Pressure equalization valve for reusable menu trays for the delivery of hot food

Abstract

Pressure equalization valve for reusable menu trays with lids for hot food deliveries, characterized in that a curved membrane, which is convex on the outside and concave on the inside, has a centrally arranged shaft on the concave side of the membrane, which extends perpendicularly from the inner membrane.

Description

[0001] The following invention concerns a pressure equalization valve for meal trays containing warm food. These meal trays, consisting of a tray and lid, are then delivered warm to the end customer shortly after preparation in the cooking process: retirement homes, nursing homes, kindergartens, schools, government offices, commercial and industrial establishments. The meal tray is often divided into several sections for meat, vegetables, potatoes, and side dishes.

[0002] The lid is designed to prevent the food contents from leaking during transport to the end customer. In common parlance, there have long been apt terms such as: Meals on Wheels. State of the art:

[0003] Almost without exception, ready-meal trays are disposable. Businesses that deliver freshly prepared meals while still warm to the end customer often find that the cost of disposable packaging is almost equal to the contents of the meal.

[0004] Good thinking suggests creating reusable meal trays with lids. This doesn't even involve the tried-and-tested deposit bottle principle; instead, the catering company and supplier take the old meal trays and lids back with them on the next delivery, clean them, and refill them.

[0005] Environmentally and resource-friendly ready meal delivery can be achieved this way: • Menu tray and lid come as injection-molded items • Plastics used are approved for food packaging • Plastics used are suitable for dishwashers • An attractive design of the menu box is possible, for example a transparent lid to allow the contents of the food to be seen before opening. • Medium to high quantities are state of the art in injection molding technology

[0006] But there is a physical problem: The cook would like to fill the food at approximately 70 degrees Celsius after cooking and close the lid for prompt shipping. However, the steam pressure at 70 degrees Celsius is already 0.3 bar. The internal pressure times the projected area determines the opening force between the meal tray and the lid.

[0007] Example: Lid area is 211 × 172mm 2 Calculating pressure times projected area yields the opening force against the lid from the inside. At a temperature of 70 degrees Celsius, this results in an opening force of 112.4 kg, assuming the meal tray and lid are sealed against spillage of liquid sauces.

[0008] The subject of this invention is the development of a suitable pressure compensation valve.

[0009] Conventional disposable trays with lids for hot meals avoid the overpressure problem by placing gas-permeable covers between the tray and lid. However, the gas-permeable seal between the tray and lid must be positioned at the very top, otherwise the sauce will leak out.

[0010] New, reusable meal trays with lids don't necessarily require a gap between the tray and lid at the very highest point to prevent spillage. Instead, a pressure equalization valve in the lid at the highest point is required.

[0011] The requirements for a new type of menu tray valve are: • Easy disassembly and assembly before and after cleaning for reuse. • Valve, if possible, not as a complex assembly that then has to be disassembled and reassembled. • The valve is best manufactured as a single piece using injection molding. • The lid should have a hole-shaped opening into which the valve can be easily inserted or pulled out. • The valve should be inserted into the lid opening with a shaft and secured on the inside of the lid to prevent it from falling out. • The valve should have the geometry of the cover on the outer skin of the cover over the entire contact area. • The valve should be injection-molded from a thermoplastic elastomer (TPE) so that it can adapt even better to the outer contour of the lid. • The Shore hardness should be between 30 (like silicone) and 70 (like hard rubber).

[0012] In the inventive activity, physical and technical experiments were initially carried out: The already production-ready injection-molded meal trays with lids, where the overpressure problem needed to be resolved, were provided with a hole-shaped opening in the lid for the valve to be developed. The mounting opening was ideally located centrally in the lid and, above all, at the highest point of the lid. The initially 3D-printed test valves made of TPE plastic then enabled numerous practical tests: • Filling temperature of the warm food at 70 degrees Celsius. • Now place the lid with the built-in valve onto the meal tray. • Transport tests and vibration tests on bumpy roads.

[0013] In these technical-physical preliminary tests, the lid now remains securely on the meal tray without being opened by the steam pressure.

[0014] The newly developed valve allows the steam pressure to escape from 0.3 bar to ambient pressure.

[0015] These tests revealed an additional physical effect: By specifically shaping the exhaust valve, it's possible to ensure that only excess pressure escapes from the inside to the outside. The valve then adheres to the lid, preventing any air from outside from re-entering the interior.

[0016] As the steam slowly cools in the container, the water in the steam condenses and a negative pressure forms in the container, which pulls the lid even more tightly onto the container.

[0017] This physical effect is actually desirable here, as it gives the lid an even firmer hold against the meal tray.

[0018] This means that the valve developed here is a one-way valve to achieve this negative pressure effect.

[0019] The valve pin, which extends inwards through the lid opening, is secured against falling out of the lid by means of undercut locking hooks.

