The processing technology of the main components of hydraulic valve

The manufacture of hydraulic valves, first of all, according to the design pattern, process documents and technical requirements carefully processed spore, valve body and other parts, followed by the selection of electrical, mechanical converters and other accessories; Finally, carefully assembled, through the test according to relevant standards to obtain high-quality products. Today, Xiaobian takes you to understand the processing technology of the main components of the hydraulic valve (valve body, valve core, valve sleeve).

01

General requirement
The hydraulic valve requires the spool to move flexibly in the valve body hole, work reliably, leak small and have a long life. In the oil pressure valve, usually the fit clearance of various slide valves is 0.005-0.035mm, the fit clearance tolerance is 0.005-0.015mm, and the tolerance of roundness and cylindricity is generally 0.002-0.008mm. For stepped spool and orifice, the coaxiality tolerance of each cylinder is 0.005-0.01mm. For a flat valve, the flatness error between the spool and the seat should not be greater than 0.0003mm. The matching surface of the spool and the valve hole generally requires a surface roughness Ra value of 0.1-0.2μm. Considering that the machining of the hole is more difficult than the outer circle.

Generally, the surface roughness Ra value of the outer circle of the valve core is 0.1μm, and the Ra value of the inner circle surface of the valve hole is 0.2μm.

It can be seen that there are strict requirements for the shape accuracy, position accuracy and surface roughness of the spool and valve hole. In order to achieve the required processing accuracy, the processing of the valve core is finished after turning, milling and grinding. The commonly used finishing methods for the outer circle of the valve core are grinding and high finish grinding. The processing of valve holes is generally carried out after drilling, reaming, comparing holes, routing holes, grinding holes, and then finishing processing. The common finishing methods of holes include fine sharpening, honing, grinding and extrusion.

02

Process equipment
The processing of hydraulic valve parts by the main domestic Hydraulic Components factories mostly adopts the process equipment combined with CNC machine tools, machining centers and high-efficiency special machines, and the auxiliary processes use general machine tools.

03

Valve body processing technology
Different types and varieties of hydraulic valve body processing technology is different. For example, the valve body of the electro-Hydraulic Reversing Valve in the ordinary hydraulic valve has a small clearance between the main hole and the spool, which requires the spool to be flexible in the main hole under high pressure, and the internal leakage rat of the valve is required not to exceed the specified value; There shall be no external leakage on each connection surface. Therefore, in the processing of the main hole and other surfaces of the valve body, high dimensional accuracy, shape accuracy and low surface roughness should be achieved.

The axial size of the valve body must also be controlled within its tolerance range to ensure that the step size of the valve core matches the correct position. The main size and accuracy requirements of the valve body are shown in the following figure.

Electrohydraulic reversing valve body processing diagram

The processing process of the electro-hydraulic reversing valve body with horizontal machining center is roughly as follows: rough milling both ends of the main holes in each plane - machining the bottom surface of the valve body and the holes on the bottom surface - machining the two ends of the valve body, the top surface and the holes in the two ends, machining the main holes and the grooves in the holes - deneedling, cleaning a main hole honing and so on.

The common structure of the servo valve shell is shown in the following figure, hole D is matched with the valve sleeve, the matching gap is 0.001-0.003mm, the surface roughness is Ra0.2μm, and the cylindricity is 0.0005mm. Hole d and the nozzle body form an interference fit, the interference swab is 0.005-0.007mm, the surface roughness is Ra0.4μm, the cylindricity is 0.0005mm, and the parallelism with the top surface is 0.03mm. In addition, there are oil filter holes, and the two ends of the plug are mostly sealed with sealing rings. In the figure, the accuracy of small and small holes is lower than the above two holes, the surface roughness is Ra1.6μm, the accuracy grade is mostly IT7-IT9, and the length-diameter ratio is 8-12. There are more oil connection holes in the shell, whose diameter is generally -1.5mm, and most of them are inclined holes, and the length-diameter ratio is within 30.

Servo valve housing structure and technical requirements

Most of the mounting holes and oil holes on the bottom surface have been standardized, and the end face of the oil holes are sealed. There are internal wall structure forms and no internal wall structure forms, the dimensional accuracy requirements are generally 1-10, and the roughness is Ra1.6μm. In order to facilitate processing, the shell structure can also be made into a combined type, that is, it is divided into several parts for processing, and then combined into one. This structure is easy to process and easy to ensure processing quality, but the strength, stiffness and tightness of the valve body are poor. The main processing procedure of the servo valve housing is shown in the following table.

04

Processing technology of valve core and valve sleeve
1. The spool of ordinary hydraulic valves is divided into slide valves and lifting valves (cone valves and ball valves), so the spool structure and its processing technology are very different.

Taking the spool of the direction control valve as an example, the processing process is described as follows: The direction control valve is a spool installed in the main hole of the valve body, and the clearance is generally about 0.01mm. It can slide axially freely in the main hole of the valve body without blocking. This requires that the spool should have high dimensional accuracy and cylindricity. Low surface roughness. To ensure high sensitivity and small leakage when the spool is reversed. The main structure size of the valve core and its technical requirements are shown in the following figure. The main manufacturing process is turning each outer circle and its end face

Reversing valve spool processing diagram
2. The valve core and valve sleeve in the electro-hydraulic servo valve are called the spool valve pair, and the orifice area is changed by the relative axial movement of the two to control the liquid flow. The manufacturing accuracy of the spool couple, especially the matching gap between the spool and the valve sleeve, the size and shape of the throttling working edge and their mutual mixing accuracy directly affect the performance of the servo valve, and also affect the service life of the servo valve. The servo valve slide valve pair has higher technical requirements than ordinary hydraulic valves, see the following table.

Technical requirements for servo valve slide valve pairs

The following figure shows the four-way intermittent throttling window valve sleeve and the full perimeter (inner ring groove) throttling window valve sleeve. The inner hole is matched with the spool to ensure a clearance of 0.001-0.003mm; The outer circle is matched with the shell to ensure the clearance of 0.001-0.003mm; Deburring at the intersection of the surface H and the inner hole B to retain the sharp edge (R is not greater than 0.0005mm); The difference in width b of 16 rectangular holes in Figure (a) is not more than 0.0lmn1; The position tolerance (usually called coplanarity) of the working edge of the four rectangular holes on the same H surface is 0.002mm.

Servo valve sleeve

The diameter of the hole in the valve sleeve is generally -19mm, and the depth to diameter ratio L/D is 7-12. The outer circle of the valve sleeve and the shell are generally sealed with a gap, and the interference fit with a small interference pull (the interference is O.002mm) is also used, or the rubber ring seal is used. When rubber sealing is used, the matching gap can be appropriately increased, but the manufacture of rubber ring grooves has strict size and roughness. The typical processing process of these two kinds of common valve sleeves is shown in the following figure.
picture
Servo valve sleeve processing process flow

Typical spool structure schematic diagram as shown in the figure below, the outer circle d and the valve sleeve hole matching grinding, to ensure the clearance of 0.001-0.003mm; Four shoulders.
picture
Servo valve spool

The axial position dimensions A, B, C of the edge are matched with the corresponding throttling working edge on the valve sleeve to ensure the overlapping address requirements; Both ends of the feedback groove are matched with the feedback rod ball to ensure a clearance of 0-0.0015mm; The shape and precision of the outer circle and groove are also very strict, so the processing of the valve core is more difficult.