EP3399191A1 - Screw compressor with multilayer rotor screw coating - Google Patents

Abstract

Screw compressor comprising a compressor housing (11) with two axially parallel mounted rotor screws (1, 2) in a compression chamber (18) mesh with each other, drivable by a drive and synchronized in their rotational movement to each other, wherein the rotor screws (1, 2) respectively a single or multi-part main body (24) with two end faces (5a, 5b, 5c, 5d) and a profile surface extending therebetween (12a, 12b) and on the end surfaces (5a, 5b, 5c, 5d) projecting shaft ends (30) in which at least the profile surface (12a, 12b) is formed in a multi-layered manner, 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 formed from a thermoplastic material, wherein in the second, outer layer (4) an inlet process supporting particles (25) or pores (32) are embedded and the thermoplas Table plastic defined a matrix for receiving the particles (25) and for forming the pores (32).

Description

The invention relates to a screw compressor comprising a compressor housing with two axially parallel mounted rotor screws, which mesh with each other in a compression space, driven by a drive and synchronized in their rotational movement to each other, wherein the rotor screws each have a one or more part body with two end faces and one in between Having extending profile surface and over the end faces projecting shaft ends, according to the preamble of claim 1 and a method for applying a multilayer coating on a metallic surface of a rotor screw or a compression space 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 intermeshing screw pair 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. Finally, by passing pressurized gases the other way round, too Work performance can be generated so that mechanical energy can be obtained from pressurized gases by means of the principle of the screw machine.

Screw machines generally have two axially parallel to each other arranged rotor screws, 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 in between and two shaft ends protruding beyond the end faces.

The rotor screws engage each other with corresponding helical toothing. Between the teeth and a compressor housing several successive working chambers are formed by the tooth space volumes. Starting from a suction area, with the rotation of the rotor screws progressing, the particular working chamber considered is first closed and then reduced continuously in volume, so that a compression of the medium occurs. Finally, as the rotation progresses, the working chamber is opened to a pressure window and the medium is ejected into the pressure window. By this process of internal compression, screw machines designed as screw compressors differ from Roots blowers which operate without internal compression.

Due to the intermeshing of the two rotor screws, a pitch circle is defined both for the rotor screw designed as the main rotor and for the rotor screw designed as a secondary rotor. The rolling circles can be represented in an end section of the toothing and it can be seen in such a representation that the rolling circles roll upon movement of the rotor screws to each other. On the rolling circles, the peripheral speeds of the rotor screw formed as a main rotor and the rotor screw formed as a secondary rotor are identical, i. There is no relative velocity between the two rotor screws in this area. However, the farther one moves away from the rolling circles radially within the profile surface, the greater are the relative speeds.

Screw machines can be used in addition to the already mentioned function as a vacuum pump or as a screw expander in various fields of technology as a compressor. A particularly preferred field of application lies in the compression of gases, such as air or inert gases (helium, nitrogen, argon, ...). But it is also possible, although this is the construction of different requirements, to use a screw machine for the compression of refrigerants, for example, for air conditioning or refrigeration applications. In the following, the term "compressed air" or "gases" refers to all process media that are compressed or expanded. In the compression of gases, especially at higher pressure conditions is usually worked with a fluid-injected compression, in particular an oil or water-injected compression; but it is also possible to operate a screw machine, in particular a screw compressor according to 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 a screw blower.

The invention relates to an oil-free, in particular dry compression. Typical pressure ratios may be between 1.1 and about 10 with dry compression, where the pressure ratio is the ratio of discharge pressure to suction pressure. The compression can be done in one or more stages. Achievable ultimate pressures can be, for example, in one or two-stage compression, for example in a range of 1.1 bar to about 10 bar. As far as at this point or subsequently in the present application also pressure data in "bar" reference is made, then such pressure data in each case relate to absolute pressures.

The invention relates to screw machines, in particular screw compressor whose rotor screws are intended not synchronized by profile engagement between the two rotor screws, but externally, for example by a synchronous transmission on the shaft ends or by separate and electronically synchronized rotor drives. In these screw machines, rotor contact results only temporarily, for example by geometric deviations of the nominal contour of the rotor screw or rotor screws or thermal differential expansion and is eliminated by removal of material provided on the rotor screws coating at the contact and friction points. This elimination of only temporarily given contact between the rotor screws takes place in an enema process. Rotor screws are usually made of steel or cast iron. The compressor housing is typically made of gray cast iron cast. There must be a small gap between the rotor screws and the compressor housing, and especially between the two rotor screws. These components must not touch each other during operation, as a metallic contact would cause starting due to the high speeds and, in the worst case, feeding. The gap between the rotor screws is realized in that both rotor screws are operated synchronized, for example by a synchronous transmission or by separate, electronically synchronized rotor drives.

On the one hand, the gaps should be as small as possible to minimize backflow of the compressed air into previous working chambers (i.e., counter to the direction of conveyance). The more backflow occurs, the higher the internal losses and the worse the efficiency of the screw machine. In the case of a screw compressor, the compression end temperature increases significantly as the return flow increases, which leads to greater thermal expansions of the rotor screws and of the compressor housing. The higher thermal expansion in turn increases the risk of tarnishing, i. it creates a self-reinforcing effect.

On the other hand, however, the gaps should also be large enough to ensure the required operational safety. If contact occurs at high relative velocities of metallic surfaces, this leads to high heat input and thermal expansion and ultimately also to seize of the components, as already described above. When dimensioning the gap, therefore, not only the manufacturing tolerances but also the thermal expansion due to high compaction temperatures and the deflection of the rotor screws due to the pressure in the working chambers have to be considered.

