Abstract: A feed bushing for single-screw extruders for the plasticizing extrusion of plastics under a high inertia resistance comprising an outer casing, a grooved bushing enclosed in the outer casing, and a cooling system. The groove bushing is assembled from a tubular grooved inset and a tubular reinforcement surrounding the grooved inset, the inset being shrink-fitted into the reinforcement with such a high shrinkage allowance that the inset is prestressed for pressure by the reinforcement for withstanding the maximum forces of inertia of the screw received in the grooved bushing. The grooved inset of the grooved bushing is made of cemented carbide, a metal oxide or other extremely hard and wear-resistant material. The reinforcement element is made of high-strength ductile steel.

Abstract: In the production of foamed thermoplastic synthetic material, synthetic material is melted in a screw extruder and fluid propellant is injected into the molten sythetic material. The residence time of the molten mixture has a determining effect in regard to uniform distribution of the propellant and thus also in regard to the uniformity of the cell structure. In order to provide for homogeneous mixing of the propellant and uniform cooling of the molten mixture, without using an excessively long screw extruder, the screw extruder is provided, downstream of a melting region thereof and of an injection opening thereof through which propellant is introduced, with flow obstruction structure which is by-passed by static mixing structure disposed outside the screw extruder. The molten synthetic material is simultaneously mixed with the propellant and cooled in the static mixing structure.

Abstract: In a single screw extruder mixer head for mixing high viscosity linear polyolefins materials employing a plurality of alternate longitudinal mixing and wiping barriers, the improvement of providing longitudinal radially-stepped regions on the opened bevelled leading edge portions of the outer surface of the wiping barriers to act as hydrodynamic wedges to the passage of polyolefin material passing between the surfaces and the inner walls of the extruder barrel; and radially-stepped opened bevelled leading edge portions of the outer surfaces of the wiping barriers and the outer circumferential surfaces of full diameter of the mixer head supporting an outer coating of gall-resistant material.

Abstract: A continuous kneader comprising a rotary screw shaft and rotatable within a cylinder for transporting a fluid axially thereof, rotary disks mounted on the shaft and each formed on each side surface thereof with radial projections and recesses arranged alternately, and fixed disks provided on the cylinder and arranged on the opposite sides of each rotary disk coaxially therewith as opposed thereto. Each of the fixed disks is formed on each side surface thereof with radial projections and recesses arranged alternately. The boundary between and defining each projection and the recess adjacent thereto on at least one of the rotary disk and the fixed disk is inclined from the radial direction so that the material supplied from a space between the shaft and the inner surface of the cylinder to the space between the rotary disk and the fixed disk is passed over the rotary disk outer periphery toward the axis of the shaft into the space between the rotary disk and the fixed disk immediately adjacent thereto.

Abstract: An improved extruder screw section and barrel assembly is provided which is especially designed for effective extrusion processing of whole or cracked grains or cellulosic materials which can subsequently be converted to alcohol. The overall assembly includes an elongated, tubular head section presenting on the interior thereof at least one relatively sharp cutting edge (preferably in the form of a spiral rib), along with an elongated, axially rotatable screw section disposed within the head section. The screw section is characterized by a series of separate, elongated, circumferentially spaced grooves generally along the length of the section which progressively decrease in depth from one side margin of the grooves to the other, in the direction of screw rotation; thus, the material being processed is, by virtue of screw rotation and the groove configuration, pushed radially outwardly against the cutting edge presented by the surrounding barrel section.

Abstract: A soap plodder for reducing wet cracking in soap comprising a barrel and a worm rotating in the barrel. The barrel has a delivery head connected thereto. The delivery head has an orifice of the same dimensions as and communicating with a bore in the worm. The worm has one or more holes therein for feeding soap into the bore and thence through the orifice.

Abstract: A plasticating extruder in which the screw conveyor includes an inner backfeed passage communicating with the channel established by the main flight of the screw conveyor and a solids-directing flight for directing unplasticated material into the backfeed passage and segregating already-plasticated material from the unplasticated material in the channel.

Abstract: Apparatus located at the output end of a screw extruder comprising a mandrel to rotate with said screw and a jacket coaxial with the mandrel and rotatable in an opposite direction of rotation to the mandrel at a speed which is steplessly adjustable. Sealing lips co-operating with abrasion rings are preferably provided on relatively moving surfaces of the jacket and stationary housings and temperature adjustment means can be provided in the jacket and the mandrel.

