TECHNICAL FIELD

The present invention relates to a filter unit or filter box for a chip conveyor for conveying cutting chips that are produced in the operation of a machine tool, such as a lathe or the like. More specifically, the proposed filter unit is used for removing different types of chips contained in a coolant fluid and/or cutting oil used in machine tools during metal working. The invention equally relates to a corresponding chip conveyor and to a method of filtering cutting fluid in a filtering chip conveyor.

BACKGROUND OF THE INVENTION

In normal operation, a machine tool, such as a lathe, produces waste material that should be removed from the workpiece being machined. In these cases, the waste material that is removed from the workpiece is generally removed in various sizes including small pieces that are generally referred to as chips. These chips mix with the coolant/cutting oil (hereafter referred to as cutting fluid) used in the machining process. The cutting fluid can be used for cooling, wash down and/or lubrication, for example. This mixture of cutting fluid and cutting chips enters the conveyor used for removing the chips from the cutting fluid. The cutting chips are thus conveyed from the receiving position to a discharge position.

The cutting fluid drains through the conveyor to the machine tool oil/coolant reservoir. Some of the chips that are mixed with the cutting fluid also pass into the machine's oil/coolant reservoir with the cutting fluid. These chips eventually build up in the machine oil/coolant reservoir and require manual intervention to clean them out, because the cutting fluid in the reservoir is generally re-circulated for further use. Thus, before the cutting fluid can be recirculated and reused, the waste material produced during the operation of the machine tool first has to be removed.

Hinge belt conveyors are widely used to convey the chips away from the cutting fluid. This type of conveyor is the most simple of all conveyors on the market, and is widely used throughout the industry. This is a very versatile product in that it is capable of taking any chip shape or size, but has generally one major drawback in that it often does not offer any filtration. This results in small chips passing through the conveyor into the cutting fluid tank which then means that the machine operator has to perform regular maintenance to clean out the tank (duration depending on the specific application).

However, filtering chip conveyors also exist and self-cleaning scraper conveyors are an example of these kinds of conveyors. They can filter out particles (chips) down to a particle size of around 500 μιτι (0.5 mm). The minimum dimension of the particles which can be filtered out of the fluid is also referred to as the filtration level. These kinds of conveyors, such as the one disclosed in WO2004/054756, typically use a self-cleaning filter box to prevent small chips (larger than the filtration level of the filter screens used) from passing out of the cutting fluid tank and being cycled back into the machine tool. One problem with such self-cleaning scraper conveyors is that they do not generally filter long chips well, especially long chips having a smallest dimension (thickness) similar to the size of the openings in the filter material. Chips are liable to become wedged in the weave of typical woven filtration meshes, and are difficult for the scrapers to dislodge. The mesh becomes clogged, and the fluid flow through the screen, and thereby the filtration performance, is markedly reduced. This is one of the reasons why self- cleaning scraper conveyors are commonly supplemented with a filter drum. This combination is better suited to applications in which a wide variety of various chip sizes and shapes are produced and in which filtration is needed.

Machines today are capable of many types of machining processes and thus produce a wide range of chip types and shapes. The currently available solutions are either inefficient (no or poor filtration) or very expensive, due to the complexity of the drum filter and self-cleaning scraper conveyor arrangements required.

It is the aim of the present invention to overcome the problems identified above. More specifically the aim is to provide a solution for filtering chip conveyors so that a high fluid through-flow can be obtained, while at the same time allowing filtration levels down to 50 μιτι or even lower. SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a filter unit for a filtering chip conveyor, the filter unit comprising:

- at least one filtration element comprising a filtration region having a plurality of first openings for permitting cutting fluid to pass through the filtration element while not permitting chips with given dimensions to pass through it; and

- at least one second opening allowing cutting fluid inside the filter unit to pass out of the filter unit through the second opening, characterised in that the filter unit further comprises:

- at least one spray element on the inside of the filter unit, the spray element being arranged to spray fluid onto the filtration element to clean at least a part of the filtration region.

The proposed filter unit has the advantage that the solution is simple, while still allowing efficient cleaning of the filter unit. More specifically chips that usually stuck to the surface of the filtration element can now be flushed away. Thus, the filter unit can be considered as being self-cleaning. This also means that the fluid through-flow can be constantly high. Also filtration of chips with very small dimensions can be achieved. For instance the filtering element can have opening with dimensions smaller than 50 μιτι.