Another requirement for oil-free, especially dry compression is to ensure good corrosion protection of the rotor screws and the compressor housing. After switching off the still hot screw compressor, it may cause condensation on the inside of the compressor housing due to moisture in the air during cooling. There is also a risk of corrosion in the case of dry compression with low-level water injection (the water evaporates essentially completely until the end of the compression process). Rotor screws and housings made of cast iron or conventional steel are particularly susceptible to corrosion.

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

In the prior art, rotor bolts of dry running screw compressors are therefore provided with a fluorine polymer / lubricating paint coating to overcome the above-mentioned problems.

The EP 2 784 324 A1 For example, describes the composition of a coating that is used in the processing 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 is composed of PTFE (specifically Teflon 954G 303), graphite and other solvents or thinners. According to the product data sheet of the manufacturer (Chemours), the substance 954G 303 is only suitable for continuous use temperatures of 150 ° C. In addition, there are other requirements through environmental and health protection. The substance 954G 303 and other ingredients of the formulation indicated in the prior art bring solvents that are highly problematic in processing. There are also increasing legal requirements for a reduction of volatile organic compounds (VOCs). In addition, the substance 954G 303 is not food grade and so far not FDA-compliant. She is rather suspected of being carcinogenic.

In addition, the coating proposed in the prior art provides only limited corrosion protection because a layer is applied which contains comparatively much 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 therefore a danger of corrosion.

In the WO 2014/018530 a coating of a high-performance thermoplastic (eg PEEK) and a first solid lubricant (eg MoS2) and a second solid lubricant (eg PTFE or graphite) is proposed. However, there is described an application in compressors with low speeds and high loads at the same time. In addition, it is provided in the coating according to the prior art that the coated surfaces are constantly in frictional contact with each other.

The invention is based on the first-mentioned prior art the task of specifying for an oil-free screw compressor with comparatively high rotational speeds of the rotor screws and a desired gap between the rotor screws with each other or the rotor screws and a compressor housing, a coating which avoids the disadvantages of the prior art and at the same time adjusts itself in a run-in process itself to a sufficiently small gap distance. This object is achieved in device-technical terms by a screw compressor, in particular an oil-free screw compressor, according to the features of claim 1, a rotor screw according to the features of claim 26 and in procedural terms with a sequence according to the features of claim 27. Advantageous developments are specified in the subclaims.

A core idea of the present invention is that in a screw compressor or in a rotor screw at least the profile surface of the rotor screw is multilayer, comprising a first, inner layer and a second, outer layer is formed, wherein the first, inner layer and the second, outer Layer both comprise a thermoplastic material or are formed from this, wherein in the second, outer layer an enema supporting particles or pores are embedded and the thermoplastic material defines a matrix for receiving the particles or for the formation of 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 central idea of the method according to the invention provides for the application of a multi-part coating to a metallic surface of a rotor screw or a compression space of a screw compressor to be coated, comprising the following steps:

• Pretreating the metallic surface to be coated,
• Applying a first, inner layer which comprises a thermoplastic material or is formed from this, on the metallic surface to be coated or on a lower layer, which may be formed in particular as a pretreatment layer, and
• Applying a second outer layer to the first inner layer,

wherein the second outer layer also comprises or is formed from a thermoplastic and wherein in the second, outer layer Embedding process supporting particles or pores are embedded and the thermoplastic material defines a matrix for receiving the particles or to form the pores.

The formation of the profile surface as a multilayered layer allows the provision of partial layers with different properties. However, a special consideration is to be seen in the fact that the second, outer layer is designed to be removed in a run-in event, if necessary, partially or almost completely, so that the profile surfaces of the intermeshing rotor screws are optimally adjusted to each other, under the concrete given conditions on site, ie Under the respective given pressure conditions, temperature conditions, etc. In this respect, the second, outer layer is more or less a self-adjusting layer.

Hereinafter, preferred embodiments for the screw compressor according to the invention or the rotor screw according to the invention are discussed, wherein at least some of you can also apply readily to the inventive method or are transferable to the method.

Preferably, the materials are chosen so that even in food applications, the removal of material or the contact of the compressed air with the first, inner layer and / or the second, outer layer is harmless, i. the materials are food compliant or FDA compliant. According to a basic idea of the present invention, therefore, a thermoplastic is generally used. Preferably, the thermoplastic material is a semi-crystalline thermoplastic material. Semi-crystalline thermoplastics are characterized by high fatigue strength, good chemical resistance and good sliding behavior. They also show 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, especially a semi-crystalline high performance thermoplastic. A high-performance thermoplastic plastic is understood as meaning a plastic which has a continuous use temperature of> 130 ° C., preferably> 150 ° C. Preferably, it is a thermoplastic concentrate, more preferably a polymer or copolymer having alternating ketone and ether functionalities, in particular a polyaryletherketone (PAEK). Specific examples of polyaryletherketones (PAEK) are:

1. i. Polyether ketone (PEK)
2. ii. Polyetheretherketone (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,
especially polyetheretherketone (PEEK) is considered preferable. 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 polyetheretherketone (PEEK) or consists at least substantially of polyetheretherketone (PEEK).

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

More preferably, the thermoplastic base substance for forming the first, inner layer and for forming the second, outer layer generally comprises a polyaryletherketone (PAEK) or is at least substantially formed from PAEK. The high-performance thermoplastic materials can also be referred to as high-performance thermoplastic or thermoplastic high-performance plastic.

