well as draft faults red as exceptions. The limits (according to which a chimney is marked as disturbing or not) can be defined in the respective UT4 limit settings.
Other periodic faults may appear disturbing in the spectrogram but will not affect the end product directly, such as chimneys in card slivers.
Nevertheless, it is important to pay attention to those cases as well, since the faults can be a sign of deterioration of machinery. One may save costs by intervening in time to avoid any damage to the respective machinery parts.
4.2.2 Multiple Periods
In very many cases, a single periodic material fault produces multiple chimneys. Multiple chimneys are the result of a periodic yarn mass variation which is not evenly shaped, i.e. not sine-shaped.
A multiple periodic fault consists of a base wavelength and of so-called harmonic wavelengths. The harmonics和声学are usually to be found at factor 1/2, 1/3, 1/4, etc. of the base wavelength.
Example:
Spectrogram and yarn board image of a bad OE yarn.
The 10cm moiré was caused by a dirty Rotor groove.
The reason for the appearance of multiple chimneys lies in the behavior of wave signals. Mathematically, it is complex (Fourier transformation), but graphically, it becomes quite evident:
Illustration of how a new wave shape (in this case a square wave) is created by adding sine waves of the base wavelength λ and further shorter wavelengths (harmonics of λ) of decreasing amplitudes.
[Of course, the rectangular waveform is not actually prevalent in textile practice]
λ/3
λ/5
λ + λ/3 + λ/5
4.2.3 Examples of common periodic fault types in textile practice
The signal shape of each of the above examples is contained in the mass diagram, but most often the shape is hardly visible or not visible at all. In a normal diagram, the length scale is too large to see short variations. Also, the high amount of random diagram peaks cover up the wave shape of the periodic fault.
In some cases, such as with very short periodic pulses (last 2 examples), the fault would be visible in the diagram as high signal peaks, and the material itself would contain regularly appearing thick places which would clearly stand out.
4.2.4 Spectrogram calculations / Finding the source of periodic faults
Every genuine periodic fault (chimney) visible in the spectrogram has its origin in the production machinery.
An exception to that rule can be a periodic fault due to material handling, for example the scraping of a roving bobbin surface, etc.
When searching the origin of the periodicity, the first step is to remember that the fault is caused by a moving machine part, usually a rotating one. It can be directly touching the material (rollers, coiling, etc.) or in the machine drive (gears, pulleys, etc.)
If the part is running smooth and perfectly uniform, it will not cause any periodic faults, of course. If it is running irregularly and/or has an uneven surface, the same uneven points of the rotating part will periodically produce a fault in the material passing out of it once per revolution, i.e. once per its circumference.
Example:
Spectrogram chimney resulting from an eccentrically running top exit roller in a cotton ring spinning drafting system and the type of yarn fault which would be produced
In the above example, the circumference of the top roller would have to be approximately
7.7cm ÷ π = 7.7cm ÷ 3.14 = 2.45cm = 24.5mm.
Normally, a top roller in a cotton drafting system has an initial diameter of around 27mm. Probably, the spinning contraction and/or repeated grinding of the roller surface are responsible for the slight difference between the theoretical and the actual roller diameter.
Systematic fault search
A good method to find the faulty part causing a periodic mass variation, visible as one chimney or an array of chimneys in the spectrogram, is following procedure:
1. Divide the chimney’s wavelength (λ) by π. π = 3.14
- If there are multiple chimneys, check if they belong together by looking for ratios of λ/2, λ/3, λ/4, etc. Then divide the main wavelength λ, the furthermost right one, by π.
2. Check if the result corresponds to any diameter of a moving part touching
the material directly at the output of the machine.
-> If there is a part with such a diameter, then it is probably the faulty element.
- If the result of λ/πis much larger than any diameter at the output, continue with step 3. - If λ/πis smaller or only slightly larger than any diameter at the output, go to step 4.
3. Divide the result λ/πby the drafting ratios present in the machine(s) until
finding the diameter of a part touching the material further back in the
machine or in a previous passage.
-> If there is a part with such a diameter, then it is probably the faulty element.
- If no such part can be found, continue with step 4.
4. Look for a possibly faulty part in the machi ne’s drive: Using the correct
gear plan, calculate the gear ratios backwards from the delivery cylinder of the machine.
-> When a gear ratio is found that, when multiplied by λ/π, results in the diameter of the delivery cylinder, then one has probably found the faulty area in the machine drive.
In a machine with several deliveries or spindles,gear faults will usually produce the same chimney height on all samples taken from a machine at the same time.
Formula:
or :
For gear faults:
ratio
For certain types of machines such as cards or very complex gear boxes, it can be necessary to use an auxiliary method to find the fault source:
A faulty (rotating) part can be searched in a machine while it is running, by flashing onto the suspected fault source with a stroboscope .
This auxiliary method is not generally recommended because of the danger involved when searching a fault on a running machine!
