Manufacturing technology of ball

The ball is the opening and closing part of the ball valve, also known as the ball core and ball. The ball rotates around the center line of the valve body to open and close the ball valve. The ball valve can cut off, adjust, distribute and change the flow direction of the medium in the pipeline. Ball valve has many advantages, which is a new type of valve widely used in recent years. Ball valves with different functions often have different balls.

Comparison of valve ball forming methods

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Foundry method

Casting method is a traditional processing method. It needs a complete set of melting and pouring equipment, as well as a large workshop and more workers. It has large investment, many processes, complex production process and environmental pollution. The technical level of workers in each process directly affects the quality of products. The problem of leakage of pores in valve balls can not be completely solved, But the blank machining allowance is large, waste is large, often found in the processing process because of casting defects make it scrap, to make the product cost increased, quality can not be guaranteed.

Forging method

Forging method is another method adopted by many domestic valve enterprises at present. It has two processing methods: one is to cut off the round steel, heat and forge it into a spherical solid blank, and then machine it. The second is to mold the stainless steel plate into a round shape on a large press to get a hollow hemispherical blank, and then machine the valve ball blank. This method has a high material utilization rate, but requires a high-power press, heating furnace and argon arc welding equipment.

Free forging

Free forging refers to a kind of processing method that the metal billet is heated and placed between the iron (upper and lower) of forging equipment to exert impact force or pressure, which makes the billet produce plastic deformation directly and obtain the forging to be produced. Classification: manual free forging, hammer free forging, hydraulic press free forging

  • Advantages: strong applicability, large flexibility, short cycle, the only way for large forgings.
  • Disadvantages: low precision, large machining allowance, low efficiency, high labor intensity.

Die forging

The formal term of die forging is called model forging. The billet is heated and then forged in the forging die fixed on the die forging equipment.
Die forging equipment: in industrial production, hammer forging is mostly used. Steam air hammer, tonnage in 5kn ~ 300KN (0.5 ~ 30t) press forging, the most common is hot forging press.
Forging ratio
Forging ratio: refers to the ratio of cross-sectional area of blank (metal) before and after forging. The calculation methods and methods are different for different processes.
When drawing, the forging ratio is y = F0 / F1 or y = L1 / l0, F0, l0 – the cross-sectional area and length of ingot or billet before drawing; F1, l0 – cross section length and area of ingot (Billet) after drawing.
Forging ratio during upsetting, also known as upsetting ratio or compression ratio, is y = F1 / F0 or y = H0 / H1, F0, H0 – cross-sectional area and height of ingot or billet before upsetting, F1, H1 – cross-sectional area and height of ingot or billet after upsetting.
Forging temperature

  • a. Initial forging temperature: the initial forging temperature can be considered as the maximum temperature of steel or alloy allowed to be heated in the furnace.
  • b. Final forging temperature: the valve parts need to have strong plasticity before the end of forging, and obtain recrystallization structure after forging.

Spinning method

Metal spinning is an advanced processing method with less and no chips, which is a new branch of pressure processing. It integrates the process characteristics of forging, extrusion, rolling and rolling. It has high material utilization rate (up to 80-90%), saves a lot of processing time (forming in 1-5 minutes), and the material strength can be doubled after spinning. Due to the small area contact between the spinning wheel and the workpiece during spinning, the metal material is subject to two-way or three-way compressive stress state, which is easy to deform. Under less power, the higher unit contact stress (up to 25-35mpa) can be obtained. Therefore, the equipment is light in weight, and the total power required is small (less than 1 / 5-1 / 4 of that of the press), It has been recognized by foreign valve industry as a kind of energy-saving valve ball processing technology, and also suitable for processing other hollow revolving parts. Spinning technology has been widely used and developed at a high speed in foreign countries. The technology and equipment are very mature and stable, and the automatic control of mechanical, electrical and hydraulic integration is realized. At present, spinning technology has been greatly developed in China and has entered the stage of popularization and application.

Common materials and grades of spheres

A. Carbon steel

  • ASTM A105    
  • ASTM A350 LF2    
  • ASTM A694 F60
  • B. Low alloy steel
  • ASTM A322 4130(AISI 4130)    
  • ASTM A322 4140(AISI 4140)

C. Stainless steel

  • C. 1 ferritic stainless steel: ASTM A182 f429 F430
  • C. 2 martensitic stainless steel: ASTM A182 f6a Class1 / class2 / class3 / class4 GB / T 1220 12cr13
  • C. 3 austenitic stainless steel: ASTM A182 F316 ASTM A182 f304
  • C. 4 duplex stainless steel: ASTM A182 F51 F53 F55 F60
  • C. 5 precipitation hardening stainless steel: ASTM A705 17-4PH

