After a brief overview of the main design goals, the manufacturing process of the opaque composite glass panel will be described in detail. The component consists of a ceramic coating, heat-treated glass and a smaller back plate, which are bonded in layers with a silicone adhesive. The backplane is segmented to form multiple connection points. While focusing mainly on the manufacturing technology and the QA-QC procedures used, this article will also discuss material properties and structural considerations to provide readers with a comprehensive overview.

Composite panels were developed for cladding components that meet the specific requirements of the project to form a uniform opaque and seamless glass surface. Mechanical fixation (Figure 1), protruding from the glass surface or through color interlayer or ceramic printing, has been agreed to be visually undesirable. Another requirement is that the combination must be used in overhead applications. Taking into account the behavior of the glass after breaking in this configuration, laminated safety glass is usually produced. In combination with mechanical fixings or supporting elements of sufficient size and/or quantity, it is necessary to ensure stability after damage.

Considering the visual intent, project details and safety considerations, the following design goals were formulated. They are used as a rough roadmap for the product development process.

By replacing a layer of glass plate with an aluminum backing plate and bonding with a silicone adhesive, the weight is reduced by more than that. 30% is possible. Select organic silicon as a suitable material for bonding glass and aluminum backplane. In the event of a glass break, laminar flow bonding provides redundancy and can safely transfer loads. The system does not require additional mechanical fixation and provides a uniform surface (Figure 2). It should be noted that silicones in laminar flow applications do not comply with current regulations (ie ETAG [1] or ASTM [2,3] or ASTM [2-4]).

The size of the backplane is limited to managing the thermal expansion between the bonding partners. This method allows the design to be optimized for the thickness of the silicone, but as the size of the backplane decreases, the number of connection points will increase.

Each backplane is connected to the supporting substructure through an adapter profile (iv.) and mechanically fixed to the backplane.

Figure 4 shows a 15 x 3 m high composite unit. There are up to 80 individual backplanes on the surface of the device.

For the structural design of the glass panel, the point load on the edge of the glass is considered to be critical. The stress level around the connection point is not important for the glass.

For the intended use, a self-leveling silicone adhesive was developed. Considering the processing time, a two-component silicone was selected. The material has been optimized for laminar flow applications. Various tests have been conducted to verify mechanical properties, long-term flexibility, adhesion, curing parameters, and pretreatment options. This leads to design concepts and application limitations for the selected bonding substrates and materials that are in direct contact with the adhesive.

The performance of silicone has been confirmed by an independent laboratory in accordance with ETAG 002 [1], ASTM C 1184 [2] and ASTM C 920 [3]. These standards provide guidance when testing material behavior, but need to be adjusted for the intended laminar flow application. The transverse elongation is limited, so the shear modulus is not equal to one-third of the Young's modulus assumed for linear applications. Table 1 summarizes the key material properties obtained through testing. 

The silicone layer is depicted using spring elements (Figure 4). These components are based on the parameters and design values ​​summarized in Table 1 and their thickness. The glass and aluminum plates are modeled using shell elements.

The area replaced by the spring element is used to convert the spring force into stress. As shown in Figure 5, due to the different stiffness of the backing element, the stress distribution in the silica gel is uneven. The verification concept considers the interaction of normal stress and shear stress of short-term and long-term loads. This method allows detailed structural inspections of all components for static loads, wind loads, seismic loads, temperature loads, and maintenance loads. For more detailed information on structural evaluation and design constraints, see [5].

The number of backplanes provides the number of fixed points, because in the event of a glass break, each backplane needs to transfer the load back to the supporting structure. The manufacturing process must allow each fixed point to be positioned within strict tolerances. The maximum deviation of any point on the surface, measured from a defined reference point, is agreed to be within +/- 2 mm.

