GB2302818A

GB2302818A - Rotating drum suction filter

Info

Publication number: GB2302818A
Application number: GB9513417A
Authority: GB
Inventors: Michael John Vials
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-06-30
Filing date: 1995-06-30
Publication date: 1997-02-05
Also published as: GB9513417D0

Abstract

A rotating drum filter 10, including replacable filter media 9 wrapped and sealed about the circumference, is partially submersed in dirty liquid 12. The filter supply pump 1 suction pipe 8, passes through otherwise solid end walls 7 via integral openings 5, to the clean liquid within the drum. The integral openings 5, also form the journal on which the drum rotates. Drawing off the filtered liquid increases the flow through the filter. A portion of the filtered flow is returned under pressure to backflush 6 the media. Additionally and where only part of the total flow is required filtered, the assembly can be arranged to filter less than the total flowrate and the excess bypassed over weirs 20 then returning to the main volume.

Description

ROTATING DRUM SUCTION FILTER This invention relates to a rotating drum suction filter.

Rotating drum suction filters are well known as specialised filter systems, or clarifiers, used where a considerable volume of contaminate is generated as part of a production process. Such a process would be metal cutting carried out on a machine tool, where the liquid coolant recirculated during the metal cutting process must be cleaned of metal chip and fine contaminate. These rotating drum suction filter systems are generally designed to be self cleaning and may include a mechanical scraper mechanism to automatically remove the accumulated contaminate; then to be conveyed to a suitable container. Suction drum filters have all free filtering area totally submersed and cannot effectively use a backflush.

Certain, not suction, rotating drum filters require that only part of the rotating drum is submersed in a pool of dirty liquid. In these filtering apparatus the rotating filter drum, covered with a filter media, acts as a positive barrier filter to limit the ingress of contaminate. Typically the filter drum is cleaned with the aid of a pressure backflush. Solids rejected by the filter are conveyed from the filter housing and the conveyor may act as the transmission to rotate the filter drum.

Such rotating drum filters employ a gravity flow of the dirty liquid from outside to in; through the filter drum. The filter media offers a resistance to this liquid flow, which leads to a differential head being generated across the filter drum. Generally rotating drum filter systems are installed beneath the machine tool coolant outlet and before the coolant holding tank, which rests on the floor. It is often not practical to increase the height (and thereby the differential pressure) between the machine tool outlet and the floor. The resistance to liquid flow then limits the use of the rotating drum filter design, requiring that a larger drum size or a coarser filter media be employed.

According to the present invention the clarified liquid within the drum is drawn off by suction using a pump. This pump then supplies clarified liquid to the machine tool, although a percentage is returned to the pressure bacidlush inside the drum to give reverse flow cleaning in the accepted fashion.

Given that the drum size, micronic filter rating and liquid filtered remain the same, the process of drawing the liquid from within the rotating drum ensures an increased differential head and therefore higher liquid flowrate through the filter drum.

Traditionally metal cutting machine tools have not required the coolant to be filtered. The coolant may often be supplied unfiltered; although a conveyor, strainer or simple weir arrangement in the main coolant holding tank may be used to remove much of the large contaminate. However recent developments on some metal cutting machine tools require that a percentage of the supplied coolant is filtered. This coolant supply might be used as 'through the tool' or 'to the tool' supply.

Additionally then the invention further allows that where the dirty flow exceeds the required filtered flow; the excess liquid is flooded via overflow ports, thereby bypassing the filter. The bypass ports may be arranged to allow overflow of the total input flow, such that the pump need only be operated as or when required. The arrangement ensures that the design is self balancing and only, but all, the excess flowrate will flood.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 & Figure 2 show a section through one end of the rotating suction drum filter apparatus and a section viewed from the side. The filter is shown partially submersed in the dirty liquid. The method of suspension is not shown, but this might be a rigidly fixed position or the whole assembly may be carried on a pontoon, thereby floating at the liquid surface. The filtered liquid is drawn from within the drum. The arrangement of the necessary pump for drawing off the clean liquid and supplying the backflush is illustrated. An arrangement for rotating the drum is also illustrated. A dedicated drive might be powered by an electric motor as shown or use any other form of motive power.A foot valve if required, and other ancillary equipment which may benefit from the protection offered by the filter may also be positioned within the drum.

Figure 3 & Figure 4 show the rotating suction filter apparatus positioned internally; within a typical conveyor and according to the additional claim, arranged only to filter part of the total flow. The main coolant holding tank lies alongside, and the excess flow is bypassed to this tank. The arrangement illustrates how the total dirty coolant flow might be returned to the conveyor serving the machine; while a percentage is filtered through the present invention. The conveyor is used also to provide the rotational drive for the drum filter.

