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Pump Casting And Valve Casting

VALVE CASTINGS

Table of Contents

Valve manufacturing materials

Due to the wide variety of valve specifications, such as general-purpose valves have gate valves, globe valves, check valves, ball valves, butterfly valves, hydraulic control valves; industrial valves have solenoid valves, regulating valves, pressure reducing valves, high-temperature and high-pressure valves, low-temperature valves and other special valves, are used in various areas of the national economy, the use of the occasion is very different, such as high temperature and high pressure, low-temperature deep cold, flammable and explosive, highly toxic, strong corrosive media and other working conditions. The material of the valve has put forward harsh requirements.

In addition to cast iron, carbon steel, alloy structural steel, but also a large number of 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 carbide, etc.. The casting, welding and processing properties of these high-alloy materials are very poor, which makes the manufacturing process very difficult. Coupled with the fact that most of these materials are high alloy, high strength, high hardness precious materials, there are many difficulties in the selection, preparation and procurement from the materials. Some materials are difficult to procure supply due to the small amount of use.

Valve manufacturing materials

Valve casting methods

  1. lost wax casting. Is able to make cast steel valve parts, such as carbon steel, stainless steel and other cast steel alloys. Lost wax casting is a precision casting method for valve parts, so you can achieve good dimensions and tolerances, smoother surface. Stainless steel valve castings are widely used in the silica-sol casting process, which is another lost wax method. This casting process can be used for butterfly valves, ball valves, etc.
  2. water-loss foam casting. This casting method is more suitable for making precision cast iron valve parts, it can also obtain good surface finish and size, this net shape or near net shape valve castings will not need machining or only need a small amount of machining allowance.
  3. sand casting. It is also a casting process for valve casting parts. Sand casting is suitable for valve castings of steel and iron. Compared with disappearing mold casting and lost wax casting, it is more suitable for manufacturing larger valve parts, so usually, more machining allowance is needed for further processing.

The valve manufacturing process

  • Step 1: Valve body manufacturing

Valve body (casting, sealing surface overlay welding)

Casting procurement (according to the standard) → into the factory inspection (according to the standard) → surfacing groove → ultrasonic flaw detection (according to the drawings) → surfacing and post-welding heat treatment → finishing → grinding sealing surface? Seal surface hardness inspection, coloring flaw detection.

  • Step 2: Valve internal parts manufacturing process
  1. The need to weld the seal surface of the internal parts such as valve flap, valve seat, etc. Raw material procurement (according to the standard) → into the factory inspection (according to the standard) → the production of billet (round steel or forgings, according to the drawing process requirements) → rough machining ultrasonic flaw detection surface (when the drawing requirements) → rough machining surfacing groove → surfacing and post-welding heat treatment? Finishing processing of each department? Grinding sealing surface? Seal surface hardness test, coloring flaw detection.
  2. Valve stem- Raw material procurement (according to the standard) → into the factory inspection (according to the standard) → the production of rough (round steel or forgings, according to the drawing process requirements)? Rough machining surfacing groove → surfacing and post-welding heat treatment? Finishing ministries → Grinding outer circle → Stem surface treatment (nitriding, quenching, chemical plating) → Final treatment (polishing, grinding, etc.) → Grinding sealing surface → Seal surface hardness inspection, coloring flaw detection.
  3. Internal parts that do not require overlay welding of sealing surface, etc. Raw material procurement (according to the standard) → into the factory inspection (according to the standard) → the production of billet (round steel or forgings, according to the drawing process requirements) → rough machining ultrasonic flaw detection surface (when the drawing requirements) → finishing processing ministries.
  • Step 3: Fastener manufacturing

Raw material procurement (according to the standard) → into the factory inspection (according to the standard) → production of rough (round steel or forgings, according to the drawing process requirements) and sampling for the necessary inspection → rough machining → finishing → spectral inspection.

  • Step 4: General assembly

Pick up parts → cleaning, cleaning → rough assembly (according to the drawings) → hydraulic test (according to the drawings, process) → after passing, disassembly, wipe clean → final assembly → commissioning with electric installation or actuator (for electric valves) → paint packaging → shipping.

  • Step 5: Product production and inspection process
  1. The raw materials of various specifications purchased by the company.
  2. Material testing of raw materials with spectral analyzer, and print out the material testing report of raw materials for backup.
  3. Cutting of raw materials with the lowering machine.
  4. Inspection personnel check the cutting diameter and length of raw materials.
  5. Forging workshop to forge the raw materials for forming treatment.
  6. Inspection personnel carry out various dimensional inspections on the forming of blanks.
  7. Workers are removing the waste edge of the blank.
  8. Sand blasting workers conduct surface sand blasting treatment on the blank.
  9. Inspection personnel carry out surface treatment inspection after sandblasting.
  10. Workers are machining the blank.
  11. Valve body sealing thread processing-employees in the processing of self-inspection inspectors to the product after the product for processing after inspection.
  12. Valve body connection thread processing.
  13. Middle hole processing.
  14. Inspection personnel for total inspection.
  15. The qualified semi-finished products are sent to the semi-finished products warehouse.
  16. Semi-finished products are plated.
  17. Semi-finished product plating surface treatment inspection.
  18. The inspection of various accessories (ball, stem, seal seat).
  19. Assembly workshop for product assembly – assembly line inspectors to inspect the product.
  20. After assembly, the products are pressure tested and dried to the next process.
  21. The final assembly workshop carries out product packaging – the packaging line inspector inspects the sealing, appearance and torque of the product. Unqualified products are never allowed to be packaged.
  22. Qualified products are bagged and packed and sent to the finished product warehouse.
  23. All the inspection records will be sorted and stored in the computer for reference at any time.
  24. Qualified products are sent to domestic and overseas via container.
valve casting

