NL8903105A - Plastic crate with hollow column - has gas-injection opening in column with sealing wall below - Google Patents

Abstract

The plastic crate comprises a bottom and upright walls, also one or more hollow vertical columns integral with the walls. The column contains a gas-injection opening leading to its interior. Inside the column clear of the top and below the opening is a wall sealing it off. The column can have other sealing devices for the openings also.

Description

Short indication: Plastic crate with hollow columns provided with a gas injection opening, as well as a method and device for manufacturing such a plastic crate.

The Applicant names A.J. van Lent in Ernst.

The invention relates to a plastic crate comprising at least a bottom and upright walls and at least one upright hollow column forming one whole with these upright walls.

Such a plastic crate is known from EP-A-15 097.

This known plastic crate has the drawback of an uneven thickness of the wall of such a hollow column. This is due to the fact that molds with long thin cores are used in the manufacture of such plastic crates, which are easily deformed during the production of the crates by the plastic mass engulfing these cores, so that an uneven wall thickness is created which, of course, the strength of the end product. adversely affect.

Moreover, this adversely affects the production speed of such crates, since too thick a wall part needs too much cooling time to cool and, on the other hand, too thin a wall part is weak.

Finally, in the manufacture of such known crates one has to work with molds in which the long thin cores have to be cooled, which makes the devices very complicated.

Namely, when the plastic mass of the columns is cooled, this mass shrinks on the cores while losing contact with the outside of the mold parts surrounding the hollow column, so that further cooling must then take place from the cooled cores. It will be clear that this also takes a lot of time.

In practice, attempts have been made to overcome the problem of wall thickness differences by piercing the wall of a column in a few places, so that the said long thin cores can rest on mold parts. One drawback is that holes are hereby visible in the final product which give rise to contamination of the inside of a column, while the relatively small supporting parts are easily damaged and / or the parts against which they are supported are damaged.

The object of the invention is now to provide a plastic crate of the type mentioned at the outset with very uniform wall thickness and in which it is possible to work with molds with uncooled, long thin cores for forming columns.

This object is achieved according to the invention in that a column is provided with a gas injection opening opening into the inner side of a column and, viewed in height direction, the inner side of the column is provided at a distance from the top of the column and below the gas injection opening, with a column sealing wall.

By applying this measure, a certain amount of a gas can be incorporated into the flowing plastic mass surrounding the long thin uncooled cores, which injected amount of gas will inflate the plastic like a balloon when these long thin cores are moved out of the mold. whereby the plastic mass of the walls is pressed against the outside of the cooled mold parts surrounding this mass. An outer layer of this mass of a column will then cool, but the layer within it will still remain fluid, so that any thickness differences of this mass will be compensated by flow.

As a result, the wall of a column will now have a very uniform thickness.

A particular advantage is that it is now possible to use uncooled long thin cores, as a result of which the devices for manufacturing such plastic crates will also become much less complicated.

The hollow columns with a gas injection opening will be closed at the bottom, since the plastic mass balloon-inflated by the injected gas mass adheres not only to the top and side walls of the mold space forming the column, but also to the tops of the long thin cores that are still partly in the mold to close off a column at a distance from its top. Preferably, the column barrier wall is located approximately at the bottom of a column since it provides a further closed column of optimal wall thickness.

A plastic crate according to the invention has favorable strength-to-weight ratios.

Conveniently, hollow columns with gas injection openings delimit at least one wall opening in an upright wall, preferably wall openings in two upright walls.

In this way, a crate of optimum strength can be obtained without complicated molds with cooled thin long cores provided with particularly good handles.

The cavity in the columns delimiting the wall openings expediently continues in an opening edge part above the wall openings.

A gas injection opening is expediently present in each opening edge part above a wall opening bounded by hollow columns near the transition to a bounding hollow column, which gas injection opening is also the injection opening for the column located next to it.

This offers the possibility to manufacture double-walled crates with optimal handles.

The invention also relates to a method for manufacturing a plastic crate comprising at least a bottom and upright walls and at least one upright hollow column which is integral with these walls by injection molding a mass into a mold, which is characterized in that at least a hollow column mold cavity member, a pressurized gas in the plastics molding material is injected through a gas injection port, which gas is held in the cavity under pressure until the end of the cooling period of the injection molding operation.

The gas injection per injection opening is expediently regulated according to the starting time and amount of gas, such that the injection always takes place after the plastic mass has passed the relevant gas injection opening and the gas forms a closed cavity in the plastic mass.

