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Rotary moulding in biscuits manufacturing

Rotary moulding in biscuits manufacturing is the process during which dough pieces are formed.

Process

During moulding the dough is placed inside the hopper and the rotary moulder machine is started. The dough that is trapped at the nip is then worked and churned, thereby forcing it through the nip. Such churning may toughen the dough, although the toughening effect will be less if the dough coming from the mixture was left to stand for at least half an hour prior to use. Such dough would emerge at a consistency that is slightly firmer than would be the case if the dough was to undergo sheeting.

The dough is pressed against the forcing roll, as well as into the moulds on the rotary moulder. The dough level is sliced off by the scraper knife along with the top of the mould. Thereafter the excess dough is pressed against the forcing roll to form a blanket which revolves with the forcing roll. The piece of dough will then be passed to the point of extraction.

A type and surface of the web are important: a thin web is typically not adequately rough, while a thick web will not go round a nose piece that is sharp. The nose piece must be sharp such that it causes the peeling away of the dough pieces. The internal mould surface is important both in terms of its smoothness and shape, to the easy removal of the piece of dough. In the event that the edges of the mould are too steep or the pattern too intricate or deep, this can pose difficulties to extraction.

Extraction is effected when the web is pressed against the dough that is being held inside the mould. The surface of the extraction roller is slightly soft, which enables the web to be pressed into the mould. This leads to two effects. First of all, the dockers will pass right through the dough to the web. Secondly, a slight excess of dough will be extruded outside the mould limits. The rolling action means that the dough has been mostly extruded at the rear of the piece, thus forming a “tail” of sorts.

When feeding dough to a rotary moulder, there are two important things to consider. First of all, the dough level in the mould hopper should be kept at a minimum so as to prevent bridging, and this entails supplying the dough in small pieces. Secondly, because the moulding roll is expensive and made of metal that is relatively soft, great care is required such that no metal pieces end up passing with the dough into the hopper.

The dough that is fed to a rotary moulder comes typically through a two roll design pre-sheeter. The dough passes to the moulder hopper on a full width conveyor before passing through a kibbler and finally falling into the hopper. The kibbler is composed of a set of rotating fingers that break the dough into cube pieces measuring no more than 50mm. From the pre-sheeter, the conveyor passes through a metal detector. This has a rejection arrangement such that any dough that is found to be containing metal fragments is taken away before it reaches the moulder and damages the moulding knife or roll.

Rotary Moulder

This is a machine that is commonly used for the production of cookie and biscuit dough pieces from the short dough. During moulding, the dough is forced into moulds in the form of the negative shape of the pieces of dough, complete with name, patterns, and type and docker holes. Excess dough is removed by scraping with a knife bearing upon the mould. Thereafter, this piece is extracted onto a web of cotton canvas or a different type of fabric.

While it is possible to sheet, gauge and cut short dough using an embossing type of cutter, the benefits to moulding include the fact that the formation and support of a sheet of dough is not necessary. In addition, this eliminates any difficulties and control of gauge. Moreover this process does not result in cutter scrap dough that requires recycling. The most important advantage of this process is that the short dough is toughened as it is gauged and worked. All the dough inside the rotary moulder has a shared history; therefore there is no cutter scrap which requires reincorporating.

The mould shape allows for the formation of a much more intricate pattern outline than the cut dough. This can provide hollow centers to the dough pieces where necessary. Very small or large pieces of dough can undergo moulding. However, there can be difficulties in extraction in the event that very thick pieces of dough have been moulded.

The rotary moulder is great to use for forming soft dough, as well as a wide variety of cookies and biscuits. The dough that is intended for moulding is first fed into the hopper. Thereafter, the forcing roller will force the dough into the cavities of the moulding roller that is made out of gun metal, engraved uniformly and coated with food grade Teflon. Excess dough will be cleared by a knife that is held in a holder made from tool steel, thereby ensuring that filling is uniform.

For the perfect transfer of moulded pieces to the web from the moulding roller, there is an adjustable rubber roller that will convey the discharge cotton web and uniformly press it against the moulding roller. The main purpose of having 3 drives is that the speed of the forcing roller will impact the density of the dough that is forced into the moulding cavity. The speed of the die roller will then impact the speed of production. The speed of the discharge web will impact the shape of the cookies or biscuits produced across or along the web.

Potential Problems and Solutions

  • Bridging of the Dough – The dough level in the hopper needs to be maintained at a minimum such that pressure differences are reduced at the nip, and excessive working of the dough is prevented.
  • Dough Piece Sticks to the Mould – When the dough piece sticks to the mould, this may prevent it from being extracted. Such a scenario may also cause a squeezing action that leaves the dough piece wedged in cross section, with some extruded behind the dough piece in a “tail” on the extraction web. This calls for a surface of the extraction web that is adequately sticky or rough to allow for good adherence of the piece of dough. The adhesion must not be too good that it poses problems with the subsequent peeling at the transfer off the web.
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