Problem solving

Motor vehicle construction: Precautions against highly flammable dusts

Wet separator makes flammable aluminium and magnesium dusts harmless

Doering GmbH&Co.KG, at Sinn in Germany's Hessen region, makes tool castings from spheroidal graphite and lamellar graphite cast iron. After casting, parts have to be deburred and cleaned of any process wastes. To remove all waste at source, Doering uses a central extraction unit supplied by Ruwac Industriesauger GmbH.

Eleven connections, three vacuums, one central filter

The eleven workstations where the castings are deburred each have a connection for a suction hose. When the operator opens the connector flap and connects up the suction hose, the extractor unit switches on automatically. The hose connectors are mounted on a piping system connected to a central filter unit. Three vacuum units, each with a 7.5 kW drive, provide the necessary suction power with a maximum air flow rate of 490 m³/h. The vacuum units switch on as required and operate at the performance level required to service the number of cleaning stations currently connected up. This saves energy. As a rule no more than two workstations are operating at any one time.

Automatic filter dedusting

The extracted air flows through a bag filter which has a total filtering surface area of 11 m². The filter has an electronic controller. When the electronic controller detects a preset pressure differential limit of 50 mbar, it triggers automatic filter dedusting. A counter current of compressed air blown through the filter shifts any dirt which then drops down into the dust container.

Safe dust container emptying

The extracted casting waste is collected in a mobile, 500-litre, tipping container. When the container is full, the operator raises the filter unit using the pneumatic system so that the container can be removed and emptied. Emptying is controlled by a photocell barrier which ensures that the operator can only lower the filter unit when the dust container is in the correct position. A tipping brake ensures that the container is tipped and emptied at a low speed only. This prevents excessive dust build up. The extraction plant installed by Doering demonstrates the advantages of fixed, centralized extraction plant in comparison with mobile industrial vacuums. Fixed plant is more compact. Centralised filtering, dedusting and emptying makes maintenance much easier. The electronic controller ensures safe, reliable operation. The capacious dust container does not require emptying very often.

Mobile vacuum for expanded polystyrene extraction

Doering also uses a standard Ruwac industrial vacuum but this time for a completely different application. The company's activities also include the production of expanded polystyrene models and patterns used to make full mould tooling. Blocks of expanded polystyrene are milled to the mould shape required. The process waste extraction equipment is built into the head of the concave miller. The technical specifications were straightforward enough. No problem here. What did cause a problem, however, was finding an efficient method for collecting up the polystyrene waste. Expanded polystyrene is very light and at the same time very difficult to compact - two characteristics which make it a very good packing material. Generally speaking, with this type of material the operator has to empty the waste container at very frequent intervals. Luckily, Ruwac came up with a purpose-built solution. The polystyrene particles are collected in a 200-litre container lined with a jute sack, mounted upstream from the vacuum. The vacuum and the flow rate are adjusted so that the volume and the polystyrene in the waste container is considerably reduced. This solution saves time and money when collecting and emptying waste material.