- Dual Hydro
- Top wraps
Blown-film extrusion is a process for forming plastic stretch films. Blown
stretch film extrusion involves a molten resin extruded through a circular
die and filling the tube with air. The air within the tube stretches the
film to obtain the desired thickness.
Typically blown film is a tougher but noisier film than cast films.
The revolutions of film applied by a stretch wrapping system to the lower
layers of a pallet or load. Typically more than one revolution is applied
to this area to increase the load stability of the unitized load. This area
typicall where machine
stretch films will break. Out automatic
stretch wrappers deploy the dual hydro stretch system to help prevent
A mechanical roller in some stretch wrap machines that provides a resistive
force that reduces the film feed rate being supplied to the load. The resulting
drag will create an increase in tension between the load and the stretch
Plastic sheeting or stretch film produced from synthetic resins. A molten
resin is extruded through a slot or flat die to form a thin film or molten
sheet. Cast stretch film typically is quieter, more transparent, and glossier
than blown film because of this process.
Cling (single side - two sided - differential)
Cling is a bonding agent added to stretch film to increase the stickiness
quality of the stretch wrap. This is desirable to allow the layers of stretch
film applied to bond to the previous layers effectively creating a single
wall of stretch film. Depending on the desired effect the bonding agent
is applied to one or both sides. It is most commonly applied using co-extrusion
where the bonding agent is a layer that is co-extruded during the manufacturing
Dual Hydro Stretch System
Dual Power Hydro Stretch provides 2 independent levels of pre-stretch: one
for the bottom of the load the other for the stress of the pallet wraped
load. Over 70 percent of film breaks occur at the bottom of the load where
the pallet meet the load. The Dual Power systems allows you to set the pre
stretch level at the bottom of the load independent of the pre-stretch level
on the rest of the load. This allows loads to be wraped tighter at higher
stretch levels and lower cost.
As a film is applied to a load the speed or velocity at which it is applied
is called film feed. The feeding of the film is rarely constant as it must
be accelerated and decelerated to compensate for the corners of the load
to keep the film tension constant. Without this corner compensation feedback
the film tension would increase as at the corners causing potential damage
or film breakage issues.
Film Force (Film Tension)
Film Force is the retaining force applied by the stretch film on the product
being wrapped. This force is typically measured in pounds. Film force is
created two ways. The second method is by delaying the film feeding out
of the carriage. During wrapping the film is fed out at a constant tension.
By delaying the response (speed) of the carriage film feed, you electronically
increase the film tension. A film force dial is typically located on the
control panel or carriage.
Film Force Release
A feature typically used on automatic stretch wrapping equipment whereby
the film force feature is disabled for a time at the beginning and end of
the cycle. This feature prevents unwanted tension at the two points during
the cycle where added tension would create problems. The stretch film pulling
out of the clamp at the beginning of the cycle and the detaching of the
trailing tail at the end of the cycle are typically remedied by film force
Is the measurement used for measuring stretch film thickness.
Film memory is the most important reason for prestretching stretch film.
Prestretching stretch film creates a memory in the film, which causes a
continuous elastic effect as the film tries to return to its unstretched
state. This ensures that the load rigidity is maintained even as the load
shifts or settles during transit. This stretch film memory that differentiates
film from non-prestretched film or other means of unitizing.
Stretch film designed to be post stretched or tensioned stretched by personnel
without equipment is called hand wrap. Typically hand
stretch film does not have the stretching abilities of machine wrap
and is wound on smaller and lighter rolls for easier manipulation.
Home position is the position of all the moving sub assemblies on a stretch
wrapping machine when they are at rest and ready to begin a new cycle.
Is the measurement of a pallet or product load across the diagonally opposite
corners. This dimension is critical in determining the overall size of a
wrapper equipment. The difference in this dimension in the largest load
to be wrapped and the smallest can also effect how the machine needs to
be designed. The equation for determining a load diagonal of any pallet
is /(L2 + W2).
Is the metric unit of measurement used for measuring stretch film thickness.
As film is stretched there is a tendency for the film to narrow (similar
to bubble gum). This narrowing of the film is called neckdown. Neckdown
reduces the coverage a revolution of stretch film provides thus potentially
increasing the number of revolutions required to wrap a pallet or load.
The larger the distance between the two rollers stretching the film (Primary
& Secondary prestretch rollers) the larger the neckdown.
As stretch film is applied to a load the stretch film is typically applied
so that the next layer of stretch film is applied over the previous layer.
This overlapping of film layers increases load retention. By slowing the
vertical movement of the stretch film carriage the larger the overlap created.
Is the amount of stretch film applied over the top of the load. As the stretch
film reaches the top of the load, the vertical movement of the carriage
can continue so that the film angles over the top of the load. The stretch
film on top creates a downward force on the pallet load. This is also used
when a plastic top sheet or corrugated top cap is applied on the top of
the load to lock them in place.
Prestretch is the process of stretching the film in a prestretch carriage
PRIOR to (Pre-) applying it to the load to be wrapped. As the stretch film
passes through the carriage it threads past two rubber rollers (Primary
roller & Secondary roller). The secondary roller is usually larger than
the primary roller and its rotational speed is geared to be faster than
the primary roller. This differential of speed where the secondary roller
is pulling the film from the primary roller causes the film to stretch between
the two, thus prestretching the film between one and the other.
Is the assembly in a stretch wrapper that stretches the film prior to applying
it to the load. Located on a vertical traveling slide, the prestretch carriage
applies a spiraling layer of stretch film to the load thus encapsulating
the load in stretch film.
Is one of two rubberized rollers located in the prestretch carriage used
to create prestretched film. The primary roller is the first rubberized
roller the film passes by and is usually the smaller of the two. Its speed
is also geared slower than the secondary roller.
Is one of two rubberized rollers located in the prestretch carriage used
to create prestretched film. The secondary roller is the second rubberized
roller the film passes by and is usually the larger of the two. Its speed
is also geared faster than the primary roller.
Tension stretch (or post stretch) is the method of stretching the film by
pulling (or tensioning) while the film is applied to the pallet. Although
this increases the film force, the load being wrapped limits this tension.
Empty PET bottles or light boxes will be crushed or damaged by high-tension
stretch. Layers of product can be swept of a pallet and film breaks also
increase as the tension stretch is increased. Not only can you use stretch
wrap machines for creating tension but Stretch
Top Sheet Dispenser
Top sheet dispenser is a piece of equipment that applies a poly sheet of
plastic top sheet to the top of a load to provide a water resistant layer.
Typically, once applied, a top sheet is subsequently wrapped with stretch
film to secure it in place. The top sheet film is unrolled, cut to size,
and applied to the load automatically by the top sheet dispenser.
Top Sheet Film or Plastic Sheeting
Is the poly plastic sheeting film that is applied to the top of the load.
Top wraps are the extra revolutions of stretch film applied to the top portion
of the load to be wrapped. As the top layers are susceptible to shifting
in transit extra layers of stretch film (top wraps) is applied. These extra
revolutions are typically set using the top wrap counter located on the