Patent Application
20220241898
The present patent application relates to a method for manufacturing machine parts, such as, but not limited to compressor, expander or vacuum pump parts.
The surface of a machine part can be provided with a coating to influence the behavior of the machine part. For oil free screw compressors, as an example, a coating is applied onto the surface of the rotor and housing to improve the operation of the oil free screw compressor. The coating serves multiple purposes. One purpose is to reduce the wear of the machine part. Another purpose is to facilitate transmission of heat through the machine part. Yet another purpose is to minimize the generation of heat during operation. Yet another purpose is to minimize leaking of air from the air chambers formed between the machine parts.
When a machine part is to be coated, it is aimed to achieve a proper adhesion between the coating layer and the machine part. Particularly when the machine part ages, a suboptimal adhesion of the coating layer may lead to a delamination of the coating layer. This decreases the operation performance of the machine part and could potentially damage the machine. To obtain a proper adhesion, the surface of the machine part is pre-treated before applying the coating. This pre-treating comprises one or multiple cleaning steps, typically mechanical and/or chemical cleaning. During cleaning, dirt and grease is removed from the machine part. The pre-treating typically further comprises a roughening operation to improve the adherence of the coating. A roughening operation can be performed, e.g. by means of sand blasting.
A drawback of known techniques to treat a surface of a machine part is the significant impact on the environment. In particular the pre-treating steps such as cleaning and roughening produce harmful waste streams. Furthermore, at least part of these operations is complex to automate such that an operator performing the operations takes a risk of coming into physical contact with these harmful waste streams.
It is an object of the present invention to improve the treatment of machine parts.
To this end the invention proposes a method for treating a surface of a machine part, the method including the steps of:
The invention is based on the insight that a laser may be used to clean a surface of a machine part and to simultaneously influence a roughness of the surface. By applying a pattern onto the surface, the surface can be cleaned and a predetermined roughness can be obtained. Furthermore, using a laser, compared to traditional cleaning and roughening operations, significantly reduces the creation of harmful waste streams. Additionally, the applying of the pattern onto the surface by means of a laser can be automated such that the burden on, and risk to operators are reduced.
Preferably the method further comprises manufacturing the machine part. In the preferred embodiment, the treated machine part is a new machine part. Alternatively, the surface of a previously used machine part is treated. This is also called a refurbished machine part.
Preferably the machine part is selected from a group consisting of at least a part of a screw rotor for an oil free screw compressor and at least a part of a housing element for such oil free screw compressor. Particularly in the field of oil free screw compressors, the surface treatment appears to be of significant importance for the operation, efficiency and life time of the compressor. Therefore particularly for oil free screw compressors, the proposed treatment is advantageous.
Preferably the step of applying the pattern comprises:
Preferably the laser is pointed towards the surface such that the laser beam impacts the surface at an angle of about 90 degrees. By impacting the surface at an angle of about 90 degrees, the majority of the laser beam energy is transmitted to the surface. Furthermore, reflection beams, which might have a harmful effect on the environment, are minimized.
Preferably operating the laser comprises displacing the laser with respect to the surface such that an impact point of the laser follows said at least one path at a predetermined speed. It is noted that the displacing is defined in a relative manner, being the laser with respect to the surface. This means that the laser can move while the surface is fixed. Alternatively, the surface can move while the laser is fixed. Further alternatively and preferably, both the laser and the surface are moved to arrive at the predetermined relative displacement of the laser with respect to the surface. By following the at least one path at a predetermined speed, the laser impacts the surface along the path. Because the path extends over the surface, the laser impacts the complete surface.
Preferably the laser is a pulse generating laser and wherein operating the laser comprises outputting the laser beam at a predetermined operating frequency and at a predetermined operating intensity. Further preferably, the predetermined speed and the predetermined operating frequency are kept in a predetermined relation with respect to each other. Further preferably, the predetermined relation is chosen such that subsequent laser beam spots are located at a point to point distance with respect to each other that is smaller than a laser surface impact diameter. The combination of these features allows to impact the surface along the path without interruption. In other words, at least the path is completely treated and no spots or surface parts can be found along the path which are not impacted by the laser beam. A laser beam spot is defined as a laser beam impact zone which is detectable on the surface.
Preferably the at least one path comprises multiple path segments, and wherein adjacent path segments show a center-to-center distance which is preferably smaller than said laser surface impact diameter. The effect of the preferred embodiment is that also between adjacent path segments, every part of the surface is treated with the laser beam. In other words, no surface part can be found in between adjacent path segments where the laser has not treated the surface.
Preferably the applying a pattern is parametrized to obtain a surface roughness of the surface higher than 1.0 Ra, preferably higher than 1.3 Ra and optionally also a surface roughness of the surface higher than 10.0 Ry, preferably higher than 15.0 Ry. Practical tests and experiments have shown that the coating can be applied with a high degree of success when the surface roughness higher than 1.0 Ra and optionally also higher than 10.0 Ry. The parameters of applying the pattern comprise laser beam intensity, displacing speed, operating frequency, distance between adjacent path segments, which may be parametrized differently for different surfaces. Particularly the machine part material significantly influences how these parameters are to be chosen to obtain the preferred surface roughness.
