CN1615184A - Method to rough size coated components for easy assembly - Google Patents

Abstract

A method for coating the surface of a screw compressor. The method includes the following steps: providing at least one of a plurality of screw compressor components, the plurality of screw compressor components including a rotor housing having at least a pair of parallel overlapping bores; a pair of mating rotors located within the bores, each rotor having helical teeth having a radially outwardly facing top and a centrally located radially inwardly facing root; then coarsely coating the surface of at least one of the plurality of components with a suitable coating, wherein the coating is applied to the surface in a generally uneven manner and has a variable thickness throughout the surface; and smoothing the suitable coating to a generally uniform thickness before final assembly of the plurality of components, the generally uniform thickness being selected to facilitate assembly of the components while maintaining coating performance specifications.

Description

Method for rough leveling of coated parts to facilitate assembly

technical field

The present invention is directed to coatings for machine components, and more particularly to methods of applying suitable coatings to compressor components.

Background technique

In a conventional screw compressor, male and female rotors disposed within corresponding parallel overlapping bores defined by a rotor housing cooperate to trap and compress a volume of air. Although two rotors are the most common configuration, three or more rotors may act together in pairs. Male and female rotors differ in lobe profile and number of lobes and gullets. For example, a female rotor may have six lobes separated by six slots, while a mating male rotor may have five lobes separated by five slots. Thus, some or all possible combinations of lobes and cogging interactions occur periodically between the rotors. The co-action between mating pairs of rotors is a combination of sliding and rolling contact that produces different wear rates. In addition to acting in pairs, the rotors also cooperate with the housing. Since multiple rotor contact combinations occur between mating pairs, the seal/leakage between different combinations may vary due to manufacturing tolerances and wear patterns. It may be the case that even if manufacturing tolerances are kept very tight with attendant manufacturing costs, it is still necessary to provide proper lubrication or other liquid injection in order to seal.

The profile configuration of the mating pair of screw rotors must provide clearance in most sections. The need to set clearances is a result of several factors including: thermal expansion of the rotors due to heating of the gas during compression; deflection of the rotors due to compression process pressure loads; sometimes the tendency to place the rotors too close to each other resulting in interfering bearings Tolerances in the bearing construction and machining on the rotor; and machining tolerances in the rotor contour itself which can also lead to interference. Superimposed on these factors are the pressure and temperature gradients that occur with the increase in pressure and temperature during the cycle from suction to discharge.

During operation this pressure gradient is generally in one direction so that the fluid pressure tends to force the rotor towards the suction side. Each end of the rotor is conventionally mounted in bearings to provide radial and axial restraint. The end clearance of the rotor on the discharge side is decisive for sealing and the fluid pressure tends to force this clearance wide.

There are certain rotor sections, such as contact strips, where zero clearance is maintained between the rotors. The portion of the rotor defining the contact zone is the area where the required torque is transmitted between the rotors. The inter-rotor loading is different for male and female rotor drives. In a male rotor drive, the inter-rotor load may be equivalent to 10% of the total compressor torque, whereas in a female rotor drive, the inter-rotor load may be equivalent to 90% of the total compressor torque. These parts are traditionally located close to the rotor pitch circle, which is the location on the rotor of equal rotational speed, resulting in rolling contact and thereby reducing or eliminating sliding contact, thus reducing wear.

In order to prevent failures resulting from rotor seizure, a large amount of end running clearance must be maintained at the discharge end of the screw compressor. Seizing occurs when the rotor discharge end contacts the compressor end casing during operation and can be caused by thermal expansion of the rotor or by intermittent contact between the rotor and end casing caused by, for example, pressure pulsations during compression.

Contents of the invention

It is an object of the present invention to provide an improved method for applying a coating to screw compressor components to reduce leakage within the screw compressor.

Another object of the present invention is to provide a method of rough coating a screw compressor component as a first step in applying a coating to a screw compressor component.

It is a further object of the present invention to facilitate assembly of screw compressor components by obtaining a more uniform surface coating by using an initial coarse coating application method and applying a smoothing step prior to assembly .

Yet another object of the present invention is to reduce excess and uneven thickness of component coatings to facilitate assembly of the components.

These and other objects, which will become more apparent hereinafter, are accomplished by the present invention.

According to the present invention, there is provided a method for applying a coating to one or more segments and/or housing bore surfaces of a screw rotor.

