Three-blade rotor molded line of roots vacuum pump

Abstract

The utility model relates to a three-blade rotor profile of a roots vacuum pump, which comprises rotors, the two rotors are arranged in a pump shell, each rotor is of a three-blade structure, and the rotor profile of each rotor is composed of a blade peak and a blade valley which are connected in sequence. A molded line from the lowest point of any blade valley to the highest point of the adjacent blade peak is formed by sequentially connecting a tip cutting circular arc AB, a tooth crest circular arc BC, an involute CD and a tooth root circular arc DE; the radius of the topped arc AB is the same as that of a pump cavity inner hole of the pump shell; the radius of the addendum arc BC is equal to that of the dedendum arc DE, the circle center of the addendum arc BC and the circle center of the dedendum arc DE are located on the same circle, namely the circumferential line of a reference circle, and the addendum arc BC and the dedendum arc DE are in transition connection through an involute CD. Gas backflow between the rotor and the pump cavity is reduced, the zero-flow maximum compression ratio of the vacuum pump is improved, and the pumping rate and the pumping efficiency of the vacuum pump are greatly improved.

Description

Technical Field

[0001] The utility model relates to the technical field of Roots vacuum pumps, and particularly relates to a three-lobe rotor profile of a Roots vacuum pump. Background Art

[0002] The air-cooled Roots vacuum pump came out in Germany in the 1980s and has been widely used in various industries. Currently, a pair of rotors are arranged in the pump cavity of the mainstream air-cooled Roots vacuum pump. For the end face profile, see Figure 1 ., and its working principle is that two rotors rotate in opposite directions relative to each other with a gap of t1 in the pump cavity through synchronous gear transmission but cannot contact each other, and the top of the rotor makes a rotational movement with a gap of t2 with the pump cavity hole. A series of continuous working chambers are formed between the inlet and outlet of the pump. When the rotors rotate, a breathing volume change occurs in the pump cavity, causing the gas to be sucked into the working chamber of the pump. Due to the meshing of the two rotors, the gas is gradually compressed, a higher pressure is formed at the inlet end of the pump cavity. As the rotors rotate, the already compressed gas is pushed from the working chamber to the outlet of the pump. At the outlet end of the pump cavity, the gas is discharged, and a lower pressure is formed in the suction cavity. This process is continuously cycled. By continuously sucking and exhausting gas, the gas is moved from the low-pressure area to the high-pressure area to achieve the purpose of vacuum extraction.

[0003] See Figure 2 ., the end face profiles of the two rotors are both composed of several arcs with unequal radii R1~R4. The two rotors are vertically arranged at 180° in the pump cavity, and the curved surfaces of the two rotors mesh with each other. The air-cooled Roots vacuum pump composed of such rotors mainly has the following defects:

[0004] (1) Since the curvature radii of the 8 arcs forming the meshing surface of the rotor are different, the 8 curved surfaces cannot be completely smoothly transitioned, resulting in uneven meshing gaps between the two rotors, making the flow rate of the vacuum pump unstable. If the rotor gap is not well controlled, it is easy to cause rubbing between the rotors, affecting the normal use of the vacuum pump;

[0005] (2) The volumetric efficiency is only about 40%, resulting in a relatively large volume of the vacuum pump;

[0006] (3) The unreasonable design of the pump profile affects the accuracy of the finished rotor, resulting in poor meshing between the two rotors, affecting the pumping efficiency of the pump and the pumping performance such as the ultimate vacuum of the pump;

[0007] (4) The rotor gap is uneven, and the rotor is prone to faults such as friction heating and jamming;

[0008] (5) The rotor stability is poor, and it is easy to cause the pump to generate noise, vibration and other conditions.

[0009] Due to the above problems, most vacuum pumps in the industry currently use three-lobe rotors. See Figure 3, the rotor is composed of three tooth profiles evenly distributed at 120° on the circumference. Each tooth profile is composed of several curves, which are connected by an arc and an involute with no inflection point to ensure the uniformity of the meshing clearance between the two rotors. However, since the curvature radius of the tip circle of the three-lobe rotor is much smaller than that of the traditional two-lobe rotor, the sealing surface of the tip circle of the three-lobe rotor is much smaller than that of the two-lobe rotor, resulting in a much larger gas reflux of the three-lobe rotor pump during high differential pressure operation than that of the two-lobe rotor pump. Eventually, the main performance indicators such as the ultimate vacuum and zero-flow compression ratio of the three-lobe rotor air-cooled Roots vacuum pump are not significantly improved compared with those of the two-lobe rotor air-cooled Roots vacuum pump. Summary of the Invention

[0010] The purpose of the present utility model is to overcome the above deficiencies and provide a three-lobe rotor profile for a Roots vacuum pump, further improving the performance indicators of the three-lobe air-cooled Roots vacuum pump and reducing the gas reflux at the top of the rotor.

