Manufacturing technology of elliptical head

General

This process is applicable to the stretch forming of elliptical heads made of carbon steel, low alloy steel and stainless steel, and other forms of heads can also be implemented with reference.

This process is a general provision used in conjunction with product process documents. In case of conflict with product process documents or special requirements in product process documents, the process documents shall prevail.

manufacturing technology of elliptical head - Manufacturing technology of elliptical head

Drawing die and lubrication

The tire mold shall be selected according to the tooling number specified in the product name detail table.
The drawing die used shall be intact, and the exhaust hole of the upper die shall not be blocked. It can be used only after it is verified to be qualified.
The upper and lower dies and hold down rings are respectively fixed on the punch and press base with studs and accessories, and the circumferential clearance is adjusted to be uniform, and the difference is ≤ 1mm.
Before stretching a head, check whether the tire mold is loose, offset and other defects. After confirmation, it can be used again.
Before stretching and pressing each head, the oxide scale, slag and other sundries on the workpiece surface of the tire mold must be removed, and the pull ring must be evenly coated with lubricant
When cold stretching the head, the upper and lower dies, the blank holder working face and the upper and lower parts around the blank shall be coated with lubricant.

Preparation of lubricant

  • Hot drawing: graphite powder + engine oil
  • Cold drawn stainless steel: talc + soap + oil

Blank preloading

In order to avoid wrinkling and bulging when stretching the thin head, the blank can be pre pressed into an arch for the first time.
When the oval head S/Di=0.6-2, the embossing R0.8-0.9Di.
For the head with large diameter and thin wall, it can be embossed for 2-3 times, from shallow to deep to the specified r value.
The weld joint reinforcement of the spliced blank must be polished to be flush with the base metal before pressing. When the plates are spliced, the distance between the outermost weld and the plate center shall be less than 0.25di, and the minimum plate width shall not be less than 300mm( Di – inner diameter of head)
After the spliced blank is embossed, it is necessary to strictly check whether there are cracks with a magnifying glass. When there is doubt, the surface flaw detection can be carried out
When the spliced blank plate is convex and cracks occur at the welded joint, the cracks shall be removed, and the welding repair and flaw detection shall be carried out according to the process requirements.

Heating and stretching

See table 4.1 for heating and final pressing temperature of head blank
Special steel grades shall be carried out according to the special process, and the composite stainless steel plate shall be heated according to the requirements of the composite layer.

Table 4.1

Texture of material

Hot working temperature ℃

 

Heating

Final pressure

Q235A、20R

1000-1050

≥700

16MnR、15MnVR、15MnVNR、12CrMoR、15CrMoR、12Cr2M01R

950-1050

≥700

OCr18Ni9、1Cr18Ni9Ti、1Cr18Ni9、00Cr19Ni11、0Cr18Ni11Ti、1Cr19Ni9、00Cr17Ni14Mo2、00Cr17Ni12Mo2、

950-1100

≥850

The blanks shall be placed in the heating furnace with support. When multiple blanks are just heated, 50 ~ 100mm thick support pads shall be added between the blanks. The blanks shall not be overlapped to prevent over burning or incomplete burning.
The concave surface of the convex head blank shall face upward.
The composite layer of the composite plate blank is upward.
When the process requires the head with heat treatment confirmatory test plate, the test plate shall be charged and discharged simultaneously with the head blank.
When the blank is heated to 800 ~ 850 ℃, it shall be insulated according to the thickness of 0.8min/mm. After the temperature of the blank is uniform, continue to raise the temperature to the heating temperature to prevent overheating or overburning.
After the head blank is discharged from the furnace, it shall be lifted to the tire mold immediately and aligned quickly to ensure the stamping temperature of the head.
The speed of stretching shall be uniform and appropriate.
The final pressing temperature of hot pressed carbon steel head shall not be lower than 700 ℃. Generally, heat treatment is not required. However, if the final pressing temperature is less than 700 ℃, stress relief annealing must be carried out. Heads with special requirements shall be subject to special process.
Stainless steel and composite stainless steel heads shall be rapidly heated (or cooled) within the range of 450 ℃ ~ 850 ℃, and the final pressure temperature shall not be lower than 850 ℃, otherwise solid fusion treatment shall be carried out.
After demoulding, the head shall be cooled to below 550 ℃ before lifting to prevent deformation.

Orthopedic

Cold straightening or local hot straightening is allowed for the head. During cold correction, split die can be used. When hammering correction, flat plate or sizing block shall be padded. It is not allowed to directly hit the workpiece. During thermal correction, the initial correction temperature is 900-l050 ℃, and the final correction temperature is not lower than 700 ℃.
The fold on the straight edge of the head shall be ≤ 1.5mm, other defects and scars shall be polished evenly and smoothly, and the polished thickness shall not be less than the minimum specified thickness.
After straightening the welded joint of the head splice, strictly check whether there are cracks. If there are cracks, they shall be removed and repaired according to the process regulations.
Head straightening and repair welding must be carried out before heat treatment, and generally only cold straightening is allowed after heat treatment.
When the cold extension head of carbon steel and low alloy steel and the final pressure temperature of blocking extension are lower than the allowable final pressure temperature of its material, the head shall be normalized.

Deviation of size and shape

Tolerance of internal diameter

Nominal thickness δn

Inner diameter Di

Tolerance of outer circumference

3<δs≤12

300≤Di≤2000

+9
-3

 

2000<Di≤4000

+12

-6

12<δs≤20

800≤Di≤2000

+12
-6

 

2000<Di≤4000

+15

-9

 

4000<Di≤5200

+18
-12

20<δs≤32

1600≤Di≤2000

+12

-6

 

2000<Di≤2000

+15
-9

 

4000<Di≤5200

+18

-12

Difference between maximum and minimum internal diameter

The difference between the maximum internal diameter and the minimum internal diameter on the same section at the end of the head e<0.5%Di, but when δs/ Di<0.005, When δs/ Di<12mme<0.8% Di and not more than 25mm.

Tolerance of total depth and straight edge height

The tolerance of total depth and straight edge height of head shall be as specified in Table 6.
Table 6 mm

Inner diameter

Total depth tolerance

Straight edge height tolerance

300≤Di<2000

1% Di

+5

-3

2000≤Di<3000

0-0.8% Di

3000≤Di<4000

0-0.7% Di

4000≤Di≤5200

0-0.5% Di

Straight edge inclination tolerance

The inclination of the straight edge of the head outward shall not be greater than 6% h, and the inclination inward shall not be greater than 4% h.

Minimum thickness of head

The minimum thickness of the formed head shall not be less than the nominal thickness minus the negative deviation cof the steel plate thickness.

Shape deviation of inner surface of head

The deviation between the shape of the inner surface of the head and the template with chord length ≥ 3/4Di shall not be greater than 1.25% Di, and the parts with deviation shall not be prominent.

Source: China Elliptical Head Manufacturer – Yaang Pipe Industry (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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