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Fiberglass winding technology-1

The filament winding process is one of the resin matrix composite manufacturing processes. There are three main forms of winding, hoop winding, plane winding and spiral winding. The three methods have their own characteristics, and the wet winding method is the most widely used because of its relatively simple equipment requirements and low manufacturing cost.

The dimensional winding process is one of the main manufacturing processes of resin-based composite materials. It is a kind of continuous fiber or cloth tape impregnated with resin glue under the condition of controlled tension and predetermined line shape, and then continuously, uniformly and regularly wound on the core mold or lining, and then at a certain temperature It is cured under the environment to become a composite material molding method for products of a certain shape. Schematic diagram of filament winding molding process 1-1.

There are three main forms of winding (Figure 1-2): hoop winding, plane winding and spiral winding. The hoop-wound reinforcing material is continuously wound on the core mold at an angle close to 90 degrees (usually 85-89 degrees) with the axis of the mandrel. The inner direction is continuously wound on the core mold, and the spirally wound reinforcement material is also tangent to the two ends of the core mold, but is continuously wound on the core mold in a spiral state on the core mold.
The development of filament winding technology is closely related to the development of reinforcing materials, resin systems and technological inventions. Although in the Han Dynasty there was a process of impregnating long wooden poles with longitudinal bamboo silk and hoop silk and impregnating them with lacquer to make long weapon poles such as Ge, Halberd, etc., it was not until the 1950s that the filament winding process truly became a composite material manufacturing technology. . In 1945, the filament winding technology was used to successfully manufacture a springless wheel suspension. In 1947, the first filament winding machine was invented. With the development of high-performance fibers such as carbon fiber and aramid fiber and the emergence of microcomputer-controlled winding machines, the filament winding process, as a composite material manufacturing technology with a high degree of mechanized production, has been rapidly developed. All possible areas have been applied.

According to the different chemical and physical states of the resin matrix during winding, the winding process can be divided into three types: dry, wet and semi-dry:

1. Dry method
Dry winding uses pre-impregnated yarn tape that has been dipped in advance and is in stage B. The prepreg tape is manufactured and supplied in a special factory or workshop. In dry winding, the prepreg tape needs to be heated and softened on the winding machine before being wound onto the core mold. Since the glue content, tape size and quality of the prepreg tape can be detected and screened before winding, the quality of the product can be controlled more accurately. The production efficiency of dry winding is higher, the winding speed can reach 100-200m/min, and the working environment is cleaner. However, the dry winding equipment is more complicated and expensive, and the interlayer shear strength of the wound product is also low.

2. Wet
Wet winding is to bundle fibers, dipped in glue, and directly wind them on a core mold under tension control, and then solidify and shape. The equipment for wet winding is relatively simple, but because the tape is wound immediately after dipping, it is difficult to control and inspect the glue content of the product during the winding process. At the same time, when the solvent in the glue solidifies, it is easy to form defects such as bubbles and pores in the product. , The tension is not easy to control during winding. At the same time, workers operate in an environment where solvents evaporate and short fibers are flying, and the working conditions are poor.

3. Semi-dry
Compared with the wet process, the semi-dry process adds a set of drying equipment on the way from the fiber dipping to the winding to the core mold, which basically drives out the solvent in the yarn tape glue. Compared with the dry method, the semi-dry method does not rely on a complete set of complex prepreg process equipment. Although the glue content of the product is as difficult to accurately control as the wet method in the process, and there is an additional set of intermediate drying equipment than the wet method, the labor intensity of the workers is greater, but the defects such as bubbles and pores in the product are greatly reduced.
The three methods have their own characteristics, and the wet winding method is the most widely used because of its relatively simple equipment requirements and low manufacturing cost. The advantages and disadvantages of the three winding process methods are compared in Table 1-1.

Main application of winding forming process

1. FRP storage tank
Storage and transportation of chemical corrosive liquids, such as alkalis, salts, acids, etc., steel tanks are easy to rot and leak, and the service life is very short. The cost of changing to stainless steel is higher, and the effect is not as good as that of composite materials. The fiber-wound underground petroleum glass fiber reinforced plastic storage tank can prevent petroleum leakage and protect the water source. The double-wall composite FRP storage tanks and FRP pipes made by the filament winding process have been widely used in gas stations

2. FRP pipes
Filament-wound pipe products are widely used in oil refinery pipelines, petrochemical anticorrosive pipelines, water pipelines, and natural gas pipelines because of their high strength, good integrity, excellent comprehensive performance, easy to achieve efficient industrial production, and low overall operating costs. And solid particles (such as fly ash and minerals) transportation pipelines and so on.