Figure 4 & Figure 5 show an alternative arrangement where the present invention is positioned 'stand-alone' as an external filter system, complete with it's own housing and according to the additional claim, arranged only to filter part of the total flow. The dirty liquid is pumped to the rotating drum suction filter, either by a pump dedicated as the filter supply pump or with flow tee'd off the main dirty liquid supply. Again excess dirty liquid is bypassed to the main holding tank.

Figure 7 shows the 'stand-alone' filter devised to sit 'piggy back' on top of the main conveyor. Some integration may result and the illustration shows outside side walls of the housing combined with the side walls ofthe conveyor.

Referring to the drawings the rotating drum suction filter 10 is positioned in the dirty liquid 12 held in a reservoir such that only part of the filter area is submersed. The liquid to be filtered must pass through the filter media 9 to reach the suction inlet pipe 8 of the pump 1. As the pump draws liquid from the inside of the rotating drum suction filter, further dirty liquid will pass through the filter media. The action of evacuating the clean liquid ensures an increased differential pressure across the filter media. In the present invention the rate at which the dirty liquid will pass through the filter media is then increased, because the pump evacuates the clean liquid.

The design of the rotating drum includes solid end plates with openings only for the suction and pressure wash pipes. The hole allowing access for the suction and backflush pipe is protected by a cylindrical tube 5, positioned concentric and protruding out from the drum. The drum rotates about these tubes on bearings which are not detailed. The two solid discs 7, are held parallel and apart by suitable cross braces, not detailed. The area between these discs is covered by the filter media 9, suitably supported, sealed and clamped. Details of the fixing of the media on the drum is not shown.

The suction and backflush pipe may enter side by side or with the backflush supply pipe passing through the centre of the suction inlet pipe, and from either or from both ends. The rotating drum suction filter is positioned such that the maximum liquid level achievable cannot flood into the inside of the drum. The drum is journaled, but the journals 5 are above the liquid and need not be sealed although where the static liquid level may be higher, then additionally seals maybe employed.. The suction inlet pipe 8 and the backflush supply pipe 4 pass through the journal and the disc to the inside of the drum.

The drum rotates so that the dirty filter media is cleaned by the backflush jets 6. The jets are powered by a portion ofthe pressure supply volume 2 being tee'd off3 the filtered liquid supply pipe.

Drum rotation may be achieved through a dedicated motor drive or where the rotating suction filter apparatus is positioned within a conveyor 15 this may be arranged to drive the rotation of the drum.

Rejected contaminate 22 is removed by this conveyor 15.

Where the rotating drum suction filter apparatus is arranged, according to the additional claim, only to filter part of the total flow, bypass ports 20 are sufficiently sized to bypass the total flow, the filtered flowrate being controlled by the operation of the pump 1. The flooded excess dirty liquid 21 is directed to the main coolant holding tank. 24.

The rotating drum suction filter may be built integral with the chip conveyor 35 and thereby be partially immersed in the dirty liquid flowpath which will overflow from the chip conveyor tank to the main holding tank 24. The overflows 20 should be sized and positioned to ensure that the liquid level cannot flood through the opening provided by the protruding cylinder 5 and into the clean side of the drum. Seals will not then be required. Although if the static level of dirty liquid is high, seals 11 may be added. The static level is determined when the system is at rest and all liquid is returned to the tanks from the machine tool. It also may be desirable to add seals 11 if the liquid will generate foam or where splashing or fume may cause dirty liquid to pass into the clean side of the drum.

Where the rotating drum suction filter is arranged 'stand-alone' the dirty liquid 12 may be supplied to the rotating drum suction filter under gravity or tee'd off 32 the main coolant supply volume 30.

The flow piped 31 to enter the rotating drum suction filter may be baffled 11 to dissipate the residual pressure. The volume delivered by the main coolant supply pump 23 shall exceed the maximum flowrate to be filtered by the rotating drum suction filter.

The dirty liquid enters the catchment tank 26 and fills this reservoir to the level of overflow 20.

Whether the rotating drum suction filter pump is running or not will only effect the rate at which the excess overflows, but some or all dirty liquid delivered to the rotating drum suction filter will always overflow, while the system is in operation. A level measurement device 28 might be included to determine if the level within the rotating drum suction filter has fallen so low that the filter pump is about to suck air. This should only occur where the supply 12 is reduced or the filter media 9 is blocked. A signal from the low level measuring device may be used to switch off the filter supply pump and or the machine tool.

