This invention concerns a continuous drawing device for straight drawing. To be more exact, the invention concerns a device whereby the means supporting the drawing clamps and carrying out re-circulation of those clamps in the drawing zone provide for adjustment of the distance between their centres in a plurality of steps separate from each other.
The state of the art covers a plurality of continuous drawing methods and devices for straight drawing operations.
Drawbenches are known which employ trolleys moving to-and-fro in the drawing direction; it is well known that these trolleys are troubled by dynamic problems since it is necessary to invert their motion regularly at each engagement and release of the material drawn by the clamps with which the trolleys are fitted. This gives rise to considerable stresses on the moving parts and to problems of guiding and controlling the moving parts. Moreover, the greatest drawback of these embodiments lies in their inability to reach high speeds.
With a view to achieving high speeds the state of the art has provided embodiments having the purpose of obtaining a continuous drawing action on the material being drawn by means of continuous movement of the drawing clamps.
According to the state of the art such clamps are positioned facing each other and parallel along a straight segment and are borne on a pair of tracked means or chains.
Along this straight segment the clamps, half of which are on one tracked means whereas the other half are on the other tracked means, firstly clamp the material and then draw it with a continuous action.
One type of known embodiment arranges that the clamps are borne and moved on the respective tracked means or chains and are secured thereto.
Another type of known embodiment provides for the tracked means or chains to be merely the means that support and recirculate the clamps; the drawing of the clamps performing the drawing operation is carried out by appropriate drawing means, such as threaded means, separate from the chains or tracked means.
These known embodiments include means to adjust mechanically the distance between centres of the tracks so as to adapt that distance to the various drawing diameters. In general, the drawing axis remains constantly the same, while both the tracked means are displaced crosswise to the drawing axis to adjust the distance between centres of the tracks according to the changes in diameter of the drawn product to be obtained.
All the known embodiments entail the problem of imperfect clamping of the drawn product between the clamps; this clamping with its mechanical actuation is not strong enough to meet the considerable drawing stresses in question in an adequate manner.
The results are not very efficient drawing operations, imperfect product quality, mechanical wear and still further shortcomings.
US-A-2,797,798 discloses a rod feeding device with tracks and with the pressure on the stock to be drawn produced by wedge-type positioning means, which serve to align the feed runs with the aperture of the die through which the stock is drawn, and by a plurality of jacks, all of which too act directly on the tracks.
This embodiment employs a combined hydraulic/mechanical system to obtain the positioning and compression action.
In fact, the positioning action is obtained by bevel gear-worm transmissions which act on two eccentrics, which act on two opposed wedge-type systems.
Instead, the system to clamp the stock is entrusted to a plurality of jacks working in sequence.
The positioning system includes also a pair of eccentric bushes which act on two motive shafts.
Starting from a drawing device according to the preamble of claim 1 (as known from US-A-2797798), the problems of the state of the art are overcome by providing a drawing device as defined in claim 1, while the dependent claims describe various embodiments of the invention.
The invention provides for the employment of known means in the drawing operation, the means including chains or tracks to support and draw the drawing clamps.
According to the invention the action of adjusting the distance between centres of the chains or tracks and the final clamping of the clamps on the material being drawn take place in at least two steps with different methods.
The first step is the approach of the chains or tracks to the drawing axis in a known manner by means of substantially mechanical operational means. In this first step one of the two chains or tracks reaches advantageously the final position it will occupy during the drawing operation, whereas the other chain or track is halted in a position near the drawing line but distanced therefrom by a required value.
In the second step, in which the product to be drawn is clamped between the clamps, the second chain or track is brought into cooperation with the first chain or track by a displacement caused by actuation by means of a fluid.
Both the chains or tracks may also be positioned at a distance from the drawing axis and then be displaced finally by actuation by means of a fluid, but this solution is more complex from a constructional and operational point of view.
The combined action of clamping mechanically and by a fluid has been found to be very efficient and gives an excellent performance even where great diameters are to be drawn. This great efficiency of performance enables drawing assemblies to be constructed with very modest dimensions even where great drawing stresses are involved.
The wear on the operational assemblies is also greatly lessened with resulting advantages.
The attached figures, which are given as a non-restrictive example, show the following:-
In Fig.1 a continuous drawing device 10 which is substantially known in itself is positioned downstream of a drawbench 11. In this example the device 10 comprises two drawing chains 12-112 located on the same plane in the neighbourhood of a drawing axis 13.
The two chains 12-112 may lie on the same horizontal, vertical or inclined plane, depending on the choice of the design work.
The two chains 12-112 are wound on their respective sprockets 14; each chain comprises an opposed straight segment on the drawing axis 13.
Each chain 12-112 bears its respective halves of drawing clamps 15-115, which cooperate in forming complete clamps on the drawing axis 13.
Both the first halves 15 and the second halves 115 of the clamps are connected to their respective chains 12-112 by suitable connection means 16.
The device 10 is equipped with means to adjust the distance between centres of the chains 12-112. The adjustment of the distance between centres is required in the initial drawing step when it is necessary to be able to apply great displacements to the clamps 15-115 at a right angle to the drawing axis 13 so as to enable the operations of introduction and gripping of the material to be drawn to be carried out.
This adjustment of the distance between centres in a direction at a right angle to the drawing axis 13 is of a modest value but is also required to adapt the chains 12-112 to the variations in the diameters to be drawn.
The means for adjustment of the distance between centres comprise a motor 17 of a suitable type that actuates a pair of threaded shafts 19 through transmissions 19.
Each threaded shaft 19 comprises two threaded segments 20-120, one having a righthand thread and the other a lefthand thread, which cooperate with their own nut screw assemblies 21-121 (see Fig.2). These nut screw assemblies 21-121 cooperate with sleeve assemblies 22-122 connected to the respective chains 12-112.
The sleeve assemblies 22-122 can slide in relation to the coordinated nut screw assemblies 21-121 and, when thrust by the latter 21-121 during rotation of the threaded shafts 19, are displaced.
According to the invention one chain 12 is brought, by means of the sleeve assembly 22 connected thereto, to a position orthogonally in relation to the drawing axis 13 by the motor 17; this position is the final one to be taken up by that chain 12 according to the pre-selected diameter to be drawn.
The other chain 112 is brought at the same time by the other sleeve assembly 122 connected thereto in the opposite direction to that of the first chain 12 to a required position in relation to the drawing axis 13, but this position is not the final position and is distant by a required value from the drawing axis 13.
The final position of the second chain 112, namely the position for clamping between the two chains 12-112 the material to be drawn, is reached with a supplementary travel of the second sleeve assembly 122. This supplementary travel is obtained by the injection of fluid under pressure into a chamber 23 positioned between the second nut screw assembly 121 and the second sleeve assembly 122.
In this example the fluid under pressure causes the second sleeve assembly 122 to slide in relation to the second nut screw assembly 121 and the second chain 112 to be displaced downwards by a value which corresponds to the play 24 in the embodiment of Fig.2.
Means 25 and 125 are included to eliminate the mechanical play proper to the system and, in particular, the play in the threaded segments 20-120 and nut screw assemblies 21-121.
Embodiments of the invention other than those described hereinbefore are possible within the scope of the invention as defined by the claims.