The above-mentioned objects and consequent advantages are achieved by the method according to the invention for coating the surfaces of screw compressors. The method comprises the steps of: providing at least one of a plurality of screw compressor components comprising a rotor housing having at least one pair of parallel overlapping bores; intermeshing rotors located within the bores engaging a set wherein each rotor has a helical lobe having a radially outward crest and a central radially inward root; followed by rough coating the surface of at least one of the plurality of components with a suitable coating, The coating is substantially applied to the surface and has a variable or excessive thickness throughout the surface; and the suitable coating is leveled to a substantially uniform thickness prior to final assembly of the parts, the substantially uniform Thicknesses are selected for ease of assembly of the part while maintaining coating performance specifications.

Description of drawings

In order that the present invention may be more fully understood, various embodiments thereof will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 is a cross-sectional view through a screw compressor;

Fig. 2 is a partial sectional view of the screw machine of Fig. 1;

Figure 3 is an enlarged view of the discharge end portion of the screw compressor of Figure 1;

Figure 4 is an enlarged portion of Figure 1 with various coatings of the present invention described;

Figure 5 is a partial cross-sectional view showing a DLC coating on a rotor end;

Figure 6 is a partial cross-sectional view showing the DLC coating on the discharge housing;

Figure 7 is a partial sectional view showing a DLC coated disc;

Figure 8 is an enlarged view of a DLC coating;

Figure 9 is a perspective view of the axial section of the rotor of Figure 1;

Fig. 10 is a schematic image of the coating before the coating leveling process of the present invention, and a finishing device for leveling the coating;

Fig. 11 is the schematic diagram of parts after implementing the coarse coating smoothing method shown in Fig. 10; And

Figure 12 is a further embodiment of the method used to achieve the results shown in Figure 11, applied exclusively to rotors, such that an uncoated rotor is used to smooth a coated rotor.

Detailed ways

In FIG. 1 a screw compressor 10 , for example a screw compressor, is depicted having a rotor housing or housing 12 in which overlapping bores 12 - 1 and 12 - 2 are arranged. A female rotor 14 having a pitch circle _PF is disposed inside the hole 12-1. A male rotor 16 having a pitch circle _PM is disposed inside the bore 12-2. The parallel axes represented by points A and B are perpendicular to the plane of Fig. 1 and separated by _a distance equal to the sum of the radius R _F of the pitch circle PF of the female rotor 14 and the radius R _M of the pitch circle _PM of the male rotor 16 . The axis indicated by point A is the axis of rotation of the female rotor 14 and is generally the center of the hole 12 - 1 , and the diameter of the hole 12 - 1 generally corresponds to the diameter of the tip circle _TF of the female rotor 14 . Likewise, the axis indicated by point B is the axis of rotation of the male rotor 16 and is generally the center of the bore 12-2, and the diameter of the bore 12-2 generally coincides with the diameter of the tip circle _TM of the male rotor 16. Typically, the centerline of the rotor and its bore is deviated by a very small amount in order to compensate for backlash and deflection. The extension of bore 12-1 passing through the overlapping section of bore 12-2 intersects line AB at the point of tangency to male rotor 16 root circle R _MR , neglecting the working clearance. Likewise, the continuation of bore 12-2 through the overlapping section of bore 12-1 will intersect line AB at the point of tangency to the circle R _FR of female rotor 14, and for female rotor 14 this common point is marked is F ₁ , and for the male rotor 16, it is marked as M ₁ .

In the depicted embodiment, the female rotor 14 has six ridges or crests 14-1 separated by six grooves or gullets 14-2, while the male rotor 16 has five grooves or gullets 16-2. -2 spaced five ridges or tops 16-1. Thus, the rotational speed of the rotor 16 is 6/5 or 120% of that of the rotor 14 . Either the female rotor 14 or the male rotor 16 may be connected to a prime mover (not shown) to serve as the drive rotor. Other numbers of male and female rotor land and groove combinations may also be used.

Referring now to FIGS. 2 and 3 , the rotor 14 has a shaft segment 14 - 3 with a shoulder 14 - 4 formed between the shaft segment 14 - 3 and the rotor 14 . Shaft section 14 - 3 of rotor 14 is supported within outlet or discharge housing 13 with one or more bearings 30 . Likewise, the rotor 16 has a shaft section 16 - 3 with a shoulder 16 - 4 formed between the shaft section 16 - 3 and the rotor 16 . The shaft section 16 - 3 of the rotor 16 is supported in the outlet housing 13 with one or more bearings 31 . The respective suction-side shaft sections 14 - 5 and 16 - 5 of the rotors 14 and 16 are supported in the rotor housing 12 with roller bearings 32 and 33 , respectively.

