Rubber Compound Processing Machines: Rubber Mixing Machines 

Some functions of rubber mixing machine are as follows:  

1. Mastication : rubber is crushed to get lower viscosity or molecular weight. This process need quite a big mechanical work. 

2. Mixing  

Rubber Mixing Principal 

Rubber mixing process is happened between 2 (two) contrary rotated rotors. The wicks of both rotors are parallel and each of rotors has different tangential speed. The distance between rotor surface (nip) is controlled by rotor with bolt regulator. 

As a result of tangential speed difference and nip constriction, rubber compound will experience displacement and pressure energy during rubber mixing. Pressure energy will enlarge displacement energy, and displacement energy will break the rubber molecule bonding (chain). With breakage of the rubber molecule bonding, it is possible for carbon and other chemicals to be mixed with rubber. 

Rubber Compound Mixing Machine Types 

1.  Opened Mixing unit (rotor) with 2 (two) long and hollow cylinders. Rotor is made from harden cast iron or steel iron, with smooth and corrosion resistance surface. Cylinder with hollow has function as hot and cold canal medium. Mixing unit (cylinder) is in opened position, and operator will do raw materials feeding and compound cutting. 

Additional rolls (stock blender) has function to collect some of rubber compound and re-feed it to the slot of both grinding machines rolls to get the better mixing. By using this stock blender, compound band will get cold faster, more uniform and plastic during the certain interval mixing time. 

To connect the mill to batch-off equipment, usually convenyor is used. Batch-off equipment has function to automate the rubber compound transfer to the next process. Inside the batch-off, rubber compound sheet is cooled by immersing it into the water or non stick solvent and dried with blow drying. Rubber compound sheet will walk on the rolls which is installed inside the batch-off and then it is cut to rubber compound sheet with certain sizes. Rubber compound sheet is stacked with laminar manner (wig-wag form) at the outlet of batch-off and transferred to the next processing machine by using conveyor. 

Other useful unit on the open mixing machines include collect equipment, safety equipment, nip controller, counter motor, transmission and wheel, heating unit cooling unit, and machine lubricant. 

2.  Non-Continuous Closed Mixing Machine 

At non-continuous closed mixing machine (internal batch mixer), rotor is located inside a closed room. The shape of machine mixing unit (rotor) is look like a bump so the rotor look like winged and displacement area is bigger. The mixing process is shorter and cleaner if compared to opened to opened mixing machine. 

Shaft, wing, and mixing room wall is made with hollow to along heating and cooling medium to pass by. The mixing process is no need the involvement of the operator except when feeding the material to the hopper and when the compound is took out from the mixing room. During the mixing process, material is pressed hydraulically by the ram. 

Non-continuous closed mixing machines are categorized in two (2) types based on rotor design or mixing method in mixing room, i.e. non-intermeshing and intermeshing types. Non-intermeshing machines type include Banburry, Bolling, and Werner-Pfleiderer machines, and intermeshing machines type include Intermix Francis Shaw and Werner Pfleiderer. 

At non-intermeshing machines type, displacement action of compound agglomeration happened inside the slot between rotor and mixing room, while at intermeshing machines type, displacement action of compound agglomeration happened inside the slot between two rotors. Intermeshing type rotor give better heat transfer, and it is suitable to use for rubber compound which is sensitive to heat with longer mixing cycle. 

A new mixing machine has been made by Italian company Firm Rutital, which is called Rutital Monomix Mixer. This machine has only one (1) biconical rotor, two (2) screws with centralized direction, and cylinder mixing room. 

Tandem Mixer 

Tandem mixer is a kind of mixing machine that combined from two (2) intermix type mixing machines and it is high rise heated. At the top of it, ram mixer is installed and at the bottom of it, ram-less mixer. Is installed. To make ram-less mixer can feed without pressure assistance and mechanical work of ram, ram-less rotor mixer must be interlocking. 

Master batch produced by top mixer is transferred directly to bottom mixer, then cooled and mixing is finished, while the next master batch has been processed and available to the next processing machine through two (2) rolls mills or dump extruder. 

Tandem mixer performance is really depended on cooling facility operation and compound properties proceeded, and this machine has cooling system that could absorb heat of master batch. Masterbatch temperature when come out from the top mixer is between 150-160°C, mixing time 3,5-4 minute. For bottom mixer, fill factor 0.45-0.47, rotation speed can be varied until 60 rpm. 

3.  Continuous Closed Mixing Machine 

Continuous closed mixing machine consist of feeder and mixing extruder. The function of feeder is as a material feeder into the mixing extruder; and function of mixing extruder is as material mixer and transferer to the next processing machine. Before entering mixing extruder, material has been softened inside the feeder. Softening inside the feeder can be done with two (2) ways i.e. with screw (sikoplast) rotor Farrel M.V.X. 

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