3. FRP pressure products
The filament winding process can be used to manufacture FRP pressure vessels (including spherical vessels) and FRP pressure piping products that are under pressure (internal pressure, external pressure or both).
FRP pressure vessels are mostly used in military industry, such as solid rocket engine shells, liquid rocket engine shells, FRP pressure vessels, deep water external pressure shells, etc. FRP-wrapped pressure pipes can be filled with liquid and gas, and will not leak or damage under certain pressure, such as seawater desalination reverse osmosis pipes and rocket launch pipes. The excellent characteristics of advanced composite materials have enabled the successful application of rocket engine shells and fuel tanks of various specifications prepared by the filament winding process, which has become the main direction of engine development now and in the future. They include the attitude-adjustable engine housings as small as a few centimeters in diameter, and the engine housings for large transport rockets as large as 3 meters in diameter.

Repair method of FRP winding pipe

1. The main reasons for the sticky surface of composite products are as follows:
a) High humidity in the air. Because water vapor has the effect of delaying and inhibiting polymerization of unsaturated polyester resin and epoxy resin, it can even cause permanent stickiness on the surface, and defects such as incomplete curing of the product for a long time. Therefore, it is necessary to ensure that the production of composite products is carried out when the relative humidity is lower than 80%.
b) Too little paraffin wax in the unsaturated polyester resin or the paraffin wax does not meet the requirements, resulting in the inhibition of oxygen in the air. In addition to adding a proper amount of paraffin, other methods (such as adding cellophane or polyester film) can also be used to isolate the surface of the product from the air.
c) The dosage of curing agent and accelerator does not meet the requirements, so the dosage should be strictly controlled according to the formula specified in the technical document when preparing the glue.
d) For unsaturated polyester resins, too much styrene volatilizes, resulting in insufficient styrene monomer in the resin. On the one hand, the resin should not be heated before gelation. On the other hand, the ambient temperature should not be too high (usually 30 degrees Celsius is appropriate), and the amount of ventilation should not be too large.

2. There are too many bubbles in the product, and the reasons are as follows:
a) The air bubbles are not completely driven, and each layer of spreading and winding must be rolled repeatedly with a roller. The roller should be made into a circular zigzag type or a longitudinal groove type.
b) The viscosity of the resin is too large, and the air bubbles brought into the resin cannot be driven out when stirring or brushing. Need to add an appropriate amount of diluent. The diluent of the unsaturated polyester resin is styrene; the diluent of the epoxy resin can be ethanol, acetone, toluene, xylene and other non-reactive or glycerol ether-based reactive diluents. The diluent of furan resin and phenolic resin is ethanol.
c) Inappropriate selection of reinforcement materials, the types of reinforcement materials used should be reconsidered.
d) The operation process is improper. According to the different types of resins and reinforcing materials, appropriate process methods such as dipping, brushing, and rolling angle should be selected.

3. The reasons for the delamination of products are as follows:
a) The fiber fabric has not been pre-treated, or the treatment is not enough.
b) The tension of the fabric is insufficient during the winding process, or there are too many bubbles.
c) The amount of resin is insufficient or the viscosity is too high, and the fiber is not saturated.
d) The formula is unreasonable, resulting in poor bonding performance, or the curing speed is too fast or too slow.
e) During post-curing, the process conditions are inappropriate (usually premature thermal curing or too high temperature).

Regardless of the delamination caused by any reason, the delamination must be thoroughly removed, and the resin layer outside the defect area must be polished with an angle grinder or polishing machine, the width is not less than 5cm, and then re-layed according to the process requirements. Floor.
Regardless of the above defects, appropriate measures should be taken to completely eliminate them to meet the quality requirements.
Reasons and solutions for delamination caused by FRP pipes
Reasons for the delamination of FRP sand pipes:
Reasons: ①The tape is too old; ②The amount of tape is too small or uneven; ③The temperature of the hot roller is too low, the resin is not melted well, and the tape cannot stick to the core well; ④The tension of the tape is small; ⑤The amount of oily release agent Too much stains the core fabric.
Solution: ①The glue content of the adhesive cloth and the glue content of the soluble resin must meet the quality requirements; ②The temperature of the hot roller is adjusted to a higher point, so that when the adhesive cloth passes through the hot roller, the adhesive cloth is soft and sticky, and the tube core can be firmly adhered. ③Adjust the tension of the tape; ④Do not use oily release agent or reduce its dosage.

Foaming on the inner wall of the glass tube
The reason is that the leader cloth is not close to the die.
Solution: Pay attention to the operation, be sure to stick the leader cloth tightly and flat on the core.
The main reason for the foaming after curing of FRP or the foaming after curing of the tube is that the volatile content of the tape is too large, and the rolling temperature is low, and the rolling speed is fast. . When the tube is heated and solidified, its residual volatiles swell with heat, causing the tube to bubble.
Solution: Control the volatile content of the tape, appropriately increase the rolling temperature and slow down the rolling speed.
The reason for the wrinkling of the tube after curing is the high glue content of the tape. Solution: Appropriately reduce the glue content of the tape and reduce the rolling temperature.

