According to warp knitted lace machine builder Karl Mayer, lace fabrics want to do one thing above all else and that is to please people. The knitting yarns interact artistically with each other to create eye-catching, delicate pattern details and attractive grounds and the expertise and know-how of specialists are needed to efficiently produce these delicate knitted fabrics with their many different patterns, the German company says.

According to Karl Mayer, the raschel lace machines used must be able to work a wide range of different lappings and process a variety of different materials and this must be done at top speed. This is said to be the ultimate challenge, especially when it comes to feeding-in the yarn to the knitting point. “It is particularly difficult to reliably knit fancy yarns, such as Lurex, bourdon or viscose yarns, at high machine speeds. This becomes even more difficult when these yarns are used as the pattern yarns, because the yarn consumption fluctuates. A large amount of yarn is used to produce the actual design elements, whereas less yarn is used when working the transition zones between them,” experts at Karl Mayer say.

Yarn feed systems

Describing the processing of more difficult fancy yarns, Karl Mayer says:  “In general, there are two ways of feeding pattern yarns on lace raschel machines. On the one hand, creels having a large number of bobbins can be used, which is ideal for conventional, standard production. On the other hand, pattern beams can be used, and these are particularly beneficial when producing small- and medium-sized runs. The advantages of these include their low space requirements, short setting-up times, low capital outlay and high level of flexibility. Because of the nature of the technology, the yarn paths are short when using pattern beams, and this is a prerequisite for processing more difficult fancy yarns, such as Lurex, bourdon or viscose yarns. The yarns may become twisted when the yarn feed paths are long.”

“However, in the past, the use of pattern beams was restricted by the yarn feed being controlled passively. During the knitting process, the yarn needed was taken off from the pattern beams and subjected to extreme stress at high speeds. This meant that the speed had to be reduced to 600 min-1. Karl Mayer has therefore developed active pattern beam drives to enable the efficiency potential of high-tech lace raschel machines to be fully exploited. The positive pattern beam drive (PPD) has already been used successfully on the JL 42/1 machine (click on image above right to enlarge), among others, and presented in ‘Kettenwirk-Praxis’ 2/2010, pp. 38-39. The second generation of PPD, with his new features and customer-oriented improvements, is now available.”

PPD increases efficiency

An electric motor at every beam is responsible for delivering different amounts of yarn accurately, even at high operating speeds. The drives are computer-controlled and are said to guarantee constant yarn tension levels, which are measured constantly in order to do this.

Karl Mayer says this allows raschel lace machines to achieve their top speed potential of up to 850 rpm and show that they are first-class machines. When processing different materials, the distortion and looping that used to be visible to a greater or lesser extent are now said to be minimised and a fabric with a perfect appearance is produced.

The positive, slip-free drive is also said to mean that time-consuming balancing and re-balancing of the pattern beams are no longer necessary, which is an advantage in terms of manpower requirements, storage and machine availability compared to operating with disc brakes.

The construction of the pattern beams that can now be produced is also said to be an additional benefit. With package diameters of 14 cm, the new style beams are said to have increased the running time by about 50% and make full use of the warping length, thus reducing downtimes compared to the old system.

In addition, Karl Mayer says, the actively driven pattern beams can also be used, for example, to work separating lines and panel borders, even when the number of repeats is small. The version fitted with disc brakes needs at least 10 to 12 threads for the yarns to run off. Compared to delivering yarns from the creel, the changeover times for pattern beams are said to be generally shorter when processing short runs and when the yarn has to be changed frequently. The capital outlay is also said to be lower and the storage requirements are minimal.

User friendliness

When developing the active pattern beam drive system for lace raschel machines, Karl Mayer says it paid particular attention to ergonomics and reliability. For example, all the operating commands and relevant parameters are input at the Operator Interface (OI) and the customer can also allocate the pattern beam drives to the individual string bars at the OI.

Karl Mayer adds that it also thought of the user as far as the care and maintenance of this new system are concerned. The drive unit is said to consist of exceptionally high, maintenance-free components and can be exchanged easily by the user. The entire concept aims to make it easier to change the pattern beams.

PBW and PPD – dual system provides additional benefits

Another Karl Mayer machine model that is said to enable the potential of high-tech raschel lace machines to be fully exploited is the PBW 130/2 pattern beam warping machine. “The machine produces precision-wound pattern beams with an optimum bi-conical structure, and thus guarantees perfect yarn running, even when processing difficult yarns. With their neat edges and perfect wind, these precision-warped yarn carriers can be let-off perfectly at lace raschel machines using the pattern beam drives,” Karl Mayer says.

According to Karl Mayer, the PBW 130/2 not only operates with a high degree of precision but it is also extremely fast. The warping speed is said to be 60% higher than that of the HDSM version.