EP3774102B1

EP3774102B1 - Pressure die for cold-drawing and inserts for a pressure die

Info

Publication number: EP3774102B1
Application number: EP19721095.8A
Authority: EP
Inventors: Luigi Vago; Edgardo VAGO
Original assignee: Pan Chemicals SpA
Current assignee: Pan Chemicals SpA
Priority date: 2018-03-28
Filing date: 2019-03-27
Publication date: 2023-09-06
Anticipated expiration: 2039-03-27
Also published as: IT201800004031A1; WO2019186421A1; EP3774102C0; ES2963456T3; EP3774102A1; MX2020010095A; CN112368088A

Description

BACKGROUND

The present invention relates to the sector of cold-drawing of rods, metal wires or, more generally, long metal objects. More particularly, the present invention relates to a pressure die for cold-drawing a rod or a metal wire. The present invention also relates to a pair of pressure and drawing inserts configured for such a pressure die.

STATE OF THE ART

As is known, the process for drawing a metal wire or rod involves introducing the metal wire or the rod into a tool which reduces its diameter. Typically, the rod or the metal wire undergoes a gradual reduction in diameter when passing through dies with an increasingly smaller drawing diameter.
During the drawing process it is known to use lubricants. Typically, the lubricants have a solid form, for example a powder or flake-like form. However, the drawing lubricants may also be in liquid form.
In order to force the lubricant into the die pressure dies are known where a step is carried out prior to the actual drawing step, said step having the task of increasing the pressure of the lubricant so that it is conveyed together with the rod or the metal wire during drawing.
IT 1269433 (Tecnovo S.r.l) describes a tool for drawing metal wires and rods, comprising a support member, which is crossed by a passage, and a drawing member which is made of material with a high hardness and is housed inside the support member and has a hole coinciding with this passage. The support member is made of at least two parts which can be combined with each other in a removable manner in order to fix the drawing member in position, inside the support member.
IT 1295286 (Tecnovo S.r.l.) describes a die for drawing rods or metal wires, with integral and rapid replacement of the drawing core and recovery thereof, comprising a reinforcement having a through-hole, wherein the aforementioned reinforcement houses inside it in a removable manner an upper member and a drawing core which are separate from each other and aligned with the aforementioned hole, where the bottom profile of the aforementioned upper member is such as to engage perfectly with the inlet of the drawing core located underneath it.
EP 0 679 112 (Paramount Die Co., Inc.) describes a die assembly for metal wires.
US 2008/0173063 A1 describes a drawing system in which the drawing heat is distributed on two or more drawing inserts.

SUMMARY OF THE INVENTION

The present invention is applicable to any long metal element, including a tube, but typically a rod or a metal wire. For the sake of simplicity, the present description will be provided with reference solely to rods. However, in the present description and in the claims, the term "rod" is understood as comprising any long metal element such as a tube, a rod or a metal wire.
The Applicant has noted that the known pressure dies comprise two inserts separated by a metal spacer, for example made of steel, or copper, or another metal, which is arranged between the two inserts in order to prevent contact between them - something which would result in breakage - and to prevent the leakage of lubricant which would result in loss of pressure and therefore less efficiency.
The drawing system described in US 2008/0173063 A1 comprises two or more drawing inserts 300, 400 and a pressure insert 200. The pressure insert 200 is kept in contact with the drawing insert 300. According to the Applicant, this configuration results in premature breakage of the pressure insert and/or the drawing insert which is in direct contact with the pressure insert. This occurs because the pressure insert is in direct contact with the first of the two drawing inserts and the pressures involved subject the inserts to high mechanical pressures.
Moreover, the pressure insert is retained by a hole inside the male fixing member 110 which is configured to engage with a thread inside the female die member 120. Therefore, it is necessary to machine separately the male closing member and the female member: the male member must be machined to form the hole for the pressure insert and the female body must be machined to form a conical hole for the die inserts 300 and 400. The machining operations carried out on two separate members must be very precise and are therefore costly.
The thread between the male closing member and the female member is situated on a relatively small diameter and therefore the locking force is necessarily limited.
The Applicant has defined the object of providing a pressure die comprising only two inserts (a single pressure insert and a single drawing insert) which are axially separated from each other so as to provide a pressure chamber. In particular, the Applicant has defined the object of providing a pressure die in which the two inserts are always in a configuration such that they are not axially in direct contact with each other or with a spacer.
The Applicant has also defined the object of providing a pressure die of the aforementioned type in which the inserts may be assembled in a simple and rapid manner.
The Applicant has defined the object of providing a pressure die of the aforementioned type in which the inserts, in particular the drawing insert, may be replaced in a simple and rapid manner. In fact, the drawing insert is subject to rapid wear and must be replaced with a certain frequency.
These targets, along with others, are achieved with a pressure die according to the present invention in which the pressure insert and the drawing insert both have a frustoconical form with the same taper angle. The inserts are configured so that they may be inserted inside a conical hole of a die housing, having a taper angle complementing that of the inserts. The dimensions of the two inserts are configured so as to leave a distance between them in the axial direction, creating a pressure chamber and preventing the possibility that the two inserts may come into contact during use of the die or owing to incorrect (or imprecise) assembly of the components. A ring nut is preferably provided for keeping the pressure insert in position with respect to the body.
According to a first aspect, the present invention relates to a pressure die comprising a die housing, a single pressure insert, a single drawing insert and a locking ring configured to lock the pressure insert with respect to said die housing,

