Analysis on the Development of Composite Material Pultrusion Technology and its Application

 

Pultrusion technology originated in the United States in 1948. In the early 1960s, there were only about 20 manufacturers, mainly in the United States. Today, there are more than 90 pultrusion process manufacturers in the United States, Western Europe, and Japan. The annual market size of pultruded composite profiles abroad is between 250,000 and 300,000 tons, of which 100,000 tons is in the United States. In 2013, my country’s pultruded product output reached 280,000 tons, accounting for about 50% of the global output. Pultruded profiles are widely used in electrical/apparatus, corrosion-resistant solutions, construction, transportation, military and consumer products.

 

Advantages of Pultrusion

 

Figure 1 Schematic diagram of pultrusion process principle.

 

Figure 2 Pultrusion production line

 

Typical pultrusion line speed is 0.5-2m/min, with high production efficiency, suitable for mass production and manufacturing of long-sized products;

 

Resin/fiber content can be precisely controlled;

 

Since the fiber is longitudinal and the volume ratio can be high (40%-80%), the axial mechanical properties of the profile can be very good;

 

Mainly reinforced with untwisted roving, the cost of raw materials is low; a variety of reinforcing materials are used in combination to adjust the mechanical properties of the product;

 

Products with complex concave and convex cross-sectional shapes can be manufactured;

 

The product quality is stable and the appearance is smooth.

 

The Development Process of Pultrusion Technology in my Country

 

Technology Source

 

1) Technical literature on pultrusion molding in Japan, Europe and the United States;

 

2) Introducing foreign pultrusion molding technology and production lines to inspire and refer to us

 

According to statistics, my country has introduced 46 pultrusion production lines from PULTREX in the UK, PC, CPE, CPA, ADVANCED COMPOSITES, PULTRUSION TECHNOLOGY, FIBERFLEX, COAST, BROTHER in the United States; TOPGLASS in Italy, INLINE FIBERGLASS, OMNLGLASS in Canada, Jincai in Taiwan Province, Jie Lide in Hong Kong and other companies. Some companies also introduced the production technology of certain pultrusion products when introducing equipment, such as glass fiber reinforced plastic rebar, pumping rod, doors and windows, etc.

 

By digesting and absorbing the technology of foreign pultrusion process and its production equipment, from original imitation to independent innovation, our comprehensive pultrusion technology has reached the international level (not advanced, let alone leading), and the introduction has played a significant role in promoting it. However, it must be pointed out that due to certain reasons, some equipment that was not advanced and was quite poor and lower than the domestic level at that time was also introduced from abroad. It was not only enterprises that suffered losses, but also institutes! Waste of foreign exchange!

 

“Huangpu Military Academy” effect

Some units that have done well in pultrusion have either actively or passively exported talents and technologies, becoming the main force of pultrusion production, and even “outperforming the master”, becoming the leader of the industry. For example, many entrepreneurs of pultrusion enterprises in the Shanghai-Nanjing area came from Xingya Fiberglass Co., Ltd. under Nanjing Fiberglass Research and Design Institute; for example, Xi’an Insulation Materials Factory introduced British pultrusion production line technology, and its technology spread to Hebei, Heilongjiang and other places…

 

No Lack of Independent Innovation

Like my country’s fiber winding, enterprises are the main body of my country’s pultrusion technology innovation. Some of them may not have high education, some are workers, peasants and soldiers, and some are demobilized soldiers, but there is no lack of innovative achievements, which will be discussed below.

 

Review of Development History

 

Initial Trial [1960s-1970s]

The Fourth Research Laboratory of Beijing Factory 251 (Beijing FRP Research Institute) during the Cultural Revolution began to study pultrusion in 1968 and passed the internal appraisal in 1974. At that time, there was no concept of pultrusion machine at all. They made do with what they had and used winch wire rope traction, thermosetting phenolic resin as the matrix to successfully draw 25×40mm FRP channel steel and 8-20mm diameter pipes.

 

Exploration (1980s)

Some research institutes, colleges and enterprises have devoted themselves to the independent research and development of pultrusion technology and equipment. For example, Jiangsu Jiuding New Materials Company has conducted in-depth research on the principle and specific component structure of pultrusion machines; Wuhan University of Technology (now University of Science and Technology) has produced small-diameter circular cross-section pull rods and antennas by pultrusion.