[0011] The purpose of the present utility model is achieved as follows:

[0012] A three-lobe rotor profile for a Roots vacuum pump, which includes a rotor. Two rotors are arranged in a pump housing. The rotor is of a three-lobe structure, and the rotor profile of each rotor is composed of a lobe peak and a lobe valley connected in sequence. The profile from the lowest point of any lobe valley to the highest point of the adjacent lobe peak is composed of a crowned circle arc AB, a tip circle arc BC, an involute CD, and a root circle arc DE connected in sequence;

[0013] The crowned circle arc AB is the same as the inner hole radius of the pump cavity of the pump housing; the tip circle arc BC and the root circle arc DE have the same radius, and the centers of the tip circle arc BC and the root circle arc DE are located on the circumference of the same circle, i.e., the pitch circle. The tip circle arc BC and the root circle arc DE are connected by an involute CD;

[0014] The center distance L between the two rotors, the radius R of the pitch circle of the rotor, and the sum of the pitch circle radii of the rotors are equal to the center distance between the two rotors, i.e., the pitch circle radius R of the rotor;

[0015] The pitch circle radius R of the rotor = L / 2 mm;

[0016] The base circle radius R0 of the rotor = R×COSα = (L / 2)×COSα;

[0017] The tip circle radius Rn of the rotor = π×L×COSα / (4×Z) = (π / 6)×R0;

[0018] COSα = 2×Z×(D - L) / (PI×A);

[0019] The rotor diameter D = L + 2Rn = L + π×A×COSα / (2×Z);

[0020] The radius of the chamfered circle $R_D = D / 2$ can be obtained.

[0021] Taking the centers of the base circle and the pitch circle as the origin of the coordinate system, the coordinate equation of the chamfered circle arc $AB$ can be obtained as follows:

[0022] $X = R_D\times\sin\alpha$, ($\alpha = 0\rightarrow5^{\circ}$),

[0023] $Y = R_D\times\cos\alpha$, ($\alpha = 0\rightarrow5^{\circ}$).

[0024] Furthermore, the coordinate equation of the addendum circle arc $BC$ is:

[0025] $X = R_n\times\sin\varepsilon$, ($\varepsilon = 0\rightarrow5^{\circ}$),

[0026] $Y = R_n\times\cos\varepsilon$, ($\varepsilon = 0\rightarrow5^{\circ}$).

[0027] Furthermore, the coordinate equation of the involute $CD$ is:

[0028] $X = X_1 + X_2 = R_0\times\cos(30 + A+\theta)+R_0\times(\theta+\tan\beta)\times\sin(30 + A+\theta)$, ($\theta = 0\rightarrow60^{\circ}$),

[0029] $Y = Y_1 + Y_2 = R_0\times\sin(30 + A+\theta)-R_0\times(\theta+\tan\beta)\times\cos(30 + A+\theta)$, ($\theta = 0\rightarrow60^{\circ}$);

[0030] Where: $\tan\beta=\tan A-\frac{\pi}{6}$.

[0031] Furthermore, the coordinate equation of the dedendum circle arc $CD$ is:

[0032] $X = R\times\cos A+R_n\times\sin\varphi$, ($\varphi = 0\rightarrow60^{\circ}$),

[0033] $Y = R\times\sin A+R_n\times\cos\varphi$, ($\varphi = 0\rightarrow60^{\circ}$);

[0034] The pressure angle $\alpha$ is a fixed value. As $\theta$ changes, the $X$ and $Y$ coordinates of the involute also change, and $\tan\beta=\tan\alpha-\frac{\pi}{6}$.

[0035] Furthermore, the coordinate points of the involute $DE$ are:

[0036] $X = X_1 + X_2 = R_0\times\cos(30+\alpha+\theta)+R_0\times(\theta+\tan\beta)\times\sin(30+\alpha+\theta)$,

[0037] $Y = Y_1 + Y_2 = R_0\times\sin(30+\alpha+\theta)-R_0\times(\theta+\tan\beta)\times\cos(30+\alpha+\theta)$.

