The present invention relates to a machine for fitting heat-shrink plastics material sleeves on objects, in particular elongate objects of small section, the sleeves being taken from a continuous sheath that is rolled up flat.
In a technique that is conventionally used in this field, this type of machine for fitting sleeves has a shaping mandrel over which the sheath is passed in order to open it, sheath drive means using motor-driven wheels which co-operate with an associated portion of the shaping mandrel to fit the open end of the sheath on an object, and cutter means that act between the shaping mandrel and the object to form a sleeve that is associated with said object.
Thus, over the last score or so years, a concept has been developed of shaping mandrels that are mounted floating and that extend vertically. On this topic, reference can be made to the following documents: FR-A-2 490 590, U.S. Pat. Nos. 3,792,807, 3,910,013, 4,016,704, 4,600,371, GB-A-1 430 090, and EP-A-0 109 105.
To transfer the sheath continuously around the shaping mandrel, the machines described in the above-specified documents use motor-driven presser wheels co-operating with backing wheels carried by the shaping mandrel, with the sheath that surrounds the shaping mandrel while traveling along it being clamped between the motor-driven presser wheels and the backing wheels which are mounted idle on axles associated with the mandrel. Those techniques are now thoroughly understood and in widespread use for fitting sleeves on objects such as flasks, bottles, and other containers.
Nevertheless, if it is desired to use sheaths of small diameter for putting on objects that are fine and elongate, i.e. sheaths of a diameter considerably smaller than 20 mm, the above technique using backing wheels mounted idle on the shaping mandrel becomes impractical. It is not possible to envisage mounting backing wheels on a shaping mandrel of diameter significantly smaller than 20 mm since such backing wheels would then be very small in diameter which would require them to rotate at very high speeds of rotation as the sheath travels along the shaping mandrel, and that would give rise to phenomena of wear and overheating that are incompatible with reasonable use on an industrial scale.
Proposals have also been made to organize the travel of the sheath over a shaping mandrel by pinching the sheath between two motor-driven wheels at an intermediate opening in the shaping mandrel.
Thus, document JP-A-1 410 808 discloses a floating mandrel type shaper having, in addition to an arrangement of wheels and idle backing wheels, a central window in which two motor-driven wheels pinch the walls of the sheath. However, the floating mandrel continues to be supported by the wheels and the backing wheels provided further up the shaper. Using the same approach, document U.S. Pat. No. 2,765,607 illustrates a floating mandrel which is constituted by two portions interconnected by side rods, with a central gap being formed in which the motor-driven drive rollers pinch the walls of the sheath. The floating mandrel is then supported by a rounded surface of the flattened top portion (which also forms an insertion spatula) bearing against the two motor-driven rollers. The bottom portion having a circular base then serves as a shaper and as a counterweight. Reference can also be made to document FR-A-2 738 797 which shows a shaper having two torpedoes interconnected by a plate where the sheath is pressed by driven wheels, or indeed to document EP-A-0 368 663 which shows a shaper having two floating mandrels, one of which is flat with a window (through which the sheath is pinched by drive wheels), while the other is torpedo-shaped, and disposed downstream from the cutter device.
In a variant, as shown in document FR-A-2 061 240, proposals have also been made to use a vertical shaper made up of two torpedoes interconnected by a rod, with drive wheels that pinch the flattened sheath in the vicinity of the rod, and with contact via four idle wheels being provided on each of the torpedoes. In that case also, the use of bearing wheels prevents the use of sheaths of small diameter.
Finally, the shaping mandrels shown in the above-mentioned documents do not really serve to solve the problem of transferring sheaths of very small diameter since inevitable phenomena of overheating and wear arise, which phenomena run the risk of damaging or even tearing the continuous sheath while it is being transferred over the mandrel. This is particularly true when it is desired to use such a machine at high rates of throughput, e.g. one hundred to two hundred sleeves fitted per minute. A sheath of diameter lying in the range 5 mm to 20 mm gives rise to a flat ribbon of narrow width (8 mm to 31 mm), and the flat ribbon is then relatively rigid and difficult to pull. The high mechanical strength gives rise to high forces that need to be overcome, from which the above-mentioned phenomena of overheating and wear arise. In addition, when rates of throughput are high, the positions of objects traveling beneath the shaper need to be controlled by using clamps or the like, thereby further complicating the structure of the fitting machine.
In general, the above-described techniques do not genuinely make it possible to optimize expanding the sheath while accurately controlling the section of the sheath as it leaves the shaping mandrel to engage on the object concerned. This makes it necessary to provide sheaths of diameter that is considerably greater than that of the objects they are to cover. Consequently, it is not possible to control the position of the sleeve in satisfactory manner, either axially or transversely. This becomes particularly critical when the sleeve is to be shrunk onto the object, in so far as the sleeve can be poorly positioned on the object and in any event shrinking needs to be that much greater. The person skilled in the art is well aware of the difficulties encountered under such circumstances, and in particular concerning attempts to control the position and the shrinking of the sleeve, above all when such a sleeve has printed wording and/or decoration thereon.
The invention seeks specifically to resolve that problem by designing a sleeve-fitting machine that gives higher performance while avoiding the above-mentioned drawbacks.