Unqualified FRP withstand voltage
Causes: ①The tension of the tape during rolling is insufficient, the rolling temperature is low or the rolling speed is fast, so that the bonding between the cloth and the cloth is not good, and the residual amount of volatiles in the tube is large; ②The tube is not cured completely.
Solution: ①Increase the tension of the tape, increase the rolling temperature or slow down the rolling speed; ②Adjust the curing process to ensure that the tube is completely cured.

Issues that should be noted:
1. Due to the low density and light material, it is easy to install FRP pipes in areas with high groundwater levels, and anti-floating measures such as piers or rainwater runoff drainage must be considered.
2. In the construction of opening tees on the installed glass steel pipes and repairing pipeline cracks, it is required to be similar to the complete dry conditions in the factory, and the resin and fiber cloth used during the construction need to be cured for 7-8 hours, and the on-site construction and repair Repair is generally difficult to meet this requirement.
3. The existing underground pipeline detection equipment mainly detects metal pipelines. Non-metal pipeline detection instruments are expensive. Therefore, it is currently impossible to detect FRP pipes after being buried in the ground. Other subsequent construction units are very easy to dig and damage the pipeline during the construction.
4. The anti-ultraviolet ability of FRP pipe is poor. At present, the surface-mounted FRP pipes delay the aging time by making a 0.5mm thick resin-rich layer and ultraviolet absorber (processed in the factory) on its surface. With the passage of time, the resin-rich layer and UV absorber will be destroyed, thereby affecting its service life.
5. Higher requirements for the depth of covering soil. Generally, the shallowest covering soil of SN5000 grade glass steel pipe under the general roadway is not less than 0.8m; the deepest covering soil is not more than 3.0m; the shallowest covering soil of SN2500 grade glass steel pipe is not less than 0.8m; The deepest covering soil is 0.7m and 4.0m respectively).
6. The backfill soil shall not contain hard objects larger than 50mm, such as bricks, stones, etc., so as not to damage the outer wall of the pipeline.
7. There are no reports about the large-scale use of FRP pipes by large water companies across the country. Since FRP pipes are new types of pipes, the service life is still unknown.

Causes, treatment methods and preventive measures of leakage of high-pressure glass steel pipes

1. Analysis of the cause of leakage
FRP pipe is a kind of continuous glass fiber reinforced thermosetting resin pipe. It is too fragile and cannot withstand external impact. During use, it is affected by internal and external factors, and sometimes leakage (leakage, burst) occurs, which seriously pollutes the environment and affects the time of water injection. Rate. After on-site investigation and analysis, the leakage is mainly due to the following reasons.

1.1, the impact of FRP performance
Since FRP is a composite material, the material and process are seriously affected by external conditions, mainly due to the following influencing factors:
(1) The type of synthetic resin and the degree of curing affect the quality of the resin, the resin diluent and curing agent, and the glass fiber reinforced plastic compound formula.
(2) The structure of FRP components and the influence of glass fiber materials and the complexity of FRP components directly affect the quality of the processing technology. Different materials and different media requirements will also cause the processing technology to become complicated.
(3) The environmental impact is mainly the environmental impact of the production medium, atmospheric temperature, and humidity.
(4) The influence of the processing plan, whether the processing technology plan is reasonable or not directly affects the construction quality.
Due to factors such as materials, personnel operations, environmental influences, and inspection methods, the performance of FRP has declined, and there will be a small number of local failures of the tube wall, dark cracks in the internal and external screws, etc., which are difficult to find during inspection, and only during use. It will be revealed that it is a product quality problem.

1.2, external damage
There are strict regulations for the long-distance transportation and loading and unloading of glass steel pipes. If you don’t use soft slings and long-distance transportation, you don’t use wooden planks. The pipeline of the transport truck exceeds 1.5M above the carriage. During the construction backfilling, the distance from the pipe is 0.20mm. Stones, bricks, or direct backfilling will cause external damage to the glass steel pipe. During the construction, it was not discovered in time that the pressure overload occurred and the leakage occurred.

1.3, design issues
High-pressure water injection has high pressure and large vibration. FRP pipes: staggered pipes, which suddenly change in the axial and lateral directions to generate thrust, which causes the thread to disjoint and burst. In addition, due to the different vibration materials in the connecting parts of steel conversion joints, metering stations, wellheads, flowmeters and glass steel pipes, the glass steel pipes are leaking.

1.4. Construction quality issues
The construction of FRP pipes directly affects the service life. The construction quality is mainly manifested in that the buried depth is not up to the design, the protective casing is not worn across highways, drainage channels, etc., and the centralizer, thrust seat, fixed support, reduction of labor and materials, etc. are not added to the casing in accordance with the specifications. The reason for the leakage of FRP pipe.

1.5 External factors
The FRP water injection pipeline passes through a wide area, most of which are near farmland or drainage ditches. The sign post has been stolen for a long service life. Rural towns and villages use mechanization to carry out water conservancy infrastructure every year, causing pipeline damage and leakage.

Post time: Aug-12-2021