Patent Application
20190160415
This application claims benefit to European Patent Application No. EP 17 204 572.6, filed Nov. 30, 2017, which is incorporated by reference herein.
The invention relates to an apparatus and a method for separating oil particles from an air stream. In particular, the invention relates to a filter element and the use thereof for separating oil particles from an air stream, for example an air stream evacuated from a spindle chamber of a machine tool.
High-performance spindles of machine tools are lubricated and cooled by an oil-air mixture. With the deaeration of the spindle interior, it is ensured that the oil mist created by the spindle operation is evacuated. The secondary contamination is in this way carried away and prevents deposits in the spindle interior. With the discharge of the oil mist, moreover, heat escapes, and so an overheating of the system is prevented.
Known methods and apparatuses for separating oil particles from the air stream evacuated from the spindle interior do not meet expectations, because either a very weak separation rate is achieved or the filter media become contaminated within a very short time. This results in an excessively high counterpressure, causing a back draught in the air stream, which in turn leads to an unsatisfactory deaeration of the spindle. An over-lubrication, elevated temperatures and excessive wear are the consequences.
In the event of a weak separation rate, particles can make their way into the ambient air, which can inflict considerable damage on man, the environment and the machine.
At issue here are so-called E-dust/mist (respirable <4 μm) and A-dust/mist (alveolar <1 μm). In the use of high-performance cooling lubricants, which are nowadays equipped, inter alia, with additives such as, for instance, droplet reducers, sub-micron particles are typically generated. High-frequency spindles, high-pressure systems, multi-shift operation and high temperatures promote the incidence of this critical particle size still further. Critical particles are diffusing particles. They are capable of penetrating even dense filter mats. This has the consequence that, although a separator can have a very acceptable residual emission value, the fraction which it does not capture contains precisely the type of particles which have been described above.
DE 20 2013 100421 describes an oil mist separator for cleaning oil mist out of the air of a work area. The separator has an at least two-stage filter, which is successively flowed through in a flow channel. The suction is realized by means of a fan in the air path behind the last filter, wherein the first filter in the flow channel is designed as the main filter and the filter arranged downstream of this in the air path is designed as the after-filter.
DE 10 2014 224 831 describes an oil filter arrangement of an oil separator having a housing. The housing has an air inlet and an air outlet, in which a multiplicity of filter elements is found. The filter elements contain a material which lies above steel in the triboelectric series.
In an embodiment, the present invention provides a filter for separating oil particles from an air stream. The filter includes a continuous side wall in which a filter material is accommodated, a completely uninterrupted floor, and a cover. The side wall is fastened between the floor and the cover and the filter material includes a fibre mixture of synthetic fibres and glass fibres. The filter material is configured such that, upon the inflow of the air stream through the filter material, the oil particles from the air stream agglomerate into drops on the surface of the material and the drops run off downwards.
The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following:
Embodiments of the invention provide improved apparatuses and methods for separating oil particles from an air stream. Embodiments of the invention provide filter elements and apparatuses for separating oil particles from an air stream, which filter elements offer a compact design and an improved filtration and have an increased service life. Embodiments of the invention further provide methods for separating oil particles from an air stream and apparatuses for performing such methods, in which methods even very fine particles are separated from the air stream and afterwards drain out of a filter material to reduce or eliminate back pressure and ensure a sustained deaeration of the system.
Using the described filter material and considering the defined inflow velocity, an efficient filtration and a passive regeneration of the filter material is successfully achieved. Passive regeneration means that the filter medium can clean itself without outside influence, such as, for example, counterflow purge air, vibratory dedusting or brush cleaning. As a result, a compact and energy-efficient apparatus for separating oil particles from the air stream can be realized.
In one or more embodiments, a filter element for separating oil particles from the air stream comprises a continuous side wall, a completely uninterrupted floor and a cover. The side wall is fastened between the floor and the cover. In the side wall is accommodated a filter material, which consists of a fibre mixture of synthetic fibres and glass fibres. Moreover, the filter material is selected such that, upon the inflow of the air stream through the filter material, the oil particles from the air stream agglomerate into drops on the surface of the filter material and the drops run off downwards. The particles having a diameter in the in the micrometre range are hence retained from the air stream. The separation process works passively without external energy and the pressure loss across the filter element remains stable over a long period. Since the oil particles agglomerate and can subsequently be drained, a saturation of the filter material by oil particles in a short operating time is avoided, and hence a longer service life and better filtration of the filter element achieved. Furthermore, the passive filter function contributes to a low energy consumption of the apparatus.
According to one or more embodiments, the side wall has a supporting element for supporting the filter material, which supporting element is preferably formed of an internal rib mesh and/or an external rib mesh. The internal rib mesh and the external rib mesh preferably consist of expanded metal or perforated sheet metal. It is possible for the supporting element to be formed from other materials and shapes.
According to one or more embodiments, the filter material possesses a weight per unit area of 50-150 g/m2, preferably of 90-150 g/m2. In an advantageous variant, a filter material having a weight per unit area of 84 g/m2 is chosen.
According to one or more embodiments, the filter material possesses a thickness within the range 0.1-1 mm, preferably within the range 0.1-0.69 mm.
According to one or more embodiments, the filter material possesses an air permeability of 80-250 m3/m2/h at 200 pa, preferably of 120-150 m3/m2/h at 200 pa. In an advantageous variant, the filter material is chosen with an air permeability of 130 m3/m2/h at 200 pa.