Thus, the object of the invention is to design a machine for fitting sleeves of heat-shrink plastics material on objects starting from a continuous sheath that is rolled up flat, the machine being entirely compatible with sheaths of small diameter, e.g. diameters lying in the range 5 mm to 20 mm, while nevertheless being capable of operating at high rates of throughput, i.e. considerably exceeding 200 sleeves fitted per minute, with the positions of the sleeves as fitted on the objects nevertheless being properly controlled.
According to the invention, this problem is resolved by a machine for fitting sleeves of heat-shrink plastics material on objects, the sleeves being taken from a continuous sheath that is rolled up flat, the machine including a shaping mandrel over which the sheath passes in order to be expanded, sheath drive means using motor-driven wheels which co-operate with an associated portion of the shaping mandrel to engage the open end of the sheath on an object, and cutter means intervening between the shaping mandrel and the object so as to form a sleeve associated with said object, the shaping mandrel being substantially horizontal and comprising two torpedoes in axial alignment interconnected by a thread-like central element, with an upstream torpedo having an upstream end forming an insertion spatula and a downstream end with a pair of smooth chamfers, and a downstream torpedo presenting an upstream end with a pair of smooth chamfers and a downstream end with a straight edge adjacent to the cutter means, each torpedo of said mandrel resting freely in an associated V-support, and the sheath drive means comprising, between the two V-supports, two adjacent pinch wheels disposed symmetrically on either side of the thread-like element of the shaping mandrel and passing in the vicinity of the chamfered smooth edges of the torpedoes, each wheel having a peripheral groove complementary to that of the other wheel so as to form a horizontal axis passage for said thread-like element.
By means of such an arrangement of two horizontal torpedoes interconnected by a thread-like central element, with the smooth double-chamfer ends thereof being free from bearing wheels, it is possible to organize the opening and rapid transfer of continuous sheaths of very small diameter. In addition, horizontal transfer makes it considerably easier to control the positions of the objects, even at high rates of throughput, e.g. by using sprocket-wheels.
It should be observed that the floating mandrel techniques described in the above-cited documents would be completely impractical for transferring a sheath horizontally.
Preferably, the insertion spatula of the upstream torpedo extends in a plane which is substantially perpendicular to the plane in which the continuous sheath is pinched between the two wheels. This makes it possible to shape the sheath around the mandrel which confers an ace-of-diamonds shape to the section of said sheath on leaving a shaping mandrel whose downstream torpedo is of substantially circular section, said shape being favorable both for transferring the sheath gently onto a cylindrical object, and for ensuring that the sheath is cut cleanly and without creasing downstream from the shaping mandrel. Naturally, it is possible to provide special shapes for the outlet section of the downstream torpedo in order to preform the sheath in ways that are adapted to the section of the object concerned.
Advantageously, the upstream torpedo and/or the downstream torpedo has two plane side facets substantially perpendicular to the plane in which the continuous sheath is pinched between the two wheels. These plane side facets decrease the side friction between the sheath and the torpedoes of the shaping mandrel, which is particularly favorable when said sheath carries a deposit of varnish or of some other material on its inside wall.
Preferably, the thread-like element is a flexible wire anchored at both ends in the torpedoes, one of the anchored ends being releasable so as to enable the length of said thread-like element between said torpedoes to be adjusted. For example, the thread-like element can be constituted by a steel wire having a diameter of about 1 mm.
Also preferably, the pairs of smooth chamfers of the upstream and downstream torpedoes are formed by sloping plane facets disposed symmetrically about a midplane containing the thread-like element and tangential to the two pinch wheels.
In particular, the pair of smooth chamfers of the upstream torpedo is formed by two plane facets sloping at about 30xc2x0, and the two pinch wheels pass tangentially over said pair of smooth chamfers, while the pair of smooth chamfers of the downstream torpedo is formed by two plane facets that slope at a smaller angle. It is also possible to provide for the pair of smooth chamfers to be defined by two fitted inserts, that are preferably interchangeable, having free facets constituting the sloping plane facets that co-operate with the pinch wheels.
A longitudinal slot can also be provided at the bottom of the V-groove of each torpedo support: such a slot makes it easier to pass the bottom fold of the sheath and avoids crumpling it.
According to another advantageous characteristic, the cutter means comprise a blade carried by a rotary arm on a horizontal axis, and said means is positioned in such a manner that its blade is flush with the straight edge of the downstream end of the downstream torpedo.
It is then preferable for the cutter blade to have two rectilinear cutting edges that meet at a leading edge and for the two cutting edges to be substantially perpendicular and arranged in such a manner that the leading edge meets the top of the sheath in the vicinity of a crease therein that results from said sheath passing over the insertion spatula or between the two pinch wheels.
The cutter means organized in this way makes it possible to obtain a perfectly clean cut that is made progressively, without folding the sheath, and in a very short length of time.
According to another advantageous characteristic of the invention, the two pinch wheels are peripherally coated in elastomer, and come into contact with each other on either side of their peripheral grooves which are trapezoidally shaped and present two facets sloping symmetrically about their midplane, forming a V that opens at an angle of about 60xc2x0, and the two pinch wheels are chamfered on their outer edges.
Advantageously, the two pinch wheels are mounted on a carrying structure capable of pivoting, preferably about a vertical axis, so as to enable the drive means as a whole to be offset laterally. It then becomes easy to take action quickly for cleaning or for the purpose of changing sheath format.