In operation, as a refrigeration compressor, the male rotor 16 is assumed to be the drive rotor, which turns the meshing rotor 14 and causes it to rotate. The co-action of rotating rotors 16 and 14 disposed within respective bores 12-2 and 12-1 drives refrigerant gas via suction port 18 into the grooves of rotors 16 and 14 which engage to trap and compress the gas volume and release The hot compressed gas is delivered to the discharge port 19 . Trapped gas acting on movable rotors 14 and 16 tends to cause discharge ends 14-4 and 16-4 to move away from outlet housing surface 13-1 creating/increasing a leak path. Movement of rotors 14 and 16 away from outlet housing surface 13-1 results in movement of rotors 14 and 16 towards surface 12-3 of rotor housing 12 or into engagement with the latter by means of shoulders 14-6 and 16-6, respectively. . In addition to the leakage path between the rotor shoulders 14-4, 16-4 and the outlet housing surface 13-1, it is also possible to The line contact between the top and holes 12-1, 12-2, respectively, is leaking. Leakage across the ridge/line contact can be reduced by using sealing oil, but the oil creates viscous losses between moving parts and must be removed from the exhaust gas.

As noted above, the contact zone is defined by a zero gap rather than by position. Figure 4 shows an enlarged portion of Figure 1 in order to illustrate the displacement of the contact strip according to one aspect of the invention. Referring to Fig. 1, the contact zone should be arranged inside the pitch circle P _F of the female rotor 14 within the range of the top part 14-1 of the female rotor and outside the pitch circle P _M of the male rotor 16 within the range of the male rotor root 16-2 .

For oil-free or oil-less compressors, the top of the rotor must be as close as possible to the rotor housing holes 12-1 and 12-2 to reduce leakage due to failure to seal with oil. If contact occurs between the rotor and the housing, excessive wear and power loss will occur due to friction between the top of the rotor and the housing. Even if the rotor is lubricated, leakage occurs through the oil seal, so the oil must be removed from the refrigerant in order to minimize the inefficiency of heat transfer as the oil circulates through the refrigeration system, and to maintain the oil necessary to Lubricate inside the compressor.

Accordingly, a low-friction, wear-resistant coating is provided on the tops or spines 14-1 and 16-1 of the rotors 14 and 16, respectively. One suitable low-friction and wear-resistant coating is the low-friction diamond-like carbon (DLC) type of coating disclosed in commonly assigned U.S. Patent No. 5,672,054, which is used locally on the blade top surface in a rotary compressor superior. This DLC coating is used to overcome lubrication difficulties associated with using new oil and refrigerant compositions. The DLC coating is not only lubricious but also wear resistant, as discussed in detail in U.S. No. 5,672,054, the entire disclosure of which is hereby incorporated by reference, the coating is composed of a hard material such as tungsten carbide and alternating layers of amorphous carbon.

Other examples of suitable low-friction and wear-resistant coatings include titanium nitride and single-layer nitride coatings of other individual materials, as well as carbide and ceramic coatings that not only have high wear resistance but also have a low coefficient of friction. Providing a low-friction and wear-resistant coating on the top of the respective rotor or on the valleys of the ridges offers a number of advantages. First, oil-free or low-oil operation is possible without excessive wear or friction for the rotor. Second, machining tolerances can be loose because some contact with the rotor bore can be tolerated. Third, due to the ability to operate with small clearances between the rotor tops or spines 14-1 and 16-1 and the corresponding rotor holes 12-1 and 12-2, the need for rotor-to-rotor hole contact is reduced or eliminated. Oil seal requirements.

Since the contact strip on the female rotor 14 is placed close to the top, two important areas on the female rotor can be covered with a single DLC coating because of the narrow spacing or overlapping of the two areas depending on the rotor profile. A separate DLC coating 40 on the female rotor as depicted in Figure 4 is optimal for ease of manufacture. Section 40-1 of coating 40 corresponds to this contact zone, while section 40-2 corresponds to the crest or ridge 14-1 closest to hole 12-1. The respective DLC coatings on the male rotor 16 are spaced more widely by a coating 60 arranged at the top of the rotor and a coating 61 arranged at the root corresponding to the contact strip.

