Braiding machine
The braiding machine is an apparatus using the automatically previously strands or cords , also ropes, catheters and other linear products today braided be or composite parts can be produced.
Working principle
The braiding threads on bobbins are passed through bobbins in a braiding machine . The bobbins are sine-shaped milled into the machine bed (braided bed) by so-called vane wheels , moving corridors, whereby the braiding threads are crossed with one another and form the braiding in the so-called braiding point. The clapper or in Austria also docke (from the North German word doll ) are the main working organs of the braiding machine. They carry the braiding bobbins on which the braiding threads are located. Furthermore, the clapper compensates for the difference in length of the thread material, which occurs due to the relative movement of the clapper to the braiding point, and at the same time applies thread tension. For this purpose lead weights were previously used, which were called "plumb bobs". Compression springs are mostly used in current braiding machines ; the use of weights is usually limited to very large braiding machines for rope production. The clappers have a thread breakage monitoring, the braiding machine with thread breakage shut off. The coils can either be moved actively or passively removed from the coil by braking. With the latter technique, either the bobbins or the bobbin holders have notches in which a pawl or pin only releases thread material (allows the bobbin to rotate) when the braiding thread has sufficient thread tension. As you can see in the picture, the bobbins of the Barmer braiding machines have spikes on the upper side, in which a latch engages. If the thread tension increases as a result of the thread being withdrawn, a weight stored in the bobbin axis is pulled up and then lifts the pawl at the top point, allowing the bobbin to rotate and release thread material. This in turn reduces the weight, the pawl locks into the prongs and brings the coil to a standstill.
The resulting mesh is constantly pulled off with rollers, aprons or other pull-offs, then wound up or fed to a further production stage, for example automatic cutting to length. For the production of fiber composite components in the field of lightweight construction, u. a. Industrial robots are used to move the braid carrier (so-called core) and thereby pull off the braid.
The structure of the braids is strongly dependent on the number of clappers. The number of bobbins can only be changed to a limited extent with conventional machine types and usually also defines the nature of the product. There are machines that only have very few clappers (e.g. three clappers) as well as large machines that can be equipped with up to 800 clappers.
While the speed was previously limited by the quality of the thread material, nowadays it is more the construction of the machine itself, especially the friction of the moving parts, especially the clapper, due to the production of synthetic fibers with significantly greater mechanical strength. The bobbins can, however, be much larger due to more precise guides, which in turn leads to shorter downtimes due to a lower number of bobbin changes. The use of injection-molded plastic mallets also reduces the inertia, which allows both higher speeds and more efficient operation.
However, the basic functional principle of today's machines is identical to that of the machines of the last hundred years.
Round braids and flat braids (strand)
The classic division of the braids is made into round braids ( hose , cord or cord ) and flat braids (strand, also called Börtel in Austria ). With flat braids , all of the bobbins move on a corridor and the braiding threads cross each other completely. Since all threads (and thus clappers) follow the same path on the gangway, one speaks of a thread or a clapper set. The smallest flat braids can be made with three threads (see braid ). Usually, but not necessarily, flat braids are made with an uneven number of braids. In comparison, round braids are basically made with two bobbin shares and thus an even number of bobbins. The two corridors required for this are phase-shifted , one cluster of bobbins always moves clockwise, the other exactly counter-clockwise. The structurally smallest round braid can be made with four threads.
Design options for braids
The braid can be structurally reinforced by feeding standing threads along the braid axis. In the case of round braids, a soul thread (also known as a core) can be integrated. If this core has a geometrically defining shape, the process is referred to as braiding or overbraiding . Braiding is used, for example, in cable insulation and in the manufacture of fiber composite components. Further standing threads can be guided through the hollow shafts of the center axes of the impellers, which allows additional reinforcement or strain relief in the direction of the goods take-off. Elastic braids are produced in such a way that standing threads made of elastomer materials are fed to the braid in a tensioned state.
In principle, the geometry of the braid is determined on the one hand by the type of braiding machine, but in particular by the number of threads and the thread thickness. Another factor is the ratio of drive and take-off speed, with which the so-called braiding density or braiding angle is set. A slow take-off speed results in a dense and thick braid (high braiding density, high braiding angle), while a fast take-off speed results in a loose and easily movable braid (low braiding density and low braiding angle).
Another factor influencing the structure of the braid is the thread tension, which is determined by changing the tension spring hardness. With harder springs, the braiding threads are tightened and the braid becomes narrower. By using different thread tensions in the bobbins, for example, a serpentine braid can be made by pulling the braid to the left or to the right from the braiding point. In a similar way, by using thinner threads in one direction and stronger threads in the opposite direction, it is possible, for example, to produce cords that are similar to a twisted rope.
Similar to woven fabrics , different types of weave can also be realized with braids. The usual braided weave is the so-called 2-braid weave, whereby one braided thread always crosses over two others (floats). This weave is comparable to the twill weave in weaving. Further bonds are the 1-braid diamond bonds in half or in tandem of the clapper, which in turn corresponds to the plain weave or the Panama weave .
Special designs
If the bobbins usually always run the same path depending on the strands or braided hose, so-called switches, similar to railway switches, can temporarily separate the tracks and bring them together again later. In this way, for example, braids with interruptions, such as buttonhole braids , can be produced.
Newer so-called 3D braiding machines, in which the bobbins are guided on cartesian or concentrically arranged braiding beds, allow highly complex patterning options and also thick-walled components through the use of these changes.
With other designs, several career circles can only touch each other tangentially, so that thin connections between two cords are created at the points of contact, such as the passepoil braids . In a similar way, a circle of cord and a circle of stranded wire can be connected to one another, so that special braids, such as a cord strand, are created, which consist of a cord with a flat wing .
