RU2633719C1 - Method of flexible design element manufacture from composite material - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: method includes filling an elongated inflatable mould with gas, applying an anti-adhesive airtight layer and a reinforcing filler layer thereon to form a workpiece, shaping the workpiece, applying a flexible airtight layer onto it, impregnating the reinforcing filler layer with a binder vacuum infusion method, curing the binder, and removing elongated inflatable shape from the workpiece. The elongated inflatable form is filled with gas to pressure of 1.175-1.225 atm. A layer of the distribution grid is applied over the anti-adhesive airtight layer. A layer of release fabric and a layer of the distribution grid are applied over the reinforcing filler. At the ends of the workpiece, the layers applied to the elongated inflatable form are clamped, except for the antiadhesive airtight layer, they are stretched, the workpiece is given an arcuate shape by bending on a curved surface. The stretched layers applied to the elongated inflatable form are re-stretched, a perforated hose is placed along the reinforcing filler. After applying a flexible airtight layer to the workpiece, a vacuum is formed under the layer and the reinforcing filler is impregnated with the binder through the perforated hose.

EFFECT: increasing reliability, reducing the number of defects on its surface.

4 cl, 1 dwg, 3 tbl, 6 ex

Description

The invention relates to the construction industry and can be used for the manufacture of curved hollow structural elements from composite material, including large ones, which can be used in the construction of arch bridges.

A large number of methods for processing polymer composite materials into products of various sizes, configurations and purposes are known. Among the many methods, the use of methods for manufacturing parts from composite materials by vacuum impregnating a reinforcing filler with a binder in a snap with subsequent curing has increased in recent times. In this method, for the impregnation of the dry filler, only the vacuum created in the cavity of the snap is used. Under the influence of this difference between the cavity of the snap and the source of the binder, the latter moves from the source to the connection point of the vacuum pump in the cavity of the snap, impregnating the filler. Vacuum impregnation methods are collectively called LRI (Liquid Resin Infusion).

A known method of manufacturing large structures from composite material using the method of vacuum infusion, which consists in the following. At least one tooling made of plastic (foam, polyvinyl chloride, polyurethane), or cork, or textured metal, or concrete, which can be either solid or hollow, is wrapped with fibrous material, after which a vacuum bag is collected and fiber material is impregnated with a binder method of vacuum infusion. The binder can be supplied both to the outer part of the internal equipment, and directly to the vacuum bag. In the case of filing a binder on the external part of the internal equipment directly into the network of supply grooves, which are interconnected into a series of smaller micro tracks, the binder flows in the direction from the equipment and penetrates the fibers of the reinforcing filler (US 5904972 A, 05/18/1999).

The disadvantage of this method is the use of rigid rigging, which requires a stationary place for the manufacture of large structures from composite material. In addition, since the tooling must lie on a hard surface, it is difficult to obtain a circular cross-section product with this method.

A known method of manufacturing complex products from polymer composite materials by infusion, which includes hermetic packaging of the workpiece (reinforcing filler, placed on technological rigid equipment) in the first vacuum bag, which is placed in the second vacuum bag, vacuuming two vacuum bags so that the pressure in the second vacuum bag exceeded the pressure in the first vacuum bag. After this, the preform is impregnated with a binder infusion method (US patent 7413694 B2, 08/19/2008).

The use of a double vacuum bag having a large thickness makes it difficult to bend the inflated cylindrical shell to give the element a given shape and can lead to the formation of defects (jamming, wrinkling) in the preform. In addition, as well as the previously considered patent, pre-made rigid technological equipment is used to shape the product.

A known method of manufacturing hollow articles from composite materials, including filling gas with an inflatable inner shell, laying on it a reinforcing filler and a binder, applying an outer additional shell of elastic material in the form of a tape to the reinforcing filler with a binder, curing the binder and removing the inner and outer shells. The inner shell is forming, made of an elastic material placed in a calibrated reinforced flexible sleeve. Before laying on the inner shell of the reinforcing filler and the binder, the inner shell is placed on a slipway, giving the hollow product a predetermined curvature. The binder used is a cold cured polymer composition. The reinforcing filler is impregnated with a binder after it is laid out on the inner surface of the shell. The binder is applied to the reinforcing filler manually - for its application using brushes, spatulas or spray guns. After curing the binder and removing the outer additional shell, the formation of subsequent layers of the reinforcing filler and the binder is carried out until the desired thickness of the hollow product is reached. The invention provides the manufacture of long products of a given curvature and constant cross-sectional diameter along the entire length of the product (RU 2488486 C1, 07.27.2013).

