Screening test rig – Key to our success!

Test rig enables Multotec to do ‘quick and dirty’ tests to assist in rapid product development.

Although we continue to do test work at the Screen Test Rig located at 32 Forge Road, the rig continues to develop and evolve as we modify it to get more accurate and representative test results.

Some recent tests that have been successfully concluded include:

• Investigating cut point, blinding and screening efficiency of MBV mats on the vibrating screen for ore containing Fluorspar from Rooiberg.

• Separating spilled SMD mill ceramic beads from chrome fines using a sieve bend, for Metanza Jubilee Plant at Hernic Site in Brits.

• Investigated fine mesh (104 μm) panel development for drainage capability and blinding.

• 3D printed jet pump for Clean-TeQ trommel to ensure no resin is damaged by the pump impeller.

• Investigated efficiency of TeePee® Snow Plow in preventing tramming of material down the screening surface.

• Wish bone adapter strips to convert Trellstep screens to our modular panels.

But as we’ve adapted the equipment, we have had to remain aware of the effect that these modifications have on the accuracy of the results obtained. For example, by fitting cross cut samples on both the over and underflow of our vibrating rig, we can obtain more representative samples to analyse – but since the rig is closed circuit, removal of these samples will affect the test population.

Likewise, an interesting discussion was started recently – how do we define ‘cut point’ from the results? Screen panels are manufactured with a certain aperture size, but because of the aperture geometry (length to width ratio’s, cross flow or with flow, etc.) and media type (elasticity, shore hardness), the size of the particles passing through are not the same as the aperture size – but the size at which the panel is able to ‘cut’ the undersize material. If an international standard or norm exists, we will of course adhere to these; what is important here is to ensure that we use the same methodologies for repeatability and comparability.

However, the rig is also there to enable us to do ‘quick and dirty’ tests to assist in more rapid product development; the reason we continue to adapt and modify the rig. A ‘picture is worth a thousand words’ adage is useful here – in the image below, key points can be identified that has evolved or is in the process of changing:

Screen Test Rig

1. The white container on the left is our student centre and laboratory where our ASTM G65 abrasion machine is located, among other equipment. We can do either wet or dry abrasion comparative tests on metallic and elastomeric materials.

2. Just noticeable on the brick wall above the lab is a WiFi access point – we have successfully wirelessly monitored test results on the screen and dumped the data onto the Hawkeye™ database. One sensor on the screen has been in position for over two years now and provides screen vibration data every time the screen is operational. Part of our Digital Transformation journey.

3. The upper container houses our control centre – we are working towards the plant being controlled by a PLC (a type of industrial PC), so we can vary pump flow rates or vibrator motor speeds, as dictated by the test work required.

4. The red oxide frame on the upper screen level has been fixed in position to take a LuCoTec control panel. This is a technology supplied by a sister company that provides better isolation than conventional vibrating screen springs. We are in the process of fitting these air bellows onto our screen rig.

5. To the right, in the darker green colour, is our slurry abrasion rig – a closed circuit system of sump, pump and ceramic lined piping. We can place different test materials under the pipe outlet in a stream of abrasive slurry and get quick comparative results of wear life on different samples. For example, which has the better wear properties – a hard drawn or annealed wedge wire?

6. In the foreground is the channel leading to the process water sump (to the left of the image). A filter using activated carbon and ceramic beads is now in place to capture all solids. The sump naturally fills with ground water and can also be replenished from the ground water sump under MATO – an opportunity to reduce our water consumption footprint.

“Scientists investigate that which already is; Engineers create that which has never been.” – Albert Einstein

Areas that we would like to change soon:

• The grey coloured high angle conveyors are areas of concern. While they perform adequately because of the flights on the belts, there is considerable spillage at the transfer points. This affects the representation of the test sample. The modification would also allow us to better control the feed rate of the closed loop system, through inclusion of a vibrating feeder or apron feeder at the bulk hopper outlet.
• A swivel chute on the vibrating screen overflow to better handle wet and dry materials.

Finally, product development and screening test work would not be feasible without an enthusiastic bunch of employees willing to do the work.

“I believe one of our successes in this regard is our use of Vaal University of Technology students. We employ them to do the test work and they have the opportunity to complete their year of practical training,” says Ian Chapman, Engineering Manager, Multotec Manufacturing.