As with the rotor top, gaps are also arranged at the rotor ends in order to form leakage paths. According to another aspect of the invention, the DLC coating can be applied at the discharge end of the rotor, at the facing surface of the discharge casing 13 or on a coated gasket arranged between the rotor and the discharge casing 13 , thereby reducing running clearances and leakage paths. Referring now to FIG. 5 , where a DLC coating is applied to the discharge ends of rotors 14 and 16 . More specifically, DLC coating 42 is applied to the discharge end of female rotor 14 and DLC coating 62 is applied to the discharge end of male rotor 16 . Since the DLC coatings 42 and 62 accommodate some contact with the outlet housing surface 13-1, leakage can be reduced through reduced end running clearance. Referring now to FIG. 6, coating 82 is applied to housing surface 13-1 rather than to the ends of rotors 14 and 16 as in the FIG. 5 embodiment. In the embodiment of FIG. 7, however, a separation member 90 is placed between the rotors 14, 16 and the housing surface 13-1. Because member 90 conforms to the cross-section of holes 12-1 and 12-2 or prevents movement relative to housing surface 13-1 in another way, it cannot rotate, so relative motion will occur between member 90 and rotor 14 and 16 between the discharge ends. Therefore, only the surfaces of the components 90 facing the rotors 14 and 16 need be provided with the DLC coating 92 . In the Figures 5-7 embodiment, the DLC coating is placed between the ends of the rotors 14, 16 and surface 13-1 such that its lubricity will protect the rotor and housing from wear during occasional contact, allowing a tight fit End running clearances and narrow leak paths.

Referring now to FIG. 8 , there is depicted a highly exaggerated cross-section of the coating, which, although designated 40 , represents coatings 40 , 42 , 60 , 61 , 62 , 82 and 92 . DLC coating 40 is made of hard double layer 40 ' and lubricating double layer 40 ". The scope of double layer thickness is 1 to 20nm, and the optimum range is between 5 to 10nm. Except wear-resistant coating, a Suitable coatings, which may be abradable or extrudable, may be applied to rotors 14 and 16, rotor shoulders 14-4 and/or 16-4, housing surface 13-1 and/or bores 12-1 and 12-2. While the entire rotor and bore can be coated, as described in FIG. provides roughly all the benefits. Although the contact zone is a gap-free region and requires precision machining, the tolerance can be relaxed relative to the interaction between the rest of the rotor lobe profile. In addition, the holes 12-1 and 12 A suitable coating of -2 can accommodate the deflection of the rotors 14 and 16 during actual operation to maintain the sealing function. Referring to Figures 4 and 9, the female rotor valley can be provided with a suitable coating 44 and the male rotor valley can be provided with a suitable coating 64. Additionally, holes 12 - 1 and 12 - 2 may be provided with a suitable coating 84 .

Various plastic suitable coatings can be used including, for example, iron phosphate, magnesium phosphate, nickel polymer amalgam, nickel zinc alloy, aluminum silicon alloy with polyester, and aluminum silicon alloy with polymethyl methacrylate (PMMA) . Conventional coating methods including, for example, thermal spraying, physical vapor deposition (PVD), chemical vapor deposition (CVD), or any suitable aqueous deposition can be used to treat the screw compressor surfaces of the present invention.

As shown in Figure 10, the preferred method of the present invention for applying the described suitable coatings on the components shown is through a rough coating and finishing or smoothing process.

According to this method, a suitable coating intended to include all coatings described herein, collectively referred to as suitable coating 100, is applied rough on the surface of a component 102 such that its cross-section represents an oversize on the component. Coat 100. The suitable coating 100 is applied roughly such that the minimum amount at any one location substantially meets the minimum coating performance requirements of the component. The surface 102 described here may be any component surface that receives a suitable coating. As shown in Figure 10, a suitable coating that is typically applied has peaks and valleys which, in the prior art, cause assembly difficulties when not removed or leveled because of interference between components created by such surface irregularities. Thus, the presence of surface irregularities such as peaks allows mating or interacting parts to have an interference fit when a desired tight fit such as a screw rotor is opposed.

Alternatively, the coating may be applied to have a generally uniform thickness, although the thickness may vary from part to part due to normal process variations. In this case, the range of allowable thicknesses can be selected such that the minimum normal build thickness meets the minimum coating performance requirements for the component. Typically coated parts in this case would have excessive thickness, thus causing assembly difficulties due to interference between the parts.

According to an embodiment of the invention, prior to assembling mating or interacting components, the coating on the components is first smoothed by a finishing device such as a bar or plate or similar 104 which removes excess coating material and conforms to the performance of the machine The indicator needs to level this surface to the minimum thickness and texture required. The finishing device is preferably held steady against the part surface until the entire surface is smoothed and leveled, as shown in FIG. 11 . For shapes such as cylinders or spheres, other means of appropriate shape can be passed over the coating to remove and smooth the surface.

