Apparatus for the treatment of seed

Seed is treated with a treatment agent within a rotary drum having rows of circumferentially spaced stirring plates mounted therein. When the drum is rotated about a substantially horizontal axis the plates raise seed from the bottom of the drum. At their uppermost positions the plates are inclined so that seed falls from the plates into a vertical passage defined between adjacent rows of plates. Treatment agent is introduced inside the drum such that the agent is applied to the seed traveling downwardly along the vertical passage.

BACKGROUND OF THE INVENTION 
The present invention relates to the treatment of seed. 
"Seed" means any plant member capable of resulting in the reproduction of a 
plant and obtained either by a sexual route, in which case it will be 
referred to as grain, or by vegetative reproduction, in which case it will 
be referred to as a plant or explant. 
A treatment means any application of a liquid or solid product to the 
surface of the seed. 
When this application results in a change in the shape of the seed, for 
example to permit mechanical sowing of individual seeds, then coating 
techniques are involved. These generally comprise, in a first stage, the 
deposition of an adhesive product onto the seed and then, optionally after 
partial drying, the deposition of a liquid charge or of a powder, a 
treatment agent, an agro-chemical product, a dye or other adjuvant which 
fertilizes or improves the germination conditions of the seed. 
When this application is carried out without changing the shape of the 
seed, for example to provide protection, and, optionally, a colour or an 
appearance, then this will be referred to as film-coating. This technique 
comprises spraying the seed to form a deposit of a liquid, frequently 
aqueous, composition of a film-forming product containing a treatment 
agent, and simultaneously drying the deposit obtained. 
These coating and film-coating techniques rely, among others, on rotary 
horizontal cylindrical drums comprising, besides the drum as such, means 
for driving it, means for distributing the charge and the treatment agent 
and, optionally, means for drying. To ensure homogenization of the 
treatment, it is known to provide stirring members inside the drum. 
However, despite a marked improvement in the quality of the coating, this 
is frequently insufficient on an industrial scale when, for example, seed 
of irregular shape is treated or when it is intended to produce a film 
coating requiring a deposit of high quality, that is to say of high 
uniformity, over the entire surface of the seed, for protection and/or for 
colouring. 
There is therefore a need to make it possible to carry out these treatments 
for protection and for improved appearance of these seeds, in order to 
improve the efficiency during the sowing. 
SUMMARY OF THE INVENTION 
According to the present invention there is provided a rotary drum, having 
a substantially cylinderical peripheral wall mounted with its axis 
substantially horizontal, and two end walls, the drum being mounted for 
rotation about said axis and defining a volume in the bottom part of which 
there is located the bed of seeds to be treated, comprising means for 
distributing the charge or the treatment agent, means for driving the drum 
in rotation and directing members, fastened to the inside of the drum, for 
stirring the bed of seed during the treatment, in which these directing 
members consist of at least one pair of vertical rows of blades of 
opposite inclination such that: 
a) each row is situated in one of the transverse zones of the volume of the 
drum substantially parallel to the latter's end walls, the two rows thus 
creating between them a substantially vertical passage for the seeds to 
flow through; 
b) the blades are inclined relative to the axis of the rotation of the 
drum; 
c) two neighbouring blades of each row subtend an angle diverging towards 
the peripheral wall of the drums; 
d) the blades of one of the rows are offset angularly relative to the 
blades of the other row, as viewed along the axis of the drum and the part 
of each blade which is used for the stirring is the radially inward part, 
spaced from the peripheral wall. 
Such an apparatus permits each seed to be introduced a substantially 
identical number of times to the means for distributing the treatment 
agent, this being done throughout the treatment period. 
The central passage for the seed to flow through is an essential feature of 
the apparatus according to the invention, this passage being substantially 
vertical. It must be sufficiently wide not to produce a shovel effect on 
the seed, that is to say not to entrain the seed towards the upper part of 
the drum and to make it shower down again in an uncontrolled fashion, 
without being excessively large, in which case the stirring of the seed is 
inadequate to ensure the homogeneity of the coating of the said seed. 
The term "blade" means a rigid shape having a surface permitting a small 
volume of seeds to be pushed from one point to another within the volume 
of the drum, that is to say to have an efficient shovel effect. This 
surface may be planar or, alternatively, to improve the recirculation of 
the seed from below onto the top and vice versa, slightly twisted to avoid 
making the seed rise back into the drum. 
In what follows, the inclination of the blades refers to the inclination of 
the latter's mean plane, that is to say the plane tangent to the surface 
at the centre of symmetry of this surface. 
The inclination of the blades, as defined above, relative to the axis of 
rotation of the turbine, determines the rate of flow of the seed in the 
central flow passage. 