The proposed filter unit can also be easily connected to a filtering chip conveyor, which is designed to be a simple filtration conveyor that can handle a multiple range of applications, material and chip types. Furthermore, brushes and/or wiper blades are not necessarily needed to clean the filter box but could be used in the function of the conveyor.

According to a second aspect of the invention, there is provided a filtering chip conveyor comprising the filter unit according to the first aspect of the present invention. According to a third aspect of the invention, there is provided a method of filtering cutting fluid for a filtering chip conveyor comprising a conveyor tank arranged to retain the cutting fluid containing chips, and further comprising a continuous conveyor belt at least partly disposed inside the conveyor tank, the conveyor belt having upper and lower flights with a filter unit between these flights, where the filter unit comprises a spray mechanism on the inside of it and a filtration element, the method comprising:

- the filter unit filtering the cutting fluid entering the filter unit;

- the spray mechanism spraying the filtration element to clean it; and

- discharging the filtered cutting fluid off the conveyor through the filter unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become apparent from the following description of non-limiting exemplary embodiments, with reference to the appended drawings, in which:

Figure 1 is a perspective view of the filtering chip conveyor according to an embodiment of the present invention;

Figure 2 is a cross-sectional view of the conveyor taken along line II- II of Figure 1 ;

Figure 3 is a side view of the conveyor illustrating in more detail one part of the conveyor of Figure 1 ;

Figure 4 is a perspective view of a filter box in accordance with an embodiment of the present invention;

Figures 5A to 5F show examples of some geometries of etched orifices of a filter plate but other mesh types on the market could be used such as woven mesh of various materials; Figure 6 is a perspective view of the filter box of Figure 4 with the filter plate removed showing also connection elements;

Figure 7 is a cross-sectional side view of the filter box showing possible connection elements although other connections such as permanent connections could be used;

Figure 8 is a side view of the tail end of the conveyor illustrating exemplary configuration of cleaning means;

Figure 9 is a side view of the tail end of the conveyor illustrating another configuration of the cleaning means; and

Figure 10 is a simplified side view of the conveyor in operation.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Next an embodiment of the present invention is described in more detail with reference to the attached figures.

Figure 1 is a perspective view showing the filtering chip conveyor 1 comprising the filter unit, in this example a filter box 3, according to one embodiment of the present invention. The conveyor 1 also comprises a conveyor tank 5 that is arranged to retain the dirty cutting fluid resulting from metal working. A conveyor belt 7, in this case a hinge belt, is at least partly disposed inside the conveyor tank 5. The hinge belt 7 is formed by connecting a plurality of metal plates with hinges into a continuous or endless caterpillar- type belt. The chips resulting from the metal working are arranged to fall inside the conveyor tank 5 from above, in the direction of the arrow W.

The hinge belt 7 is arranged to be turned around a tail-end sprocket/disk 9 (shown in Figure 8) and discharge end sprockets (not shown in the figures) and rotated as a belt conveyor. In the figures the tail end is referred to by "Te" and the discharge end by "De". A motor 1 1 is also shown and is used for rotating the belt 7. The path of travel of the belt is substantially horizontal in the lower part of the conveyor 1 , as can be seen in the figures. The belt has upper (reference "U") and lower (reference "L" shown in Figure 2) portions

substantially parallel to one another in the lower part of the conveyor 1 . The upper portion travels in a first direction, whereas the lower portion travels in a second direction, the second direction being opposite to the first direction, in the lower portion of the conveyor 1 . The arrow R in the figures shows the direction of rotation of the belt 7. The upper portion is arranged to carry the large chips to the discharge end De to be discharged off the belt 7. A chip reservoir (not shown in the figure) is used to store the discharged chips.

In Figure 1 , there is also shown the filter box 3 on the inside of the belt, i.e. between the upper U and lower L portions of the belt 7 for filtering the cutting fluid. By placing the filter box 3 on the inside of the belt 7 the filter box 3 is protected from large chips. There can be one or more boxes linked in the same conveyor depending e.g. on the flow rate required, the amount of cutting fluid used and frequency of cleaning. For instance, if a considerable amount of cutting fluid is needed, then the number and/or size of the boxes 3 should be increased. The box(es) could be anywhere in the horizontal load section. As illustrated by the figure, the filter box 3 has an opening 13 on the vertical side wall through which the filtered cutting fluid can be drained to a clean cutting fluid reservoir (not shown). From the clean cutting fluid reservoir the filtered cutting fluid can be pumped to the machine tool for reuse.