[0038] Compared with the prior art, the beneficial effects of the present utility model are as follows:

[0039] The present utility model provides a three-lobe rotor profile for a Roots vacuum pump. The profile is convenient to process, the clearance between the rotor and the pump chamber and the clearance between the two rotors are uniform. By providing a crown relief arc section on the end face profile of the three-lobe rotor, the gas backflow between the rotor and the pump chamber is reduced, the maximum compression ratio at zero flow rate of the vacuum pump is increased, and the pumping speed and pumping efficiency of the vacuum pump are greatly improved. The Roots vacuum pump applying the three-lobe rotor profile of the present utility model has good sealing effect, high vacuum degree, better pumping efficiency, low energy consumption, better reliability and wider application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 FIG. 9 is an end view of a two-lobe rotor of an existing Roots vacuum pump.

[0041] Figure 2 FIG. 13 is an end face profile diagram of a two-lobe rotor of an existing Roots vacuum pump.

[0042] Figure 3 FIG. 17 is a schematic structural diagram of a three-lobe rotor of an existing Roots vacuum pump.

[0043] Figure 4 FIG. 21 is a schematic structural diagram of the present utility model.

[0044] Figure 5 FIG. 25 is a top view of the present utility model.

[0045] Figure 6 FIG. 29 is an end face profile diagram of the three-lobe rotor of the present utility model.

[0046] Figure 7 FIG. 33 is a schematic diagram for comparing the improvement of the rotor top circle of the present utility model.

[0047] Figure 8 FIG. 37 is a design diagram of the line from the lobe peak to the adjacent lobe valley of the three-lobe rotor of the present utility model.

[0048] Wherein:

[0049] Pump housing 1, rotor 2, lobe peak 21, lobe valley 22. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] To better understand the technical solution of the present utility model, the following will be described in detail with reference to the relevant drawings. It should be understood that the following specific embodiments are not intended to limit the specific implementation modes of the technical solution of the present utility model, and they are only the implementation modes that the technical solution of the present utility model can adopt. It should be noted first that the description of the positional relationship of each component herein, such as component A is located above component B, is based on the relative positions of the components shown in the drawings, and is not intended to limit the actual positional relationship of each component.

[0051] Embodiment 1:

[0052] Refer to Figures 4 - 8 , Figure 4 a structural schematic diagram of the present utility model is drawn. As shown in the figure, a three-lobe rotor profile of a Roots vacuum pump includes a pump casing 1 and two rotors 2 arranged inside the pump casing 1. Both rotors 2 are of a three-lobe structure, and the rotor profile of each rotor 2 is composed of a lobe peak 21 and a lobe valley 22 connected in sequence. The profile line from the lowest point of any one of the lobe valleys to the highest point of the adjacent lobe peak is composed of a crowned circle arc AB, a tip circle arc BC, an involute CD, and a root circle arc DE connected in sequence, that is, a crowned circle, a tip circle, an involute waist circle, and a root circle connected in sequence form the three-lobe rotor profile;

[0053] The crowned circle arc AB has the same radius as the inner hole radius of the pump cavity of the pump casing 1; the tip circle arc BC and the root circle arc DE have equal radii, and the centers of the tip circle arc BC and the root circle arc DE are located on the circumference of the same circle, namely the pitch circle. The tip circle arc BC and the root circle arc DE are connected by an involute CD for transition.

[0054] The rotor end face profile is determined by establishing a mathematical equation to obtain the profile parameters of the rotor, and finally the rotor end face profile data is obtained.

[0055] 1. The number of teeth of the three-lobe rotor Z = 3;

[0056] The pressure angle α of the rotor = 30°;

[0057] (If the pressure angle is large, the volumetric efficiency is low; if the pressure angle is small, the volumetric efficiency is high, but the rotor strength decreases. Generally, taking 30° is an ideal empirical value;

[0058] Usually when designing a Roots vacuum pump, first determine the center distance L (mm) between the two rotors of the Roots vacuum pump according to the suction volume of the vacuum pump, and the radius R (mm) of the pitch circle (or called the pitch circle) of the rotor. The sum of the pitch circle radii of the rotors is equal to the center distance between the two rotors, that is, the pitch circle radius R of the rotor.

[0059] 2. Rotor pitch circle radius R:

[0060] R = L / 2 mm;

[0061] 3. Rotor base circle radius R0:

[0062] R0 = R×COSα = (L / 2)×COSα;

[0063] 4. Rotor tip circle radius Rn:

[0064] Rn = π×L×COSα / (4×Z) = (π / 6)×R0;

[0065] COSα = 2×Z×(D - L) / (PI×A);

[0066] 5. Finally, the rotor diameter D is obtained:

[0067] D = L + 2Rn = L + π×A×COSα / (2×Z);

[0068] 6. The radius of the tip - relieved circle RD:

[0069] RD = D / 2;

[0070] Taking the centers of the base circle and the pitch circle as the coordinate origin, a coordinate system is constructed;

