RU2243093C1 - Method of manufacturing of a prepreg and a device for its realization - Google Patents

Abstract

FIELD: chemical industry; manufacturing of prepregs.

SUBSTANCE: the invention is pertinent to chemical industry and to the methods of production of the prepregs - semi-finished items representing fibrous filler impregnated with a binding agent in a fixed weight ratio and ay be used in many industries at manufacturing structures out of reinforced composite materials, for example, vertical web members, rods, supports, pipes, containers and balloon tiers, with a filler in the form of the glass, organic and carbon filaments reprocessed using a "dry" winding technique. The method provides for coiling of the filler on a mandrel in spools, degassing and filling in with the binding agent. The filler coiling on a mandrel is made with volume of a free space equal to the required ratio of the binding agent and not less than 0.2 from the total volume of the formed spool. The degassing is conducted in a chamber for no less than 4 hours at a residual pressure not exceeding 10 mmHg. Filling in of the inter-fiber and inter-filament spaces of the spools with the binding agent is made by dipping of the spools with the filler under the same conditions of vacuum in the binding agent medium. When the volume of the binding agent above the spools exceeds the volume of inter-fiber and inter-filament spaces in the spool the chamber pressure is lifted up to the value no less than atmospheric pressure and keep the spool in the volume of the binding agent for no less than 4 hours. Then they wait till surplus of the binding agent flows down. The device for realization of the method contains: a vacuum chamber with a vacuum pump, a vacuum gate and a manometer; a container with the binding agent and spools with the filler. In the container with the binding agent there is a loading perforated platform with a central rod perpendicular to a plane of the platform and linked with a mechanism for pushing the platform down. The spools with the filler are installed on the loading perforated platform interleaving with the intermediate perforated demountable platforms. Between mandrels of the spools and the central rod there are load disks. The invention ensures a raise of quality of wettability of filaments and impregnation of a filler in a prepreg, reduction of inter-fiber and inter-filament porosity prior to beginning of an impregnation process, that allows to improve tightness of the items produced out of prepregs.

EFFECT: the invention ensures a raise of quality of wettability of filaments and impregnation of a filler in a prepreg, reduction of inter-fiber and inter-filament porosity and improvement of tightness of the items produced out of prepregs.

2 cl, 3 dwg

Description

The invention relates to the chemical industry in the field of polymers and the technology for the manufacture of semi-finished prepregs, which are a fibrous filler impregnated with a binder in a certain weight ratio [1], and can be used in many industries in the manufacture of structures made of reinforced composite materials, for example truss racks, rods, supports, pipes, containers and cylinders, with filler in the form of glass, organic and carbon filaments processed by the method of “dry” winding.

Several methods for making prepregs are known.

The most common of these is the method of passing a fibrous filler in the form of a thread, tow or tape through a bath with a binder solution. The filler is impregnated by the free binder pump method or with a squeezing device [2].

The process of impregnation of the filler is divided into two stages, which are often combined in time. The first stage is the application of a layer of liquid binder on the surface of the filler, the second is the impregnation of the filler, i.e. penetration of the binder deep into the structure of the material. The second, technological stage is a typical diffusion process [3]. The penetration of the binder deep into the structure of the impregnated material is prevented by the air inside the filler, which creates a pressure head. Moreover, the latter increases as the binder penetrates into the structure of the filler filaments. Therefore, to improve the quality of impregnation and reduce gas inclusions in the structure of finished fiberglass, it is advisable to impregnate under vacuum [2].

Conducted microstructural studies of fiberglass reinforced plastics showed that the relative porosity of the material is a very important characteristic of the quality of the processes of molding, impregnation and curing of fiberglass. The main reason for the appearance of pores is the air contained in the threads, roving, ribbons, as well as captured during the impregnation process.

In addition, the cause of the appearance of pores may be air inclusions contained in the binder, the amount of which depends on the type of binder, the speed of winding during molding, the viscosity and wettability of the binder [3].

Obviously, it is possible to eliminate or reduce porosity with more thorough evacuation of both the filler and the binder during its impregnation [4].

