The Valve Manufacturing Process and Processing Process

At first glance, there are not many valve parts, simple structure, and average precision. They are simple parts in the machinery industry, but the core sealing parts of the valve are particularly demanding. The valve manufacturing process is complicated and the technical difficulty is also great. Today we mainly introduce the manufacturing process and processing process of the valve.

 

Manufacturing process

1. Manufacturing materials

Due to the wide variety of valves and specifications, for example, general valves include gate valves, globe valves, check valves, ball valves, butterfly valves, pneumatic pinch valve, and hydraulic control valves; industrial valves include special valves such as solenoid valves, regulating valves, pressure reducing valves, high temperature, and high-pressure valves, and cryogenic valves. They are used in various fields of the national economy, and their use occasions are very different, such as high temperature and high pressure, low temperature and cryogenic, inflammable and explosive, highly toxic, strong corrosive media, and other working conditions, which put forward strict requirements on the material of the valve.

 

 

In addition to cast iron, carbon steel, alloy structural steel, CrNi stainless steel, CrMoAl nitrided steel, CrMoV heat-resistant steel, CrMnN acid-resistant steel, precipitation hardening steel, duplex stainless steel, low-temperature steel, titanium alloy, and Monel are also widely used, Inconel, Hastelloy, and G0CrW cemented carbide, etc. The casting, welding, and processing properties of these high-alloy materials are very poor, which brings great difficulties to the manufacturing process. In addition, these materials are mostly high-alloy, high-strength, and high-hardness precious materials, and there are many difficulties in material selection, material preparation, and procurement. Some materials are difficult to purchase and supply due to their small usage.

 

2. The structure of the casting blank

Most of the valve blanks are made of complex thin-shell castings, which not only require good appearance quality, but also the dense internal quality and good metallographic structure. They must not have pores, shrinkage holes, sand inclusions, cracks, and other defects. Therefore, the casting process is complicated and the heat treatment technology is difficult. In the machinery industry, the difficulty of casting the pressure-bearing thin shell castings of valves is much more complicated and difficult than the castings of other mechanical components.

 

 

3. Machining process

Since most of the high-strength, high-hardness, and high-corrosion-resistant materials have poor cutting performance, such as high-alloy stainless steel and acid-resistant steel, they all have the disadvantages of high toughness, high strength, poor heat dissipation, high chip viscosity, and strong work hardening tendency. It is difficult to achieve the required dimensional accuracy and smoothness. This brings certain difficulties to machining tools, processes, and equipment. In addition, the valve sealing surface has high requirements for machining accuracy, matching angle, smoothness, and matching sealing pairs, which brings great difficulty to mechanical processing.

 

4. Process arrangement of valve parts

The main parts of the valve are not many, the structure is relatively simple, the machining accuracy of most sizes is not high, and the exterior is relatively rough, which gives the impression of simple machinery. In fact, the "three degrees" (flatness, smoothness, hardness) of the sealing surface of the heart sealing part of the valve is very demanding. The matching degree of the sealing pair composed of the two sealing surfaces must reach zero-to-zero in order to meet the zero leakage of the airtightness test. This kind of rough benchmark to ensure the zero-to-zero requirement of the heart part is the big technological difficulty of valve processing.

 

5. Valve test and inspection

Valves are important opening and closing and regulating components of pressure pipelines, and the working conditions of pressure pipelines are extremely different, such as high temperature and high pressure, low temperature and deep cold, inflammable and explosive, highly toxic, and strong corrosion. However, the test and inspection conditions of valve manufacturing cannot meet the same requirements as the working conditions. 

 

Various international and domestic valve test standards stipulate that the test is performed with gas or water as the medium under conditions close to normal temperature. There is a fundamental hidden danger. Valve products that pass the normal factory test may have problems with material selection, casting quality, and seal damage under harsh actual working conditions, which may be difficult to meet the use requirements, and significant quality may occur. accident. It's no wonder that some old valve experts who have been working for a lifetime have become more cautious and worried as they grow older.

