In my work with three-roller plate rolling machines, I have come to appreciate the critical role of the hydraulic drive system for the working roller. This system not only ensures precise control and efficiency during the rolling process but also significantly influences the overall performance of the machine. Understanding the intricacies of the hydraulic drive system helps in optimizing operations and reducing maintenance costs. In this article, I will explore the components and functionality of the hydraulic drive system for the working roller, sharing insights that can enhance both performance and reliability in plate rolling applications.

Le three-roller plate rolling machine is based on the principle of three points forming a circle, using the rotary motion of the working roller and adjusting the change of the relative position of the working roller to produce continuous plastic deformation of the metal sheet, and bending it into a cylindrical, conical, or arc Processing and forming equipment for equal-shaped workpieces. In this paper, based on a detailed analysis of the hydraulic motor drive system of the working roller, the cause of the failure is explained, and a reasonable and feasible solution is proposed.

1. Working Principle of Hydraulic Drive System

The tilt-down three-roller plate machine à rouler is composed of an inverted head mechanism, a left frame, an upper working roller, two lower working rollers, a right frame, a hydraulic motor driven by a lower working roller and a hydraulic motor driven by an upper working roller, etc., as shown in Figure 1. Show. The left frame and the right frame are installed on the whole base with a welded structure and connected by connecting rods to increase the rigidity of the whole machine. The position of the upper working roller is fixed, and the two lower working rollers can move up and down along the oblique guide grooves on the left and right frames respectively. The rotary motion of the working rollers is the main transmission system, which is installed on the side of the right frame, and the inverted head mechanism is installed on the side of the left frame. The tilting and resetting movements are controlled by the inverted head cylinder.

The upper working roller of the three-roller rolling machine is driven by a hydraulic motor through a planetary reducer, and the two lower working rollers (that is, the left lower roll and the right lower roll) are directly driven by the hydraulic motor. The principle diagram of the hydraulic drive system of the working roller is shown in Figure 2, which is composed of three independent hydraulic circuits of the upper roll, the lower left roll and the lower right roll. 

In order to ensure the quality of the products processed by the plate rolling machine, the working speed of the three working rollers, such as the upper roller, the lower left roller, and the lower right roller, is required to be stable and adjustable, and cannot be changed by the influence of other mechanisms to ensure the smooth delivery of the plate. Into. The upper working roller and the two lower working rollers serve as the main drive rolls, which can not only realize the forward and reverse rotation, but also provide the winding torque for the rolling of the sheet material by applying the pressure of the upper working roller and the two lower working rollers The sheet is rolled into cylindrical, cone and other shapes. For this purpose, three special hydraulic circuits are provided, that is, each working roller is supplied with a set of special hydraulic power oil sources, forming an independent hydraulic circuit that is not affected by other mechanisms, so as to realize the stable and adjustable speed of the working roller.

In Figure 2, the oil tank stores hydraulic oil, heat dissipation and dirt in the precipitated oil; the upper suction roller, the lower left roller and the lower right roller suction filter are coarse filters to ensure the cleanliness of the oil entering the three independent hydraulic circuits ; The hydraulic pump and its drive motor are the power source of the hydraulic circuit of the upper roller, the lower left roller and the lower right roller; the pressure gauges respectively indicate the working pressure of the three hydraulic pump outlets; the electromagnetic overflow valve controls the hydraulic motor of the upper roller and the hydraulic pressure of the lower left roller respectively The working pressure of the motor and the hydraulic motor of the lower right roller also has the unloading function to realize the two-stage pressure regulation function. When the working roller is not working, the unloading is used to achieve energy saving; the electro-hydraulic directional valve controls the upper roller motor and the lower left roller motor The forward, reverse and stop of the motor and the lower right roller motor; the buffer valve group limits the maximum working pressure on both sides of the upper roller, lower left roller and right lower roller motor. The working roller drive motor is a two-way quantitative motor, which can be forward and reverse to realize the two-way movement of the plate.

2. Improve scheme design

The above working roller hydraulic circuit is used as an example for analysis. When the hydraulic motor drives the upper roller to rotate, if the electro-hydraulic directional valve is suddenly switched to the neutral position or the direction is changed, a large impact will be generated, affecting the service life of the upper roller hydraulic motor 26. In Fig. 2, the electro-hydraulic directional valve 17 has an O-type central function. During the process of switching the electro-hydraulic directional valve 17 to the neutral position to brake the upper roller, the inlet and outlet of the hydraulic motor 26 are both The electro-hydraulic directional valve 17 is closed in the neutral position. 

Due to the inertia effect, a high-pressure chamber is formed at the oil outlet of the hydraulic motor 26, and a vacuum chamber is formed at the oil inlet, that is, the pressure on the outlet side of the hydraulic motor 26 increases, thereby generating braking force, and relying on the buffer valve on that side to limit the pressure Reduce hydraulic shock. After the buffer valve group 20 (or 21) is opened, the high-pressure side oil can be directly discharged into the low-pressure side pipeline at the vacuum chamber, and then the oil can enter the motor oil inlet to reduce the occurrence of vacuum. This connection method of the buffer valve group is called the direct oil filling method, and its disadvantage is that it cannot fully compensate the oil quantity required by the oil inlet. In addition, due to the internal leakage of the hydraulic motor itself and the electro-hydraulic directional valve (the electro-hydraulic directional valve uses a spool valve structure), and the oil inlet is not connected to the low-pressure pipeline or the oil tank, and it cannot be supplemented by external oil. Therefore, oil replenishment is not sufficient. It is because of insufficient oil replenishment that the oil inlet is kept in a vacuum state for a long time, causing cavitation, which greatly reduces the service life of the hydraulic motor.

In order to completely solve the phenomenon of vacuum and cavitation at the oil inlet of the hydraulic motor, an improved solution for the paired use of the one-way charge valve and the buffer valve is proposed: the oil is fully supplied to the oil inlet of the hydraulic motor through the one-way valve, To avoid vacuum phenomenon; buffer valve can not only reduce the hydraulic shock caused by the electro-hydraulic directional valve in the neutral position, but also make the hydraulic motor brake smoothly; the electro-hydraulic directional valve adopts M-type neutral function. The improvement scheme is shown in Figure 3.

In the improvement plan, the buffer valve 6 and four one-way valves form a full-bridge buffer oil supply circuit. The buffer check valve 1 or 2 can ensure that the high-pressure oil in the left or right chamber can pass through the buffer valve 6, and the reverse flow is blocked by the buffer check valve on the low pressure side, that is, the oil on the high pressure side cannot pass through the low pressure side The buffer check valve flows to the low-pressure line on that side. The charge check valve (3 or 4) plays the role of charge in two directions (the hydraulic motor needs to be forward and reverse, and two charge check valves need to be set) to replenish the low-pressure side pipeline, and its charge pressure It is set by the back pressure valve 5, and the back pressure of oil replenishment is generally set at 0.3～0.5MPa. Due to the back pressure of oil replenishment, this oil circuit can play the role of complete oil replenishment. The high-pressure oil generated by the inertia of the hydraulic motor passes the check valve 1 or 2 and is then subjected to pressure-limiting overflow by the buffer valve 6. The set pressure of the buffer valve 6 limits the maximum pressure at the outlet of the hydraulic motor. The magnitude of the set pressure determines the magnitude of the motor braking torque. This improved solution can not only play a buffering role, but also achieve the purpose of complete oil supplement.