WO2019072721A1 - OIL-FREE COMPRESSOR - Google Patents

Abstract

The present invention relates to an oil-free compressor (1) having at least one piston (3) guided in an associated cylinder (2), which has at least one piston ring (4) and one piston shaft (5), wherein - the at least one piston shaft (5) a directly applied sliding layer (6) has with a polymer from the group PAI, epoxy compounds, PEEK, PEK, PEKK, PAEK and a solid lubricant from the group graphite, MoS ₂ , WS ₂ , hBN, PTFE and ZnS, preferably WC as hard material particles, the piston ring (4) is made of PTFE, - a cylinder running surface (7) of the cylinder (2) is coated with a nickel-containing liner layer (8).

Description

 Oil-free compressor

The present invention relates to an oil-free compressor having at least one piston guided in an associated cylinder.

Compressors are widely known from the prior art, in particular in the field of turbochargers, for example, and can generally be found in

oil-lubricated and so-called oil-free compressors are divided.

Particularly in oil-free compressors in which oil is not available as a lubricant, the lowest possible sliding resistance of pistons in associated cylinders for a low-wear operation, a long

Lifespan and high cost-effectiveness of vital importance. In order to obtain the lowest possible sliding resistance, pistons are generally already made with films stuck in particular in a shaft region

Polytetrafluoroethylene (PTFE) known. The disadvantage of such adhesively bonded coatings, however, are their relatively small

Temperature resistance and their comparatively manageable life expectancy.

The present invention therefore deals with the problem of overcoming the disadvantages known from the prior art.

This problem is inventively achieved by the subject matter of

independent claim 1 solved. Advantageous embodiments are

Subject of the dependent claims. The present invention is based on the general idea of considering and completely optimizing the entire tribological system in an oil-free compressor for the first time by tribologically optimizing both a cylinder surface, a piston ring of an adjustable piston and the piston itself. The oil-free compressor according to the invention in this case has at least one in an associated cylinder translationally adjustable piston, which in turn has at least one piston ring and a piston skirt.

According to the invention, at least the piston skirt of the piston has a sliding layer with a polymer from the group PAI (polyamide-imide), epoxy compounds, PEEK (polyetheretherketone), PEK (polyetherketone), PEKK (polyetherketone ketone), PAEK (polyaryletherketone), a solid lubricant from the group graphite, MoS ₂ (molybdenum disulfide), WS ₂ (tungsten disulfide), hBN (hexagonal boron nitride), PTFE (polytetrafluoroethylene) and ZnS (zinc sulfide) as well as hard material particles like WC (tungsten carbide). In addition, the piston ring of polytetrafluoroethylene (PTFE) is formed and a cylinder surface of the

Cylinder is coated with a nickel containing as a main component liner layer. Through this tribological system of piston with sliding layer, PTFE piston ring and cylinder surface with liner layer not only the friction of the piston in the cylinder can be significantly reduced, but also can now also by the directly applied to the piston shaft sliding layer, the resulting friction at the temperature to can be reduced to 30 K, resulting in a lower friction and less wear of the piston ring and thus its life and the lifetime of the overall system can be significantly increased, since in particular the piston ring is the weakest link in relation to the entire system. Furthermore, the now no longer applied as a film sliding layer, but the applied directly on the piston skirt sliding layer is more temperature resistant, whereby higher operating parameters are made possible for an oil-free piston compressor. For example, in an oil-free compressor, the has to provide a predefined discharge pressure, which previously could only be achieved with two compressor stages, now only one

Compressor be provided, resulting in a significant cost savings.

In an advantageous development of the solution according to the invention, the sliding layer has a thickness dG of 45 μιτι <dG <00 μιτι, preferably of 70 μιτι <dG <90 μιτι. The sliding layer according to the invention is thus considerably thinner than previously used PTFE films, which had a thickness of about 300 μιτι. Due to the thinner sliding layer, which is also applied directly to at least the piston skirt, but also to an entire circumferential surface, including ring portion, of the piston, a lesser clearance between the piston and cylinder can be carried out, resulting in a considerable noise emission reduction.

In a further advantageous embodiment of the compressor according to the invention, the sliding layer is applied by screen printing. In screen printing, the material of the sliding layer is printed by a fine-meshed fabric on the surface to be printed, wherein it by means of the

Screen printing method is particularly possible evenly and evenly coated curved surfaces in the present case. In a further embodiment, the coating may be in a special

Multiple injection method can be applied. The multilayer coating requires special intermediate drying steps, these are with respect to a

economic mapping of the process in an IR (infrared) method feasible. In a further advantageous embodiment of the solution according to the invention, the liner layer on the cylinder running surface of the cylinder mainly nickel and in particular additionally silicon carbide (SiC).

