referring to fig1 a - 1d , important mold position steps in the process of producing a puffed cereal wafer or cracker are shown . the mold comprises an upper mold 1 and a lower mold 2 , both heatable by means of embedded heating elements ( not represented ) and movable upwardly and downwardly by being directly driven by hydraulic cylinders as illustrated and explained below . upper and lower molds generally have punch elements ( 1 ′, 2 ′) which are slidably receivable in a ring mold 3 ( preferably fixed but not always required ) so as to form therewith a hermetically sealed molding cavity . in fig1 a the mold cavity is open and provides a feeding cup for dropping food - starch containing raw material 4 therein by lower mold 2 having been partially retracted within ring mold 3 while upper mold 1 is lifted . in fig1 b shows pressure - baking of raw material 4 being crushed , compressed and heated in a closed cavity by descending the upper mold into the ring mold and then pressurizing either one or both of upper and lower molds . the starch in the raw material is gelatinized , becomes amorphous and moisture including chemically bound water of the raw material is driven off and builds up a high internal vapour pressure which is suddenly released as shown in fig1 c by quickly retracting upper and / or lower punches relative to one another within the ring mold . as a result the compressed raw material explosively expands thereby forming a puffed or popped wafer filling the expansion chamber space defined between the upper mold , the lower mold and the ring mold . as shown in fig1 d the upper mold is in a lifted position again , whereas lower punch is moved in the upward direction to raise the cracker to a discharge position flush with the upper surface of the ring mold . a sliding plate of the raw material feed system will push then the puffed cracker from the raised lower mold surface into a discharge chute where after the baking - puffing cycle can start anew . in fig2 a - 2b , overall side views of a puffing apparatus are shown comprising a multi - cracker mold , i . e . the upper and lower molds ( 1 , 2 ) include a plurality of die punches ( 1 ′, 2 ′) which are slidably receivable in a plurality of corresponding die holes ( not shown ) of a stationary ring mold 3 . lateral to the apparatus there is mounted a raw material supply system 6 comprising a raw material supply line 7 ( conduit or hopper ) and sliding plates ( 8 , 8 ′) having suitable perforations and back plates to supply a desired amount of grain or pellet material to each die cavity of the ring mold . power means ( 9 , 9 ′, 9 ″), e . g . air cylinders drive the plates in sliding movements relative to one another and to the ring mold . more in particular , a dosage mechanism ( 8 ′) driven by cylinder ( 9 ′) brings an exact amount of raw material from supply line ( 7 ′) into a transport plate ( 8 ). said transport plate is driven by cylinder ( 9 ) and positions the raw material precisely over each lower punch element ( 2 ′) being then in a cup forming feed position , i . e . received partly within ring mold openings ( 3 ′). release plate ( 8 ″) driven by cylinder ( 9 ″) is then actuated to drop or release raw material from transport plate ( 8 ) into said ring mold cups or cavities . on the back side of each movable mold , i . e . on top of upper mold 1 and at the bottom of lower mold 2 , there is mounted an upper hydraulic cylinder 10 and a lower drive cylinder 11 , both independently actionable in the upward and downward direction to raise or descend said mold elements over a precisely controlled distance and / or to transmit molding pressure to the raw material in the mold cavity according to the desired process stages . mounting plates ( 10 ′, 11 ′) attached to apparatus frame ( 12 ) form support and fixation members for top and bottom hydraulic cylinders ( 10 , 11 ) and also bear and guide the connection thereof with the movable mold elements ( 1 , 2 ). the hydraulic cylinders are powered by a hydraulic oil circuit illustrated schematically in fig3 . as can be seen from fig3 , the oil circuit comprises a high - pressure oil line pr , powered by a pump unit p , and a return line r flowing return oil back to of tank t . the pump unit p is designed to afford continuous availability of high - pressure oil at a precise constant pressure in feed line pr for a sufficiently broad range of desired oil feed rates . at least one puffing apparatus , generally a plurality of puffing machines a 1 , a 2 etc ., is connected to the pressure line pr and the return line r . in each apparatus high - pressure oil is supplied from line pr to upper cylinder c 1 and lower cylinder c 2 for driving respective mold elements schematized by the numerals 1 and 