OPTIMIZATION OF THE WATER HYDRAULIC INTENSIFIER PUMP USED IN THE WATER JET CUTTING SYSTEM OF PAPER MACHINE

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1 89 OPTIMIZATION OF THE WATER HYDRAULIC INTENSIFIER PUMP USED IN THE WATER JET CUTTING SYSTEM OF PAPER MACHINE HYVÖNEN M., KOSKINEN K.T., and VILENIUS M.J. Tampere University of Technology Institute of Hydraulics and Automation P.O. Box Tampere Finland There are only few water hydraulic high pressure pumps in the market and most of them are very expensive to buy and maintain. A Finnish company has developed a new type of water hydraulic intensifier pump in which the control valve is integrated in the plunger. This means faster response in the change situation of the plunger and more compact size of the pump. The prize of the pump is also reasonable. This paper deals with the optimization of the intensifier pump using computer simulation and experimental measurements. The aim of the work is to improve the characteristics and reliability of the pressure intensifier pump. The effect of integrated control valve characteristics to intensifier pump properties is discussed. The optimum performance is studied via variation of significant parameters of the intensifier pump. The other aim of the work is to develop a reliable water jet cutting system for paper machine industry. The intensifier pump is to be used in the water flow source in the cutting system. One other aim of the work is to increase the basic knowledge of water hydraulics and to increase the life time of the water hydraulic components used in water hydraulic systems which has high demands for reliability. Keywords: water hydraulic, jet cutting 1 INTRODUCTION Even if degree of Finnish paper machine technology is very high modern paper cutting methods, such as water hydraulic high pressure paper cutting, are not very common used. One reason for this is high demands of reliability of used components. On the other hand there can be seen many reasons for use of water hydraulics in the paper machine environment. Most of the piping are all ready made of stainless steels and there are large amount of different kind of waters available in the paper machine environment.

2 9 2 EGDE TRIM WATER CUTTER FOR PAPER INDUSTRY Water jet cutting has been used in industry since 7 s when the first applications came to market the USA. Water jet cutting can be used from paper to metal, for example cutting the turbine vane made from titan. Water jet cutting can be divided roughly to normal and abrasive cutting. Normal cutting means cutting with pure tap water. In abrasive cutting small hard particles are added to water. In water jet cutting the high pressure (1 4MPa) water is leaded through orifice (diameter.1.4 mm, see Figure 1) which develops narrow water jet which speed is about 4 1 m/s. When the water jet is pointed to cut material it develops surface pressure which is bigger than crushing strength of the cut material. Surface of the material is crushed and water penetrates to hair crack and transfers disengaged parts away. Properties of cutting can be affected by changing the water pressure, diameter of the orifice, cutting distance and speed of cutting. The shape of the cutting jet stream is also very important. /1,2,3/ Figure 1. Basic principle of water jet cutting. /2/

3 91 Figure 2. Cutting head of the edge trimmer Edge trimmer means the machine which is used to cut the edge of the paper before the paper is rolled to the barrel. Traditionally the paper edge is cut with blade type cutters. Blade cutters are not very reliable and this problem has opened the market for new type of edge trimmer which uses modern water hydraulics. The most critical component of the system is the high pressure pump which has to include following demands: Pressure at least 7 bar, Maintenance period (change of seals etc.) over 4 hours, Fast and easy maintenance, high reliability and life time. The prototype of the edge trimmer has been made and it has been tested several times in the paper machine environment and laboratory. In the Figure 2 can be seen cutting head of the edge trimmer. The cutting head consist special type of cutting table which can be automatically moved and sapphire cutting nozzle. This type of machine features some excellent properties compared to traditional blade cutters. Cut paper edge reduces problems (e.g. glued edges, damages of soft roll edge, wavy edges and reeling) in the paper machine, calendar and slitter-winder and enables speed increase. Cutting works well regardless of cross directional movement of the web and even narrow and moist paper edge can be cut. Adjustment of cutting width is done using linear unit and pulse gauge and small infra heaters can be used for dehydrating the moist edge of the web. The nozzle is made of sapphire nozzles and it can last several months. Cutter can be controlled either using the field control case, the control and display panel or the automatic operating system of the paper machine. Cutting does not produce any dust.