Silicon carbide particles in turn have a high hardness and a high melting point, whereby the wear resistance of the liner layer can be significantly increased.

Suitably, the liner layer about 2 to 6 wt .-% silicon carbide. Already such a small amount of silicon carbide is sufficient for the increase of

Abrasion resistance, without affecting the slip resistance properties of the surrounding nickel matrix of the liner layer would be affected.

Suitably, the liner layer has a thickness di_ of 40μηη <di_ <Ι ΟΌμηη, preferably di_ = 50μηη. Already such a thin liner layer allows on the one hand an effective sliding layer for the cylinder surface and thus the cylinder and on the other hand, the increase in wear resistance by the silicon carbide embedded in the nickel matrix.

In a further advantageous embodiment of the solution according to the invention, an intermediate layer is present between the liner layer and the cylinder.

especially in the manner of a nickel-nickel layer, with a dz of 4μηη <dz <40μηη applied. Such a pre-nickel layer serves in particular as

Adhesive layer for the later applied thereto liner layer, but may only be necessary due to the process.

Suitably, the liner layer has a center roughness of R _a about 0.1 μιτι, which can be prepared in particular by means of honing. In the case of such _a mean roughness value of R _a approximately 0.1 μm, there are no visible processing traces left and the surface is substantially smooth. This can be a particularly low-wear movement of the piston and in particular the piston ring can be achieved on the liner layer, whereby the life of the piston, the piston ring and thus overall of the compressor can be increased.

 Other important features and advantages of the invention will become apparent from the dependent claims, from the drawings and from the associated

Description of the figures with reference to the drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

Show, in each case schematically,

Fig. 1 is a sectional view through an oil-free invention

 Compressor,

Fig. 2 is a detail sectional view in the region of the piston skirt of the

 Piston with overlay thereon,

Fig. 3 is a detail sectional view through a cylinder wall with

Liner layer and intermediate layer. According to FIG. 1, an oil-free compressor 1 has at least one piston 3 that is translationally adjustable in an associated cylinder 2 and that has at least one piston ring 4 and one piston shaft 5.

According to the invention, the piston 3 now at least in the region of his

Piston shaft 5 a sliding layer 6 (see also Fig. 2), with a polymer from the group polyamide-imide (PAI), epoxy compounds, PEEK, PEK, PEKK, PAEK and a solid lubricant from the group graphite,

Molybdenum disulfide (MoS ₂ ), tungsten disulfide (WS ₂ ), hBN (boron nitride), PTFE

(Polytetrafluoroethylene) and zinc sulfide (ZnS), preferably tungsten carbide (WC), the latter being a hard material particle. In addition, the piston ring 4 is formed of polytetrafluoroethylene (PTFE), and a cylinder barrel surface 7 of the cylinder 2 is provided with a nickel (Ni) as a main component

Liner layer 8 (see FIG. 3) coated. By created in this way tribological system of cylinder 2, piston 3 and piston ring 4, a particularly low-wear and thus a high life expectancy exhibiting compressor 1 can be created.

The sliding layer 6 in this case has a thickness dG of 45μηη <dG <Ι ΟΌμηη, preferably of 70μηη <dG <90μηη (see Fig. 2). This is significantly thinner compared to previously stuck on the piston skirt 5 from the prior art PTFE films, whereby a significantly reduced clearance between the piston 3 and the cylinder 2 is adjustable, whereby the noise emission can be significantly reduced.

By the direct application of the sliding layer 6 at least on the piston shaft 5, a particularly adhesive-resistant application and, as already mentioned, a significantly lower overall thickness of the sliding layer 6 can be achieved. A possible application form for the sliding layer 6 is the screen printing process, which is not only a high-quality, but also inexpensive application of the sliding layer 6 allows at least the piston shaft 5.

By selecting the plastic polytetrafluoroethylene for the piston ring 4, this can slide very smoothly, that is, with low sliding resistance, on the cylinder surface 7 along. In addition, the static friction is just as large as the sliding friction, so that a transition from standstill to movement, especially at the start of the compressor, can take place without jerk. In addition, PTFE is difficult to wet and hardly stick, since

For example, the contact angle with water is 126 °. It is also of particular advantage that PTFE is extremely resistant to all bases, alcohols, ketones, gasolines and oils and has operating temperatures of up to 260 °.