Figure 4 is an exemplary perspective illustration of one possible filter box 3, shown the bottom side up. When in operational position, the filter box 3 has in this example four substantially vertical sides and two substantially horizontal ends, i.e. the bottom part and the top part. One of the side walls is a front panel, and has the opening 13 so that the filtered cutting fluid can be drained through this opening 13 to the clean cutting fluid container. The filter box could also incorporate more than one of this type of opening 13. The box can also incorporate round ends / sloped faces, depending on specific applications.

In this example, the bottom part has a filtering or filtration element 15, such as a screen (i.e. filter plate screen) or mesh that is arranged to filter the dirty cutting fluid. The filter plate 15 is advantageously made of one of a variety of materials, including metals, glass or plastics. The other sides of the box 3 are metal, plastic or glass walls that do not allow the cutting fluid to penetrate into the box 3 through these walls. It is to be noted that the number of sides being fitted with the filter plate 15 is not limited to one. Also, instead of the bottom side being fitted with the filter plate 15, any other side could be equally fitted with the filter plate 15. The filter plate can be welded in or bolted in.

In this example the filter plate 15 has a thickness of less than 0.3 mm and a plurality of openings or orifices in a filtering region. The orifices are arranged in an array, and in the illustrated examples are etched profiled or non- profiled orifices, and may be etched as straight-through holes with parallel sides orthogonal to the filter plate 15, as shown in Figure 5F. However, Figures 5A to 5E show some flared orifice geometries which offer advantages of easier cleaning and/or less clogging. In all cases in Figures 5A to 5E, the cutting fluid passes through the plate 15 from top to bottom. Flared upper portions 17 allow particles which lodge in the upper portion of the orifice to be easily brushed out by the brushes, wipers or scrapers which pass across the upper surface of the plate 10, if such brushes are used. Flared downward portions 18 ensure that any particles which pass through the narrowest (waist) region of the orifices can then travel freely through the lower part of the orifices. Etched orifices can be made significantly smaller and more evenly-shaped and -sized than perforations (mechanically stamped holes), and without burring. Perforations can be made down to 0.5 mm, while etched orifices can be made down to 0.2 mm or 0.1 mm. Mechanical perforation also entails the use of a thicker plate, while etched plates can be made much thinner (0.2 or 0.1 mm, for example). Thinner filter plates, having shorter through-holes than thicker plates, are also less likely to clog.

Profiled orifices, etched in arrays by photo etching or chemical milling, for example, permit much smaller apertures than are possible with mechanical perforations, and result in much finer filtration. In addition, the etching process enables a much closer distribution of the orifices in an array. In this way, it is possible to greatly increase the open proportion of the plate from a typical value of between 5% and 10% for a perforated plate to more than 18% for an etched plate. The maximum open proportion which is possible using mechanical perforations reduces as the perforations become smaller, so a trade-off between hole size and fluid flow is inevitable. Open proportions of etched plates, on the other hand, are not constrained by such a trade-off, and proportions as great as 40% are possible, even with orifice sizes of 0.2 mm or less. In this way, etched filter plates allow the fluid flow to be greatly increased, while the minimum filtered particle size is greatly decreased. At the same time, the filter plate has very flat, burr-free surfaces which can be smoothly and efficiently swept, sprayed, wiped or scraped, if needed, by the wiping elements arranged on the inside of the conveyor belt. In any case, the teachings of the invention are not limited to any specific type of filter plate, i.e. it can be for example a very simple mechanically perforated mesh as well.

Figure 6 shows the filter box 3 of Figure 4 with the filter plate removed. The filter box has on the inside an internal flush or spray system to clean the filter plate(s) 15 from the inside out. The flush system has spray elements 20, which in this example are longitudinal elements, such as spray bars or pipes, and an internal piping system 22 having distribution hoses connected to the spray pipes 20. The spray pipes are arranged to spray through openings fluid onto the filter plate 15 in order to clean the orifices of the filter plate. The sprayed or flushed fluid can be e.g. liquid, such as clean cutting fluid or coolant, or a gas, e.g. air, such as compressed air. The fluid flush can be run constantly, periodically or intermittently depending e.g. on the frequency of cleaning required to suit various applications. The control of this frequency can be managed by using a solenoid valve on the supply tube to the filter box 3. The flush can be also initiated only when a predetermined event takes place. This event can be the amount of the cutting fluid flow through the filter plate, the weight of the filter plate together with the stuck chips on it, etc. For instance, the flush can be initiated only when the cutting fluid flow through the filter plate drops below a given value or when the weight of the filter plate together with the chips exceeds a given value. The flow and pressure of the flush cutting fluid pump (not shown) can also vary depending on the particular application.

