EP3399191B1 - Screw compressor with multilayer rotor screw coating - Google Patents

Description

The invention relates to a screw compressor comprising a compressor housing with two rotor screws, which are mounted axially parallel therein and mesh with one another in a compression chamber, can be driven by a drive and are synchronized with one another in terms of their rotational movement, the rotor screws each having a one-part or multi-part base body with two end faces and one in between have profile surface and projecting over the end faces shaft ends, according to the preamble of claim 1, and a rotor screw according to the features of claim 26, and a method for applying a multilayer coating on a metallic surface of a rotor screw or a compression chamber of a screw compressor according to the features of Claim 27. Screw machines, whether as screw compressors or as screw expanders, have been in practical use for several decades. Designed as screw compressors, they have displaced reciprocating compressors as compressors in many areas. With the principle of the interlocking pair of screws in the form of the rotor screws, not only gases can be compressed using a certain amount of work. The use as a vacuum pump also opens up the use of screw machines to achieve a vacuum. After all, by passing pressurized gases through it the other way round Work output are generated so that mechanical energy can be obtained from pressurized gases using the principle of the screw machine.

Screw machines generally have two rotor screws arranged axially parallel to one another, one of which defines a main rotor and the other a secondary rotor. The rotor screws each have a one-part or multi-part base body with two end faces and a profile surface running between them, and two shaft ends projecting above the end faces.

The rotor screws mesh with corresponding helical teeth. Between the teeth and a compressor housing, several successive working chambers are formed by the tooth space volumes. Starting from a suction area, as the rotor screws rotate, the working chamber in question is first closed and then continuously reduced in volume, so that the medium is compressed. Finally, as the rotation progresses, the working chamber is opened to a print window and the medium is pushed out into the print window. This internal compression process differentiates screw machines designed as screw compressors from Roots blowers that work without internal compression.

The meshing of the two rotor screws defines a pitch circle both for the rotor screw designed as a main rotor and for the rotor screw designed as a secondary rotor. The pitch circles can be represented in an end section of the toothing and it can be seen in such a representation that the pitch circles roll against one another when the rotor screws move. On the pitch circles, the circumferential speeds of the rotor screw designed as the main rotor and the rotor screw designed as the secondary rotor are identical, i.e. there is no relative speed between the two rotor screws in this area. However, the farther away radially within the profile surface from the pitch circles, the greater the relative speeds.

Screw machines can be used in addition to the function already mentioned as a vacuum pump or as a screw expander in various fields of technology as a compressor. A particularly preferred area of application lies in the compression of gases such as air or inert gases (helium, nitrogen, argon, ...). However, it is also possible, although this places special structural requirements, on a screw machine for compressing refrigerants, for example for air conditioning systems or refrigeration applications. If "compressed air" or "gases" is used in the following, this includes all process media that are compressed or expanded. When compressing gases, especially at higher pressure ratios, a fluid-injected compression, in particular an oil- or water-injected compression, is usually used; however, it is also possible to operate a screw machine, in particular a screw compressor, on the principle of dry compression. With oil-free compression, no oil is injected into the compression chamber for cooling and lubrication. The compressed air does not come into contact with oil during the compression process. In the low pressure range, screw compressors are sometimes referred to as screw blowers.

The invention relates to an oil-free, in particular dry compression. Typical pressure ratios for dry compression can be between 1.1 and approx. 10, the pressure ratio being the ratio of the discharge pressure to the suction pressure. The compression can take place in one or more stages. Achievable final pressures can be, for example, in a range from 1.1 bar to approx. 10 bar, in particular with one- or two-stage compression. Insofar as pressure information in "bar" is also referred to at this point or subsequently in the present application, such pressure information relates in each case to absolute pressures.

The invention relates to screw machines, in particular screw compressors, the rotor screws of which are not intended to be synchronized by profile engagement between the two rotor screws, but externally, for example by a synchronous gear on the shaft ends or by separate and electronically synchronized rotor drives. In these screw machines, rotor contact only occurs temporarily, for example due to geometric deviations in the target contour of the rotor screw or rotor screws or due to thermal differential expansions, and is eliminated by removing material from a coating provided on the rotor screws at the contact and friction points. This removal of a temporary contact between the rotor screws is done in one running-in process. Rotor screws are mostly made of steel or cast iron. The compressor housing is typically made of gray cast iron poured. There must be a small gap between the rotor screws and the compressor housing and in particular also between the two rotor screws. These components must not touch each other during operation, as a metallic contact would lead to start-up due to the high speeds and, in the worst case, lead to seizure. The gap between the rotor screws is realized in that both rotor screws are operated synchronized, for example by a synchronous gear or by separate, electronically synchronized rotor drives.

On the one hand, the gaps should be as small as possible in order to minimize backflows of the compressed air into previous working chambers (i.e. against the conveying direction). The more backflow occurs, the higher the internal losses and the poorer the efficiency of the screw machine. In the case of a screw compressor, the compression end temperature rises significantly with increasing backflow, which leads to greater thermal expansions of the rotor screws and the compressor housing. The higher thermal expansion in turn increases the risk of tarnishing, i.e. there is a self-reinforcing effect.

On the other hand, however, the column should also be large enough to ensure the required operational safety. If metallic surfaces come into contact at high relative speeds, this leads to high heat input and thermal expansion and ultimately also to component seizure, as already described above. When dimensioning the gap, the thermal expansion due to high compression temperatures and the deflection of the rotor screws due to the pressure in the working chambers must therefore also be taken into account in addition to the manufacturing tolerances.

Another requirement for oil-free, especially dry compression is to ensure good corrosion protection of the rotor screws and the compressor housing. After the screw compressor, which is still hot, is switched off, condensation can form inside the compressor housing due to the moisture in the air. There is also a risk of corrosion if the compression is dry with water injection (the water evaporates completely until the end of the compression process). Rotor screws and housings made of gray cast iron or conventional steel are particularly susceptible to corrosion.

It is known from the prior art that rotor screws are partially made of stainless steel. However, this is very expensive and complex to manufacture. Similar to the rotor screws, this also applies to the compressor housing.

In the prior art, rotor screws of dry-running screw compressors are therefore provided with a fluoropolymer / lubricating lacquer coating in order to eliminate the problems mentioned above.

The EP 2 784 324 A1 For example, describes the composition of a coating that is used in the refurbishment or overhaul of the rotor screws of a dry-running screw compressor. The worn coating on the rotor screws is removed and replaced with a new coating. This coating consists of PTFE (specifically Teflon 954G 303), graphite and other solvents or thinners. According to the manufacturer's product data sheet (Chemours), substance 954G 303 is only suitable for long-term use temperatures of 150 ° C. There are also other environmental and health protection requirements. The substance 954G 303 as well as other components of the recipe given in the prior art bring with them solvents which are extremely problematic in processing. There are also increasing legal demands for a reduction in volatile organic compounds (VOCs). In addition, the substance 954G 303 is not food-safe and therefore not FDA-compliant. Rather, it is suspected of being carcinogenic.

In addition, the coating proposed in the prior art offers only limited corrosion protection because a layer is applied which contains a comparatively large amount of graphite. If this relatively soft layer is damaged, for example by scratches, the metallic base body of the rotor screw is exposed locally and there is a risk of corrosion.

In the WO 2014/018530 a coating of a high-performance thermoplastic (eg PEEK) as well as a first solid lubricant (eg MoS2) and a second solid lubricant (eg PTFE or graphite) is proposed. However, an application for compressors with low speeds and at the same time high loads is described there. In addition, the coating according to the prior art provides for the coated surfaces to be in constant frictional contact with one another.

In the pamphlets US2003 / 0126733 A1 and EP0190823 A1 Screw machines are disclosed which have rotor screws coated with multiple layers of polymer.

Starting from the first-mentioned prior art, the invention sets itself the task of specifying a coating for an oil-free screw compressor with comparatively high rotational speeds of the rotor screws and a desired gap between the rotor screws with one another or between the rotor screws and a compressor housing, which avoids the disadvantages in the prior art and at the same time adjusts itself to a sufficiently small gap distance in one running-in process. In terms of device technology, this object is achieved by a screw compressor, in particular an oil-free screw compressor, according to the features of patent claim 1, a rotor screw according to the features of patent claim 26 and in terms of process technology with a sequence according to the features of patent claim 27. Advantageous further developments are specified in the subclaims.

