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Why Are the Vessel Heads Heated ?


Vessel Heads are an indispensable and important part of pressure vessel equipment in the petrochemical, atomic energy, food, pharmaceutical and other industries.

We all know that during the production process, pressure vessel heads are heated. So do you know why vessel heads are heated?

Reasons for heating of large stainless steel vessel heads and heads with thickness over 14mm: the size of heads is large, the plate thickness is thick, the deformation resistance is great and it is not easy to deform. Heating can improve the plasticity of the material and reduce the deformation resistance.

Reasons for heat treatment of cold-pressed and spun heads: After cold-pressed deformation (spinning is also carried out under cold state), hardness and strength of vessel heads increase, plasticity and toughness decrease and process hardening phenomenon appears. Heat treatment can eliminate this phenomenon, improve the plasticity and toughness of the material and reduce the hardness. Heating and heat treatment are not the same thing, but when heating and forming, the residual heat after forming has the effect of heat treatment, so the tank heads after hot pressing generally do not need to be heat treated again.

Vessel Head is an indispensable and important part of pressure vessel equipment in petrochemical, atomic energy, food, pharmaceutical and other industries. The processing technology is divided into: cold processing and hot processing, literally, the two are different processing technologies, the differences are as follows.

Thermal processing features.

1. Due to heating, material deterioration will occur, resulting in a decrease in corrosion resistance of stainless steel tank heads, which is not suitable for processing stainless steel heads

2. Heating forming causes thermal expansion of mould and cooling shrinkage of tank head, making the size difficult to control and consistency poor

3. Surface oxidation is serious and difficult to remove after forming of large vessel head.

Features of cold processing

1. No need to heat, no material deterioration, especially suitable for stainless steel tank head processing

2. No heating, no dimensional change due to cold shrinkage, regular shape, accurate dimension and good consistency

3. No need to heat, the surface of the vessel head after forming keeps the surface of the raw material smooth, and the appearance is beautiful.

What are the ways to heat the vessel head?

There are three main ways to heat the head, namely direct heating, indirect resistance heating and induction heating.

Resistance direct heating refers to heating by directing the current to the press die or the product.

Resistance indirect heating means heating with various external heating elements (such as graphite, nichrome alloy, molybdenum and other heating elements).

And induction heating means that the current is fed into the induction coil, causing the die and the product placed in it to be heated by eddy currents.

The way of direct heating of the tank head by resistance is simple to operate, but it is easy to cause uneven heating in the process of heating and consumes a lot of electric energy. Therefore, energy-saving heating method should be preferred in the heating process of hot pressed head moulds.

Matters needing attention in the heating process of standard stainless steel vessel head

1. When the standard stainless steel tank head blank is heated in the heating furnace, it should be heated with support when it is placed. If there are more than one piece, they should not be stacked to avoid the appearance of over-burning or perhaps impermeable burning.

2. When the blank is heated to 800℃-850℃, it should be insulated according to the rules, and then continue heating after the temperature of the blank is evenly distributed all over.

3. After the standard vessel head blank comes out of the furnace, it shall be quickly corrected on the tire die to ensure the stamping temperature of the head.

4. When stretching, the speed of stretching shall be moderate.

5. If it is a standard head, then the final pressing temperature should not be lower than 850℃, otherwise solid melting treatment should be carried out.

6. After the head is demoulded, lifting can only be carried out after the temperature drops below 550℃to avoid deformation of the head.

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