Generally speaking, for the multilayer construction of the layers comprising thermoplastic material according to the present invention, the first, inner layer and the second, outer layer structurally differ, even if the same thermoplastic material 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 smaller proportion of particles and / or pores. The proportion of thermoplastic material in the first, inner layer based on the total mass is at least 60 wt .-%, preferably at least 70 wt .-%, more preferably at least 80 wt .-%, more preferably at least 95 wt .-%, further preferably at least 100% by weight. The proportion of thermoplastic 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, with a minimum proportion of 5% by weight of particles, further preferably provided by 10 wt .-% of particles. If, on the other hand, only pores are provided in the second, outer layer instead of particles, the proportion of thermoplastic in the second, outer layer can also be more than 95% by weight. The volume fraction of pores on the second outer layer is preferably above 5%, more preferably above 10%, whereas the pore content of the first inner layer is below 5%, more preferably below 2%.

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

In one possible embodiment, the particles of the second, outer layer, which support an inlet process, comprise abrasive and / or lubricating particles. It is thus possible to provide a second, outer layer only with abrasive particles or alternatively provide only with lubricating particles. Furthermore, it is 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 provided mixed, wherein the ratio of the abrasive particles to the lubricating particles change over different areas of the second outer layer can.

According to a preferred embodiment, the particles comprise microspheres (microspheres), in particular 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. Micro-hollow spheres are very light, hollow microscopic-sized spheres filled with air or inert gas. The shell of the micro-hollow spheres may in particular consist of one of the following materials: alumina (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ) or of glass and the latter in particular of borosilicate glass (borosilicate glass). Borosilicate glass spheres, which are hollow on the inside, are offered by 3M as "glass bubbles", are in powder form, are chemically inert, non-combustible and non-porous. An average ball diameter is for example 20 μm with an average wall thickness of 0.7 μm. When using such micro-glass bubbles they burst during the run-in process. They provide due to their hardness (they are relative to the binder matrix of the second, outer layer significantly harder) for the necessary abrasion and provides local, tiny, evenly distributed over the surface points of attack for a coating abrasion with an opposing surface, such as opposite rotor screw, whereby an undesirable or harmful, large-scale flaking of the layers with the respectively associated opposite surface, such as the profile surface of an opposite rotor screw or 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 which support an inlet process have a higher hardness than the matrix defined by the thermoplastic, the hardness being measured or defined according to Shore.

In a likewise optionally possible embodiment of the present invention, the particles of the second, outer layer which support an inlet process have a lower hardness than the matrix defined by the thermoplastic, the hardness being measured or defined in accordance with Shore.

According to a particularly preferred aspect of the present invention, the first, inner layer is bonded to the second, outer layer by reflow. This results in a particularly stable, durable and reliable connection between the first, inner layer and the second, outer layer. This allows a relatively reliable anchoring of second, outer layer, even if the second, outer layer has a relatively high proportion of particles or pores and thus would have relatively poor adhesive properties, for example, in a theoretical attachment directly on the metallic 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 material, in particular a thermoplastic high-performance plastic, in particular PEEK, can be stated by weight and, for example, the particle-binder mass ratio can be given as P / B. The binder represents the already mentioned matrix of thermoplastic material for receiving the particles.

• 0,03 ≤ P/B ≤ 1,0 bezogen auf die jeweiligen Masseverhältnisse. Ein bevorzugter Bereich für den Gesamtfüllstoffanteil liegt bei 0,15 ≤ P/B ≤ 0,35.

In order that the respective properties of the particles in the second, outer layer can be utilized and produce an effect, minimum amounts are to be determined as preferred. On the other hand, proportions of particles can not be increased arbitrarily. The particles are bound in the binder, ie the matrix of thermoplastic material. The higher the particle content, the more the particle properties affect, but the worse the particles themselves can be bound in the binder matrix, in particular in the PEEK. For the total particle fraction advantageously applies:

• 0.03 ≤ P / B ≤ 1.0 based on the respective mass ratios. A preferred range for the total filler fraction is 0.15 ≦ P / B ≦ 0.35.

• Partikel: Graphit: 0,3 ≤ P_Graphit/B ≤ 0,75 mit P_Graphit als Masse des Graphit.
• Partikel: Glashohlkugeln: 0,05 ≤ P_{Glashohlkugeln}/B ≤ 0,5 mit P_{Glashohlkugeln} als Masse der Glashohlkugeln.

Alternatively, the following can also be specified as preferred ranges for specific particles:

• Particle: Graphite: 0.3 ≤ P _Graphite / B ≤ 0.75 with P _Graphite as mass of graphite.
• Particle: Glass hollow spheres: 0.05 ≤ P _{hollow glass spheres} / B ≤ 0.5 with P _{hollow glass spheres} as the mass of hollow glass spheres.

According to a preferred embodiment 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 corrosion protection.

A further preferred aspect of the present invention defines the second, outer layer as a running-in area partially abrading and / or partially plastically deforming, thus adapting to the concrete operating conditions inlet layer. The running-in layer is designed in such a way that it can be adapted to the concrete operating conditions and can ensure that a favorable gap dimension is established with respect to a mating surface.

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

Graphite, hexagonal boron nitride, carbon nanotubes and talcum reduce friction as a solid lubricant. The materials can be removed relatively well, i. it turns a favorable run-in behavior. Graphite is relatively soft relative to the binder matrix. Talc is also comparatively soft and acts as a lubricant with a low abrasive effect. It is also water repellent and waterproofing.

Fluoropolymers such as PTFE, PFA, FEP (with average particle sizes of approx. 2 μm to 30 μm) also act as solid or dry lubricants. They are added to the thermoplastic resin of the binder matrix, such as the PEEK, in powder form and do not dissolve in wet paint in the following processes for forming the second outer layer. They are rather soft relative to the binder matrix and thus provide in particular for good lubricating, lubricating and non-stick properties.