[0071] 1. The coordinate equation of the arc AB of the tip - relieved circle is:

[0072] X = RD×SINα, (α = 0 → 5°),

[0073] Y = RD×COSα, (α = 0 → 5°);

[0074] 2. The coordinate equation of the arc BC of the tooth tip is:

[0075] X = Rn×SINε, (ε = 0 → 5°),

[0076] Y = Rn×COSε, (ε = 0 → 5°);

[0077] 3. The coordinate equation of the involute CD is:

[0078] X = X1 + X2 = R0×COS(30 + A + θ)+R0×(θ + tgβ)×SIN(30 + A + θ), (θ = 0 → 60°),

[0079] Y = Y1 + Y2 = R0×SIN(30 + A + θ)-R0×(θ + tgβ)×COS(30 + A + θ), (θ = 0 → 60°);

[0080] where: tgβ = tgA - π / 6;

[0081] 4. The coordinate equation of the arc CD of the tooth root is:

[0082] X = R×COSA + Rn×SINφ, (φ = 0 → 60°),

[0083] Y = R×SINA + Rn×COSφ, (φ = 0 → 60°);

[0084] The pressure angle α is a constant value. As θ changes, the X and Y coordinates of the involute also change. tgβ = tgα - π / 6;

[0085] 5. The coordinate points of the involute DE are:

[0086] X = X1 + X2 = R0×COS(30 + α + θ) + R0×(θ + tgβ)×SIN(30 + α + θ),

[0087] Y = Y1 + Y2 = R0×SIN(30 + α + θ) - R0×(θ + tgβ)×COS(30 + α + θ);

[0088] Volumetric utilization coefficient of the three - lobe vacuum pump:

[0089] λ0 = π / 3×[COSα×(1 + π×(COSα) / 18)] / [(1 + π×(COSα) / 6)2];

[0090] When the pressure angle α is 30°, substituting into the above formula, the rotor volumetric efficiency is λ0 = 0.4942;

[0091] Pumping speed of the vacuum pump:

[0092] S = (πd2 / 12)×L×n×λ0×λh×10 - 7 (L / S);

[0093] Where:

[0094] λh - The suction coefficient is 0.85,

[0095] d - Rotor diameter, unit mm,

[0096] L - Rotor length, unit mm,

[0097] n - Pump speed, unit rpm;

[0098] Considering factors such as thermal expansion, bearing clearance, and machining accuracy, the clearance of the air - cooled Roots vacuum pump is usually determined according to the following formula;

[0099] Clearance between the top circles of the two rotors and the inner hole of the pump chamber:

[0100] δ1 = ((0.075 / 100) + (0.12×Δt / 1000))×D, unit mm;

[0101] Meshing clearance between the two rotors:

[0102] δ2 = ((0.15 / 100) + (0.12×Δt / 1000))×D, unit mm;

[0103] Where: D - Diameter of the rotor top circle (or inner hole of the pump body), unit mm;

[0104] Δt - Rotor temperature rise, unit °C.

[0105] Working principle:

[0106] By comparing two types of rotor end profiles and conducting technical comparison and analysis, it is found that the difference in the cross-sectional area of the sealing surface between the rotor tip circle and the inner hole of the pump chamber is relatively obvious. The cross-sectional area of the tip seal surface of the two-lobe rotor is larger than that of the three-lobe rotor. Figures 1 - 3 Therefore, in the present utility model, the sealing part between the tip circle and the inner hole of the pump chamber is subjected to a tip-cutting treatment, and a tip-cut circle is formed at the top of the rotor. The tip-cut circle is concentric with the center of the rotor, and the theoretical radius of the tip-cut circle is the same as the radius of the inner hole of the pump chamber. When machining the rotor, the clearance value t2 between the rotor and the inner hole of the pump chamber can be removed. Thus, the sealing performance between the tip circle of the three-lobe rotor and the inner hole of the pump chamber can be improved, the gas reflux during the operation of the air-cooled Roots vacuum pump can be more effectively blocked, the compression ratio and ultimate vacuum of the vacuum pump can be increased, and the performance parameters such as the pumping speed of the vacuum pump at high pressure differences are significantly improved.

