Device for controlling the speed of a mandrel in continuous retained-mandrel rolling mills

A device for controlling the speed of a mandrel in a continuous retained-mandrel rolling mill, such device comprising a rod having a double rack provided at one end with a means for removably securing an end of a mandrel and a number of pinions engaging the rack on the rod, each pinion being driven in rotation by a corresponding motor-driven shaft which, via respective clutches is connected to a motor and speed-reducing group provided with a brake for each motor-driven shaft. Further, the device includes a second set of pinions engaging the rack on the rod, each pinion being driven in rotation by a corresponding motor and speed-reducing group provided with a brake.

BACKGROUND AND SUMMARY OF THE INVENTION 
The invention relates to a device for controlling a speed of the mandrel in 
continuous retained-mandrel rolling mills. 
It is known that when a perforated bloom secured to a mandrel is 
continuously rolled, the rolls in the various housings subject the mandrel 
to tensile forces which, if the mandrel was loosely mounted, would drive 
it at a speed which varied during the rolling operation. It is also known 
that variations in the speed of the mandrel through the successive 
housings will result in unacceptable defects in the final rolled tube. 
Accordingly, to avoid this serious disadvantage, the mandrel must be moved 
at a controlled speed. 
To this end continuous rolling mills used for the aforementioned method of 
rolling are fitted with devices which oppose the tensile forces exerted by 
the rolls on the mandrel and move it at a predetermined speed through the 
successive housing. In the prior art, these devices are usually called 
"mandrel-retaining devices", whereas a rolling mill fitted with such 
devices is called a "continuous retained-mandrel rolling mill". 
The retaining devices used hitherto are mainly of the screw or hydraulic 
kind. 
In the prior art screw devices, one end of the mandrel is suitably shaped 
(i.e. the mandrel head) and engages a corresponding seat formed centrally 
in a cross-member, the ends of which are formed with two female threads 
each coupled to a screw having a length adapted to retain the mandrel so 
that it moves over a required predetermined distance. 
In the hydraulic devices, the cross-member bearing the mandrel head is 
laterally secured to oil actuated cylinders which have the stroke required 
for retaining the mandrel so that it moves in the desired manner. 
It is particularly difficult to control the speed of a mandrel since, 
during lamination, the tensile forces exerted on the mandrel may vary 
suddenly as the mandrel is engaged by the successive housings. Furthermore 
the tensile forces, particularly in large rolling mills, may reach peaks 
of 400 tons, so that the mandrel moves at speeds of up to 1 m/second. 
Consequently, screw retaining devices give satisfactory results only at 
moderate speeds and moderate, constant loads. However, screw retaining 
devices are quite inadequate for high speeds or loads, since the specific 
pressures on the sliding surfaces, the speed of sliding and the difficulty 
of lubrication result in rapid deterioration of the screw and thread 
couplings. 
In hydraulic retaining devices, the heavy loads accompanied by sudden 
variations in intensity produce resonance effects owing to the 
compressibility of the hydraulic fluid and the resilience of the tubes, 
thus causing the mandrels to vibrate sufficiently to break the lubricating 
layer interposed between the mandrel and the rolled bloom. As is well 
known, a break in the lubrication adversely affects the life of the 
mandrels, resulting in variations in the tensile force exerted on the 
mandrel, and resulting in further resonance in the hydraulic retaining 
device, with a cumulative negative effect on the entire rolling operation. 
The invention is based on the problem of devising a mandrel-retaining 
device in continuous retained-mandrel rolling mills. The device includes 
structural and functional characteristics which completely obviate the 
aforementioned disadvantages of the prior art. 
To accomplish the result, according to the invention, the device comprises: 
a rod having a double rack provided at one end with a means for removably 
securing an end of a mandrel, 
a number of pinions engaging the rack on the rod, each pinion being driven 
in rotation by a corresponding motor-driven shaft which, via respective 
clutches is connected to: 
a motor and speed-reducing group provided with a brake for each 
motor-driven shaft. 
According to another feature of the invention, the device comprises a 
second set of pinions engaging the rack on the rod, each pinion being 
driven in rotation by a corresponding motor and speed-reducing group 
provided with a brake.

