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Hydraulic Presses: Essential Principles & Types

Last updated:
May 5, 2024
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1. The working principle of the hydraulic press

The hydraulic press is made according to Pascal’s principle, using the pressure energy of the liquid to drive the machine to work. The working principle of the hydraulic press is shown in Figure 3-61. Two containers filled with liquid of different sizes (areas A 1 and A 2 respectively) are connected and sealed to prevent the liquid in both containers from leaking.

Figure 3-61 Working principle of the hydraulic press
Figure 3-61 Working principle of the hydraulic press

1—Small plunger
2—Large plunger

When a downward force F 1 is applied to the small plunger, the unit pressure exerted on the liquid is p=F 1 /A 1 . According to Pascal’s principle: in a sealed container, the liquid pressure is equal in all directions, and the pressure is transmitted to every point of the container.

Therefore, the large plunger in another container generates an upward thrust F 2 ,

2 =pA 2 =F 2 (A 2 /A 1 ).

It is evident that by increasing the area of the large plunger, a small force F 1 on the small plunger can obtain a large force F 2 on the large plunger. Here, the small plunger is equivalent to the plunger in a hydraulic pump, while the large plunger is the plunger in the working cylinder of a hydraulic press.

2. Characteristics and classification of hydraulic presses

(1) Characteristics of hydraulic presses.

Hydraulic presses are machines that operate under static pressure, using the static pressure of liquids to deform workpieces. This is fundamentally different from other forging equipment (such as crank presses, forging hammers, screw presses), and hydraulic presses also have the following characteristics:

① It is easy to obtain high pressure.

The larger the tonnage of the equipment, the more prominent this advantage of the hydraulic press, whereas the increase in pressure by mechanical mechanisms is limited by the strength of the components.

② The working pressure can be adjusted.

Some hydraulic presses can use several levels of working pressure overload in one working cycle to protect the mold.

③ It is easy to obtain a large working stroke.

Hydraulic presses are easy to obtain large working strokes, and can generate rated maximum pressure and maintain pressure for a long time at any position of the working stroke. This is particularly beneficial for pressing processes with long working strokes, such as deep drawing of sheet metal and extrusion of profiles.

Convenient for transportation.

The adjustable hydraulic system achieves various stroke speeds, this speed adjustment is stepless and easy to operate.

Hydraulic presses have a simple structure and can adapt to multi-variety production.

Low working vibration and noise.

Hydraulic presses operate smoothly with less impact, vibration, and noise. They have low requirements for factory foundations. They are beneficial for environmental protection and improving workers’ working conditions.

Easy to implement automated production.

However, hydraulic presses also have some disadvantages. For example, they have high requirements for sealing technology; poor sealing can lead to fluid leakage, affecting the efficiency of the machine and polluting the environment. Due to the flow resistance of the fluid, the maximum working speed of the hydraulic press is limited.

(2) Classification of hydraulic presses.

Hydraulic presses are divided into 10 groups according to their uses.

① Forging hydraulic press

Used for free forging, ingot breakdown, and die forging of non-ferrous and ferrous metals.

② Stamping hydraulic press

Used for stamping various sheet metals, including single-action, double-action, and rubber mold stamping.

③ Primary use hydraulic press

Used for various processes, commonly referred to as a universal or general-purpose hydraulic press.

④ Straightening and press-fitting hydraulic press

Used for part straightening and assembly.

⑤ Laminating hydraulic press

Used for pressing plywood, particle board, fiberglass reinforced materials, etc.

⑥ Extrusion Hydraulic Press

Used for extruding various metal wires, pipes, rods, profiles, and workpieces for deep drawing, perforating, and other processes.

⑦ Compression Hydraulic Press

Used for pressing various powder products, such as powder metallurgy, synthetic diamonds, thermosetting plastics, and rubber products.

⑧ Baling and Compacting Hydraulic Press

Used for compacting metal chips and scrap into blocks and bales, and for baling non-metallic materials.

⑨ Other Hydraulic Presses

Such as mold development, cable covering, wheel axle pressing, and other specialized processes.

⑩ Manual Hydraulic Press

A small hydraulic press used for testing, press-fitting, and other manual processes that do not require great force.

The working medium of hydraulic presses mainly includes two types: those using emulsified water as the working medium are called hydraulic presses, with a nominal pressure generally above 10000kN. Those using oil as the working medium are called oil hydraulic presses, with a nominal pressure generally less than 10000kN.

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