JPS6127601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic press device that adjusts pump pressure so that it always increases by a differential pressure in response to fluctuations in load pressure.

[Conventional technology]

Wet molding of powders such as ferrite and ceramics is performed in a molding press while driving a pressing piston at a constant speed. For example, in the case of ferrite powder, the molding is performed through a filtration process, a compaction process, and a pressure holding process while being pressed at a constant speed (0.1 to 0.5 mm per second) by a piston. In the filtration process, water in the ferrite powder is removed, so the load pressure hardly increases even if the piston is driven at a constant speed. Once the water removal is almost complete, the powder begins its compaction process.
Here, the density of the powder increases in accordance with the pressure applied by the piston, and the load pressure also increases. When the compaction of the powder is completed, the load pressure is held at the maximum value for a short time and the molding cycle is completed. Wet compaction of ferrite powder usually takes 1 to 3 minutes, of which about two-thirds is for the filtration process, about one-third is for the compaction process, and several seconds is for the pressure-holding process.

Conventionally, a hydraulic circuit as shown in FIG. 4 has been used for hydraulic forming that draws such a load pressure increase curve. The hydraulic pump 1 is driven by a motor 2, and the discharge flow rate is constant. The hydraulic oil is supplied to an actuator 4 having a hydraulic cylinder 5 and a piston 6 via a flow control valve 3 . In the case of constant speed molding, it is necessary to keep the hydraulic oil passing through the flow control valve 3 constant, so the flow control valve 3 is controlled so that the throttle becomes larger as the pressure difference between both ends becomes larger. The piston 6 is driven at a constant speed by the hydraulic oil whose flow rate is adjusted to a constant level by the flow rate control valve 3, and molding is performed. The pressure of the hydraulic oil coming out of the hydraulic pump is maintained at a constant pressure P ₀ by the relief valve 7, and the load pressure applied to the actuator 4 is
The maximum value of P ₁ is set by the relief valve 8.

Note that the relief valve 7 is provided with an on-off load valve 9, and the relief valve 7 is opened when there is no load.

[Problem that the invention seeks to solve]

When wet molding of ferrite or ceramics is performed using such a hydraulic circuit, the relationship between the pump pressure P ₀ and the load pressure P ₁ is as shown in FIG. 5. In FIG. 5, the slope formed by the pump pressure (P ₀ ) curve and the load pressure (P ₁ ) curve represents energy loss. Energy not used for forming is consumed in the form of an increase in the temperature of the hydraulic oil. This is because excess hydraulic oil generates heat when it is discharged from the relief valve 7. As the temperature of the hydraulic oil increases, the viscosity decreases, and leakage of the hydraulic oil from various valves and the hydraulic cylinder 4 increases. For this reason,
The pressurizing capacity of the hydraulic press decreases.

In order to reduce the energy loss of the hydraulic press, it is possible to increase the load pressure P ₁ and shorten the molding time, but there is a limit to increasing the load pressure P ₁ . This is because even if the load pressure _P1 is increased, filtration will not be carried out quickly, and instead the seal of the piston 6 will be damaged. Therefore, in the case of wet molding of ferrite particles with a particle size of 1 μm, the molding time is at least about 40
In reality, it took about 200 seconds for particles with a particle size of 0.7 μm. For this reason, a system in which the pump pressure P ₀ is kept constant cannot avoid large energy losses.

SUMMARY OF THE INVENTION In view of these problems, it is an object of the present invention to provide a hydraulic press device for molding that minimizes the energy loss of the hydraulic press and achieves a stable pressurized state.

[Means for solving problems]

The hydraulic press device for molding of the present invention includes a hydraulic pump with a constant discharge flow rate, a molding actuator,
Provided between the hydraulic pump and the actuator,
A flow control valve that adjusts the flow rate of hydraulic oil and a load pressure are detected, and the pump pressure is determined by the following formula: P ₀ (t) = P ₁ (t) + △P (However, P ₀ (t) and P ₁ ( t) are the pump pressure and load pressure, respectively, expressed as a function of time, and △P is the minimum differential pressure required for the flow rate of the flow control valve to be constant. The invention is characterized in that it has a device for.

〔Example〕

An embodiment of the present invention will be described with reference to FIG. The same numbers are used for parts that correspond to the apparatus of FIG. Note that the case of constant speed molding will be explained here.