A key concept of the present invention is that in the case of a screw compressor or a rotor screw, at least the profile surface of the rotor screw is formed in multiple layers, comprising a first, inner layer and a second, outer layer, the first, inner layer and the second, outer layer Layer both comprise or are formed from a thermoplastic, wherein particles or pores supporting a run-in process are embedded in the second, outer layer and the thermoplastic defines a matrix for receiving the particles or for forming the pores.

• Vorbehandeln der zu beschichtenden metallischen Fläche,
• Aufbringen einer ersten, inneren Schicht, die einen thermoplastischen Kunststoff umfasst bzw. aus diesem gebildet ist, auf die zu beschichtende metallische Fläche oder auf eine Unterschicht, die insbesondere als Vorbehandlungsschicht ausgebildet sein kann, und
• Aufbringen einer zweiten, äußeren Schicht auf die erste, innere Schicht, wobei die zweite äußere Schicht ebenfalls einen thermoplastischen Kunststoff umfasst bzw. aus diesem gebildet ist und wobei in der zweiten, äußeren Schicht einen Einlaufvorgang unterstützende Partikel oder Poren eingebettet sind und der thermoplastische Kunststoff eine Matrix zur Aufnahme der Partikel bzw. zur Ausbildung der Poren definiert.

A key idea of the method according to the invention provides for the application of a multi-part coating to a metallic surface to be coated of a rotor screw or a compression space of a screw compressor, comprising the following steps:

• Pretreatment of the metallic surface to be coated,
• Applying a first, inner layer, which comprises or is formed from a thermoplastic, to the metallic surface to be coated or to an underlayer, which can in particular be designed as a pretreatment layer, and
• Applying a second, outer layer to the first, inner layer, wherein the second outer layer likewise comprises or is formed from a thermoplastic and in the second, outer layer particles or pores that support a running-in process are embedded and the thermoplastic defines a matrix for receiving the particles or for forming the pores.

The formation of the profile surface as a multi-layer layer allows the provision of partial layers with different properties. A special consideration can be seen in the fact that the second, outer layer is designed to be partially or almost completely removed in one run-in process, so that the profile surfaces of the interlocking rotor screws are optimally adjusted to one another, namely under the specific conditions on site, ie under the given pressure conditions, temperature conditions, etc. In this respect, the second, outer layer is more or less a self-adjusting layer.

Preferred configurations for the screw compressor according to the invention or the rotor screw according to the invention are discussed below, at least some of which can also easily be applied to the method according to the invention or can be transferred to the method.

The materials are preferably selected such that the removal of material or the contact of the compressed air with the first, inner layer and / or the second, outer layer is harmless even in food processing applications, i.e. the materials are food-compatible or FDA-compliant. According to a basic idea of the present invention, a thermoplastic is therefore generally used. The thermoplastic is preferably a partially crystalline thermoplastic. Semi-crystalline thermoplastics are characterized by high fatigue strength, good chemical resistance and good sliding behavior. They are also very wear-resistant.

1. i. Polyetherketon (PEK)
2. ii. Polyetheretherketon (PEEK)
3. iii. Polyetherketonketon (PEKK)
4. iv. Polyetherketonetherketonketon (PEKEKK)
5. v. Polyetheretheretherketon (PEEEK)
6. vi. Polyetheretherketonketon (PEEKK)
7. vii. Polyetherketonetheretherketon (PEKEEK)
8. viii. Polyetheretherketonetherketon (PEEKEK)
   und/oder Copolymere davon und/oder Gemische davon,

wobei besonders Polyetheretherketon (PEEK) als bevorzugt angesehen wird. In einer besonders bevorzugten Ausgestaltung umfasst der thermoplastische Kunststoff zur Ausbildung der ersten, inneren Schicht und/oder der thermoplastische Kunststoff zur Ausbildung der zweiten, äußeren Schicht Polyetheretherketon (PEEK) oder besteht zumindest im Wesentlichen aus Polyetheretherketon (PEEK).In a preferred embodiment, the thermoplastic is a high-performance thermoplastic, in particular a partially crystalline high-performance thermoplastic. A high-performance thermoplastic is understood to mean a plastic that has a continuous use temperature of> 130 ° C, preferably> 150 ° C. It is preferably a thermoplastic concentrate, more preferably a polymer or copolymer with alternating ketone and ether functionalities, especially a polyaryl ether ketone (PAEK). Particular examples of polyaryl ether ketones (PAEK) are:

1. i. Polyether ketone (PEK)
2. ii. Polyether ether ketone (PEEK)
3. iii. Polyether ketone ketone (PEKK)
4. iv. Polyether ketone ether ketone ketone (PEKEKK)
5. v. Polyetheretheretherketone (PEEEK)
6. vi. Polyether ether ketone ketone (PEEKK)
7. vii. Polyether ketone ether ether ketone (PEKEEK)
8. viii. Polyether ether ketone ether ketone (PEEKEK)
   and / or copolymers thereof and / or mixtures thereof,

polyether ether ketone (PEEK) in particular being regarded as preferred. In a particularly preferred embodiment, the thermoplastic material for forming the first, inner layer and / or the thermoplastic material for forming the second, outer layer comprises polyether ether ketone (PEEK) or at least essentially consists of polyether ether ketone (PEEK).

The use of polyphenylene sulfide (PPS) and polyamides (PA), in particular PA11 or PA12, as thermoplastic is also possible.

The thermoplastic base substance further preferably generally comprises a polyaryl ether ketone (PAEK) for forming the first, inner layer and for forming the second, outer layer, or is at least essentially formed from PAEK. The high-performance thermoplastics can also be referred to as high-performance thermoplastic or as thermoplastic high-performance plastic.

In general, it applies to the multilayer structure of the layers comprising thermoplastic according to the present invention that the first, inner layer and the second, outer layer differ structurally, even if the same thermoplastic is used. The first, inner layer is preferably particle-free or pore-free or in any case has a smaller proportion of particles and / or pores than the second, outer layer, preferably a significantly lower proportion of particles and / or pores. The proportion of thermoplastic in the first, inner layer, based on the total mass, is at least 60% by weight, preferably at least 70% by weight, further preferably at least 80% by weight, further preferably at least 95% by weight preferably at least 100% by weight. The proportion of thermoplastic material in the second, outer layer is preferably at least 50% by weight and, when particles are used in the second, outer layer, at most 95% by weight, a minimum proportion of 5% by weight of particles, further preferably 10% by weight of particles is provided. On the other hand, if instead of particles only pores are provided in the second, outer layer, the proportion of thermoplastic material in the second, outer layer can also be over 95% by weight. The proportion by volume of pores in the second, outer layer is preferably above 5%, further preferably above 10%, whereas the proportion of pores in the first, inner layer is below 5%, preferably below 2%.

More preferably, the first, inner layer is formed without particles or pores that support a running-in process, but at least essentially homogeneously. Of course, this is not an abstract theoretical homogeneity, but the first, inner layer is comparatively homogeneous in relation to the second, outer layer, which comprises particles or pores that support the running-in process and in any case has no specifically introduced inhomogeneities.

In one possible embodiment, the particles of the second, outer layer that support a running-in process comprise abrasive and / or lubricating particles. In this respect, it is possible to provide a second, outer layer only with abrasive particles or alternatively to provide only with lubricating particles. It is also possible to provide both abrasive and lubricating particles in the second, outer layer. Finally, it is conceivable to define areas in which only abrasive particles or only lubricating particles are provided or areas in which both types are mixed, the ratio of the abrasive particles to the lubricating particles also changing over different areas of the second outer layer can.

According to a preferred embodiment, the particles comprise hollow microspheres (microspheres), in particular made of aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ), thermoplastic or glass, in particular borosilicate glass (borosilicate glass) or are formed from these. Hollow microspheres are very light, hollow spheres of microscopic dimensions that are filled with air or inert gas. The shell of the micro hollow spheres can in particular consist of one of the following materials: aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ) or of glass and the latter in particular of borosilicate glass (borosilicate glass). Balls made of borosilicate glass, which are hollow on the inside, are offered by 3M as "Glass Bubbles", are in powder form, are chemically inactive, non-flammable and non-porous. An average sphere diameter is, for example, 20 µm with an average wall thickness of 0.7 µm. When using such micro glass hollow spheres, these burst during the running-in process. Due to their hardness (they are much harder relative to the binder matrix of the second, outer layer), they also provide the necessary abrasion and offer local, tiny, evenly distributed points of attack for coating removal in case of frictional contact with an opposite surface, e.g. the opposite rotor screw, whereby an undesired or harmful, large-area chipping of the layers with the respectively assigned opposite surface, such as the profile surface of an opposite rotor screw or in the event of contact between the rotor screw and the compressor housing, is avoided.