According to one or more embodiments, the filter material has a surface resistance of at least 1012 Ohm. That has the advantage that, as a result of the air friction, unnecessarily static loads are not generated within the filter medium. The load promotes the adherence of suspended particles and can alter the surface tension of liquids, so that a run-off can be made more difficult.
According to one or more embodiments, the filter element has the form of a hollow cylinder. The filter element can assume a different shape, for example conical. A conical element, in particular when it is suspendingly mounted, promotes the run-off of a drop.
According to one or more embodiments, the filter material has a multiplicity of folds for the enlargement of the filter area. In a preferred variant, the folds run in a vertical direction in order to promote the agglomeration of the oil particles into drops and the run-off of the drops.
According to one or more embodiments, the depth of the folds in the radial direction equals 10-30 mm. In a preferred variant, a depth of 25 mm is chosen. In a variant, the fold spacing is chosen in dependence on the inner diameter of the filter material and the thickness of the material.
In one or more embodiments, the filter material is designed with reinforcing elements in order to attain more mechanical stability of the filter material.
In one or more embodiments, the filter element is dimensioned such that the ratio between the height of the filter element and the external diameter of the side wall of the filter element is 1 or greater in order to obtain an optimum between the mechanical stability of the filter element and the efficiency of the filtration.
In one embodiment or more embodiments, an apparatus for separating oil particles from the air stream comprises a filter element, a housing, an inlet for the laden air stream, an outlet for the separated air stream and a drain for oil. An inflow velocity of the air stream is dimensioned such that, upon the inflow of the air stream through the filter material, the oil particles from the air stream agglomerate into drops and the drops run off downwards. The inflow velocity is a relevant factor for enabling the agglomeration of the oil particles.
According to one or more embodiments, an apparatus is provided that includes a diffuser disposed between the side wall of the housing and the filter element. As a result, the air stream is guided via the diffuser as evenly as possible into the expansion chamber, in which also the filter element is found, and the inflow velocity is readjusted. This results in an optimal ratio between filter area and inflow velocity.
According to one or more embodiments, the inflow velocity lies within the range 0.1-2.5 m/min, preferably within the range 0.1-0.55 m/min. The inflow velocity outside this range has an adverse effect on the efficiency of the filtration by preventing the agglomeration of the oil particles. Since the aerosols can penetrate too deeply into filter medium, the drainage becomes less efficient and the differential pressure across the filter element increases.
One embodiments comprise an application of a filter element in an apparatus for separating oil particles from the air stream. The apparatus comprises a filter element, a housing, an inlet for the laden air stream, an outlet for the separated air stream, and a drain for oil. An inflow velocity of the air stream is dimensioned such that, upon the inflow of the air stream through the filter material, the oil particles from the air stream agglomerate into drops and the drops run off downwards. The inflow velocity is a relevant factor for enabling the agglomeration of the oil particles.
According to one or more embodiments, a method is provided for separating oil particles from an air stream, wherein the laden air stream is conducted into an expansion chamber, in which a pleated, vertically arranged filter material consisting of a fibre mixture of synthetic fibres and glass fibres is found. The filter material and the inflow velocity of the air stream are chosen such that, upon an inflow of the air stream through the filter material, the oil particles from the air stream agglomerate into drops on the surface of the filter material and the drops run off downwards.
According to one or more embodiments, methods are provided in which a filter material having a thickness within a range 0.1-1 mm, a weight per unit area of 50-150 g/m2, an air permeability of 80-250 m3/m2/h at 200 Pa, and a surface resistance of at least 1012 Ohm is utilized. The laden air stream is conducted through the filter material at an inflow velocity within the range 0.1-2.5 m/min. In one or more variants, the filter material has a bursting strength (according to Mullen) of 300 kPa. In one or more embodiments, the filter material has a temperature resistance of 65° C. to 80° C.
On one side wall of the housing 2 is disposed an inlet 5 for contaminated air. On the cover of the filter element is provided an outlet 6, through which the cleaned air stream leaves the housing 2. In the floor 8 of the housing 2 is provided a drain 7 for the separated oil, which drain is periodically opened by a valve (not represented) in order to let the collected oil flow out. Close to the inlet 5 is optionally disposed a perforated metal sheet 9 as a diffuser for the distribution of the incoming contaminating air in the housing.
Advantageously, the filter element 3 has at the bottom a completely uninterrupted floor. The choice of material for the floor is dependent on the application. For the embodiment represented in
The filter element further has a cover 36, which is fixedly connected to the filter material and the rib mesh and on which the outlet 6 for the cleaned air stream is disposed. As shown in
A pleated filter material is used to obtain an optimal filtration. Pleated means that the sheet-like filter material 32 is folded in a zigzag shape. The filter material represented in
A preferred embodiment of the apparatus 1 is operated such that the laden air stream flows at an inflow velocity of 0.55 m/min from outside to in through the filter material 32. Advantageously, the filter material 32 additionally has a bursting strength (according to Mullen) of 300 kPa and a temperature resistance of 65° C. to 80° C.
The embodiment represented in
The separation process thus functioned passively for over 5,000 hours, thus without introduction of an external energy such as compressed air, electric current, etc., wherein the pressure loss across the filter element remained stable, below 6 mbar. It has been shown during operation that the oil mist in the filter material agglomerated into drops, which ran off downwards without clogging the filter material in the measurement period, so that it is possible to speak of a self-regenerating process.
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. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below.
The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17 204 572.6 | Nov 2017 | EP | regional |