The number of spray or flush pipes 20 in the box 3 is two in the example shown, but there could be more or fewer of them depending e.g. on the width of the conveyor and the particular application. The spray pipes are either fixed in position or they can move, e.g. by rotating or by a translational motion, i.e. they can move longitudinally e.g. parallel to the side edges of the filter box. The surface of the filter plate and the flow of the cutting fluid from the spray pipe 20 form an angle β between them. This angle is normally between 30 and 90 degrees to maintain efficient cleaning. However, when the spray is directed upward, then this angle is preferably not 90 degrees or very close to this angle. In this way it can be guaranteed that the cleaning flow directed upward does not meet any possible counter flow from the cutting fluid dripping down from the filter plate 15. However, when the spray pipe 20 rotates about its longitudinal axis, then the angle β varies and can take all the possible values, i.e. full rotations or 360 degrees are possible. It is also possible to vary the spraying pressure, or it can be constant during the spraying operation. This pressure variation can be made dependent on the angle β. For instance, when the angle β is 90 degrees, the pressure is the smallest, and can increase progressively when the deviation from this angle increases. It is also possible to vary the angular velocity of the spray pipe 20. For instance, the angular velocity can be the highest when the angle β is substantially 90 degrees, and this velocity can be progressively decreased when the deviation from this angle increases. If the filter box 3 has only one spray pipe 20, then it is located in the box so that it is substantially equally far from the opposing ends of the filtration region.

Figures 6 and 7 show also a first connection element or coupling 24 on the filter box 3 and a second connection element or coupling 26 to be mounted to the conveyor 1 . In this example these connection elements are quick connections that allow the box to be removed easily without disturbing the pipe work. This is useful for maintenance, but fixed piping and boxes could be also used in order to reduce cost or simplify the assembly, but this would make maintenance more difficult. The quick connections mean that the first connection element 24 can be simply inserted by pushing it into the second connection element 26. When these two elements are connected together the clean cutting fluid can be fed from the second connection element 26 through the first connection element to the piping 22 in the filter box 3. From the piping 22 the cutting fluid can then be fed to the spray pipes 20 to be sprayed to the filter plate 15. Quick connections are not critical to the function of the invention but complementary, fixed connections would also work but limit the ease of serviceability.

The flush works by spraying cutting fluid at the internal (clean) side of the filter plate 15 to push the chips off the filter plate internally. The chips are then carried out by cleaning means, such as rigid bars or cleats 28, when the chips pass to the bottom of the conveyor 1 and are carried out by the cleaning means 28 on the belt as is explained more in detail later. As illustrated in Figures 2, 3 and 8 to 10, in this example there are provided cleats 28 on the outer surface of the belt 7 to clean the conveyor tank 5. The nature of the chips to sink to the bottom of the conveyor 1 also ensures that, as the belt 7 rotates, any small chips are automatically carried out of the conveyor 1 too. The cleats 28 are arranged so that they do not touch the conveyor tank 5, to prevent wear and tear. For instance, a space of a few millimeters could be left between the conveyor tank 5 and the cleats 28.

Different configurations for the cleats 28 are better illustrated in Figures 8 and 9. These figures are side views of the tail end Te of the conveyor 1 . In Figure 8, the cleats 28 that are made of metal in this example have an angle of 90 degrees with respect to the flat metal plate of the belt part that is between two hinges. In other words, the cleats 28 are perpendicular to the belt 7. However, as the cleats 28 are attached to the flat metal plate of the belt 7 between two hinges, the space does not remain constant between the conveyor tank 5 and the cleats 28 in the tail end of the conveyor tank 5 even if the tail part of the conveyor tank 5 is rounded. This can be clearly seen in Figure 8, where the distance d1 between the cleat end and the conveyor tank 5 is greater in the tail end part of the conveyor 1 , compared with the distance in the flat bottom part of the conveyor 1 , due to the path taken by rigid hinge plates.

