Glass Industry Turns to BRECO and BRECOFLEX
With their shiny façades, modern skyscrapers, hotels and shopping centres have an elegant and futuristic appearance. Architects employ ever larger glass elements up to 18 m in length as a design feature. The dimensions of the insulated glazing production lines have increased accordingly. The world’s largest glass industry machine line currently being completed at Bystronic glass in Neuhausen in Baden-Württemberg, measures 160 m in length. Four different BRECO® and BRECOFLEX® timing belts are used – from standard belts to special custom-designed high-performance timing belts – for transporting the heavy glass weighing several tons and for driving the complex processing machines.
Insulated glazing consists of at least two glass window panes (standard) and up to four glass window panes (high end) separated by special spacer bars. Most glass panes are covered with a special coating to achieve maximum R-values. The space between the panes is filled with noble gases like Argon and Krypton. The spacer frames can be made of different materials such as aluminium, stainless steel, plastic or composite materials, and are bonded to the glass via the primary seal. This primary seal consists of polyisobutylene and is responsible for the gas tightness of the construction. The unit consisting of glass panes and spacer frame is filled with gas and pressed to the required dimension. In the last production step, the joint on the outer edge between the panes is filled with secondary sealant such as silicone. Once this secondary sealant has cured, the panes are firmly bonded together, gas-tight and ready for further processing or transport to the construction site.
Insulated glazing production line. Graphic: Bystronic glass
BRECOFLEX® timing belts transport glass elements weighing 7 tons
In insulated glazing production lines, the glass panes are tilted back at an angle of 6° from the vertical. They lie against rear panels equipped with small rollers, or are held at the rear by horizontal support beams with small rollers.
The glass panes are processed at a total of six stations in Bystronic’s production lines:
- The automatic edge deletion machine for removing metal coatings from the edge of the glass pane (e.g. UV protection).
- The glass pane washing machine for complete cleaning of the glass panes.
- The inspection station for checking for dirt and scratches and for bonding the spacer frames with the primary sealant.
- The turning station for turning the glass elements when required.
- The assembly and gas filling press where the glass panes are precisely positioned with the spacer frame, filled with gas and pressed to the required dimension.
- The automatic sealing machine which bonds and fills the joint on the outer edge between the panes, for example, with silicone.
The glass elements always lie on strong transport rollers or on the back of coated timing belts.
The timing belt drives perform three functions:
- They transport the glass elements through the 160 m long line,
- they feed the glass elements for CNC processing (automatic edge deletion and sealing machine), and
- they serve to precisely position the glass panes to a few tenths of a millimetre in the assembly and gas filling press.
The BRECOFLEX® AT10 timing belt was not able to provide the required tensile forces and stiffness in this machine line for transporting the huge glass panes measuring up to 18 m in length and 3.3 m in height. The next standard size is type AT20. However, the large teeth of the AT20 inevitably lead to larger deflection rollers and timing belt pulleys.
Timing belt drives in a row with the coated BRECOFLEX® ATS15 for transport and precise positioning during CNC processing. Photo: Mulco
Customer visit to the timing belt manufacturer
Stephan Kammerer, development manager at Bystronic glass, explains: “The pitch of 15 mm was exactly the right size for design and performance. BRECO offers this pitch in series production. However, we had a few special requirements, therefore four of our design engineers visited the timing belt specialist in Porta Westfalica with a catalogue of questions and concrete tasks. Our objective was to achieve the perfect design and configuration of the timing belt for our application.”
Engineer René Preßler, technical customer consultant at Mulco’s sales partner, Hilger u. Kern, initiated the visit for Bystronic glass at BRECO in Porta Westfalica. Higher stiffness of the timing belt was at the top of Stephan Kammerer’s list of requirements. The product development manager explains: “We position the glass elements against a positioning rod. Due to the elongation of the 3.5 m long belt span under the load of several tons, the belt contracted by a small amount after positioning the glass panes, which slightly changed the position of the glass panes. A tolerance of 0.5 mm must not be exceeded. Therefore maximum stiffness of the tension member is crucial for the quality of the insulated glazing panes.”
