Environmental and quality benefits accrue from investment.
“Today’s chemically-bonded sand metalcasting facilities are under increasing pressure to reduce costs and their impact on the environment, while improving and maintaining casting quality. One of the ways to meet these requirements is to invest in sand reclamation,” says Peter Petersen, Sales Director of Endeco Omega.
“Cost reductions after installing sand reclamation are made by reusing the sand after casting, buying less new sand and, with some systems, actually reducing the binder content at the mixer.”
“Due to less sand being dumped, there is an obvious reduction to the impact on the environment. Casting quality is improved by using less resin at the mixer and improving the sand grain’s characteristics so that it becomes more rounded. A more rounded sand grain has less surface area so requires less binder and can also lead to better compaction, which ultimately means less resin, less gas and better surface finish.”
Endeco Omega was engaged in 2015 to supply and install a new sand reclamation plant at Steloy’s Tungsten Road foundry facility
The rear of the Omega Gamma 15LL vibratory sand processor
Reclamation requirements
“In order to reclaim the sand, the equipment must first reduce the lumps back to grain size, then remove all the coarse/agglomerated sand grains, dust and fines. The sand must be cooled before reuse, and a portion of the binder removed to stabilise the LOI”
Characteristics of the sand
“After reclamation, the shape of the grain changes due to the attrition part of the process, where sand grains rub against other sand grains. The effect is that all sharp edges are removed and extracted from the sand as dust. It is also important that the AFS or average grain size does not change dramatically from that of the new sand first used. Therefore it is important the type of reclamation is not too harsh or damaging to the sand grain. The silica content of the sand should be as high as possible, and the Acid Demand Value (ADV) should be as low as possible, particularly if an acid based system such as furan resin is to be used.”
Grain shape
“The four main sand grain shapes are rounded, sub-angular, angular and compounded. The best type of grain shape is rounded, and so long as the correct type of equipment is used, this should be the shape of the sand grain after processing. It is also useful to note that the cavities of the natural sand grain become filled with resin, again leading to the more rounded shape, therefore requiring less resin absorption at the mixer.”
Options
“Three main options for sand reclamation include primary attrition, secondary attrition and thermal.”
Primary attrition
“Primary attrition can be further broken down into three main types: primary attrition–low level, primary attrition-high level, and combined shake-out/attrition.”
“High level refers to the loading height of the attrition unit. This type would typically be positioned in a pit and fed via a separate shakeout and vibratory feeder. It would not have its own shakeout deck and would be used where heavy castings or high throughputs would be processed.”
The Omega Gamma 15LL vibratory sand processor with a throughput of up to 15tph and a deck loading of 5,000 kilograms. Specifically fabricated for this machine is an acoustic booth that accounts for industrial noise and dust reduction
Accompanying the Omega Gamma 15LL vibratory sand processor is a reverse jet type dust extraction unit operating at 16,400m3 an hour and a PV 10 pneumatic conveyor
“Low-level units are floor mounted requiring no special foundations and can be used as a shake out as well as attrition unit. This type of plant is usually more compact, easier to maintain, and has a low investment cost. The main limitation is the maximum load capacity of three tons and a maximum throughput of 15 tons per hour.”
“Combined shakeout/attrition units are usually mounted in a pit but can take much higher load capacities.”
“All three types of primary attrition unit will consist of a heavy duty shakeout grid, a secondary perforated plate screen made from Hardox™ steel with 6mm diameter apertures, a third screen usually of stainless steel with 1.6mm apertures with a wedge cross section to enable a certain amount of self-cleaning, and finally a 1.4mm square aperture mesh screen for final sand classification. The actual attrition process takes place between the shakeout grid and the area prior to the final mesh screen. Here there should be sufficient retention to enable grain scrubbing and binder removal. With any type of attrition unit, there should always be the facility to remove flash metal, chills, reinforcing bars and other non-sand contamination. Therefore, a clean-out door should be provided to enable quick and easy access to the screen areas.”
Secondary attrition
“Secondary attrition can be employed after the primary attrition unit to enable further binder removal. These units are suitable especially for the alkaline phenolic process and can give typical levels of reclaim sand as the Furan process. Secondary attrition is also not as costly to purchase or operate as thermal, so it can be considered a cost effective alternative to thermal reclamation.”