wherein said die housing comprises a conical longitudinal through-hole having a single taper angle from a first larger-diameter inlet end to a second smaller-diameter outlet end;
wherein the pressure insert is inserted into the conical longitudinal through-hole and positioned close to the inlet end, wherein the drawing insert is inserted into the conical longitudinal through-hole and positioned close to the outlet end, and
wherein the pressure insert and the drawing insert are tapered with a taper angle complementing the taper angle of the conical longitudinal hole and have dimensions such that they are not in contact with each other and define a pressure chamber for a drawing lubricant.

Unlike the solution described in US 2008/0173063 A1 there is a single drawing insert. According to the present invention, the drawing insert is never in contact with the pressure insert. Moreover, in the present invention, both the drawing insert and the pressure insert are inserted into a conical hole formed in the die body. The single conical hole in the die body offers significant advantages during its formation both as regards the tolerances which can be obtained and the machining costs.
The taper angle of the longitudinal through-hole is preferably between 1° and 10°, more preferably between 1° and 6° and even more preferably between 1° and 4°.
According to preferred embodiments, the taper angle of the longitudinal through-hole is 3°.
According to one embodiment, the die housing is a male member and the locking ring is a threaded female member configured to engage a thread of the die housing. This aspect is very advantageous. In fact, in the die housing according to the present invention, the conical through-hole is formed for the single pressure insert and the single drawing insert. The (female) locking ring engages a thread on the outer surface of the die housing. Therefore, the thread between the die housing and the locking ring extends over a surface having a larger diameter than that in the solution described in US 2008/0173063 A1 . Therefore the locking action is firmer and more reliable in the present invention. Moreover, the hexagon formed at the top has a bigger diameter and this improves the capacity for tightening the locking ring with respect to the die housing.
The smaller diameter of the pressure insert, preferably, is greater than the larger diameter of the drawing insert.
According to a second aspect, the present invention relates to a pair of inserts, i.e. a kit, comprising a pressure insert and a drawing insert for a pressure die, the pressure die comprising: a die housing and a locking ring configured to lock the pressure insert with respect to the said die housing,

wherein said die housing comprises a conical longitudinal through-hole having a taper angle from a first larger-diameter inlet end to a second smaller-diameter outlet end;
wherein the pressure insert is configured to be inserted into the conical longitudinal through-hole and positioned close to the inlet end; wherein the drawing insert is configured to be inserted into the conical longitudinal through-hole and positioned close to the outlet end,
wherein said pressure insert and said drawing insert are tapered with a taper angle complementing the taper angle of the conical longitudinal hole, and
wherein the smaller diameter of the pressure insert is greater than the larger diameter of the drawing insert such that, when inserted into the conical longitudinal hole, they are not in contact with each other and define a pressure chamber for a drawing lubricant.

The taper angle is preferably between 1° and 10°. According to a preferred embodiment the taper angle is 3°.

