Yan-jun XIAO，Jia-yu ZHU，Li-hu HE

Hebei University of Technology，Tianjin 300130，China

Design and simulation of hydraulic system of perlite sound absorption plate forming machine

Yan-jun XIAO?，Jia-yu ZHU，Li-hu HE

Hebei University of Technology，Tianjin 300130，China

A hydraulic system of bi-directional hydraulic press is designed according to the pressing process of perlite sound absorption plate，and the simulation model of the hydraulic system is built based on AME Sim software to analyze dynamic characteristics of the working cylinders．The results of the flow-time graphs and pressure-time graphs show that the design of this system，which is feasible，can meet the production needs and provide theoretical basis for the practical design and parameter optimization of the hydraulic system．

Hydraulic forming machine，AME Sim，Simulation

1．Introduction

With the aggregate of expanded perlite，configured with inorganic adhesive as well as curing agents，perlite sound absorption plate is a kind of new building material by extrusion molding and drying processes.Combining the functions of sound absorption，fire prevention，thermal insulation，heat insulation，etc，it effectively solves the technical problems of various kinds of external walls and roofing materials，and has a broad market prospect［1］.

Generally the frame of hydraulic forming machine is three-beam-four-column type that the upper and lower beams form a rigid closed frame and the cylinder piston rod connects with the movable beam rigidly with a guide pillar［2］.Based on the existing hydraulic machine technology structure，this paper designs a perlite sound absorption plate hydraulic forming machine which uses the composited frame with acing cylinder.In order to better meet the needs of production，the hydraulic system of this forming machine is designed to be double-loop and doublepump which can actualize the extrusion of both the upper and the lower cylinder at the same time.

2．The pressing process of perlite sound absorption p late

According to the production needs of perlite sound absorption plate，this forming machine has two types of manual and automatic operation.The manual operation is mainly for the installation and adjustment of the mould，setting initial state under automatic mode and debugging the system，etc［3］.The production process under automatic mode contains nine steps as follows.

1）The famale mold rises to form a cuboid space.

2）Fill the famale mold to the same height（using artificial，semi-automatic or automatic ways according to the production automation）.

3）Clean the extra powder.

4）In order to prevent the escape of the powder when pressing，the famale mold rises a bit to be higher than the powder surface.

5）The upper mold falls slowly to contact with the powder.

6）The upper mold and the lower mold press slowly at the same time until the powder reaches the thickness of the finished product.

7）The famale mold falls and finishes the ejec-tion.

8）The upper mold rises and the finished product can be collected.

9）The lower mold falls to its original position and at this point an operating cycle is over.

The diagram of automatic pressing process is shown in Figure 1 as follow.

Figure 1.The pressing process of perlite sound absorption plate

3．The working principle of the hydraulic system

According to the forming process requirements and the test results of perlite sound absorption plate，the hydraulic forming machine designed in this paper generated 1MN pressure with both the upper mold and the lower mold pressing together.12 MPa is selected to be the loading oil pressure of the system to avoid the leakage at some joints when the system pressure is too high［4］.According to the requirements of the mechanical structure and pressing process of the forming machine，the hydraulic system diagram of pressing step is shown in Figure 2 as follow.

Figure 2.Working diagram of the hydraulic system

This system adopts double pumps of high-pressure pump 17 and low-pressure pump 20 to supply oil.When the system starts up，the electromagnetic relief valves are in a normally open state and two pumps return oil through relief valve 15 so that the two pumps start in low load.When the system works，the electromagnetic valve 15 is closed to provide 4 MPa pressure for the system.The key actions of electromagnetic valves in the entire working process are as follows.

When the famale mold works，with the directional valve11 in left station，the famale mold cylinder drives the famale mold to rise until it is in place and then maintains the accuracy of its position by mechanical limit structure.When the upper mold rapidly falls，the prefill valve 2 opens to add oil，and the directional valve is set to right station.When the upper mold reaches the pressure contact of the preset and is going to press，close the electromagnetic relief valve 14 and set the pressure to 8 MPa.The system then has 12 MPa pressure by reason of the series of the two electromagnetic relief valves 14 and 15. Meanwhile close the prefill valve of the upper mold cylinder and set the directional valve 6 to left station，and the lower mold cylinder will rise；set the directional valve 3 to left station，then the upper mold cylinder will link the lower mold cylinder to get12 MPa pressure.When the upper and lower mold cylinders reach another pressure contact and the press is finished，the upper mold cylinder unloads while the lower mold cylinder maintains pressure.At the same time，set the directional valves10 and 11 to right station and the famale mold cylinder will drive the famale mold to fall back to the normal position to expose the finished product.Collecting the product and setting the directional valve 6 to right station，the lower mold will fall by gravity and the next cycle of work will begin.

Because the system of forming machine in this paper is designed to press with the upper and lower mold cylinders working together，the finished product of perlite sound absorption plate can be guaranteed to have uniform density and high quality.The use of double-loop and double-pump system can meet the process requirements of large flow and rapid press.

