PROCESS FOR MANUFACTURING A PLASTIC CRATE BY INJECTION MOULDING, AND PLASTIC CRATE MANUFACTURED BY SAID PROCESS

Abstract: A plastic crate has a bottom (1) and upright side walls (2 to 5). The two short side walls (4, 5) are provided near the top side with a handle (8, 9) bounded at the bottom side by a handle opening (10, 11). Each handle (8, 9) is made hollow with a substantially closed outer wall enclosing at least one cavity. Each handle (8, 9) which is integral with the remainder of the crate is provided with at least one bore (16) of relatively small size by means of which the at least one cavity in the handle (8, 9) is connected to the environment. The crate is manufactured by injection moulding. The hollow handles (8, 9) are formed by injecting gas under pressure into the stream of liquid plastic material for the formation of each handle.

Description: The present invention relates to a process for manu- facturing a plastic crate by injection mouding, said crate having a bottom and upright side walls, at least one of the side walls being provided near the top side with a handle bounded at the bottom side by a handle opening, the handle having a substantially closed outer wall which is integral with the remainder of the crate, the process comprising the steps of injecting a liquid plastic material into a mould cavity corresponding to the shape of the crate to be manufactured, until the mould cavity is substantially filled, cooling the injected plastic material, and opening the mould. Such a process is disclosed in US-A-3,506,154. In this known process an expanded or foamed resin is injected directly into a mould cavity. That part of the cellular material directly touching the mould cavity walls will be immediately chilled and form a high density non-porous skin, whereas the expanded material in the region between the mould cavity walls will remain a low density material. In this manner the hollow space between the outer and inner walls forming the bottom and the side walls will automati- cally include a cellular material. The known process has the disadvantage that the crate can only be manufactured from an expanded or foamed resin and that for manufacturing a double-walled crate a relati- vely large amount of material is needed. Moreover, with the known process the possible shapes of a crate are limited. The object of the invention is to provide a process which does not have these disadvantages. This object is achieved by a process of the abovemen- tioned type which is characterized in that a gas under pressure is injected into the stream of liquid plastic material for the formation of the handle, in such a way that at least one cavity is formed in said liquid material and that said material is blown against the wall of the mould cavity part for the handle, the gas pressure is maintained during the cooling of said material, and the gas pressure is released just before opening of the mould. By means of the process according to the invention many types of crates can be manufactured having relatively thin walls and having one or more handles which are sufficiently strong to carry the weight of the full crate and which lie comfortably in the hand. Through the process according to the invention the quantity of material required for the handle can remain limited. The mould used in the process can be relatively simple. This permits optimum fitting of cooling channels in the mould, so that the cycle time can be relatively short. The gas holds the walls of the handle pressed against the inside wall of the mould part concerned, which optimizes the cooling process. Preferred embodiments according to the process according to the invention are described in the process subclaims. The invention also relates to a plastic crate manufactured by injection moulding having a bottom and upright side walls, at least one of the side walls being provided near the top side with a handle bounded at the bottom side by a handle opening, the handle having a substantially closed outer wall which is integral with the remainder of the crate, characterized in that the handle is hollow, the wall of the handle enclosing at least one cavity which is connected to the environment by a bore of relatively small size in the wall of the handle. US-A-3,506,154 discloses a plastic crate having handles which are hollow. However, this crate is manufactured by a rotational moulding process and the wall of each handle does not enclose a cavity which is connected to the environment by a bore of relatively small size in the wall of the handle. The invention will now be explained in greater detail with reference to the following example of an embodiment shown in the drawings, in which: Figure 1 is a view in perspective of a possible embodiment of a crate according to the invention; Figure 2 is a side view on an enlarged scale of the crate of Figure 1 in the direction of the arrow II; Figure 3 is a view of a side wall of the crate of Figure 1, provided with a handle, in a section along the line III-III in Figure 2; Figure 4 is a top view of a side wall of the crate of Figure 1, provided with a handle, partially in a section along the line IV-IV in Figure 2; and Figure 5 shows a detail V of Figure 4 on an enlarged scale. The crate shown in Figure 1 comprises a bottom 1, two long upright side walls 2 and 3, and two short upright walls 4 and 5. The side walls of the crate are made double-walled, the inner wall of the double wall being removed locally, so that openings 6, 7 are produced in the side walls 2, 3 and 4, 5. The two opposite short side walls 4, 5 are each provided at the top side with a handle 8, 9, which at the bottom side is bounded by handle opening 10, 11. In the crate according to the invention the handles 8 and 9 are made hollow with a substantially closed wall 12 (see Figs. 3 and 4). The crate described above, with the exception of the handles, is moulded in a conventional manner by liquid plastic material being injected into a mould cavity in a mould corresponding to the shape of the crate, until the mould cavity is substantially filled, the injected plastic material is cooled, and the mould is then opened. According to the invention, each of the handles 8, 9 is formed by injecting gas under pressure into the stream of liquid plastic material for the formation of a handle 8, 9, in such a way that at least one cavity 13 is produced in said liquid material, and said material is blown against the wall of the mould cavity part for the handle. During the cooling of this material the gas pressure is maintained, and the gas pressure is released just before the mould is opened. The handles 8, 9 thus formed are subsequently integral with the remainder of the crate and can be designed with rounded edges 14, 15. The injection of gas under pressure into the stream of liquid plastic material for forming a handle 8, 9 can take place through a gas injection aperture which is provided in such a way in the mould cavity part for the handle in question that at the moment that the mould cavity part for the handle is not yet entirely filled with material this aperture is situated in the core of the material which has flowed in at the time. At that moment gas under pressure is injected through the gas injection aperture into the liquid plastic material. The formation of a cavity in a product made of plastic material by the injection of gas under pressure into the material is known per se, but not for the formation of a hollow handle on a crate. It is certainly not known to use this technique for the formation of a hollow part in a product made of plastic material at or in the vicinity of a flow seam, as is the case with the present invention. According to a particular embodiment of the process according to the invention, the material for each of the handles 8, 9 is introduced from the two sides into the mould cavity part for the handle 8, 9 in question, and the injection of gas under pressure takes place at the point where the material flows merge in the mould cavity part in question, at the moment that these material flows merge, and before the mould cavity part is completely filled. The gas injection aperture in this case lies approximately at the centre of the outside wall of the handle 8, 9. With this embodiment of the process according to the invention a crate of the type shown in the figures is obtained, the hollow handles 8, 9 each being provided with at least one bore 16 by means of which the cavity 13 in the handle 8, 9 is connected to the environment. According to another embodiment of the process according to the invention, the material for each of the handles 8, 9 is introduced from one of the two sides into the mould cavity part for the handle 8, 9 in question, and the injection of the gas under pressure takes place near the side of the particular mould cavity part where the material is being introduced, at the moment that the front of the material flow has just passed the gas injection point. The material for forming the handles 8, 9 then merges near the handles with the material of the remainder of the crate. The bore in each handle 8, 9 is then situated near one of the sides of the handle, for example at a point which is indicated by reference number 17 in Figure 2. According to yet another embodiment of the process according to the invention, the material for each of the handles 8, 9 is introduced from the two sides into the mould cavity part for the handle 8, 9 in question, and the injection of gas under pressure takes place near the sides of the particular mould cavity part where the material is introduced, at the moment that the fronts of the two material flows have just passed the gas injection points. The fronts of the two material flows meeting each other approximately at the centre of the handle are now pressed with great force against each other, thus causing a very intense fusion. With this embodiment of the process according to the invention, a crate is formed in which the two handles 8, 9 each contain two cavities which are separated from each other by means of a partition situated approximately in the centre of the handle, and in which each cavity is connected to the environment by means of its own bore. In Figure 2 the two bores near the ends of the handle 8, 9 are indicated by the reference numbers 17 and 18. In the example of an embodiment the invention is described for a crate of a specific shape. The invention is not, however, limited to such a crate and can be used just as well for crates or trays of a different shape and of different dimensions, with or without a lattice.

