Economical vacuum supply for lost foam casting process

Maulburg - GussStahl Lienen (GSL) produces high-quality steel castings using the lost foam casting process for a range of areas in engineering and in equipment and vehicle construction. Its good reputation in the industry is based not last on its more than 20 years of experience with this special casting process. When it comes to the vacuum supply for the moulds, GSL relies on vacuum technology by the company Dr.-Ing. K. Busch GmbH.
Tyr rotary lobe blowers from Busch on GSL's lost foam casting plant

With its lost foam production line, GussStahl Lienen produces steel castings with weights ranging from 0.2 to 100 kg. GSL also maintains a furan cold resin moulding shop for cast steel and its own model assembly. GSL has been active in the lost foam process for more than 20 years and has built up a considerable wealth of experience over this period. The lost foam process enables cast steel to be cast into components with corresponding geometry. Through the use of evaporable foam models (known as ‘lost' models) burr-free and dimensionally accurate castings with an exceptional surface quality for mould-intensive casting products can be cast in an undivided mould.

The foam models, combined into clusters, are then coated with a thin ceramic finish that is permeable to gas and subsequently dries. The model clusters are then moulded in a binderless, fine-grained mould material. The vibration compresses the sandy mould material, which then coats the foam model. Vacuum is applied from below prior to the start of the casting process. This vacuum is tasked with further compressing the mould material, thereby providing the mould with the necessary stability. When the casting process starts, the vacuum extracts the vapours and gases generated by the evaporation of the foam model. This guarantees that the liquid metal completely fills the hollow space that was predetermined by the foam model and that no entrained gases or cavities are formed in the metal. The vacuum pumps direct the extracted gaseous and vaporous foam residue to the afterburning. Thanks to this lost foam process, GSL operates a virtually emission-free casting process with a low energy requirement and a closed mould material cycle. Vacuum technology makes an important contribution to this.

Originally, the lost foam moulding plant at GSL was fitted with two liquid ring vacuum pumps that were each driven by a 22 kW motor. These vacuum pumps required a certain level of maintenance. They were operated using water as an operating fluid, which flowed through the pumps in a partial cycle. This meant that water quantity monitoring and water tracking had to be performed constantly. In addition, the extracted gases sometimes accumulated in the water as aggressive condensates and attacked the materials inside the liquid ring vacuum pumps such that individual parts constantly needed to be replaced. This led to inconvenient downtimes for the casting plant, which is operated in two shifts. For operations manager Klaus Buchholz, this was a situation that he did not want to have to put up with for much longer. He contacted the company Dr.-Ing. K. Busch GmbH to obtain a replacement for his liquid ring vacuum pumps.

We could have supplied him with two adequate liquid ring vacuum pumps, made from materials that were resistant to the generated condensates. However, our vacuum specialists took a different approach and came to look at the process on site in Lienen. As a result of this, they recommended a different technical solution to Klaus Buchholz, the operations manager: replace both liquid ring vacuum pumps with a single Tyr rotary lobe blower and fit a filter upstream of the blower. The Tyr rotary lobe blower has the same pumping speed as the two liquid ring vacuum pumps that were previously used put together. Thanks to the non-contact rotary technology, it does not require any operating fluid, which means that the compression of the extracted gases and vapours is a completely dry procedure. It is therefore impossible for condensates to accumulate in the operating fluid, as was previously the case with the liquid ring vacuum pumps. The very small particles or condensates sucked in are separated in the upstream filter, meaning that they do not even enter the blower.

With this solution, operations manager Klaus Buchholz was able to resolve multiple problems at once: the vacuum supply is absolutely reliable and the output is consistent. Even after more than a year of operation, the Tyr rotary lobe blower from Busch has never failed. The improvement in energy efficiency is also clear to see: the Tyr rotary lobe blower is fitted with a 22 kW drive motor, which it uses to generate the same pumping speed and vacuum performance by itself as was previously generated by two liquid ring vacuum pumps that each had 22 kW motors. This means that the energy costs have been exactly halved.

The benefits at a glance:

    •  50% energy saving
    •  No downtimes caused by repairs
    •  Reliable and constant pumping speed
    •  Low level of maintenance work
    •  No operating fluid
    •  Low space requirement

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