The invention is applied to coiling machines with a rotary coil-forming head, employed on semi-worked stock arriving from hot-rolling such as round pieces, wire, rods or other, with a diameter of up to 5.5 mm.

The inserts according to the invention can also be used, thanks to their high level of resistance to wear, on drawing devices and at the inlet to the coil-forming head.

BACKGROUND OF THE INVENTION The state of the art includes machines to obtain coils from metal wire of various diameter comprising a rotary coil-forming head equipped with a coil-forming tube into which the half-finished product arriving from the rolling mill is introduced.

The rotation of the coil-forming head, as the metal wire, be it smooth or with protuberances, passes through it, subjects the relative tube to strong stresses which can compromise its structural integrity and/or initial geometric configuration.

The stresses are added to the tangential thrusts of the metal wire passing through, causing particularly bad conditions of friction, and therefore of wear on the inside of the tube.

This causes the machine to become unbalanced, as the tube becomes more worn, and therefore it needs re-balancing.

Moreover, the optimal inner trajectory of the metal wire is altered, which prejudices the formation of the coils.

For this reason, when the tube of the coil-forming head is made, it is integrated and lined on the inside with auxiliary elements with a high level of resistance to wear.

This embodiment, although it guarantees the coil-forming tube a longer life and therefore needs fewer interventions, it entails problems connected with the high costs of supplying and renewing the tube, which are caused by its more complex structure, and because it can only be partly interchanged.

The state of the art, for example in US-A-4.074.553, includes tubular inserts made of anti-wear material, introduced and clamped inside the coil-forming tube, which have abutment and automatic centering ridges on the outer surface which allow them to be assembled so as to define a transit conduit of the wire inside the tube.

These anti-wear inserts are costly, difficult to assemble and moreover they have a longitudinal size which cannot be less than set values, which entails problems in positioning them inside the tube.

This embodiment also entails problems during the replacement of the inserts, necessarily entailing the dis- assembly of the coil-forming tube or even the tube together with the relative rotary support.

Because of the particular and specific conformation of the inserts, they cannot possibly be interchanged.

Another problem which these anti-wear inserts involve is that they entail an increase in weight.

With the present speeds at which the rolled stock is delivered to the coiling machine, and the speeds which may be obtained in future, this increase in the weight of the coil-forming tube, with the consequent increase in inertia, entails serious problems which can only be solved by using bigger and stronger supporting and moving structures, with

consequent increases in costs, power used, manipulation, maintenance and otherwise.

The present Applicant has devised, tested and embodied this invention to overcome these shortcomings, preserving the tube from premature wear yet without entailing excessive increases in weight and therefore in inertia of the rotary structure, and to obtain further advantages.

SUMMARY OF THE INVENTION The invention is set forth and characterised in the main claim, while the dependent claims describe other characteristics of the main embodiment.

The purpose of the invention is to achieve anti-wear inserts for a coil-forming tube in coiling machines which are simple, functional and practical, and which do not entail a great increase in weight, and therefore in inertia, of the rotary tube, thus allowing the inserts to be adapted to increasing rolling speeds.

Another purpose of the invention is to allow resetting of the machine to be carried out quickly and hence with reduced interruptions to the cycle and very limited costs.

A further purpose of the invention is to make more manageable the operations to insert and remove the anti-wear inserts into/from the tube, so that these can be carried out by a single worker.

A further purpose of the invention is to make anti-wear inserts of a single type, simple in geometry and therefore economical to produce and with the characteristic that they can be adapted to the coil-shaped development of the tube.

The anti-wear inserts according to the invention are applied substantially to every tubular device to guide and draw metallic wire; the following description refers to a rotary tube for a coil-forming head but it must be understood that the field of the invention is not limited to

this application.

The anti-wear inserts according to the invention substantially consist of an annular body made of at least two coaxial parts solid with each other.

A first annular element, or outer element, is made of a metal of great lightness and coupling adaptability and has an outer diameter mating with the inner diameter of the coil-forming tube inside which the anti-wear inserts are to be introduced.

The metal of which this outer element is made may be a normal steel, or stainless steel, aluminium, titanium or similar.

The second annular element, or inner element, is made of a hard metal of great resistance to wear through friction and defines an inner cavity inside which the metal wire to be coiled is introduced and slides.

The metal of which this inner element is made can be, for example, titanium carbide or a"tough metal"with similar characteristics.

