Q: What's the difference between semi and fully automatic stretch wrapping machines?
A: Semi-automatic stretch wrapping machines are normally used in low volume applications where no more than 30 loads an hour need to be wrapped. These machines require that the load be brought to the machine either by fork lift (high profile) or by pallet jack (low profile). After the load is placed on the turntable or in the wrapping area, an operator must attach the film to the load, press the start button, then detach and secure the film tail to the load at the end of the wrapping cycle.
An automatic stretch wrapping system does not require an operator, except to load film. Loads are usually transferred to the machine via a powered conveyor. Once in the wrapping area, the machine begins the wrapping cycle automatically. A load height sensing photo eye tells the film carriage how high to wrap. At the end of the cycle, the film tail is automatically cut and either brushed down or heat sealed to the load. The pallet load is then conveyed out of the wrapping area and the machine is ready for the next load. With Portable Automatic machines, the loads are brought to and removed from the machine by lift truck. The driver starts the cycle with a hanging pendant switch. Automatic systems can process anywhere from 30 to 120 loads per hour.
Q: What's the difference between turntable and rotary tower machines?
A: Turntable stretch wrapping machines wrap by turning a load on its turntable while the film carriage ascends and descends on a fixed mast. Both high and low profile turntable semiautomatic machines can handle load weights ranging from 3,500 to 6,000 pounds. Automatic turntable machines generally use conveyor systems to transport loads.
Rotary tower stretch wrapping systems wrap by rotating the film carriage around a load, which stands still and does not rotate. Your basic decision to use one type or another depends on your load type, floor space configuration and speed requirements. Generally, rotary tower machines are better for loads that are very heavy, light, fragile or unstable. In many cases, shrink wrap rotary tower machines have a more compact footprint making them ideal when floor space is at a premium. Stretch wrapping rotary machines can usually achieve higher throughput speeds as well because loads need not be rotated at high speeds.
Q: What is powered film prestretch and why is it so important?
A: Powered prestretch refers to the method of 'prestretching' the stretch film prior to load application. The film carriage uses an electric motor to turn two specially surfaced rollers, which rotate at different speeds. The stretch film, which is threaded around these rollers, is prestretched making it much stronger and able to contain shifting loads. This process also increases the yield of the film roll making stretch wrapping a very economical way to unitize pallet loads.
At our standard prestretch rate of 260% (available on most models), 1 foot off the supply roll becomes more than 3.6 feet of film wrapped on the load! We offer rates of up to 425% for high performance applications.
Q: What about stretch wrapping long loads?
A: Orbital stretch wrappers are designed to wrap long loads by passing the product through a horizontally oriented wrapping ring to produce a tightly wrapped bundle. As the product is conveyed through the ring, film is spiraled around the load much like wrapping the handle of a tennis racket. This method of shrink wrapping effectively holds product together while providing a high degree of protection from moisture and dirt. Orbital machines are available in both semi- and fully automatic models.
Selecting A Stretch Wrap Machine
Choosing the right stretch wrap machine for your packaging operation should be a carefully thought out project. Requirements should be gathered in order to narrow down the choices. The following are some questions that should be considered.
- What type of load? (Ex stable, unstable, heavy, light, fragile, uniform surface, mild or great irregularity of surface, tall, short, wide, etc.)
- What stretch wrap packaging throughput speed do you require and is floor space an issue?
- How much do you want to invest in a stretch wrapper?
- Do you want an operator run system using existing forklifts or pallet jacks to bring loads to the wrapping area? Or do you want a completely automatic system that does not require an operator and uses a powered conveyor to transport loads to and from wrapping area?
- Do you want a stretch wrap system to achieve optimal pre-stretch film performances and thereby gain more secure loads while using less film?
Types of Stretch Wrap Systems: Semi Automatics / Simple Automatics / Fully Automatics
Stretch wrap machines are either semi-automatic (good for less than 30 loads per hour), simple automatic (enables stretch wrapping start and finish without operator leaving a forklift) or fully automatic (standard choice for medium to high volume packaging operations). An important difference between semi-automatic and an automatic system, is semi automatics requires more labor resources and have lower output speeds. Review of daily output requirements by a packaging consultant will determine what type of system is most appropriate for a packaging operation.