In an optionally possible embodiment of the present invention, the particles of the second, outer layer that support a running-in process have a higher hardness than the matrix defined by the thermoplastic, the hardness being measured or defined according to Shore.

In a likewise optional embodiment of the present invention, the particles of the second, outer layer that support a running-in process have a lower hardness than the matrix defined by the thermoplastic, the hardness being measured or defined according to Shore.

According to a particularly preferred aspect of the present invention, the first, inner layer is connected to the second, outer layer by melting. This results in a particularly stable, permanent and reliable connection between the first, inner layer and the second, outer layer. This allows a relatively reliable anchorage of the Ensure the second, outer layer, even if the second, outer layer has a comparatively high proportion of particles or pores and thus, for example, would have relatively poor adhesive properties if it were theoretically attached directly to the metallic base body or on a metallic surface. In this context, it must also be noted that the proportions of the particles based on the proportion of the thermoplastic, in particular a high-performance thermoplastic, in particular PEEK, can be specified by weight and for example the particle / binder mass ratio can be stated as P / B. The binder is the matrix made of thermoplastic material for receiving the particles.

In order that the respective properties of the particles in the second, outer layer can be used and have an effect, minimum quantities should preferably be specified. On the other hand, proportions of particles cannot be increased arbitrarily. The particles are bound in the binder, i.e. the matrix made of thermoplastic material. The higher the particle content, the stronger the particle properties have an effect, but the worse the particles themselves can be bound in the binder matrix, especially in PEEK. The following advantageously applies to the total particle fraction:
0.03 ≤ P / B ≤ 1.0 based on the respective mass ratios. A preferred range for the total filler fraction is 0.15 P P / B 0,3 0.35.

Alternatively, the following can also be defined as preferred ranges for concrete particles:
Particles: Graphite: 0.3 ≤ P _graphite / B ≤ 0.75 with P _graphite as the mass of the graphite.

Particles: hollow glass spheres: 0.05 ≤ P _{hollow glass spheres} / B ≤ 0.5 with P _{hollow glass spheres} as the mass of the hollow glass spheres.

According to a preferred consideration of the present invention, the first, inner layer defines a substantially homogeneous coating and thus a corrosion protection layer for the metallic surface covered by the first, inner layer. As already mentioned, the first, inner layer can be provided as a very homogeneous layer, which thus adheres well to the metallic surface to be coated and thus offers good protection against corrosion. A further preferred aspect of the present invention defines the second, outer layer an infeed layer that is partially removed and / or plastically deformed in the infeed process, and thus an inlay layer that adapts to the specific operating conditions. The run-in layer is designed in such a way that it can adapt to the specific operating conditions and, in relation to a counter surface, can ensure that a favorable gap dimension is established.

According to a further advantageous embodiment of the present invention, the particles contained in the second, outer layer comprise graphite or can be formed from graphite. However, the particles can also comprise the following materials: hexagonal boron nitride, carbon nanotubes (carbon nanotubes CNT), talc (or talc), polytetrafluoroethylene (PTFE), perfluoroalkoxy polymers (PFA), fluoroethylene propylene (FEP) and / or another fluoropolymer.

Graphite, hexagonal boron nitride, carbon nanotubes and talc all reduce friction as a solid lubricant. The materials can be removed relatively well, i.e. there is a favorable running-in behavior. Graphite is relatively soft relative to the binder matrix. Talc is also comparatively soft and acts as a low-abrasive lubricant. It is also water-repellent and waterproof.

Fluoropolymers, such as PTFE, PFA, FEP (with average grain sizes of approx. 2 µm to 30 µm) also act as solid or dry lubricants. They are mixed in powder form with the thermoplastic plastic of the binder matrix, such as PEEK, and do not dissolve even with wet paint in the subsequent processes for forming the second, outer layer. They are rather soft relative to the binder matrix and therefore ensure good lubricating, sliding and non-stick properties.

Alternatively or additionally, the particles can also comprise the following materials: aluminum dioxide (Al ₂ O ₃ ), silicon carbide (SiC), silicon dioxide (SiO ₂ ) and / or glass (in particular borosilicate glass).

As an alternative or in addition to the particles, pores can also be incorporated in the second outer layer. Pores are to be understood as cavities which have an extent of at least one, the largest dimension 1 µm. The incorporation of such pores in the manufacturing process can be achieved, for example, by mixing in suitable foams (for example by chemical additives which act as blowing agents). Overall, the pores can form an open-pore or a closed-pore structure. The pores advantageously have a size of at most a few micrometers and are further advantageously at least substantially homogeneously distributed within the second outer layer.

Pore-like cavities can also be created using hollow micro spheres with a thermoplastic shell (plastic microspheres). The thermoplastic shell encloses a gas that expands when heat is applied and increases the volume of the hollow sphere. Micro hollow spheres of this type made of a plastic shell can be present as particles in expanded or non-expanded form. A polymer matrix with hollow particles embedded in it is sometimes referred to in the specialist literature as syntactic foam. It should also be mentioned that functional textures can be created on the surface of the coating, in particular with plastic microspheres. This can be used to influence gap flows, for example.

The incorporation of pores or pore-like cavities in the second, outer layer causes the second, outer layer to compress plastically to the layer thickness required in each case during the running-in process, and a relatively good gap dimensioning is thus automatically established.

• Besseres Handling vor oder während der Verarbeitung (bessere Fließeigenschaften, weniger Staubentwicklung)
• Bessere Dispergierbarkeit. Eine wasserunlösliche Substanz kann in Mikrokapseln eingeschlossen werden, damit sie in einem wässrigen Medium dispergierbar ist. Auch eine elektrostatische Aufladung oder das Risiko einer allmählichen Verklumpung (Agglomeration) kann durch Verkapselung verringert werden.
• Möglichkeit der Kombination inkompatibler Substanzen
• Verhinderung von vorzeitigen chemischen Reaktionen mit anderen Mischungskomponenten
• Beeinflussung elektrostatischer Eigenschaften

According to a further advantageous embodiment, the particles are in microencapsulated form. In microencapsulation, at least one first substance (active ingredient) is surrounded by a second substance (the shell material or the shell). A distinction is made between monolithic microcapsules with a solid core and reservoir microcapsules with a liquid core. The shell is made of plastic, for example. The advantages of microencapsulated particles are in particular:

• Better handling before or during processing (better flow properties, less dust generation)
• Better dispersibility. A water-insoluble substance can be enclosed in microcapsules so that it is dispersible in an aqueous medium. Electrostatic charging or the risk of gradual clumping (agglomeration) can also be reduced by encapsulation.
• Possibility of combining incompatible substances
• Prevention of premature chemical reactions with other mixture components
• Influencing electrostatic properties

In an advantageous embodiment, microencapsulated lubricants embedded in the second, outer layer are released under mechanical stress predominantly in the running-in phase. In this way, the running-in process can be lengthened, for example. There is less frictional heat and consequently a lower risk of breakouts of the second, outer layer.

Of course, it is also conceivable to incorporate further particles or pigments, for example titanium dioxide (TiO ₂ ), into the second, outer layer.

In a preferred embodiment, the layer thickness of the first, inner layer before entry is between 5 μm and 50 μm. In order to achieve a layer thickness of, for example, 50 μm, the first, inner layer can also be applied in several layers, for example two layers of 25 μm each, in order to achieve a total layer thickness of 50 μm for the first, inner layer. The layer thickness is always the dry layer thickness (DFT, Dry Film Thickness).

The layer thickness of the second, outer layer before running in is preferably 10 μm to 120 μm. The dry film thickness (DFT) is also addressed here. The second, outer layer can also be applied in several layers. It is advantageous to make the layer thickness the thicker the larger the diameter of the rotor screws. The total layer thickness of the first, inner layer and second, outer layer can therefore preferably be in a range from 15 μm to 170 μm.