Any and all dirty liquid 21 bypassing the filter will be collected within the area contained by the outer walls 27 ofthe 'stand-alone' rotating drum suction filter and returned to the main holding tank 24.

Claims

1 A rotating drum suction filter comprising an assembly in the form of a drum, covered about the circumference with filter media and having solid disc ends, excepting that a cylinder is formed from the disc, concentric to the centreline of the drum and protruding outward, to act both as a journal and seal such that the rotating drum suction filter can be suspended and rotated partially submersed in dirty liquid, and filtered liquid can be drawn off through a suction pipe connected to the filtered coolant supply pump and directed to the lowest portion of the drum and entering through the opening provided by the protruding cylinder.

2 A rotating drum suction filter as claimed in Claim 1, wherein a portion of the filtered flow is returned by means of pipework tee'd off the supply side of the filtered liquid supply pump and entering the rotating drum suction filter through the opening provided by the protruding cylinder, and is directed to the highest portion of the drum, there to backflush off the contaminate collected on the outside the filter.

3 A rotating drum suction filter as claimed in Claim 1 or Claim 2, wherein the suction pipe and the backflush pipe may enter through a common opening provided by the protruding cylinder from one end only of the rotating drum suction filter or opposed to one another and from each end, and may be side by side or arranged such that the backflush supply pipe passes through the suction supply pipe.

4 A rotating drum suction filter as claimed in Claim 3, wherein the suspension support for the rotating drum suction filter may hold the assembly in a fixed position relative to the dirty liquid level or may be a pontoon allowing the assembly to float partially submersed in the dirty liquid.

5 A rotating drum suction filter as claimed in Claim 4, wherein the opening provided by the protruding cylinder may be sealed about the pipes, to further ensure that dirty liquid cannot enter to the clean side of the filter.

6 A rotating drum suction filter as claimed in Claim 5, wherein additional equipments' such as a foot valve, temperature gauge or level gauge are also positioned within the filter, being thereby protected by the rotating drum suction filter.

7 A rotating drum suction filter as claimed in Claim 3 or Claim 6, wherein the rotation of the drum is achieved by a dedicated drive, including motor or motor and gearbox powered by fuel or electric hydraulic or pneumatic or where the backflush flow is also used to power the rotation of the drum.

8 A rotating drum suction filter as claimed in Claim 7 wherein the dirty liquid flowrate is in excess of the filtered flowrate drawn off by the rotating drum suction filter pump and where the excess flow is then bypassed over weirs to an additional or main holding tank.

9 A rotating drum suction filter as claimed in Claim 8 wherein the rotating drum suction filter assembly either is integrated into the initial tank or conveyor system or alternatively is separate from the initial tank or conveyor system.

10 A rotating drum suction filter as claimed in Claim 9 wherein the rotating drum suction filter integrated with the initial tank or conveyor system and thereby partially submersed in the dirty liquid contained uses the side walls of that tank or conveyor system to contain the dirty liquid and house the overflow weirs which shall be positioned to ensure that all flow can be overflowed at a level below the opening provided by the protruding cylinder of the rotating drum suction filter.

11 A rotating drum suction filter as claimed in Claim 10 wherein the rotating drum suction filter is separate from the initial tank or conveyor system and is housed within it's own housing to which dirty liquid is delivered under gravity flow or pumped, either by a dedicated rotating drum suction filter supply pump or with a portion of flow tee'd off the main dirty liquid supply pump.

12 A rotating drum suction filter as claimed in Claim 11 wherein the housing provides a catchment tank for the dirty liquid such that the rotating drum suction filter is partially submersed in the dirty liquid and the side walls of that catchment tank include the overflow weirs which shall be positioned to ensure that all flow can be overflowed at a level below the opening provided by the protruding cylinder of the rotating drum suction filter and then collected in an outer housing to be directed to the additional holding tank.

13 A rotating drum suction filter as claimed in Claim 12 wherein the housing provides a catchment tank for the dirty liquid and a dedicated conveyor to remove contaminate from within the catchment tank.

14 A rotating drum suction filter as claimed in Claim 9 or Claim 13 wherein the rotation of the drum is achieved by a dedicated drive, including motor or motor and gearbox powered by fuel or electric, hydraulic or pneumatic or where the backflush flow is also used to power the rotation of the drum or where the conveyor mechanism used within the initial tank or conveyor system or the separate housing is employed.