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Save sacks of cash

Form Fill Seal (FFS) is a method of packing dry products into a low cost container better known as a ‘bag or sack’ which is suitable for distributing that product to the end user.    

With Form Fill Seal the bag is formed on the bagging machine from a roll of plastic film, immediately filled with product and then sealed shut – without the need for any operator intervention.     Form Fill Seal has been widely adopted for filling small bags from 25g-500g with product ranging from potato crisps to dog food and polyfilla – now that the technology has “grown up” and Form Fill Seal is a serious contender for packing large bags up to 50kg.   

In contrast pre-made bags and valve sacks are supplied as individual items which are filled by a bagging machine then closed along the top by sewing, or sealed with ultra sound. In the case of a fully automatic packing line for pre-made bags an operator is required to load piles of bags into the magazine, with a semi-automatic line he applies the empty bags onto the filling spout and also feeds them through the bag top sewing or heat sealing machine.  
After filling the bags are palletised, building them up into a pile of 40 or 60 bags to make unit load of 1 or 1.5 tonnes (which is the optimum unit load for economic transport and distribution).

What types of Form Fill Seal bagging machines are available?
Vertical or flat film Form Fill Seal – a flat sheet of film is fed off the roll and pulled over a forming collar, overlapped and made into a tube which is sealed longitudinally.    The product being filled is dropped into the tube of film, when the bag is full the sealing jaws simultaneously weld the top of the just filled bag and the bottom of the next bag. A knife then cuts the two bags apart.   A vertical Form Fill Seal can make either pillow bags or bags with a side gusset. It can punch a handle into the top of the bag and can be adapted for handling powdery products. It is a compact machine and takes up less floor space than other types of Form Fill Seal machine.

Horizontal, tubular Form Fill Seal – this machine converts a roll of flat or gusseted tubular film into a bag which is then applied to the filling spout, filled and sealed.

This machine is mechanically more complicated than the vertical Form Fill Seal machine, it can make pillow type and gusseted bags. With the addition of a corner sealing unit, the gussets on each side of the film are folded and sealed together in order to make bags with a square block end – beautiful presentation.

It is normally favoured for high-speed applications but is relatively expensive for low speed bagging.

‘C’ type Form Fill Seal – with this machine bags are made from a reel of film which has been folded into a ‘C’ or ‘U’ shape. The machine forms the bag by making a seal down both sides; the bag is transported to the filling spout through which the product is dropped into the bag. The top of the bag is then heat-sealed or can be closed by sewing.

This ‘C’ type machine cannot make gusseted bags, however if a fold is made in the bottom of the ‘U’ shape then it can make block bottom bags. The machine is not suitable for packing dusty or wet products. The base model of a ‘C’ type Form Fill Seal machine is less expensive than the other two types of machine.

Why is adoption of Form Fill Seal growing?
Advances in polymerization technology and the development of co-extruded plastics means that films are not only stronger and able to seal on powders but can be thinner in gauge and lighter – which means that they are less expensive and can also pass through the Form Fill Seal machine faster.

At the same time Form Fill Seal machinery manufacturers have been innovating and it is now possible for them to pack fine powders. They have also dramatically improved film sealing technology by providing finite control of heat and pressure when welding the film together, as a consequence the FFS concept is more reliable and versatile than it was previously.

Another recent development which will boost the up take of Form Fill Seal is the ability to print a scanable barcode and product information onto the film before it is converting into a bag within the Form Fill Seal machine.

This means that customers can use a generic film and print specific product information – such as product name, product type, batch number and a readable barcode incremental number onto every bag.
Because the print details and barcode information can be changed instantaneously the advantage is that the machinery user does not have to change film roll if he changes the product he is packing. Therefore he can minimalise his stock of bagged products.

Trapped air
It is worth mentioning at this point that air is a problem when filling any kind of open mouth bag (this is not a problem with valve sacks immediately where the product is ‘forced’ or ‘pressurized’ into the sack and excess air escapes through perforations or the porosity of the side wall of the valve sack. Even with powders which settle spontaneously immediately on filling an amount of air is left in the filled bag between the top of the product and the seal, in the area called the ‘ullage’.

De-aerating powders during filling
The top of the bag can be ‘pushed-in’ or ‘squeezed’ but it is impossible to remove this unwanted air 100% unless the bag is vacuum packed.  In the case of multi-wall paper bags, the excess air escapes through the porosity of the paper, multi-ply bag construction also allows labyrinth air passage - the different layers of a multi-ply bag can be perforated at different points in each layer through which entrained air can escape or through the stitching at the top of the bag.

Removing trapped air when bagging with Form Fill Seal
The best way to minimize trapped air when Form Fill Seal bagging is to reduce the amount of air trapped in the product, this includes pre-settling or conditioning of the powder  in a hopper above the Form Fill Seal machine, de-aerating with a porous vacuum probe during filling which physically sucks the air out of the product.

With Form Fill Seal, trapped air cannot be ignored because bags containing air which cannot escape will pop or burst when they are palletized. So an acceptable solution has to be found when evaluating Form Fill Seal.  However the problem of trapped air in the ullage area of the bag still remains.

With vertical Form Fill Seal you can make bags with a perforated ‘over lap’ seal offering a labyrinth through which air can escape and on a Horizontal Form Fill Seal machine you can purchase tubular film which is made from a flat sheet folded into a tube with a perforated overlapped strip between the two vertical seals, which provide an escape route for trapped air.  Alternatively the bag or film can be fitted with a one way valve, or vented after filling with some alternative, patented methods.

How much will the Form Fill Seal bagging machine cost?This table provides a comparative cost for the three types of Form Fill Seal bagging machine.
The maximum bagging speeds (although there will be some exceptions) are approximate. Capital costs are approx and ex manufacturers’ factory. Cost of the machine includes a simple product dosing device.
The Golden Rules.
Unfortunately there isn’t a ‘Golden Rule’ or one solution which fits all businesses.
Each business has an individual identity, the product they pack, and they way they package it is tailored to suit the method of distribution and their customers’ requirements and expectations.
On pure economic grounds Form Fill Seal is hard to resist and it often essential if a company is to remain competitive.
One thing is apparent – the constant improvements in film and machine technology will be increase the adoption of Form Fill Seal technology.