Steps and basis for selecting valves

1.Selection steps

  1. clarify the use of the valve in the equipment or device, to determine the working conditions of the valve: applicable media, working pressure, working temperature, etc.
  2. determine the nominal diameter of the pipeline connected to the valve and the connection: flange, threaded, welded, etc.
  3. to determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage, etc.
  4. according to the medium transported by the pipeline, working pressure, working temperature to determine the selected valve shell and internal parts of the material: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc.
  5. select the type of valve: closed-circuit valves, regulating valves, safety valves, etc.
  6. determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc.
  7. to determine the parameters of the valve: for automatic valves, according to different needs to determine the allowable flow resistance, discharge capacity, back pressure, etc., and then determine the nominal diameter of the pipeline and the diameter of the seat hole.
  8. determine the geometric parameters of the selected valve: the length of the structure, flange connection form and size, the size of the valve height direction after opening and closing, the size and number of connected bolt holes, the entire valve external dimensions, etc.
  9. the use of available information: valve catalogs, valve product samples, etc. to select the appropriate valve products.
valve product

2.Select the basis of the valve

In understanding the steps to master the selection of valves, should further understand the basis for the selection of valves.

  1. the use of the selected valve, the use of working conditions and manipulation control mode.
  2. the nature of the working medium: working pressure, working temperature, corrosive properties, whether it contains solid particles, whether the medium is toxic, whether it is flammable, explosive media, the viscosity of the medium and so on.

3. the requirements of the valve fluid

characteristics: flow resistance, discharge capacity, flow characteristics, sealing grade, etc.

  1. installation size and size requirements: nominal diameter, and pipeline connection and connection size, size or weight limit, etc.
  2. additional requirements for the reliability of the valve product, service life and explosion-proof performance of the electric device, etc.
  1. In the selection of parameters should be noted.

If the valve is to be used for control purposes, the following additional parameters must be determined: method of operation, maximum and minimum flow requirements, pressure drop for normal flow, pressure drop when closed, and maximum and minimum inlet pressure of the valve.

Based on the above basis and steps for selecting valves, a reasonable and correct selection of valves must also be based on a detailed understanding of the internal structure of the various types of valves so that the right choice can be made for the preferred valve.

The final control of the pipeline is the valve. Valve opening and closing parts control the way the medium flows in the pipeline, the shape of the valve flow channel so that the valve has certain flow characteristics, which must be taken into account when selecting the most suitable valve for installation in the pipeline system.

Why are pumps and valves often linked together?

Pumps and valves are often linked together because of the use of occasions. That is, there are pumps where there are generally valves, and some places often need pumps. They are both used in places where liquids are transported. Of course, valves are also used for gases. Vacuum pumps are also associated with gases.

Pump valve definition: valves not used for pumps or valves with a pump role.

The main difference between casting valves and forging valves

Casting is the material in the mold as a whole pouring molding, it has a uniform stress distribution, there is no restriction on the direction of pressure. Forgings are pressed by the same direction of force, it has internal stress directional, and can only withstand directional pressure. The same material, the same wall thickness of castings and forgings, in strength and crystal phase structure, forgings are better than castings. For the globe valve, the same poundage, the same material castings globe valve wall thickness to thicker than forgings. Its pressure strength is equal to that of forgings. Casting requirements for the casting process is relatively high, the most important feature is that you can make a more complex shape, the body structure of the globe valve and the flow channel are irregular, casting can be a one-time molding, as long as the process is good, you can cast the body of the large diameter globe valve. For example, the United States VTON forged globe valve, imported forged ball valve, imported forged globe valve caliber can be up to 20 inches. Forgings are better dense, but for too complex flow and shape can not be formed at once, often need to be modular, separate forging and then welded together, so the size of the forgings are somewhat limited.

Forgings are often not machined to produce complex, streamlined runners. The runners are machined by turning and form many sharp corners inside the transition, which can easily cause uneven stress and cracking. At the same time, the modular welded design, forged globe valve seat bore is relatively fixed, in some globe valve size, its bore is small, affecting the flow capacity. This results in increased flow resistance of the globe valve and reduced efficiency of the entire system.

Due to the limitations of the forging process in large size globe valve, and to save costs, many manufacturers usually use the center part of the valve body castings, forgings at both ends of the structure. Whether castings, forgings. In the processing, there are possible product defects. The main defects of castings are in trachoma, bubbles, etc.; the main defects of forgings are in large grains, cold hardening phenomenon, cracks, cracks, etc. In order to obtain qualified product quality, the corresponding castings need heat treatment to eliminate the stress in the casting process, while using X-ray, magnetic particle flaw detection, penetration inspection and other detection means. For forgings, this requires strict heat treatment of the weld and the corresponding inspection methods to ensure. Forgings often require ultrasonic inspection. In addition, it should be mentioned that the welding process is very strict, the welding engineer’s qualification is the key.

Shut-off valve

The main standards for the common implementation of the gate valve

  1. GB/T 12232-2005 general-purpose valve flange connection iron gate valve
  2. GB/T 12234-2007 steel gate valve with stud connection bonnet for oil and gas industry
  3. GB8486-87 General Technical Regulations for Gate, Globe, Ball and Check Valves with Internal Thread Connection
  4. GB8465.1-87 “female threaded connection gate valve, globe valve, ball valve, check valve basic size iron gate valve
  5. JB/T53162-1999 “gate valve product quality classification
  6. JB/T5298-91 “steel flat gate valve for pipeline
  7. JB/Z243-85 “gate valve static pressure life test procedures
  8. JB/TQ648-8 “iron butt plate gate valve
  9. JB/T53200-94 “iron counter-priced flat gate valve product quality classification
  10. JB/T53242-94 “steel flat gate valve product quality classification

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