Instead, where available, the RPM (rotations per minute) displays of the machine should be read. Auxiliary general formula:
4.2.5 Calculation examples of periodic faults originating in drafting systems
1)
Yarn Spectrogram chimney at λ ≈ 8.2cm : Diameter d = λ ÷ π = 8.2cm ÷ 3.14 = 2.61cm ≈ 26mm = diameter of exit top roller of ring frame
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Application Training Manual
2)
λ
λ/2
λ/3
λ/4
Yarn Spectrogram chimney at λ ≈ 3.6m, the other chimneys are regular fractions of λ :
a) Diameter d = λ ÷π ÷ draft factor = 360 cm ÷ 3.14 ÷ main draft (30×) = 3.82cm
-> no such part exists in the middle of the ring frame’s drafting system.
b) 3.82cm ÷ break draft (1.2×) = 3.18cm
-> no such part exists at the entry of the ring frame’s drafting system or the exit of the
roving frame’s drafting system.
Solution: 360cm ÷ main draft (30) = 12cm = apron length L of cracked apron (the apron length is already a circumference).
3)
Yarn Spectrogram chimney at λ ≈ 2.9m :
a) Diameter d = λ ÷π ÷ draft factor = 290 cm ÷ 3.14 ÷ main draft (30×) = 3.08cm
-> no such part exists in the middle of the ring frame’s drafting system.
b) 3.08cm ÷ break draft = 3.08cm ÷ 1.2 = 2.57cm ≈ 26mm = diameter of top input roller of
ring frame
4)
Yarn Spectrogram chimney at λ ≈ 3.4m :
a) Diameter d = λ ÷π ÷ draft factor = 340 cm ÷ 3.14 ÷ main draft (30×) = 3.61cm
-> no such part exists in the middle of the ring frame’s drafting sys tem.
b) 3.61cm ÷ break draft = 3.61cm ÷ 1.2 = 3.01cm ≈ 30mm = diameter of top exit roller of
roving frame
5)
Yarn Spectrogram chimney at λ ≈ 32m :
a) Diameter d = λ ÷π ÷ draft factor = 3200 cm ÷ 3.14 ÷ total draft ring frame(36×) =
28.31cm
-> no such part exists at the entry of the ring frame’s drafting system or the exit of the
roving frame’s drafting system..
b) 28.31cm ÷ total draft roving frame(8×) = 3.54cm ≈ 35mm = diameter of top exit roller of
drawframe
4.2.6 Calculation exa mple of a periodic fault caused in the machine’s gear sector
Spectrogram with chimney at λ = 3cm
Gear sector of ring frame
Calculation:
a) Diameter d = λ ÷π = 3.0 cm ÷ 3.14 = 0.96cm
-> No such part exists at the exit of the ring frame’s drafting system.
b) Gear ratio back to faulty gear = λ÷ diameter(shaft) ÷ π =30mm ÷ 25.4mm ÷ 3.14 =
0.376
-> The fault happens at every 0.376 revolutions of the delivery shaft.
Therefore, the bad part revolves 1 ÷ 0.376 = 2.66 times faster than the delivery shaft. c) Search for gear ratio: 85 teeth ÷ 32 teeth = 2.66
-> Solution: The fault’s origin is the 32-tooth gear or it is on the same axis than that gear. Note: If a yarn spectrogram periodicity such as above is at a very short wavelength, it is quite possible that the fault is generated in the machine’s gear sector. The fault would then be apparent on all samples tested from the same machine side. Of course, gear faults can also be of longer wavelengths than the shaft diameter × π.
4.3 Drafting Faults
Another type of irregularity which is clearly visible in spectrograms is a drafting fault.
It is an exaggerated crest (hill) which results from poor fiber control in a drafting zone. Example of the origin of drafting faults:
Spectrogram of a ring-spun yarn with typical pointed crests resulting from both bad
pre- and main draft settings. The main draft factor is the ratio of the 2 wavelengths at the hill crests: 1m15cm : 6.5cm ≈ draft factor 17.7 .
Drafting faults are created and influenced by non-optimal settings of one or several of the following factors: - Gauge distance between the drafting rollers (Nip) - Roller Pressure - State of the roller’s surfaces - Humidity of material and surrounding climate
When searching to eliminate drafting faults, one would look for the main cause in one of those factors first.
In many cases though, a compromise has to be found, since certain materials are more critical. Example: Combed cotton drawframe slivers, where the fibers are highly parallel and thus slippery and difficult to draft optimally at a reasonable speed.
A drafting fault hill is to be found at a wavelength of about 2.8 × average fiber length .
If the drafting fault hill does not lie around 2.8 × average fiber length, one has to divide the wavelength λ of the hill crest by 2.8 × average fiber length in order to get the approximate draft factor back to the origin of the fault.
Formula:
4.3.1 Examples of drafting faults originating in different process stages
Drafting faults originating in 1) the main draft zone of the ring frame (pressure set too low) and 2)
the break draft zone of the finisher drawframe (gauge open too wide)
1)
Yarn Spectrogram showing a drafting fault at λ ≈ 6cm
Average fiber length ≈ 6cm ÷ 2.8 ≈ 2.14cm = 21.4mm. In this case, the draft factor is 1, since the main draft of the ring frame output is bad.