[0020] The shape of the locking mechanism is designed in such a way that it can be inserted through the opening hole in the lid when slightly compressed and clicks into place against the inside wall of the lid when the valve membrane rests on the lid.

[0021] In tests with different valve geometries, it has been shown to be advantageous to let the sealing membrane sit on the top of the cover under slight spring preload when the locking of the valve stem snaps into place on the inside of the cover.

[0022] The travel of this spring preload should be as large as possible and maintain a similarly uniform spring force throughout the entire spring travel. Disc springs in machine components have this desired flat spring characteristic. The application of the physical properties of disc springs is now to be integrated into the valve. The inventive implementation is achieved by shaping the outer sealing membrane. Similar to disc springs, the spring membrane of the seal then no longer contacts the cover on the outside over the entire sealing surface, but only at the outer edge along an annular contact line.

[0023] However, it is disadvantageous to achieve the spring travel by elastic stretching of the valve stem: The achievable spring travel is then very small and there is no flat spring characteristic curve for pressing the valve membrane onto the outside of the lid of the menu tray.

[0024] This allows the valve pin, which protrudes through the opening in the lid to lock from the inside, to be made much more dimensionally stable.

[0025] The correct thickness of the now convexly curved valve membrane is crucial for the desired valve function. Selecting the Shore hardness (30-70) of the thermoplastic elastomer (TPE) allows the responsible specialist to determine the thickness of the sealing membrane for spring travel, spring force, and tightness. Fig. 1 shows an example of a currently series-produced plastic injection-molded meal tray (2) with a closed lid (1) Fig. Figure 2 shows the meal tray (2) with the lid (1) in the open position. The opening (3) for inserting the valve is already present in the center of the lid. However, the meal tray (2) with the lid (1) are not the subject of this invention. The novel valve makes these two injection-molded parts made from expensive injection molds usable. Fig. Figure 3 shows an embodiment of the valve in four main views: top view (8), bottom view (4), front view (6), side view (7), section (11), section (9) and four perspectives (5), (10), (12) and (13). Fig. 4 shows the menu tray (2) with lid (1) in section and the valve (14) in the non-installed state (N) and in the installed state (E) and with two detailed enlargements not installed (N) and installed (E). Fig. 5 shows a section of the valve (14) in the non-installed state (N) and in the installed state (E), significantly enlarged: one can see the thin-walled, outwardly convexly curved membrane (18a) connected to a centrally arranged shaft (19a), which projects inwards through the cover (1) and, after snapping into place on the inner cover wall (1), brings and holds the outer membrane (18a) under spring tension.

[0026] An advantage of designing the outer sealing membrane (18a) with a convex, outwardly curved, thin-walled design is the almost constant spring force with increasing deformation of the outer sealing membrane (18a) until the locking (20a) takes place on the inner cover wall (1).

[0027] Reason: Here, a transmission invention is created from the previously known machine element, the disc spring. This consists in integrating a disc spring-like geometry into a novel injection-molded part (14).

[0028] A further advantage of this shape of the diaphragm (18a) is that the contact surface (23a) of the diaphragm (18a) for sealing extends to the outermost annular region (19a). This increases the contact pressure of this valve (14) compared to a full-surface contact with the cover (1).

[0029] A further advantage is that the internal steam pressure can escape safely through this easily deformable membrane (18a).

[0030] A further advantage of the design of this membrane seal (18a) is that tight manufacturing tolerances of the sealing element (14) and the cover (1) now play a subordinate role in ensuring a secure sealing function if the membrane (18a) is not pulled completely flat on the cover (1).

[0031] When developing this product, the responsible specialist ensures that after the hooks (20a) of the shaft (19a) have engaged, a residual curvature (21a) of the sealing membrane (18a) always remains on the inside of the lid (1). This allows the excess pressure to escape safely to the outside.

[0032] The shaft (19a) of the membrane (18a), which is provided with locking hooks (20a), is wide-slit lengthwise (22a) so that the locking hooks (20a) can be pushed through the opening (3) of the cover (1) after being compressed and then engage.

Claims

[1] Pressure equalization valve for reusable meal trays with lids for hot food deliveries characterized by that a curved membrane which is convex on the outside and concave on the inside has a centrally arranged shaft on the concavely curved side of the membrane which extends perpendicularly from the inner membrane. [2] Pressure compensation valve according to claim 1 characterized by that the shaft is slotted lengthwise [3] Pressure compensation valve according to claim 1 and 2 characterized by that the shaft is provided with locking hooks. [4] Pressure compensation valve according to claims 1, 2 and 3 characterized by that the active surface of the locking hooks faces the concave surface of the membrane. [5] Pressure compensation valve according to claims 1, 2, 3 and 4 characterized by that the membrane and shaft with locking hooks consist of one part. [6] Pressure compensation valve according to claims 1, 2, 3, 4 and 5 characterized bythat the pressure compensation valve is an injection-molded part made of spring-elastic plastic.

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