Manufacture and Application of Spiral Half Pipe Jacket for Single Cone Vacuum Dryer

The multifunctional pulse vacuum single-cone dryer is one of the new generation of agitating vacuum dryers developed by Wuxi ZhangHua Machinery according to the process requirements of the fine drying bag production line in the fine chemical industry. It adopts advanced process design and manufacturing technology and can process wet powder and filter cake. , pastes and slurries and other materials, especially suitable for products with large specific gravity, high viscosity and high sensitivity or containing toxic or explosive solvents. The single cone pulse mixing dryer is suitable for low vacuum operation and can be applied to other stages of the process, including: reaction-crystallization, heating-cooling, sterilization, liquid-solid separation and degassing

With the development of modern chemical industry, chemical production tends to large-scale and large-scale development, the output of a single production device is increasing, and the single-cone vacuum dryer is also gradually developing to large-scale. At this time, the diameter of the single-cone dryer increases, and the cone lengthens, especially when the jacket pressure is higher than 1.0MPa, the wall thickness of the inner cylinder increases, which increases the difficulty of the design and manufacture of the vacuum single-cone dryer, correspondingly It also increases the manufacturing cost of the equipment.

Therefore, it is more economical and reasonable to achieve the purpose of thinning the wall and increasing the pressure bearing capacity of the inner cylinder by selecting a suitable jacket structure.

The type and characteristics of the heating jacket of the single cone vacuum dryer
(1) Integral jacket
For the heating or cooling of stirring equipment, the most commonly used jacket type is the integral jacket, which is a container with a slightly larger diameter placed outside the equipment. It has the characteristics of mature processing technology, simple structure and convenient manufacture, so it has been widely used in the selection of chemical equipment design.

The disadvantage is that the heating area is limited by the geometry of the cylinder and cannot be made too large.
(2) Jacket with spiral deflector
The spiral guide plate is set in the jacket, which can not only guide the fluid in the jacket, better heat or cool the material in the container, but also reduce the calculated wall thickness of the container cylinder due to the reduced calculated length of the external pressure. . The disadvantage is that when the size of the deflector is large, it cannot be installed between the cylinder and the jacket, such as increasing the distance between the cylinder and the jacket or increasing the number of deflector circles and the wall thickness of the cylinder to reduce the diversion The method of plate size is a method of putting the cart before the horse. Furthermore, the cylinder, reinforcing ring, and jacket are all rigidly connected. Different materials and temperatures will generate great stress, so this structure should be avoided as much as possible.

(3) Half (round) pipe jacket
The semi-circular pipe jacket structure is divided into spiral type and pipe-row type according to the arrangement form, and divided into standard semi-circular pipe and bow-shaped pipe according to the shape of the semi-circular pipe. Compared with the overall jacket, the semi (circular) pipe jacket has the following characteristics: simple structure, strong pressure bearing capacity, and can effectively reduce the design wall thickness without changing the operation status of the container, save materials and reduce equipment costs , and can improve the strength and rigidity of the equipment against external pressure, and facilitate maintenance. This advantage is more obvious especially for large single-cone vacuum dryers with harsh external pressure conditions.

The disadvantage is that there are many welds and a large amount of welding, which brings certain difficulties to processing and manufacturing, and also increases the workload of non-destructive testing.
Problems and Analysis of the Manufacturing of the Spiral Half Return Pipe Jacket of the Single Cone Vacuum Dryer

Spiral semicircular pipe jacket (hereinafter referred to as half pipe) equipment has been widely used in European and American countries, and Germany has formed a standard in 1979. Compared with ordinary jacketed vessels, half-pipe equipment has the advantages of good cylinder stress, high heat transfer efficiency, energy saving and saving steel consumption, etc. It is a relatively reasonable and advanced jacket structure at present.

Wuxi ZhangHua Machinery conducted in-depth research on some manufacturers responsible for manufacturing, and learned that the manufacturing problem of the half-pipe jacketed container is one of the main problems affecting its promotion and application.
(1) Half pipe forming problem
Some manufacturers manufacture this part of the half pipe by using a ready-made round pipe, rolling it into shape according to the outer diameter of the cylinder, and then marking it. After scribing, go up the milling machine to mill off half of the pipe (it can't be used) to make it.