 

 

Valve manufacturing process

  

The first step: the manufacture of the valve body

Valve body (casting, sealing surface surfacing)

Procurement of castings (according to standards)➱in-factory inspection (according to standards)➱surfacing welding groove➱ultrasonic inspection (according to drawings)➱surfacing and post-weld heat treatment➱finishing processing➱grinding sealing surface➱sealing surface hardness inspection and coloring inspection.

 

Step 2: Manufacturing process of valve trim

1) Internal parts that need to be welded on the sealing surface, such as valve clack, valve seat, etc.

Procurement of raw materials (according to the standard) ➱ inspection in the factory (according to the standard) ➱ production of blanks (round steel or forgings, according to the drawing process requirements) ➱ rough machining of the ultrasonic flaw detection surface (when required by the drawing) ➱ rough machining of surfacing grooves ➱ surfacing and welding Post heat treatment➱finish all parts➱grind the sealing surface➱test the hardness of the sealing surface and color flaw detection.

 

2) Stem

Procurement of raw materials (according to the standard) ➱ factory inspection (according to the standard) ➱ production of blanks (round steel or forgings, according to the drawing process requirements) ➱ rough machining of surfacing grooves ➱ surfacing and post-weld heat treatment ➱ finishing each part ➱ grinding the outer circle ➱Surface treatment of valve stem (nitriding, quenching, electroless plating) ➱final treatment (polishing, grinding, etc.) ➱grinding the sealing surface ➱ sealing surface hardness inspection, color flaw detection.

 

3) There is no need to weld the internal parts of the sealing surface, etc.

Procurement of raw materials (according to the standard) ➱ inspection in the factory (according to the standard) ➱ making blanks (round steel or forgings, according to the process requirements of the drawings) ➱ rough machining the ultrasonic flaw detection surface (when the drawing is required) ➱ finishing various parts.

 

Step 3: Fastener manufacturing

Fastener manufacturing standard DL439-1991.

Procurement of raw materials (according to the standard) ➱ in-factory inspection (according to the standard) ➱ making blanks (round steel or forgings, according to the process requirements of the drawings) and sampling for necessary inspections ➱ rough processing ➱ finishing ➱ spectrum inspection.

 

Step 4: Final assembly

Receiving parts➱Cleaning and cleaning➱Rough assembly (according to drawings)➱Hydraulic test (according to drawings, process)➱After qualified, disassemble and clean➱Final assembly➱Commissioning with Denso or actuator (for electric valve)➱Paint Packaging ➱ Shipment.

 

 

Step 5: Product production and inspection process

1) Various specifications of raw materials purchased by the company.

2) Use a spectrum analyzer to test the materials of the raw materials, and print out the test report of the raw materials for backup.

3) Use a blanking machine to cut raw materials.

4) The inspector inspects the cutting diameter and length of the raw material.

5) The forging workshop performs forging and forming of raw materials.

6) Inspectors conduct various size inspections of the blanks.

7) Workers are cutting off the rough edges.

8) Sandblasting workers perform surface sandblasting treatment on the blank.

9) Inspectors conduct surface treatment inspections after sandblasting.

10) Workers perform rough machining.

11) Valve body sealing thread processing---employees perform self-inspection during processing. Inspectors perform post-processing inspections on products after processing.

12) Valve body connection thread processing.

13) Middle hole processing.

14) The inspector conducts the general inspection.

15) The qualified semi-finished products are sent to the semi-finished products warehouse.

16) Semi-finished products are electroplated.

17) Inspection of electroplating surface treatment of semi-finished products.

18) Inspection of various accessories (ball, valve stem, sealed valve seat).

19) Product assembly in the final assembly shop—the assembly line inspectors inspect the products.

20) The assembled product undergoes pressure testing and drying to enter the next process.

21) The final assembly workshop conducts product packaging—the packaging line inspectors inspect the product’s tightness, appearance, and torque. Unqualified products must never be packaged.

22) The qualified products are packed in bags and sent to the finished product warehouse.

23) All inspection records will be classified and stored in the computer for inquiries at any time.

24) Qualified products are sent to home and abroad through containers

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