Rubber conveyor belts for sealing purposesCOMPANY PROFILESIG Societa` Italiana Gomma SpA is a renowned Italian manufacturer of rubber conveyor belts. More than 50 years of experience in this industry means that the company is at the forefront of the industry, with excellent references in the majority of the world.
The customer-oriented approach that distinguishes SIG SpA means that it is possible for it to meet its customers needs in an extremely flexible way, especially when customization and the development of new products is required.
The entire manufacturing activity is located at SIG’s factory close to Milan in Italy where the company’s sales and R&D resources are also located.
INTRODUCTIONFor decades, conveyor belts have been the most suitable method to convey loose materials over variable distances, from a few metres to a few kilometres. The application fields are varied; more often, rubber conveyor belts are used in non-conventional sectors, such as the one that is described in this article.
Indeed, there are specific applications where rubber conveyor belts are not even used for handling purposes, but to protect and prevent the material conveyed by another belt from being scattered. This is the sector in which Sealtex belts, which are characterized by high crosswise stiffness and longitudinal flexibility, offer performances that were inconceivable up to a few years ago.
Environmental protection requirements, which are increasingly included in project specifications of modern conveyor systems, allowed significant development of the aforesaid technology in the last few years. Thanks to its mechanically simple system, it offers striking solutions to different problems.
APPLICATIONS OF THE SEALTEX BELTThe picture (Fig. 1 above) schematically shows the effectiveness of a Sealtex belt. It is installed above another conveyor belt and allows for the displacement of material loading and unloading points as required, as well as keeping the conveyor structure sealed in the remaining part of its development.
Thanks to their flexibility of use, Sealtex belts are typically installed along port quays. Here, the need to empty ship holds or to unload the material into different points within the storage area, requires the presence of movable openings along the entire development of the conveyor.
There are different technologies to meet the aforesaid requirements, but it is unquestionable that the use of a rubber belt offers incomparable simplicity of use, reduced maintenance, perfect sealing and essential absence of mechanical interferences.
So, for example, next to the loading hopper that receives the material from a continuous ship unloading system, it is possible to lift the Sealtex belt to offer suitable space and, by means of suitable chutes, the material can correctly reach the conveyor belt below.
Similarly, if you need to load a set of tanks or a large storage area, the Sealtex belt passes over the unloading movable carriage (tripper) and then it goes back to the original position after having surpassed the obstacle.
In both cases, loading and unloading carriages are equipped with suitable roller ways to allow lifting and re-positioning the Sealtex belt.
There are also simpler applications to cover the tunnels that pass on the side of the conveyor and that usually connect lower silos or contain pipes and service cables. Often, in the aforesaid cases, it is enough to adopt belts with reduced performances compared with Sealtex; however sometimes the use can be compared with the above-mentioned cases, for example when the project includes specific safety requirements because people may have to walk directly on the Sealtex belt.
The last evolutions of this covering and sealing technology provide for the use of the Sealtex belt in conveyor systems with telescopic belt. In the aforesaid projects, the Sealtex belt has to be fixed to the movable unloading end, while the fixed part of the conveyor includes a winder that recovers the exceeding part when the conveyor is shortened. The Sealtex belts are usually manufactured starting from 600–800mm widths for silo channels and openings, up to widths of more than 2m to cover and seal high-capacity belts being used for continuous loading or unloading of ships.
CONSTRUCTION DETAILSThe Sealtex belt is self-bearing because, for layout needs , it can be held only on its edges by means of specific side supports (Fig. 2). Indeed, to allow the passage of hoppers or movable unloading systems, it is not possible to support the belt in crosswise direction by means of nets or metal crossbars. This project restriction adds to the need to be able to lift the belt next to loading and unloading openings by means of very small diameter rollers. Fig. 3 clearly stresses these needs.
So, it is possible to understand the peculiarity of this type of belt that has to oppose suitable longitudinal flexibility to high crosswise stiffness. The manufacturer of the Sealtex belt is in charge of designing a product that, as a consequence, must be able to exploit the elasticity of rubber and of synthetic fabrics, and steel stiffness, as well.
At historical level and, for some manufacturers it is still a topical technology, the belts for the aforesaid applications were manufactured by dipping a set of steel bars into the rubber. The aforesaid bars had a suitable cross-section, which allowed obtaining the desired stiffness. At present, the available materials make it possible, on the contrary, to obtain the same results by using less steel quantities and automated manufacturing methods.
The design of the Sealtex belt provides for two layers of high elastic-modulus steel cables in the peripheral areas of the belt cross-section, thus allowing maximizing the inertia modulus of the system and the subsequent ‘beam effect’. This way, if you define the diameter and the density of steel cables and the
distance between the two respective layers, you can obtain the stiffness level that is required by design specifications.