Therefore, this part of the half-pipe consumes a lot, and the processing amount is also large, and its relative cost is relatively high, and it is difficult to ensure the roundness of the inner diameter of the half-pipe after processing.
(2) The self-weight non-circular problem of the cylinder
Because this type of equipment is relatively long, it is only possible to put the equipment down and assemble and weld half pipes on the cylinder joint. Due to the self-weight of the equipment itself, even if it is rounded, it will become out of round after it is laid down.

However, some manufacturers did not take any measures, and directly assembled and welded the half pipes on the barrel joints, which caused hidden dangers in the future use of the equipment.
(3) Assembly problem of spiral half pipe and cylinder

The half-pipes made are first fixed on the wall of the device, and then the butt welds between the half-pipes are welded, so that the processing technology has caused the half-pipes to have no room for shrinkage after welding. Therefore, a large assembly stress will be left between the butt welds of the half pipe. This assembly stress is generally expressed as tensile stress, which can easily cause welding cracks and reduce the tensile strength of the weld.

Therefore, its processing technology needs to be improved.

Manufacturing solution of spiral half-pipe jacket for single-cone vacuum dryer
In response to the above problems, Wuxi ZhangHua Machinery spent more than a month reviewing the technical materials related to the manufacture of spiral half-pipe jackets in Japan, Germany and other countries. In a month's time, I finally found the specific manufacturing scheme design of the spiral half-pipe jacket of the single-cone vacuum dryer and the method to solve the above problems.
(1) roll forming
The half-pipe jacket is made of steel plate instead of the round pipe, and then roll-formed with a self-made half-pipe rolling machine.

The steel strips are formed on the rolling machine according to the pressure vessel "Round Rolling Process Code" to make the roundness meet the requirements of 10 and 13 of the pressure vessel GB150-89.
(2) Assembly of the spiral semicircular tube outside the cylinder
The manufacturing process of the spiral semi-circular tube is complex, with both the change of the helix radius and the change of the helix lead angle, which increases the difficulty of manufacturing. Once the manufacturing size is not in place, it will make assembly and welding more difficult. There are many butt joints of spiral semi-circular pipes, and the fillet welds are relatively long. In order to ensure the welding quality, the butt joints must be completely penetrated. However, it is difficult to detect flaws in the fillet welds of semi-circular pipes, and it is difficult to find internal defects (such as clamping slag, incomplete penetration, porosity, cracks, etc.).

This brings a lot of potential dangers to the use of equipment, so special technological measures have been formulated to solve the above difficulties.
(3) Cylinder preparation before welding
First erect the welded cylinder on the platform, confirm the upper position of the cylinder (0°, 90°, 180°, 270°) again, and draw the trajectory of the spiral semicircular pipe on the above four orientation lines In this way, the accuracy of the assembly can be guaranteed, and then the spiral semi-circular tubes are assembled and welded sequentially from bottom to top. For this purpose, tooling blocks and wedge blocks are made, so that the semi-circular tubes can be closely attached to the cylinder, so that the butt joints are staggered The amount is small, which is beneficial to ensure the welding quality.

(4) Welding process
In order to achieve full penetration of the butt joints, V-shaped grooves, blunt edges (1±1) mm, gaps of 2 to 3 mm, single-sided welding and double-sided forming are adopted, and welders are specially trained for welding.

For the circular fillet weld, in order to ensure its welding quality, after welding and heat treatment, in addition to the surface flaw detection inspection, a water pressure test and an air tightness test are also carried out. Once a leak is found, repair the welding in time and re-detect the flaw and press again. (After rigorous calculation, increase the test pressure to a certain multiple, and keep the pressure for a long enough time).
(5) Pressure test
Due to the complex structure of the single-cone vacuum dryer, the weld seam is too long and the welding position is poor, in order to ensure the welding quality, it is necessary to carry out a pressure test on the external coil after welding and heat treatment, and both the water pressure test and the air tightness test are done. , to meet product requirements.
The single-cone vacuum dryer spiral semi-circular tube jacketed reactor has high technical requirements, complex structure, and great manufacturing difficulties. It is necessary to fully consider the difficulties in the manufacturing and assembly process, formulate reasonable process measures and make necessary auxiliary tooling in advance.

During the manufacturing process, the parts are formed in strict accordance with the drawings and process requirements, and the deformation of the large flange after welding is prevented during the assembly and welding process, so as to improve the welding quality of the coil and the cylinder and control all key difficulties.