Particularly advantageously, during the gas injection, a core is guided from at least one mold cavity part in which a hollow column is formed, while a closed hollow column is subsequently formed in that mold cavity part by the molding mass with the gas injected therein.

Particularly advantageously, the cores are guided out of the mold cavity parts of the mold so that their tops are located mainly in the stacking surface below the wall of the crate, after which the crate is kept in its final shape during the cooling period, while with the gas pressure the plastic mass, the walls of the hollow columns are kept pressed against the cooled mold inner wall, and the gas pressure in the cavities is reduced to atmospheric pressure before the mold is opened.

Using such a method, a plastic crate according to the invention can be manufactured with optimum strength.

Finally, the invention relates to a device for injection molding a plastic crate with at least one bottom and upright walls, and upright hollow columns forming one whole with these walls, comprising a mold which in closed condition encloses a mold cavity substantially in the shape of the crate. as well as cores in mold cavity parts of the mold for forming hollow columns, characterized in that the mold is provided with gas injection means for injecting gas into the mold cavity parts forming the hollow columns, gas discharge means for discharging injected gas after cooling of the shaped product discharge temperature and a passage in the mold wall for passing the gas injection means.

Core movement limiting means are particularly advantageously present in order to be able to move the cores from the mold cavity parts to the lower boundary of the mold cavity with closed mold.

In this way, upright columns with optimum uniform wall thickness are obtained.

The device is expediently also provided with gas injection control means for starting each gas injection.

The device is particularly advantageously provided with core output means for feeding the cores from a closed mold cavity part, which output means are efficiently coupled to the gas injection control means.

In addition, there are advantageously means for independently controlling the start of the gas injections to the individual injection points.

Particularly advantageously, the means for independently controlling the start of each gas injection cooperate with control means coupled to core output means for withdrawing the cores from the respective mold cavity parts, independently of each other, but each depending on the gas injection in a mold cavity part for the formation of the respective hollow column.

The invention will now be elucidated on the basis of an exemplary embodiment in which:

Fig. 1 - shows a perspective view of a plastic crate according to the invention;

Fig. 2 - a top view of a detail of a plastic crate according to the invention;

Fig. 3 - a section according to line III-III;

Fig. 4 - a bottom view of a plastic crate according to the invention;

Fig. 5 - a detail of a part of a mold for forming a hollow column plastic crate, a thin core being in a column mold cavity part; and

Fig. 6 - a formed hollow column after removing a core from a column mold cavity part.

Fig. 1 shows a plastic crate 1 comprising a bottom 4 formed of intersecting ribs and upright walls 2 and 3, respectively.

Such a plastic crate is expediently also provided with a compartment division 13.

On the inside of the upright walls of the crate there are hollow columns 5 for reinforcing such a relatively thin-walled crate. These columns 5 are hollow with an internal column cavity 9.

Also, as shown in Fig. 2, the column 5 is provided with a gas injection opening 6. On the other hand, the hollow columns 5 are completely closed by a column sealing wall 14 which is spaced from the top 23 of the column 5 and below the gas injection opening 6.

The crate of handle-forming wall openings 7 is expediently provided in two upright walls 2 situated opposite each other, the hollow columns extending on either side of the wall opening are mutually connected by a hollow opening edge part 8.

Fig. 5 shows part of a mold 15 with a mold cavity part 16 for forming a hollow column 5. Mold mold part 16 of the mold has an uncooled thin long core 10.

In the hitherto known molds for the production of such plastic crates with hollow columns, on the other hand, the cores 10 are made coolable, which complicates the device.

Furthermore, a passage 27 is arranged in the wall 17 of the mold, through which a gas-injecting member 18 is guided in the plastic mass 22 which is located between the free top 19 of core 10 and the mold cavity part inner wall 20 of mold cavity part 16 situated above it, for forming hollow column 5. By means of the gas injection member 18, an amount of gas 21 can be pressed into the plastic mass.

The movement of the core 10 from the column mold cavity part of the mold causes the gas mass 21 to inflate the plastic mass 22 present, which is located in the mold cavity part between core 10 and the inner wall of this mold cavity part, thereby forming column sealing wall 14.

The cores 10 are expediently moved out of a mold cavity part 16 for a column 5 until the free top 19 of the core 10 is almost in the stacking surface 11 under the walls 2 or 3 of the crate.

Core movement limiting means in the form of stop 12 are present for carrying the cores 10 to the correct height from the mold cavity parts 16.

