5 April 2002

Dont expose film to stress

THE overstretching and subsequent breakage of plastic film on big bale silage was one of the most common problems Graham Robson, technical manager at United Agricultural Twine (UAT), was called out to last season.

And its root causes could not always be blamed on the manufacturer, he claims. "The vast majority of cases I saw could have been prevented by some simple maintenance.

"Over-stretching causes the film to neck down more than it should, making a narrower neck of film going on to the bale.

"This will, in turn, affect the amount of film overlap and some parts of the bale will have less than the necessary four layers of film. That will lead to splitting once the bales have been stacked."

Mr Robson says the best way to avoid necking down is to clean the pre-stretch unit rollers whenever a build-up of tack occurs. This is likely to happen much more frequently in hot weather, when rollers should be checked at least once a day.

Another factor which can cause film breakage is the condition of the pressure roller springs.

"If these springs are poorly maintained or wearing out, it will lead to a lack of tension and the film will become wrinkled. The film will not then be able to hold tight to the bale and achieve a good air seal."

Checking the bale film width will reveal whether the film is being stretched correctly, says Mr Robson. This can be done by measuring the width of the film web on the circular end of the bale.

"When the correct 70% stretch is applied, 750mm width film should neck down to 590-600mm. With the narrower 500mm film it should measure 390-400mm."

Mr Robson also questions the way UK farmers stack their round bales. "In the rest of Europe, round bales are always stacked on their ends. That means the part of the bale with the most layers of plastic is exposed, which gives greater protection from bird damage. Plus the bales stay firmer when they are stacked end up."

&#8226 How do you think round bales should be stacked and why? Contact the Machinery Editor, farmers weekly, Quadrant House, Sutton, Surrey SM2 5AS or e-mail andrew.collings@rbi.co.uk &#42