The gaps and layer thicknesses are ideally matched to one another in such a way that there is minimal play between the rotor screws and between the rotor screws and the compressor housing when the rotor screws are installed in the compressor housing. The assembled rotor screws should just be able to be turned against each other. If the layer thickness is so large that there is an oversize, the rotor screws can only be installed in the housing with the application of force and force. The play during assembly is advantageous because then the rotor screws defined, for example via a synchronous gear, can be synchronized. The relative angle of rotation of the rotor screws to each other is permanently fixed.

The second, outer layer adheres better to the first, inner layer than directly to the metallic surface of the component to be coated, for example to the base body of the rotor screw. This is because the thermoplastic, for example the PEEK, of the second layer merges with the thermoplastic, for example the PEEK, of the first layer. As the proportion of particles increases, the proportion of thermoplastic plastic in the binder matrix, in particular the proportion of PEEK, decreases accordingly. As a result, the function of the thermoplastic, in particular PEEK, as a binder matrix is also weakened.

If the second, outer layer was applied directly to the metallic surface, for example to the base body of the rotor screw, then with increasing proportion of the particles there would be less binder matrix part available which can bond to the metallic surface.

When the screw compressor is started up, as already mentioned, the compression temperature leads to thermal expansion and bending of the rotor screws and subsequently to the rotating rotor screws and between the rotating rotor screws and the stationary compressor housing. With this contact, the second, outer layer is partially removed. The rotor screws shrink, locally to different degrees, and only where components touch. Depending on the respective deformations and deviations from the target geometry of the rotor screws and possibly the compressor housing, the second, outer layer is removed in different sizes, in part. As already mentioned, this removal is referred to as the running-in process and should only take place in the second, outer layer, the running-in layer. The running-in process essentially only takes place once, when the screw compressor is started up for the first time. It is advantageous to carry out the running-in process carefully. It is advantageous to adapt the running-in process to the later area of application of the screw compressor. A variable-speed drive (eg permanent magnet motor or synchronous reluctance motor) of the screw compressor is particularly advantageous for a careful running-in process. This enables the drive speed to be defined during the running-in process and increased in time up to the maximum intended operating speed. In contrast, a fixed speed drive (e.g. with a conventional asynchronous motor without a frequency converter) would drive the screw compressor very quickly at the high speed required for dry compression with the risk that the coating could be damaged due to the extremely short running-in process. The running-in process can take place, for example, on a separate running-in test bench. However, the entire machine (screw machine including drive, etc.) is advantageously already equipped with a variable-speed drive, so that the running-in process can take place during the initial start-up of the machine intended for the customer. The elaborate intermediate step (assembly and disassembly on the running-in test bench) could thus be omitted. In this way, an unnecessarily high removal of the second, outer layer can be avoided, which would otherwise lead to an increased undesired backflow against the conveying direction.

The hard or abrasive particles absorbed in the second, outer layer ensure that the softer material of the friction partner is removed. Comparatively soft particles (based on the hardness of the thermoplastic that defines the binder matrix) ensure that the second, outer layer in which they are located can be removed very quickly and easily by a harder friction partner. In contact areas in the profile area of the rotor sections with no or low relative speeds of the two rotor screws to one another during operation (i.e. in or near the rolling circles or rolling areas), high surface pressures occur simultaneously, so that, for example, the thin-walled micro-glass hollow spheres in the second, outer layer advantageously break open and thus ensure the necessary abrasion or loss of layer thickness in the second, outer layer on both rotor screws. According to a preferred aspect of the present invention, the sharp breaking edges of the micro glass spheres that arise during the breaking open support the abrasive process. A loss of layer thickness can also be achieved through pores enclosed in the second, outer layer, with plastic deformation due to compression or collapse of the pores occurring here.

This prevents undesirable constant pressing of the rotor screws against each other. Among other things, this has a favorable effect on the service life of the coating and on the service life of the bearings. Overall, this adaptability of the second, outer coating, particularly in or near the rolling region of the screw rotors, advantageously improves the smoothness of the screw compressor.

In contact areas of the rotor screws with comparatively high relative speeds to one another, i.e. in areas with increasing radial distance from the pitch circles, soft particles such as graphite can be removed relatively easily due to the large relative speeds of the friction partners, i.e. the second, outer layer also runs in well in these areas. Graphite in particular also has the advantage that it is comparatively inexpensive and does not smear on the counter surface.

According to a preferred embodiment of the present invention, the base body of the rotor screw is formed from steel and / or cast iron.

According to the invention, it is also advantageous, in addition to the profile surface or the profile surfaces, to coat further sections of one or both rotor screws and the compressor housing in a corresponding manner in a corresponding manner.

With regard to the rotor screw itself, the end faces can also be coated with a first, inner layer and a second, outer layer, the first, inner layer and second, outer layer both comprising or being formed from a thermoplastic and the second, outer layer has a running-in process supporting particles or pores, the thermoplastic defines a matrix for receiving the particles or for forming the pores. However, it can also be provided that only one of the two end faces, preferably only the pressure-side end face, as described above, is coated with both the first, inner layer and the second, outer layer, while the opposite end face is only coated with the first, inner layer.

Furthermore, sections of the shaft ends can also be covered with thermoplastic material according to the first, inner layer. Advantageously, however, sections of the shaft ends are also uncoated, ie without a layer made of thermoplastic material according to the present invention Mistake. Any other coating of these sections is unaffected.

The functional areas of a compressor housing essentially consist of a suction area, the rotor bore, a pressure area as well as sealing and bearing seats. In the case of a screw compressor, the process medium, for example the air to be compressed, flows from the suction area to the rotor bore and through a pressure window to the pressure area.

The suction area is located on the inlet side of the compressor housing and extends from a suction nozzle of the compressor housing to the rotor bore. In the rotor bore, which comprises two partial bores matched to the rotor screws, the rotor screws are each stored with very small gaps (radial housing gaps) and form working chambers within the compression chamber. The compression space is the interior space defined by the rotor bore in the compressor housing. A flat end face in the compressor housing with a very small axial gap to the two pressure-side rotor end faces is referred to as the pressure-side housing end face. Accordingly, the end face in the compressor housing with the shortest axial distance from the suction-side rotor end faces is referred to as the suction-side housing end face.

The pressure range extends from the end of the compression chamber to a pressure port on the compressor housing.

Sealing seats in the compressor housing (housing-side sealing seats) are used to hold seals, specifically air or fluid seals and oil seals. In the following, the term air seal should always be understood to include a seal for other media. Likewise, the term "oil seal" should always be understood to include a seal for other bearing lubricants.

Bearings (e.g. roller bearings) for the two rotor screws are mounted in bearing seats in the compression housing. Furthermore, sealing seats (rotor-side sealing seats) are also provided on the shaft ends of the rotor screws. A distinction is made between seal seats for air seals and seal seats for oil seals, which are typically arranged side by side on the shaft ends of the rotor screws. The sealing seats for the Air seals are located on both sides of the rotor screw in close proximity to the suction-side and pressure-side rotor end faces. Following this and consequently further away from the rotor end faces, the seal seats for the oil seals are arranged.

The oil seals prevent oil from entering the storage area into the compression area of the screw compressor. The air seals, on the other hand, prevent the compressed air or the conveyed fluid from escaping from the compression space.

Furthermore, bearing seats are also provided on the shaft ends on which, for example, the roller bearings are located. The bearing seats usually adjoin the sealing seats.

• dem Saugbereich (vom Saugstutzen des Schraubenverdichters bis zum Beginn des Verdichtungsraums),
• der Rotorbohrung mit den Teilabschnitten für beide Rotorschrauben,
• den beiden Gehäusestirnflächen (saugseitige und druckseitige Gehäusestirnfläche),
• dem Druckbereich (vom Ende des Verdichtungsraums bis zum Druckstutzen des Schraubenverdichters)
• sowie den Dichtungssitzen.

It is also advantageous, as already mentioned in part, to coat further sections of the rotor screws and the compressor housing in order to coat the profile surface of the rotor screws. The entire inner region of the compressor housing, which comes into contact with the fluid to be conveyed, for example the air to be compressed, can be coated with a first, inner layer, which comprises or is formed from a thermoplastic. This area to be coated consists of

• the suction area (from the suction port of the screw compressor to the beginning of the compression chamber),
• the rotor bore with the sections for both rotor screws,
• the two housing faces (suction-side and pressure-side housing faces),
• the pressure range (from the end of the compression chamber to the discharge port of the screw compressor)
• as well as the sealing seats.

