Mass finishing techniques are often used to uniformly prepare and finish work-pieces, but the compounds and liquids used to remove fines and other debris from work-pieces must be dealt with to ensure a repeatable process application. Cleaning and/or recycling waste water produced in the mass finishing process is easily achieved with centrifuge technology and provides opportunities to be more environmentally responsible and save money in the form of reduced labor and materials (cleaning agents and compounds).
How Centrifuges Work
In a centrifuge, waste materials including media and metal fines are often referred to as effluent. The effluent to be cleaned either flows directly from the mass finishing system to the centrifuge by gravity or is transported to the centrifuge by a lifting (pump) station. Larger solid particles are prevented from entering the collecting tank by a filter to prevent them from plugging up and damaging the subsequent pumps.
A stirring device in the collecting tank holds the solid fines in suspension. A powerful, low-maintenance diaphragm pump transports the effluent from the collecting tank to the rotary drum of the centrifuge. The rotational speed up to 3000 RPM separates the liquid from the solid phase: While the solid particles contained in the effluent are deposited on the drum wall as sludge, the cleaned process water is picked up by a peeling nozzle and transported (“recycled”) back to the mass finishing, or other, system.
Periodically, the cleaned process water is collected in a clear water tank and then pumped to the finishing system. The sludge has usually a residual water content of about 20 percent. It can be easily removed from the system by a polyurethane basket that is inserted into the rotational drum.
Benefits of Recycling
Rosler Process Water Recycling Systems can be connected to virtually any mass finishing machine. Most mass finishing processes such as de-burring, precision grinding, rough grinding, radiussing, or polishing are considered wet processes. Water and cleaning agents (compounds) are the carriers for removal of media and metal fines.
Regardless of the industry, centrifuges offer recycling benefits by separating contaminants from reusable process fluid and enabling equipment to reuse process fluids. These environmentally friendly, closed loop operations can result in up to 95 percent savings of water and compounds. Without separation and recycling, the compounds and water would need to be replenished with each mass finishing batch, resulting in increased cost in the form of compound and water consumption.
Recycling process water also saves money by reducing waste water treatment and disposal fees. Water discharge must comply with federal, state, and local regulations. Depending on the process specifics, including original state of the work-piece, compounds used, and resulting pollutants removed, the investment cost of a centrifuge can provide a cost savings over excessive waste water treatment.
Many Process Water Circulation Systems can be adapted to any mass finishing application. Semi- and fully-automatic centrifugal systems are available.
Semi-automatic centrifuges offer excellent cleaning results in a “plug and play” configuration. Their compact, space-saving design also allows for easy placement close to processing machines. Cleaned liquid is collected and transferred into an adjacent clean water tank or directly to the processing machines. Movable base frames are also available to allow for the cleaning of contaminated industrial liquids from machines at different locations.
In these designs, sludge must be manually removed from the vessel by hand. Often resembling potter’s clay, the sediment should be removed according to manufacturer specifications and disposed of as waste.
Fully automatic centrifuges offer more maintenance-friendly options for applications with large water and sludge volumes where the manual removal of sludge is not feasible. Depending on the manufacturer and options selected, these centrifuges may contain a gear-powered peeling knife which continually rotates in a rotary drum or a stationary knife which moves within a slowly rotating drum to peal sludge without placing any load on the drum bearings.
In either case, fully automatic centrifuges do not require manually removal of the sludge as found in semi-automatic models. Nearly every mass finishing application can benefit from the integration of a centrifuge.
Cost savings can be realized in a number of ways from eliminating the need for filter materials to increased machine up-time as a result of fewer process fluid change overs. The ability to reuse process fluids also reduces chemical disposal costs and helps meet municipal environmental standards. Minimal operator intervention results in reduced labor costs as well cost savings from eliminating other outdated waste water techniques.