The gas mass 21 is supplied from gas supply container 24 from which a pipe 25 can be connected to the gas injector means 26. The gas injector means 18, a hollow tube, are passed through a mold wall lead-through 27 in mold cavity part 16.

Core outlet members 28 are efficiently provided for moving core 10 out of mold cavity part 16, which are efficiently coupled via control means 31 to gas injection control means 29 known per se. This permits constant gas pressure to be maintained in the plastic mass 22 in order to obtain the desired optimum wall thickness of the columns.

Of course, separate gas injection control means 29 may also be provided, each of which controls the gas supply to separate gas injection means 12 at the different injection sites.

For discharging gas from the cavities 9 of the hollow columns 5 after cooling the mold, gas discharge means 30 are present, for instance a pipe 30 which can be opened after cooling of the product, so that the gas mass 21 from all hollow columns 5 can be opened simultaneously. can escape.

Claims (14)

Plastic crate at least comprising a bottom and upright walls as well as at least one upright hollow column forming an integral part with these upright walls, characterized in that a column (9) is provided with a gas injection opening (6) opening in the inner side of a column and viewed in height direction, the inside of the column is provided with a column sealing wall (14) at a distance from the top of the column and below the gas injection opening. Plastic crate according to claim 1, characterized in that the hollow columns (9) are further closed except for the gas injection openings. Plastic crate according to claim 1 or 2, characterized in that hollow columns (5) with gas injection openings define at least one wall opening in an upright wall, preferably wall openings in two upright walls (2) situated opposite one another. Plastic crate according to claim 3, characterized in that the cavities (7) in the columns (5) delimiting the wall openings (7) continue in an opening edge part (8) above the wall openings (7). Plastic crate according to claim 3, characterized in that in each opening edge part (8) above a wall opening (7) bounded by hollow columns (5) near the transition to a bounding hollow column (5) there is a gas injection opening (6), which gas injection opening (6) is also the injection opening for the adjacent hollow column (5). Method for manufacturing a plastic crate comprising at least a bottom and upright walls and at least one upright hollow column forming an integral part of these walls by injection molding a mass into a mold, characterized in that at least in a mold cavity part (16) a hollow column (5) injects a pressurized gas into the plastic mass through a gas injection port (27) which pressures gas into the cavity until the end of the cooling period of the injection molding operation. Method according to claim 6, characterized in that the gas injection per injection opening (27) is regulated according to the starting time and the amount of gas such that the injection always takes place after the plastic mass has passed the relevant gas injection opening and the gas has a closed cavity in the plastic mass forms. Method according to claims 6 or 7, characterized in that during the gas injection a core (10) is guided from at least one mold cavity part in which a hollow column (5) is formed, while a closed hollow column (5) is subsequently formed in that mold cavity portion through the molding mass with the gas injected therein. Method according to claim 8, characterized in that the cores (10) are guided out of the mold-mold cavity parts so far that their top sides lie mainly in the stacking surface (11) below the wall (2) or (3) of the crate. , after which the crate is kept in its final shape during the cooling period, while the walls of the hollow columns (5) are pressed against the cooled mold inner wall with the gas pressure in the plastic mass, and the gas pressure in the cavities before opening the mold is reduced to atmospheric pressure. 10. Device for injection molding a plastic crate with at least one bottom and upright walls and with these walls an upright hollow upright columns comprising these molds, which in closed condition encircles a mold cavity substantially in the shape of the crate and cores in mold cavity parts of the hollow-column forming mold characterized in that the mold is provided with gas-injecting means (12) for injecting an amount of gas (21) into the mold cavity parts (16) forming the hollow columns, gas-discharging means (30) for discharging injected gas after cooling the molded crate to discharge temperature and a passage (27) in the mold wall for passage of the gas injector means. Device according to claim 10, characterized in that core movement limiting means (12) are provided for moving cores (10) out of the mold cavity to the lower limit (11) of the mold cavity when the mold is closed. Device according to claim 10 or 11, characterized in that the device is provided with gas injection control means (29) for starting each gas injection. Device according to claims 10-12, characterized in that the device is provided with core output means (28) for feeding the cores (10) from a closed mold cavity part (16), which output means (28) are efficiently coupled to the gas injection control means (29). Device according to one or more of the preceding claims 10-13, characterized in that in addition to the means (29) for independently controlling the start of the gas injections to the individual injection points, gas discharge means (30) for simultaneous discharge. of the gas from all hollow parts (9) of the formed plastic crate.