MechChem Africa March 2019

⎪ Products and industry news ⎪

Dispersible polymer powders for biocide-free wall paints added until just prior to application, thus eliminating the need for adding biocides during production. As the paint dries, all that evaporates is water. Thanks to the polymers, the paint adheres well and has good spreading properties.

Munich-based chemical company, WACKER, will be introducing its new NEXIVA product line at this year’s European Coatings Show. According to the company, with these dispersiblepolymerpowders,manufactur- ers can now produce interior wall paints in powder form. The technology does not require the addition of biocides andoffers key advantages when it comes to storing and transporting paints. Mostwallpaintsareproducedusingwa- ter-based binders or rawmaterials. When used in paints, however, water provides a favourable environment for microbes and bacteria. In order to kill these organisms, the paints are typically formulated with biocides to make them last longer. There is however a problem with biocide use. Once the paint has been ap- plied to the wall and begins to dry, liquid components evaporate, allowing biocides to escape into the air. In some people, bio- cides can trigger allergic reactions upon inhalation or skin contact. By developing NEXIVA, WACKER has now created a technology for the pro- duction of biocide-free paints based on spray-dried polymeric binders suitable for producing interiorwall paints in either liquid or powder form. Paint manufactur- ers can use NEXIVA to create individual paint formulations, just as they can with traditional binders in dispersion form. Powder paints remain stable, even without the addition of preservatives. Water for redispersing the paints is not

In addition, paints are easier to trans- port and store when they are in powder form, as they weigh less, for instance, and can be packaged differently from liquid paints. Unlike traditional wall paints, pow- dered versions do not freeze in the cold, nor do they thickenwhen exposed toheat. www.wacker.com

Paint containing NEXIVA: in powder form (left) and redispersed with water (right).

Expanded metal remains cost effective material stove-enamelled, plated and galvanised.” “One of the most important features of expanded metal is its inherent struc- tural integrity and strength,”Quinlan says, adding that this also permit light and air to pass freely through it. The company produces expanded metal with a raised mesh, known as Mentex, and with a flat- tened surface, known as Flatex.

Mentis Expanded Metal continues to be aneconomical and cost-effectivematerial, since the manufacturing process ensures optimum material integrity and strength and allows it to be used for a wide range of applications. LanceQuinlan, national technical sales consultant, Andrew Mentis explains that the material is made by slitting and ex- panding a solid sheet of metal into a web of diamonds. “High quality local mild steel is used in the manufacturing process, but any other ductile metal is also suitable,” he explains. “The metal sheet can, in fact, be ex- panded up to ten times its original size, losing no material in the process and resulting in a remarkably light mesh,” he says. “Thefinishedproduct canbepainted,

The range of mesh sizes and thick- nesses of both Mentex and Flatex is extensive, ranging fromthe smallestmini- meshes with openings of 2.0×4.0 mm and a thickness of 0.4millimetres to the larger versionswithopenings of 75×200mmand a thickness of 6.0 mm. The expanded metal can be bent, shaped to radii, angled or notched. www.mentis.co.za

The basics about blasting: A CTC course All mining operations require blasting at one stage or another. Blast hole drilling is used in miningwhereahole is drilled into the surface rock, packedwith explosives and detonated. The aimof this technique is to induce cracks in the inner geology of the surrounding rock, making deeper mining possible.

Three types of explosives are permitted, each being designed for a particular type of operation for maximum safety – and only approved detonators may be used for coal mine blasting. The CTC in Emalahleni offers an interna- tional recognizedUnderground and Surface blasting qualification. Theminimumrequire- ments for this qualification are Gr11 with mathematics and English as subjects. When the basic training is completed, students receive a log book to completed on the mine where they are employed, and for private students, CTCwill arrangeaccess toa mine forwork experience.When all modules are completed, a Board Preparation will be booked and a final practical assessment underground. After the learner has completed all of the above, the student will be allowed tomake a booking for the DMR Blasting Board Exam. www.ctctraining.co.za

severity from I to III. Methane gas is re- leased during the coal mining process. And in underground coal mines, such as those in Emalahleni, there is an increased risk because the coal dust can explode as a direct result of the ignition of flammable gases such as methane or operation-induced igni- tion caused by either blasting, machinery or faulty equipment. “Ignition can be caused by the shock- waves created by the blasting itself, hot gassy products of the detonation mixing with methane and air, and/or hot solid particles ejected by the explosives reach- ing the methane gas mixture,” explains JohanVenter, managing director of Colliery Training College (CTC). For coal mining, specifically designed explosives and detonators are required in order to ensure a safe blasting process.

The drilling of blast holes is traditionally used when the mine would like to explore themineral compositionor potentialmineral yield of an area that is being considered for futuremining. Blast holes can be considered a fundamental step in the exploration pro- cess of minerals, including coal. Blast hole drilling is specifically used in coal mining to break up the rock and hard minerals in order to extract the coal. But when it comes to coal mining, all seams are considered to contain gas and the degree of the gas problem present may vary in

March 2019 • MechChem Africa ¦ 37