A known method of obtaining a tape prepreg, which consists in continuously winding the threads from the spool at a high speed (about 20 m / min), pulling them through the bath with a binder solution, where they are impregnated. Then the threads are formed with a special handler in a tape and immersed in a drying chamber. The dried tape is wound onto a take-up reel with the separation paper being inserted between the layers, which protects the prepreg from gluing [1].

The disadvantages of this method include damage to the fibers of the threads during their passage through the rotating and rubbing guides, squeezing rollers in the impregnation bath and the drying chamber. And since at high speeds the impregnation time is short, the adhesion of the fibers to the binder is not enough, there is no uniform impregnation of the fibrous filler of the prepreg.

In the patent of Germany No. 2932742, 1981, describes a method of impregnation of threads on bobbins binder. During this impregnation, the thread is wound on a perforated rigid mandrel, so that a homogeneous bobbin is formed in which the amount of free space corresponds to the desired volume of binder, which is fed into the slot of the mandrel after the initial passage of air through the bobbin under pressure. Impregnation ceases when small bubbles appear on the surface. The compressed air supply is then turned off.

The disadvantage of this method is that it is not possible to completely remove air from the interfiber space when impregnated. In addition, the binder also has air. In the subsequent manufacture of products from such prepregs, micropores appear in the structure of the material after curing, which leads to a decrease in the tightness of the finished product.

The prototype adopted the method of producing the prepreg [1] p. 71, in which the most important step is the evacuation of the filler forming the prepreg, drying and impregnation in a vacuum chamber.

The prototype method consists in the following: a filler thread located in a vacuum chamber is wound from bobbins, evacuated, dried and enters a bath with a binder, also located in a vacuum chamber, passes a squeezing device, a drying oven, a calibrating device and wound on a drum. The purpose of evacuation is to remove gas inclusions from microcracks and interfiber space in the filler threads for free penetration of the binder into them.

The disadvantage of the prototype is that not all microcracks and interfiber spaces have time to fill up with a binder, which leads to a decrease in the tightness of the finished product.

An analogue of the proposed device is a small-sized installation for receiving tape prepregs [1], p. 72, Fig. 1.19.

The installation comprises an impregnating bath with squeezing rollers, a thread distributor forming a tape from them, a feeding roller, a cylindrical belt drying chamber with a drum, between which there are six belt conveyors between two lateral disks, a coil with a prepreg ribbon on a winding device, a heater, a blower fan, suction fan.

The disadvantages of the analogue are the bulkiness of the chamber, the duration of the natural removal of gas inclusions and, as a consequence, the actual enveloping, rather than the impregnation of the threads, and the return of the binder leads to its large costs and impairs its quality.

A prototype of the invention is a device for producing a prepreg [1], p. 71, Fig. 1.18.

This installation contains a vacuum chamber, a vacuum pump, a heater, a binder level compensator, a squeezing device, a drying oven, a reel with a separation film, a calibrating device, a heater, a receiver, a filter, a vacuum shutter, a bath with a binder, creel with filler, a distribution drum.

The disadvantage of the prototype is the short time of degassing of the filler, in addition, the filler, immersing immediately in the binder, is enveloped by it and does not penetrate into the interfiber (unburnt) space. The installation itself has large dimensions and cost.

The objectives of the invention are to improve the quality of the wettability of the fibers and the impregnation of the filler in the prepreg, the reduction of interfiber and interfacial porosity before impregnation, which leads to increased tightness of products made from prepregs. In addition, the device for implementing this method is compact and inexpensive to manufacture.

These problems are solved by the fact that in the method of manufacturing a prepreg, including winding the filler on the mandrel in the bobbins, evacuating and filling with a binder, winding the filler on the mandrel is produced with a free space equal to the required binder content and not less than 0.2 of the total volume of the formed bobbin, and evacuation is carried out in the chamber for at least 4 hours at a residual pressure of no higher than 10 mm Hg, and filling the spool and interfiber space of bobbins with binder is done by placing bobbins with filler m under the same conditions of vacuum into the binder, and when the volume of the binder above the bobbin reaches a value greater than the volume of the inter-fiber and interfiber space in the bobbin, the pressure in the chamber is raised to a value not lower than atmospheric and the bobbin is held in the binder for at least 4 hours, after which allow excess binder to drain.