The particles may alternatively or additionally 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).

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

Pore-like cavities can also be produced by micro hollow spheres with thermoplastic microspheres. The thermoplastic shell encloses a gas that expands by the supply of heat and increases the volume of the hollow sphere. Such micro-hollow spheres of a plastic shell can be present as particles in expanded or non-expanded form. A polymer matrix with embedded therein hollow particles is sometimes referred to in the literature as syntactic foam (syntactic foam). By the way, it should be mentioned that functional textures can be produced on the surface of the coating, in particular with plastic microspheres. Thus, for example, split flows can be advantageously influenced.

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

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

• Better handling before or during processing (better flow properties, less dust)
• Better dispersibility. A water-insoluble substance may be entrapped in microcapsules to be dispersible in an aqueous medium. Also an electrostatic charge or the risk of gradual clumping (agglomeration) can be reduced by encapsulation.
• Possibility of combining incompatible substances
• Prevention of premature chemical reactions with other mixture components
• Influence of 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. As a result, the running-in process, for example, can be extended in time. There is less frictional heat and consequently a lower risk of breakouts of the second, outer layer.

Of course, it is 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 shrinkage 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 in each case, in order to achieve a total layer thickness of 50 μm for the first, inner layer. With layer thickness here is always the dry film thickness (DFT, Dry Film Thickness) designated.

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

The gaps and layer thicknesses are ideally matched to one another in such a way that there is still minimal clearance between the rotor screws and between the rotor screws and the compressor housing when mounting the rotor screws in the compressor housing. The assembled rotor screws should just be able to rotate against each other. If the layer thickness is so great that an excess occurs, then the rotor screws can be mounted only in the housing under force and force. The game during assembly is advantageous because then the rotor screws defined, for example, via a synchromesh, can be synchronized. The relative angular position of the rotor screws is permanently fixed to each other.

The second, outer layer adheres better to the first, inner layer than directly on the metallic surface of the component to be coated, for example on the main body of the rotor screw. Because the thermoplastic material, for example, the PEEK, the second layer merges with the thermoplastic material, such as the PEEK, the first layer. As the proportion of particles increases, the proportion of the thermoplastic polymer of the binder matrix, in particular of the PEEK portion, decreases accordingly. As a result, the function of the thermoplastic material, in particular of the PEEK, weakened as a binder matrix.

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

When commissioning the screw compressor - as already mentioned - due to the compression temperature for thermal expansion and bending of the rotor screws and consequently to a contact of the rotating rotor screws and between the rotating rotor screws and the stationary compressor housing. In this contact, a partial removal of the second, outer layer takes place. The rotor screws come in, locally varying degrees of force and only where components touch. Depending on the respective deformations and deviations from the desired geometry of the rotor screws and possibly the compressor housing, a different sized, partial removal of the second, outer layer thus takes place. This removal is, as already mentioned, referred to as run-in process and is only in the second, outer layer, the inlet layer, play. Essentially, the run-in process takes place only once when the screw compressor is first put into operation. It is advantageous to perform the run-in process carefully. It is advantageous to tune the inlet process to the later application of the screw compressor. Particularly advantageous for a gentle running-in process is a variable-speed drive (eg permanent magnet motor or synchronous reluctance motor) of the screw compressor. This allows the drive speed to be defined during the run-in process and increased in time to the maximum operating speed to increase. In contrast, a fixed speed drive (eg with a conventional asynchronous motor without a frequency converter) would drive the screw compressor very quickly with the high speed required in dry compression with the risk that the coating could be damaged due to the extremely short run-in process. The inlet process can take place, for example, on a separate inlet test bench. Advantageously, however, the entire machine (screw machine incl. Drive, etc.) is already equipped with a variable-speed drive, so that the running-in process can take place during the first start-up of the machine intended for the customer. The complex intermediate step (assembly and disassembly on the inlet 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 counter to the conveying direction.

The hard or abrasive particles received 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, which defines the binder matrix) ensure that the second, outer layer in which they are located can be removed particularly 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 each other during operation (ie in or near the rolling circles or rolling areas), high surface pressures simultaneously occur, so that, for example, the thin-walled micro-glass hollow spheres in the second, outer layer advantageously break up and thus ensure the necessary abrasion or layer thickness loss in the second, outer layer on both rotor screws. According to a preferred aspect of the present invention, the sharp rupture edges of the micro-glass-wool spheres resulting from rupture support the abrasive process. A layer thickness loss can also be achieved by pores trapped in the second outer layer, in which case a plastic deformation occurs due to compression or collapse of the pores.

As a result, an undesirable constant pressing of the rotor screws against each other is prevented. Among other things, this has a favorable effect on the lifetime of the coating as well as on the service life of the bearings. Overall, the smoothness of the screw compressor is advantageously improved by this adaptability of the second outer coating, especially in or near the rolling area of the screw rotors.

In contact areas of the rotor screws with comparatively high relative speeds to each other, i. In areas with increasing radial distance to the rolling circles, soft particles, such as graphite, due to the large relative speeds of the friction partners to each other relatively easy to remove, i. the second, outer layer also runs well in these areas. Straight graphite also has the advantage that it is relatively inexpensive and does not lubricate on the opposite surface.

