HOFFMANN Pressure Belt Filter System 3 x DBF 3.0

Task:

Planning, construction and supply of a turnkey central filter system for a new production building supplying 10 - 12 machining centers with finely filtered emulsions without use of filter paper.

Key data:
Coolant:	Emulsion containing mineral oil
Type of machining:	Milling and grinding
Fabricated parts:	Turbine blades
Grinding materials:	Corundum grinding disks with continuous dressing process and alternative CBN grinding disk
Coolant requirement:	140 l/min. per machine, at 70 bar and 200 l/min. at 4 bar for flushing of the ways
Required filter fineness:	10 µ
Availability:	96 %

Design:

3 central pressure belt filters, each with a filter capacity of 1,360 l/min. and an active filtration area of 3 square metres for each filter, were installed in a separate filter farm. Each system supplies 4 processing machines via a loop pipeline. A high-pressure pump is installed upstream of each processing machine to ensure a supply capacity of 140 l/minute. Only very fine impurities and corundum particles are produced in this machining process, on account of the high-speed grinding and continuous dressing processes employed. The pressure belt filters are lightly precoated with filtration aids to achieve the required level of filtration.

The soiled emulsion is pumped into the soiled tank section of the filter system via a return pump station. To prevent impurities being deposited and formation of bacteria at an early stage only round tanks with conical bottoms are used.

HOFFMANN chillers, each with a refrigerating capacity of 100 KW ensure a stable emulsion temperature at all times.

The continuous emulsion treatment is assisted by an oil separator and an emulsion mixing device.

All work processes are controlled and monitored by a PLC (Siemens Simatic). The individual components are linked with one another by a filed bus system (Profibus) spanning all connected buildings.

Visualization devices (Siemens operator panels) at all components provide a clear overview for all ongoing processes, as well as options for diagnostics and parameterization. Remote diagnosis can be performed using the built-in modem.

Results:

Despite the very high level of corundum a filtration fineness <10 µm is maintained. Also the amount of filter aid consumed is very low. The initial emulsion has been used for a long period now, thanks to permanent monitoring of the emulsion and by preventing any accumulation of soiling or bacteria in the machines, return pumping stations, filter vessels and piping.

The requisite surface quality of the machined turbine blades was achieved from the very start. The maintenance costs have been assessed by the customer as being extremely low.