The first concept is to try to connect the panels to the supporting structure by folding. Manufacturing tests show that this method is difficult to control. The selected design is based on the connection pins located in the adapter configuration file. The adapter profile is mechanically fixed on the aluminum tray. Using custom-made lifting frames, each lifting frame is fixed with a row of panels spanning a short length of glass, and the fixed point position can be controlled within the required tolerance range (Figure 7). The rotation of the aluminum plate will not affect the accuracy of the fixed point position.

The lifting frame requires a smaller manufacturing tolerance of +/- 2 mm, because all equipment and manufacturing tolerances will add up and eventually exceed the agreed tolerance. The manufacturing tolerance of the lifting positioning frame is required to be less than 1mm, and the measurement is started from its stakeout point.

The frame is equipped with adapters connected to the actual connecting bolts, as well as pressure elements that press the panel into the silicone bed to ensure that the distance between the outer glass surface and the connecting bolts is limited (Figure 8). Use silicone gaskets to maintain the distance between glass and aluminum. Silicone gaskets are cast from the same silicone material used for laminar flow applications.

Although the lifting frame provides precise positioning for a row of panels, the tolerances between adjacent frames also need to be considered. To ensure that two adjacent frames are within the agreed tolerances, a processing table is required (Figure 9). These tables are equipped with a peripheral profile that receives the connector element (Figure 10).

These connector elements can be positioned within 1/10 mm along the machine tool. After positioning the adjustable connector using high-precision measuring equipment, the components have been grouted in place to eliminate the risk of position errors during mass production. The table allows the use of stakeout references to precisely locate the glass unit. Since the glass used in the size of the process itself is subject to tolerances, an agreement has been reached on the pay-off edge. All glass tolerances are pushed to the defined joints. The flexible edge evacuation is designed to solve the glass tolerance and minimize any follow-up work.

A custom silicone pump designed for processing layered silicone runs along the track, servicing 16 processing stations (Figure 11). After the machine is cleaned and the glass is placed on the table, the pump will apply the required amount of silicone. Once a large enough positioning frame area is applied, 2 operators place the frame on the machine bed and clamp it in place (Figure 12).

Repeat this process until the glass is completely covered. In order to shorten the cycle time of the elevator, 5 elevator frames are combined into a process elevator. Each frame is connected using the same quick connector to fix the elements on the table. After completion, the composite panel was allowed to stand for 24 hours before repositioning to allow the manufacture of new units.

The described manufacturing equipment allows accurate positioning of the components within the 20-minute allowable silicone processing time. 1750 exterior wall units with a size of 10-15 mx 3 m can be successfully manufactured on the manufacturing line with prototype features.

The use of new methods and materials for large-scale manufacturing requires strict quality assurance and control systems. In order to reduce human error, all manual cleaning processes have been replaced by automated methods. The glass is machine cleaned, and the aluminum plates are packaged and delivered from the anodizing plant, and plasma treated before processing.

All system-related parameters (such as surface treatment methods, adhesion, mechanical strength) are tested and tested before implementation, and checked at the same time as manufacturing to ensure consistent quality. Control the size of the composite components on the processing table, and measure the actual bolt positions to identify deviations.

The manufacturing process of the composite glass panel has been described in detail. Outlines the key aspects considered during the development process. Facts have proved that it is possible to develop and implement new technologies and methods on a project basis. When contacting new technologies, the open mind of all parties involved is crucial.

(1) EOTA ETAG 002-1, Part 1 of Structural Sealant Glass System. 2012. (2) ASTM C 1184-13, Standard Specification for Structural Silicone Sealants. 2013. (3) ASTM C 920-11, Standard Specification for Elastic Joint Sealants. 2011. (4) ASTM C 1401-09a, Standard Guide for Structural Sealant Glass. 2009. (5) Doebbel, F.; Muller, United States; Teich, M. Marinitsch, S.: Nobel layered silicone applications. In: Challenge Glass 4 & COST Action TU0905 finals. Lausanne, 2014, pp. 347-352.

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