D. Nickel base alloy

  • ASTM B564 Moenl400  
  • ASTM B564 NO6625(Inconel625)

National standard:

  • ASTM: American Society for testing and materials
  • Aisi: American Iron and Steel Institute standard
  • GB: Chinese national standard
  • JIS: Japanese industrial standard
  • Material writing: National Standard + standard number + material brand

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Technical conditions of sphere

Selection of cross section diameter of ball valve passage

In the design and calculation of ball valve, the first step is to determine the diameter of the ball’s channel, which can be used as the basis for other parts of the calculation. The minimum diameter of the ball channel should meet the requirements of the corresponding standards.
When designing the national standard ball valve, the minimum diameter of the full bore ball valve shall comply with GB / T 19672-2005 technical conditions for pipeline valves or GB / T 20173-2006 petroleum and natural gas industries pipeline transportation piping system valves.
When designing American standard ball valve, the minimum diameter of full bore ball valve shall comply with apl6d-2008 / is014313:2007 petroleum and natural gas industry pipeline transportation system pipeline valve.
According to the standard of reducing ball valve, for the valve with nominal size DN ≤ 300 mm (npsl2 in), the diameter of the nominal size of the valve shall be reduced by one specification according to the inner diameter specified in the standard; For DN350 (npsl4) ~ N600 (nps24) valves, the diameter of the nominal size of the valve shall be reduced by two specifications according to the inner diameter specified in the standard; For the valve with nominal size DN > 600mm (nps24in), it shall be agreed with the user. For the ball valve without standard provisions, the cross-sectional area of the ball passage shall not be less than 60% of the rated cross-sectional area of the pipeline, and it shall be designed in the form of reducing diameter, so as to reduce the structure of the valve, reduce the weight, and reduce the force on the sealing surface of the valve seat and the opening and closing torque. Generally, the ratio of valve nominal size DN to ball channel diameter D is equal to 0.78. At this time, the resistance of the ball valve will not be too large.

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Common types of heat treatment for spheres

  • ASTM A105: normalizing
  • ASTM A350 LF2: quenching and tempering
  • ASTM a694 F60: quenching and tempering
  • ASTM a322 4130 / 4140: quenching and tempering
  • ASTM A182 f6a class 2: quenching and tempering (secondary tempering)
  • ASTM A182 f304 / F316 / F51 / F53 / F55 / F60: solution treatment
  • ASTM A705 17-4PH: precipitation hardening (quenching + secondary artificial aging)

Electroplating on the surface of sphere

Why electroless plating?

Objective: to improve the wear resistance or corrosion resistance of the ball in practical use

Why is the electroplating amount of carbon steel the largest?

Carbon steel is easy to rust and its surface hardness is low. In order to prevent corrosion and save cost, the amount of carbon steel electroplating is the largest

Why electroplating stainless steel materials?

The main purpose is to improve the surface hardness of the ball, so as to improve the wear resistance in use.

Common species (classification)

Electroless nickel phosphorus plating (refer to ASTM b733)

Classification by alloy type of coating:

  • Class I: P no requirement.
  • Class II: lower phosphorus (1-3%).
  • Class III: low phosphorus (2 ~ 4% P): hardness as plated 620-750hk.
  • Class IV: medium phosphorus (5 ~ 9% P): widely used to meet the wear resistance and corrosion resistance.
  • Class V: high phosphorus (> 10%): it has excellent salt spray resistance and acid resistance in various occasions, and the coating with phosphorus content more than 11.2% is considered to be magnetic.

Classification according to thickness and service conditions:

  • SC0  0.1 μ M — minimum service condition
  • SC1     5 μ M — light load condition
  • SC2   13 μ M — moderate use condition
  • SC3   25 μ M — medium service condition
  • SC4   75 μ M — severe service condition

Classification according to post plating heat treatment:

  • Class 1 – as deposited, not heat treated.
  • Class 2 – Minimum hardness of 850hk produced by heat treatment at 260-400 ℃.
  • Class 3 – heat treatment at 180-200 ℃ for 2-4 hours to improve coating adhesion and prepare for elimination of hydrogen embrittlement.
  • Class 4 – heat treatment at 120-130 ℃ for more than 1 hour increases the adhesion (adhesion) of aluminum alloy and carburized steel.
  • Category 5 – heat treatment at 140-150 ℃ for more than 1 hour to improve the adhesion of coatings on aluminum, non age hardening aluminum alloy, copper and copper alloy.

Note: it is generally recommended that the hardness of ball heat treatment should be 500 ~ 650hv or 600 ~ 850hv or above, and choose from the three.

Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (

(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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