4 92 3 WATER HYDRAULIC PRESSURE INTENSIFIER PUMP Most of the high-pressure pumps in the market are three piston plunger type pumps. There are also few radial piston pumps and pressure intensifier type pumps. Some of the pumps in the market which can be used in edge trimmer are presented shortly below. Three piston plunger pumps are big, heavy and expensive to buy and maintain. But they are also more reliable than axial- and radial piston pumps. Lifetime of the pump is mainly determined by crankshaft mechanism and the maintenance interval by seals and valves. Lifetime of the pump is between 4 8 hours and seals and valves have to be changed after 1 hours (values based on the tests with one high quality three piston pump). There are about dozen of plunger pumps in the market which can be used in the edge trimmer. There are many critical sliding surfaces in the water hydraulic axial and radial piston pumps and because of that there are only a few reliable water hydraulic axial and radial piston pump in the market which can be used in edge trimmer. In the market there are also a couple of pressure intensifier pumps which can be used in edge trimmer. Typical pressure intensifier pump is linear plunger type in which the reciprocating plunger generates the pressure in chambers placed to both ends. The plunger is moved hydraulically and by choosing hydraulic primary side area ratio bigger than area ratio of the plunger head in the secondary side the generated pressure is bigger. There are also at least one intensifier pumps based to rotational movement. The prices of the intensifier pumps are mostly high. In the Figure 3 is presented Dynaset HPW 8 pressure intensifier pump which has been chosen to be water volume flow source in the edge trimmer. Hydraulically controlled 3/2-valve is placed inside to the plunger. The water chambers and oil chambers are hermetically divided from each other. Maximum water pressure of the pump is 8 bar. Figure 3. Dynaset HPW 8 in the edge trimmer.

5 Operation principle of the pump A diagrammatic section of the intensifier pump is presented in figure 4. The main parts of the pump are the plunger (8), the control valve (9), hydraulic chamber (6), high pressure chambers (1, 2 and 3), suction chamber (4) and two suction check valves (11) and two pressure check valves (1). The hydraulically controlled control valve is placed in the plunger. This allows the fast response of the change of the direction of the plunger. This also means that the pressure drop in the changing situation is not very big which is very important in the paper cutting system. Supply oil volume flow is leaded to the chamber (5). Water volume flow is directed to the inlet port of the pump (4). Pressure at the oil supply line is set to wanted level, for example 2 bar. The plunger starts to move to left and the piston generates (theoretical) 8 bar pressure at the left water chamber (2) because the area ratio is 4. When the piston is at the left hand side the control line (13) is connected to supply oil volume and the pressure at the chamber (7) rises and the valve starts to move to left. This closes the tank edge of the valve and opens the pressure edge of the valve. The pressure at the chamber (6) rises to same level as the supply pressure and because the area ratio is 1/2 the piston starts to move to the right developing 8 bar pressure to chamber (3). When the piston reaches the right hand side the control line (13) is opened to the tank side and the pressure falls in the control chamber (7) of the valve and the valve moves to right and the working cycle starts again from the beginning. Orifice (12) is needed to compensate the leakage flow though clearance of plunger. Figure 4. A diagrammatic section of the intensifier pump.

6 94 Figure 5. Working principle of the Dynaset HPW pressure converter. In the Figure 6 is presented the measured pressure at the injection nozzle. As it can be seen from the Figure pressure decreases in the worst case from 8 bar to the 3 bar. This happens when the plunger changes the direction in the left end. This can t be allowed in the edge trimmer because the cutting energy is not high enough to cut all fibers of the moving paper line. The reason for the pressure drop at the nozzle was studied by computer simulation. Simulation model of the intensifier pump is discussed more in the in the paper Simulation of special type of pressure intensifier pump used in water jet cutting systems, Bath Workshop on Power Transmission and Motion Control (PTMC 99), September, 1999, Bath, United Kingdom. Water pressure, injection nozzle.2mm Pressure [bar] Figure 6. Measured pressure at the injection nozzle.

7 Experimental verification of the model The simulation has been verified by experimental measurements. Position of the plunger is measured using LVDT-transducer. To connect the tap of the LVDT-transducer to the plunger the water head of the pump was modified. A hole was drilled to the head and a sealing head was designed to between high pressure water chamber and LVDT-transducer. The diameter of the tap was minimized to minimize friction forces of the tap. Pressures were measures from chambers 1 (or 2 or 3), 4, 5 and 6 pressure transducers (see Figure 4). Pressure transducers were positioned as near as possible the measured chamber to minimize damping. Verification of the model was made with several different operation points. In this work only one verification point is presented as an example. Viscosity of the oil in simulation was 3 cst (in measurements used oil was H32, temperature 4 C). Simulated and measured position of the plunger, nozzle.2 mm Position [mm] Simulated Measured Simulated and measured pressures, nozzle.2 mm 9 8 Left water chamber (measured) Left water chamber (simulated) 7 Pressure [bar] Supply pressure (simulated) 2 Supply pressure (measured) Oil control chamber (simulated) 1 Oil control chamber (measured) Figure 7. Simulated and measured position of the plunger of the pump (left) and simulated and measured pressures of the pump (right).