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

According to the invention, it is also advantageous in addition to the profile surface or next to the profile surfaces under certain circumstances to coat further portions of the one or both rotor screws and the compressor housing in a corresponding manner in a multi-layered 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 the second, outer layer both comprising or being formed from a thermoplastic, and the second, outer layer having an inlet process assisting particles or pores, the thermoplastic material defines a matrix for receiving the particles or for forming the pores. But it can also be provided that only one of the two end face, preferably only the pressure-side end face, as described above, both with the first inner layer and the second outer layer, the opposite end face, however, is coated only with the first, inner layer.

Furthermore, portions of the shaft ends may still be coated with thermoplastic according to the first, inner layer. Advantageously, however, sections of the shaft ends are also uncoated, ie without a layer of thermoplastic material according to the present invention Mistake. Any other coating of these sections is prohibited.

The functional areas of a compressor housing essentially consist of a suction area, the rotor bore, a pressure area and 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 port 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 mounted with very small gaps (radial housing gaps) and form working chambers within the compression space. As compaction space defined by the rotor bore interior in the compressor housing is called. 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 discharge nozzle of the compressor housing.

Sealing seats in the compressor housing (housing-side sealing seats) are used to accommodate seals, specifically air or conveying medium seals and oil seals. In the following, the term air seal always a seal for other fluids to be understood with. Likewise, should always be understood by the term "oil seal" also a seal for other bearing lubricant.

Bearings (eg 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. Here, a distinction is made between sealing seats for air seals and sealing seats for oil seals, which are typically arranged side by side on the shaft ends of the rotor screws. The seal seats for the Air seals are located on both sides of the rotor screw in the immediate vicinity of the suction side and the pressure side rotor end face. Subsequently, and further away from the rotor end faces, the sealing seats for the oil seals are arranged.

The oil seals prevent oil from entering the storage area in the compression area of the screw compressor. The air seals, however, prevent leakage of the compressed air or the compressed conveying fluid from the compression chamber.

Furthermore, bearing seats are still on the shaft ends on which, for example, the bearings are provided. The bearing seats usually follow the seal 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 advantageous, in addition - as already mentioned in part - to coat the profile surface of the rotor screws and other sections of the rotor screws and the compressor housing. 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, may 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 intake of the screw compressor to the beginning of the compression chamber),
• the rotor bore with the sections for both rotor screws,
• the two housing end faces (suction-side and pressure-side housing end face),
• the pressure range (from the end of the compression chamber to the discharge nozzle of the screw compressor)
• as well as the seal 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, the inlet process supporting particles or pores and in which the thermoplastic material has a matrix for receiving the particles or to form the Defined pores, coated. Likewise, such a second, outer layer can be applied to the pressure-side housing end face.

Suction area and pressure range 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 region and the pressure region instead of the first inner layer proposed here or the combination of the first, inner and second outer layer proposed here. On the sealing seats in the housing, a second, outer layer according to the invention can also be applied. As an alternative to coating the sealing seats with first, inner layer or first, inner layer and second, outer layer, it is also possible that the seal seats 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 not provided with a coating according to the present invention. The bearing seats in the housing, however, may not be coated. Again, that the bearing seats must not be provided with a coating according to the invention; Of this it is possible to use any other, in particular film-like coating, for example to increase the sliding properties.

The function of the inlet layer between the rotor screw as a moving part and compression chamber of the compressor housing as stationary part runs quite as described above, ie when commissioning the screw compressor it comes due to the compression temperature to thermal expansion of rotor screws and compressor housing and the bending of the rotor screws. As a result, it may, for example, come to a touch of rotor screws and rotor bore or of rotor end faces and housing end faces, in particular of the pressure-side rotor end face and pressure-side housing end face. In this contact, the partial removal of the second, outer coating takes place, as intended according to the invention. The faces come in accordingly. It should be noted here that the pressure-side axial end gap is particularly important for efficient compaction. This face gap should ideally be very small. The pressure-side axial end gap is set defined during the assembly of the rotor screws in the compressor housing (usually with an accuracy in the range of less than 1/100 mm and eg by means of spacers). It is also particularly important for efficient compaction that the radial gap between rotor screws and rotor bore is very small.

As possible embodiments, in particular the following coating variants are conceivable, although this list is by no means exhaustive and also other combinations appear conceivable: Rotor screw 1 (eg secondary rotor) (profile area) Rotor screw 2 (eg main rotor) (profile area) Pressure side rotor end face Suction-side rotor end face Rotor bore in the housing Pressure-side housing end 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 compressing, in particular dry-compressing screw compressor.

In 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, wherein the second, outer layer also comprises or comprises a thermoplastic is formed from this and wherein in the second, outer layer an inlet process supporting particles or pores are embedded and the thermoplastic material defines a matrix for receiving the particles or to form the pores. The steps indicated are preferably also in the order given.

The various material possibilities for the thermoplastic material, which is a so-called high-performance thermoplastic material, have already been discussed in connection with the device-technical aspects of the present invention. These statements are referred to here. Quite generally, it is again stated that the thermoplastic material may be a polyaryletherketone (PAEK), with polyetheretherketone (PEEK) being considered to be 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 robotically 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 coating or wet paint, with regard to the coating provided here, the following should be noted:

• Powder coating: Particles are admixed in powder form to the likewise mostly powdery thermoplastic material, in particular the powdered PEEK.
• Wet paint: Particles and thermoplastic, in particular PEEK are mixed in each case in powder form, advantageously in water with dispersant. The particles and the PEEK powder do not dissolve in the dispersion but a suspension is formed. In particular, in the application of a wet paint method for the Application of the first inner layer, a bleeding of the first layer must be provided. This flash-off of the first layer preferably comprises heating the coated wet components to about 120 ° C to evaporate the water over a predetermined period of time. Only then should the second, outer layer be applied in the wet or dry state.