The rotor bore with the two sections for both rotor screws can advantageously in addition to the first, inner layer with the second, outer layer according to the invention, which has a run-in process particles or pores and in which the thermoplastic material has a matrix for receiving the particles or for forming the Pores defined, coated. Such a second, outer layer can also be applied to the pressure-side housing end face.

The suction area and pressure area can also be provided with such a second, outer layer. However, it is alternatively also possible to apply a different corrosion protection layer to the suction area and the pressure area instead of the first, inner layer proposed here or the combination of the first, inner and second, outer layer proposed here. A second, outer layer according to the invention can also be applied to the sealing seats in the housing. As an alternative to coating the seal seats with the first, inner layer or first, inner layer and second, outer layer, it is also possible for the seal seats to remain uncoated in the housing. “Uncoated” is to be understood here in the sense that the sealing seats in the housing are not provided with a first, inner layer and / or a second outer layer, that is to say not with a coating according to the present invention. The bearing seats in the housing, however, must not be coated. It also applies here that the bearing seats must not be provided with a coating according to the invention; Any other, in particular film-like coating, for example to increase the sliding properties, is unaffected.

The function of the run-in layer between the rotor screw as the moving part and the compression chamber of the compressor housing as the stationary part is entirely as described above, i.e. when the screw compressor is started up, the compression temperature causes thermal expansion of the rotor screws and the compressor housing and the rotor screws to bend. As a result, the rotor screws and the rotor bore may come into contact, for example, or the rotor end faces and the housing end faces, in particular the pressure-side rotor end face and the pressure-side housing end face. With this contact, the second, outer coating is partially removed, as intended according to the invention. The end faces shrink accordingly. It must be taken into account here that the axial end gap on the pressure side is particularly important for efficient compression. This forehead gap should ideally be very small. The axial face gap on the pressure side is set in a defined manner when installing the rotor screws in the compressor housing (usually with an accuracy in the range of less than 1/100 mm and, for example, using spacers). It is also particularly important for efficient compression that the radial gap between the rotor screws and the rotor bore is very small.

The following coating variants are particularly conceivable as possible exemplary embodiments, although this list is by no means exhaustive and further combinations also appear conceivable: Rotor screw 1 (e.g. secondary rotor) (profile area) Rotor screw 2 (e.g. main rotor) (profile area) Rotor face on the pressure side Rotor face on the suction side Rotor bore in the housing Pressure-side housing face version 1 First inner layer + second outer layer (hard) First inner layer + second outer layer (hard) First inner layer + second outer layer (hard) OR first inner layer + second outer layer (soft) OR first inner layer First inner layer + second outer layer (hard) OR first inner layer + second outer layer (soft) OR first inner layer First inner layer + second outer layer (hard) OR first inner layer + second outer layer (soft) OR first inner layer First inner layer + second outer layer (hard) OR first inner layer + second outer layer (soft) OR first inner layer Variant 2 First inner layer + second outer layer (soft) First inner layer + second outer layer (soft) Variant 3 First inner layer + second outer layer (hard) First inner layer + second outer layer (soft) Variant 4 First inner layer First inner layer + second outer layer (soft)

In a preferred embodiment of the present invention, the screw compressor is an oil-free, in particular dry-compressing screw compressor.

In the case of the coating method already mentioned, the core consideration is that a second, outer layer is applied to a first, inner layer which comprises or is formed from a thermoplastic, the second, outer layer likewise comprising or is formed from this and wherein particles or pores supporting a running-in process are embedded in the second, outer layer and the thermoplastic defines a matrix for receiving the particles or for forming the pores. The specified steps preferably also take place in the specified order.

The various material options for the thermoplastic, which is a so-called high-performance thermoplastic, have already been discussed in connection with the technical aspects of the device of the present invention. Reference is made to these statements here. It is generally stated once again that the thermoplastic can be a polyaryl ether ketone (PAEK), polyether ether ketone (PEEK) being regarded as particularly preferred.

The coatings can be applied, for example, as a water-based wet paint coating with conventional spray coating equipment (e.g. HVLP guns, electrostatic, airless) or electrostatically as a powder coating, manually or robot-controlled. Robot-controlled painting offers the advantage of high process reliability with uniform layer thicknesses and small tolerances.

• Pulverlack: Partikel werden in Pulverform dem ebenfalls meist pulverförmig vorliegenden thermoplastischen Kunststoff, insbesondere dem pulverförmig vorliegenden PEEK, beigemischt.
• Nasslack: Partikel und thermoplastischer Kunststoff, insbesondere PEEK werden jeweils in Pulverform, vorteilhafterweise in Wasser mit Dispergiermittel gemischt. Die Partikel und das PEEK-Pulver lösen sich in der Dispersion nicht auf, sondern es entsteht eine Suspension. Insbesondere bei der Anwendung eines Nasslackverfahrens für die Aufbringung der ersten inneren Schicht muss ein Ablüften der ersten Schicht vorgesehen werden. Dieses Ablüften der ersten Schicht umfasst bevorzugterweise ein Aufheizen der beschichteten nassen Bauteile auf ca. 120 °C zur Verdunstung des Wassers über einen vorgegebenen Zeitraum. Erst dann sollte die zweite, äußere Schicht im nassen oder trockenen Zustand aufgebracht werden.

With regard to the production of powder paint or wet paint, the following should be noted with regard to the coating provided here:

• Powder coating: Particles are added in powder form to the thermoplastic, which is also usually in powder form, in particular the powdered PEEK.
• Wet paint: Particles and thermoplastic, in particular PEEK, are each mixed in powder form, advantageously in water with dispersant. The particles and the PEEK powder do not dissolve in the dispersion, but a suspension is created. Especially when using a wet paint process for the Application of the first inner layer requires ventilation of the first layer. This flashing off of the first layer preferably comprises heating the coated wet components to approximately 120 ° C. in order to evaporate the water over a predetermined period of time. Only then should the second, outer layer be applied wet or dry.

The first, inner layer and / or the second, outer layer can be applied as a wet paint or powder paint. According to a further preferred aspect of the invention, the first, inner layer and the second, outer layer are burned in such that the thermoplastic melts. In this respect, the stoving can take place after each layer has been applied; alternatively, it is also conceivable to first apply the two or more layers and only then to burn them in in a single firing process.

The first, inner layer and the second, outer layer are preferably baked at temperatures of approximately 360 ° C. to 420 ° C. until the thermoplastic, in particular the PEEK, has melted and forms a homogeneous layer on the surface to be coated is sufficiently liable. The stoving can take place in particular in a convection oven or inductively. As already mentioned, baking is also possible after each layer has been applied. Finally, it should be mentioned that it is also possible to increase the layer thickness of the second, outer layer and then to post-treat, in particular re-grind, to set a desired layer thickness.

Before applying the first, inner layer, the metallic surface to be coated should be pretreated. This pretreatment preferably comprises degreasing and further preferably further conditioning of the metallic surfaces, for example by roughening the surfaces, by blasting or etching or by applying a pretreatment layer defining a conversion layer, for example phosphating or applying a nanoceramic. The surface pretreatment can also include sandblasting and subsequent chemical cleaning with a suitable solvent (eg alkaline cleaner, acetone) in order to promote good adhesion of the first, inner layer. Degreasing can advantageously be carried out before sandblasting - by burning off at high temperature (pyrolysis).

• Minimierung der Umweltbelastung,
• phosphatfrei ablaufender Prozess und
• insgesamt kostengünstigerer Prozess.

A nanoceramic coating (eg based on titanium or zirconium) can first be applied to the correspondingly pre-cleaned metallic surface. Nanoceramic coatings are a further development of the known phosphatization. Advantages of a nanoceramic coating compared to phosphating are in particular:

• Minimization of environmental pollution,
• process free of phosphate and
• overall cheaper process.

In this respect, the nanoceramic coating is a special pretreatment layer that can be regarded as an underlayer with respect to the first, inner layer and / or the second, outer layer. However, layers other than sub-layers are also conceivable.