It has been noted that very uniform results are obtained when the width 
(i.e. the axial length) of the central passage is approximately one third 
of the axial length of the drum. Similarly, an inclination of 30.degree. 
to 60.degree., preferably of 40.degree. to 50.degree., is advantageous. 
Furthermore, the blades in the apparatus according to the invention are 
such that two neighbouring blades, one belonging to one row and the other 
belonging to the other row of opposite direction, which are therefore of 
different inclination, form between them an angle diverging towards the 
periphery of the drum, so that the seed starting from the top of the bed 
of seed is guided back towards the central flow passage. This angle is 
generally between 30.degree. and 60.degree. and preferably between 
40.degree. and 50.degree.. 
Furthermore, the blades of one row are not opposite those of the other row, 
but are offset angularly, as viewed along the axis of the turbine. This is 
important, in order to ensure both an undisturbed downward flow of the 
seed (no seed blockage between the bottom part of the blades) at the same 
time as stirring of the seed coming from an upper blade with that situated 
on an opposed lower blade. 
Lastly, and in contrast with numerous known devices, the part of the blades 
which is used for the stirring must end at a certain distance from the 
neighbouring end walls of the drum. This distance is generally small but 
must be sufficient to permit the lateral seed to slide downwards and to 
fall back into the cycle of the general movement towards the centre. 
Thus, bearing in mind this condition and the dimensions of the central flow 
passage, the orthogonal projection of the blades on the drum axis is 
always smaller than one half of the axial length of the drum and is 
preferably approximately close to one third of this length. 
All the above parameters may be modified as a function of the nature, the 
shape and the quantity of the seed to be treated, of the type of method 
applied, and of the required effect on the seed. In all cases, stirring of 
such quality is obtained that, on average, the seed passes the same number 
of times under the spray of the treatment product. 
The blades described above may be solid or hollow or perforated and may be 
made of any material provided that it is sufficiently resistant to 
abrasion, non-adhesive to the charges applied onto the seed and inert 
towards the treatment products. 
Similarly, the drum may be solid or perforated, especially if an external 
suction or blowing device is provided particularly for drying the seed. 
The above description applies to a pair of rows of blades, but it is quite 
obvious that, in order to increase the capacity and/or the throughput of 
the unit, the device according to the invention may comprise a number of 
pairs of rows of blades in series, that is to say coaxial with the first 
row, and capable of being identical with or different from the first in 
size and inclination.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
FIGS. 1 and 2 show a horizontal cylindrical drum 1 having transverse end 
walls 4 and 5 and a cylindrical peripheral wall 6. The drum is capable of 
being rotated about its axis 2 by driving means which are not shown, and 
is provided in its interior with means 3 for distributing a treatment 
product, for example nozzles for spraying an aqueous dispersion of a 
film-forming product, or powder distributors. Inside the drum 1, in each 
of the parts of the volume which are close to the end walls 4, 5 
respectively, there are two rows 6 and 7 of blades 6a, 6b, 6c, and 7a, 7b, 
7c secured by means of the fastenings 61, 62, 63 and 71, 72, 73 
respectively, onto the cylindrical wall 8. These blades are inclined at 
45.degree. C. relative to the axis of the drum, and are arranged 
symmertrically relative to the diametral plane of the drum (cf. FIG. 2), 
that is to say the blades are offset by 120.degree. C. relative to one 
another in this plane. Lastly, row 7 is offset by 60.degree. C. relative 
to the row 6. These two rows of blades create a central flow passage 8, 
the width of which (i.e. the axial length of which) advantageously 
represents one third of the axial lenght 1 of the drum. The bed of seed is 
indicated by 9 when the drum is at rest and by 10 when it is in operation. 
It can be clearly seen that, as a results of the arrangement of the 
blades, the seed is stirred in a paticularly homogeneous manner. 
Each blade includes a proximal edge 20A located closet to the central flow 
passage 8, and a remote edge 20B located farthest from the flow passage 8. 
The remote edge 20B is spaced from the peripheral wall 6 and the adjacent 
end wall 4 (or 5) to form therebetween a space S along which seeds can 
slide as expalined earlier herein. It will be appreciated that the width 
dimension of the passage 8 (i.e., its dimension parallel to the axis 2) is 
slightly greater than one-third of the longitudinal spacing between two 
planes P, P' in which the remote edges 20B of the two rows of blades lie, 
as is evident from FIG. 1. 
FIG. 3 shows diagrammatically a drum 11 according to the invention, 
comprising five pairs of rows, 12, 13, 14, 15, 16 of blades 12a, 12b, 13a, 
13b, 14a, 14b, 15a, 15b, 16a, 16b of the type described in FIGS. 1 and 2. 
In this construction, however, the axial lenght of the free space forming 
a central flow passage for 14 seeds is relatively less, being 
approxiamtely one third of the axial lenght of each of the blades.