Abstract: A high output extruder screw which produces throughputs at lower temperatures and lower specific energy input. The screw has a feed section, a first short transition section, a first metering section, a second short transition section and a second metering section wherein the screw diameter increases from the feed section to the second metering section. There is also provided a method for extruding specific ethylene polymers.

Abstract: An easily-movable plug seal that is susceptible to quick and ready longitudinal adjustment in the central, lengthwise bore of an internally differentially heated (or cooled) extruder screw for sequentially diverse and distinct heat controlled zones within the extruder barrel is comprised of at least a single, cup-like member that is adequately flexible and supple to be flared laterally outwardly and urged into tight wall contact to make a sealing engagement against the internal screw bore wall upon pressurization of the interior of the plug seal member by the heat transfer fluid being passed into and applied within the screw.

Abstract: Apparatus for applying a reactant gas to an extrudable polymer, as, for example, a carbonate resin having the phenolic hydrogen end atoms replaced by stress corrodant preventive groups which are halohydrocarbon groups or a silane groups or the hydrogen end atoms replaced by a capping group having fluorescent properties to provide ultraviolet light and stress corrosive protection.

Abstract: A processing shaft for screw machines for working materials of solid, liquid, plastic or highly viscous consistency, which processing shaft comprises a driving shaft with several sleeve-type work segments mounted thereon. Clamping means are associated with each two of adjacent end faces of said work segments for sealingly pressing said adjacent end faces against each other in axial direction, and a gas-filled O-ring received in grooves of the adjacent end faces for being compressed between said end faces. Each of the grooves has an annular zone against which said O-ring is pressed and in which any machining indentations having a peak-to-valley height of more than 2 .mu.m extend concentric to the driving shaft.

Abstract: A plasticizing screw which has a feed zone, a plasticizing zone, and a metering zone. In the feed zone the screw has a single flight which forms a feed channel and which feeds solid material to the plasticizing zone. At the beginning of the plasticizing zone, a secondary or barrier flight is introduced to divide the feed channel into a solids channel and a melt channel. The solids channel is cut deeper than the feed channel at the beginning of the plasticizing zone so as to be able to accommodate all of the solids contained in the feed channel even though its width is substantially less than the width of the feed channel. The depth of the solids channel gradually decreases as it approaches the end of the plasticizing zone.The depth of melt channel is shallow at the beginning of the plasticizing zone and gradually deepens as it approaches the end of the plasticizing zone so as to accommodate all of the plasticized material.

Abstract: A mixer-cooler device for the extrusion of thermoplastic foams comprising: a pair of radially foraminous tubular cylindrical blocks, clamped in axial alignment against opposite faces of a barrier disk by means of a headplate for connection with an extruder barrel and a headplate for connection with an extrusion head, the disk having an axial circular aperture; an advancement screw sealingly rotatable within the blocks, connectable with a screw of the extruder to constitute an extension of this latter screw, the advancement screw having an intermediate barrier section sealingly rotatable in the aperture of the disk; a tubular casing sealingly connecting the two headplates to form a tubular collector channel embracing from the outside the foraminous zones of the two blocks; and a system of passages in the headplates, blocks and disk for the circulation of a coolant liquid for the two blocks.

Abstract: A method is disclosed for the extrusion of low-density linear polyolefin materials having high viscosities, wherein such materials are continuously fed to and through a rotary extruder having feeding, transition and metering sections which comprises employing, in the extruder screw forming such sections in cooperation with the cylindrical interior of the extruder housing, opened leading edges for the screw flights of said sections; and gall-resistant coated surfaces on the screw flights of said sections.

Abstract: Method and apparatus in which a selected coating is applied to specific surfaces within a plasticating extruder to change the coefficient of friction between the solids being conveyed in the extruder and the specific surfaces in such a way as to improve solids conveying and thereby increase the production effectiveness of the extruder.

Abstract: Apparatus and method in which the temperature of the barrel inner surface and the temperature of the screw conveyor outer surface of a plasticating extruder are varied, alternately, in repeated steps, independent of one another along at least a portion of the solids conveying zone of the extruder, while a production effectiveness parameter simultaneously is monitored, until the monitored production effectiveness parameter is optimized and the production effectiveness of the extruder is at a desired maximum.

