Field of the invention
This invention relates to an apparatus for driving roll stands at selectively different speed ratios and generally to continuous rolling mills of the type which produce cods, bars and the like, and is concerned in particular with an improved apparatus on driving successive roll stands at selectively different speed ratios.
2. Description of the Prior Art
In modern day rolling mills operating with widely varying rolling schedules and at extremely high speeds exceeding 100 m/sec., there is a growing need to drive successive roll stands with selectively different drive ratios. This is particularly true in rod mills, where so-called "mini" blocks are employed to further reduce and/or size entire families of products by selectively rendering inoperative or "dummying" preceding stands along the rolling line. The gear boxes of existing drive trains have various drawbacks and are either unable to adapt to the wide ranging demands imposed by current rolling schedules, or they are excessively large and expensive.
An objective of the present invention is to provide an improved gear transmission system which is readily adaptable to driving successive roll stands at multiple selectively different drive speed ratios.
Companion objectives include the provision of a multiple ratio gear box which is both compact and low cost as compared to conventional designs.
SUMMARY OF THE INVENTION
The gear transmission system of the present invention includes a pair of drive shafts and at least one idler shaft, all journalled for rotation about parallel axes. The drive shafts are adapted for coupling to the input shafts of two successive roll stands on a mill pass line, and one of the drive shafts or the idler shaft is additionally adapted to be driven by an external source, e.g., the output shaft of an associated gear box or a drive motor. First and second gear trains each comprise drive gears freely rotatable on the drive shafts, and an idler gear fixed to the idler shaft for rotation therewith. At least some of the gears in each gear train have different numbers of teeth. Clutches are employed to selectively couple the drive gears of each gear train with their respective drive shafts, resulting in the drive shafts coupled to the input shafts of two successive stands being driven at selectively different drive speed ratios.
These and other features, objectives and advantages of the present invention will become more apparent as the description proceeds with reference to the accompanying drawings wherein:

Accordingly, there is provided an apparatus for driving roll stands selectively different speed ratios, said apparatus comprising:
a pair of drive shafts and at least one idler shaft;
means for journalling said drive shafts and said idler shaft for
rotation about parallel axes;
means for coupling each of said drive shafts to one of input
shafts;
means for driving one of said drive shafts;
a first drive gear freely rota table on each of said drive shafts and
a first idler gear on and fixed relative to said idler shaft, said
first drive gears and said idler gear being in an intermeshed
relationship to provide a first gear train;
a second drive gear freely rotatable on each of said drive shafts
and a second idler gear on and fixed relative to said idler shaft,
said second drive gears and said second idler gear being in an
intermeshed relationship to provide a second gear train; and
clutch means for selectively coupling the drive gears of first and
second drive trains to their respective drive shafts.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 is a diagrammatic illustration of a gear box in accordance ivith the present invention, with its drive shafts coupled to the input -hafts of two successive rolls stands in a rolling mill;
Figure 2 is a sectional view on an enlarged scale taken through one >f the clutch assemblies shown in Figure 1;
Figures 3A - 3D are schematic illustrations depicting the various relative ratios available between two output shafts with the gear box shown in Figure 1;
Figures 4A and 4B are schematic illustrations depicting placement of the idler shaft and gears at alternative locations;
Figure 5 schematically depicts another embodiment incorporating multiple idler shafts; arte
Figure 6 depicts the application of the invention to a four stand rolling block.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
Referring initially to Figures 1 and 2, two roll stands 10, 12 are shown positioned successively along a mill pass line P. Typically, the roll stands will be grouped together into a "block" 14, and each will include a pair of work rolls 16. The work rolls are mounted in cantilever fashion on the exposed ends of roll shafts contained within the stand housings. The roll shafts are driven by internal gearing via input shafts 18. Although not shown, it will be understood that the work rolls of the successive stands have their axes staggered by 90° in order to effect twist free rolling. All of this, including the internal drive arrangements for the roll stands, is well known to those skilled in the art and thus does not require any further explanation. See for example U.S. Patent Nos. 5,577,405 and 5,280,714, the disclosures or which are incorporated herein by reference.
A gear box containing a transmission system in accordance with the present invention is shown at 20. The gear box contains a pair of drive shafts 22, and in this embodiment, one idler shaft 24. Bearings indicated typically at 26 serve to journal the drive and idler shafts 22, 24 for rotation about parallel axes.