• Gutes Einlaufverhalten der zweiten, äußeren Schicht ermöglicht kleine Spalte zwischen den Rotorschrauben und dem Verdichtergehäuse und damit eine effizientere Verdichtung.
• Gleichzeitig wird ein sehr guter Korrosionsschutz durch die erste, innere Schicht gewährleistet und damit die Lebensdauer der derart beschichteten Bauteile verlängert.
• Das Einlaufen findet nur in der zweiten, äußeren Schicht statt; die erste, innere Schicht dient als Korrosionsschutz. Dadurch lassen sich die beiden Anforderungen Korrosionsschutz und Einlaufverhalten (gezielt getrennt voneinander) optimieren.
• PEEK ist für den Einsatz in Umgebungen mit Lebensmittelkontakt geeignet (FDA-konform). Auch die unterschiedlichen Partikel sind lebensmitteltaugl ich.
• PEEK ist umweltfreundlich: PEEK-Dispersionen sind meist auf Wasserbasis und haben sehr niedrige Anteile an flüchtigen, organischen Verbindungen (VOC). Die Applikation der unterschiedlichen Schichten ist ohne Gesundheitsrisiken und erscheint insbesondere nicht krebserregend.
• Es ist eine sehr gute Chemikalienbeständigkeit gegeben, was vor allem dann von Belang ist, wenn andere Gase als Luft verdichtet werden sollen bzw. wenn die Ansaugluft unter Umständen kontaminiert ist.
• Die Eigenschaften der Beschichtung bleiben bei Kontakt mit Wasser, Feuchtigkeit und Dampf unverändert. Im Vergleich zu anderen Fluorpolymerbeschichtungen hat gerade PEEK eine sehr geringe Wasseraufnahme, d.h. das Risiko eines Quellens der Beschichtung ist deutlich reduziert. Dieser Aspekt erscheint insbesondere für Schraubenverdichter, die nach dem Prinzip der Wasser-Mindermengeneinspritzung arbeiten, vorteilhaft.
• Es ergibt sich für das Betriebsverhalten des Schraubenverdichters eine hohe Laufruhe (die zweite, äußere Schicht gewährleistet ein gutes Einlaufverhalten; auch bei ständigem Reibkontakt entsteht kein unerwünschtes "Drücken" der Rotorschrauben gegeneinander).
• Darüber hinaus zeigt die zweite, äußere Schicht, die insbesondere auch die äußerste Schicht definiert, ein sehr geringes Anhaften, so dass kein Schmutz anhaftet, der zum Klemmen zwischen den Rotorschrauben oder zwischen Rotorschrauben und Verdichtergehäuse führen könnte.

With regard to the invention and the described exemplary embodiments, the following can be stated:

• Good run-in behavior of the second, outer layer enables small gaps between the rotor screws and the compressor housing and thus more efficient compression.
• At the same time, very good corrosion protection is guaranteed by the first, inner layer and thus the life of the components coated in this way is extended.
• The shrinkage only takes place in the second, outer layer; the first, inner layer serves as corrosion protection. This allows the two requirements of corrosion protection and running-in behavior (specifically separated from each other) to be optimized.
• PEEK is suitable for use in food contact environments (FDA compliant). The different particles are also food-grade.
• PEEK is environmentally friendly: PEEK dispersions are mostly water-based and have very low levels of volatile organic compounds (VOC). The application of the different layers is without health risks and in particular does not appear to be carcinogenic.
• The chemical resistance is very good, which is particularly important when gases other than air are to be compressed or when the intake air is contaminated under certain circumstances.
• The properties of the coating remain unchanged upon contact with water, moisture and steam. Compared to other fluoropolymer coatings, PEEK in particular has a very low water absorption, ie the risk of the coating swelling is significantly reduced. This aspect appears to be particularly advantageous for screw compressors that operate on the principle of low-volume water injection.
• The operating behavior of the screw compressor is very smooth (the second, outer layer ensures good running-in behavior; even with constant frictional contact there is no undesired "pressing" of the rotor screws against each other).
• In addition, the second, outer layer, which in particular also defines the outermost layer, shows very little adhesion, so that no dirt adheres, which could lead to jamming between the rotor screws or between the rotor screws and the compressor housing.

In addition, the multilayer coating proposed here has a high temperature resistance and good resistance to temperature changes.

Finally, fluoropolymer-free coatings are required in some areas (e.g. in the tobacco industry). With some of the particles mentioned, fluoropolymer-free coatings can be achieved.

Figur 1

einen Stirnschnitt eines erfindungsgemäßen Rotorschraubenpaars;

Figur 2

zwei miteinander verzahnte Rotorschrauben in perspektivischer Ansicht;

Figur 3

ein Ausführungsbeispiel einer erfindungsgemäßen Rotorschraube, die hier konkret als Nebenrotor ausgebildet ist;

Figur 4

ein Ausführungsbeispiel einer erfindungsgemäßen Rotorschraube, die hier konkret als Hauptrotor ausgeführt ist;

Figur 5

eine schematische Schnittansicht eines Schraubenverdichters;

Figur 6

eine Explosionsdarstellung eines Schraubenverdichters;

Figur 7

eine schematische Ausführungsform der mehrschichtigen Beschichtung einer Rotorschraube vor dem Einlaufen;

Figur 8

eine schematische Ausführungsform der mehrschichtigen Beschichtung einer Rotorschraube nach dem Einlaufen;

Figur 9

schematisch eine nur einschichtige Beschichtung eines Abschnitts einer Rotorschraube;

Figur 10

eine alternative Ausführungsform einer mehrschichtigen Beschichtung einer Rotorschraube vor dem Einlaufen;

Figur 11

die Ausführungsform der mehrschichtigen Beschichtung einer Rotorschraube nach Figur 10 nach dem Einlaufen;

Figur 12

einen Ablauf eines bevorzugten Ausführungsbeispiels des erfindungsgemäßen Beschichtungsverfahrens.

The invention is also explained in more detail below with regard to further features and advantages based on the description of exemplary embodiments and with reference to the accompanying drawings. Here show:

Figure 1

an end section of a pair of rotor screws according to the invention;

Figure 2

two interlocking rotor screws in perspective view;

Figure 3

an embodiment of a rotor screw according to the invention, which is specifically designed here as a secondary rotor;

Figure 4

an embodiment of a rotor screw according to the invention, which is specifically designed here as a main rotor;

Figure 5

a schematic sectional view of a screw compressor;

Figure 6

an exploded view of a screw compressor;

Figure 7

a schematic embodiment of the multilayer coating of a rotor screw before running in;

Figure 8

a schematic embodiment of the multilayer coating of a rotor screw after running in;

Figure 9

schematically shows a single-layer coating of a section of a rotor screw;

Figure 10

an alternative embodiment of a multi-layer coating of a rotor screw before running in;

Figure 11

the embodiment of the multi-layer coating of a rotor screw Figure 10 after running in;

Figure 12

a sequence of a preferred embodiment of the coating method according to the invention.

In Figure 1 1 shows an end section of a pair of rotor screws according to the invention comprising a rotor screw 1 designed as a secondary rotor and a rotor screw 2 designed as a main rotor. It is shown purely schematically that a profile surface 12a, 12b of the rotor screw 1, 2 each has a first inner layer 3 and a second, outer layer 4 is coated. The rotor screws 1, 2 mesh with one another, ie they engage with one another with their teeth. The pitch circles already mentioned are identified by the reference symbol 22 for the rotor screw 1 designed as a secondary rotor and by the reference symbol 21 for the rotor screw 2 designed as a main rotor.

In Figure 2 the toothed rotor screws 1, 2 are shown in a perspective view. Both rotor screws 1, 2 engage with one another with the already mentioned profile surfaces 12a, 12b or are toothed or screwed together. Perpendicular to the respective axis of rotation of the rotor screws, the profile surfaces 12a, 12b are delimited at each end by end surfaces 5a, 5b, 5c, 5d, the end surface 5a being a pressure-side end surface of the rotor screw 1 designed as a secondary rotor, and the end surface 5c being a suction-side end surface. In the case of the rotor screw 2 designed as a main rotor, the pressure-side end face is designated by the reference symbol 5b and the suction-side end face by the reference symbol 5d.

Above the end faces 5a, 5b, 5c, 5d projecting in the axial direction projecting shaft ends 30 are formed, each forming a shaft 16 in pairs for a rotor screw 1, 2. A rotor-side seal seat 7b for an air seal, a rotor-side seal seat 7a for an oil seal and a rotor-side bearing seat 9a, 9b are formed on the shaft ends 30. The rotor-side sealing seat 7b is designed for an air seal adjacent to the end face 5a, 5b, 5c, 5d, whereas the rotor-side bearing seat 9a, 9b is provided more towards the distal end of the shaft end 30. Between the rotor-side bearing seat 9a, 9b and the rotor-side sealing seat for an air seal 7b, the already mentioned rotor-side sealing seat 7a is provided for an oil seal.

