The invention relates to an improved rotating head for producing cans or jars (technically called a rollina or rolling seamer), and to the machine containing the head.

The rolling seamer of a can-making machine is used to crimp the lid of the can to the cylinder constituting the can body. For this purpose a peripherally-shaped idle roller is used to bend and crimp the edges of the sheet metal to be attached one on top of the other, see e.g. EP3397409 The well-known rolling seamers consist of a roller made of a hard, stainless material (e.g. stellite) in which the seats for a pair of bearings are obtained.

Known rolling seamers have several problems.

Since the roller is made of very hard material, for its machining it requires very expensive tools which tend to break easily if not operated with the utmost care. Then, the adjustment of the bearing pair to determine the minimum clearance and/or preload has to be performed by a specialized technician with rather high mounting times, especially when performing maintenance The short life of the bearings imposes high maintenance costs, to which the costs of the oil or grease lubrication system (specific for foodstuffs) are added.

Improving this state of the art and obviating at least one of these problems is the primary object of the invention.

Another object is to make a rolling seamer that is simple to build, inexpensive, reliable and long lasting.

One or more objects are achieved by what is defined in the attached claims, wherein the dependent ones define beneficial variants.

A first aspect of the invention relates to a rolling seamer for a can or jar seaming machine, or generally to a rolling seamer for seaming cans or jars. The rolling seamer comprises: an outer seaming roller that coaxially contains an inner bearing, wherein the bearing comprises a ring rotatable on rolling elements and coaxial to the roller, and the ring and the seaming roller are made of ceramic.

The ceramic parts ensure high strength and durability, greater than that of their metal counterparts, and do not need to be repaired at the end of their working life.

The inner bearing is preferably formed of two (or more) coaxial ceramic rings rotatable on rolling elements, and in particular consists only of two coaxial ceramic rings rotatable on rolling elements.

Preferably, the rolling seamer comprises rolling elements mounted to slide on a track formed on the outer surface of the or of each ring and on a track formed on the inner surface of the seaming roller.

Usually the most delicate part of the rolling seamer is the bearing, which determines the working life of the rolling seamer or the frequency of maintenance. The aforementioned design of the bearing allows its working life to be extended, at least as long as that of the ceramic roller, so the overall working life of the rolling seamer is increased.

Preferably a seal is mounted on the rings to keep the lubricant water-tightly inside the bearing; in particular, the annular space created between one or each ring and the roller for the rolling elements contains or is filled with grease, particularly food-grade grease. The adoption of grease, which is denser than oil, facilitates the containment of the lubricant inside the rolling seamer to avoid leakage In addition, the grease makes it possible to eliminate maintenance by lubrication during the life of the bearing. In some conditions it is possible to provide for water lubrication or a total absence of lubrication.

A second aspect of the invention relates to a seaming machine comprising the aforementioned rolling seamer in one or each variation. The machine, especially if it comprises a rotary table with a plurality of peripheral rolling seamers, is able to produce cans with reduced costs and less maintenance.

The advantages of the invention will be clearer from the following description of a preferred embodiment of a rolling seamer, referring to the accompanying drawing in which

- Fig. 1 shows a cross-sectional view of a rolling seamer for cans.

A rolling seamer 10 is mountable on a fixed or rotating support of a seaming machine (not shown) to assemble the lid and center body of a can or jar.

The seaming is done in a known manner by means of an outer seaming roller 12 having a seaming edge 14 The roller 12 is mounted idle around an inner bearing 30 so as to rotate about a Z-axis. The Z-axis is also the axis of symmetry for the rolling seamer 10.

The bearing 30 is formed of two concentric, superimposed rings 32, 34 that are coaxial to the Z axis. The diameter of the rings 32, 34 is the same but not necessarily.

Between each of the rings 32, 34 and the roller 12 is a respective crown of rolling balls 36. The balls of one crown have centers lying in a plane Y1 and the balls of the other crown lie in a plane Y2. The planes Y1 , Y2 are parallel to each other, not coincident and spaced apart, and orthogonal to the Z axis. On the facing surfaces of the roller 12 and the two rings 32, 34, raceways are obtained for the balls 36, in particular, the raceways are concavities with curvature complementary to that of the balls 36.

The balls 36 are made of ceramic or plastic.

The two rings 32, 34 and the roller 12 are made of ceramic (ceramic has a longer operative life than metal) Note the difference with the structure in EP3397409: in the rolling seamer 10 the balls 36 touch the rings 32, 34 on one side and the roller 12 on the other, while in EP3397409 the bearing is formed of concentric rings of different diameters. Since the roller 12 is made of ceramic it is not possible to use the bearing structure in EP3397409, In fact, for the roller 12 to perform its seaming function, it is necessary for the bearing to be inserted by interference inside the roller 12. The operational interference with which the bearing should be inserted causes a tensile stress in the roller that is not compatible with the mechanical strength characteristics of the ceramic, thereby causing its premature failure.

The construction of the rolling seamer 10 allows the use of discs 32, 34 with larger diameters than EP3397409, so the bearing 30 is more resilient and longer-lasting, so much so that it can equal the life of the roller 12, which is longer than a common metal roller.

This way the estimated service life of the entire rolling seamer 10 is at least twice as long as usual. In addition, there is no need for automatic lubrication systems. Another advantage is that the rolling seamer 10 is disposable, i.e. it does not require maintenance (ceramic parts are not regenerated) and is completely replaceable at the end of its life.

Between the roller 12 and the rings 32, 34 there remains a space S, which contains the balls 36. The space S is preferably filled with lubricant (e.g. food-grade grease) and may be enclosed, at the opposite edges of the rings 32, 34, by two (optional) seals 50. The seals 50 prevent leakage of grease from the bearing to seamed products, e.g. delicate products such as foodstuffs.

An (optional) cylindrical cage 60, e.g. made of plastic, is arranged around the rings 32, 34 at their contact plane The cage 60 serves to axially distance the balls 36 and to keep them in position inside the rolling seamer 10. The monolithic design of the two rings 32, 34 ensures precision in operation and little need for post-installation adjustment.

A variant envisages to use rolling elements other than balls, such as rollers, while keeping everything else the same. Ball bearings are the optimal solution because they combine a high load-carrying capacity with very low rolling friction. However, even though they have higher friction, (conical, cylindrical or barrel-shaped) rollers have higher load carrying capacities than balls, so they may be preferable in some applications.