Dimension a hydraulic circuit

for a 40T press

(Spreadsheet)

The specification states to size a hydraulic circuit to operate a press cylinder.

We have a double-acting cylinder with a length of 30cm. The diameter of the piston is 160mm and the diameter of the rod is 110mm.

The pump will be driven by an electric motor.

The maximum effort must be 40 tons, the cylinder must come out in 20 seconds.

 

1- The hydraulic diagram

 

 

Schema dimensionnement circuit presse 2

 

2-Pressure calculation

 

     2-1 Piston surface

 S = π*R² 

S : Surface in cm².

R : Piston radius in cm (16/2=8cm).

S = π *8²

S= 200,96 cm².

    2-2 Pressure required

P = F/S

P : Pressure in bar.

F : Force in daN or Kg.

S : Piston surface in cm².

P = 40000/200.96

P = 199 bars : rounded to 200 bars.

We will take an external gear pump installed under load. (Tank above the pump).

 

3- Flow Calculation

 

    3-1 Cylinder speed

The length of the cylinder 30 cm or 0.3 m must be exit in 20 seconds.

Is : 0.3/20 = 0.015 m/s

     3-2 Flow required

Q = 6*S*V

Q : Flow in l/min.

S : Piston section in cm².

V : Cylinder speed in m / s.

Q = 6*200.96*0.015

Q = 18.08 l/min rounded to 18 l/min.

 

4- Calculation Displacement of the pump

The electric motor runs at a speed of 1500 rpm.

Q = q*N/1000

Q : Flow in l/min.

q : Capacity of the pump in cm3 / revolution.

N : Rotation speed in rpm.

18 = q * 1500/1000

18 = q* 1.5

q = 18/1.5

q = 12 cm3/t.

 

5- Directional valve size

The maximum flow rate through the directional valve is the pump flow multiplied by the cylinder section ratio.

Section Ratio: The difference between the piston surface and the annular surface.

Q = 18 *2 = 36 l/min.

We will choose a monoblock directional valve type 6/3 open center can pass 40l / min. The pressure relief valve is integrated in the directional valve.

 

6- Tank size

In industry, the size of the tank is 4 to 5 times the flow of the pump.

In on-board circuits (public works- agriculture) the size of the tank is between 0.8 to 2 times the flow of the pump.

More precisely, the tank must contain the useful volume (volume of the cylinders + pipes) + the tidal volume (return volume of the cylinders + volume of the accumulators) + the volume of sky (15% of the useful volume + tidal range).

We will take a tank of 35 l.

 

7- Power of the electric motor

P = p * Q / 540

P : Power in KW.

p : Pressure in bar.

Q : Flow in l / min.

P = 200 * 18 / 540

P = 6.66 KW we will take a standard engine 7.5 KW.

 

8- Power of the exchanger

If the installation only works for a few minutes a day, it is not necessary to install an oil cooler.

Otherwise, it is advisable to take an exchanger that can dissipate 35% of the installed power.

6.66 * 35/100 = 2.33 KW.

 

9-Pipe dimension

The dimensioning of the inside diameter of the pipes is done thanks to the chart below. 

 

9-1 Fluid velocity in pressure pipes:

0 to 50 bars : 5m/s

50 to 150 bars : 5 à 6 m/s

150 to 250 bars : 6 à 8 m/s

Greater than 250 bars : 8 à 10 m/s

9-2 Fluid velocity in the return lines:

2 to 3 m/s

9-3 Fluid velocity in drainage pipes:

0.5 m/s

9-4 Fluid velocity in suction lines:

Gear pump: 0.8 à 1.5 m/s

Piston pump: 0.5 à 0.8 m/s

9-5 sizing:

The suction line 18 l / min (item 1) will be: ø 3/4

The pump outlet pressure line 18 l / min (item 2) will be: ø 3/8

Pressure lines A and B 36 l / min (items 3 & 4) will be: ø 1/2

The return line 36 l / min (item 5) will be: ø ¾

 

10-Filtration

The installation is considered not very sensitive to pollution, a filter on the return of 20μm allowing 40 l / min will be sufficient.

 
 
 

 

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