Claims: Process for manufacturing a plastic crate by injection moulding, said crate having a bottom (1) and upright side walls (2 to 5), at least one of the side walls (4, 5) being provided near the top side with a handle (8, 9) bounded at the bottom side by a handle opening (10, 11), the handle (8, 9) having a substantially closed outer wall (12) which is integral with the remainder of the crate, the process comprising the steps of injecting a liquid plastic material into a mould cavity corresponding to the shape of the crate to be manufactured, until the mould cavity is substantially filled, cooling the injected plastic material, and opening the mould, characterizing in that a gas under pressure is injected into the stream of liquid plastic material for the formation of the handle (8, 9), in such a way that at least one cavity (13) is formed in said liquid material and that said material is blown against the wall of the mould cavity part for the handle, the gas pressure is maintained during the cooling of said material, and the gas pressure is released just before opening of the mould. Process according to claim 1, characterized in that the material of the handle (8, 9) is introduced from the two sides into the mould cavity part for the handle, and the injection of the gas under pressure takes place at the point where the material flows merge in the mould cavity part in question, at the moment that these material flows merge, and before the mould cavity part is completely filled. Process according to claim 1, characterized in that the material for the handle (8, 9) is introduced from one of the two sides into the mould cavity part for the handle, and the injection of the gas under pressure takes place near the side of the particular mould cavity part where the material is being introduced, at the moment that the front of the material flow has just passed the gas injection point. Process according to claim 1, characterized in that the material for the handle (8, 9) is introduced from the two sides into the mould cavity part for the handle, and the injection of the gas under pressure takes place near the sides of the particular mould cavity part where the material is being introduced, at the moment that the fronts of the material flows have just passed the gas injection point. Plastic crate manufactured by injection moulding having a bottom (1) and upright side walls (2 to 5), at least one of the side walls (4, 5) being provided near the top side with a handle (8, 9) bounded at the bottom side by a handle opening (10, 11), the handle (8, 9) having a substantially closed outer wall (12) which is integral with the remainder of the crate, characterized in that the handle (8, 9) is hollow, the wall (12) of the handle enclosing at least one cavity (13) which is connected to the environment by a bore (16; 17, 18) of relatively small size in the wall of the handle. Crate according to claim 5, characterized in that the handle contains only one cavity (13), and the bore (16) is situated approximately in the centre or near one of the sides of the handle (8, 9). Crate according to claim 5, characterized in that the handle contains two cavities which are separated from each other by means of a partition lying approximately in the centre of the handle, and each cavity is connected to the environment by means of its own bore (17, 18). Crate according to claim 7, characterized in that the bores (17, 18) are situated near the sides of the handle (8, 9).

Inventors: ROSKAM, KLAAS
Applicants: WAVIN B.V.
Application year: 1990
Main classification: B29C45
IPC codes: B29C45, B65D25