BRIEF DESCRIPTION OF THE FIGURES

There now follows a detailed description of the present invention, provided by way of a non-limiting example, to be read with reference to the accompanying drawings, in which:

Figure 1 and Figure 2 are two longitudinally sectioned views of the pressure die according to an embodiment of the present invention, the difference consisting in the machining tolerance of the inserts;
Figures 3.1 and 3.2 show a front view and a longitudinally sectioned view of the die housing;
Figures 4.1 and 4.2 show a front view and a longitudinally sectioned view of the locking ring of the die housing;
Figures 5.1 and 5.2 show a pressure insert;
Figure 5.3 shows another pressure insert according to the present invention; and
Figures 6.1 and 6.2 show a drawing insert according to the present invention.

DETAILED DESCRIPTION

A pressure die according to an embodiment of the present invention is shown schematically in Figures 1 and 2. In particular, Figures 1 and 2 are two longitudinal sections which show the same pressure die according to the present invention. However, depending on the machining tolerance, the two inserts may be arranged in different positions and create a pressure chamber with a different size. In other words, their relative position may be different.
The pressure die is denoted overall by the number 1. It comprises a die housing 10, a closing or locking ring 20, a first insert 30 and a second insert 40. The first insert 30 is a pressure insert, while the second insert 40 is a drawing insert.
Depending on the diameter of the body to be drawn and/or the reduction in diameter which is to be obtained, the pressure die 1 (and consequently also the single components) may have different dimensions. Merely by way of a non-limiting example, below in the present description a die for drawing a rod with an initial diameter of 5.5 mm, so as to obtain a final diameter of 4.7 mm, with a reduction therefore of about 27%, will be described. Dies according to the present invention may be made for larger diameters or smaller diameters and for various reduction percentages of the diameter.
An embodiment of the die housing 10 is also shown in Figures 3.1 and 3.2. According to the embodiment shown, the die housing 10 comprises a substantially cylindrical male body with an outer surface provided with a thread 11. According to an embodiment, the outer diameter is about 28 mm and comprises an outer surface M27x1.5. Obviously this is an example and the die housing 10 could have a different diameter and/or be threaded with a different thread.
The outer surface of the die housing further comprises, preferably, at least one groove 12 for a resilient sealing ring (O-ring).
The outer surface of the die housing further comprises, preferably, a hexagon-shaped section 13.
The die housing 10 comprises a longitudinal through-hole 14. The longitudinal through-hole 14 is a tapered hole. The taper angle 15 of the longitudinal through-hole 14 (measured with respect to the longitudinal axis X-X of the housing) may be between 1° and 10°, preferably between 1° and 6° and even more preferably between 1° and 4°. According to a preferred embodiment, the taper angle 15 is 3°. The larger diameter of the longitudinal through-hole, still with reference to the specific example, may be about 14 mm.
The taper angle 15 remains unchanged over the whole length of the conical longitudinal through-hole, from a first (larger-diameter) inlet end 141 to a second (smaller-diameter) outlet end 142.
The die housing 10 is preferably made of a metallic material, for example steel and in particular stainless steel.
The female locking ring 20 is configured to engage the male die housing 10 and lock the insert 30 inside the longitudinal through-hole 14. More particularly, the locking ring 20 comprises a substantially cylindrical body with a threaded hole 21 configured to engage the outer threading 11 of the die housing 20. The head of the locking ring 20 comprises a longitudinal through-hole 24. When the die housing 10 and the locking ring 20 are joined together (by means of the outer thread 11 of the die housing 10 and the inner thread 21 of the locking ring 20), the axis X-X of the longitudinal through-hole 14 of the die body 10 preferably coincides with the axis Y-Y of the longitudinal through-hole 24 of the head of the locking ring 20. The longitudinal through-hole 24 of the head of the locking ring 20 is preferably open, tapered like a funnel outwards, as indicated by means of the number 27 in Figure 4.2.
Preferably, the locking ring 20 also comprises a shaped hexagon section 23.
The outer surface of the locking ring 20 also comprises, preferably, a seat 22 for a resilient sealing ring (O-ring).
The locking ring 20 is preferably made of a metallic material, for example steel and in particular stainless steel.
With reference now to Figures 5.1 and 5.2 a pressure insert 30 suitable for being mounted inside the pressure die 1 according to Figures 1 and 2 will now be described.
The pressure insert 30 is a substantially frustoconical body with a larger base 31 which corresponds to the inlet mouth for the rod (not shown) and a smaller base 32 which corresponds to the outlet for the rod. The advancing direction of the rod is indicated by the arrows IN and OUT.
The taper angle 35 of the drawing insert 40 corresponds to (complements) the taper angle 15 of the longitudinal through-hole 14 of the die housing 10. According to the present invention, the taper angle 35 (if necessary excluding the first section 33' in the vicinity of the larger base) is between 1° and 10°, preferably between 1° and 6° and even more preferably between 1° and 4°. According to a preferred embodiment, the taper angle 35 is 3°.