Other special designs are the so-called pack braiding machines, in which two or more sets of bobbins run on a mostly square or rectangular braiding bed. In combination with high thread tensions, braids are produced in this way, which are used in particular in sealing technology ( stuffing box ).
For the production of fiber composite components by means of braiding , so-called radial braiders are preferably used, in which the clapper is arranged on the inside of a ring, whereby the length compensation of the fiber material is kept low, which minimizes fiber damage caused by the process , especially with fiber materials sensitive to transverse forces such as carbon .
Historical
The first traces of a mechanical braiding device can be found in a book by Georg Philipp Harsdörffer, which was published in Nuremberg in 1653. According to the author, the device described there, which was driven by a hand crank, was invented in Utrecht. Around a century later, in 1748 the Englishman Thomas Walford from Manchester was granted a patent for a braiding machine for the first time. In the Wupper valley, Johann Heinrich Bockmühl is considered to be the inventor of this machine, although only improvements to the braiding machine can be traced back to him. The industrial production of braiding machines, at that time still sometimes referred to as belt gear or belt table , began in Germany around 1880. The manufacturers in Wuppertal -Barmen were leaders in this field . This braid, as they were often called, marked the beginning of industrialization in many places . Especially in areas where water power was available to drive the water wheel , these factories were built before electrification. Later these drives were replaced by steam engines or locomotives .
The braiding machines were arranged side by side on so-called braiding tables . These were simple wooden frames that had a drive shaft lengthways and that powered the machines individually via bevel gears . These machines were switched on by simply moving the machine so that the gears meshed. The expressions engaging and disengaging for switching on or switching off the machine also come from this time . The individual tables were driven by a transmission .
This thread break monitoring is remarkable in view of this time, as this purely mechanical automatic system without a sensor system known today was only available on these machines. On the side of each clapper there is a slider or a flap which is held in height by the thread tension via deflection levers or pulleys. If the thread breaks, the slide falls down and, as it is passed, pushes a laterally arranged release rod outwards or meshes with a switch, which in turn disengages gears. As a result, the machine or even just this braid is put out of operation without inevitably causing a fault in the braid (see illustration of thread breakage) .
Since weaving machines , similar products ( narrow fabrics produced), such monitoring was not possible at that time, the error-free flat braids triggered a large extent on the products of previously been known weaving. It was not until the 1970s that braiding machines were largely replaced again by the invention of needle looms and crochet galloon machines , which are much more productive.
The well-known manufacturers of braiding machines naturally settled in the areas where the braiding industry also predominated. Well-known industrial areas that had a large number of such products were the Wuppertal area in Germany and the Waldviertel (also known as the Bandlkramerland ) and the Vienna Basin in Austria . In Vienna itself, for example, the seventh district of Neubau was such an area. Street names such as Bandgasse or Seidengasse are still reminiscent of this time.
Since the braiding industry has migrated heavily to low-wage countries in the last thirty years , but only mass-produced goods are produced there, the number of braiding machines in Europe is now very low. In recent years, however, there has been an increased use of special braiding machines outside of the classic textile sector. These special machines are mainly used in the production of fiber-reinforced plastics , but also in the medical sector, for example the production of stents . The machines used here are based on braiding machines for the textile industry , but some are heavily modified in order to be able to process carbon , glass and aramid fibers as well as very fine metal wires .
Application examples
- Rubber strands that are used as pull-in elastic in garments
- Candle wicks in the form of braided cords
- Snakes or ricracks that are sewn on as decorative braid
- Shoelaces ( shoelaces ).
- Climbing ropes as multi-layered round braids
- So-called pull-in stockings, in which the short section of braided hose is pulled together to grasp a cable or hose and pull it into a protective tube or cable duct, similar to a Chinese finger trap
- Braided electrical lines in which the cable sheath is either protected by a braid (e.g. iron supply line) or replaces it (so-called pendulum cord for hanging lamps with automatic retractor, or recently more and more often for headphone cables), in order to achieve greater flexibility Cable to reach
- Braids for plastic reinforcement (e.g. made of carbon , glass , aramid fibers )
- Copper strands that are used as a ground connection in vehicle batteries.
- Desoldering braid .
- Hose braids, which are used in the sanitary sector due to their kink resistance (steel wires around rubber hose)
- Braided shielding of coaxial cables
- Thermal insulation hoses
literature
- Bernhard Lepperhoff: The braiding . Leipzig ( 1914 )
- Herbert Vogler: Was the braiding machine invented in Barmen? . Band- und Flechtindustrie, 36 (1999), pp. 43-46
Web links
Individual evidence
- ↑ Harald Engels: Handbook of narrow textiles: the braiding technology; Part 1: Machines and processes for the production of conventional braids . Ed .: FB Textile and Clothing Technology, Niederrhein University of Applied Sciences, Mönchengladbach. Department of Textile and Clothing Technology, Niederrhein University of Applied Sciences, Mönchengladbach 1994.
- ↑ Yordan Kyosev: 1 - Introduction: the main types of braided structure using maypole braiding technology A2 - Kyosev, Y. In: Woodhead Publishing (Ed.): Braiding Technology for Textiles (= Woodhead Publishing Series in Textiles ). Woodhead Publishing, 2015, ISBN 978-0-85709-135-2 , pp. 1-25 ( sciencedirect.com [accessed January 14, 2017]).
- ↑ Megabraider. Retrieved January 14, 2017 (English).
- ↑ Textile materials for lightweight construction: Techniques - Processes - Materials - Properties . Springer-Verlag, Berlin Heidelberg 2011, ISBN 978-3-642-17991-4 ( springer.com [accessed April 5, 2019]).
- ↑ Recent Developments in Braiding and Narrow Weaving . Springer International Publishing, 2016, ISBN 978-3-319-29931-0 ( springer.com [accessed April 5, 2019]).