 

Beijing Factory 251 successfully drew motor slot wedges and egg-shaped cross-section profiles, the latter of which are used to produce parallel bars and high and low bars. This complete set of technology and pultrusion production line was transferred to Tianjin Lisheng Sporting Goods Company, whose products were successfully used in the 1990 Asian Games, and Lisheng won an award for this project.

 

In 1985, Harbin FRP Research Institute took the lead in introducing American pultrusion machines. The following year, Qinhuangdao Huabodao Yao FRP Factory and Xi’an Insulation Materials Factory introduced British PULTREX pultrusion machines. Subsequently, no less than 46 units were introduced in various places. .

 

Progress (1990s)

Shashi Steel Pipe Factory and Qinhuangdao Yaohua FRP Factory began to produce FRP sucker rods.

 

Jinzhou developed FRP door and window technology, and a glass door and window craze was set off in China. FRP windows are a good product, but due to price and other reasons, they have not been expanded, and the actual annual output has never exceeded 500,000 square meters.

 

Harbin FRP Research Institute has vigorously developed pultrusion technology, and developed grain machine booms, oil pumping rods, tourist (pocket) tents, 110-500KV synthetic insulator pultrusion core rods, pultrusion molding units, and compiled the “Test Method for Mechanical Properties of Pultruded Glass Fiber Reinforced Plastic Rods” standard, which won the third prize of the ministerial scientific and technological progress in the building materials industry.

 

Its articles published in the “Fiber Composite Materials” journal were cited by many aviation departments and other departments; 30 crawler pultrusion machines were manufactured, but unfortunately they were not promoted in time.

 

The book “Fiberglass Pultrusion Technology and Products” edited by Yue Hongjun, the then chairman of Sino-Italian FRP Company, was published. This is the only monograph on pultrusion in China so far, and it still promotes the progress of pultrusion technology.

 

A private enterprise in Wuxi has developed online film coating technology for pultrusion of vegetable greenhouse poles.

 

The subway contact rail protection cover designed by Wuhan University of Technology and manufactured by Harbin FRP Research Institute and Shandong Wucheng North FRP Factory was successfully used in the Tehran Metro in Iran.

 

Many pultrusion product production and equipment manufacturing companies have emerged.

 

Advancing into Depth and Breadth (since the 21st century) Pultrusion winding, online braided pultrusion, resin injection impregnation, fiber pre-tensioning, microwave heating of non-metallic molds for pultrusion, induction heating of steel molds and other technologies have been gradually promoted.

 

The technical content and added value of pultrusion production equipment and its products have been improved. Facing both domestic and foreign markets, the application field of products has been broadened. Pultrusion complete sets of technology and pultrusion products have entered the markets of developed countries such as Europe, the United States and Japan.

 

Technological Progress in Recent Years

 

Raw and Auxiliary Materials

 

Reinforcement Materials

 

Compared with plied yarn, the direct untwisted roving for pultrusion produced by my country’s glass fiber pool kiln drawing can better exert the mechanical properties of the fiber and improve the quality of pultruded products. The fibers of glass fiber continuous filament felt are randomly distributed, the structure is loose and elastic, and it is easy to be impregnated with resin during pultrusion molding, which can improve the lateral strength of the product and improve the surface quality. For a long time, products imported from the United States have been used.

 

In the past few years, manufacturers have been producing in Nanjing and Danyang. It is known that the continuous felt production line designed by Jiangsu Jiuding New Materials Co., Ltd. and American experts has been put into production. Jiuding itself produces pultruded profiles, and its continuous felt must have good comprehensive properties such as processability.

 

Bulked yarn is conducive to improving the interface, improving mechanical properties, and improving the surface quality of pultruded products. Domestic enterprises that have introduced Canadian technology to produce door and window profiles have long adopted it, but unfortunately, the majority of pultrusion industry has not yet had this concept. In the final analysis, it is probably a price issue.

 

Glass fiber stitched felt has been widely used by pultrusion industry. It is not easy to cause product cracking when using only untwisted coarse yarn, and it greatly increases the lateral strength.

 

Glass fiber and polyester surface felts have been domestically produced and used for pultrusion, and there are also felts that are printed and used for pultrusion product surface decoration. Glass fiber/synthetic fiber composite yarn (similar to Twintex) can be used to produce pultruded thermoplastic fiberglass products.

