Wrapping method
A method for wrapping a load with a film by a wrapping machine including an unwinding apparatus provided with a reel of the film includes moving the wrapping apparatus and the load in relation to one another and unwinding from the reel an established effective length of film per revolution of the wrapping apparatus or of the load. The established effective length of film is calculated with the formula: where: S f . initial length of film is determined on the basis of dimension and/or shape of the load; ω: rotation speed around a wrapping axis of the unwinding apparatus or of the load; V t : movement speed of the unwinding apparatus parallel to the rotation axis; ω max: maximum rotation speed around the wrapping axis of the unwinding apparatus or of the load; Δ corr : corrective parameter.
1. A method for wrapping a load with a film using a wrapping machine including an unwinding apparatus provided with a reel of film, comprising the steps of
(a) moving said unwinding apparatus and said load in relation to one another;
(b) unwinding from said reel an established length of film per revolution of said unwinding apparatus or of said load, said established length of film being calculated with the formula:
L
fe
=
2
π
(
S
f
2
π
)
2
+
(
V
t
ω
)
2
×
(
1
-
Δ
corr
×
ω
ω
max
)
where
S f is an initial length of film determined on the basis of one of dimensions and shape of said load;
ω is a rotation speed of said unwinding apparatus or of said load around a wrapping axis;
V t is a movement speed of said unwinding apparatus or of said load parallel to said rotation axis;
ω max is a maximum rotation speed of said unwinding apparatus or of said load around said wrapping axis; and
Δ corr is a corrective parameter.
2. A method according to claim 1 , wherein said moving step comprises
(a) rotating said wrapping apparatus and said load in relation to one another around said rotation axis at said rotation speed; and
(b) moving said unwinding apparatus or said load parallel to said rotation axis at said movement speed in order to wrap said load in a series of strips or bands of film having a helical path.
3. A method according to claim 2 , wherein said series of bands with a helical path has a helix pitch P e defined by the equation:
P
e
=
V
t
ω
2
π
=
V
t
n
60
where
n is said rotation speed expressed in revolutions per minute.
4. A method according to claim 1 , wherein said moving step comprises rotating said wrapping apparatus and said load in relation to one another around said rotation axis at said rotation speed in order to wrap said load in a series of strips or bands of film having a circular path.
5. A method according to claim 1 , wherein said corrective parameter has a percentage value between −3 and +3.
6. A method according to claim 1 , wherein said initial length of film is calculated as one of a perimeter of said product and a prestretching percentage applied to said film before wrapping the load.
7. A method according to claim 1 , wherein said unwinding step comprises rotating at least a first roll of said unwinding apparatus by an established number of revolutions of said wrapping apparatus or of said load to enable said established length of film to be unwound.
8. A method according to claim 1 , wherein said rotation speed and said movement speed are substantially constant average speeds.