Pultrusion
The extrusion process (including pultrusion or pultrusion ) is a continuous production process for the production of fiber-reinforced plastic profiles.
History
Early in 1954, Ernst Kühne the extrusion process ( pultrusion ) in a technological laboratory development of an international electrical group. He succeeded in the first drawing products with glass rovings - impregnated with epoxy resin - own manufacture. Apart from the actual production Ernst Kühne developed previously required to machinery, the exact shape drawing tools. The first electrical, chemical and mechanical parameters of a pultruded profile were determined at this time. After the founding of the first European Pultrusionsunternehmens, the Ernst Kuehne plastic factory was.
At the same time developed WB Goldworthy as one of the pioneers of fiber composite technology, the extrusion process in the United States. The emphasis here, however, in the production of aluminum on polyester resin base, while Ernst Kuehne dealt mainly with profiles based on epoxy resin.
Beginning of the 1960s there were about 20 manufacturers - mainly in the U.S. - while nowadays about 90 manufacturers serving the main markets in the USA, Europe and Far East world. In Europe alone, the market volume is estimated at 16,000 tons per year.
Starting materials
A fibrous composite material consists of a reinforcing fabric embedded in a matrix. As the matrix, both thermoset and thermoplastic polymers may be used. A thermosetting matrix systems the relatively inexpensive polyester resins, vinyl ester resins and epoxy resins are used.
To special features such as sliding properties to improve subsequent deformation under heat and abrasion resistance, and thermoplastic fiber composites can be produced. The matrix systems are mainly polyamides, polypropylenes and polyethylenes used.
Predominantly synthetic fibers as a reinforcing material of glass, carbon and aramid are used, which can be used as roving, scrims, woven or nonwoven fabrics. Thus, the properties can be varied over a wide range in absolute terms and in their relation between longitudinal and transverse direction.
Method
The basic structure of a pultrusion system consists of the following elements:
- Fiber shelf
- Fiber guides
- Impregnating
- Molding or Härtungswerkzeug
- Puller
- Cutting unit
In the pultrusion process, the fiber rovings over fiber guides from a multi-storey coil stock in the resin bath, the impregnator out. The fibers pass through several stations preform so that they are brought up to the desired profile shape. At the fiber guides mats, woven fabrics, nonwovens or can be integrated into the process to adjust the mechanical properties compared to that of a purely unidirectional reinforcement, as is achieved by fibers optimize / to.
Basically, one can distinguish between the following three methods for resin impregnation:
When the method, the reinforcing fibers are introduced from above and drawn through an open resin bath in which the fibers are deflected by means of pinholes. This method is the most commonly used for the production of pultruded profiles, in particular with a simple cross-sections. The impregnation and the impregnation takes place in an open resin bath through which the dry fibers are drawn. The deflection of the fibers into and out of the bath of resin is carried out by guide aperture.
This procedure is particularly used in the manufacture of profiles with cross-sections geometrically complex. The reinforcing fibers are passed without deflection through the resin bath, so that the impregnation unit will run through horizontally. Nearby preform stations that resemble the later profile shape at the entry and exit side of the resin bath. The smeared by the fiber guides matrix is trapped under the padding mangle with a tub.
During the injection process, the reinforcing fibers are guided without deflection by Imprägnierwerkzeug. This tool has the shape of the profile, and extends to the inside. In this cavity, the resin is injected from both sides transversely to the fiber direction. This method finds application in the production of simple profiles with high volumes.
In a cooled mold with a length of 0.5 m to 2.5 m then C will find the ultimate shape of the profile and the hot curing at temperatures between 100 ° C instead of 200 °. The finished profile, and thus the fibers together with the matrix system, and the reinforcing material are pulled by a subsequent pulling device, for example in the form of a caterpillar take-off or pneumatic grippers continuously and at a constant speed from the tool (thus the English name pultrusion from to pull - pull and extrusion - the -press). The grippers work according to the so-called alternating principle: During a gripper under pressure clamps the profile, drives the other back to the initial situation. At the end of the gripping path of the second gripper handles the drawing, without an interruption occurs in promoting. The drawing rate of the process is adapted to the wall thickness, the complexity of the profile cross-section as well as to the matrix system. Usually is a process speed of 0.1 m / min to 1.2 m / min.
Scope
The pultrusion process is suitable to produce (relatively) low-cost fiber-reinforced plastic profiles. The quality of the composite thus obtained is. Due to the high curing temperature and the constant conditions well above the achievable with cold cured hand process quality Higher quality can be achieved by consuming prepreg autoclave process.
A special problem is the control of the curing reaction of the resin at high profile cross-sections, which can lead to shrinkage cracks the so-called "center cracks ".
In particular, the rate of production, coupled with the high degree of automation and the associated lower costs, creates fiber-reinforced plastic profiles, produced by pultrusion, new application fields, such as a constructive substitute for steel sections in building construction, light construction or in areas with high corrosion. These profiles are defined in EN 13706-1 ... 3.
The same applies to the manufacture of fiberglass - reinforcement. Application and properties of these products are regulated by an approval of the relevant construction product DIBt.
A limitation of the use of pultruded GRP profiles until recently was given by the fact that in this method only straight profiles could be produced. In the figure, " Various Pultruded just " some exemplary profiles are shown.
Recent modifications of the method
Whereas in the standard procedure due exclusively straight profiles can be produced by the process flow, wherein the profile is pulled through a stationary mold, is achieved by a reversal of the process of this problem.
This reverse process, called the radius pultrusion, was developed in 2008 by the Thomas GmbH Co. KG Technology Innovation. In contrast to the standard method, in this method, the mold cavity of which corresponds to the course of the desired profile, to move gradually on the resulting profile. Being in this process simply existing gripper holds the profile during the forward movement of the mold and gives the resulting profile in the backward movement of the mold free again, as shown in the illustration process flow of Radiuspultrusion.
With this method and its variants, it is possible to produce almost any curved profiles, for example, screw-shaped profile.