“The basic principle of secondary attrition is to use a spinning drum at high speed to propel sand against sand and the force of the rubbing adjusted via the patented system of internal ceramic wheels. This allows just the right force to be applied to remove the binder whilst not harming the sand grain.”
“The two types of secondary attrition are hard and soft. The soft system uses the centrifugal method only and is more suitable for the furan process where not as much binder removal is required. The hard system uses the centrifugal method, as well as a pair of squeeze rollers that force the sand grains together to give greater attrition and binder removal. This type of unit is more suitable for reclaiming alkaline phenolic, silicate and green sand back to the core shop.”
The sand is transported to the G10 sand cooler/classifier with a throughput of up to 10 tons an hour and includes an evaporative water-cooling tower. The reverse jet type dust extraction for the cooler classifier operates at 5,500m3 an hour and also includes a PV 10 pneumatic conveyor
Omega’s unique low level range of mechanical reclamation plants mean that they can be installed without pits or special foundations
“In the case of the hard system, the spinning drum and the squeeze rollers have ceramic outer linings to give a much longer lifetime. Also, the pressure of the squeeze rollers can be varied to suit different sand grain structures and different levels of binder removal. The sand can be passed through the unit up to three times (three separate cells) to further reduce the binder on the sand.”
Thermal reclamation
“One hundred percent of all binder and other organic material is removed with thermal reclamation. The sand is generally better quality than when it was first purchased.”
“Typically, a thermal unit will run on either natural or propane (LPG) gas and operate at temperatures of between 600C and 750C depending on the type of binder used. The sizes range from 250kg/hour up to 12 tons per hour.”
“For alkaline phenolic systems, a special inhibitor must be premixed with the sand to prevent the alkaline salts from causing low temperature fusing of sand grains and ‘fritting’ of the sand bed.”
“Thermal reclamation with the addition of pre- and post-mechanical scrubbing can also be used for reclaiming green sand back to the core shop.”
Sand cooling and classification
“Often overlooked, the sand cooler/classifier is equally as important as the attrition unit because unless we remove all of the dust and fine particles from the sand, we will not see a reduction in loss on ignition (LOI) at the mixer.”
“Typically, a cooler/classifier would be a fluidised bed type with a copper tube heat exchanger for sand cooling. The fluidising air and the extracted air must be finely balanced to provide a negative pressure inside the fluidising chamber. This pressure can be adjusted according to the amount of fines in the sand.”
“Fluidised sand is not abrasive; therefore copper tubes can be employed as the heat transfer medium. Using copper, the cooling system can cool the sand from 300C to within 6C of the water supply temperature.”
“While no two metalcasting facilities are the same and all have different sand systems and requirements, many variations of sand reclamation plants are available. All that has to be determined is the amount of binder removal required and the level of investment.”
“Modern sand reclamation plants have evolved in such a way that even the smallest metalcasting facility can be accommodated in terms of floor space, investment and running costs.”
“We were approached by our client, Steloy Castings to help the company achieve cost savings in its sand department which would ultimately lead to an improvement in casting quality, minimise dumping and improve dust control. We had previously installed a mould pusher in the company’s Cobalt Street foundry. This facility produces static castings in stainless steel and high alloy metals for the petrochemical, pump and valve, pulp and paper, steel, and cement industries. Technical capabilities enable the production of sand castings ranging from 0.5 to 2,000 kilograms.”
“However we were tasked with upgrading the sand requirements for the Tungsten Street foundry, also situated in Bronkhorstspruit, Gauteng.”
Inside one of Steloy’s foundries
Steloy uses a CNC machining centre for pattern making
“This facility was established in 1990 to produce castings in cast iron, SG iron, nickel iron and a variety of carbon steel castings for the railway, ferro alloy, pump and valve and petrochemical industries. The foundry allows for the semi-automated mass production of castings from two kilograms to 50 kilograms and has three resin bonded moulding lines – light, medium and floor – for castings from two kilograms to 2 200 kilograms.”