According to a variant, outside the first element there is a third element, coaxial to the other two, consisting of a toothed ring whose teeth couple, with their front surface, with the inner cavity of the coil-forming tube.

The inclusion of the third toothed element reduces the friction with the inner wall of the tube and facilitates the operations of inserting and removing the inserts into/from the tube itself.

According to a variant, the inner cavity of the inner element has a first connection or lead-in segment and a second substantially cylindrical segment.

According to another variant, the outer element has at least a circumferential hollow to make it lighter. In a further variant the outer element has angled bevels at the

front ends which, by allowing the scale which has accumulated in the connection zone of the insert and the tube to be removed and discharged, facilitate the removal of the insert.

The extraction procedure is advantageously preceded by a blowing cycle which allows to remove impurities, consisting of scale and particles, which can hinder the sliding of the inserts inside the tube.

The outer surface of the outer element of the anti-wear inserts is curved or rounded, which facilitates both the production process and their insertion/removal.

The limited longitudinal size of the anti-wear inserts makes them extremely adaptable to the coil-shaped development of the forming tube. This adaptability is increased by the shape of the front faces of the inserts which allows them to be arranged in continuous contact even in the curved segments of the tube.

The anti-wear inserts can be inserted inside the tube, and extracted therefrom, by means of a flexible cable element or a similar or comparable element.

Therefore, the anti-wear inserts according to the invention achieve a high resistance to wear, allowing to use the forming tube for a plurality of successive coiling cycles without altering the mechanical characteristics of the coil-forming head, or the stability or balance thereof.

At the same time, the weight of the tube is maintained within limited values by choosing a light material for the outer element of the inserts.

BRIEF DESCRIPTION OF THE DRAWINGS The attached Figures are given as a non-restrictive example, and show a preferential embodiment of the invention wherein: Fig. 1 is a front view of a coil-forming tube with

replaceable anti-wear inserts according to the invention; Fig. 2 is a section from A to A of Fig. 1; Fig. 3 is a front view of an anti-wear insert according to the invention; Fig. 4a is a section from B to B of Fig. 3; Fig. 4b shows a variant of Fig. 4a.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT The coil-forming tube 11 for a coiling machine has inside anti-wear inserts 10 according to the invention with an annular shape defining an inner cavity 12. The anti-wear insert 10 consists, in this case, of three coaxial elements solid with each other.

A first outer element consists of a toothed ring 16 made of light metal and with good coupling characteristics.

The front surface 17a of the teeth 17 of the ring 16 couples with the inner surface of the tube 11 with reduced friction, so that all the operations to insert/remove the inserts 10 into/from the tube 11 are facilitated. Moreover, the ring 16 has an outer diameter"D"which is slightly less than the inner diameter of the forming tube 11 to allow easy insertion.

Inside the toothed ring 16 there is a first element, or outer bush, 14 also made of light metal. In the variant shown in Fig. 4b this outer bush 14 has a hollow 18 on the circumference which makes it lighter and further reduces the overall weight of the insert 10.

Inside the outer bush 14 there is a second element, or inner bush, 15 which defines axially the inner cavity 12 through which the metal wire to be coiled is introduced and passes.

The inner bush 15 is made of special, extremely hard metal and therefore extremely resistant to wear, such as to allow

repeated, successive coiling cycles without entailing damage and the need for maintenance or replacements. The inner bush 15 defines a flared segment 12a for the introduction of the metal wire followed by a cylindrical segment 12b of a diameter"d"which is sized in correlation to the diameter of the metal wire.

The insert 10 has rounded front faces, with an outer convexity so that they adapt better to the geometry of the forming tube 11; they define bevels 10a which facilitate the discharge of the scale and particles which have accumulated in the successive passes of the metal wire. The longitudinal dimension"1"of the anti-wear inserts 10 is between 20 and 40 mm, advantageously assuming a nominal value of around 30 mm.

The anti-wear inserts 10 are removed (Fig. 2) by means of a flexible metal cable 13 which, at the two ends, has means to constrain the anti-wear inserts 10.

In this case, a constraining element is shown of the removable type, consisting of a nut 19 associated with a thread made at one end 13a of the cable 13.

The removal of the anti-wear inserts 10 from the forming tube 11 may be preceded by a blowing cycle to remove the scale and particles which have accumulated in the interstices between the tube and the inserts, this removal being facilitated by the inclusion of the front bevels 10a.