To overcome this problem, the cleats 28 can be bent or tilted backwards (when considered in the direction of rotation of the belt), as illustrated in Figure 9. In this variant the cleats 28 have two straight parts with a predetermined angle between them. The cleats 28 thus form an angle a with respect to the flat plate of the belt 7, as illustrated by the figure. This angle can be, for example, in the range of 30-60 degrees, to keep the space between the conveyor tank 5 and the cleats 28 constant as far as possible. Here in the tail end Te the distance d2 between the cleat ends and the conveyor tank 5 remains constant, even around the curve. The first part of the cleats is used for attaching the cleat to the flat metal plate, and is therefore parallel to the metal plate. The second part is inclined with respect to the first part, and thus forms an angle a with respect to the flat metal plate of the belt 7. In other words, the cleats 28 are angled in a way that the extreme end (protruding end) of the cleat 28 in the tail end Te is in line with the pivot point of the belt 7 to ensure that this extreme end remains a fixed distance d2 from the conveyor tank 5 in the tail end Te. Other variants are also possible. For instance, the conveyor 1 may have both types of cleats 28.

Above a filtering chip conveyor 1 was described in accordance with an embodiment of the present invention. In essence, in this embodiment the proposed conveyor 1 is a hinge belt conveyor with at least one filter box 3 incorporated therein and internal cleaning means 20 to clean the box(es) 3 automatically.

The operation of the conveyor 1 according to one example is explained next with reference to Figure 10, using the same reference numerals as in the figure.

A. Large chips are stopped and taken out by the continuous

hinge belt 7 on the outside surface of the belt 7.

B. Some small chips wash through or around the hinge belt 7 and fall to the bottom of the conveyor tank 5 over time.

C. The cleats 28 swipe the bottom surface of the conveyor 1 to gather any small chips that have fallen to the bottom of the conveyor tank 5.

D. Internal liquid or compressed air spray from inside of the filter box 3 is used to clean the filter box 3 as the belt 7 rotates. Any small chips that are blown off by the flush fall to the bottom of the conveyor tank 5, and are collected by the part described in C.

E. As the parts described in C rotate around the end of the

conveyor 1 , the small chips are held against the conveyor tank 5 of the conveyor 1 and lifted onto the top of the conveyor belt 7.

F. All chips are discharged from this part of the conveyor 1 .

G. The filter box 3 contains at least one filter plate 15 to filter all the cutting fluid as it passes through the box 3 and into the tank, ensuring that only clean filtered cutting fluid can pass out of the conveyor 1 . The filter box 3 is mounted between the upper and lower belt flights. As shown in the figure, the conveyor 1 has three flights: two horizontal flights and one inclined flight that connects the lower and upper level horizontal flights. In this example the bottom surface of the box 3 contains the filter plate 15, so that the cutting fluid can enter the box 3 through the bottom while the level of the cutting fluid in the conveyor tank 5 increases. While in operation, the filter box 3 in this example is at least partly disposed in the cutting fluid. In some implementations the filter box can be placed above the dirty cutting fluid situated inside the conveyor tank 5.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive, the invention being not restricted to the disclosed embodiment. Dual, triple or numerous filter plates 15 in the same filter box 3 could be used. Layered filtration to finer and finer levels could also be considered. The filter boxe(s) can be removably connected or fixed to the tank 5. The box 3 could consist of one large box. Furthermore, the filter plate 15 could also form part of the tank 5 of the conveyor 1 . Moreover, the conveyor can also comprise second cleaning means, such as brushes, on the inner side of the belt 7 to clean the filter box 3 as the belt 7 rotates. Thus, the natural rotation of the belt 7 can be used for cleaning the box 3. The brushes can be made of nylon, and may be placed in the middle of the flat metal part of the belt, i.e. the part between the hinges. It is also possible for the brushes to be made of other polymers and metals. The second cleaning means could also be in the form of wiping blades to clear the filter box 3. However, as the filter box is already cleaned with the internal spray mechanism, in some implementations the conveyor 1 does not have the second cleaning means at all. Other variations of the disclosed embodiment can be understood and effected by those skilled in the art in practising the claimed invention, from a study of the drawings, the disclosure and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used. Any reference signs in the claims should not be construed as limiting the scope of the invention.