“Steloy Castings was founded 30 years ago and, besides the two foundries in Bronkhorstspruit, has another one in Krugersdorp, Gauteng specialising in the production of static and spun cast tubes in stainless steel, high temperature steel and high alloy steels specifically for the petrochemical sector. The core of the facility consists of a fully equipped spun cast tube manufacturing plant and in-house pull boring and machining facilities. From this plant, they are able to produce sand castings from 0.5 to 2 400 kilograms and centrifugally cast tubes can be supplied in as-cast, partially machined and fully machined conditions.”
“The 460-employee company is one of very few foundries in the world capable of casting process tubes in high-alloy steel. The cast components that the company manufactures are supplied to customers in the pumps and valves, petrochemicals, chemicals, steel, power generation, ferroalloys, rolling stock, glass, aluminium and pulp and paper industries. Besides the OSHAS 18001 safety management standard, the company fully complies with the ISO 14001:2004 environmental management standard, the ISO 9001:2008 quality management standard and the OHSAS 18001:2007 occupational health and safety management standard. The company also fully complies with Pressure Equipment Directive EC 97/23. This means that the company is accredited to produce castings in materials that include carbon, low-alloy steels and stainless steels to manufacturers of pressure vessels for sale into the European common market.”
Rail Division and capital equipment investments
“Two and a half years ago, the company decided to increase its presence in supplying castings to the rail sector. Cast components play a small but crucial part in rolling stock, especially in bogies and motor components for coaches, wagons and locomotives. The company has been supplying cannon boxes, U-tubes, axle boxes, horn frames and other components to Transnet Engineering for more than 15 years.”
“A Rail Division was formed, and along with this a capital investment programme was implemented to increase capacity to improve product quality and NDT practices, to adhere to environmental requirements and to extend the production and manufacturing services with investment in machine tools to supply finished, machined components.”
“The company has now been selected by several original-equipment manufacturers to supply components for projects for new locomotives and metro trains in South Africa. One of the prerequisites was to acquire the International Railway Industry Standard (IRIS) certification, which the company has now done.”
“Apart from being the third South African company to achieve this certification the company is the only local foundry with IRIS accreditation. The IRIS standard focus is – among others – on human resource management, personnel evaluation, gap analysis and scheduled training, all factors that dovetail perfectly with the existing skills development programmes in South Africa.”
Investment in sand reclamation plant
Endeco Omega was engaged in 2015 to supply and install a new sand reclamation plant at the company’s Tungsten Road foundry facility.
Included in the equipment lineup is an Omega Gamma 15LL vibratory sand processor with a throughput of up to 15tph and a deck loading of 5,000 kilograms. Specifically fabricated for this machine is an acoustic booth that accounts for industrial noise and dust reduction.
Accompanying the Omega Gamma 15LL vibratory sand processor is a reverse jet type dust extraction unit operating at 16,400m3 an hour and a PV 10 pneumatic conveyor.
Steloy have also invested in new CNC equipment including a Victor Vturn-36
Steloy has invested in a CMM machine to meet the quality requirements for the rail transport industry
The sand is then transported to the G10 sand cooler/classifier with a throughput of up to 10 tons an hour and includes an evaporative water-cooling tower. The reverse jet type dust extraction for the cooler classifier operates at 5,500m3 an hour and also includes a PV 10 pneumatic conveyor.
“Omega’s unique low level range of mechanical reclamation plants mean that they can be installed without pits or special foundations. The low level range is also very compact in design and can fit into very small areas inside or outside of the foundry,” explained Petersen.
“Omega’s mechanical reclamation plants use the non-aggressive, dry attrition method of binder removal, which means that fragile sand grain structures can be effectively reclaimed without sand degradation. In fact, the scrubbing action of the attrition units will round the sand grains and make them more suitable for no-bake moulding. Also, due to four stages of sand scrubbing, a good reduction in LOI can be achieved.”
“This new capital investment will massively improve our carbon footprint, and lead to increased efficiency and reduce our dependence on deliveries of dried silica sand,” said Dannie Slabbert, MD of Steloy Castings.
For further information contact Roy Dias of Endeco Omega on TEL: 011 907 1785 or email roy@endeco.co.za, or Peter Petersen of Mondeco on 079 448 1277 or email peter@mondeco.co.za or visit www.endeco-omega.co.za