Preferably the coating is applied in multiple layers. Further preferably the method further comprises of applying a first coating layer onto the surface of the machine part before the step of applying a pattern, and wherein the applying a coating is applying a second coating layer onto the patterned surface. This might be useful when quality of the first coating layer is insufficient, and the surface needs a new coating. In the latter case, applying the laser pattern will remove the first coating layer and will prepare the surface for good adhesion with the second coating layer. The quality of the first coating layer may be deemed insufficient after the machine parts have been used. The quality of the first coating layer may also be deemed insufficient directly after applying this layer, for example when something went wrong during manufacturing.
Preferably the coating has any one of compositions as described in one of European patent application No. 14155385.9, European patent application No. 17169341.9 and Chinese patent application No. CN 105132086.
The invention further relates to an oil free screw compressor comprising a rotor and a housing, at least one of which is at least partly treated according to the invention.
The accompanying drawings are used to illustrate presently preferred non-limiting exemplary embodiments of devices of the present invention. The above and other advantages of the features and objects of the invention will become more apparent and the invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which:
The method according to a preferred embodiment of the invention includes the steps of
In an alternative embodiment, the invention includes the steps of:
The method according to the invention is particularly useful for manufacturing coated machine parts, such as for example screw rotors or compressor housings for oil free screw compressors, for scroll or tooth compressor manufacturing. Similarly, the method can be applied for manufacturing rotors, housings or shafts of expanders (e.g. screw expanders), vacuum pumps (e.g. vacuum claw) or low pressure applications (for example screw blowers).
According to a particular way of carrying out the invention, the step of applying the coating onto the patterned surface, includes applying any coating composition as described in European patent applications Nos. 14155385.9 and 17169341.9, which are both incorporated into this application in their entirety by reference, at least for the purpose of providing technical features relating to the application of the coating and for the purpose of providing technical features of the coating composition itself. Obviously, the invention is not limited to these specific coating compositions, but also other types of coatings could be applied.
Further, the polytetrafluoroethylene bonded solid lubricant as disclosed in Chinese patent application CN 105132086 could be used as coating material and may be applied according to any of the methods as described in this Chinese patent application, which is incorporated into this application by reference at least for the purpose of providing technical features relating to the application of the coating and for the purpose of providing technical features of the coating composition itself.
More specifically, the coating material used in a method according to the invention could be polytetrafluoroethylene bonded solid lubricant prepared with polyamide-imide resin and epoxy resin as binders, polytetrafluoroethylene, melamine cyanurate and molybdenum disulfide as solid lubricants and a mixed solvent as a diluent and may further contain various fillers and a modification additive. The lubricant can be coated on the surfaces of the machine part and may be subjected to heating and solidification to form polytetrafluoroethylene bonded solid lubrication coating layers.
The coating material applied in a method according to the invention may contain a thermoplastic material such as for example, but not necessarily polyaryletherketone (PAEK), polyetheretherketone (PEEK). Additives may be included into the coating material such as for example Aluminium oxide (A1203), Silicon dioxide (Si02), glass (e.g. Borosilicate glass). Graphite may be included into the coating material, either or not in combination with any of the above-mentioned compounds.
Any of the following particles may be included in the coating material, either alone or in combination with any other compound or additive:
Alternatively, the composition of said coating material may be as follows:
A particular formulation of the new coating may be as follows:
Tests have shown that the step of applying a pattern onto a surface of the machine part can entirely or partly eliminate the need of roughening said surface, e.g. by means of sandblasting, while a good adhesion of the coating material onto the machine part surface can be assured. Said machine part is typically a metal part, for example cast iron.
The present invention further relates to a method of refurbishing a machine part, such as for example a rotor or a rotor housing of a compressor, expander or vacuum pump, said method comprising the step of:
According to a specific embodiment, said method further comprises the step a′ of applying a pattern onto the laser treated surface, prior to applying the new or additional coating layer.
According to an additional preferred characteristic of the invention, step a′ is performed by means of a laser which applies the pattern onto the surface.
The laser applied in the present invention is preferably a pulsed laser because the application benefits from the production of pulses with a predetermined, large, amount of energy. Since the pulse energy is equal to the average power divided by the repetition rate, the predetermined amount may be reached by lowering the frequency of pulses so that more energy can be built up in between pulses. In laser ablation for example, a small volume of material at the surface of a work piece can be evaporated if it is heated in a very short time, whereas supplying the energy gradually would allow for the heat to be absorbed into the bulk of the piece, never attaining a sufficiently high temperature at a particular point.
