Increased adhesion strength
Increased environmental resistance of bonds
Design engineered to increase tile pullout force
Ceramic Tile Bond Failure
There are a number of causes of ceramic tile bond failure, including the following:
- The primer and adhesive systems that are used by most manufacturers of ceramic lagging provide a good initial bond when applied at the specified coating weight, but field experience attests to bond failure as service time extends. Laboratory testing by Elastotec has also identified that some widely used ceramic bonding systems deteriorate with exposure to moisture.
- An effective bond between ceramic tiles and rubber requires a minimum coating weight of primer and adhesive. A number of ceramic lagging manufacturers apply primer and adhesive using a spray application, making it difficult to ensure that the required minimum primer/adhesive coating weight is obtained on all tile surfaces and leading to tile/rubber bond failures.
- Lagging designs that only bond the ceramic tile on the back face results in less of the tile surface area bonded, leaving the edge of the tile exposed as a potential weak point for bond failure (see photos above).
- Bond strengths between the ceramic tile and the rubber backing can be lower than the applied shear forces from high tension conveyor belts, resulting in tile pull out. The selection of the optimum primer/adhesive/rubber combination is crucial to obtaining high strength long lasting bonds between the tiles and the rubber compound.
Tile Adhesion Testing
Elastotec has undertaken extensive outdoor testing of ceramic/rubber bond performance and has found that a number of primer/adhesive systems recommended by adhesive suppliers, provide a bond that initially offers rubber tear adhesion but, after prolonged exposure to moisture and UV, rapidly deteriorates.
Elastotec checks the integrity of the bonds throughout the outdoor testing process, where the tile/rubber bond is under constant stress. The testing is done by bending a strip of ceramic laging into a tight circle, with the ceramic tiles on the outside of the circle. The sample is then held in this position during the outdoor exposure period. The results are recorded at regular intervals and have been used to identify the optimum primer/adhesive system for long-term adhesion performance.
Outdoor Ageing Tile Bond Testing
|Primer||Adhesive||Initial Bond as Manufactured||Loss of Bond Strength After Ageing|
|1 Mth||2 Mth||3 Mth||4 Mth||5 Mth||6 Mth||3 Years|
Additional testing has been carried out to increase the adhesion strength between the rubber backing and the aluminium oxide tiles, as well as the steel for the pulley shell. This testing was undertaken using the tension pull method – (see photo and table opposite).
Based on the results of the Outdoor Ageing Tile Bond Testing, the Tension Pull Adhesion Testing and production considerations the adhesive system of Primer A3 and Adhesive B2 was selected for Hot Vulcanised Ceramic Lagging (HVCL), as this provided the best performance.
Importantly, the testing program has identified improvements in the ceramic/rubber bond strength, as well as eliminating the deterioration in bond strength due to moisture and UV exposure. This technology is an important and unique component of the HVCL.
Tile Coating – Primer & Adhesive
Elastotec uses a proprietary dipping process for the coating of the ceramic tiles with primer and adhesive, which ensures that all tile surfaces receive the necessary minimum coating weight of primer and adhesive. To date, more than 5,000,000 tiles have been coated using this method and there have been no reported bond failures.
Direct Bond Ceramic Lagging
Direct Bond Ceramic Lagging (DBCL) with Elastotec Direct Bond Adhesive (DBA) provides the highest adhesion levels between the aluminium oxidfe tiles and the steel pulley shell with bond strengths typically in the range of 20-25 MPa. Elastotec set an internal specification for tile adhesion of 20 MPa minimum – this is roughly 3 times the adhesion strength that can be achieved with a rubber.
The DBCL bond is rigid and as a result there is no cushioning of the tiles from impact when material is caught between the belt and the pulley.
An additional factor to be considered with the rigid bond is the lack of flexibilty under shear load as found in applications where high tension belts are used. This can result in excessive wear of the bottom belt cover.