8 96 In the Figure 7 is presented the measured and simulated position of the plunger and the measured and simulated pressures in the verification point. It can be seen from Figure 7 that simulated curves corresponds very well to measured curves. 3.3 Reason for vibrations and variation of operational parameters In the Figure 8 is presented simulated position of the plunger and valve, simulated pressures of oil and water volumes and simulated oil volume flow through valve orifice and control lines. When the plunger reaches the left end pressure at the control valve oil volume (7) rises because length of the plunger clearance is decreasing. When the pressure reaches the value in which the control valve starts to change the direction pressure at valve oil volume deceases because of so called kick-down effect of the valve (area ratio of the valve changes if the valve is in minimum or maximum position).valve moves to left and comes to overlap area and the tank edge of the valve closes. Because of the oil volume flow through pressure edge clearance of the valve and valve orifice pressure at oil volume (6) starts to rise. Pressure at left water volume (2) is still high and at right volume (3) low so the force resultant is to right. This means that even small increase in the pressure at the oil volume (6) is enough to move the plunger to the other direction (to right). Length of the plunger clearance is now rapidly increasing and the volume flow through clearance decreasing. The pressure at control valve volume (7) is still bigger than oil pressure at volume (6) so the direction of the oil volume flow through the valve orifice is still out of the control valve volume. So the valve has to move back to right. When the valve moves back to area where tank edge is opened the pressure at oil volume (6) decreases and plunger moves again to the left. The vibration cycle starts again from beginning. This happens as many times as the pressure at the oil volume (6) rises over the pressure at the control valve volume (7) and the direction of the oil volume flow through valve orifice is to valve volume. Now the valve has no other direction to move than left. The pump does not vibrate when the water volume flow is over 2 l/min (up to maximum 3 l/min). The reason for this is on the other hand bigger kinetic energy of the plunger (changing of the direction of the plunger is slower) and on the other faster degrease of the pressure in the water chamber (smaller force which tends to move the plunger back). Operation of the pump has been studied by variation of the operational parameters (see Figure 9) of the pump, such as, clearances of the plunger and sleeve, clearance of the control valve, size of the control valve orifice, length of the overlap of the control valve, effect of tank peak pressure, viscosity of the hydraulic oil. Optimization of the pump is discussed more on paper Water Jet Cutting System for Paper Machine, Proceedings of The Sixth Scandinavian International Conference on Fluid Power, May 26-28, 1999, Tampere, Finland.

9 97 Position of the control valve,5,45,4,35 Position [m],3,25,2 Overlap,15,1,5 2,5 2,6 2,7 2,8 2,9 3 3,1 3,2 3,3 3,4 3,5 Oil volume fllow through valve orifice and control lines Oil volume flow through control lines Q [l/min] Oil volume flow through valve orifice -1 2,5 2,6 2,7 2,8 2,9 3 3,1 3,2 3,3 3,4 3,5 Position of the plunger,46,45,44,43,42,41 Position [m],4,39,38,37,36,35,34,33,32,31,3 2,5 2,6 2,7 2,8 2,9 3 3,1 3,2 3,3 3,4 3,5 Simulated pressures Pressure [bar] ,5 2,6 2,7 2,8 2,9 3 3,1 3,2 3,3 3,4 3,5 Figure 8. Simulated position of control valve and plunger,

10 98 Overlap of the valve Clearance of the plunger and the sleeve Control and opening areas of the valve Clearances of the valve Size of the orifice of the valve Figure 9. Some operational parameters of the pump 3.4 Operation of the pump with optimized parameters In the Figures 1, 11 and 12 are presented the simulation results for the intensifier pump when the clearance between plunger and sleeve, control valve orifice and clearance between control valve and plunger are in optimum area. Mechanical restrictions are also taken account and other parameters are the same as before. It can be seen from the Figures that the plunger does not vibrate at the left end change situation and the pressure drop is also smaller than before, about 5 bar. The simulations made with greater water flow volumes shows that the pump works properly, too. It can also be seen that the valve does not tend to vibrate any more in the overlap area (see Figure 12). Viscosity of the oil in the simulations was 3 cst but the pump seems to work properly up to 1 cst.

11 99 Simulated position of the plunger with optimum parameters,5,45,4,35 Position [m],3,25,2,15,1,5 2,5 3 3,5 4 4,5 5 5,5 6 Figure 1. Simulated position of the plunger (optimal parameters). Simulated pressures with optimum parameters Pressure [bar] ,5 3 3,5 4 4,5 5 5,5 6 Figure 11. Simulated position of the control valve (optimal parameters). Position of the control valve with optimum parameters,5,45,4,35 Postion [m],3,25,2,15,1,5 2,5 3 3,5 4 4,5 5 5,5 6 Figure 12. Simulated pressures (optimal parameters).

12 1 4 CONCLUSIONS Operation of water hydraulic edge trimmer for paper industry has been discussed and used water hydraulic high-pressure intensifier pump has been introduced. One verification result for simulation model of the intensifier pump has been shortly introduced and discussed. Reasons for vibration of the plunger which causes pressure decrease in the cutting nozzle has been shortly discussed and simulation results of optimized pump has been presented. 5 REFERENCES /1/ Momber Andreas, Handbuch Druckwasserstrahl Technik Beton-Verlag GmbH, Düsseldorf 1993 /2/ Sakkara Isto, Vesisuihkuleikkauksen soveltaminen, dipl. Työ, TTKK. /3/ Vilppo Jukka, Vesisuihkuleikkaus: Menetelmän periaate ja käyttö, VTT 1986, tiedote ACKNOWLEDGEMENTS The support of Dynaset Oy and ES-Systems Oy is greatly acknowledged.