2 . return or displacement oil originating from a piston chamber of the double - action cylinders ( c 1 , c 2 ) is flowed back to return line r . the oil flow requirements for each cylinder are physically and functionally integrated in a manifold m 1 of upper cylinder c 1 , respectively a manifold m 2 of lower cylinder c 2 , which manifolds unite the necessary oil supply / flow connections including valves needed for the piston chambers of each cylinder and which is disposed on top of the cylinder body as a constitutive part thereof . the functioning of the manifold is depicted in fig4 a - 4c for the hydraulic cylinder connected to the upper mold element . the piston stroke in the downward direction is performed by actuating simultaneously poppet valves 1 - 1 and 1 - 4 . oil from pressure line pr enters manifold at port p and flows to cylinder port a in upper piston chamber via valve 1 - 1 . at the same time valve 1 - 4 is opened to enable back - flow of displaced oil from lower piston chamber through port b to the return tank line r . during this stroke the valves 1 - 2 and 1 - 3 remain closed . when effecting a reverse stroke in the upward direction the valves 1 - 2 and 1 - 3 are activated such that pressure oil flows from port p via valve 1 - 2 to port b of the lower piston chamber , whereas at the same time oil displaced in the upper piston chamber can flow from port a via valve 1 - 3 to the tank return line r . at this stage valves 1 - 1 and 1 - 4 are then closed . the manifold oil flow line from intake port p to cylinder port a further preferably contains a ( over -) pressure valve 2 * located between valve 1 - 1 and port a . this allows to regulate the desired molding or crushing pressure for each apparatus individually according to the type and amount of raw material ( grains , broke , pellets etc .) fed into the mold cavity , respectively according to the kind of puffed food cracker desired . in addition a part g may be provided which serves as a connection for mounting a ( safety ) manometer . fig5 a - 5c show a particular improvement to the material dosing part of the raw material supply system ( 6 ) already explained above in connection with fig2 . in detail , fig5 a shows a first position of the near dosing mechanism which is open to the feed fine ( 7 ) and is comprised of a holding or dosing plate ( 8 ′) of suitable thickness having therein cup forming dosage apertures ; said holding plate constitutes the bottom of raw material feed conduit ( 7 ) and its top and bottom surfaces are delimited by upper and lower perforated plates ( 8 *, 8 **) which are arranged to slide together parallel to dosimeter plate ( 8 ′) when actuated by cylinder means ( 9 ′). the position of perforated plates ( 8 *, 8 **) as depicted in fig5 a enables the dosage apertures or cups to be filled with starch - containing raw material . in fig5 b the perforated plates are shifted to the right thereby closing the dosimeter cups to the raw material entry side but at the same time opening the cup bottom towards a transport plate ( 8 ), in fact a second apertured holding plate cooperating with a perforated back plate ( 8 ″), whereby the raw material content of the dosimeter cups in plate ( 8 ′) is then released — within a closed environment — with maximum accuracy in ( preferably wider ) openings / cups provided in transport plate ( 8 ), having a hole configuration similar to that of the dosimeter plate and of the ring mold cavity pattern . by actuating drive means ( 9 ) and ( 9 ″), cf fig2 , the raw material is transported to the ring mold position and dropped in the respective mold cavities ( 3 ′). thus the provision of a holding / dosimeter plate ( 8 ′), combined with perforated sliding plates ( 8 *, 8 **), “ in addition ” to a conventional dosing or holding / transport plate system ( 8 , 9 ; 8 ′, 9 ′) allows a constantly more accurate supply of precisely metered quantities of raw material to the mold cavities without any losses or spill over of granular or other material which is normally unavoidable in conventional feeding slides of puffing machines . fig6 shows an improvement in the design of the peripheral mold or ring die wherein the upper and lower punches ( 1 ′, 2 ′) of the movable mold elements must be slidably received in a fluid - tight manner . the ring mold , for instance for a multi - cracker die ( e . g . 