This includes AFS 25/35, AFS 45/55 and AFS 60/70.
The Silica Quartz mine, situated outside Delmas, on the border of Mpumalanga and Gauteng, has been supplying high-grade silica sand and grit to the glass, industrial, mining, filtration and leisure industries. Extensively used in water purification, filtration, separation and the glass industry, the product is dried and sized to meet the specific needs of customers. The mine has been in operation since 1972 and Silica Quartz is among the largest producers of high-quality silica in South Africa, used primarily in the production of glass and graded sand. The operation comprises of an open pit, crushing, and wet and dry screening processing plants for full beneficiation.
An overhead view of the wet screen plant that feeds the PLC controlled hydro-sizing plant
The impressive opencast mine has now opened Silica Quartz Wash Plant 3 to service the foundry industry with high-grade alluvial silica sand, one of the most commonly used sands in the foundry industry.
“Moulding sand is at the heart of the sand casting process. It must hold a shape well and capture the fine details of a casting, yet be permeable enough to allow gases to escape. Under the strain of having the moulding pattern removed from it, or while it is filled, it cannot crumble or sink on itself. When it is turned upside down it must not lose its form. The parts of a mould have to stay true while clamped together,” explained Le Roux Roets, one of the partner’s instrumental in getting a joint venture (JV) agreement in place with the owners of the Silica Quartz mine.
The Silica Quartz Wash Plant 3 is producing 125 tons-per-hour of AFS graded alluvial silica sand but the plant has the capacity to go up to 250 tons-per-hour or 30 000 tons-per-month
“Silica sand, or quartz sand as it is sometimes referred to, used in the manufacture of cores and moulds with synthetic binding agents such as furan and cold-box, must be well-defined and to the greatest extent possible, dust-free. Therefore, a process was developed that involves scrubbing and washing the sand, as well as hydro-screening it, before kiln drying with natural gas and the sorting into the final standard grading,” continued Roets.
“The purpose of this process is to achieve high sintering temperatures, low foreign body content and a high degree of chemical purity, which meet our customers’ requirements in all aspects – both for foundry use as well as for a wide range of industrial purposes. Apart from standard grading the process makes it possible to produce a wide range of special grading tailored to our customer’s needs.”
“Silica sand is quartz that over time, through the work of water and wind, has been broken down into tiny granules. In metal casting silica’s high fusion point (1760°C) and low rate of thermal expansion produce stable cores and moulds compatible with all pouring temperatures and alloy systems. Its chemical purity also helps prevent interaction with catalysts or the curing rate of chemical binders. Following the casting process, core sand can be thermally or mechanically recycled to produce new cores or moulds.”
The hydro-sizing plant consists of a jet-sizer that splits the material into five different sizes and eight hydro-sizing boxes – two sets of four that run parallel
“In metal production, silica sand operates as a flux to lower the melting point and viscosity of the slags to make them more reactive and efficient. Lump silica is used either alone or in conjunction with lime to achieve the desired base/acid ratio required for purification. These base metals can be further refined and modified with other ingredients to achieve specific properties such as high strength, corrosion resistance, or electrical conductivity. Ferroalloys are essential to specialty steel production, and industrial sand is used by the steel and foundry industries for de-oxidation and grain refinement.”
Silica Quartz mine
“The mine has been producing silica sand manufactured to ISO9001 accreditation. The operation comprises an open pit, crushing, and wet and dry screening processing plants for full beneficiation in the industries that it supplies. It produces 220 000 tons of wet sand per year consisting of 160 000 tons per year of glass sand and 60 000 tons per year of float glass sand and 80 000 tons per year of dry sand for the filtration and other industries.”
Le Roux Roets, Mine Manager Thabo Sebeya and Johan Stoltz
“The mine’s policy is that everything that it creates should be saleable and conform to all environmental policies. The specifications of the silica sand that are required for the industries that it has been servicing up until now has resulted in a sizeable amount of ‘waste’ sand being available for further processing.”
Sand manufacturing experience
“My partner in the JV agreement with the Silica Quartz mine, Johan Stoltz, and I have had many years of experience ‘manufacturing’ silica sand for the foundry industry. We both worked at the processing facility producing foundry sand from the alluvial sand deposit located at Donkerhoek near Cullinan, before the company was sold.”