In another embodiment, particularly applicable to mating or interacting parts such as screw compressor rotors, as shown in Figure 12, to accomplish this smoothing process, the actual mating part is used for the newly coated part. Thus, for example a component 102 of a screw rotor of a screw compressor is rough-coated with a suitable coating. Its uncoated or mating screw rotor 104 that has been coated by this process is then moved into mating alignment with the coated screw compressor and relative to the coated screw compressor, wherein the A mated rotor was used to remove excess peaks and smooth out valleys, resulting in a flat coated mated rotor. If the mating, flat part is not already coated, it must be held at a pre-defined optimum distance in order to obtain the desired coating thickness on the other part. This mating, flattened part may be a primary fixture, that is, it may be a permanent tool used to finish any number of rotors 102 to fit with their respective rotors 104 .

Although the invention has been specifically described and illustrated in terms of a twin rotor screw compressor, it is also applicable to screw compressors employing three or more rotors. The invention is therefore limited only by the scope of the appended claims.

Claims (16)

1. method that is used for applying the screw compressor surface may further comprise the steps:

At least one parts in a plurality of Screw Compressor Parts are provided, and described a plurality of Screw Compressor Parts comprise the rotor case with at least one pair of parallel overlapping hole; The cooperation that is positioned at described hole is to the rotor that is meshing with each other, and each described rotor has the helical form lobe herein, and described lobe has radially outer top and radially inner root placed in the middle;

With the surface that is fit at least one parts in the rough-coated described a plurality of parts of coating, wherein said coating is applied on the described surface and has the variable thickness that spreads all over described surface, and is applied to equably on the described surface with roughly excessive thickness; And

With the smooth roughly homogeneous thickness that arrives of described suitable coating, described roughly homogeneous thickness process is selected so that assemble described parts easily when keeping the coating performance index before the described a plurality of parts of final assembling.

2. the method for claim 1 is characterized in that, described planarization step also comprises the step of mobile device, and described device is used for the described surface of smooth adjacency.

3. method as claimed in claim 2 is characterized in that, describedly is used for smooth device and comprises finishing bar or fixture.

4. method as claimed in claim 2 is characterized in that, describedly is used for smooth device and comprises the parts that cooperate with described at least one parts of a plurality of parts.

5. method as claimed in claim 4 is characterized in that, at least one parts comprises screw rotor in described a plurality of parts, and described component comprises intermeshing screw rotor.

6. method as claimed in claim 5, it is characterized in that, described intermeshing screw rotor has the surface of being meshing with each other, wherein said planarization step also comprises the location and rotates the described rotor that is meshing with each other, make the described surface that is meshing with each other be positioned in and leave on the described surperficial preset distance that described preset distance is chosen so that allow the described coating of the described surfacing that is meshing with each other.

7. method as claimed in claim 2 is characterized in that, described surface is the surface at the described lobe of described rotor top.

8. method as claimed in claim 2 is characterized in that, described surface is the surface of the described lobe root of described rotor.

9. method as claimed in claim 2 is characterized in that, described surface is the surface in described hole.

10. method as claimed in claim 6 is characterized in that, described surface is the surface at the described lobe of described rotor top.

11. method as claimed in claim 6 is characterized in that, described surface is the surface of the described lobe root of described rotor.

12. method as claimed in claim 6 is characterized in that, described surface is the surface in described hole.

13. a method that is used for applying the screw compressor surface may further comprise the steps:

At least one parts in a plurality of Screw Compressor Parts are provided, and described a plurality of Screw Compressor Parts comprise the rotor case with at least one pair of parallel overlapping hole; The cooperation that is positioned at described hole is to the rotor that is meshing with each other, and each described rotor has helical form lobe and teeth groove placed in the middle; Be arranged on the outlet housing at the place, discharge end of described rotor case; Each described rotor has the discharge end towards described outlet housing;

With the surface that is fit at least one parts in the rough-coated described a plurality of parts of coating, wherein said coating is applied on the described surface and has the variable thickness that spreads all over described surface, and is applied to equably on the described surface with roughly excessive thickness; And

With the smooth roughly homogeneous thickness that arrives of described suitable coating, described roughly homogeneous thickness process is selected so that assemble described parts easily when keeping the coating performance index before the described a plurality of parts of final assembling.

14. method as claimed in claim 13 is characterized in that, described surface is the surface of the described discharge of described rotor end.

15. method as claimed in claim 13 is characterized in that, described surface is the surface of described outlet housing.

16. method as claimed in claim 13 is characterized in that, is placed on the described discharge end of described rotor and the member in the middle of the described outlet housing, described member has the surface of discharging the end towards described rotor, and described surface is the surface of described member.

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