Machine for the abrasive machining of cylindrical parts

Machine for the abrasive machining of cylindrical parts, on which the parts to be machined are driven in rotation and in axial translational motion by supporting and driving means. The machine comprises a plurality of bands (17) of abrasive cloth having grains of increasing fineness in the direction of axial translational motion (A) of the parts to be machined, advancing means for unwinding each band (17) from a reel of new cloth continuously during the machining and for rewinding it onto a reel of worn cloth, bearing means for applying each band (17) with a predetermined pressure onto the parts to be machined, and oscillation means (18, 19, 20) for driving the said bearing means in an oscillating movement in axial translational motion. The invention is used, for example, for the superfinishing of shock-absorber rods, of cylindrical rollers, etc.

The present invention relates to a machine for the abrasive machining of 
cylindrical parts, comprising means for supporting the parts and for 
driving them in rotation about their axes and in axial translational 
motion, and machining means comprising a plurality of stations for 
abrasive machining with grains of increasing fineness, succeeding one 
another in the direction of axial translational motion of the parts and 
acting successively on the parts during the axial translational motion of 
these. 
A known machine of this type, used for the superfinish machining of 
cylindrical parts, such as shock-absorber rods, cylindrical rollers, etc., 
comprises, as a device for supporting the parts and for driving them in 
rotation and in axial translational motion, two rollers cooperating with 
the parts to be machined in the manner of centreless grinding wheels in a 
row. The machining means consist of a succession of abrasive stones whose 
applied pressures on the part to be machined are continuously adjustable 
and different according to the quality of the stones used. Each of these 
stones is supported by a pneumatic or hydraulic jack, and the jacks, (of 
which there are usually six, eight or ten), arranged in succession in the 
direction of the axial translational motion which the parts execute under 
the effect of the supporting and driving rollers, carry stones of finer 
and finer grains, thus making it possible to bring a part to the desired 
superfinished state in one pass. 
This machining technique has proved successful, but requires an adaptation 
of the quality of the stones to the part to be machined in terms of both 
the hardness and the material of the part to be machined. It is therefore 
necessary, for each type of part to be machined, to select a set of 
machining stones of grains of different finenesses, these stones being 
adapted to the operation to be carried out. Moreover, the method of 
production of these abrasive stones does not always make it possible to 
obtain perfect homogeneity, particularly where so-called sulphured stones 
are concerned, a lack of homogeneity being capable of causing a "calking", 
that is to say a clogging of the stones, resulting in defective machining. 
Moreover, the number of successive stones necessary to bring a part from a 
specific initial state to a specific superfinished state is relatively 
large. 
The object of the present invention is to provide a machine for abrasive 
machining which, whilst being of simple structure and reliable operation, 
eliminates the risks and imponderables of the known machines for machining 
with abrasive stones, thus ensuring a more uniform machining at a reduced 
cost. 
On the machine according to the invention for the abrasive machining of 
cylindrical parts, on which the parts to be machined are driven in 
rotation and in axial translational motion by supporting and driving 
means, the machining means comprise a plurality of bands of abrasive cloth 
having grains of increasing fineness in the direction of axial 
translational motion of the parts. The machining means comprise, 
furthermore, advancing means for unwinding each band of abrasive cloth 
from a reel of new cloth continuously during the machining and for 
rewinding it onto a reel of worn cloth. The machining means comprise, 
moreover, bearing means for applying each band of abrasive cloth with a 
predetermined pressure onto the parts to be machined. Finally, the 
machining means comprise oscillation means for driving the said bearing 
means in an oscillating movement in axial translational motion. 
The replacement of the abrasive stones of the known machining machines by 
bands of abrasive cloth experiencing a continuous advancing movement makes 
it possible, for an equal or even better machining quality, to reduce 
considerably the number of machining stations necessary for bringing parts 
from the same initial state to an equal or even better superfinished 
state. Moreover, the machine according to the invention ensures this final 
state with clearly increased reliability, because the continuously 
advancing bands of abrasive cloth used on the machine according to the 
invention eliminate the disadvantages associated with the abrasive stones 
used on known machines. 
Preferably, the means for supporting the parts to be machined and for 
driving them in rotation and in axial translational motion comprise two 
rollers cooperating with the parts to be machined by means of the 
so-called "centreless effect". 
The means for the bearing of the bands of abrasive cloth on the parts to be 
machined preferably comprise a plurality of bearing rollers carried by a 
plurality of jacks fastened to a stage movable in axial translational 
motion under the action of oscillation control means. 
Thus, only the jacks and the bearing rollers carried by these jacks are 
driven in an oscillating movement which, as is well known, is necessary to 
give the parts the requisite surface state, whereas the reels of new cloth 
and the reels of worn cloth as well as the means for advancing the bands 
of abrasive cloth are stationary. Nevertheless, the bands of abrasive 
cloth, in their part located between the reels of new cloth and the reels 
of worn cloth, can easily follow the oscillating movements of reduced 
amplitude of the bearing rollers. 
Preferably, the means for advancing the bands of abrasive cloth comprise a 
system for the common driving of all the reels of worn cloth of the 
machine. 
These advancing means can preferably comprise a geared motor driving a 
shaft, from which all the reels of worn cloth are driven by means of belt 
transmissions. 
To simplify the replacement of the reels of new cloth and reels of worn 
cloth, it is advantageous if each abrasive-machining station comprises two 
spindles with an inflatable elastic diaphragm, for the purpose of the 
pneumatic flanging and unflanging of the reel of new abrasive cloth and of 
the reel of worn abrasive cloth on the two spindles.

