How are valves made?
How are valves made?
At first glance, there are not many parts of the valves, simple structure and general accuracy. In the mechanical industry, they are simple parts, but the core sealing parts of the valve are particularly demanding. Valve manufacturing process is complex and difficult. Which process characteristics should we pay attention to?
Due to the variety and specification of the valve, it is applied in various fields of national economy, and its application occasions vary greatly, such as high temperature and pressure, low temperature and deep cold, flammable and explosive, highly toxic, strong corrosive medium and other working conditions, which put forward strict requirements for the valve material.
In addition to cast iron, carbon steel and alloy structural steel, CrNi stainless steel, CrMoAl nitriding steel, CrMoV heat-resistant steel, CrMnN acid resistant steel, precipitation hardening steel, duplex stainless steel, low-temperature steel, titanium alloy, Monel alloy, Inconel alloy, Hastelloy and g0crw cemented carbide are also widely used. The poor casting, welding and processing properties of these high alloy materials make the manufacturing process very difficult. In addition, most of these materials are precious materials with high alloy, high strength and high hardness. There are many difficulties in material selection, material preparation and procurement. Some materials are difficult to purchase and supply due to their small use.
Structure of casting blank
Most of the valve blanks are thin-walled castings with complex structure, which not only require good appearance quality, but also dense internal quality and good metallographic structure, without defects such as porosity, shrinkage cavity, sand inclusion and crack. Therefore, its casting process is complex and heat treatment technology is difficult. In the mechanical industry, the casting difficulty of the blank of the pressure bearing thin shell casting of the valve is far more complex and more difficult than that of other mechanical components.
Machining process of valves
Due to the poor cutting performance of most high strength, high hardness and high corrosion-resistant materials, such as high alloy stainless steel and acid resistant steel, which have the disadvantages of high toughness, high strength, poor heat dissipation, large chip viscosity and strong processing hardening tendency, it is difficult to achieve the required dimensional accuracy and finish, which brings certain difficulties to machining tools, processes and equipment. In addition, the requirements of valve sealing surface in machining accuracy, matching angle, finish and matching sealing pair are also very high, which brings great difficulty to machining.
Process arrangement of valve parts
The number of main parts of the valve is not many, the structure is relatively simple, the processing accuracy of most dimensions is not high, and the outside is relatively rough, which gives the impression of a simple machine. In fact, the heart sealing part of the valve is extremely precise, and the “three degrees” (flatness, smoothness, hardness) of the sealing surface is very high, as well as the coincidence degree of the sealing pair composed of two sealing surfaces must reach zero to zero, so as to meet the zero leakage of the air tightness test. It is the biggest technological difficulty of valve machining to guarantee the precise zero to zero requirements of heart parts with rough benchmark.
Testing and inspection of valves
The valve is an important opening and closing and regulating element of the pressure pipeline, and the operating conditions of the pressure pipeline are very different, such as high temperature, high pressure, low temperature, deep cold, flammable and explosive, highly toxic and strong corrosion. However, the test and inspection conditions of valve manufacturing can not meet the same requirements of the working conditions. The international and domestic valve test standards stipulate that the gas or water is used as the medium for the test under the conditions close to the normal temperature. There is a fundamental hidden danger, that is, the valve products passing the normal factory test may not meet the use requirements due to material selection, casting quality and seal damage under harsh actual working conditions, and there will be major quality accidents. It’s no wonder that some old valve experts who have worked for a lifetime are more restrained and worried as they get older.
Have you been shocked by the characteristics of valve manufacturing process? Let’s get more knowledge! It seems that simple valves are not so easy to manufacture? So, how to make the valve step by step?
Step 1: Valve body manufacturing
Valve body (casting, sealing surface overlaying)
Purchase of castings (as per the standard) ➱ incoming inspection (as per the standard) ➱ weld overlay groove ➱ ultrasonic flaw detection (as per the drawing) ➱ weld overlay and post weld heat treatment ➱ finishing ➱ grinding sealing surface ➱ hardness inspection and dye detection of sealing surface.
Step 2: Manufacturing process of valve internals
A. Internal parts such as valve disc and valve seat to be hardfacing
Purchase of raw materials (according to the standard) ➱ incoming inspection (according to the standard) ➱ production of blank (round steel or forging, according to the drawing process requirements) ➱ rough machining of ultrasonic flaw detection surface (when required by the drawing) ➱ rough machining of weld overlay groove ➱ surfacing and post weld heat treatment ➱ finishing of all parts ➱ grinding of sealing surface ➱ hardness inspection and dye detection of sealing surface.
Purchase of raw materials (according to the standard) ➱ incoming inspection (according to the standard) ➱ production of blank (round steel or forging, according to the drawing process requirements) ➱ rough machining of weld overlay groove ➱ surfacing and post weld heat treatment ➱ finishing of all parts ➱ grinding of outer circle ➱ surface treatment of valve rod (nitriding, quenching, chemical coating) ➱ final treatment (polishing, grinding, etc.) ➱ grinding of sealing surface ➱ hardness inspection and dye detection of sealing surface.
C. Internal parts without hardfacing
Purchase of raw materials (according to the standard) ➱ incoming inspection (according to the standard) ➱ production of rough (round steel or forging, according to the drawing process requirements) ➱ rough machining of ultrasonic flaw detection surface (when required by the drawing) ➱ finishing of all parts.
Step 3: Fastener manufacturing
Fastener manufacturing standard dl439-1991.
Purchase of raw materials (according to the standard) ➱ incoming inspection (according to the standard) ➱ making rough (round steel or forging, according to the drawing process requirements) and sampling for necessary inspection ➱ rough processing ➱ finishing ➱ spectral inspection.
Step 4: General Assembly
Pick up parts ➱ clean, clean ➱ rough assembly (according to the drawing) ➱ hydrostatic test (according to the drawing and process) ➱ after qualified, disassemble and clean ➱ final assembly ➱ and electrical assembly or actuator commissioning (for electric valves) ➱ paint packaging ➱ shipping.
Step 5: Production and inspection process
- 1. All kinds of raw materials purchased by the company.
- 2. Use spectrum analyzer to test raw materials, and print out the test report of raw materials for backup.
- 3. Cut raw materials with cutting machine.
- 4. The inspector shall inspect the cutting diameter and length of raw materials.
- 5. The forging workshop processes the raw materials by forging and forming.
- 6. The inspector inspects the size of the blank.
- 7. The worker is cutting the edge of the blank.
- 8. Sanding workers sandblast the rough surface.
- 9. The inspector shall conduct surface treatment inspection after sand blasting.
- 10. Workers machine the blanks.
- 11. Valve body sealing thread processing – the employees conduct the post processing inspection on the products after processing by the self inspection and inspection personnel.
- 12. Valve body connection thread processing.
- 13. Middle hole processing.
- 14. The inspector shall conduct the general inspection.
- 15. Qualified semi-finished products are sent to semi-finished products warehouse.
- 16. Semi finished products are electroplated.
- 17. Semi finished product plating surface treatment inspection.
- 18. Inspection of all kinds of accessories (ball, stem, seal valve seat).
- 19. Product assembly is carried out in the General Assembly Workshop – the inspectors of the assembly line inspect the products.
- 20. After assembly, the product goes through pressure test and drying to the next process.
- 21. The general assembly workshop shall carry out product packaging – the packaging line inspector shall inspect the sealing, appearance and torsion of the product. Unqualified products must not be packed.
- 22. 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 inquiry at any time.
- 24. Qualified products are sent to domestic and foreign countries through containers.
Source: China Valve Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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