 

T700 carbon fiber has been successfully used in pultrusion molding to manufacture cable cores, pumping rods (belts) and other products. The worrying thing is that T700 is a Japanese product, and the current price is as cheap as 185 yuan/kg. It is certainly beneficial to our pultrusion production enterprises, but many of our carbon fiber enterprises with high investment suffered losses in the entire industry last year, and the stability of product quality needs to be improved. ……2) Matrix resin and its additives

 

The most commonly used resin for pultrusion molding is unsaturated polyester resin (UPR), which requires good activity and thermal stability. The products of mainstream resin manufacturers can mostly meet the process requirements.

 

The curing agent used for UPR for pultrusion has also improved: after the early formula TBPB (tert-butyl perbenzoate) + MEKP (methyl ethyl ketone peroxide) brought by the equipment introduced from the United States, the TBPB + BPO (benzoyl peroxide) brought in by Taiwanese businessmen, the latter increases the pultrusion speed by 40% to 60% compared with the former; now TBPB + TBPO (tert-butyl peroxyethyl ethyl ketone), its pultrusion speed can be 50% faster than the second, and the surface quality of the profile has been improved. BPPD (diphenyloxyethyl peroxydicarbonate) is known as a new type of high-efficiency curing agent for pultrusion. It can be used alone or with TBPB and (or) TBPO. The pultrusion speed can reach 2m/min at mold temperature T1=85~140℃, T2=130~170℃.

 

The domestic new phenolic resin is used for pultrusion, achieving good technical and economic results. It is mostly used to manufacture products that require flame retardancy and low smoke. It also has good acid resistance and temperature resistance. The performance of domestic phenolic gel coat is better than that of imported products. Our epoxy resin is successfully used to produce insulating rods, reverse osmosis pipes and other products.

 

Two-component thermosetting polyurethane resin (PUR) has high activity, fast pultrusion speed, mechanical properties (especially interlaminar shear strength) and chemical corrosion resistance better than traditional resins, high lateral strength without continuous felt, and fiber content of up to 80%Wt, so it is cost-effective. There are four domestic companies that use it to produce pultruded products. The PUR used is purchased from Bayer, a German company, and Huntsman, an American company. There are no official products from domestic companies yet.

 

Process (in chronological order)

 

Online pultrusion foaming to produce PU heat and sound insulation blocks

 

Figure 3 Tianjin Yuhua online pultrusion foaming PU production line

 

In-situ Reaction Pultrusion of PMMA (Shanghai Jieshijie, Institute of Chemistry, Chinese Academy of Sciences) Using low-viscosity PMMA (methyl methacrylate) (or acrylic mixture) prepolymer as the impregnation liquid and a specially formulated free radical initiator as the initiation system, a continuous fiber-reinforced polymethyl methacrylate composite material was manufactured through a continuous in-situ impregnation pultrusion process.

 

In this composite material, complete fiber impregnation and controllable fiber-resin interface bonding were achieved, so that the performance of continuous fiber-reinforced PMMA composite materials can be regulated.

 

Table 1 Performance of different fiber-reinforced PMMA composites

 

Figure 4 SEM photo of the cross section of pultruded composite material

 

Pultrusion

 

Figure 5 Schematic diagram of the winding process

 

Figure 6 Part of the pultrusion molding process

 

Online Weaving and Pultrusion

Figure 7 Schematic diagram of online braided pultrusion process (CCIA)

 

Resin Injection Technology

 

Figure 8 Flow chart of pultrusion molding by resin injection molding

 

 

Figure 9 Resin injection system layout

 

Electromagnetic Induction Heating of Metal Molds

Figure 10 Schematic diagram of electromagnetic induction heating

 

Prepreg Pultrusion Technology

 

Figure 11 Prepreg pultrusion process flow chart

 

 

Figure 12 Prepreg preforming (China Southern Airlines)

 

Fiber Pre-tensioning (Tianjin Jinmao) Before the fiber enters the mold, tension is applied as appropriate, and the longitudinal strength and stiffness of the pultruded product are increased by 10%-20%.

 

Large Diameter Epoxy Fiberglass anaerobic rod pultrusion technology Using technologies such as no release agent and vacuum injection resin, the maximum rod diameter that can be drawn is 130mm (according to Mr. Martin from the United States, the maximum rod diameter is 42mm, and the pultrusion line speed is 0.7m/min).