As shown in Figure 5.1, the pressure insert 30 comprises a suitably shaped longitudinal through-hole 34. The longitudinal through-hole 34 of the pressure insert 30 comprises a more open first section 341 which defines the inlet bell, a second conical section 342, a third substantially cylindrical section 343 and an outlet bell 344 which opens out towards the pressure chamber 50.
According to embodiments, the pressure insert 30 has a length of about 10-20 mm, preferably 10-15 mm and even more preferably 10-12 mm.
According to embodiments, the pressure insert 30 has a larger base 41 with a diameter D30 of about 10-20 mm, preferably 10-15 mm and even more preferably 14-15 mm.
According to embodiments, the third substantially cylindrical section 343 has a length of 1-7 mm, for example 2 mm.
The inlet bell may have an angle α of 80°, while the outlet bell may have an angle β of 60°.
Preferably, the pressure insert 30 is made of hard material, for example sintered tungsten carbide, which is optionally cobalt-based.
Depending on the machining tolerance, the pressure insert may be in the position shown in Figure 1 (maximum tolerance), in the position shown in Figure 2 (minimum tolerance) or in any intermediate position.
Figure 5.3 shows a variant of the pressure insert 30 in which no drawing takes place. The main difference lies precisely in the fact that the second section 342 is also cylindrical with the same diameter as the third section 343. The diameter of the cylindrical section substantially corresponds to the diameter of the rod which passes through it.
With reference now to Figures 6.1 and 6.2 a drawing insert 40 suitable for being mounted inside the pressure die 1 according to Figures 1 and 2 will now be described.
The drawing insert 30 is a substantially frustoconical body with a larger base 41 which corresponds to the inlet mouth for the rod (not shown) and a smaller base 42 which corresponds to the outlet for the rod which has undergone drawing.
The taper angle 45 of the drawing insert 40 corresponds to (complements) the taper angle 15 of the longitudinal through-hole 14 of the die housing 10. According to the present invention, the taper angle 45 (if necessary excluding the first section 43' in the vicinity of the larger base) is between 1° and 10°, preferably between 1° and 6° and even more preferably between 1° and 4°. According to a preferred embodiment, the taper angle 45 is 3°.
As shown in Figure 6.1, the drawing insert 40 comprises a suitably shaped longitudinal through-hole 44. The longitudinal through-hole 44 of the drawing insert 40 comprises a first more open section 441 which defines the inlet bell, a second conical section 442 which defines the surface for reducing the diameter of the rod, a third substantially cylindrical section 443 inside which the diameter of the drawn rod is consolidated and an outlet bell 444 for discharging the drawn rod. Typically, drawing occurs in the last portion 442' of the second section 442.
According to embodiments, the reduction surface 442 of the drawing insert 40 forms an angle of 4° to 30°, for example 16°.
According to embodiments, the third substantially cylindrical section 443 has a length of 1-7 mm, for example 2 mm and has a diameter 444 of about 4-5 mm, for example 4.6 mm.
The outlet bell may have an angle β of 60°.
Preferably, the drawing insert 40 is made of hard material, for example sintered tungsten carbide, which is optionally cobalt-based.
The smaller base 31 of the pressure insert 30 has a diameter d30 which is larger than the diameter D40 of the larger base 41 of the drawing insert 40.
In order to assemble the pressure die 1 according to the present invention, the drawing insert 40 is inserted firstly into the through-hole 14 of the die housing 10. The diameter of the larger base 41 is designed so that the drawing insert 40 is positioned close to the smaller-diameter end 142 of the said hole (Figure 1). Then the pressure insert is also inserted into the through-hole 14 of the die housing and is positioned close to the larger-diameter end 141 of the through-hole 14. The diameter of the smaller base 32 of the pressure insert 30 is always greater than the larger base 41 of the drawing insert 40. In this way, the two inserts 30, 40 never come into contact with each other and a pressure chamber 50 is created.
Then the locking ring 20 is screwed to the die housing 10. By screwing the locking ring 20 to the die housing 10 (advantageously by means of the hexagons 13 and 23) the pressure insert 30 is retained inside the die housing and does not risk being pushed out by the pressure of the lubricant which is created during drawing of the rod.
The pressure chamber 50 is configured to collect the lubricant (not shown) removed from a container upstream of the die 1 and drawn along by the rod during its high-speed movement inside the pressure insert 30. The high-pressure lubricant present in the pressure chamber 50 adheres to the surface of the rod before it enters into the drawing insert 40.
If it is required to replace the drawing insert 40 and/or the pressure insert 30, the locking ring 20 is unscrewed and the two inserts 30, 40 are pushed in the opposite direction to the direction of insertion. Thus, the two inserts 30, 40 are freed and may be extracted and replaced.
Advantageously, the through-hole 14 is smooth and unthreaded. In the same way, the conical outer surface of the two inserts 30, 40 is smooth and unthreaded.