Abstract: An extruder for the preplasticization of thermoset molding resins is disclosed. The extrusion machine includes a screw that rotates in a heated cylinder and compresses the fed-in pulverulent thermoset resinous material against a predetermined ramming pressure until it is plasticized. At the discharge end of the screw cylinder a receiving cylinder is disposed which has a hydraulic discharge piston which continuously retracts when an adjustable pressure head has been exceeded.

Abstract: In order to provide adaptability to a variety of material properties in a worm feed extruder for processing of synthetics or rubber, individual feed worm segments (7) and cylinder segments (10) surrounding the feed worm segments are provided at desired locations, the feed worm segments and cylinder segments being constructed divisible in the axial direction to enable these feed worm segments to be exchanged for feed worm segments of differing geometry. Removal of the cylinder (2, 3) or withdrawal of the feed worm (1) from the cylinder is thus avoided in the case where the feed worm is to be adapted to various material properties.

Abstract: An improved injection unit for a plastic materials injection molding machine, having a plastification cylinder and a cooperating rotatable and axially movable plastification screw, both supported and guided on tie rods by means of a carrier bridge, the plastification cylinder being axially adjustable and clampable in relation to the carrier bridge by means of a threaded adjustment nut cooperating with a threaded end portion of the plastification cylinder and a central threaded clamping sleeve cooperating with a stationary thrust plate, the latter being permanently secured to the carrier bridge.

Abstract: A system and method of temperature control for a plastics extruder uses a deep well sensor and a shallow well sensor in each temperature control zone along an extruder barrel. The temperature indications of these sensors are not combined. The shallow sensor detects temperature near the barrel surface. An associated controller compares the sensor temperature with a manually preset temperature set point. The differences between the detected and set temperature are used by the controller to effect heating or cooling of its associated temperature control zone. Each deep sensor is located proximate the bore in which the plastic is moved. The deep sensor temperature indication is compared with the set point of a second controller. Variations of the deep temperature from the set point generate an error signal that is applied to the first, shallow well temperature controller to vary its set point.

Abstract: A screw extruder for processing thermoplastic materials wherein a vacuum is applied to the feed opening for the material and/or to a filling section of the cylinder for the purpose of reverse degasification, said extruder having a simultaneously rotating pressure piece between a screw and a back pressure bearing and having a stationary end piece disposed on the screw side in front of the rotating pressure piece and sealing means comprising at least two axially spaced radial sealing rings and a vacuum source to apply vacuum to an annular interspace formed between the sealing rings.

Abstract: An extruder for thermoplastics having a directly motor-driven high-speed feed screw which mechanically force-feeds raw plastic pellets, pushing them forward under high pressure into a heat-transfer zone for melting, and finally through a static mixer, to deliver a pressurized homogeneous melt to an extrusion die. Melt pressurization results entirely from the mechanical force-feeding action of the screw rather than through the viscous shear action found in conventional screw extruders.

Abstract: A screw extrusion press having longitudinally extending bores in the wall thereof for heating or cooling the cylinder wall by passage therethrough of a temperature control medium. The passages are divided into sets of three adjacent passages with each set of three passages so connected to one another by annular passages which are divided off into respective portions for each set that medium supplied to an inlet manifold provided in a connecting flange at one end of the cylinder passes through a radial bore into a first passage of each set, flows along that passage to the other end of the cylinder, passes into a respective portion of the annular passage, passes into the second passage of each set, passes back along the cylinder into a respective portion of the annular passage and passes into the third passage of the set to pass along the cylinder, through a radial bore into an outlet manifold in a connecting flange at the other end of the cylinder and thence to an outlet connection.

Abstract: Apparatus for removing a cylinder forming the whole or part of the cylinder of a screw extruder, comprising a supporting arm on one end of which the cylinder is pivotally supported, and a further supporting arm to one end of which the other end of said supporting arm is pivoted, the other end of said further supporting arm being pivotally mounted on a base of the screw extruder. Adjusting means may be provided between the cylinder and the outer support arm to adjust the height and inclination of the cylinder, such adjusting means preferably comprising a plate on the support arm, three adjusting set screws in the plate to bear against the cylinder and securing screws to hold the cylinder in the set position.

