DE2031890A1 - Process for the production of a multi-walled hollow body - Google Patents

Description

Joseph Lucas (Industries) Ltd. June 26, 1970 Great King Street
Birmingham / England

Method for producing a multi-walled

Hollow body

The invention relates to a method of manufacture a multi-walled hollow body, in particular made of plastic molding compounds.

According to the state of the art, in many areas of application, e.g. in container construction, materials for hollow bodies processed, which must have different properties on their outer surface than on their inner surface. For example, if containers for corrosive liquids are manufactured, a synthetic resin is used that is not attacked by the liquid to be stored, but that is has the disadvantage of not having sufficient strength properties to form the container alone. It consists in In many areas of technology there is a need to manufacture hollow bodies that have different properties on their outer surface. sit than on their inner surface.

The object of the invention is to provide a method for producing a multi-walled hollow body, in particular, but not exclusively, from plastic molding compounds. According to the invention, preforms arranged one above the other are deformed in a mold representing the outer shape of the hollow body by a blow molding process, the inner preform being blown together with the further preforms by blowing gas into the inner preform. In accordance with the terminology used in the manufacture of hollow glasses, the preform is also called KfQoel, and that in the machine blowing of hollow glass st 207 009885/1926

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glasses are then transferred into the finished form and blown out.

In the following, exemplary embodiments of the invention are explained with reference to the drawing. Show it:

Pig. 1 is a sectional view of part of an injection molding machine for producing hollow, double-walled Bodies according to a method according to the invention,

Fig. 2 is a sectional view of part of an injection molding machine for forming a three-walled hollow body according to a method according to the invention,

Fig. J is a sectional view, partially schematic, of a Mold which can be used together with the injection molding apparatus of FIGS.

The embodiment according to FIG. 1 of the drawing is based on the idea of producing a container which has an outer wall made of polyvinyl chloride and an inner wall made of polyethylene. To produce such a container, a hollow, inner polyethylene preform 10 is produced by the injection molding process through the press nozzle of an injection molding head 11 essentially simultaneously with the injection molding of a hollow, outer PVC preform 12 by means of the die of a second injection molding head 13 > . The injection molding head I3 surrounds the inner preform 10 so that the parisons are arranged coaxially to one another and> are extruded together into a split mold 20, which represents the outer shape of the container to be produced. The mold is then closed and encompasses the preforms with the exception of the Areas to be inflated by the subsequent process step. As long as the two preforms are in a partially molten state, further deformation takes place according to the blow molding behavior,

that means that air is under pressure inside the interior Parcel 10 is supplied so that it is inflated within the outer preform. When the inner preform is under The pressure of the air expands, the outer surface of the inner preform fuses with the inner surface of the outer preform and both preforms expand together until the outer surface of the outer preform is the wall of the mold 20 reaches and takes its shape. The compressed air will then held inside the molded container until the inner and outer skin of the container are cooled and solidified whereupon the air is deflated and the mold 20 is split to allow removal of the container. ' The container produced in this way has an outer wall made of FVC with the properties of strength, Flame retardant and good weather resistance and an inner wall made of polyethylene with the property of a good chemical resistance. This container is suitable for long outdoor use and does not suffer a deterioration in properties depending on the effects of ultraviolet light and weather conditions.

The compressed air is preferably the interior of the preforms through a channel 25 in a mandrel 24 of the injection molding machine 11, 13, although other common blowing arrangements, |

for example from the bottom of the preforms or from the Sides the preforms made using a retrievable Needles that penetrate the preforms can be used. Advantageously The temperature and pressure of the blowing agent will depend on the material that the preforms are made of forms, set.

According to one modification, the inner preform has an im essential regular shape and consists of one chemically resistant material while the outer preform has an irregular shape and is made of a durable material. The outer pro

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form has cantilevers or attachment points that support a Allow layering or wall mounting of the item.

In another modified embodiment, the inner preform is made from a chemically resistant material and the outer preform made of polystyrene., so that the outer surface of the article to be manufactured by means of a Vacuum metallization process can be designed.