In a device for implementing this method, comprising a vacuum chamber with a vacuum pump, a vacuum valve and a manometer, as well as a container with a binder, bobbins with filler, a perforated cargo platform with a central rod perpendicular to the plane of the cargo platform and connected with a mechanism for dumping the latter, with bobbins with filler installed on the cargo platform, alternating with intermediate perforated removable platforms, and between mandrels OBIN and central core arranged trucks wheels.

The invention is illustrated by drawings.

Figure 1 shows a General view of the device.

Figure 2 shows the process of impregnation of bobbins with filler binder.

Figure 3 shows the process of removing excess binder after impregnation of bobbins with filler.

In the figures:

1 - a vacuum chamber;

2 - capacity with a binder;

3 - cargo perforated platform;

4 - intermediate perforated removable platforms;

5 - viewing window;

6 - locking platform;

7 - reset mechanism;

8 - cargo disks;

9 - mandrels;

10 - sealing cover of the vacuum chamber;

11 - bobbins with filler;

12 - a vacuum valve;

13 - pressure gauge;

14 - a binder;

15 - a vacuum pump;

16 - removable handle;

17 - rod for suspension of a cargo perforated platform;

18 - excess binder;

19 - the central rod.

The prepreg manufacturing process is performed in the following sequence:

- on the mandrel 9 a filler of the required width is wound, which can be used, for example, glass fiber or glass tape, providing a free space in the bobbin with filler of at least 0.2 of the total volume of the formed bobbin with filler 11 (Fig. 1).

If the filler is treated with a sizing agent, for example, in the form of a paraffin emulsion, then the prepared bobbins with the filler are preliminarily subjected to heat treatment at a temperature of at least 450 ° C for at least 2 hours to remove this emulsion.

The filler must be formed into a bobbin with such a volume of free space so that it is equal to the required binder content in the prepared prepreg. That is, the bobbin must be wound with a certain density, determined by the tension force. The required binder content is determined by the density of the bobbin winding. It was established experimentally that to ensure a binder content of 30-35% in the impregnated filler, the volume of free space in the filler bob should not be less than 0.2 of the total volume of the formed bobbin.

- bobbins with filler 11 are fixed on a perforated cargo platform 3, while the free space in the mandrels 9 for winding bobbins between them and the central rod 19 is filled with cargo disks 8, and intermediate perforated removable platforms 4 are installed between the bobbins (Fig. 1);

- bobbins with filler 11 are rigidly fixed by the locking platform 6, and the cargo perforated platform 3 is held in suspension by a dumping mechanism 7, for example, an electromagnetic mechanism mounted on the inner surface of the sealing cover of the vacuum chamber 10 (figure 1);

- in the container with a binder 2, located inside the vacuum chamber 1, is poured the estimated amount of binder 14 (figure 1);

- the sealing cover 10 of the vacuum chamber with a suspended cargo perforated platform 3 and bobbins with fillers 11 are installed on the vacuum chamber 1 (figure 1);

- using a vacuum pump 15 remove the gas medium from the vacuum chamber 1, where there are bobbins with filler 11 and a binder 14 (figure 1);

The removal of the gas medium is up to a residual pressure of not higher than 10 mm Hg The magnitude of such pressure is determined experimentally and ensures complete removal of air from the interfiber space of the bobbin and the subsequent high-quality (without porosity) binder impregnation of the bobbin.

- after pumping air from the vacuum chamber 1, the inter-fiber and inter-filament space of the bobbins with filler 11 and from the binder 14 to a residual pressure of not higher than 10 mm Hg (by gauge 13) is held for 4 hours (figure 1).

During this time, the air completely manages to move away from the interfiber and interfiber space of the bobbins with filler, and it is removed along the entire thickness of the bobbin, starting from the outer layers of the filler, in which the removal of air begins from the moment vacuum begins, and ending with the deepest layers adjacent to the outer surface mandrels 9, on which the filler is wound;

- under vacuum using a dumping mechanism 7, for example an electromagnetic mechanism, lower the bobbins with filler 11 together with the cargo perforated platform 3 into the binder 14, and immersion is carried out at the bottom of the tank with a binder 2 with a clearance A equal to, for example, 10-15 mm , which is the necessary value in excess of the amount of free space of the bobbins. Only in this case, after filling the interfiber space of the bobbins with a binder, they will not be exposed.