One of the significant drawbacks of the described method is the manual method of applying a binder to the reinforcing filler, which does not guarantee its uniform distribution over the entire surface of the filler and the completeness of impregnation, and can also lead to the appearance of drops and sagging on the underside of the product. This may cause the formation of internal defects and zones with different internal stresses. Defects that occur in parts made of polymer composite materials during their manufacturing process significantly degrade their performance and dramatically reduce reliability. Another significant drawback of the method is the multi-stage set of thickness of the product: each subsequent layer of filler is applied to the previous one, already impregnated and cured, which increases the manufacturing time of the product and affects the reproducibility of its properties.

Thus, all the methods described above are quite difficult to implement for the manufacture of large-sized arch structures.

The closest analogue of the proposed method is a method for manufacturing a hollow structural element from composite material, which can be used as a building material, including filling an elongated inflatable form with gas, applying an intermediate layer (release adhesive airproof), a reinforcing filler and a flexible airproof layer, imparting the obtained arc-shaped preform, impregnation of the reinforcing filler with the binder method of vacuum infusion, curing e blanks and removal from it of an elongated inflatable shape. Giving the workpiece an arcuate shape is carried out in a curved annular snap with a given inner surface by hard gripping the ends of the workpiece with clamps and pressing it to the surface of the tool, with these clamps, the workpiece is simultaneously stretched to straighten the layers applied to it. An arched shape of the workpiece is attached in a snap in the form of a half ring with an inner surface of a given shape, while to maintain the appropriate shape of the surface of the workpiece, the elongated inflatable shape is repeatedly blown (US 8591788 B2, 11.26.2013).

The disadvantage of the prototype method is that the stretching of the layers together with the inflatable form reduces the degree of straightening of the layers, which during the curing process leads to the formation of defects (folds, bubbles, bends) on the surface of the resulting arched structural element. In addition, the inflatable mold may be damaged due to the hard grip of the ends of the workpiece together with the specified mold with metal clamps.

The technical task of the invention is to develop a method that allows you to quickly and efficiently get hollow structural arched elements from composite material, including bulky, both in stationary and in the field.

The technical result of the invention is to increase the reliability of the method of manufacturing a hollow structural element from composite material, as well as reducing the number of defects on its surface.

The technical result is achieved due to the fact that the proposed method for manufacturing a hollow structural element from composite material, including filling an elongated inflatable shape with gas, applying an anti-adhesive airtight layer and a layer of reinforcing filler on it to obtain a workpiece, giving the workpiece an arched shape, applying a flexible airtight layer to it , impregnating a layer of reinforcing filler with a binder by vacuum infusion, curing the binder and removing from the workpiece long inflatable form, characterized in that the elongated inflatable form is filled with gas to a pressure of 1.175-1.225 atm, a distribution mesh layer is applied to the anti-adhesive airtight layer, a layer of sacrificial fabric and a distribution mesh layer are applied to the layer, after which the layers applied to the elongated inflatable shape , in addition to the anti-adhesive airtight layer, clamp at the ends of the workpiece and stretch, after giving the workpiece an arcuate shape, the clamped layers are again stretched, placed along a After filling a perforated hose, after applying a flexible airtight layer to the workpiece, a vacuum is created under the specified layer and the reinforcing filler is impregnated with a binder through the perforated hose.

A blank for the manufacture of a hollow structural element from composite material is shown in the drawing, on which the following elements are indicated:

1 - elongated inflatable form,

2 - thermal insulation layer,

3 - release adhesive airtight layer,

4 - layers of the distribution grid,

5 - a layer of sacrificial tissue,

6 - layer reinforcing filler,

7 - airtight layer.

The proposed method is as follows.

On a gas-filled (for example, air) elongated inflatable mold (cylindrical elastic shell), an anti-adhesive airtight layer is first laid, which can be made, for example, of polyethylene, polyamide, polypropylene, fluoroplastic.

A distribution grid layer is applied over the release layer of an airtight layer and a preform (reinforcing filler) of a predetermined structure (weaving angle) and thickness (number of braided layers) of carbon bundles is braided.

After that, it is advisable to blow and roll the elongated inflatable form with a braided preform (billet) in such a way as to avoid distortions, a significant change in the angle, fractures and kinks of carbon bundles. When assembled, such a blank can be easily stored and conveniently transported to the bridge construction site, on which arch elements are made directly.