4．Simulation of hydraulic system

4．1．Introduction of the simulation software AMESim

AMESim is an software introduced by Frenchcompany MAGINE to do a hydraulic system modeling［5］，simulation and dynamic analysis specially.It provides a perfect simulation environment and most flexible solution for hydraulic transmission［6］.Users can use the existing models or establish new sub model elements to construct the actual prototype needed by optimization design.Adopting the standard ISO icons and multi-port flow charts which are easy to identify，AMESim is convenient for users to build complex system and specific examples of application. Its perfect time-domain and frequency-domain analysis tools provide a guarantee for the static and dynamic characteristics of the system［7］.

4．2．The establishment of simulation model

To establish a simulation model，the principle is that the model should be as simple as possible to meet the requirements.So some non-principle factors which have little effect on dynamic characteristics can be ignored［8］when establishing the dynamic model of the hydraulic system of perlite sound absorption plate forming machine.Take for instance the pressing process of perlite sound absorption plate 600 mm× 600 mm×20 mm，6 pieces per minute，this paper establish the hydraulic simulation model as follow in Figure 3.

Figure 3.The simulation model of hydraulic system

4．3．Analysis of the simulation process and results

In the simulation analysis，set the displacement parameter of high-pressure pump to 150 mL／r and the speed parameter to 1 500 r／min while the lowpressure pump to 100 mL／r and 1 500 r／min.

In the processes when the famale mold rises and the upper mold rapidly falls，the input signal of the electromagnetic valve 14 is 1，which means conducted and no pressure；the input signal of the electromagnetic valve 15 is 0 and the parameter is set to 1. 5 MPa，which makes the whole system to produce 1. 5 MPa pressure.The flow-time graphs and pressure time graphs of the piston bottom，in the processes when the famale mold rises and the upper mold rapidly falls，are shown in Figure 4～Figure 7 as follows.

Figure 4.The flow-time graph when the famale mold rises

Figure 5.The pressure-time graph when the famale mold rises

Figure 6.The flow-time graph when the uppermold rapidly falls

Figure 7.The pressure-time graph when the upper mold rapidly falls

As can be seen from the graph，it takes 1.8 s for the famale mold to rise，and 3.7 s for the upper mold to fall.For 10 s，the required time to press each plate，the 5.5 s is too long to meet the requirement of high efficiency.

Therefore，parameter of the electromagnetic valve 15 can be adjusted to make the time observed until the most appropriate pressure is selected.By comparison of the results of different parameters，the conclusion shows that when the pressure of the electromagnetic valve 15 is set to 4 MPa，the times for the famele mold to rise and upper mold to fall，1.2 s and 2.2 s，are the most appropriate as shown in Figure 8 and Figure 9.

Figure 8.The flow-time graph when the famale mold rises（4 MPa）

Figure 9.The flow-time graph when the upper mold rapidly falls（4 MPa）

When the pressing begins，the input signal of the electromagnetic valve 14 is set to 0 and the parameter is set to 8 MPa.Because of the series of the two electromagnetic valves14 and 15，the whole system will produce 12 MPa pressing pressure.At the same time，the directional valve 3 is set to right station to make the upper and lower mold cylinders connected.The parameters of the upper and lower mold cylinders are set as shown in Figure 10.

Figure 10.The parameters of the upper and lower mold cylinders when pressing

When the upper and lower molds are pressing together，the flow-time graphs and pressure-time graphs are shown in Figure 11～Figure 14 as follows.

Figure 11.The flow-time graph of the upper mold cylinder when pressing

Figure 12.The pressure-time graph of the upper mold cylinder when pressing

Figure 13.The flow-time graph of the lower mold cylinder when pressing

Figure 14.The pressure-time graph of the lower mold cylinder when pressing

As can be seen from the graph，the pressure of the upper and lower mold cylinder rises fast and pressing process can be finished in 2 s.Because there are some other steps later such as mold unloading，the upper mold rapidly rising and the lower mold rapidly falling（no longer to repeat for the simulation process is similar with the above），finishing the pressing process in 5～6 s can meet the production needs.Besides，the comparation of Figure 8，F(xiàn)igure 9 and Figure 11 show that the pressure for the famale mold to rise and the upper mold to fall is smaller while the pressure for the upper mold and lower mold to press is larger，but both the time can meet the needs.That is，according to the pressure set before and after the pressing process，the hydraulic system of perlite sound absorption plate forming machine designed in this paper has certain feasibility.In addition，some time parameters obtained in the process of simulation can provide basis for the subsequent programming.For example，the time 1.2 s，which is for the famale mold to rise and the pressing time 2 s，can make the unloading time determined in programming.

5．Conclusion

This paper designs a hydraulic system of bi-directional hydraulic forming machine according to the pressing process and production needs of perlite sound absorption plate.AMESim software is used to establish the simulation model of this hydraulic system，and analyze dynamic characteristics of the working cylinders.By changing the relevant parameters and comparing the analytical results，it can be determined that this system has certain feasibility，and can meet the production needs.In addition，some results shown in the flow-time graphs and pressure-time graphs also provide important theoretical basis for subsequent programming.

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10.3969／j.issn.1001-3881.2014.18.014

2014-04-21

?Yan-jun XIAO，Associate professor.E-mail：xxyyzz1976＠126.com