Line Weight Management in Moulding Unit

Nowadays to get optimum fuel efficiency, productivity, and better output most of the companies selecting higher width moulding unit which starts from 1mt to 2mt.

Commonly moulding units are used for processing short dough variants.  Owing to cost pressure and other economy of operations it is suggested that we should avoid giving more weight to the consumer other than declared weight.  So in process control weight management is imperative.

Moulding unit and weight control

Normally in biscuit moulding unit if you want to adjust the weight you move the forcing roller and extraction pressure of the rubber roller.  Very occasionally knife setting disturbed.  In some cases speed of the forcing roller adjusted to reduce or increase the weight.( this is crude method).
  
In case of knife adjustments 
 
As in the case of moulder knife, the position affects the amount of extrusion of dough around it.Thus, the higher the knife position, the greater the amount of dough in the mould. Conversely, the lower the knife position, lesser the dough in the mould.
At the extraction  point, higher extraction pressure causes lower weight, tailings and wedging (especially in bigger rectangular products) and lower pressure leads to pickups and broken biscuits.

Points for weight variations

Following poitns to be checked for weight variation

a)    Mixing in-consistency
b)    Not proper and equal standing time between mixings
c)    Variation in extraction pressure 
d)    Dough level in the moulder hopper 
e)    Variation in knife height and knife edge without any chipping
f)    Variation in knife holder straightness/ or bend in holder
g)    Knife holding pin should be solid and holds the rod without any looseness
h)    Knife spring load.
i)    Straightness of forcing roller.

Mixing time and temperature of the dough are also having a very minimum role in weight control.

In order to have uniform mixing consistency, accuracy in weighment and SEQUENCE, in addition, to be strictly followed. For maintaining the constant standing time,mix out time to be maintained and matched  with mfg line consumption. Any plant gap to be accounted and mixing out to be adjusted accordingly. 

Rubber roller pressure should be always minimum and more extraction pressure will lead to tailing and wedging which will contribute for weight variations. Operator should understand and adjust the pressure roller slightly from the begging to till the end of the each batch as if the running time is more than 20mts per batch there will be a weight variation between the start to the end of the batch.

 Level of the dough in the hopper to be kept at minimum(1/3th of hopper) to reduce pressure difference at the nip for which dough intake by moulder and rate of dough feeding to be matched.It is always recommended to feed dough in nibbled form in lumps using an effective kibbling system.

Weight variation across the lines

The most critical factor in a process line is to control and maintain the line weight within narrow range. The best result achieved is 2% (2 g variation for 100 of product in each line). The various factors for weight variation across the lines were examined and they are:

• Moulder knife height variation (from working side to non working side)
• Moulder knife deflection
• Damaged moulder knife/cup
• Cup depth variation, ( while fitting the cup extreme care)
• Wornout gear teeth of moulder
• Moulder web scraper knife setting variation
• Moulder web tensioning variation  (Operating Side  to Non-Operating Side)
• Rubber Roller pressure variation  (Operating Side to Non-Operating Side)
• Bigger dough pieces(more than 25 mm )
• Dough level variation across the hopper
• Dough level height variation across the hopper
• Rubber roller hardness recommended is 70-75 mho
• Knife holding bracket deflection
• Knife holding pin setting
• Knife holding spring load.
• Speed setting and synchronizing of  forcing roller speed, rubber roller speed and extraction web speed.
• Forcing roller distance from moulder should be equal from ws to nws.

In order to have better weight control and uniform weight in all the lines,the aforesaid points are to be checked and following precautions and corrections  to be taken,

• Moulder knife height to be checked across the unit and ensured perfect in dimensions and fittings Moulder knife to be fixed properly and level should be uniform throughout the moulder width.
• Moulder knife to be checked for any deflection by using  surface table and ensured for uniform surface.
• Damaged moulder knife and cup to be replaced immediately.
• Precision engineering work required for cup fixing in the moulder cylinder and  level  of all cups should have uniform depth .
• Worn out gear of moulder to be replaced immediately.
• Residue Scraper knife setting to be uniform and even across the extraction web.
• Dough breakers/kibblers to be incorporated to break and minimize dough piece size to 25 mm and below.
• Extraction web tension and presuure to be maintained uniform in both control and non control sides.
• Dough level across the hopper to be maintained uniform by cross feed conveyors .If the line is not equipped with cross feeding system, dough leveling rods to be introduced.
• Hardness of the rubberized roller to be periodically checked at various points and in case of abnormal variation in shore hardness, extraction roller rubberisation to be replaced.
• Also check the knife bracket pin holding whether pin got cracked inside due to wear and tear and load on the machine. This should be checked at least once in 3 months.

Moulder knife

Single angle knife (10°) and double angle knife (30°&10°) are commonly used. However possibilities of improving the knife performance for better dough fill control to be explored with machinery suppliers.

Moulding conveyor material specifications 

The woven conveyors are made out of nylon and cotton threads. Length is warped with Nylon and then width is wept with pre –shrunk cotton.  (pl remember the cotton should be pre shrunken threads)  Otherwise once you put the web and run it, it may shrunk.  The surface should be adequately rough and sticky for better adherence. Optimum thickness (1.5mm to 2mm ) is ideal.

SUMMARY

Line wise weight checking to be carried out at frequent intervals. Collection and weighment of wet pieces to  be carried out swiftly to eliminate consistency variation errors. Many samplings to be carried out and interpreted for root cause analysis and corrective action. For better results, sample collections to be carried out by transferring the dough pieces to panner web and stopping the web for checking line weight.
It is also important to check the line weight after baking after checking and setting the line weight.  Mostly it will be alright but any baking variation may lead to weight variation marginally.  But ensuing both pre bake and after bake will give more confidence to the company that excess give away is not done and proper weight control will definitely save more cost to the company.

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