1. Selection of Roving Frames, Installation Quality, and Maintenance Quality Control

(1) Equipment Selection

There are many manufacturers of roving frames on the market today, both domestic and foreign, offering various models. Each brand has its own advantages and disadvantages. Users can select suitable models based on their product types, product grade requirements, and budget conditions.
The purpose of equipment selection is to:

  • meet production requirements,
  • avoid unnecessary investment,
  • and ensure that the equipment always remains in good operating condition.

(2) Equipment Installation

After selecting the model, installation becomes a central and fundamental step in ensuring product quality.
If capable, the user may install the machine themselves; otherwise, it is best to invite the equipment manufacturer or skilled technicians from peer companies to perform installation and commissioning.
It is essential to have professionals strictly control the process so that future production can be carried out smoothly and efficiently.

(3) Maintenance Quality

Daily maintenance is the most fundamental aspect of routine management.
Key requirements: thorough, comprehensive, and leaving no dead corners—meaning all maintenance must be executed properly and completely.

2. Control of Roving Tension

For the roving to be wound smoothly onto the bobbin, the bobbin winding speed must be slightly higher than the delivery speed from the front roller. This creates tension and tension drafting in the roving between the front roller and the bobbin, which is critical in roving production.
It influences both the roving spinnability and the quality of the final yarn.

 

Generally, maximum elongation should not exceed 3%.

Differences in elongation between cops on the same machine, between front and back rows, and between machines of the same product should be controlled below 1.5%.

The section of roving between the front roller and the flyer top has lower twist due to twist loss and is longer in length; combined with flyer vibration at high speed, it is prone to unexpected elongation.

Adjustment guideline:
At the early winding stage, when the roving forms the second layer at the lower part of the bobbin, the roving end may shake slightly but should not form wave-like motion.

If the upper section is too tight → winding speed is too high → elongation excessive → move the belt starting position upward on the cone drum.

If roving gradually becomes tight during spinning → the belt moves too little each time → reduce the tension gear number.

Conversely, increase the tension gear number.

Factors affecting roving tension include:
roving count, front roller speed, twist, cotton quality, temperature & humidity, and machine condition.

Roving tension variation affects roving evenness and mass variation—key indicators of roving quality.
Since roving contains fewer fibers and lower twist than yarn, excessive tension easily causes unexpected elongation, worsening evenness and increasing end breaks.

When tension variation is large, roving mass unevenness increases significantly and should be controlled within 1.1%.

Low tension results in loose roving formation, causing difficulties in storage and unwinding, leading to increased unevenness and weight variation.

Example:
On roving frames with poor false-twist effects spinning 100% cotton, front-row quality is often worse than back-row quality due to tension differences.
Good false-twist effectiveness may cause back-row tension to exceed the front row.

Therefore, strict control of roving tension is essential.

3. Process Control of the Roving Frame

Main process parameters include: roving count, spindle speed, draft, roller gauge and apron spacing, roller pressure, twist coefficient, winding density, condenser and trumpet diameters, and flyer presser turns.

(1) Roving Count

Determined by the drafting capability of the ring frame, yarn count, and product quality, primarily based on yarn count.
Heavier rovings produce coarser yarn.
If too heavy, higher drafting at the ring frame may negatively affect yarn evenness.
Now, some mills increase roving count to 10 g/10 m and use V-draft on ring frames, still achieving good yarn quality—worth promoting.

Total draft on the roving frame depends on yarn count and sliver count, as well as drafting system type.
Since ring spinning is moving toward higher draft, roving draft can be set lower, which benefits quality.
For double-short-apron drafting, draft can be slightly higher than 3-over-4 drafting, typically 5–12 times.

(2) Draft Distribution

Determined by drafting system and total draft.
When the main draft zone has strong drafting capability, more draft should be allocated to it.

Experience shows:

With constant sliver count and roving count, higher back draft results in poorer evenness.
Thus, when the main draft zone has good conditions, the back draft should be set lower.

Back Draft Reference:

For double-apron drafting: 1.08–1.40.
In FA series roving frames, 1.1 gave optimal evenness.

Too much pressure or inconsistent pressure on rollers leads to significant spindle-to-spindle variation.

When roving count is heavy, a larger back draft helps avoid fiber layer separation.
When spinning yarn for knitting, to prevent long thin faults, select smaller total draft and smaller back draft.

For 3-over-4 drafting:

When sliver count is light, use small back draft: 1.17–1.36.

(3) Spindle Speed

Large-package high-speed roving frames operate at 1000–1500 r/min.
Roving count should not be too light; otherwise unexpected drafting increases, causing more breaks.

(4) Twist Coefficient

Longer, finer, more uniform fibers → lower twist

Shorter, coarser, less uniform fibers → higher twist

Twist ensures roving can withstand winding and unwinding tension and improves fiber control in ring spinning’s back zone.

Excessive twist: uneven strength, roller slippage on ring frames, hard ends, and more breaks.
Insufficient twist: unexpected drafting and more breaks, causing uneven roving.

(5) Roller Gauge & Pressure

Gauge depends on fiber length.
Too small → fiber damage, hard ends.
Too large → irregular fiber movement, poor CV.

Roller pressure provides clamping force to prevent slippage and drafting layers.
Clamping quality affects roving evenness, mass variation, and defects.

On spring-loaded drafting arms:

Original roller gauges vary with roving weight.

For roving > 5 g/10 m: use 4.5 mm, 5 mm, 5.5 mm, 6 mm gauge.

Small gauge + adequate pressure improves evenness but requires regular pressure calibration to avoid spindle variation.

(6) Condenser Sizes

The front and middle condensers provide additional friction control.

Front: matched to roving count

Middle: matched to sliver count

(7) Spindle & Flyer Conditions

Spindle runout should be ≤ 0.03 mm

Excessive runout → more breaks, uneven roving

Flyers must be statically and dynamically balanced

Presser pressure must be appropriate

Arm spacing must avoid collision or abrasion

Improper presser curvature → uneven winding and defects

Regular cleaning and calibration reduce wear and ensure stable operation.

4. Effect of Drafting Force on Process Quality

Drafting force itself is not a process parameter, but must be considered when designing drafting processes. It is related to:

(1) Draft Ratio

When draft = 1 → no fiber movement → drafting force = 0
As draft increases → force rises rapidly → then increases slowly once fibers start sliding
Maximum drafting force depends on sliver count, roller gauge, fiber packing density, and fiber straightness.

(2) Drafting Force vs. Roving Twist

Higher twist → higher drafting force
At low draft, the influence of twist is small because twist decay occurs at high draft.

(3) Roller Gauge

Large gauge → small effect
Once gauge becomes too small → drafting force increases rapidly due to fibers entering back nip.

(4) Fiber Density in Drafting Zone

Higher fiber density → higher drafting force
Smaller condenser openings increase fiber friction and drafting force.

(5) Fiber Fineness, Length, Straightness

Finer, longer fibers → higher friction → higher drafting force
Curled or entangled fibers → higher force
Straight, parallel fibers → lower force

(6) Relative Humidity

Within 35%–75%: every +10% RH → drafting force +8%
At excessively high humidity → hard ends occur.

5. Conclusion

Proper and skilled use of roving frames is a key link in textile engineering.
Only with a deep understanding of each parameter can high-end yarns be produced effectively.