The consistency of grain size, which includes roundness, allows users to reduce resin consumption and the stability increases productivity, thus saving on costs. Because of the consistency of the material, coating on the sand is regular and this in turn decreases gassing problems while giving superior permeability on the moulds and cores
“During that period we designed and manufactured the equipment that when it had processed the raw material, it was a sought after product in the foundry industry.”
“We have now put this experience into practice in the new venture that materialised because of the need by the Silica Quartz mine to process waste material from the primary manufacturing operation. We analysed the material and found that it would be a perfect silica sand for the metallurgical and foundry industry, once we had done further processing. The reserves of the mine are more than 25 years so we do not expect to be compromised on supply.”
New processing equipment
“Even though the material has already been through a washing cycle the initial processing of our product begins on the 250 ton-per-hour primary wet screen before being fed into our fully automated, PLC controlled hydro-sizing plant, where the loadcells and linear actuators are in 24/7 communication. This allows us to cut material to precise AFS specifications with a consistent 98.5% grade.”
The new rotary drum drier specifically designed to dry silica sand
“This hydro-sizing plant consists of a jet-sizer that splits the material into five different sizes and, eight hydro-sizing boxes – two sets of four that run parallel. Our IP on this plant is in the dense media separation on the silica quartz sand. Sizing takes place physically on the grain. This is followed by sieve analyses of the feed and we have found that over 85% of our grain sizes meet the AFS grading requirements.”
“This consistency of grain size, which includes roundness, allows users to reduce resin consumption and the stability increases productivity, thus saving on costs. Because of the consistency of the material, coating on the sand is regular and this in turn decreases gassing problems while giving superior permeability on the moulds and cores.”
Once the silica sand has been dried it is then sent to a storage area
“This plant is a critical element of the whole process and with all the automation and technology that we have incorporated, it is not a ‘throw together’ plant.”
“We are currently producing 125 tons-per-hour of sand but the plant has the capacity to go up to 250 tons-per-hour or 30 000 tons-per-month. If we increase the input of our wet screening process, we can increase our capacities according to demand.”
New drying equipment
“Once processed through the hydro-sizing plant, material is stockpiled according to its grade. From there it is transported to our rotary drum drier. Again, through Johan’s technical and mechanical experience and having been involved in the sand manufacturing industry for many years, we incorporated our own IP into the new rotary drum drier specifically designed to dry silica sand.”
“Currently we are processing between 50 and 60 tons-per-hour in this plant. All dried material is stored in a purpose built 3 000m² under roof building, again according to specification.”
“Delivery to client is done via our dedicated bulk tanker service.”
Foundry sand product
“More than 70% of our product is being delivered to foundries throughout South Africa. The primary target market is ferrous foundries. However, all other types of foundries use our product including the whole spectrum of non-ferrous foundries. For example, the AFS 60/70 specification that we manufacture is used by bronze foundries that are wanting a very fine or smooth finish to their castings.”
All dried material is stored in a purpose built 3 000m² under roof building, again according to specification. Silica Quartz manufactures the full spectrum of AFS specification foundry sand. This includes AFS 25/35, AFS 45/55 and AFS 60/70
“This same AFS 60/70 specification is also widely sought after in the refractory industry and it is a market that we will be targeting.”
“We manufacture the full spectrum of AFS specification foundry sand. This includes AFS 25/35, AFS 45/55 and AFS 60/70.”
“Industrial sand plays a critical role in the production of a wide variety of ferrous and non-ferrous metals and castings and is an essential part of the ferrous and non-ferrous foundry industry. Metal parts and components ranging from engine blocks to pumps and valves are cast in a sand and/or clay mould to produce the external shape, with a resin-bonded core creating the desired internal shape. These are costly components to produce and any defects or flaws found in them can have a devastating result on the foundry. If we can help with reducing scrap rates and reworking by supplying the foundries with quality sand, then we feel we have achieved our aim.”
For further details contact Le Roux Roets of Silica Quartz on 083 309 9955 or TEL: 013 665 7900 or visit www.silq.co.za