Graphite separation from machining oil in grey cast iron machining

Wastewater treatment

Case study on the fine filtration of coolant emulsion (KSS) at a machining center for aluminum-magnesium die-cast alloys. A centrifugal separator continuously removes fine particles and magnesium compounds, ensuring stable process conditions and preventing deposits.

Case Study: Fine Filtration of Coolant Emulsion at DGS Druckguss Systeme AG

At DGS Druckguss Systeme AG in St. Gallen, aluminum-magnesium die-cast components are machined on a machining center equipped with a downstream coolant cleaning system.

The system operates with a coolant emulsion volume of approximately 1,200 liters, with a daily addition of 100–150 liters of fresh water. However, the existing filtration system was not capable of removing very fine particles, which accumulated in the coolant over time.

Due to the presence of magnesium, a chemically reactive base metal, reactions occur with oxygen dissolved in the water, forming magnesium salts. The concentration of these salts can be monitored via water hardness (°dH). At values between 70° and 90° dH, magnesium precipitates and forms a hard, scale-like layer.

This leads to several operational issues:

Blockages in internal cooling channels of tools
Increased pump wear
Problems with seals in motor spindles
Deposits on tool holders and guide elements

Solution

To solve these issues, DGS Druckguss Systeme AG installed a high-performance centrifugal separator from STA for the removal of fine particles and magnesium. The separator was integrated into the system in a bypass configuration.

The continuous removal of fine particles significantly improved the process. Deposits in tool channels are prevented, and less magnesium dissolves in the coolant due to immediate separation.

The centrifuge achieves a separation performance of up to 1,910 g. This means that particles with a density difference of at least 2% compared to the carrier fluid are separated 1,910 times faster than under natural sedimentation conditions.

The separated particles accumulate at the edge of the sludge insert, which is manually replaced (approx. 1.5 kg of magnesium per shift). The cleaned liquid is removed via a skimming device and returned to the coolant system.

The centrifuge continues to operate even during downtime of the machining center, ensuring continuous cleaning of the coolant.