Latest developments in reverse rollercoating19 June 2004
Bergi have harnessed their years of experience to the new generation of rollercoaters acquired from the acquisition of Incoma (now integrated into the Bergi Group along with Tanmac). They now offer working widths from 1800mm to 3400mm with machines which can work in synchro, reverse and both synchro/reverse modes, for processing skins, splits, sides and whole hides (see Leather International, December 2003, page 32). The latter is ideal for processing leathers for automotive and furniture upholstery as well as garment leather applications. Each machine can hold up to four engraved rollers (three for the Supercoat 3400 models) and they have an option of extra gantries for storing and working with additional rollers. The high level of production and competition created by tanners' customers in terms of novel finishing applications have led to Bergi developing more and more flexible machines. The latest models have to be capable of producing specific applications such as the latest developments in stucco finishes for corrected grain or for upgrading full grain leather as well as special finishes and sealers, also in reverse mode for soft leathers. Finishing upholstery hides At present, Bergi's greatest demand is for their Supercoat R 3400 (reverse mode) machine which has been designed for finishing whole automotive and furniture upholstery hides. The greatest advantage of this machine is that the assembly system for conveying the hides is in a fixed position, whereas all the adjustments such as thickness, entry, exit etc are all adjusted on the coating roller. This allows the tanner the advantages of feeding in soft hides, thanks to the automatic alignment of the patented feeding device with the engraved coating roller. The working thickness can be adjusted independently on the left and right sides for the best coating results on the leather. It has been generally understood that if the hides are soft, staked but not trimmed, with holes, scratches or cuts near the edges, then the hide may get stuck under the coating roller when working in the reverse mode. This may also happen if inappropriate machine settings have been applied. The important difference with other rollercoaters is that the Supercoat has a unique (patented) device called ABS, which thanks to its sensitivity, automatically detects if a hide starts getting stuck or folds over. ABS will immediately lift the coating roller and the hide can be removed with minimum damage. The machine can then be easily and immediately reset and the hide can be re-introduced after trimming. The operators of this machine very much appreciate the speed and ease of cleaning. It may be opened and any working area cleaned in a matter of a few seconds. Also, the washing tank can be easily removed and washed with a pressure washer. An alternative to Bergi's reverse only model, is their Supercoat/RS model which is the only existing whole hide dual mode (reverse and synchro) rollercoater. This model is especially suitable for tanners and dressers who process small lots of leather in both reverse and synchro modes, where purchasing two different machines is not justified. The basic design characteristics of the dual mode machine together with its special accessories allow a quick change between the reverse and synchro modes. This model has separate forward and reverse doctor blades and two detaching devices, one installed at the outfeed of the rubber transport conveyor and another at the outfeed of the coating roller (patented). This allows the machine to be installed in front of a drying tunnel or a spray line. The dual mode model, which was launched at Tanning Tech last year, is already working successfully in commercial tannery production. Upgrading furniture upholstery hides - new stucco method Recently, the stucco method of upgrading has been evolving using a rollercoater instead of a manual application. These new processes are realised using a combination of suitable chemicals and machinery. Bergi's rollercoater models, Supercoat R and Supercoat RS, are now able, with the use of specific stucco rollers, to apply a stucco finish covering defects such as scratches, horn rakes and other marks without applying excess finish on the unaffected areas. Results obtained so far have shown that 2.5-3.0g per sq ft for leather with superficial defects and 3.5-4.0g per sq ft for deeper defects is adequate. After applying the stucco with a rollercoater, the leather is transferred to a tunnel dryer with a working temperature between 70°C to 80°C followed by a hide stacker. After 24 hours rest, the leather may be buffed. For superficial defects, the buffing process is done in two steps: first with coarse paper followed by a fine buffing paper. For deeper defects, the buffing process is done: first with coarse buffing paper, then hand stucco for the deepest defects only, followed by buffing with a fine paper. The hides should rest for a few hours following the hand stucco application. Production can vary from 120 to 180 hides per hour using the stucco finishing system with a rollercoater. If this process is done correctly, the double-stucco method will give the leather a better mechanical resistance and improvements have been seen on crack test results. At this point, the leather is ready for finishing. With the Supercoat R 3400 or RS installed in front of a spray line, it is possible to finish leather in a single passage. The first coat is applied with the rollercoater, details of which vary according to the type of leather and then immediately afterwards, wet-on-wet, it is sprayed in the spray booth, followed by drying and sealer coat in a second spray booth. This type of finishing line has found a lot of interest in the tanning industry as the main advantages of coating by rollercoater are savings of approximately 40% in finishing chemicals as well as the cost and safety benefits in reductions of environmental discharge during processing. In the reverse mode, it is also possible to apply oils and waxes to obtain impregnated leather on soft leather for furniture upholstery. The action of the finish application roller makes the waxes penetrate the leather, and the characteristics obtained are a pleasant two-tone pull-up effect. Finishing automotive leathers Many automotive leather tanneries are now using the rollercoater for medium and heavy coatings. Here the hides are normally quite uniform and of good quality. The automotive applications require quite rigid qualitative standards. Machines such as the Supercoat R 3400 and RS have been designed to meet these standards, especially to allow constant results over time by easily and precisely controlling the machine's parameters. A particular problem has been solved by Bergi with their range of specially manufactured helicoidal coating rollers which avoid excessive and early wear. For garment leather skins or sides, the Versus Soft machine can be supplied either in the reverse or the synchro and reverse models. The special feed system for the leather and the new helicoidal rollers enable soft leather as thin as 0.5mm to be processed. The detaching device makes it possible to work in-line with dryers and/or spray lines. For working in the synchro mode, the Versus soft model has two alternative methods for full grain and splits. To work in-line on full or corrected grain with a spray line, without moving the machine, the operator simply installs the engraved roller detaching device (patented). Then the leather can be removed by hand which is practical with the Versus model as it has a short conveyor. This method has a major advantage over spray finishing in terms of finish chemical savings. For soft splits for upholstery or garments, the process mentioned above is the same. However, compared to grain leather or corrected grain leather, splits present a different problem. When working in reverse mode with splits, the nap is raised giving an 'orange peel' effect on the finish which is not required. Therefore, Bergi have developed a new helicoidal roller for coating splits without lifting the nap. Consequently, the finished split becomes smoother with less finish applied. Environmental concerns When using rollercoaters to apply finish to leather, there are significantly lower VOCs, (volatile organic compounds) in the air. Roller-coating not only saves on chemical finishing products but is also environmentally less polluting even when combined with a spray line. With health and safety and environmental matters in mind, Bergi have developed a dry filtering unit, which has been patented, called Ecotiss. Ecotiss is to be installed on existing spray booths (see Leather International, December 2003, page 31).