Figure 3 shows an embodiment of a rotor screw 1 designed as a secondary rotor, as it is already based on the Figure 2 has been described. Here, too, the profile surface 12a is coated with a first, inner layer 3 and a second, outer layer 4. The two end faces 5a, 5c are also coated with a first inner layer 3 and a second, outer layer 4. The shaft ends, on the other hand, are only coated between the end faces 5a, 5c and the bearing seats 9a with a first inner layer 3 (with the omission of a second, outer layer 4), the bearing seats 9a however being free, ie without a coating corresponding to the first, inner one Layer 3, that is, are formed without coating with a thermoplastic.

Figure 4 shows an embodiment of a rotor screw 2 formed as a main rotor, as it is already based on the Figure 2 has been described. Here, too, the profile surface 12b is coated with a first, inner layer 3 and a second, outer layer 4. The two end faces 5b, 5d are also coated with a first inner layer 3 and a second, outer layer 4. The shaft ends, however, are only coated between the end faces 5b, 5d and the bearing seats 9b with a first inner layer 3 (with the omission of a second, outer layer 4), the bearing seats 9a, however, being free, ie without a coating corresponding to the first, inner layer 3, that is, are formed without coating with a thermoplastic.

Figure 5 shows a schematic sectional view of a screw compressor 20 with a compressor housing 11 and mounted therein two paired rotor screws 1, 2, namely a rotor screw 2 designed as a main rotor and a rotor screw 1 designed as a secondary rotor. The rotor screws 1, 2 are each rotatable via suitable bearings 15 stored in a compression chamber 18 defined by a rotor bore 19 in the compressor housing 11 in a bearing seat 10 on the housing side. Seals 14b and 14c, which are each accommodated in a housing-side sealing seat 8a for the oil seal and in a housing-side sealing seat 8b for the air seal, on the one hand prevent compressed air from escaping from the compression space 18 and on the other hand prevent oil from penetrating into the compression space 18 Compression chamber 18 in the compressor housing 11 is laterally delimited by a rotor bore 18 which has two partial bores which are adapted to the diameters of the rotor screws 1, 2. On the face side, the compression space is delimited by a pressure-side housing face 6a and a suction-side housing face 6b. The pressure-side housing end surface 6a, the suction-side housing end surface 6b and the rotor bore 18 are preferably also provided with the multilayer coating according to the invention comprising a first inner layer 3 and a second outer layer 4.

The rotor screws 1, 2 are fixed in relation to one another in their rotational position and their profile surfaces 12a, 12b, in particular theirs, via a synchronous gear 13 respective rotor flanks are kept at a distance. A drive power can be applied to the shaft 16 of the rotor screw 2 designed as a main rotor, for example by means of a motor (not shown) via a clutch (not shown). A suction area 23 of the screw compressor can be seen at the suction-side end of the rotor screws 1, 2 screwed in pairs.

In Figure 6 One embodiment of a screw compressor 20 is illustrated in an exploded view. The compressor housing 11 delimits the compression space 18. Ambient air is drawn in via a suction nozzle 27 and reaches the suction area 23 of the screw compressor. After compression via the rotor screws 1, 2, the compressed compressed air is expelled from the compressor housing 11 via a pressure connection 28.

In Figure 7 is the multilayer coating on the profile surface 12a of the rotor screw 1 along the line AA in Figure 3 illustrated. First, the first inner layer 3 is applied to a base body 24 of the rotor screw 1. The second, outer layer 4 is applied to the first, inner layer 3 — completely covering it. According to the invention, the second, outer layer 4 comprises particles 25 that support a running-in process, for example thin-walled micro-glass hollow spheres. Alternatively or additionally, pores 32 can also be incorporated, which supports the plastic compressibility of the second, outer layer.

Figure 8 shows the multilayer coating along the line AA with a rotor screw 1 Figure 3 after the running-in process.

Figure 9 shows a one-piece coating on the shaft end 30 of the rotor screw 1, which is provided in the area of the rotor-side seal seat 7a for the oil seal and the rotor-side seal seat 7b for the air seal, covering both seal seats 7a, 7b. Specifically, there is a section along the line BB in Figure 3 shown. The first, inner layer is arranged here to cover the base body 24 and thus offers good and reliable corrosion protection.

Figure 10 shows an alternative multilayer coating for a profile surface 12a, 12b in the case of a rotor screw 1, 2. Instead of using FIG Figure 8 Particles 25 described are pores 32 in the second, outer layer embedded, which were incorporated, for example, by a foaming process before or during the application of the second, outer layer, for example in the wet coating process.

Figure 11 shows the multilayer coating Figure 10 after a running-in process. It can be seen that some layer areas have been removed or compressed. Some of the pores 32 are also removed with parts of the layer or compressed due to the counter pressure that is absorbed, so that overall a plastic deformation of the second, outer layer 4 has been effected as a running-in layer.

Figure 12 also shows schematically a flow chart for a possible embodiment of the coating method. In a step sequence S01 to S04, the metallic surface to be coated, for example the surface of a rotor screw to be coated, is pretreated. Step S01 involves degreasing the surface by burning it off at high temperature (pyrolysis). In the subsequent step S02, the surface is blasted, in particular sandblasted. After blasting, step S03 follows in which the surface is cleaned again chemically, for example using acetone. In step S04, a nanoceramic coating is subsequently applied in the exemplary embodiment described here.

This is followed by application of the first, inner layer 3, the first, inner layer 3 being applied as a wet paint in the present exemplary embodiment. However, alternative methods are also conceivable, for example application in the dry state as a powder coating. The wet paint is prepared for the first, inner layer beforehand, whereby the thermoplastic in the form of PEEK is mixed in powder form in water with dispersant. A suspension is formed which is applied to the pretreated surface in step S10. In a subsequent step S11, the applied wet paint is dried or vented. For this purpose, in step S11 the rotor screw coated with the wet paint for the first layer is heated to approximately 120 ° C. to evaporate the water. In a step S12, which can optionally also be omitted, the first layer is baked. The baking takes place at temperatures of approx. 360 ° C to 420 ° C, for example in a forced air oven or inductively, until the PEEK has melted and a homogeneous layer has formed.

The second layer is applied in steps S20, S21, S22 largely analogous to steps S10, S11, S12. For this purpose, a wet lacquer is again prepared, whereby the same thermoplastic as in the application of the first layer, comprising or having PEEK as the thermoplastic, is expediently, but not necessarily, used. For this purpose, the PEEK in powder form is mixed with the particles supporting the running-in process, for example the thin-walled micro-glass hollow spheres, in particular made of borosilicate glass, together with water and dispersant. The second, outer layer 4 is applied in step S20 directly to the first, inner layer 3, which is already baked in the present exemplary embodiment. However, it is also possible to leave step S12, namely the burning in of the first layer, aside and to burn in the first, inner layer 3 and the second, outer layer 4 together. Here, too, the application of the second, outer layer in step S20 is followed by a step of drying or venting the second, outer layer. For this purpose, the rotor screw to be coated is heated again to approx. 120 ° C. in step S21 or kept at this temperature. After the second, outer layer has dried sufficiently, the second, outer layer is baked in at step S22 at temperatures of approximately 360 ° C. to 420 ° C., for example in a forced air oven or in an inductive manner.

Optionally, a step S23 (not shown) can follow, but this should preferably be avoided. In a step S23, the second, outer layer 4 could be regrinded in order to achieve the desired dimensioning by regrinding when the second, outer layer is formed with an oversize. As already mentioned, it is preferred, however, to use the methods as shown in FIG Figure 12 shown to achieve.