Directly at the place of manufacture of the arch, the workpiece is unfurled and filled with gas (for example, air) to a pressure of 1.175-1.225 atm. At insufficient pressure (less than 1.175 atm), the elongated inflatable form after impregnation of the preform with a binder will settle under the weight of the impregnated preform and will not keep an even cylindrical shape, dents will form in the product, and the diameter along the entire length of the product will turn out to be uneven. If the equipment is pumped (pressure over 1.225 atm), then during the curing process, which proceeds with the release of heat, the gas inside the inflatable mold will expand and its integrity may be impaired.

In the manufacture of hollow structural elements from composite materials, epoxy-based binders are often used, characterized by heat generation due to isothermal reactions during curing. Thermal effects can cause leakage in an elongated inflatable shape. To prevent this, before curing the workpiece, it is recommended to replace the elongated inflatable mold with a similar one with a heat-insulating layer applied on it, which is a layer of foamed thermoplastic (polyurethane foam or polyethylene foam) with a layer of metallized foil applied to its outer surface. In addition to preventing overheating of the inflatable mold, this will also allow maintaining a high temperature in the area of curing of the preform, accelerating the curing process.

This can be done as follows. An elongated inflatable mold filled with gas (air), similar in size to the one onto which the preform is braided, for example, is used to attach a heat-insulating layer with a layer of metallized foil to the outside. Further, the ends of the shells (with a braided preform and with a heat-insulating layer) are connected to each other, for example, also using adhesive tape. Manually or with clamps, they fix an air-tight release layer with a braided preform and begin to pull out an inflatable form from under them at the free end. In this case, the elongated inflatable mold is replaced with a similar one with a heat-insulating layer inside the preform.

The heat-insulating layer is placed in the workpiece immediately before the reinforcing filler is impregnated with a binder at the construction site, since the workpiece with the heat-insulating layer is a thick, poorly bending structure and is difficult to transport.

If necessary, to compensate for the stresses acting on the hollow structure when the loads change, the braided preform can be strengthened by laying on it additional layers of reinforcing filler of various structures (bundles, fabrics, etc.). To fix the layers relative to each other, the surface of the preform and each subsequent layer of reinforcing filler placed on the preform is proposed to be treated with a 3-10% binder solution used in vacuum impregnation. Processing can be carried out by spraying a binder solution from a spray bottle. During processing, a thin binder film is formed on the surface of the filler, which provides a snug fit of the layers to each other and prevents their displacement. In addition, when using a sublayer, the filler structure itself is fixed, the displacement and bending of the threads is prevented both during assembly of the preform and during subsequent impregnation, which is especially important for unidirectional and rarefied structures, as well as woven sleeves with a given weave angle.

After the final set of preforms, a metal ring is placed on both sides of the product at a distance of 15-20 cm from the ends between the preform and the release adhesive airtight layer, and a clamp is placed on top of the preform and clamped with bolts with a force sufficient to prevent the clamp from moving relative to the tooling. Thus, the reinforcing filler is fixed in the workpiece.

Sacrificial fabric and a layer of a distribution grid are placed on the prepared preform and the workpiece is placed on a curved surface to give the product an arched (arched) shape of a given contour.

Cables are attached to the metal rings on the inside and the layers are stretched with an effort of up to 4 tons. In the process of stretching, the filaments and fibers of the carbon filler (preform) are stretched, aligned, creases and folds on the preform formed by bending the workpiece on the slipway are eliminated to give an arcuate shape. Due to the fixation of the preform with metal rings and ties, all layers of the filler in the preform are stretched and evenly straightened.

Then, at a distance of 15-20 cm from the metal rings, plastic clamps are installed on the inside of the preform, after which stretching cables are removed, and the metal rings are replaced with plastic ones.

After replacing the rings, a flexible, airtight layer is applied to the workpiece, under which a spiral perforated tube is placed on the preform to supply the binder.

Having thus collected a vacuum bag for infusion impregnation, the system is checked for leaks.

Subsequent impregnation of the reinforcing filler with a low viscosity binder through a flexible spiral perforated tube is carried out by creating a vacuum of 0.01-0.05 atm.