Abstract: An extruder for working rubber and other elastomeric compounds having an extruder screw with a feed section, metering section and a transition section. The transition section has a plurality of working sections in succession with each section having a pair of helical flights defining a pair of primary channels. One of such helical flights has a flight that leads off to define a secondary channel for leading off the portion of the compound subjected to a shearing action from the primary channels. The primary channels decrease in volume while their axial width remains the same. The secondary channel increases in axial width and depth to accommodate the worked rubber compound.

Abstract: In a resin moulding screw provided with helical flight and valley, the bottom surface of valley is divided into a plurality of portions along a dividing line, and the divided portions are alternately displaced in the radial direction to form wavy contours. Barriers are provided to cross the dividing line to form dams which prevent intercommunication of the valleys at the bottom of the screw groove to prevent decrease of the thrust pressure along the flight for efficiently blending and melting solid and molten resins.

Abstract: A machine for processing plastics materials having a screw mounted in a housing and made up of a plurality of screw members in the form of collars on a drive shaft, whereby screw members to suit a particular material treatment are secured against rotation on the drive shaft and can be exchanged when required for other screw members, the machine including a thrust arrangement to press the screw members axially into close engagement with one another, the thrust arrangement comprising a divided thrust ring axially supported on the drive shaft at least at one of the end zones thereof, thrust or draw bolts, which act on the adjacent end surface of the adjacent outermost one of the screw members or on a frontal surface of a guide ring bearing against the outermost one of the screw members, and a sleeve closely surrounding the periphery of the divided thrust ring.

Abstract: A rotatable scroll for a rubber extruding machine comprising a series of vanes in the base of channels in the scroll to redirect the material into a surface layer and to direct lumps of material to one edge of the channel and a ramp or ramps over which the lumps flow with a small clearance between the ramp and the barrel.

Abstract: Extrusion apparatus for manufacturing blow moulded sheets of expanded polystyrene wherein, following an extruder there is a static cooler/mixer member comprising inner and outer cooling surfaces defining between them an annular passage, the inner cooling surface having a star-shaped outline when viewed in cross-section with the points of the star extending at an oblique angle to the longitudinal axis. Preferably the star-shaped outline is provided by folded metal strips several of which are provided alternately angled and staggered with respect to one another.

Abstract: A control system for a plastic extruder which automatically controls both the melt pressure and the melt temperature of the plastic material at the outlet of the extruder barrel. The extruder barrel is divided into a plurality of heating zones and a zone temperature control means individually controls the temperature of each zone in accordance with predetermined zone temperature set points. A melt temperature control means automatically adjusts certain zone temperature set points such that the actual melt temperature is maintained at its desired value. The speed of a rotatable extruder screw is controlled by a melt pressure control means such that the actual melt pressure is maintained at its desired value. In accordance with the present invention, a separate feedforward controller and separate feedback controller are provided in the melt temperature control loop and in each zone temperature control loop such that independent specification of set point and disturbance responses can be achieved.

Abstract: A detachable coupling provided between the helix and drive shaft of an injection molding machine is provided by a flattened end of the helix shaft received within a fork-shaped end of the actuation shaft so that respective boreholes are aligned for receiving therethrough a pin. An axially slidable locking sleeve is movable between a position preventing movement of the pin and a position permitting removal of the pin, and a resiliently urged locking detent ball and groove are provided at each of the positions.

Abstract: An apparatus for the extrusion of thermofusible materials which are applied while being heated comprises a prefusion and feeding chamber, a heating element for the prefusion and feeding chamber, a shaft capable of rotation at the base of the chamber, the shaft while in rotation mixing the thermofusible material and an extruder comprising an extrusion screw axially connected to said shaft. The extrusion screw is located in a cylindrical tubular structure which is provided with an exit for the thermofusible material. Preferably the shaft is located at a predetermined distance from the bottom wall of the prefusion chamber whereby a passageway is formed between the bottom wall and the shaft, the chamber and the shaft being so dimensioned that the shaft during rotation forces the entire mass of thermofusible material through the passageway.

Abstract: A fluid mixing apparatus having means for producing vortex-like motions of the fluids introduced therein, one embodiment of such an apparatus, for example, using two concentrically mounted inner and outer members, preferably cylindrical, moveable relative to each other at rotational speeds such as to produce the desired vortex-like motions of the fluids introduced into the region therebetween. In one embodiment thereof, the vortex-like motions may be obtained at relatively low rotational speeds by the use of V-shaped grooves on the inner member. In addition, suitable means can further be used to generate a de-stabilizing force for the fluids in a direction substantially perpendicular to the velocity streamlines thereof to further enhance the mixing effectiveness and to improve the quality of the mix, such de-stabilizing force in one embodiment, for example, being generated by the application of an electric field across the region between the inner and outer members.

