(Published in Cast Metal Times, February/March 2003)
This article looks at some of the innovative designs offered by the DISA organisation for the blast cleaning of both iron and aluminium castings. Brief mention is also made to DISA systems designed to automate the fettling process.
Although the DISA organisation is synonymous with the supply of vertical-jointed boxless moulding systems, it is also a major producer of shotblast and shot-peening systems. The range of machines produced by DISA Industrie AG is impressive, covering almost every requirement of manufacturing industry. DISA’s designs bring together the accumulated experience of four famous names in the production of shotblasting equipment — Georg Fischer, BMD, Vogel & Schemmann and Goff.
The range of machines available to the foundry industry covers virtually every possible need. For example, there are models available for the following duties: The blast cleaning of iron castings, unaffected by tumbling, in batch-type machines (BB, ST and DTC); the fully automatic and flexible blast cleaning of castings in continuous through- feed barrels and the cleaning of flat thin-walled castings within wire-mesh machines (CT, DT and WM); the blast cleaning of parts susceptible to breakage and impact damage on hanger-type machines and the cleaning of gravity-and pressure-diecast parts in automatic finishing cells (SPH and WM), and the blast cleaning of iron and aluminium automotive and engine castings, including sand, gravity - and pressure-diecast versions (DS, DV and CR).
Apron-conveyor machines
One of the most frequently specified blast machines in the castings industry is the apron-conveyor unit, where batches of components are rolled and tumbled in a continuously troughing conveyor beneath a high velocity stream of abrasive. 
Models range from rubber-belt versions with maximum capacities as low as 180 kg (BB85) to substantial slatted-steel conveyor types capable of accepting loads of up to 5,500 kg (ST-70-430). Although individual machines can employ relatively simple systems for loading and unloading, there are many instances where a series of machines has been integrated into a fully automatic system. These layouts allow for the transfer of preweighed batches of components to appropriate shotblast units within the complex, the performing of a pretimed blasting sequence, and the subsequent retrieval of the parts, all according to a predetermined program.
An alternative to the apron-conveyor design is the use of an open-topped polygon-shaped trough which is designed to rock backwards and forwards along its longitudinal axis through about 120˚. As in the case of the apron-belt versions, the castings are tumbled beneath the blast stream. Amongst the advantages of these DTC-type machines are fast load/unload cycles, the absence of moving parts in the blast zone which might lead to the jamming of workpieces and low maintenance requirements.
Continuous – throughput units
Where a foundry needs to process considerable volumes of castings, continuous throughput machines are frequently specified. DISA Industrie have developed two versions, one based on the apron-conveyor concept (CT) and the other on the rocking polygon trough (DT). In the case of the CT models, castings are progressed into and out of the apron-conveyor section through rotating barrels. Vibratory trough conveyors are employed to charge and discharge the machine. The throughfeed polygonal drum is usually fed and discharged directly by vibratory conveyors. The design of the CT and DT units lends itself to integration in the layout of mechanised production line whereby castings can be transferred directly from a rotary knockout/cooling drum to the shotblast system.
Where foundries need to process fragile thin flat castings, such as stove components, DISA offer the continuous wire-mesh conveyor concept (WM), whereby parts resting on the surface of the conveyor are cleaned by abrasive projected from above and below.
Hanger – type designs
Not all castings can withstand tumbling under a stream of abrasive. Some are too fragile, or in the case of aluminium components, easily bruised or scored. Yet others are too large or unwieldy to be treated in such a manner. As a result, another wellknown solution is to suspend castings from an overhead mounted hanger arrangement designed to rotate its load as it passes through a vertical curtain of abrasive. At the bottom of the scale is the extremely versatile SPH spinner hanger shotblast unit which can not only accept a wide variety of ferrous castings but has also proved ideal for the surface treatment and deburring of small aluminium components. These models are available with maximum capacities of, respectively, 100, 300 and 600 kg. The machine does not require any foundations and consists, mainly, of the housing with the revolving blast chamber divided into two compartments, the blast wheel units and the abrasive separating system. Each compartment is equipped with a spinner hook to receive the hangers with the parts to be cleaned. The loading area of the machine is open, so one compartment can be unloaded and reloaded, whilst parts are blast cleaned in the other section.
Within the HT series of overhead monorail machines there is a wide range of arrangements for the transport of casting loads into, out of or through the cabinets and blast rooms. Systems can be designed for any application. However, loads of up to 10,000 kg per hanger can be accommodated on power and free conveyors, whilst similar loads can be suspended from electric overhead monorails with automatic drive mechanisms. Even heavier loads — up to 50,000 kg — can be handled on monorail crane systems fitted with lifting gear.
Advanced cleaning systems
Even more advanced blast cleaning systems have been developed to meet the needs of foundries producing automobile and commercial vehicle castings, and in particular blocks and heads. These continuous throughput models (DS and DV) utilise manipulator devices which serve to sieze and manipulate the castings under the blast stream. The components are not only rotated under the abrasive, but can be maintained in a predetermined position or set in a rocking motion. During rotation of the castings, the spent abrasive is continuously discharged, so cavities, such as water jackets, remain unclogged, thus further facilitating the cleaning operation. The manipulators are mounted on a rotating faceted pillar which progresses the castings around a totally-enclosed doughnut-shaped enclosure, past the blast wheels. Such units are available in different capacities, ranging from one manipulator and two blast wheels to eight manipulators with 12 blast wheels. The fastest machine works at a cycle time of 10 sec, providing a throughput of up to 360 components per hr. Some systems have been especially designed for cleaning aluminium castings produced in sand moulds or by pressure-diecasting.
Given the advanced design and capacity of these specialised blast cleaning machines, it is not surprising that they often form part of integrated fettling lines which incorporate a variety of operations including decoring, deburring, opening of passageways, grinding, breakoff operations and sawing. Such DISA layouts can conduct these tasks individually or interlinked, fully automatically.
Fettling Systems
For those foundries seeking to automate their fettling operations, DISA have introduced the DISAMAT fettling cell which incorporates a six-axis robot. This device picks up the prepositioned parts in turn and subsequently carries out the required grinding and cut-off operations, before unloading them onto a conveyor belt. Such cells can be employed in the fettling of between 1,000 and 100,00 castings per year, either as individual workpieces weighing 20 to 100 kg, or as clusters measuring 650 by 600 by 350 mm max.
One of DISA’s latest acquisitions has been the French company SERF SA, specialists in the supply of plant for the automated clipping and trimming of iron and aluminium castings. Whereas trimming, using accurate tooling, has long been one of the principal means of divesting pressure-diecastings of fins and surplus metal, the clipping of joint-line flash and residual gating systems from aluminium and iron sand castings has been relatively uncommon. However, the situation is rapidly changing as an increasing number of foundries adopt clipping procedures as an alternative to manual chipping and grinding.
The process offers a number of advantages, including high output; accurate removal of surplus metal, even in the case of complex and relatively inaccessible joint lines; the generation of easily remeltable croppings; absence of grinding dust — and hence the need for expensive extraction facilities, and the avoidance of potential physiological disabilities, such as vibration white finger.
Given the range of DISA Industrie’s equipment for the cleaning and subsequent fettling of a very wide range of iron and aluminium castings, it is not surprising that this article has only touched on the attributes of the main models in the company’s portfolio. However, it has demonstrated that the company is able to offer one-stop solutions to the founders’ shotblasting requirements.