In the haulage business, having your trucks sent back from the weighbridge because of over-weight or under-weight containers is a costly exercise.
A new loading system installed at Malteurop Australia now fills 25-tonne containers to within 20kg of the target weight. This equates to less than ±0.1% variation from the target payload, and is significantly better than the requested performance.
Malteurop Australia needed to resolve a weighing issue when filling 40ft containers with malt. When fully loaded and check weighed at the weighbridge, a 40ft container could be found to be overweight. At this point in the supply chain, rectifying an overweight container means there will be obvious double handling and additional production costs.
Overweight trucks were being returned from the weighbridge so that excess product could be removed. This process could mean vacuuming the product out or piercing the plastic liner. The outcome of this also adds the risk of poor container presentation to the customer.
Double handling and increased production costs are also an issue where underfilled containers occur. Underfilling means trucks return to the filling station to receive additional product to meet the specification for the load.
Malteurop Australia approached Active Weighing Solutions for a weighing solution that would enable containers to be loaded within ±0.5% of the total batch. The specification also required the loading system to run at 90t/h (taking about 15-16min to load a nominal 25t batch).
Custom design and 3D modelling
Active Weighing Solutions proposed a pivoted weigh screw conveyor (PWS-C) as a solution to improve out-loading weighing accuracy. Pivoted weigh screw feeders and conveyors fully enclose the product stream and are particularly useful where weighing accuracy is important, the product flow is consistent, and the material is dusty or hazardous.
This weighing solution is also suited to restricted space situations. (And in this case there was very limited room available in the plant to retrofit more equipment into the loading system.)
Active Weighing Solution’s engineers visited the site and measured up the existing plant. They created a CAD 3D model of the proposed solution. The model showed the existing plant constraints and the location of a custom designed screw pre-feeder and a pivoted weigh screw conveyor.
This visual representation helped plant management to truly understand how the finished weighing equipment would fit into the available space. The operations manager said that “being able to view a 3D model of the finished product assisted in presenting the concept in a graphic and transparent way. That clarity and understanding the special arrangement made the project much simpler to put forward, justify and ultimately deliver.”
The entire pre-feeder and pivoted weigh screw conveyor installation is contained on an existing mezzanine situated above the truck loading position. This location has the additional benefit of providing workers with easy access to carry out routine maintenance.
The CAD modelling and attention paid by Active Weighing Solutions engineers to careful measurement also aided easy installation of the upgrade to the container loading system.
Engineered for accuracy
Applying a constant weight model design approach to a pivoted weigh screw application ensures the highest possible accuracy. This is achieved through matching screw diameter, pitch, fill capacity and speed, and considering these parameters along with flow rate and material bulk density.
The accuracy that can be achieved in each situation depends a great deal on accommodating these design criteria and parameters, and the real-world applications. Pivoted weigh screws perform at their optimum when operating at a constant weight, delivering the same accuracy across the whole operating range.
The configuration required for Malteurop Australia called for a pivoted weigh screw with pre-feeder. The pre-feeder controls the rate of feed into the pivoted weigh screw and allows the screw to run at a constant weight, and therefore with the highest possible accuracy.
According to Active Weighing Solutions Director Nigel Saul: “The pivoted weigh screw is a great alternative for dusty and toxic products or applications where there is very little height available. We can reliably get within less than ±0.5% if material testing can be performed or ±2% using static weights.”
Active Weighing Solutions
03 9873 7677