The method described above allows the manufacture of objects whose inner and outer surfaces are different have chemical and physical properties, e.g. a petrol tank can be manufactured with an outer skin made of a Rigid, impact-resistant material that does not have high resistance has the ability to dissolve gasoline and its inner wall is completely resistant against a dissolving action of the gasoline, however, does not have the rigidity or impact resistance which is necessary for the container if it were to be made from this material alone. Consequently, objects can after the process according to the invention, the inner and outer surfaces of which complement one another, desirable The material possesses such properties, while in an object that does not consist of several walls it must be chosen that there is a compromise between the properties desired for the inner and outer surface of the article Is found.

In the second embodiment of the invention shown in FIG. 2 of the drawing, a three-wall structure is provided. Three preforms 14, 15 * 16 are cast into a mold by means of corresponding injection molding heads Vf, 18, 19. The preforms are arranged one inside the other and are further deformed in the manner already described above by means of a blow molding process in order to produce the three-walled object.

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The inner and outer walls of the item are made of one material or two materials that make up the inner and outer surfaces give the object the desired properties, the middle wall is made of a material that has the desired physical property and gives these to the object, for example tensile strength and / or flexural strength.

According to a further embodiment, a woven fibrous or machine-made mesh or a Mat can be placed between the preforms, e.g. in case I of the two-walled article, the mesh or the mat is placed in the mold and the outer preform around the outside of the mesh or mat and the inner preform on the inside of the mesh or mat is poured. This net or mat must be suitable to be expanded to the shape of the article to be manufactured. When the preforms are inflated, the mesh or the mat expanded together with the preforms and the preforms connect with each other through the spaces in the mesh or in the mat. The application Such nets or mats are particularly suitable where the properties of the material from which the hollow body is made | is not with the requirements placed on the subject be fully reconciled without the use of some extra support elements. It can too two or more preforms of the same material are inflated together with a mat or net between them, to make a multi-walled shape from a single material, the Hetz or the mat as a support and stiffening element owns.

In any case, the preforms can be processed by injection molding. (Injection molding teohniques) where the inner preform is brewed as an insert on which the outer Preform is cast or vice versa ^ so that after renewed

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Heating the preforms together to the desired shape are blow moldable. Injection molding (extrusion) of the preforms is preferred, however, since transfer molding processes the materials ,, · from which preforms can be made, limited to those that have the same softening point.

The device shown in FIG. 3 is intended to produce an uninterrupted tubular hollow body which has an outer skin made of polypropylene and an inner skin made of nylon. The one in Pig. Illustrated apparatus I is used to prepare an inner nylon preform 30 together with an outer preform 21 m made of polypropylene% injection molding process, wherein the nylon preform wirdo 30 extruded inside the polypropylene preform 21 coaxially arranged preforms 30, 21, after the Spritzg ' The inner preform is then forced into the inner preform through the mandrel of the injection molding machine and the preforms inflated simultaneously with their introduction into the movable, divided molds 22, so that an uninterrupted tubular hollow body is produced, the outer shape of which is given by the shape of the mold elements 22, the halves of the molds 22 are arranged on parallel, continuously revolving belts 23 worn, the egg have a straight strand whose length is such that the time it takes for a mold to run from the beginning of the straight strand to the end of the straight strand is equal to the cooling time of the material to be deformed. The coaxially arranged polypropylene and nylon preforms 30-21 are extruded between the halves of a first form when the halves come to lie opposite one another at the beginning of the straight run of the conveyor belts. Ba both preforms are noo§

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are in a semi-molten state causes the Supply of compressed air to inflate the preforms into the Shape into it until they have taken its shape. When the inner nylon preform is expanded under pressure, its outer surface engages the inner surface of the polypropylene preform 21. After this, the two preforms expand together, until the outer surface of the polypropylene bulb 21 comes into contact with the inner surface of the mold 22 and adapts to it.

