Разработка ионно-плазменной технологической установки для нанесения функционального покрытия на крышки масляных фильтров, страница 36

,                                               (5.7)

l/s.                                        

From pump speed it was chosen 3 turbo-molecular pumps MAG 2000 СT [23].

For maintenance of work of three TMP it is used 3 forepumps DRYVAC100S with pump speed equals S=100 m³/h=27.8 l/s [23].

Table 4.1. Spilling characteristics of the turbo-molecular pump MAG 2000 СT

Table 4.2. Spilling characteristics of the vacuum pump DRYVAC100S

4.2.1 Definition of design characteristics of the first section of vacuum system

The scheme of the first section of vacuum system is presented in figure (4.1).

In system it is used three turbo-molecular pumps. We shall consider the first section from the vacuum chamber up to one of pumps, having accepted an assumption, that on each pump is necessary one third from total leakage

Figure 4.1. The scheme of the first section of vacuum system

The general conductivity of the section of vacuum system from high-vacuum pump with productivity l/s up to pumped out object is described by dependence:

                                                    (4.8)

 l/s.

We define preliminary ratio between conductivity of separate sections:  ; conductivity of valve DN 250  l/s [23], conductivity of the pump is equal to infinity. For consistently connected elements the general conductivity is determined by following expression:

,                                    (4.9)

then

,

 l/s.

Constructively we appoint lengths of pipelines L₂=58 sm, L₄= 21 sm. We define a gas flow mode on the pipeline on limiting pressure of the vacuum chamber  and diameter of an entrance branch pipe of the pump d_вх=25 sm. Free length of gas  molecules (expressed in sm.) depending on pressure:

,                                               (4.10)

 sm.

We define criterion Knudsen - the attitude of free length of gas  molecules  to the effective size:

,                                                        (4.11)

.

As the received ratio is more, than 1,5, a gas flow mode in the pipeline - molecular.

For a molecular flow mode diameter of the pipeline is determined by following dependence:

,                                                  (4.12)

 sm.

Constructively is accepted d2=d4=dвх then conductivity at the input in the pump is equal to infinity.

We define conductivity of pipelines with amendment to diameter:

,                                                    (4.13)

 l/s,

 l/s.

Let's define input conductivity in object (the characteristic sizes а=1,83 m,b=0,83 the m,l=0,86) by dependence:

,                                     (4.14)

where φ=1,22 at а/b=2,2.

 l/s.

The general conductivity of system from pumped out object up to the vacuum pump is determined from expression:

,                                    (4.15)

 l/s.

The use factor of the vacuum pump is equal:

,                                              (4.16)

 - hence, the system is calculated correctly.