WM Thermoforming Machines SA is offering the automatic rim rolling machinery for clients who are looking for improved product quality of their conical cups or containers. These rimming units are widely used in the production of disposable cups made of Polystyrene, Polypropylene, APET or PLA.
Disposable cups most likely require a rolled rim on the upper part of the mouth of the cup. The rimming process rounds off the edge by folding the lip under the rim. The result does not only provide a more comfortable contact when drinking from the cup but at the same time provides a greater rigidity to the product. Disposable plastic cups are mostly being produced on a “form-punch” thermoforming machine for simultaneous forming and punching in the same station. These machines have a tilting lower half-mould which rotates 75 degrees, allowing the automatic extraction of the products from the mould, followed by the stacking and conveying process of the product. Alternatively, a thermoforming machine with a large forming area is used in combination with a separate high-speed horizontal trim press for cutting out the perimeter of the cups.
The raw material used in the thermoforming process will determine which of the two systems will be most suitable. Polystyrene has a good dimensional stability and a very low shrinkage rate during the cooling process allowing the cups to be finished in a separate trim press station. For all polypropylene products, it is necessary to form and cut in the same station in order to guarantee a constant perimeter cut tolerance. On the other hand, the perimeter cut tolerance will be affected negatively when producing in a separate forming and trim press station as the shrinkage of the material will take place due to the cooling down of the sheet between the two stations. In addition to the previously mentioned thermoforming process, very high production capacities are mostly handled by “in-line” plants which also incorporate the sheet extrusion process. These production lines go from processing the raw material of pellets up to the packing of the finished product. Here we are talking about a true production island.
WM Thermoforming Machines SA designs and manufactures both of above-mentioned production systems. A very common in-line product is the 200cc disposable cup with production levels of 125,000 up to 200,000 cups/hour in polypropylene and polystyrene respectively. Taking above into consideration, WM has created two different types of automatic rimming machinery covering both types of production lines that are adjusted to the characteristics of the material to be processed. We developed in other words a specific rim roller for polystyrene cups and another for polypropylene and PET.
The two units mainly differ in the length of the rim-rolling screw (longer screw for polypropylene and shorter screw for polystyrene cups) as well as in the infrared heating system. When rimming polypropylene the heating occurs along the total length of the three rim-rolling screws creating a closed heating chamber while the cups are passing through the screws.
Now, the rimmed cups are automatically transported on a conveyor belt before reaching the downstream units for counting, film sleeving and boxing.
When the cups leave the punch and die mould or in-line trim press station, the upper edge of the cup has been formed into an inverted U-shape. The size and thickness of the edge are critical and must be considered carefully when designing and manufacturing the mould. It is important to maintain all these parameters during the thermoforming process in order to ensure a perfect flange and an adequate uniform aesthetic appearance.
The rim-rolling screws are obviously the heart of the system and the profile of the grooves that constitute the thread of the screw are being produced according to the type of cup, stacking passage and material to be used taking into account the dimensional shrinkage value of the material.
Ultimately, there is a very wide range of cups with different diameter openings. Just think of the difference between a classic coffee cup and a beer glass. For this reason, the rim-rolling screws can be easily exchanged according to the design of the cup and adjusted in relation to the cup’s diameter. The retooling of the rimming machine is very simple. In a few steps, the operator will be able to make fast, easy and safe production changes.
WM Thermoforming Machines SA has more than twenty years of experience in designing and manufacturing these kind of ancillary units, completing in this way its thermoforming machinery product range, whether they are “in-line” with extruders or “off-line “machinery with material fed on a reel.