While the two preforms are deformed by the blow molding process the first mold 22 moves according to the j Path of the straight run of the two bands 23 and the two Parts of a second form 22 come into an opposite position at the beginning of the straight run and adjoin the first form, which has already been moved on. In addition, the inner and outer preforms become continuous produced by means of the injection molding heads and the work process can thus run continuously with the result that a continuous length of a double-walled, tubular Hollow body of the desired shape is produced.

Be at the end of the straight stretch of the two conveyor belts the opposing halves of the molds separated and the now solidified tubes exposed. If the he | desired length of the tube is present, the hollow body of the preforms separated by cutting, the separating process also serves to seal the ends of the preforms against each other, as already described above, around the Maintain air pressure within the preforms.

The hollow body shape produced by this method has an outer polypropylene wall that has good protective effects in one Acid environment unfolds and an inner wall made of nylon, which is suitable for holding and transporting gasoline. A such tubular container can be used with advantage on various types of vehicles. An adjustment

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to the intended type of use can be made by appropriate Material selection of the inner wall and outer wall of the container can be made easily.

In a modification, the outer preform is cast with an axially extending portion that is thicker than the remainder of the preform. The thicker area is pressed into the tool mold during the closing of the halves of the molds to produce stiffening ribs or mounting flanges that are located on the exterior of the tubular hollow body, while the remainder of the preform is inflated so that it takes the shape of the mold, which then also has the remainder of the tube. Such an arrangement is useful where, for example, the inner wall of the tube is made of a material that is resilient and has poor creep resistance properties, and where the outer wall is made of a material that provides strength to the tube.

When it is necessary to make a three-walled tube, the apparatus of FIG. 2 is used to cast three coaxially arranged preforms into the continuous mold of FIG. 5. The preforms are then inflated together to produce the final shape of the three-walled tube. The inner wall and the outer wall consist of one material or two different materials which have the desired chemical properties on the inner surface and on the outer surface of the hollow body, while the intermediate wall consists of a material which possesses the desired physical properties and imparts the finished article . If, for example, thermal insulation is required, the material of the partition wall can have the expanded form.

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If the preforms are not in relation to the molds 22 to ■ are moving, then the outer surfaces need the Tubes not be B-cylindrical, as shown in FIG. 3. For example, tubes of the Wire roll type (coneertinatype) are produced, or Tubes that are undercut, or have protrusions on their outer surfaces, then taking the shape of the outer ones The face of the tube is a separation of the halves of the mold on the End of the straight run permitted. ".

Claims 2

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Claims (7)

Claims; lj A method for producing a tubular hollow body, in particular from plastic molding compounds, characterized in that preforms (10, 12s I ¹ IJ 15 * 16; 30 , 21) are deformed, whereby by blowing gas into the inner preform (10, 14, 30) this is inflated together with the further preforms. (12, 15, 16 * 21). 2. The method according to claim 1, characterized in that the preforms (10, 12j 14, 15 ,lös 21, 30) by injection » casting process, preferably one inside the other. 3. The method according to claim 1 or 2 _S, characterized in " that two preforms (10, 12; 21, 30) are used to produce a double-walled hollow body" 4. The method naah claim 1 or 2 _S, characterized in that three preforms (14, 15, 16) are used to produce a three-walled hollow body, J 1, characterized 5. A method according to any one of claims to 4 characterized in that a stretchable on the shape of the article to be produced mesh or mat between the inner and outer preform, and in that the web or the mat simultaneously with the blow molding of the molding is stretched. 6 * Procedure naofc eine dei ⁵ claim © I big r / Vt t * ae, ^f the form (22) © us of a \ ^f l <Hsü! il Iiα *. -ο »oils l) PFi.ehfeo & l® © iaaraioi? in s ι ..,. r «*" ¹ free Qaäiasoa usalau ^ saöea - ii - 20318 are that the preforms (30, 21) are introduced into the space between the mold segments of the belts (ZJ) and are inflated with an amount corresponding to the port movement speed of the belts (2j5.), 7. The method according to any one of claims 1, j5, 4 and 5 j thereby characterized in that the preforms by transfer molding (Injection mouling), the inner preform forming a molded body around which the outer preform is pressed. 009885/1926 j Blank page