In an advantageous development of the solution according to the invention, the liner layer 8 has a thickness di_ of 40μηη <di_ <Ι ΟΌμηη, particularly preferably of di_ of about 50μηη. Since the main component of the liner layer 8 is nickel, a highly effective sliding layer for the cylinder surface 7 and thus the cylinders 2 can be created with this. In addition, the

To be able to increase wear resistance and thus also the life expectancy of the liner layer 8, this silicon carbide (SiC), in particular in such a way of silicon carbide particles 10, in a weight percentage of 2-4 wt%. In this case, silicon carbide and / or silicon carbide particles 10 are used, which are embedded in the nickel matrix and which have a diameter ds of 1 μιτι <ds <4μηη, preferably a diameter of ds of about 2.5 μιτι. The particle diameter ds is thus considerably smaller than the thickness di_ of the liner layer 8 and thus easily integrated into this. Looking again at Fig. 3, it can be seen that between the liner layer 8 and the cylinder 2, an intermediate layer 9 is applied with a thickness dz of 4μηη <dz <40μηη.

After the application of the liner layer 8 or after the application of both the intermediate layer 9 and the liner layer 8, the cylinder surface 7 is preferably honed, in order to be able to produce a high surface quality. By honing in particular a center roughness of R _a of about 0.1 m can be achieved, so that preferably no more processing traces are present.

With the inventive compressor 1 and the piston 3 inserted therein, the piston ring 4 and the liner layer 8 on the cylinder surface 7, a tribological system can be created for the first time, which not only due to high wear resistance and low sliding friction has a long service life, but also is inexpensive to produce. By the indirect application of the sliding layer 6 on the piston shaft 5, a sticking of a PTFE film, as was done so far, omitted, whereby the sliding layer 6 can be made significantly thinner in itself, which brings significant advantages in terms of reducing the noise emissions.

By admixing fine-scale hard materials, such as e.g. WC, can the

Wear resistance of the sliding layer 6 can be increased on the piston 3. The chemical composition of the lubricating varnish or sliding layer 6 enables better heat dissipation via the cylinder wall 7 and thus significantly reduces the operating temperature. A particular advantage is that the layer thickness of the bonded coating or the sliding layer 6 is significantly lower in comparison to the prior art (PTFE films) and thus the temperature removal is simplified.

This leads to the fact that the piston ring 4 is loaded less and thus the wear on the piston ring 4 decreases significantly.

Claims

claims 1 . Oil-free compressor (1) with at least one in an associated  Cylinder (2) guided piston (3) having at least one piston ring (4) and a piston shaft (5), wherein  - The at least the piston shaft (5) directly applied  Sliding layer (6) comprising with a polymer from the group PAI, epoxy compounds, PEEK, PEK, PEKK, PAEK and a Solid lubricant from the group graphite, M0S ₂ , WS ₂ , hBN, PTFE and ZnS, preferably WC as hard material particles,  the piston ring (4) is made of PTFE,  - A cylinder surface (7) of the cylinder (2) with a nickel  having coating liner layer (8) is coated. 2. Compressor according to claim 1,  characterized,  the sliding layer (6) has a thickness dG of 45μηη <dG <Ι ΟΟμηη, preferably of 70μηη <dG <90μηη. 3. Compressor according to claim 1 or 2,  characterized, that the sliding layer (6) is applied by screen printing or multiple spraying. 4. Compressor according to one of the preceding claims,  characterized,  the liner layer (8) comprises silicon carbide (SiC). 5. Compressor according to claim 4,  characterized,  the liner layer (8) comprises about 2 to 6% by weight silicon carbide. 6. A compressor according to claim 4 or 5,  characterized,  that silicon particles (10) of the liner layer (8) have a diameter ds of 1 μιτι <ds <4 μιτι, preferably have a diameter ds of 2.5 μιτι. 7. A compressor according to any one of claims 1 to 6,  characterized,  the liner layer (8) has a thickness di_ of 40μηη <di_ <Ι ΟΟμηη, preferably a thickness di_ of 50μηη. 8. A compressor according to any one of claims 1 to 7,  characterized,  that between the liner layer (8) and the cylinder (2) has a  Intermediate layer (9) with a thickness dz of 4μηη <dz <40μηη is applied. 9. A compressor according to any one of claims 1 to 8,  characterized, the liner layer (8) has a mean roughness value of R _a "0.1 μιτι. 10. A compressor according to any one of claims 1 to 9,  characterized, that the liner layer (8) is honed to a mean roughness value of R _a "0.1 μιτι.