A flexible spiral binder supply tube, for example, made of fluoroplastic or silicone, is located along the entire length of the arch element and is wrapped around its circumference at the ends of the product. Thus, the propagation front of the binder during the impregnation process is not distributed over individual regions, but covers the entire length of the arch element and is evenly distributed along the length and circumference of the product. This is also facilitated by the presence of layers of the distribution grid on both sides of the reinforcing filler. The use of sacrificial tissue, absorbing excess binder, avoids the formation of drops and smudges of the binder on the cylindrical surface of the product and, accordingly, further reduce the number of defects on the surface of the product.

As polymeric cold curing binders, epoxy, epoxy vinyl ester, and polyester compositions with a low viscosity (0.5-1.5 Pa · s) are used. The impregnation process ends after the binder is completely consumed, after which the vacuum system is turned off and the impregnated product is left for complete curing.

If the hollow structural element is manufactured in the field in the cold, then due to low temperatures the curing process of the binder may not take place. In this case, to initiate it before impregnating the reinforcing filler with a binder, the workpiece must be placed in a room with an air temperature not lower than + 20 ° С.

If the indicated temperature is not possible to maintain before and during the impregnation of the binder with a layer of reinforcing filler, to achieve the equality of the temperatures of the binder and the reinforcing filler, the binder is heated to impregnation to a temperature of 20-25 ° C, and the workpiece with a flexible airtight layer is placed in a perforated sleeve, in which from one or both ends produce a boost of warm air with a temperature of 20-40 ° C. The placement of the workpiece in a corrugated sleeve with warm air can additionally accelerate the curing process by approximately 2.5-2 times (from 10-12 to 4-6 hours). After the layer of reinforcing filler is impregnated with a binder in the specified sleeve, pressurization of hot air with a temperature of 80-90 ° C is also carried out from one or both ends for the most complete curing of the binder in the composite material.

After the curing of the binder, auxiliary layers are removed - air-release, flexible, air-tight (vacuum bag), sacrificial and distribution grid layers, the spiral binder supply tube and the elongated inflatable mold are removed, for which it is first blown off and then removed from the cured article.

At the finished product - a hollow arch element, the edges are cut (leveled) to a predetermined size and a quality assessment is carried out, namely:

- check the compliance of the obtained geometric dimensions with the specified (chord, length, inner diameter, wall thickness of the product),

- determine the number of defects in the volume of the product by the acoustic impedance method with a DAMI-C09 flaw detector with a resolution of 5 mm.

After alignment of the structural element on the carbon fiber samples cut off from the edges, the following physical properties are determined:

- the mass fraction of the polymer matrix (for example, by burning a binder from a carbon fiber sample with subsequent weighing of the residue),

- carbon fiber density according to GOST 15139-69.

Examples of implementation.

Under various conditions, 6 hollow structural elements were made of composite material of an arched shape.

Initially, an elongated inflatable mold with a diameter of 250 mm, a length of 5.8 m from a gas-containing fabric, pre-filled with air through the nozzle, was wrapped with an anti-adhesive airtight layer. An infusion mesh was laid over the release layer of an airtight layer and layers of reinforcing material were braided.

Materials for the manufacture of hollow structural elements are shown in table 1.

The ends of the braided reinforcing filler were fixed with tape.

Then, the elongated inflatable mold was blown off and rolled up, avoiding distortions, angle changes, kinks and kinks of the reinforcing filler bundles forming the preform, packed in a plastic film and transported the workpiece to the place of construction work.

In the field, an inflatable mold with a woven preform (blank) was deployed and filled with gas (air).

For examples 2-5, a heat-insulating layer of isolon (0.5 mm thick) consisting of foamed polyethylene with a metallized coating of (TU 2244-037-00203476-2012) was placed in the blank between the elongated form of the gas-containing fabric and the release adhesive airtight layer. The heat-insulating layer was placed metallized side to the preform as follows. On the elongated inflatable mold filled with air, similar to the one on which the preform was braided, a heat-insulating layer was attached (with tape), after which the ends of the inflatable shells were connected with adhesive tape. An air-tight release layer with a woven preform was fixed and an elastic sheath was pulled from an air-tight gas-containing fabric at the free end. Thus, inside the preform, the elastic shell of the airtight gas-containing fabric was replaced with a similar one with a heat-insulating layer.

For examples 2, 3, 4, 6, the braided preform was strengthened by laying on it additional layers of reinforcing filler. To combine the layers, first the main reinforcing fabric, and then each subsequent layer was treated with a binder solution, applying it from the spray gun.

