In 2018, Stokman was approached by a customer who operated a dredger. The problem was that the tubes of the lower rollers worn away too quickly.
A high-quality conveyor belt roller is a requirement for these types of vessels because they operate in the most severe conditions, such as storm and salty seawater. In addition, contrary to onshore heavy-duty (and medium-duty) conveyor belt systems, a ship is naturally exposed to additional influences. These are caused, among other things, by the rocking motion and the rolling of the ship due to rough water, as well as during unloading by the unloading system. The motions of the ship adversely affect the running of the conveyor belt. In addition, the customer has opted to toe in the lower rollers of the parallel belt*. During unloading, the conveyor belt is pushed to the centre of the belt track due to the toe-in. Toe-in means that the rollers are not perpendicular to the running direction of the belt, causing additional friction. Due to the friction, in combination with the abrasive effect of the sand, the path of contact of the rollers wears away faster.
* Parallel belt: Belt line on the deck of the ship, running parallel to the cargo hold.
This was also the reason to determine, in consultation with the customer, how this could be prevented in the future. Since a one-size-fits-all solution is not always possible, we carried out a pilot with rollers covered with polyurethane (abbreviated PU or sometimes also PUR). We can finish the rollers in various levels of shore hardness and different properties, depending on the application. The right choice of polyurethane is a trade-off between wear resistance and application. After all, Stokman has a wide range of customers ranging from the food sector to the waste processing industry, all with varying requirements.
In January 2019, it was decided to install rollers with 2 different levels of shore hardness.
The difference became noticeable relatively quickly. One type is worn, whereas the other shows no signs of wear yet. The rollers present in the system are measured every 2 months to monitor the wear. Depending on the wear and the total life of the roller, it can ultimately be concluded whether the additional cost of the polyurethane outweighs the cost of a smooth steel roller. It may be a bit too early to take a definitive position on the most effective configuration, but the early signs are promising.
It is of course of great importance that medium-duty and heavy-duty bulk handling systems and, in particular, conveyor belt systems, suffer as little downtime as possible. Downtime means less efficiency and higher costs. An even more effective configuration in extreme conditions is of course possible. Our customers expect us to always look for the best solution, together. This blog is only one example of many from our daily practice.