witzerland-based Rieter developed AEROpiecing technology for its R 40 automatic
rotor-spinning machine some three years ago. Since then, more than 500 R 40 machines with
AEROpiecing have been operating under mill conditions. The high-precision, high-speed robots on
this machine are equipped with improved modules and updated software for this purpose. The ComfoRo®
yarn produced using AEROpiecing technology displays outstanding running properties in downstream
processing. The absence of faults in this ComfoRo yarn – which has a visible impact right
through to the end product – in combination with the positive properties of the rotor yarn is
arousing great interest and opening up new markets. The distinguishing features of AEROpiecing
technology include: enhanced robot and machine efficiency of the R 40; reproducible,
yarn-like piecings; fewer stoppages in downstream processing; fewer rejects due to
substandard quality in the end product; and new prospects for the processability of
What Is AEROpiecing?
The customary piecing process had drawbacks related to the introduction of the thread into the
rotor. During piecing, the thread end had to contact the fibers in the rotor groove within
milliseconds through the draw-off tube and the draw-off nozzle. The process dictated that this was
achieved by means of a fixed thread discharge length. The discharge length into the rotor could be
changed only by adjusting the feeding depth of the thread into the draw-off tube, thus making
simultaneous, constant thread discharge into the rotor difficult. The range of variation in piecing
quality was too wide in some cases.
The AEROpiecing process uses a thread accumulator in the robot. This system conveys the thread
as far as the draw-off nozzle outlet
(See Figure 1). From this position, the end of the thread is discharged into the rotor.
However, to ensure that the discharge length can be changed, the thread length is adjustable. This
task is performed by the pneumatic AEROpiecing thread accumulator, into which the required
discharge length is fed and pulled. When the piecing process starts, the loop of yarn pulled in is
released for discharge into the rotor by switching off the vacuum. Patents have been applied for
with reference to this simple and retrofittable solution.
The starting point for AEROpiecing technology was the use of high-speed video technology. This
enabled the piecing process occurring in the millisecond range to be analyzed and systematically
Figure 1: AEROpiecing process with variable thread discharge
Detecting Piecings In The End Product
A further challenge posed by the
analysis of piecing quality using AEROpiecing is the detection of piecings because they are
difficult to visually identify in the end product. In order to demonstrate this quality feature to
customers, piecings were marked with bleached fibers. A special method used during piecing enables
extraneous fibers to be introduced into the already rotating rotor shortly before piecing, without
disturbing the piecing process. These extraneous fibers are then integrated into the piecing zone.
The piecings marked with extraneous fibers then become clearly apparent in the finished fabric
under ultraviolet light.
Measuring Process For Documentation Purposes
No standardized measuring and
analysis processes are available that can be used to assess quality in the case of piecing
technology as a specific technical subject field. Therefore, Rieter has drawn up a new and more
suitable standard for documenting the new quality level of piecings produced using AEROpiecing.
Stereomicroscope with digital scanning: The piecings are scanned digitally in
sections using a stereomicroscope. The images are combined into an overall picture by means of
special software. The different fiber structure and fiber orientation of piecings produced using
AEROpiecing and conventional methods can be seen clearly in the pictures.
Tenacity/elongation graph: In order to demonstrate piecing quality, a large number
of piecings were produced using AEROpiecing with the robot on the R 40 rotor spinning machine.
These piecings were tested for tenacity and elongation behavior (count-related tensile strength and
breaking elongation) in a textile testing laboratory. The individual readings are presented in the
form of a bivariate point distribution in a stress-strain diagram
(See Figure 3). The outliers — especially the weak points — are very important for the
assessment in this case, because they can result in downstream processing malfunctions causing
considerable production loss.
The characteristic curves in the
stress-strain diagram show that a stick slip effect occurs in the tenacity/elongation behavior of
some piecings. This is apparent in the diagram from a characteristic curve with a drop in the
(See Figure 4). Readings of this kind reveal considerably more significant weak points
than the presentation of tenacity and elongation. Because this behavior could have very disturbing
effects in downstream processing, the stretch recovery from the tenacity/elongation characteristic
curve was also included in the assessment in further analysis. Stretch recovery is represented by
the surface (integral) below the characteristic curve.
Work/mass graph: A further quality feature of piecings is an increase in mass.
This is shown in relation to the stretch recovery of the given piecing
(See Figure 5). The relevant increase in mass of the piecing was also measured in the
textile testing laboratory. Determining the increase in mass is complicated. To date, no automated
measuring process is available. The mean increase and maximum increase in mass, and the length of
the piecing must therefore be determined visually in each measuring diagram. Shown as a bivariate
point distribution in the stretch recovery/mass increase diagram, those piecings can be marked
which are accepted by the machine’s yarn clearers on the basis of the specified limit values
(identical with yarn clearing on the machine).
Length/mass-peak graph: Finally, the piecing length/mass peak diagram is referred
to for assessing the quality of the piecings. A percentage scale relative to the rotor
circumference has been entered for the length axis
(See Figure 6). In this case, the length of a rotor circumference corresponds to a value
of 100 percent. It is apparent from this diagram how clearly the new AEROpiecing technology differs
from conventional piecing methods. The very narrow variation range of the piecings produced using
the AEROpiecing process represents a considerable quality advantage.
Editor’s Note: Frank Baier is an associate of Rieter Ingolstadt Spinnereimaschinenbau AG,