After the final set of preforms, a metal ring was placed on both sides along the edges of the workpiece at a distance of about 15-20 cm from its ends between the preform and the release adhesive airtight layer, and a clamp was clamped on top of the preform and clamped.

On the surface of the prepared preform according to examples 1, 3-5, a sacrificial fabric was laid out (separating porous fiberglass fabric coated with SK2RE260-1BR40PR10030 polytetrafluoroethylene), and for all examples, an infusion mesh distribution grid. Then the workpiece was placed on the slipway to give it an arcuate (arched) shape of a given contour.

Ropes were attached to metal rings on the inside and the workpiece was stretched on a slipway (with a force of up to 4 tons). On the stretched billet, metal rings were replaced with plastic clamps, tensile cables were removed, a flexible spiral tube (fluoroplastic F-4 or silicone SK2RIM260-1) was placed with two points for supplying a binder, and a vacuum bag for infusion treatment was assembled.

After checking the assembled system (vacuum bag with a binder supply system) for leaks, the binder was impregnated by creating a vacuum of 0.01-0.05 atm. After the binder is completely consumed, the vacuum system is turned off and the impregnated product is left for complete curing. After the curing of the binder, auxiliary layers were removed: a vacuum bag, a distribution mesh, a sacrificial fabric, a spiral binder supply tube and a cylindrical tooling with a release adhesive airtight layer, for which equipment from a gas-containing fabric was blown off and removed from the cured article together with an release adhesive airtight layer.

The finished product was twisted into a given size and its quality was assessed - it was checked that the obtained geometric dimensions corresponded to the given (chord, length, inner diameter, wall thickness of the product), the number of defects in the volume of the product was determined by the acoustic impedance method with a DAMI-C09 flaw detector with a resolution of 5 mm.

Technological parameters and auxiliary materials for the manufacture of a hollow structural element are shown in table 2.

The characteristics of the resulting hollow structural element are shown in table 3.

As can be seen from the data presented in table 3, the proposed method for manufacturing a hollow structural element from composite material allows minimizing the number of defects on its surface due to the used technique of straightening layers deposited on an elongated inflatable mold, using a distribution grid and a perforated hose during vacuum infusion and pressure inside inflatable form 1,175-1,225 atm. In addition, the exclusion of hard gripping by the metal clamps of the ends of the workpiece together with the inflatable mold excludes the possibility of its damage during stretching of the layers.

Claims (4)

1. A method of manufacturing a hollow structural element from a composite material, including filling an elongated inflatable shape with gas, applying an anti-adhesive airtight layer and a layer of reinforcing filler to obtain a preform, arcing the workpiece in an arched shape, applying a flexible airtight layer to it, impregnating a layer of reinforcing filler with a bonding method vacuum infusion, curing the binder and removing elongated inflatable molds from the preform, characterized in that the elongated inflatable the filling form is filled with gas to a pressure of 1.175-1.225 atm, a distribution mesh layer is applied to the anti-adhesive airtight layer, a layer of sacrificial fabric and a distribution mesh layer are applied to the reinforcing filler layer, after which the layers applied to the elongated inflatable shape are clamped at the ends, in addition to the anti-adhesive airtight layer preforms and stretch, after giving the preform an arcuate shape re-stretch the clamped layers, place a perforated hose along the reinforcing filler, after application I create a vacuum under the specified layer on the flexible air-tight layer blank and impregnate the reinforcing filler with a binder through a perforated hose. 2. The method according to p. 1, characterized in that before giving the preform an arched shape to one end of an elongated inflatable shape, a similar-sized gas-filled elongated inflatable shape is attached with a heat-insulating layer located on its surface, which is a layer of polyurethane foam applied to its outer surface a layer of metallized foil, fix all the layers deposited on an elongated inflatable mold, and for the free end pull out the specified form from under them, thereby replacing the elongated inflatable shape to form a thermally insulating layer. 3. The method according to p. 1, characterized in that before the binder is impregnated with a layer of reinforcing filler, the binder is heated to a temperature of 20-25 ° C, and the workpiece with a flexible airtight layer is placed in a perforated sleeve into which warm air is charged with a temperature of 20-40 ° C, after impregnating a layer of reinforcing filler with a binder in the specified sleeve also produce pressurization with hot air with a temperature of 80-90 ° C. 4. The method according to p. 1, characterized in that on the layer of reinforcing filler spread additional layers of reinforcing filler, which is treated with 3-10 wt.% A binder solution used to impregnate a layer of reinforcing filler by vacuum infusion.

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