Abstract: Method and apparatus for aspirating and propelling waste yarn into extruder or molding machine which comprises using a forwarding jet or yarn aspirator to feed a created wad of yarn into a hopper feeding pellets to an extruder or molding machine or the like, the operation being further characterized in providing a hood extending into the hopper to protect the wad until it can be picked up within the pellet mass flowing downwardly over and around the provided hood.In one embodiment of the method a godet roll is used, powered by a motor, for feeding the yarn to the aspirator at a controlled, desired speed. In a modification of the method, once the wad is being taken into the pellet mass and is being drawn by the extruder screw or by other means feeding a molding machine, etc., the air to the aspirator can be shut down in part or totally.

Abstract: A screw, particularly an extruder screw for rubber or plastics materials, comprising a plurality of hollow screw components juxtaposed in end-to-end relation, a coupling sleeve disposed over the or each joint between two adjacent screw components, each end of each screw component which is joined to another screw component having axially extending external splines on an external face thereof and the or each coupling sleeve having axially extending internal splines on an internal face thereof to engage with the external splines on the ends of the screw components to secure the screw components and the coupling sleeve or sleeves against relative rotation, and means, preferably a bolt coupling end members of the screw, to secure the screw components and coupling sleeve or sleeves against relative axial movement.

Abstract: A single extruder provided with a hopper at one end and a restricted nozzle at the opposite end and two press-screws arranged coaxially in one another within an outer jacket, each of said screws being provided with a male thread for feeding in the direction of said nozzle, said male threads extending into an outer annular space between said jacket and the outer press-screw and extending into an inner annular space between said two press-screws, said threads being oppositely oriented, means to rotate the outer of said press-screws and means maintaining the inner of said two press-screws stationary, said outer press-screw being provided with window-like openings communicating with said inner press-screw in the area of said hopper and separate feed means in said hopper to separately feed to said outer annular space and to said inner annular space through said window-like openings, the improvement consisting in that a rotating mixing element is positioned between said nozzle and said press-screws and attached to

Abstract: A one-screw extruder in which the mechanical thrust function is assigned to a first portion of the screw and of the cylinder, and in which the uniform heating of the material to be extruded is the function of a second portion, thus making it possible for each of the two portions to be specialized and to obtain a better performance of the extruder as a whole.

Abstract: An extruder apparatus with an extrusion screw having an end member which blends molten and solid thermoplastic materials moving through the apparatus into a uniformly fluxed consistency, and a method for uniformly fluxing and blending thermoplastic materials. The extrusion screw end member is provided with a conical terminus forming an annular shoulder with openings extending therethrough.

Abstract: An installation is provided for extruding plastic material comprising a screw extruder having a cylinder provided with a hopper near the rearward end of said cylinder and with an extrusion head secured to the forward end of said cylinder, and at least one pump having a delivery pipe connected to at least one port disposed in the wall of said cylinder for delivering an additional fluid product to said extruder through said port or ports during the extrusion operation, the inner surface of said cylinder including a zone provided with grooves extending downstream starting from said hopper over a limited distance, said port or ports opening out into one or more of said grooved zone, said grooved zone being followed by a smooth zone, the inside diameter of which is less than the maximum diameter measured from the bottoms of said grooves, and wherein said screw extruder is of essentially uniform dimensions at the point of said zone and the portion of said screw extruder immediately upstream thereof.

Abstract: A housing for an elongated opening such as a cylindrical passage which has a portion subject to severe conditions such as abrasion, heat, pressure, wear or corrosion which tend to deteriorate the wall of said opening, has a replaceable sleeve in the opening only at the portion exposed to such severe conditions. The housing, illustrated as a metal barrel for a plastic injection molding apparatus, has an elongated aperture or bore having a cross section larger than the desired cross section of the passage. A metal tubular inner sleeve defining the passage is held in the bore of the housing by a tight fit. The sleeve has at least one groove extending longitudinally on the exterior of the sleeve which forms a cavity with the housing wall. The end of the groove at at least the exposed end of the sleeve is closed by a closure portion or ridge. The sleeve can be removed by drilling a hole through the closure portion to permit access to the groove cavity and permit introduction of explosive material into the cavity.