With reference to
While the laser beam is pointed towards the surface and operates at a predetermined operating frequency, the beam moves over the surface along a path 2. The paths 2a and 2b forms a pattern 2 which covers the surface to be treated. The pattern 2 comprises multiple path segments.
The laser is configured with a laser beam diameter. Optical elements of the laser, in combination with the distance between the laser source and the surface, determine the diameter of the impact zone of the laser beam on the surface. The impact diameter is illustrated in
The pulse frequency and the speed with which the laser beam moves over the surface determines a distance between adjacent laser beam impact zones in a path segment on the surface. This distance is illustrated in
Tests and simulations have shown that a laser pulse impact on a metal surface typically removes, by burning or evaporating, the impurities such as grease, dirt, old coatings which are present on the surface. Furthermore, the laser pulse impact creates a miniature crater in the surface of the metal. The crater depth and shape depends on the type of metal, and can be experimentally determined by the skilled person.
Laser pulse frequency and laser speed determine distance 3 between adjacent impact zones 1 in a single path segment 2a, 2b. Path segment distance 4 determines the distance between laser impact zones 1 in adjacent paths 2a, 2b. The pulse intensity determines the depth of the miniature crater in the surface, which form the impact zones 1. The pulse diameter determines the diameter and also influences the depth of the crater in the surface which forms the impact zones 1. At least the above-mentioned parameters may be balanced to obtain a predetermined roughness on the surface.
The parameters are balanced to obtain a surface roughness of the surface higher than 1.0 Ra, preferably higher than 1.3 Ra and preferably also a surface roughness of the surface higher than 10.0 Ry, preferably higher than 15.0 Ry. Ra is defined as arithmetical mean value, measured in μm of the absolute values of the profile departures from the mean line within a sampling length. The sampling length may be predefined between 0.2 and 3.0 mm. The mean line is a reference line having the form of the geometrical profile and position so that within the sampling length, the sum of the squares of the profile departures from this line is at a minimum. Ry is defined as the distance measured in μm between the highest profile peak and the lowest profile valley in the profile diagram, measured vertically, within the sampling length.
The measurement of the arithmetic mean roughness Ra and Ry of the surface is preferably made in accordance with ISO 4287:1997. A skilled person may determine the parameters, based on the teaching provided above, to arrive at the preferred roughness of the surface. It will be clear that different surface materials will require different parameters.
Preferably, the pattern is chosen to arrive at a surface roughness of maximum 3 Ra, preferably maximum 2.7 Ra. Instead of increasing the roughness by applying a pattern, the roughness may also be decreased. In particular, by increasing the overlap of adjacent laser beam spots, for example by decreasing the path segment distance 4 and/or by lowering the speed to decrease the distance between adjacent laser beam impact zones in a path segment, the roughness is decreased.
The laser beam impacts at least substantially the complete surface when the laser beam speed along the path 2 is chosen such that adjacent laser beam impact zones show a center to center distance 3 which is smaller than the laser impact diameter 5 and when the distance between adjacent paths 2a and 2b is smaller than the laser impact diameter 5.
The invention is particularly developed for treating surfaces of rotors 15 and housing parts of oil free compressors. The coatings of such machine parts are applied with high mechanical precision and the machine parts with the coatings are used in extreme conditions. Therefore pre-treatment of the surface, ensuring that the application of the coating is optimal, is preferred.
When applying a pattern onto a surface with a complex three-dimensional shape such as the surface of a rotor 15, the apparatus 10 comprises preferably at least three degrees of freedom, more preferably four degrees of freedom, most preferably five degrees of freedom. In the shown example, the rotor 15 is rotatable about an upright axis. Furthermore, at least the optical elements 12 of the laser, preferably also the laser source, may be moved up and down, illustrated with arrow 17, and may be moved towards and away from the machine part 15, illustrated with arrow 18.
Preferably the optical elements 12 of the laser, and more preferably also the laser source 11, may be rotated about a horizontal axis such that the laser beam 13 can be oriented partly downward and partly upward towards the rotor 15. This allows the laser beam 13 to impact the surface substantially perpendicular even when different surface segments show different orientations with respect to the rotor axis. Alternatively, the rotor 15 may be rotated about a lying axis to change the impact angle of the laser beam 13 relative to the upward axis of the rotor 15. By operating the different movements of the apparatus 10, the laser beam 13 can be pointed towards the rotor surface, at least for the majority of the surface, substantially perpendicular.
The same technique may be applied for treating parts of the compressor housing, as will be explained hereunder with reference to
The setup of
The setup of
The invention is not limited to the embodiments described above by means of example, or to the method steps listed above by way of better illustrating the invention, however, a method according to the invention of manufacturing a machine part can be realized in many ways, without departure from the scope of the invention.
This application is a National Stage of International Application No. PCT/EP2020/067333 filed Jun. 22, 2020, claiming priority based on U.S. Application No. 62/865,357 filed Jun. 24, 2019.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/067333 | 6/22/2020 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62865357 | Jun 2019 | US |