64 mini - cakes of 25 mm in diameter ), comprises a die mounting plate containing a plurality of die holes which is stationary by being fixed to the vertical frame posts ( 1 , 2 ) of the apparatus , about midway between upper and lower supports ( 10 ′, 11 ′) of the hydraulic drives ( 10 , 11 ). each die hole includes an internal sleeve or a bushing that is elastically mounted to die hole and die plate , such that in use the bushing has a self - aligning or - centering property within the die hole relative to the slidably entering punches . the elastic mounting may be realized by retaining rings or circlips ( circular and small die holes ) and by screwable fastening elements ( bolts and nuts , etc .) for large dies and polygonal shapes . the self - aligning die bushings prevent wear , damage and premature failure of dies or punches , incl . production interruptions due to possible misalignments caused by temperature and thermal expansion differences between die and punch components . the apparatus according to the invention is furthermore very advantageous in terms of process monitoring , controls and adjustments . as a matter of fact the high precision and quick response of the novel hydraulic drive system makes it easier to control the process steps , since all process movements and piston displacements are controllable in terms of time units resp . actuation times of valves in the oil manifold , without need of electromechanical contact , relay or stop means . in practicing the invention , all process movements , cf . fig1 , and process temperatures are controlled by a plc , e . g . a central plc for a plurality of puffing machines , and are visualized ( or selectively visualizable for each connected machine ) on a monitor screen or control panel . the process control system comprises the following features and / or steps : 1 . cup time : bottom cylinder retracts ( goes down ) and retracted punches of lower mold form feeding cups within ring mold dies to allow the raw material to be dropped in mold . 2 . start time : top cylinder extends ( goes down ) and upper mold punch goes down inside ring mold die . 3 . press time : bottom cylinder extends and lower mold punch is displaced upwardly , compressing the raw material between the two punches . 4 . bake time : all valves remain closed , both cylinders and punches are kept stationary . 6 . bottom expansion : bottom cylinder retracts ( mostly ) simultaneously with top cylinder . 7 . expansion delay : delay time of expanded / puffed product inside the retracted punches or expansion - opened molds to allow shape control of finished product . 8 . thickness control : bottom cylinder extends and recompresses already expanded product to a given extent , thereby controlling shape , thickness and surface flatness ( optional ). 9 . out time : top cylinder retracts upper mold above ring mold and bottom cylinder extends so that lower mold punch pushes finished product out of ring mold .// thereafter the cycle starts anew with step 1 including the supply of starch - containing raw material into the mold cavities . the above process parameters are simply optimised by empirical testing , trial and error and easily adjustable according to raw material kind , cracker type ( shape , thickness , . . . ) and desired cracker properties such as texture , crispiness etc . the direct hydraulic drive of the puffing molds in the new combination of super fast actuation of cylinder pistons and continuous availability of a constantly high oil pressure from a common or central high pressure oil line enables the above testing , optimisation and control to be carried out in conditions of increased accuracy , flexibility and reliability and this in much less time than previously possible . this also applies to industrial cracker production in terms of cracker quality and waste generation . since a big number of puffing machines are connectable to said central oil line , the new system of puffed cracker manufacture may give rise to substantial savings in power consumption and equipment costs , especially when running a large - scale cracker plant . although particular embodiments and working modes of the invention have been illustrated and described , it is clear that numerous modifications , applications and combinations are possible without departing from the key teaching of the invention . in this connection the extent of protection is only limited by the scope of the following claims .
an apparatus for making puffed food products from starch - containing raw materials . the apparatus has a baking and molding chamber defined by several heatable mold elements . the mold elements are individually actuated by direct hydraulic drive systems . the hydraulic power for these drive systems is selectively derived from a common oil pressure supply system which provides continuously high oil pressure to the direct hydraulic drive system for each mold element . the apparatus also has an improved feed system enabling the supply of raw material into the mold cavity such that no material gets spilled and each mold receives an accurate predetermined quantity of raw material .