The present invention relates to the production of an engraved cylinder
for use on machines designed for roller finishing of hides, artificial hides, fabric,
synthetic materials and the like.
As it is known in carrying out the finishing operation in the field
of .the tannery industry, roller-machines are used in particular, more commonly
known as dabbing machines or «roller-coaters», in which the hides are carried by
a lower roll or a rubber mat and pressed against an opposing embossed roller consisting
of an engraved cylinder, which ensures the application to the surface of the hide
of a uniform film of liquid product, previously distributed over the engraved surface
of the said cylinder by means of one or several scrapers.
The engraved cylinder can rotate in "synchro", that is to say in a
manner in accordance with the direction of movement of the hide, or in "reverse",
that is to say in a manner contrary to the aforesaid direction.
The complete success of the hide finishing operation depends on many
factors, among which the regular feeding of the hide into the restricted zone, that
is to say that comprised between the engraved cylinder and the underlying roller
or conveyor mat, and depends above all on an optimum application to the hide of
the liquid impregnation product.
The conveying and application action of the finishing liquid product
is achieved by means of the honeycombs, which form the honeycomb embossed surface
of the engraved cylinder.
The embossing pattern may be of the negative impression type, used
mainly for processing-work in "synchro", where the quantity of product applied to
the hide is dependant on the dimensions of the honeyccmb, or of the positive impression
type, used in the main for processing-work in "reverse", whereby the quantity of
product to be applied to the hide, in addition to the dimensions of the honeycomb,
also depends on the speed of rotation of the engraved cylinder.
Honeycombs with a negative impression are formed by small non-communicating
cells, of a pyramidal or truncated-pyramidal shape with a base in the form of a
square, hexagon or profile of whatsoever other polygon, of which the angle to the
apex is variable between 30° and 120°.
The result of the coating of the product on the surface of the hide
to be pigmented or coloured is associated with the quantity of product contained
in each individual cell or honeycomb and by the spreading potential of the product
itself.
Operationally, a large number of small honeycombs per unit of surface
of the engraved cylinder allows an improved product application effect to be achieved
in relation to the use of an engraved cylinder having a honeycomb of a larger type
of dimensions.
Notwithstanding this, even with an embossed surface having a high
honeycomb density the processed hide will never result in a perfectly smooth and
mirror-like surface.
Honeycombs with a positive impression consist of a series of inter-communicating
channels, which demarcate projections located in uniform manner and present a continuous
triangular shape or truncated-pyramid shape, with a square or rhomboid base, having
an angle to the apex varying between 30° and 120°.
Such honeycombs with a positive impression have the advantage of being
able to distribute a large quantity of product, which is directly proportional to
the speed of rotation under "reverse" working conditions of the engraved cylinder,
thus allowing a very smooth processed hide surface to be obtained, resulting from
the spatula-like effect of the projections of the engraved roll.
The simpler configuration with a positive impression, is the type
so-called "continuous helical groove".
In the present state of the art, the honeycombs with a pattern of
positive impression having a continuous helical pattern, of essentially triangular
cross-section, are produced with a helix angle sloping at 45°, that is to say with
an axial pitch equal to the circumferential pitch, that value being the maximum
possible used by the producers of engraved cylinders easier to produce to achieve
satisfactory operation with the rolled finishing effect.
Such types of honeycombs, though having the advantage of extremely
simple production, suffer two notable disadvantages:
- the feeding of the hide into the restricted zone is particularly difficult,
making soft hides impossible to process;
- owing to the slope of the helix, the product to be applied tends to convey itself
towards the end of the cylinder, thus causing its irregular distribution over the
hides to be pigmented or coloured.
The use of engraved cylinders with positive impression honeycombs,
in which the patterned face consists of intercrossing helical channels, inter-communicating
in such a way as to form truncated pyramid projections with a square or hexagonal
base, only eliminates the disadvantage of the lateral conveying of the product to
be applied, but not the difficulty arising from the insertion of soft skins and
in addition, when using high viscosity products, the patterning tends to mark the
impression of the aforesaid projections on the surface of the hide or of the support
to be pigmented.
Theoretical investigation of the behaviour of the fluid product to
be spread over the hides and laboratory experimental tests have demonstrated however
that positive results may be obtained with honeycombs having a helix slope with
a minimum angle value of 50° up to a maximum angle value of 89°, in relation to
the viscosity of the product to be applied, using low viscosity products (0 cps)
to products with a high viscosity (10,000 cps).
In particular, when working under "reverse" conditions with the above
helix slope angles of the grooves any tendency to a knurling impression effect on
the surface of the hide can be eliminated.
In addition, as shown by feasibility tests, as the helix slope value
increases, approaching a maximum value of 89°, the insertion operation of the said
hide into the restricted zone is facilitated and the negative effect of the lateral
accumulation of the product on the cylinder is all the smaller.
In addition, under "synchro" working conditions, with helix slope
values in excess of 50°, the release of the product from the base of the groove
Pattern is facilitated and prevents the front border of the hide, the first to enter
the restricted zone, from sticking to the patterned roller, owing to the adhesion
effect caused by the fluid product and dropping only thereafter, giving rise to
folds or curling, which damage or make the processed hide completely useless.
Finally, a high value of helix slope prevents air being entrained
into the fluid mass of product to be distributed which, causing an absence of homogeneity
of the aforesaid product, is the cause of irregular distribution and consequently
does not allow a smooth and mirror-like surface to be achieved.
As an example of the state of art, it can be cited the document DE-A-3927365;
however this device is provided with helical patterns belonging to two separate
structures and so they intersect each other. This causes the formation of sharp
corners that, when i n contact with the objects to be worked, cause frictions, with
resulting difficulties of advancing for the hides and creation of turbulences in
the liquid products to be applied to the hides.
Aim of the invention is to overcome these disadvantages with a simple device; this
is achieved by means of a cylinder with the features of the characterizing part
of the claim 1.
Such characteristics are illustrated by way of the appended drawings,
provided for non-restrictive illustration purposes wherein:
- Fig.1 shows a patterned roller with the central part engraved with a helical
pattern of grooves,
- Fig.2 represents a detailed view of the pattern, consisting of grooves, for
which in the interest of clarity, the parameters are shown which determine the angle
of slope of the helix in relation to the axis of the body of the cylinder.
- Fig.3 represents a detailed sectional view of the profile of the helical grooves
according to line III-III in Fig. 2.
As may be seen from the illustrations the roller 1 has a cylindrical
part bearing a patterned surface 2 achieved by way of the grooves 3, of triangular
section and helical development.
The said grooves 3 are reciprocally separated and demarcated by the
helical projections 4 of trapezoidal section and helical development.
In Fig.2 a detailed diagrammatic view of the pattern formed by the
grooves is shown, and for greater clarity the parameters determining the helix angle
of slope in relation to the axis of the body of the cylinder 1, the angle being
determined by the following formula:
α = arc tan (D × πPe)
wherein:
- Pe = p x z =
- the helix pitch, matching the space by which one point of the helix advances,
parallel with the axis of the cylinder, during the course of one full rotation.
where
- p =
- distance between two contiguous grooves of the helix.
- z =
- number of helixes contained in one helix pitch.
- D =
- cylinder external diameter
- D x π =
- external circumference of the cylinder