The first, inner layer and / or the second, outer layer can be applied as a wet paint or powder coating. According to a further preferred aspect of the invention, the first, inner layer and the second, outer layer are baked, such that the thermoplastic melts. In this respect, the baking can be done after application of each layer; Alternatively, however, it is also conceivable first to apply the two or more layers and then to burn them in a single firing process.

The first, inner layer and the second, outer layer are preferably baked at temperatures of about 360 ° C to 420 ° C until the thermoplastic, in particular the PEEK is melted and forms a homogeneous layer on the surface to be coated sufficiently liable. The burn-in can be done in particular in a convection oven or inductively. Optionally, as already mentioned, baking is possible even after application of each layer. It should finally be mentioned that it is also possible to increase the layer thickness of the second, outer layer and then to post-treat for setting a desired layer thickness, in particular to regrind.

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

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

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

• Minimization of environmental impact,
• phosphate-free running process and
• overall cheaper process.

In this respect, the nanoceramic coating is a special pretreatment layer which can be regarded as a lower layer with regard to the first, inner layer and / or the second, outer layer. However, other layers are also conceivable as sublayers.

• 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 lebensmitteltauglich.
• 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 or the described embodiments, the following can be stated:

• Good run-in behavior of the second, outer layer allows small gaps between the rotor screws and the compressor housing and thus a more efficient compaction.
• At the same time a very good corrosion protection is ensured by the first, inner layer and thus extends the life of such coated components.
• The shrinkage takes place only in the second, outer layer; the first, inner layer serves as corrosion protection. This allows the two requirements of corrosion protection and run-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 food grade.
• PEEK is environmentally friendly: PEEK dispersions are mostly water-based and have very low levels of volatile organic compounds (VOCs). The application of the different layers is without health risks and in particular does not appear carcinogenic.
• There is a very good resistance to chemicals, which is especially important if other gases than air to be compressed or if the intake air is possibly contaminated.
• The properties of the coating remain unchanged on contact with water, moisture and steam. In comparison to other fluoropolymer coatings PEEK has a very low water absorption, ie the risk of swelling of the coating is significantly reduced. This aspect appears to be particularly advantageous for screw compressors which operate on the principle of water-limited injection.
• It results in a high running smoothness for the operating behavior of the screw compressor (the second, outer layer ensures a good run-in behavior; even with constant frictional contact there is no undesirable "pressing" of the rotor screws against each other).
• In addition, the second, outer layer, which also defines in particular the outermost layer, shows a very low 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 thermal shock resistance.

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

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 will be explained below with regard to further features and advantages with reference to the description of exemplary embodiments and with reference to the accompanying drawings. Hereby show:

FIG. 1

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

FIG. 2

two interlocked rotor screws in perspective view;

FIG. 3

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

FIG. 4

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

FIG. 5

a schematic sectional view of a screw compressor;

FIG. 6

an exploded view of a screw compressor;

FIG. 7

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

FIG. 8

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

FIG. 9

schematically a single-layer coating of a portion of a rotor screw;

FIG. 10

an alternative embodiment of a multilayer coating of a rotor screw before shrinkage;

FIG. 11

the embodiment of the multilayer coating of a rotor screw after FIG. 10 after arriving;

FIG. 12

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

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

In FIG. 2 the interlocked rotor screws 1, 2 are shown in a perspective view. In this case, both rotor screws 1, 2 with the already mentioned profile surfaces 12a, 12b engage one another or are interlocked or screwed together. Perpendicular to the respective rotor screw axis of rotation, the profile surfaces 12a, 12b each end by end faces 5a, 5b, 5c, 5d limited, wherein the end face 5a a pressure-side end face of the secondary rotor designed as a rotor screw 1 and the end face 5c denotes a suction-side end face. When designed as a main rotor rotor screw 2, the pressure-side end face is denoted by the reference numeral 5b and the suction-side end face by the reference numeral 5d.

Above the end faces 5a, 5b, 5c, 5d projecting in the axial direction protruding shaft ends 30 are formed, each pair for a rotor screw 1, 2 form a shaft 16. At the shaft ends 30, 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. In this case, the rotor-side seal seat 7b for an air seal adjacent to the end face 5a, 5b, 5c, 5d is formed, whereas the rotor-side bearing seat 9a, 9b is more provided to the distal end of the shaft end 30. Between the rotor-side bearing seat 9a, 9b and the rotor-side seal seat for an air seal 7b, the already mentioned rotor-side seal seat 7a is provided for an oil seal.

FIG. 3 shows an embodiment of a trained as a secondary rotor rotor screw 1, as they themselves already with reference to the FIG. 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, however, are coated only between the end faces 5a, 5c and the bearing seats 9a with a first inner layer 3 (omitting a second, outer layer 4), wherein the bearing seats 9a, however, free, ie without a coating corresponding to the first, inner Layer 3, that are formed without coating with a thermoplastic material.

FIG. 4 shows an embodiment of a trained as a main rotor rotor screw 2, as they themselves already with reference to the FIG. 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 coated only between the end faces 5b, 5d and the bearing seats 9b with a first inner layer 3 (omitting a second, outer layer 4), wherein the bearing seats 9a, however, free, ie without a coating corresponding to the first, inner layer 3, that are formed without coating with a thermoplastic material.

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

About a synchromesh 13, the rotor screws 1, 2 are set in their rotational position against each other and their profile surfaces 12a, 12b, in particular their 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 coupling (not shown). At the suction end of the pairwise screwed rotor screws 1, 2, a suction region 23 of the screw compressor can be seen.

