The invention relates to a screw cap with a disk-shaped top part and a flange edge with an inner thread adjoining the outer circumference and extending perpendicular to the top part, wherein a bung opening with a bung plug having an automatic venting device is inserted in the center of the top part of the screw cap. Such screw caps are typically used for closing the upper fill opening of large volume pallet containers that have a fill volume of, e.g., 1000 liter.
Large-volume pallet containers are increasingly used for storing and transporting hazardous liquid contents (like e.g., chemicals). These pallet containers have an inner plastic container which is placed on a bottom pallet and a support jacket which is made of a tubular cage which closely surrounds the inner container and is secured to the bottom pallet. A corresponding screw cap (typical having a nominal width of 150 mm, 240 mm or larger) is used for closing the fill opening located in the top of the inner container. The fill opening in the top of the inner plastic container has a raised flange edge with an outside thread, onto which the screw cap is screwed, with an interposed seal providing gas- and liquid-tightness.
For example, EP-B 0 858 955 discloses a particular screw cap with an automatic venting device for use with pallet containers. In this conventional embodiment, the venting device is housed in a bung plug that is screwed in. The sealing element is here a thin membrane disk made of rubber or plastic which is formed so as to yield elastically due to its low material-specific stiffness in response to a reduced pressure in the container, with its thin outside edge admitting air into the container interior.
However, with this embodiment, the diminishing elasticity of the thin membrane disk over time is disadvantageous. The membrane disk must also be protected from upwardly splashing fill material by a splash guard, because otherwise the membrane disk would be at great risk to adhere to the bung plug, thus preventing the intended admission of air.
When dispensing hot, slowly cooling contents, but in particular when rapidly withdrawing liquid content from the lower discharge fitting, a reduced pressure is disadvantageously generated in the container of large-volume pallet containers, so that the thin-wall inner plastic container collapses, unless countermeasures are taken. Typically, when fully discharging the liquid content, the screw cap is simply manually unscrewed or loosened from the fill opening by an operator, until a volume of air equal to the volume of the discharged liquid can enter the interior of the plastic container. However, an operator oftentimes forgets to loosen the screw cap before withdrawing the liquid or to close the screw cap after the liquid content has been withdrawn. In particular in automated production processes, which involve storage of liquid components in pallet containers and sequentially supply to the production process, the screw cap can no longer be operated by hand, so that screw caps with automatic venting devices must be employed.
It is an object of the present invention to provide a screw cap or bung plug with automatic venting device, in particular for large containers such as pallet containers, to prevent generation of an undesirable reduced pressure inside the container, and hence to reliably prevent the container from collapsing. The screw cap or bung plug with an automatic venting device should have simple design and should be easy to manufacture at low cost and resist adhesion due to splattered content.
The object is attained by the invention the features set forth in claim 1. Additional advantageous embodiments of the present invention are recited in the dependent claims.
According to the invention, a core component of the venting device is a disk-shape valve disk made of plastic, with a separate resilient element also made of plastic, wherein the resilient element is arranged below the valve disk and has at least three elastic spring legs. The installation of the prefabricated injection molded plastic parts in the screw cap or bung plug is relatively simple and cost-effective, with the separate resilient element ensuring that the valve disk opens and closes reliably. The bung plug has a through opening for air with a diameter of about 20 mm (±2 mm), allowing unimpeded airflow of up to 200 l/min. This approach effectively prevents the thin-walled inner plastic container from imploding or collapsing, when the liquid content is withdrawn. The venting device can therefore prevent reduced pressure in the container from causing undesirable indentations in the container wall or depressions in the top of the thin-walled inner plastic container. The ventilation opening allows proportionate admission of air in the screw cap of the fill opening and a steady outflow without undesirable gurgling and without detrimental generation of a reduced pressure in the container interior, when content is withdrawn from the lower withdrawal fitting of a pallet container.
The present invention is characterized more particularly by the following features:
According to a preferred embodiment of the invention, the venting device is implemented as a conventional two-inch bung plug (70×6) with an outside diameter of about 70 mm.
An exemplary embodiment of the invention will now be described in more detail with reference to the drawings, which show in:
A bung fitting opening is arranged in a bung fitting with an inner thread in midsection in the disk-shaped top part of the screw cap 1 for threaded engagement of a bung plug 3 with a venting device in a gas- and liquid-tight manner by means of another sealing ring 4. The actual venting device is made of three separate parts, namely a valve disk 5, a resilient element 6 and an adapter ring 7. A cover 8 with a seal is placed on the outside of the bung plug fitting to guarantee authenticity, which is in turn covered by a cap 9 to protect against ingress of rainwater, when the pallet container is stored outside.
The large sealing ring 2 seals the screwed-on screw cap 1 in the closed state against the upper end face of the flange edge in the top of the inner plastic container of the pallet container. The bung plug 3 is screwed by way of the smaller sealing ring 4 into the bung opening in the bung fitting with inner thread in midsection of the screw cap 1. The venting device, comprised of the separate components valve disk 5, resilient element 6, and adapter ring 7, is inserted into the bung plug 3 from below. The bung plug 3 is covered on the outside or from atop, respectively, by means of the cover 8 with seal of authenticity and the cap 9.
The bung plug 3 depicted in
When constructed as separate parts, the valve disk 5 can be made of an elastically softer plastic material (HD-PE) and the resilience element 6 of a harder or stiffer plastic material (HD-PE) with a greater spring return characteristic.
For a permanent and non-releasable connection, the inside of the ring flange 23 of the bung plug and the outside of the adapter ring 7 are provided with a longitudinal and/or transverse groove profile 24. The adapter ring 7 can also be affixed in the ring flange 23 of the bung plug 3 with an adhesive or welded by ultrasonic welding.
All components of the bung plug with a venting device have a comparatively simple construction and can be easily installed together; they are made essentially of a thermoplastic material HD-PE (High Density Poly Ethylene) and can be recycled and reused without requiring further separation or sorting.
To illustrate the operation,
The bung plug 3 has for the venting device an unobstructed air passage opening 15 (without interfering cross brace) with a diameter of about 20 mm (±2 mm), allowing sufficient airflow of up to 200 l/min. The air passage opening 15 can be closed with a valve disk forming a sealing element and placed on the resilient element. The central opening of the valve disk 5 is firmly pressed onto the ring flange 18 (diameter abroad 20 mm) of the resilient element 6. The valve disk, resilient element, adapter ring and bung plug or screw cap are made of HD-PE plastic. The valve disk is urged in front of the air passage opening in the bung plug by three or four spring legs secured on the outer edge of the resilient element. The spring legs are formed as ribs on a partial circle and are supported on the outside against a radial ring flange of the screw cap or the adapter ring on a large diameter of about 40 mm. For a cost-effective solution, the valve disk with the integrated resilient element is made of a separate prefabricated HD-PE injection molded part. The valve disk automatically opens under a reduced pressure and closes automatically when the reduced pressure is removed, due to the spring force of the resilient element and/or the return force of the three spring legs.
Number | Date | Country | Kind |
---|---|---|---|
20 2006 000 600.1 | Jan 2006 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/EP2007/000212 | 1/11/2007 | WO | 00 | 6/30/2010 |