Claims

A pressure die (1) comprising a die housing (10), a single pressure insert (30), a single drawing insert (40) and a locking ring (20) configured to lock the pressure insert (30) with respect to said die housing (10),
wherein said die housing (10) comprises a conical longitudinal through-hole (14) having a single taper angle (15) from a first larger-diameter inlet end (15) to a second smaller-diameter outlet end (142);

wherein the pressure insert (30) is inserted into the conical longitudinal through-hole (14) and positioned close to the inlet end (141); wherein the drawing insert (40) is inserted into the conical longitudinal through-hole (14) and positioned close to the outlet end (142); and

wherein the pressure insert (30) and the drawing insert (40) are tapered with a taper angle (35, 45) complementing the taper angle (15) of the conical longitudinal hole (14) and have dimensions such that they are not in contact with each other and define a pressure chamber (50) for a drawing lubricant.
The pressure die (1) of claim 1, wherein the taper angle (15) of said longitudinal through-hole (14) is between 1° and 10°.
The pressure die (1) of claim 2, wherein the taper angle (15) of said longitudinal through-hole (14) is 3°.
The pressure die (1) of claim 1, 2 or 3, wherein said die housing (10) is a male member and said locking ring (20) is a threaded female member configured to engage a thread (11) of said die housing (10).
The pressure die (1) of any one of the preceding claims, wherein the smaller diameter (32) of the pressure insert (30) is greater than the larger diameter (41) of the drawing insert (40).
A kit (30, 40) comprising a pressure insert (30) and a drawing insert (40) for a pressure die (1), the pressure die comprising: a die housing (10) and a locking ring (20) configured to lock the pressure insert (30) with respect to said die housing (10), wherein said die housing (10) comprises a conical longitudinal through-hole (14) having a taper angle (15) from a first larger-diameter inlet end (15) to a second smaller-diameter outlet end (142);
wherein the pressure insert (30) is configured to be inserted into the conical longitudinal through-hole (14) and positioned close to the inlet end (141); wherein the drawing insert (40) is configured to be inserted into the conical longitudinal through-hole (14) and positioned close to the outlet end (142),

wherein said pressure insert (30) and said drawing insert (40) are tapered with a taper angle (35, 45) complementing the taper angle (15) of the conical longitudinal hole (14) and

wherein the smaller diameter (32) of the pressure insert (30) is greater than the larger diameter (41) of the drawing insert (40) such that, when inserted into the conical longitudinal hole (14), they are not in contact with each other and define a pressure chamber (50) for a drawing lubricant.
The kit (30, 40) of claim 6, wherein said taper angle (15) is between 1° and 10°.
The kit (30, 40) of claim 7, wherein said taper angle (15) is 3°.