Abstract: An apparatus useful for the extrusion of high melting slippery plastic resins comprising a screw element which operates rotatably within a close-fitting barrel having cut into the interior surface thereof a shallow and narrow groove of the same hand and substantially the same lead as the screw element.

Abstract: A commercially feasible, high-output extrusion apparatus and method is provided for producing vegetable protein based meat analogue products characterized by discrete, untwisted, manually separable meat-like layers and at relatively high production rates. The method involves passing hot, moist, pretreated vegetable protein material through an extruder barrel and causing formation of a first choke of the material intermediate the ends of the barrel, subdivision of the material downstream of the first choke point in the presence of steam for thorough cooking and moisturizing of the material, rechoking of the subdivided material adjacent the extrusion end of the barrel, and extrusion of the material as a dense, layered meat analogue product.

Abstract: Methods are provided for processing expandable thermoplastic materials with a typical compression relief design extruder screw having a helical flight for advancing and working a thermoplastic material. The screw is modified to shorten the feed and compression sections and to include a plurality of force-producing components in at least the compression section of the screw such that at least some portion of the components in any one turn of the flight lie in one plane essentially normal to the axis of rotation of the screw and such that the walls of the flight are uninterrupted. This arrangement controls the location of the rupturing or fragmenting of what is referred to as the solid bed and controls the manner in which it is fragmented to provide an extrudate at a die end of the extruder which has a constant temperature and which is uniform throughout each successive section of the thermoplastic material.

Abstract: A feeding screw assembly of a molding machine for plasticizable masses, particularly, plastics and rubber, comprises a passage part of the screw which has a passage therethrough having mixing means therein for intermixing a plasticizable material which passes through the passage. The material is diverted into the mixing passage which extends completely through the length of the mixing part by communicating passages located upstream for the inflow of the material and downstream for the discharge of the material after it is mixed. The construction may also include a passage portion which comprises an annular displaceable part having an end or side bounding a communicating passage upstream and which will move in a direction to close off this passage after a part of the other material has been fed into the mixing passage.

Abstract: An apparatus is provided for the mixing and extruding of thermo-plastic and thermo-setting materials in which a rotor member is rotatable within a barrel member. The members are provided with interacting rotor and barrel helical grooves in the mixing stage of the apparatus which includes a rotor to barrel stock transfer zone and a barrel to rotor stock transfer zone. The grooves of the rotor and barrel members, in the rotor to barrel zone, being sized, with the extrusion capacity of the helical groove in the rotor member decreasing and with the helical groove in the barrel member providing the extrusion capacity for the material. With such a construction relative rotational movement between the barrel and rotor members forces material or stock from the groove in the rotor member into the groove of the barrel member at an approximate uniform rate along the length of the rotor to barrel zone.

Abstract: A molding machine has a feed screw arrangement which plasticizes a material and which injects the plasticized material into a mold. The feed screw arrangement includes an input shaft which is mounted in a housing for rotation relative thereto and for axial displacement with and relative to the housing, the input shaft having a splined end portion which extends outwardly of the housing. The housing is mounted on a support for angular displacement about a pivot axis, and a drive is mounted on an auxiliary support for movement with respect to the support for the housing. The drive has an output shaft which has a central opening adapted to matingly receive the splined end portion of the input shaft when coaxial therewith. Relative axial displacement of the two shafts from an extended position in which the splined end portion is matingly received in the central recess to a retracted position in which the shafts are disengaged frees the feed screw arrangement for pivoting about the pivot axis.

Abstract: Disclosed is a screw extruder having an upstream feed section in which the bore and screw is of substantially larger diameter than that in a downstream melting section. The two screws are structurally separable and may be operably independent of each other. The extruder is constructed for removal of the smaller screw outwardly through the downstream end of the extruder. Various arrangements for driving the two screws are disclosed herein.

Abstract: Powderous, granular, and/or liquidous substances such as thermoplastic or elastomeric materials are mixed with each other or with fillers, additives, etc. in that the mixing operation is continued until a predetermined amount of mixing work has been expended. The mixing operation can be controlled as to its entire duration on that basis as well as with regard to completion of intermediate steps.