A hydraulic pump 1 is driven by a motor 2, and hydraulic oil is supplied to an actuator 4 having a hydraulic cylinder 5 and a piston 6 via a flow control valve 3. The flow rate control valve 3 is controlled so that the throttle becomes larger as the pressure difference between both ends increases, so that a constant flow rate always flows. As a result, the piston 6 is driven at a constant speed. The maximum value P ₁ max of the load pressure P ₁ applied to the actuator 4 is set by the relief valve 8 .
The pressure of the hydraulic oil is reduced by the pressure difference due to the flow control valve 3, and this pressure difference is necessary for controlling the speed of the actuator. Note that the hydraulic pump 1 has a property that the discharge flow rate is constant, the pump pressure is the minimum when the load is 0, and the pump pressure increases as the load increases.

The device for controlling the pump pressure P ₀ which is the main point of the present invention includes a relief valve 7 and a proportional electromagnetic pressure control valve 10 in this embodiment. The proportional electromagnetic pressure control valve 10 electromagnetically adjusts the relief valve 7 according to an electric signal, and controls the pump pressure P ₀ in proportion to the electric signal. The specific control method is as shown in FIG. First, the load pressure _P1 is detected by a pressure transducer pickup and converted into an electrical signal. After amplifying this electrical signal, it is sent to the control system. The control system generates a signal that gives the desired P ₀ from the load pressure P ₁ signal using the following equation.

P ₀ (t) = P ₁ (t) + △P Here, load pressure P ₁ and pump pressure P ₀ are expressed as functions of time, and P ₀ (t) is smaller than P ₁ (t) due to differential pressure. It is set larger by ΔP. Although it is desirable that the differential pressure ΔP is as small as possible from the viewpoint of preventing energy loss, if it is too small, the flow rate of the hydraulic oil flowing through the flow rate control valve 3 will become unstable. Therefore, the differential pressure ΔP is set to the minimum value required for the flow rate of the flow rate control valve 3 to be stable and constant. In the case of wet molding of ferrite powder, ΔP is approximately 10 Kg/cm ² . The value of this △P is that the output of hydraulic pump 1 is 140
Even if it is different from Kg/cm ² or 210Kg/cm ² , it is essentially the same. The relationship between P ₀ and P ₁ is as shown in FIG.

In the above embodiment, pump pressure control is performed by providing the proportional electromagnetic pressure control valve 10 as a device for adjusting the relief valve 7;
It is also possible to control it alone.

Furthermore, the apparatus of the present invention can also be used for non-constant speed molding in which the flow rate of the flow rate control valve 3 is variable. In this case, the flow rate of the flow rate control valve 3 is increased during the filtration process, specifically to increase the filtration rate within an allowable range. However, the filtration process is still long enough, and the entire molding process takes several tens of seconds.
In order to save energy, it is necessary to minimize the difference between P ₁ and P ₀ . Similarly, pressure control in such a case is performed using the pressure control valve 10 as follows: P ₀ (t)=P ₁ (t)+
Do this so that ΔP is obtained.

Although the case of wet forming has been described above, the hydraulic press device of the present invention is not limited to this, and can be applied to all presses in which the load pressure _P1 fluctuates as shown in Fig. 3 and the forming time is relatively long. It is.

〔effect〕

By controlling the pump pressure of the present invention, the energy loss becomes ΔP×pressure molding time (T), which is minimized. Such hydraulic press equipment has a maximum load pressure
This is particularly advantageous for systems in which low load pressures persist for a relatively long time until P ₁ max is reached (eg wet forming of ferrites and ceramics).

Due to the significant reduction in energy loss, the temperature rise of the hydraulic oil can be effectively prevented. Accordingly, it is possible to prevent a pressure drop and fluctuations in the pressurized state due to an increase in the leaves of the hydraulic oil, and stable molding can be performed with minimum energy.

In addition, since the hydraulic press device of the present invention controls the pump pressure using a relief valve on the pump side, the overall structure of the device is simple and there is no risk of accidents such as excessive pressure rise. It also has advantages.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a hydraulic press device according to an embodiment of the present invention, FIG. 2 is a chart diagram of pump pressure control in the hydraulic press device of FIG. 1, and FIG. 3 is a diagram showing the pump pressure and FIG. 4 is a schematic diagram of a conventional hydraulic press device, and FIG. 5 is a diagram showing the pump pressure and load pressure of the device shown in FIG. 4. 1...Hydraulic pump, 3...Flow control valve, 4...
Actuator, 7, 8... Relief valve, 10...
…Proportional solenoid pressure control valve.

Claims (1)

[Claims] 1. A hydraulic pump with a constant discharge flow rate, a molding actuator, a flow control valve provided between the hydraulic pump and the actuator to adjust the flow rate of hydraulic oil, and a flow control valve that detects load pressure. , the pump pressure is expressed by the following formula: P ₀ (t) = P ₁ (t) + △P (where P ₀ (t) and P ₁ (t) are the pump pressure and load pressure, respectively, expressed as a function of time. , ΔP is the minimum differential pressure required for the flow rate of the flow rate control valve to be constant).