As illustrated in FIGS. 1 and 2, a machine according to the invention for 
the abrasive machining of cylindrical parts, for example the 
superfinishing of shock-absorber rods or of cylindrical rollers, 
comprises, on a stationary stand 1, an assembly 2 for supporting the parts 
to be machined (not shown) and for driving them in rotation and in axial 
translational motion. The assembly 2 comprises, in a way known per se, two 
cylindrical rollers 3 arranged side by side and driven in rotation in such 
a way that the parts to be machined, brought one behind the other on the 
two rollers at one end of these, are simultaneously driven in rotation 
about their axes and driven in axial translational motion by the two 
rollers 3 as a result of a so-called "centreless" effect, as is well 
known, for example, for centreless grinders in a row. 
The spacing of the two rollers 3 is adjustable for the purpose of adapting 
the supporting assembly 2 to parts to be machined of different diameters. 
The stand 1 carries, furthermore, a bracket 4, on which are mounted a 
plurality of abrasive-machining units 5 arranged one behind the other in 
the direction of axial translational motion of the parts to be machined on 
the supporting assembly 2 (arrow A in FIG. 2). 
A stage 6 fixed to the bracket 4 carries, for each machining unit 5, a 
reserve reel 7 of new abrasive cloth and a rewinding reel 8 of worn 
abrasive cloth. The rewinding reels 8 are driven by a geared motor 9 
installed on the column 4 by means of a belt transmission 10. 
The column 4 carries, moreover, a stage 11, on which a stage 13 carrying a 
plurality of jacks 14 is mounted movably in horizontal translational 
motion by means of slideways 12. Each jack 14 carries, at the lower end of 
its piston rod, a bearing roller 15 mounted in rotation on a yoke 16 (see 
FIGS. 3 and 4). 
As emerges particularly from FIGS. 1 and 2, a band of abrasive cloth 17 
goes from each reserve reel 7 to the corresponding rewinding reel 8, at 
the same time passing over a bearing roller 15. 
The stage 13 is coupled by means of a connecting rod 18 to an eccentric 19 
driven by a motor 20. 
The diagram of FIG. 5 shows that all the belt transmissions 10 driving the 
abrasive-cloth rewinding reels 8 for the purpose of the continuous advance 
of the cloths 17 drawn off from the reserve reels 7 are controlled by the 
gear motor 9 by means of a common shaft 21. 
According to the Figure, each rewinding reel 8 driven by a belt 
transmission 10 and each reserve reel 7 is mounted on a spindle 22 
carrying an elastic diaphragm 23 inflatable by means of compressed air 
arriving by way of a revolving joint 24 at the spindle 22 mounted in 
rotation by means of bearings 25. 
When a part brought, for example, by a conveyor arrives on the rollers 3 at 
the left end in FIG. 2, the jack 14 of the first machining unit 5 is 
controlled in such a way that the abrasive cloth of this first unit is 
applied by the pressure roller 15 of this jack 14 against the part to be 
machined. As a result of the so-called centreless effect, the part to be 
machined is driven in rotation about its axis and in axial translational 
motion, thus causing it to come successively into contact with the 
abrasive cloths of the other machining units 5. Because the bands of 
abrasive cloth of increasing fineness of the successive machining units 5 
are driven continuously during the machining, the successive parts are all 
subjected to identical machining conditions, as a result of which parts of 
uniform quality are obtained. 
Of course, the embodiment described above and illustrated by the 
accompanying drawings has been given only as a non-limiting indicative 
example and many modifications and alternative versions are possible 
within the scope of the invention. Thus, the number of successive 
machining units on the same machine can differ from three, this number can 
be increased according to the quality demanded for the machined parts. 
Furthermore, for changing the reserve reels and the rewinding reels, it is 
possible to employ means other than spindles with an inflatable diaphragm.