2a)
Sliver Spectrogram of the same material lot as the yarn with drafting fault at λ ≈ 32cm Draft from faulty zone to sliver: Draft factor ≈λ÷(2.8 × average fiber length) =32cm ÷ (2.8 ×
22mm) = 32cm ÷ 6.16cm = 5.19 ≈ 5.22
-> The calculated draft nearly coincides with the drawframe’s main draft, therefore the fault lies in the break draft zone
2b)
Yarn Spectrogram showing a drafting fault at λ ≈ 90m
Draft from faulty zone to sliver: Draft factor ≈λ÷(2.8 × average fiber length)
=90m ÷ (2.8 × 22mm) = 9000cm ÷ 6.16cm = 1460 ≈ [ 36 × 8 × 5.22 = 1503]
The calculated draft nearly coincides with the draft factor from the ring frame output back to the middle of the drawframe’s drafting system. The factor is [Total draft ring frame × Total draft roving frame × main draft drawframe].
Therefore, the fault lies in the finisher drawfra me’s break draft zone.
4.4 Special Spectrogram faults
In some cases, there are chimneys and hills in the spectrogram which come from causes other than the classical ones described in the previous pages.
The following cases are some of the most common types of additional faults found in staple spinning:
4.4.1 Coiler periodicity
Example:
Sliver Spectrogram with a coiler periodicity chimney ; λ = each winding of the can sliver A coiler period in a sliver is often not regarded as a serious fault, since in most cases it will vanish after the next processing stage, i.e. roving (or finishing).
Often, the coiler period is due to a moisture difference between the material exposed to air in the middle of the can and the stacked layers of sliver windings which cover each other.
If that is the case, it is recommended to test a can directly from the machine with as little delay as possible.
Bad coiler periods however, which are due to truly defective sliver coilers, will be visible as long wavelength periods in the spectrograms of the subsequent processing stages. 4.4.2 Protection twist periodicity
In a roving frame, a certain twist is given to the roving in order to protect the fibers from slipping apart. If the twist is too hard, the material becomes harder to draft evenly, and the above twist periodicity can occur.
If the twist is too soft, the fibers fray open easily and tend to form more fly in ring spinning and laps on rollers.
Even when the roving twist is optimal, certain machine settings can worsen the twist periodicity, such as the roving frame twisting tension, the ring frame roller pressure and apron pressure, the type of apron distance plates, etc. These settings can also influence the amount of long thick and thin places in the yarn.
Example:
Yarn Spectrogram with roving periodicity chimney atλ ≈ 44cm
Roving with a twist length of 1.2cm
λ roving period = roving twist length* [cm] × total draft ring frame = 1.2cm × 36 = 43.2cm ≈ 44cm
*(twist length [cm] = 100 ÷ twist /m or 2.54 ÷ twist / inch)
4.4.3 Faults caused by Autolevellers
Example:
Drawframe sliver spectrogram with draft-type fault at λ ≈ 35cm
Drawframe autoleveller control
Often, spectrogram faults due to a badly adjusted autoleveller have a nearly identical shape and wavelength range as draft faults.
4.4.4 Comber periodicity
In combing machines, the fibers are soldered, i.e. joined together periodically at a certain length interval.
If the adjustments at each combing position and on the machine table are not optimal, a strong periodic fault can arise due to the soldering.
Example:
Comber spectrogram with a chimney at λ ≈ 45cm
Material flow on a cotton comber and the resulting periodicity in the table slivers and output sliver
Calculation example:
λ combing period = soldering length × draft lap to table × draft table to output sliver
= 0.4cm × (64 kTex ÷ 4 kTex) × ( 4 kTex × 8 ÷ 4.5 kTex) = 45.51 cm ≈ 45cm
Qty. of laps = 8 Lap
= 64.0 kTex
Soldering
= 4.0 mm
Table sliver = 4.0 kTex Output sliver
= 4.5 kTex
Application Training Manual
4.4.5
Card faults
In a modern short-staple or worsted spinning mill, card spectrogram faults will not be visible anymore at the end of the preparation line, i.e. after the output of autoleveler drawframes. Nevertheless, it is important to search the source of any chimneys or high areas in those spectrograms, which can be due to mechanical misalignment or dirty elements. In such cases, secondary negative effects such as fiber damage or an increased amount of neps and impurities in the output sliver can be the result.
When searching spectrogram faults in cards, it is not necessary to search the diameters and draft ratios of the carding elements in the calculation. The cylinder, doffer, etc., which run with different surface speeds and fiber material density on them, do not actually draft the material in the conventional sense.
The formula used in this case is:
In modern cards, the output speed and RPM indication of the important carding elements can be read off a display.
Example:
Card sliver spectrogram with periodic fault at λ ≈ 18cm
Simple schematic of a card with the 3 main revolving elements
Calculation:
λ = Output speed ÷ RPM = 80 m/min ÷ 450 m/min = 0.177m = 17.7cm ≈ 18cm
-> The cylinder drum is the cause of the spectrogram chimney and would have to be checked.
Output speed = 80 m/min Doffer RPM = 1300 1/min Cylinder RPM = 450 1/min Licker-in RPM = 850 1/min