In FIG. 6 an embodiment of a screw compressor 20 is illustrated in an exploded view. The compressor housing 11 limits the compression chamber 18. About a suction nozzle 27 ambient air is sucked in and enters the suction region 23 of the screw compressor. After compression via the rotor screws 1, 2, the compressed compressed air is discharged through a discharge nozzle 28 from the compressor housing 11.

In FIG. 7 is the multi-layer coating on the profile surface 12a of the rotor screw 1 along the line AA in FIG. 3 illustrated. On a main body 24 of the rotor screw 1, first, the first inner layer 3 is applied. On the first, inner layer 3 - this completely overlapping - the second, outer layer 4 is applied. The second, outer layer 4 comprises according to the invention an inlet process supporting particles 25, for example, thin-walled micro-glass bubbles. Alternatively or additionally, pores 32 can also be incorporated, which supports the plastic compressibility of the second, outer layer.

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

FIG. 9 shows a one-piece coating on the shaft end 30 of the rotor screw 1, which is provided in the region of the rotor-side seal seat 7a for the oil seal and the rotor-side seal seat 7b for the air seal both sealing seats 7a, 7b overlapping. Specifically, a section along the line BB in FIG. 3 shown. The first, inner layer is here the main body 24 arranged overlapping and thus provides a good and reliable corrosion protection.

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

FIG. 11 shows the multilayer coating after FIG. 10 after a running-in process. It can be seen that some layer areas are removed or compressed. Some of the pores 32 are also removed with parts of the layer or compressed on the basis of the recorded backpressure, so that altogether a plastic deformation of the second, outer layer 4 as an inlet layer was obtained.

FIG. 12 schematically shows a flowchart for a possible embodiment of the coating process. In a step sequence S01 to S04, a pretreatment of the metallic surface to be coated, for example the surface of a rotor screw to be coated, takes place. In this case, the step S01 comprises a degreasing of the surface by burning at high temperature (pyrolysis). In the subsequent step S02, the surface is blasted, in particular sandblasted. After blasting, a step S03 follows, by again cleaning the surface by chemical means, for example by means of 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, wherein the first, inner layer 3 is applied as a wet paint in the present exemplary embodiment. But there are also alternative methods conceivable, for example, an application in the dry state as a powder coating. In this case, the wet paint for the first, inner layer is prepared in advance, wherein the thermoplastic material in the form of PEEK is mixed in each case in powder form in water with dispersant. The result is a suspension, which is applied in step S10 on the pretreated surface. In a subsequent step S11, the applied wet paint is dried or flashed off. For this purpose, in step S11, the rotor screw coated with the wet paint for the first layer is heated to about 120 ° C. to evaporate the water. In a step S12, which may optionally also be omitted, the first layer is burned in. The firing takes place at temperatures of about 360 ° C to 420 ° C, for example in a convection oven or inductively until the PEEK is melted and has formed a homogeneous layer.

In steps largely analogous to steps S10, S11, S12, S20, S21, S22, the second layer is applied. For this purpose, a wet paint is prepared again, expediently - but by no means necessarily - the same thermoplastic material as in the application of the first layer - comprising or having PEEK as thermoplastic - use. For this purpose, the PEEK is mixed in powder form with the inlet process supporting particles, such as the thin-walled micro-glass bubbles, in particular 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 omit step S12, namely the baking of the first layer, and to burn in first, inner layer 3 and second, outer layer 4 together. 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 approximately 120 ° C. or kept at this temperature in step S21. After sufficient drying of the second, outer layer takes place in step S22, a baking of the second outer layer at temperatures of about 360 ° C to 420 ° C, for example in a convection oven or in an inductive manner.

Optionally, a step S23 (not shown) may follow, but should preferably be avoided. In a step S23, regrinding of the second, outer layer 4 could take place in order to achieve a respectively desired dimensioning by regrinding when forming the second, outer layer with oversize. As already mentioned, however, it is preferred that the respective desired dimensioning of the layer structure already with the methods as shown by FIG. 12 shown to achieve.

LIST OF REFERENCE NUMBERS

1, 2

rotor screw

3

first, inner layer

4

second outer layer

5a, 5b, 5c, 5d

faces

6a

pressure-side housing end face

6b

suction-side housing end face

7a

Rotor-side seal seat for an air seal

7b

Rotor-side seal seat for an oil seal

8a

Housing-side seal seat for an oil seal

8b

Housing-side seal seat for an air seal

9a, 9b

rotor-side bearing seat

10

housing-side bearing seat

11

compressor housing

12a, 12b

profile surface

13

synchromesh

14b

poetry

14c

poetry

15

camp

16

wave

18

compression chamber

19

rotor bore

20

screw compressors

21

Pitch circle (main rotor)

22

Pitch circle (secondary rotor)

23

suction area

24

body

25

particle

27

suction

28

pressure port

30

protruding shaft ends

32

pore

Claims (30)

