Silage Film – Unwrapped!
29/11/2007 - A guide to selecting the right wrap for you By Andrew Makin, Agricultural Division Sales Manager, Integrated Packaging
As film technology and consumer needs have developed, more and more silage film options have become available.
Farmers and contractors now have a growing number of choices in film colour, thickness, revolutions and manufacture. Selecting the most suitable bale wrap for your operation can prove difficult and your choice might not be the best if you do not have all the information you require.
To get the best outcome – i.e., a successful and efficient wrap every time – among the key things you need to consider are quality, film properties, application methods, maintenance and set up of machinery
Film quality should always be the key consideration in the selection process. Manufacturing standards are not enforced for silage film, so it’s important to go with a well known and proven brand.
Next a whole series of questions arises: should I go for a high quality blown?, cast?, pre-stretch?, mono? or co-extrusion? And what does it all mean?
While there are two different manufacturing methods to create stretch film (blown or cast) blown film is the preferred manufacturing method to achieve a higher quality film. Blown film performs better than cast film in tear resistance, holding power, yield and cling making it ideal to contain silage. Cast manufactured bale wrap should be avoided; the higher air permeability causes poorer quality silage.
Mono or single layer blown film was used on the first ever bales to be wrapped. Technological developments in extrusion and resins have led to co-extruded (multi-layer) blown film and most recently to the range of pre-stretched films.The essential difference between mono and co-extruded blown film apart from the number of layers is the ability of manufacturers to draw on different resins with individual characteristics to enhance the films properties for performance.
For example, a co-extruded film may consist of a tough central layer to increase puncture and tear resistance, a soft inner layer to increase lamination for a tight air seal, and an outer layer with high UV stabilisers to offer maximum field life.
Presently, pre-stretched films represent the next generation in film technology. These are thinner silage films manufactured via a cold stretching process to optimise the blown film’s properties. This results in higher tear and UV resistance plus excellent air permeability, tack and film life. Pre-stretched film is stronger, more cost effective and generates less waste. The increased roll running lengths also reduce down time with fewer roll changes.
Pre-stretch films are available in a range of gauges and your selection should depend on your fodder handling and management systems. Multiple handling or transporting of wrapped bales is matched to the heavier gauge pre-stretch films. For extended film life and premium protection conventional 25 micron plastic or 30 micron films are best.
The use of 30 micron is more economical at four layers compared to 6 layers of 25 micron. It’s best to consult the manufacturer to ensure you select the correct gauge and achieve the maximum benefits of pre-stretch.
Film Application and Machine Maintenance
Next, application of silage film and machine maintenance also plays an important role in ensuring your silage film performs as intended.
There are three vital points to remember;
1. Central Application: The film must always be applied so the centre of the film roll touches the centre of the bale. If it’s too high or low, you’ll increase your wrapping costs and affect good film application.
If the completion of the first full coverage of the bale on both sides finishes on the same bale revolution, you’ll know the film height is correct.
2. Clean Rollers: All quality stretch films contain tackifiers that assist in the lamination of the film layers to create anaerobic (oxygen free) conditions required for a successful fermentation. This film tack builds up over a period of time on the pre-stretcher head rollers and causes inconsistent film stretching. The rollers must be regularly cleaned of this tack build up using a white sprit cleaner. Petrochemical products such as petrol or diesel should be avoided as they can react with the film affecting wrap performance. There are also speciality cleaners available.
3. Tension: The tension of the film pre-stretcher rollers against the film roll during application must be consistent throughout the entire roll length. With 17 years experience, I’ve found this is the most common issue faced during the busy wrapping season.
Worn or poorly maintained springs can reduce film yield, commonly noticed by loose or wrinkly film towards the end of the film roll. In severe cases the film “runs on” to catch and tear. A quick fix method with many of different brands of wrappers is to place shims behind the springs to increase the force, alternatively replace the worn springs.
Lastly, whether you’re using an individual turntable, satellite or tubeline wrapper there are several bale wrap options to give you the most economical bale wrap. Individual round and square bales need a minimum application of four film layers, applied with 50 percent film overlap and 55 percent pre-stretch to give satisfactory performance over the storage season.
Tubeline type wrappers for round and square bales need a minimum of six film layers. The additional layers are required with tubeline wrapping systems as the normal loss in bale dry matter creates stress on the film in the cross direction. Tubeline types are also ideally suited to the use of pre-stretch films as there is no additional stress applied to the film after wrapping.
Basically good silage wrapping and greater cost benefits are achieved when operational requirements and quality product meet with diligent maintenance and accurate application. It is also important to seek the right advice from informed parties.
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