The method to calculate the stiffness of the Sealtex belt derives from well-known elastic deformation equations for steels, with empirical (Fig. 5) and non-linear corrections to the model due to the presence of a different elastic means, rubber, which binds the two layers of steel cables one to the other in a non-
homogeneous way. Fig. 4 is representative, as it shows the result of a bending test where you can clearly see an abnormal deformation in the test piece, with respect to the behaviour of a simple steel beam.
It was previously mentioned that people may have to walk on the Sealtex covering belt: it is a crucial requirement to establish the stiffness level of the same belt. However, you cannot omit specific phenomena, such as the accumulation of water, the possibility of snow falls at a port, even if it is a remote possibility. In particular, slight differences in height for the two side supports are used to prevent water stagnation.
On this subject, particular importance is given to the size of side supports: they must be sufficiently large as to provide for a stable support to the belt, without allowing excessive side displacements that, on their turn, may cause the belt to fall from the supports.
Last but not least, it is absolutely necessary to supply the correct longitudinal tension to the belt to prevent twisting due to inevitable frictions that are generated during the movement of loading and unloading carriages. To assure it, an end of the belt is firmly fastened to the structure of the conveyor, while the other end is tightened by using a gravity counterweight.
CONCLUSIONSModern belt conveyor systems must preserve the features of the conveyed material and prevent it from being scattered within the relevant areas.
Particular loading and unloading needs not always allow using fixed enclosing structures; it is the typical application of Sealtex covering and sealing belt. It is a valuable component that comes from the same construction technology of rubber conveyor belts, which is expressly designed to be self-bearing and, at the same time, flexible to allow creating temporary material loading and unloading openings.
So, it is a simple solution that requires a thorough analysis of the requirements and the conditions of use, as well as a suitable design of the bearing structure, of tensioning and displacement systems, with special attention to the construction of the belt.
Bedeschi commissions two transshippers — ‘Ore Fabrica’ and ‘Royal Sesa’
into the holds of the Ore Fabrica, by using the same shiploader, to be retrieved by the cranes later on.
The system is fully remotely operated, and is capable of working in conditions up to 2.5m of wave height and wind up to 20ms. The table shows some of the salient features of the cargo handling system:
In the year 2012 two transshippers on which cargo handling systems have been supplied by Bedeschi have been commissioned — Ore Fabrica and Royal Sesa. One is for discharging iron ore from ocean going vessels and other one is for loading iron into them.
With the commissioning of floating transfer station (FTS) Ore Fabrica the world has witnessed a totally new phenomenon. The FTS Ore Fabrica is the world’s largest transshipper. It is set to revolutionize the way iron ore transportation is done in the world. To take advantage of the economy of scale, i.e. the larger the size of the vessel the lower the unit freight of the cargo,Vale has ordered vessels in excess of 400,000dwt, known as Valemax, to transport iron ore from Brazil to the Far East. Since these huge vessels cannot be accommodated in most of the ports, there was a need of a transshipment device, which could transfer the iron ore from the Valemax vessels into more manageable Capesize vessels. For this the transshipper which has been implemented is Ore Fabrica which is of 280,000dwt capacity.
The transshipper is fitted with five Liebherr-made cranes and each one feeds a separate 50m3 hopper located adjacent to them. Cargo is extracted from the hoppers by variable speed drive belt feeders, which deliver the cargo on a longitudinal conveyor belt. A combination of cross conveyor and another longitudinal conveyor, then leads the iron ore to a mobile shiploader capable of delivering cargo at 5,000tph (tonnes per hour) to the shuttle vessel’s holds. Thus the cargo transfer is done in a triple banking operation, with the FTS Ore Fabrica in the middle and the Valemax and shuttle vessel on either side. In case there is no shuttle vessel available then the cargo is loaded The system was commissioned in the first half of 2012, and is presently carrying out operations in Subic bay, Philippines. After the successful commissioning of the system, Bedeschi has received a repeat order for designing and supplying equipment for a second transshipper Ore Sossego, from Vale, the implementation of which is under way.
The second system which has recently completed the successful trial run is the FTS Royal Sesa. This system is implemented for Sesagoa and will be used for transferring iron from barges into ocean going vessels up to Capesize in Goa, India. The system comprises of two hoppers which receive
cargo from two Liebherr cranes. Each hopper is equipped with a variable-speed drive belt feeder, which feeds cargo to an array of conveyor system leading to a shiploader capable of delivering cargo at 3,000tph into ocean going vessels.
The shiploader is fitted with a shuttle system through which cargo can be delivered into all parts of the holds of the vessel. All the systems have been designed by Bedeschi and manufactured in- house in Italy, before being shipped to China where they were installed on the FTS Royal Sesa, under Bedeschi supervision. Trial runs of the system have been carried out successfully. The system will now be transported to India to commence operations.