DETAILED DESCRIPTION OF THE INVENTION 
In the drawings, references 1 and 2 denote two sides of a conventional 
bearing structure 3 inside which two rectilinear parallel guides 4, 5 are 
longitudinally secured and bear a rod 6 which can move and extends 
longitudinally between sides 1, 2. Similar racks 7, 8 having a similar 
pitch are formed above and below rod 6, which has a substantially 
rectangular cross-section and a predetermined length. Rack 7 kinematically 
engages three pinions 9, 10, 11 borne loosely by sides 1, 2, the axes of 
rotation of the pinions being perpendicular to the sides and equally 
spaced along the sides. Rack 8 kinematically engages three pinions 12, 13, 
14 likewise loosely held by sides 1, 2, their axes of rotation being 
perpendicular to the sides and offset relative to the axes of the 
abovementioned pinions 9, 10, 11. Since all the pinions 9-14 are 
identical, the following description by way of example is given with 
reference to only one pinion, i.e. 9. 
In FIG. 2, each pinion substantially has an orifice 15 formed at the 
opposite ends with hub portions 6-7 by means of which, with interposition 
of bearings shown diagrammatically at 18 and 19, the pinion is loosely 
held by sides 1, 2. 
Reference 20 denotes a motor-driven shaft extending axially through orifice 
15 in the pinion. Bearings diagrammatically indicated at 21 hold shaft 20 
away from the inner walls of orifice 15. The portion of the shaft 20 which 
projects from the side 2 is secured in known manner to a conventional 
speed-reducing unit diagrammatically indicated at 22 and actuated by a 
d.c. motor 25, with interposition of a brake 23 and coupling 24. 
A known clutch, e.g. a disc clutch bearing the general reference 26, is 
secured in a conventional manner to shaft 20 which projects from the side 
1. The casing 27 of the clutch 26 rotates integrally with pinion 9. 
The set of pinions 9-14, and the associated clutches 26, reducing gears 22, 
brakes 23 and d.c. motors 25 form a slow control unit (CL) used for 
retaining the mandrel as will be described hereinafter. Racks 7, 8 of rod 
6 also engage identical pinions 28, 29 rotatably mounted on the sides 1, 2 
of the housing structure 3. Each pinion 28, 29 is actuated by a d.c. motor 
125 fitted with a corresponding brake 123 and a speed-reducing gear 122. 
Pinions 28, 29 and the associated motor systems form a rapid control unit 
(CV) actuating the rod 6 as will be described hereinafter. 
Rod 6 has a substantially hook-shaped end 30 for removably securing the 
head 31 of a mandrel 32 which, after being inserted into an axially bored 
bloom (not shown) is used for rolling the bloom in a continuous 
retained-mandrel rolling mill, of which the aforementioned slow and rapid 
control units constitute an integral part according to the invention. 
The device according to the invention operates as follows: 
In an initial state, all the d.c. motors 25, 125 are inoperative, brakes 
23, 123 are closed, and all the clutches 26 are uncoupled. Under these 
conditions, pinions 9-14 of the slow control unit CL and pinions 28, 29 of 
the rapid control unit CV rest loosely on the respective motor-driven 
shafts 20, which are motionless. 
Next, mandrel 31 is rapidly fitted into a corresponding axially-bored bloom 
so that the bloom can be rolled. To this end, the hook-shaped end 30 of 
rod 6 fits into the mandrel head 31 and the rapid control unit CV is used. 
More particularly brakes 123 of unit CV are opened and the d.c. motors 125 
are switched on. Rod 6, which is actuated by pinions 28, 29 engaging the 
racks 7 and 8, acts in practice as a thrust member on mandrel 32, at a 
speed which depends on the speed of the d.c. motors 125. 
After mandrel 32 has been fitted into the corresponding perforated bloom, 
motors 125 are stopped. 
Next, after all the clutches 26 of the slow control unit CL are engaged and 
the respective brakes 23 have opened, unit CL is ready to operate at the 
same time as the bloom secured to mandrel 32 is rolled. Unit CL is adapted 
to control the speed at which the associated mandrel and bloom are 
conveyed through the successive housings, and effectively counteracts the 
tensile forces exerted on the mandrel by the rolls. 
The aforementioned function of controlling the mandrel speed is performed 
by a number of motors 25 which, via respective speed-reducing gears 22, 
motor-driven shafts 20 and corresponding engaged clutches 26, control the 
rotation of pinions 9-14 and consequently control the motion of the rod 6 
having a double rack 7,8. 
At the end of the rolling operation all the motors 25 are stopped, brakes 
23 are locked and clutches 26 are uncoupled, after which the rapid control 
unit CV is actuated in the opposite direction from that described for 
fitting the mandrel to the bloom, and the mandrel 32 can be rapidly 
extracted from the rolling mill. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded as a departure 
from the spirit and scope of the invention, and all such modifications as 
would be obvious to one skilled in the art are intended to be included 
within the scope of the following claims.