Roll Grind Filtration
A secondary operation to hot and cold roll steel production is roll maintenance which requires grinding steel rolls to very precise tolerances after a given production time until the rolls have to be resurfaced or replaced. The roll grinding operation is especially critical to maintain high quality rolled product.
The rolls are ground using an abrasive wheel that contacts the rotating roll and moves down the length of the roll removing surface material while being flushed with clean coolant. The resulting contaminants consist of the wheel stone, wheel adhesive, and fine steel from the roll, collectively called swarf. The swarf must be continuously removed from the coolant of individual or multiple grinding machines by means of an individual or central filtration system. The filter system, depending on the capacity, would include; a deep bed gravity filter or a flatbed vacuum filter, a two compartment tank, clean supply, & filter feed pumps, and related controls.
The filter, depending on the equipment configuration, can receive the dirty coolant and swarf directly by gravity from the grinder as shown in Figure 1 or via a filter feed pump from the reservoir tank as shown in Figure 2. The reservoir tank would have two compartments with dedicated clean and dirty compartments. Depending on the flow capacity of the roll grinder(s), the filter can be a deep bed gravity type with an extended drying zone or deep bed vacuum filter with extended drying zone, which offers many other advantages.
As the coolant is sprayed against the grinding wheel and roll, heat is removed from the surface by the coolant and carries the newly produced swarf to the filter or into the dirty compartment of the tank. The filter collects the swarf on the filter media, within the filter bed, which advances very slowly. This produces a deep swarf filter “cake” that helps remove very fine particles from the coolant. Clean coolant then drains from the filter to the tank’s clean compartment where the clean supply pump delivers the coolant back to the roll grinder (s) at the required flow and pressure.
A deep bed gravity filter with extended discharge ramp can accommodate a swarf thickness of 6” to 8” and is typically used when the roll grinder has a dedicated filter / filter system. Two models are available designated as our GSF15 or GSF30. The GSF15 has a pool depth of 15” (381 mm) and the GSF30 has a pool depth of 22” (558 mm). Both have patented positive labyrinth double side seals to eliminate migration from the dirty side of the filter into the clean compartment below. The filter can incorporate an optional vacuum feature which has a number of benefits as described below.
Benefits of Air Vacuum Filtration:
• The operating vacuum is generated totally independent of the liquid flow with a low HP vacuum producer.
• The air vacuum concept shears away the presence of potential tramp oil at the media entrance area to prevent premature “blinding” of the media since the filter bed is open to atmosphere.
• The vacuum is used as a tool to dewater the swarf on the discharged spent media resulting in very dry swarf .
• The vacuum producer allows natural aeration of the coolant to minimize the growth of anaerobic bacteria.
• The filter never goes offline during the short movement of the filter media. The height of the liquid pool and vacuum allows an increased pressure drop across the media for continuous filtration.
• The conveyor system is not immersed into the dirty liquid and is fully supported with the ability to use virtually any industrial type filter media including lightweight polyesters. The design allows the media to be carried through the filter as opposed to being pulled / dragged or the use an auxiliary hold down devices.
Both filters incorporate our Controlled Level Index feature (CLI) to further enhance the performance of the operation. The feature allows a consistent liquid level within the bed of the filter for continuous but extremely slow indexing of the filter media. The feature minimizes migration of solids through the clean end of the media during media movement and provides a uniform pressure drop across the media due to the consistent liquid level within the bed of the filter while maintaining a maximum pressure drop across the filter media and where applicable a consistent operating vacuum with a minimum amount of operating energy.
Our optional Spent Media Rewinder/Swarf Separator re-winds the spent media after separating the collected swarf from the filter media.
Unlike OEM filter systems which incorporate a combination of a shallow bed, seal less filter and magnetic separator, our concept allows 100% of all contaminants to be removed by one efficient device in a very dry condition while maximizing coolant clarity.