Screw compressor comprising a compressor housing (11) with two axially parallel mounted rotor screws (1, 2) in a compression chamber (18) mesh with each other, drivable by a drive and synchronized in their rotational movement to each other, wherein the rotor screws (1, 2) respectively a single or multi-part main body (24) with two end faces (5a, 5b, 5c, 5d) and a profile surface extending therebetween (12a, 12b) and on the end surfaces (5a, 5b, 5c, 5d) projecting shaft ends (30) , characterized in that
at least the profile surface (12a, 12b) is multilayered, comprising a first, inner layer (3) and a second, outer layer (4), wherein the first, inner layer (3) and the second, outer layer (4) are both comprise a thermoplastic or are formed from this,
wherein in the second, outer layer (4) an inlet process supporting particles (25) or pores (32) are embedded and the thermoplastic material defines a matrix for receiving the particles (25) and for forming the pores (32). 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, in particular a semi-crystalline, high-performance thermoplastic. 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 polyaryletherketone (PAEK) or consists at least essentially of a polyaryletherketone (PAEK). 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 polyetheretherketone (PEEK) or consists at least essentially of polyetheretherketone (PEEK). Screw compressor according to one of claims 1 to 4,
characterized in that
the first, inner layer (3) without an inlet process supporting particles (25) or pores (32), but at least substantially homogeneously formed. Screw compressor according to one of claims 1 to 5,
characterized in that
the inlet-assisting particle (25) of the second, outer layer (4) comprises abrasive and / or lubricating particles. Screw compressor according to one of claims 1 to 6,
characterized in that
the particles (25) are in microencapsulated form, wherein at least one first substance is surrounded by a second substance as the enveloping material. Screw compressor according to claim 6,
characterized in that
the particles (25) comprise microspheres (microspheres), in particular of aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ) or of thermoplastic material, in particular of these. Screw compressor according to claim 6,
characterized in that
the particles (25) comprise micro-hollow spheres (microspheres) of glass, in particular borosilicate glass, or of glass, in particular borosilicate glass. Screw compressor according to one of claims 1 to 9,
characterized in that
the particles (25) of the second, outer layer (4) which support an inlet process have a higher hardness (according to Shore) than the matrix defined by the thermoplastic. Screw compressor according to one of claims 1 to 9,
characterized in that
the particles (25) of the second, outer layer (4) which support an inlet process have a lower hardness (according to Shore) than the matrix defined by the thermoplastic. 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. 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. Screw compressor according to one of claims 1 to 13,
characterized in that
the second, outer layer (4) in the inlet process partially abrasive and / or partially plastically deforming, therefore defines an adapting to the specific operating conditions inlet layer. Screw compressor according to one of claims 1 to 14,
characterized in that
the particles comprise graphite or are formed from graphite. Screw compressor according to one of claims 1 to 15,
characterized in that
the particles include: Hexagonal boron nitride, carbon nanotubes (CNT), talc, polytetrafluoroethylene (PTFE), perfluoroalkoxy polymers (PFA), fluoroethylene-propylene (FEP), and / or another fluoropolymer. Screw compressor according to one of claims 1 to 15,
characterized in that
the particles include: Alumina (Al ₂ O ₃ ), silicon carbide (SiC), silicon dioxide (SiO ₂ ), and / or glass, in particular borosilicate glass. Screw compressor according to one of claims 1 to 17,
characterized in that
the layer thickness of the first, inner layer (3) before shrinkage amounts to 5 μm to 50 μm. Screw compressor according to one of the preceding claims,
characterized in that
the layer thickness of the second outer layer (4) prior to shrinkage is 10 μm to 120 μm. Screw compressor according to one of the preceding claims,
characterized in that
the base body (24) of the rotor screw is formed from steel and / or cast iron. Screw compressor according to one of claims 1 to 19,
characterized in that
at least portions of the shaft ends (30) uncoated, at least not coated with a thermoplastic material. Screw compressor according to one of claims 1 to 21,
characterized in that
at least portions of the shaft ends (30) are coated with the first, inner layer (3) of thermoplastic material. 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) multilayer comprising a first, inner layer (3) and a second, outer layer (4) coated are, wherein the first, inner layer (3) and the second, outer layer (4) both include or are formed from a thermoplastic, wherein in the second, outer layer (4) an inlet process assisting particles (25) or Pores (32) are embedded and the thermoplastic material defines a matrix for receiving the particles (25) and for forming the pores (32). Screw compressor according to one of claims 1 to 23,
characterized in that
Inner walls, such as a lateral surface of a rotor bore (19), pressure-side and / or suction-side housing end faces (6a, 6b) of the compression space (18) are coated at least with a first layer (3), preferably also with a second layer (4), wherein the The first layer (3) and the second layer (4) both comprise or are formed from a thermoplastic and wherein in the second, outer layer (4) an inlet process supporting particles (25) or pores (32) are embedded and the thermoplastic resin defines a matrix for receiving the particles (25) or for forming the pores (32). 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. Rotor screw for use in a screw compressor according to one of the preceding claims, wherein the rotor screw (1, 2) has a one-part or multi-part main body (24) with two end faces (5a, 5b, 5c, 5d) and an intermediate profile surface (12a, 12b) and over the end surfaces (5a, 5b, 5c, 5d) projecting shaft ends (30),
wherein at least the profile surface (12a, 12b) is multi-layered, 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 a thermoplastic or are formed from this,
characterized in that
in the second, outer layer (4) an inlet process supporting particles (25) or pores (32) are embedded and the thermoplastic material defines a matrix for receiving the particles (25) and for forming the pores (32). Method for applying a multilayer coating to a metallic surface of a rotor screw or a compression space of a screw compressor to be coated, comprising the following steps: Pretreating the metallic surface to be coated, Applying a first, inner layer (3), which comprises or is formed from a thermoplastic, onto the metallic surface to be coated or onto a lower layer, which may in particular be in the form of 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 and wherein in the second, outer layer (4) an inlet process supporting particles (25) or pores (32) are embedded and the thermoplastic a Matrix for receiving the particles (25) and for forming the pores (32) defined. 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 coating. Method according to claim 27 or 28
characterized in that
the first, inner layer (3) and the second, outer layer (4) are baked so that the thermoplastic melts. 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, eg phosphating or applying a nanoceramic.

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