Couplings 28 connect the drive shafts 22 to the input shafts 18 of the roll stands, and one of he drive shafts is additionally coupled as at 30 to the output shaft 32 of another associated gear box a drive motor (not shown).
A first gear train includes intermeshed drive gears G1, G2 freely rotatable on the drive shafts
and an idler gear G3 fixed relative to the idler shaft 24 and in meshed engagement with drive gear
A second gear train similarly includes intermeshed drive gears G4, G5 freely rotatable on the drive
hafts, and an idler gear G6 fixed relative to the idler shaft and in meshed engagement with drive gear
Clutch assemblies 34 are interposed between the freely rotatable drive gears on each of the drive
rafts.
As can best be seen in Figure 2, each clutch assembly includes an externally toothed circular Moulder 36 on the drive shaft 22. The adjacent drive gears have cylindrical hubs 38 which terminate at similarly configured externally toothed circular shoulders 40. An internally toothed sleeve 42 is permanent permanently engaged with the external teeth of the shoulder 36 on shaft 22, and is axially adjustable of opposite directions as indicated at 44 to selectively engage one or the other of the externally nothed shoulders 40 of the adjacent drive gears thereby effecting selective alternative coupling of the drive gears to their respective drive shaft.
The drive gears G1 and G2 have different numbers of teeth, as. do the drive gears G4 and G5
and the idler gears G3 and G6. Figures 3 A - 3D illustrate the different drive ratios available with the
msmission system shown in Figure 1 For example, with the clutch sleeves 42 adjusted to the
positions shown in Figure 3 A, the resulting drive ratio will be provided by gears G1 and G7 In Figure
!-$, the drive ratio is provided by gears G4 and G5 In Figure 3C, the drive ratio is provided by drive
tears G2 and G4, and in Figure 3D by drive gears G1 and G5.
It will thus be seen that with a compact arrangement of three shafts and six gears, four different drive ratios between two output shafts are selectively achievable by simply adjusting two intches.
The present invention is easily adaptable to different equipment layouts, as depicted for example in Figures 4A and 4B which show the idler shaft 24 at different locations. Moreover, as lepicted in Figure 5, by adding an additional idler shaft 46 with idler gears G7, Gg and clutch 48, and by making the idler, gears G3, G6 freely rotatable on idler shaft 24 with an additional clutch 50 operative therebetween, a total of six different gear ratios can be achieved. The concept can be expanded even further by adding additional idler shafts, idler gears and clutches. Other expanded applications are possible by repeatedly using either the embodiments disclosed herein, or modified embodiments encompassed by the scope of the appended claims. For example, as depicted in Figure 1 three gear transmission systems A, B and C of the types described above can be coupled together, vvsth one input shaft 48 providing power to four output shafts 50a, 50b, 50d and 50a driving four successive roll stands (not shown). With this arrangement, four ratios are available between shafts 50a and 50b, between shafts 50b and 50c, and between shafts 50c and 50d, for a total of sixty four different speed combinations for the four stand sequence.

WE CLAIM:-
1. An apparatus for driving roll stands (10, 12) at selectively different speed ratios, said apparatus comprising:
- a pair of drive shafts (22) and at least one idler shaft (24);
- means (26) for journalling said drive shafts and said idler shaft for rotation about parallel axes;
- means (28) for coupling each of said drive shafts to one of input shafts;
means (30, 32) for driving one of said drive shafts;
a first drive gear (G1, G2) freely rotatable on each of said drive
shafts and a first idler gear (G3) on and fixed relative to said
idler shaft, said first drive gears and said idler gear being in an
intermeshed relationship to provide a first gear train;
a second drive gear (G4, G5) freely rotatable on each of said drive
shafts and a second idler gear (G6.) on and fixed relative to said
idler shaft, said second drive gears and said second idler gear
being in an intermeshed relationship to provide a second gear
train; and
clutch means (34) for selectively coupling the drive gears of first
and second drive trains to their respective drive shafts.
2. An apparatus as claimed in claim 1, wherein the idler shaft (24) of each drive train is interposed between said drive gears.
3. An apparatus as claimed in claim 1, wherein said drive shafts (22) and idler shaft being journalled for rotation about parallel axes and one of said drive shafts is coupled to output shaft by coupling means.
4. An apparatus for driving roll stand at selectively different speed ratios substantially as hereinbefore described with reference to the accompanying drawings.