Turntable Stretch Wrap Systems
These stretch wrap machines use a film carriage on a fixed mast, to apply stretch film as it ascends and descends and rotates the load. This type of system can meet the needs of most applications. Semi-automatics are designed for use with a forklift (high profile turntable) or a pallet jack (low profile turntable) and automatics are normally used with a conveyor.
Overhead Stretch Wrap Systems
These stretch wrap machines use a rotating film carriage to apply stretch film as it moves around the load. Overhead stretch wrappers are freestanding and are available in semi-automatic, simple automatic, and fully automatic. This style of stretch wrapping is ideal for loads that are significantly light, fragile, and unstable or for loads that are too heavy for turntable systems.
Also referred to as: Straddle Stretch Wrappers, Overhead Stretch Wrappers, Rotary Tower Stretch Wrap Machine, and Rotary Arm Stretch Wrappers
Horizontal Stretch Wrap Systems
These stretch wrap machines apply stretch wrap with a rotating film carriage that moves around a load as it passes through a horizontal ring. An automatic stretch bundler is ideal for products and loads that do not use a turntable system or overhead system or if banding or enhanced packaging is required.
Also referred to as: ring wrapper, orbital, horizontal pallet wrapper & ring.
Which Stretch Film To Use?
Selecting the right stretch film is very important to maximizing output performance of your stretch wrap machine. Proper pairing of stretch wrap machinery and stretch film will ensure stronger loads and optimal film efficiencies. Today's high capacity stretch wrap machines require film rated for use with the RPM of the machine. As a rule of thumb use the machine stretch film levels and stretch film equipment RPM to determine what type of stretch film is required. Such as
250% stretch at 30 RPM = High Performance
200% stretch at 15 RPM = Moderate Performance
150% stretch at 12 RPM = Low Performance
Stretch Wrapper Terms
Brake Roller: A mechanism on a stretch wrap machine that reduces the rate at which the film feed is dispensed to the load and as such increases tension between the stretch film and the load.
Dancer Bar: A pivoting roller found on many stretch wrap machines that measures film feed requirements. Component will accelerate and decelerate film feed on corners to sustain a continuous film force (film tension) on the load or pallet.
Film Feed: The speed at which the film is supplied to the load is the film feed. Film feed rate adjusts as needed on load corners to maintain consistent film tension.
Film Force: The retaining tension of the film put on the object wrapped is referred to as film force or film tension. This is usually measured in pounds. A film force dial is commonly placed on the carriage or control panel.
Film Force Release: Automatic stretch wrappers typically have a film force release feature so that added film tension is released when it is not wanted. This feature helps make the automatic stretch wrapping process easier to set up and detach at end of cycle
Horizontal Stretch Wrapper: Fast efficient stretch wrap solution system that wraps loads not suited for turntables or overhead straddles or requires banding or enhanced packaging solutions. Common system options include: power thru conveyor, product stabilizers and accumulation conveyor.
Load Diagonal: The measurement diagonally across opposite corners of a pallet or load is referred to as the load diagonal. The dimension of the largest and smallest load diagonal is necessary to determining stretch wrap machine size. The measurement is calculated as (L2 + W2).
Prestretching: The process of stretching the film before applying it to the load is referred to as pre-stretching. This is carried out in the pre-stretch carriage, where the stretch film threads between the two carriage rollers (primary roller and secondary roller) and is mechanically elongated as the second roller rotates faster than the primary.
Simple Automatic: A step up from semi automatics but does not include all the features offered by fully automatics. Main feature is providing remote access to initiate wrap start and finish without having to leave forklift.
Wrap parameters: Adjustable load retention settings available on the stretch wrap machine. Typical setting variables include: film force, rotation speed (turntable or rotary arm), pre-stretch carriage vertical speed, bottom wraps and top wraps.