 

Continuous Glass Fiber Reinforced PU Foam Product Production Technology

 

Figure 13 Continuous glass fiber reinforced polyurethane/phenolic foam sandwich panel production line

 

Reaction Injection Pultrusion Technology

Figure 14 Reaction injection pultrusion process line

 

Figure 15 Reaction injection pultrusion die

 

Hybrid Composite Pultrusion Technology

 

Pultrusion Machine and Related Equipment design and manufacturing technology

 

Reinforcement/Anchor Manufacturing Technology

 

Curved Profile Production Technology

 

Application of Pultruded Products

 

Figure 14 Market of pultruded composite materials in Europe, America and Japan

 

The market in developed countries is mainly electronic appliances, construction, industrial equipment, transportation, and amusement facilities. My market is similar to theirs. Here are some examples: 1) Protective cover for mobile communication base station antenna.

 

High Temperature Resistant Composite Insulator Core Rod

 

Transmission Cable Carbon Core

 

Figure 15 CFRP core and traditional steel core transmission cable

 

Figure 16 CF cable core production line

 

Bridge

 

Figure 17 A pedestrian bridge built in Spain using fiberglass profiles manufactured by Nanjing Sibeier Company

 

Doors and Windows

 

Figure 18 Fiberglass windows are superior to traditional windows

 

Grille

 

Figure 20 Grilles are widely used in industry, transportation, municipal administration and other fields

 

CFRP Continuous Pumping Rod

Figure 21 Carbon fiber reinforced composite material anti-eccentric wear continuous pumping rod (Shengli Oilfield Xinda Group)

 

Metro Third Rail (Contact Rail) Protection Cover

Figure 22 Third rail protection cover and its support

 

Figure 23 The Tehran subway in Iran uses protective covers produced by Harbin Fiberglass Research Institute and Shandong North Company

 

Subway Evacuation Platform

Figure 24 The subway evacuation platform uses phenolic resin pultrusion profiles

 

Helicopter Platform

 

Figure 25 Helicopter platform

 

Railway Track Sleepers

 

Figure 26 Glass fiber reinforced polyurethane sleepers

 

Reverse Osmosis Pipe

Figure 27 Dalian Shengquan’s reverse osmosis pipes made by winding and weaving are successfully used in water treatment

 

Scaffolding

Figure 28 Scaffolding assembled by pulling fiberglass pipes

 

Ladder

 

Figure 29 GRP ladder

 

Parallel Bars

 

Figure 28 The horizontal bar of the parallel bars and high and low bars is pultruded fiberglass

 

Comments and Suggestions

 

Comments

 

1) According to statistics, the number of pultrusion machines in mainland my country has reached 3,000, which is very impressive in terms of quantity. Although the industry is uneven, overall, our pultrusion development has stepped over the low-level stage;

 

2) We must face up to the fact that there are very few truly original things in China. For example, the approved national invention patents such as “online weaving pultrusion” and “in-mold resin injection” were already available abroad in the last century, which shows that there is a lack of learning and communication and a narrow view of the world. Some people believe that we are 20 years behind developed countries in terms of technological research level. Although the United States and Europe are now purchasing profiles and pultrusion equipment in my country, it is mainly due to price factors;

 

3) Enterprises have become the main body of innovation. It is hoped that relevant universities and research institutes will leverage their own advantages and truly achieve the combination of production, learning and research, so as to actively promote technological progress and industrial upgrading.

 

Suggestions

 

1) Actively develop new products facing domestic and foreign potential markets, so that they are at the top of the technology and market competition;

 

2) Develop and adopt new resins, curing agents, and curing systems to increase the pultrusion line speed;

 

3) Use the principle of mechanical relative motion to develop special-shaped products. For example, Germany’s “reverse pultrusion technology” in recent years is an example;

 

4) Develop fiber-reinforced thermoplastic pultrusion technology and its products, and consider using glass fiber/synthetic fiber composite yarn, which has a simpler process;

 

5) Develop prepreg pultrusion;

 

6) Further develop microwave heating and electromagnetic induction heating technology to increase pultrusion line speed, save energy, and reduce mold preheating time.

 

7) Finland’s Fiberline Company has set up a factory in Tianjin to produce wind turbine blade components and other products. Can my powerful enterprises step out of the country in light of the current situation?