[0107] The pumping efficiency of the air-cooled Roots vacuum pump: η = Km / (Km + (Sth / Sv) + (Sv / Sth)

[0108] The pumping speed of the air-cooled Roots vacuum pump: S = Sth × η = Sth × Km / (Km + (Sth / Sv) + (Sv / Sth) 1.5 )

[0109] In the formula: η—the pumping efficiency of the air-cooled Roots vacuum pump 1.5 )

[0110] S—the actual pumping speed of the air-cooled Roots vacuum pump, unit L / s

[0111] Sth—the designed pumping speed of the air-cooled Roots vacuum pump, unit L / s

[0112] Km—the maximum compression ratio at zero flow rate of the air-cooled Roots vacuum pump

[0113] Sv—the pumping speed of the fore-vacuum pump, unit L / s

[0114] From the formula, it can be obtained that the pumping efficiency and actual pumping speed of the air-cooled Roots vacuum pump have a certain proportional relationship with its maximum compression ratio at zero flow rate and the size of the fore-vacuum pump. The larger the maximum compression ratio at zero flow rate and the larger the pumping speed of the fore-pump, the higher the pumping speed and pumping efficiency of the air-cooled Roots vacuum pump should be correspondingly.

[0115] By improving the end profile of the three-lobe rotor, the gas reflux between the rotor and the pump chamber can be reduced, the maximum compression ratio at zero flow rate of the vacuum pump can be increased, and thus the pumping speed and pumping efficiency of the vacuum pump can be greatly improved.

[0116]

[0117] ​The above are only specific application examples of the present utility model, which do not constitute any limitation to the protection scope of the present utility model. Any technical solutions formed by equivalent transformation or equivalent substitution fall within the scope of the rights protection of the present utility model.

Claims

1. The profile of a three-lobe rotor of a Roots vacuum pump, characterized in that: It includes a rotor (2). Two rotors are arranged inside a pump housing (1). The rotor (2) has a three - lobe structure, and the profile curve of each rotor (2) is composed of a lobe peak (21) and a lobe valley (22) connected in sequence. The profile curve from the lowest point of any lobe valley to the highest point of the adjacent lobe peak is composed of a crowned - circle arc AB, a tip - circle arc BC, an involute CD, and a root - circle arc DE connected in sequence; The crowned - circle arc AB has the same radius as the inner - hole radius of the pump cavity of the pump housing (1); the tip - circle arc BC and the root - circle arc DE have equal radii, and the centers of the tip - circle arc BC and the root - circle arc DE are located on the circumference of the same circle, i.e., the pitch - circle. The tip - circle arc BC and the root - circle arc DE are connected by an involute CD for transition; The center distance L between the two rotors, the radius R of the pitch - circle of the rotor, and the sum of the pitch - circle radii of the rotors is equal to the center distance between the two rotors, i.e., the pitch - circle radius R of the rotor; The pitch - circle radius R of the rotor = L / 2 mm; The base - circle radius R0 of the rotor = R×COSα=(L / 2)×COSα; The tip - circle radius Rn of the rotor = π×L×COSα / (4×Z)=(π / 6)×R0; COSα = 2×Z×(D - L) / (PI×A); The rotor diameter D = L + 2Rn = L+π×A×COSα / (2×Z); It can be obtained that the crowned - circle radius RD = D / 2; Taking the centers of the base - circle and the pitch - circle as the coordinate origin to construct a coordinate system, the coordinate equation of the crowned - circle arc AB can be obtained as: X = RD×SINα, (α = 0→5°), Y = RD×COSα, (α = 0→5°).

2. The three-lobe rotor profile of a Roots vacuum pump according to claim 1, characterized in that: The coordinate equation of the tip - circle arc BC is: X = Rn×SINε, (ε = 0→5°), Y = Rn×COSε, (ε = 0→5°).

3. The three-lobe rotor profile of a Roots vacuum pump according to claim 1, characterized in that: The coordinate equation of the involute CD is: X = X1+X2 = R0×COS(30 + A+θ)+R0×(θ + tgβ)×SIN(30 + A+θ), (θ = 0→60°), Y = Y1+Y2 = R0×SIN(30 + A+θ)-R0×(θ + tgβ)×COS(30 + A+θ), (θ = 0→60°); In the formula: tgβ = tgA - π / 6.

4. The profile of the three-lobe rotor of a Roots vacuum pump according to claim 1, wherein: The coordinate equation of the root - circle arc CD is: X = R×COSA+Rn×SINφ, (φ = 0→60°), Y = R×SINA+Rn×COSφ, (φ = 0→60°); The pressure angle α is a fixed value. As θ changes, the X and Y coordinates of the involute also change, and tgβ = tgα - π / 6.

5. The three-lobe rotor profile of a Roots vacuum pump according to claim 1, wherein: The coordinate points of the involute DE are: X = X1+X2 = R0×COS(30 + α+θ)+R0×(θ + tgβ)×SIN(30 + α+θ), Y = Y1+Y2 = R0×SIN(30 + α+θ)-R0×(θ + tgβ)×COS(30 + α+θ).

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