It does not make sense to increase the volume of the binder in order to lower the reels deeper, in view of the low coefficient of utilization of the binder.

The vacuum provides not only the removal of air from the inter-fiber and inter-filament space of the filler bobbins, but is the medium providing the best conditions for the wettability of fibers and filler filaments.

- when completely immersed in a binder 14 of bobbins with a filler 11, the pressure in the vacuum container is raised to a value not lower than atmospheric, the sealing cover of the vacuum chamber 10 is opened, using a removable handle 16, the container with the binder 2 is pulled out and kept in it for at least 4 hours of bobbin with filler 11 (figure 2);

An increase in pressure in the inner container for binder 2 to a value not lower than atmospheric serves as a necessary condition for the forced impregnation of bobbins with filler immersed in the binder, while the binder tends to fill the vacuum cavities formed between the fiber and interfacial spaces in the bobbins. The exposure time of the bobbins with filler 11 in the binder 14 is established experimentally and is determined from the condition of uniform quality impregnation of the filler with a binder over the entire depth of the layers of bobbins.

- at the end of the impregnation process, bobbins with filler 11 are lifted from the binder 14 with the loading platform 3, fixed on a rod for suspension of the platform 17, allow excess binder 18 to drain (Fig. 18), the mandrels 9 are removed from the soaked bobbins with filler 11 and sent on winding the product.

In the implementation of this technical solution, a positive effect is achieved due to the fact that the use of preliminary evacuation of both the inter-fiber and inter-filament spaces of the bobbins with the filler, and the binder itself reduces the inter-fiber porosity during the impregnation of the filler and almost completely eliminates the presence of pores in the finished product material and thereby provides the necessary level of tightness of products such as pipes, cylinders and containers.

It was experimentally established that the pipe wall thickness equal to 1-1.2 mm ensures helium gas permeability of not more than 1.5 · 10 ^-9 cm ³ · cm / cm ² · s · atm.

The proposed method for the manufacture of the prepreg provides a uniform thickness of the bobbins with filler impregnation with a binder, and the vacuum process reduces the porosity in the structure of the prepreg and the finished product.

Sources of information

1. Bulanov I.M., Vorobey V.V. Technology of rocket and aerospace structures from composite materials. Publishing House MSTU. N.E. Bauman, M., 1998, p. 15, p. 71, p. 72.

2. Tsyplakov O. G. Manufacture of shipboard large fiberglass products. L .: Shipbuilding, 1967

3. Tsyplakov O. G. Fundamentals of the formation of fiberglass shells. L .: Engineering, 1968

4. Collection of articles. Processing methods and properties of reinforced plastics. All-Russian Research Institute of Aviation Materials, ONTI, M., 1968

Claims (2)

1. A method of manufacturing a prepreg, including winding the filler on the mandrel of the bobbin, evacuating and filling with a binder, characterized in that the winding of the filler on the mandrel is produced with a free space equal to the required binder content and at least 0.2 of the total volume of the formed bobbin, and evacuation is carried out in the chamber for at least 4 hours at a residual pressure of no higher than 10 mm Hg, and filling the bobbin space between the fibers and the baffle with a binder is carried out by placing bobbins with filler in the same conditions vacuum in the binder and when the volume of the binder above the bobbin reaches the volume of the inter-fiber and interfacial space in the bobbin, the pressure in the chamber is raised to a value not lower than atmospheric and the bobbin is kept in the binder for at least 4 hours, after which excess binder is drained. 2. A device for the manufacture of a prepreg containing a vacuum chamber with a vacuum pump, a vacuum valve and a manometer, a container with a binder, bobbins with filler, characterized in that a perforated freight platform with a central rod perpendicular to the plane is inserted into the container with a binder above the binder mirror perforated cargo platform and associated with the discharge mechanism of the latter, while on the cargo perforated platform installed bobbins with filler, alternating with intermediate perforated annymi removable platforms, and between the mandrel reels and central core arranged trucks wheels.

Images