Bystronic glass development manager Stephan Kammerer (on the left) and engineer René Preßler, technical customer consultant at Mulco’s sales partner Hilger u. Kern. Photo: Mulco
Customized development and endurance tests
In a development project for Bystronic glass, BRECO equipped the ATS15 timing belt in comparison to the standard timing belt with a special thicker tension member specially designed to achieve the necessary stiffness and to withstand the occurring tensile forces. René Preßler explains: “The larger diameter of the tension member means that as the timing belt runs around the pulley, the diameter on which the neutral fibre of the tension member lies becomes larger. Therefore the timing belt pulleys have to be adapted to the diameter of the new timing belt to compensate for the change in length. This has to be taken into consideration when calculating the costs.”
In addition, it was necessary to prove in practice that the frictional heat created at the stainless steel support rails by the weight of the glass panes was adequately dissipated. The green textile-like nylon tooth facing PAZ was used for reducing the friction. Stephan Kammerer adds: “We had endurance tests carried out at BRECO in which the temperature increase of the belt was tested with the maximum permissible line load of 400 kg/m at two operating speeds. The results were very positive. We now use the friction pairing PAZ/stainless steel on all support rails subjected to high loads in our machines.”
Inspection station: Dirt and scratches are made visible in front of the black background with special lighting. On the top left, the gripper beam; on the top right, the support beam with smaller rollers. Photo Mulco
Warping of the timing belt
A last problem had to be solved regarding the ATS15 timing belt: the coating on the back of the belt. When a wide timing belt is coated on the back, the coating process causes varying tensions in the belt.
This leads to slight warping of the timing belt transverse to the direction of run. In the case of small light-weight glass panes, the warping can lead to undesired movement of the glass on the belts, and negatively affects the positioning accuracy in the machine.
Stephan Kammerer explains: “BRECO again recommended the optimum configuration and suitable thickness of the coating for this. It was 100% successful.
The belts are not subject to warping and we achieved the necessary stiffness. The backing has the required hardness and the PAZ coating reduces friction and wear, and the power requirement.”
View from below of the inspection station: BRECOmove timing belts hold the heavy gripper beam with threefold safety. Photo: Mulco
In the inspection station, the glass panes are not held by support panels, but by several horizontal 18 m long support beams. These support beams can be adjusted to the height of the glass elements. BRECO® and BRECObasic® AT10 timing belts are used here as traction mechanisms.
An additional beam with a length of 18 m, called a gripper beam, positions the spacer frame in relation to the top edge of the glass. Unlike the support beams, the gripper beam is in front of the glass and therefore in the operator’s area.
“In order to meet the strict safety guidelines, it was necessary to provide proof that the timing belts used can hold three times the rated load. The new BRECOmove high-performance timing belt is ideal for this task,” says Stephan Kammerer.
View from the rear of one of the five assembly and gas filling presses installed side-by-side Photo: Mulco
Much in demand for vertical axes: BRECOmove AT10 polyurethane timing belt
The BRECOFLEXmove timing belt was originally developed purely for power transmission with an improved tooth geometry, friction reducing film and a reinforced tension member. The safety that BRECOmove – as open length version – offers against tearing is so high that it is also ideal for use in vertical axes. René Preßler explains: “Demand for this product with the field engineers at Mulco’s sales partners was so high that the date of the series launch was brought forward.
BRECO excels in realising demanding development projects for its customers. Mulco partners’ field engineers are the consulting link in this process. On the one hand, they offer their customers exceptional solutions. On the other hand, they promote the further development of products by the timing belt manufacturer.”
A clever solution: One joined BRECO® AT10 timing belt drives four spindle drives in the huge assembly and gas filling press Photo: Mulco