Reference symbol list

1, 2

Rotor screw

3rd

first, inner layer

4th

second outer layer

5a, 5b, 5c, 5d

End faces

6a

pressure-side housing face

6b

front face of the housing

7a

rotor-side seal seat for an air seal

7b

rotor-side seal seat for an oil seal

8a

seal seat on the housing for an oil seal

8b

Housing-side seal seat for an air seal

9a, 9b

rotor-side bearing seat

10th

bearing seat on the housing side

11

Compressor housing

12a, 12b

Profile area

13

Synchronized gearbox

14b

poetry

14c

poetry

15

warehouse

16

wave

18th

Compression space

19th

Rotor bore

20th

Screw compressor

21st

Pitch circle (main rotor)

22

Pitch circle (secondary rotor)

23

Suction area

24th

Basic body

25th

particle

27th

Suction port

28

Discharge nozzle

30th

protruding shaft ends

32

Pores

Claims (30)

1. Screw compressor, comprising a compressor housing (11) with two rotor screws (1, 2) mounted therein in an axially parallel manner, which mesh with one another in a compression space (18), can be driven by means of a drive and are synchronized with one another in their rotational movement, wherein the rotor screws (1, 2) each comprise a single-part or multi-part main body (24) with two end faces (5a, 5b, 5c, 5d) and a profiled surface (12a, 12b) extending therebetween, as well as shaft ends (30) projecting beyond the end faces (5a, 5b, 5c, 5d),
   wherein at least the profiled surface (12a, 12b) is formed in a multi-layer manner, comprising a first, inner layer (3) as well as a second, outer layer (4), characterized in that the first, inner layer (3) and the second, outer layer (4) both comprise or are made from a thermoplastic material, wherein particles (25) or pores (32) promoting a running-in process are embedded in the second, outer layer (4), and the thermoplastic material defines a matrix for receiving the particles (25) or for forming the pores (32).
2. Screw compressor according to claim 1, characterized in that the thermoplastic material for forming the first, inner layer (3) and the second, outer layer (4) is a high-performance thermoplastic material, in particular a semi-crystalline high-performance thermoplastic material.
3. Screw compressor according to claim 1 or 2, characterized in that the thermoplastic material for forming the first, inner layer (3) and the second, outer layer (4) comprises a polyaryl ether ketone (PAEK) or at least substantially consists of a polyaryl ether ketone (PAEK).
4. Screw compressor according to one of claims 1 to 3, characterized in that the thermoplastic material for forming the first, inner layer (3) and the second, outer layer (4) comprises polyether ether ketone (PEEK) or at least substantially consists of polyether ether ketone (PEEK).
5. Screw compressor according to one of claims 1 to 4, characterized in that the first, inner layer (3) is formed without particles (25) or pores (32) promoting a running-in process, but at least substantially homogeneously.
6. Screw compressor according to one of claims 1 to 5, characterized in that the particles (25) of the second, outer layer (4) promoting a running-in process comprise abrasive and/or lubricating particles.
7. Screw compressor according to one of claims 1 to 6, characterized in that the particles (25) are present in microencapsulated form, wherein at least a first substance is surrounded by a second substance as enveloping material.
8. Screw compressor according to claim 6, characterized in that the particles (25) comprise micro hollow spheres (microspheres), in particular of aluminum oxide (Al₂O₃), silicon dioxide (SiO₂) or of thermoplastic material, in particular are formed from these.
9. Screw compressor according to claim 6, characterized in that the particles (25) comprise micro hollow spheres (microspheres) of glass, in particular borosilicate glass, or are formed from glass, in particular borosilicate glass.
10. Screw compressor according to one of claims 1 to 9, characterized in that the particles (25) of the second, outer layer (4) promoting a running-in process have a higher hardness (according to Shore) relative to the matrix defined by the thermoplastic material.
11. Screw compressor according to one of claims 1 to 9, characterized in that the particles (25) of the second, outer layer (4) promoting a running-in process have a lower hardness (according to Shore) relative to the matrix defined by the thermoplastic material.
12. Screw compressor according to one of claims 1 to 11, characterized in that the first, inner layer (3) is connected to the second, outer layer by melting.
13. Screw compressor according to one of claims 1 to 12, characterized in that the first, inner layer (3) forms a substantially homogeneous coating and thus a corrosion protection layer.
14. Screw compressor according to one of claims 1 to 13, characterized in that the second, outer layer (4) defines a running-in layer which is eroding and/or plastically deforming in certain areas during the running-in process and thus adapts to the concrete operating conditions.
15. Screw compressor according to one of claims 1 to 14, characterized in that the particles comprise graphite or are formed from graphite.
16. Screw compressor according to one of claims 1 to 15, characterized in that the particles comprise:
    hexagonal boron nitride, carbon nanotubes (CNT), talcum, polytetrafluoroethylene (PTFE), perfluoroalkoxy polymers (PFA), fluorinated ethylene propylene (FEP) and/or another fluoropolymer.
17. Screw compressor according to one of claims 1 to 15, characterized in that the particles comprise
    aluminum oxide (Al₂O₃), silicon carbide (SiC), silicon dioxide (SiO₂), and/or glass, in particular borosilicate glass.
18. Screw compressor according to one of claims 1 to 17, characterized in that the layer thickness of the first, inner layer (3) before running-in is 5 µm to 50 µm.
19. Screw compressor according to one of the preceding claims, characterized in that the layer thickness of the second, outer layer (4) before running-in is 10 µm to 120 µm.
20. Screw compressor according to one of the preceding claims, characterized in that the main body (24) of the rotor screw is formed of steel and/or cast iron.
21. Screw compressor according to one of claims 1 to 19, characterized in that at least sections of the shaft ends (30) are not coated with a thermoplastic material.
22. Screw compressor according to one of claims 1 to 21, characterized in that at least sections of the shaft ends (30) are coated with the first, inner layer (3) of thermoplastic material.
23. Screw compressor according to one of claims 1 to 22, characterized in that in addition to the profiled surface (12a, 12b) of at least one rotor screw (1, 2), one or both end faces (5a, 5b, 5c, 5d) are coated with a multi-layer coating comprising a first, inner layer (3) and a second, outer layer (4), wherein the first, inner layer (3) and the second, outer layer (4) both comprise or are made from a thermoplastic material, wherein particles (25) or pores (32) promoting a running-in process are embedded in the second, outer layer (4), and the thermoplastic material defines a matrix for receiving the particles (25) or for forming the pores (32).
24. Screw compressor according to one of claims 1 to 23, characterized in that inner walls, such as a jacket surface of a rotor bore (19), pressure-side and/or suction-side housing end faces (6a, 6b) of the compression chamber (18) are coated at least with a first layer (3), preferably also with a second layer (4), wherein the first layer (3) and the second layer (4) both comprise or are made from a thermoplastic material, and wherein particles (25) or pores (32) promoting a running-in process are embedded in the second, outer layer (4), and the thermoplastic material defines a matrix for receiving the particles (25) or for forming the pores (32).
25. Screw compressor according to one of claims 1 to 24, characterized in that the screw compressor is an oil-free compressing, in particular dry-compressing, screw compressor.
26. Rotor screw for use in a screw compressor according to one of the preceding claims, wherein the rotor screw (1, 2) comprises a one-part or multi-part main body (24) having two end faces (5a, 5b, 5c, 5d) and a profiled surface (12a, 12b) extending therebetween as well as shaft ends (30) projecting beyond the end faces (5a, 5b, 5c, 5d), wherein at least the profiled surface (12a, 12b) is formed in a multi-layer manner, comprising a first, inner layer (3) and a second, outer layer (4), characterized in that the first, inner layer (3) and the second, outer layer (4) both comprise or are formed from a thermoplastic material, wherein particles (25) or pores (32) promoting a running-in process are embedded in the second, outer layer (4) and the thermoplastic material defines a matrix for receiving the particles (25) or for forming the pores (32).
27. Method for applying a multi-layer coating to a metallic surface to be coated of a rotor screw or a compression chamber of a screw compressor, comprising the following steps:

    - pretreatment of the metallic surface to be coated,

    - applying a first, inner layer (3), which comprises or is formed from a thermoplastic material, to the metallic surface to be coated or to an underlayer, which may be formed in particular as a pretreatment layer, and

    - applying a second, outer layer (4) to the first, inner layer (3),
    wherein the second, outer layer (4) also comprises or is formed from a thermoplastic material and wherein particles (25) or pores (32) promoting a running-in process are embedded in the second, outer layer (4), and the thermoplastic material defines a matrix for receiving the particles (25) or for forming the pores (32).
28. Method according to claim 26, characterized in that the first, inner layer (3) and/or the second, outer layer (4) are applied as a wet paint or as a powder paint.
29. Method according to claim 27 or 28, characterized in that the first, inner layer (3) and the second, outer layer (4) are baked in such a way that the thermoplastic material melts.
30. Method according to one of claims 27 to 29, characterized in that the pretreatment of the metallic surface to be coated comprises degreasing and preferably further conditioning of the metallic surface, for example by roughening the surface, by blasting or etching or by applying a conversion layer, for example phosphating or applying a nanoceramic.

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