1. Open mixer mixing technology

 

The mixing process includes three aspects:

 

Three processes: open mill mixing can be divided into three stages: ①packing roller ②feeding powder ③turning.

 

1. When the unsaturated rubber is processed on the open mill, four different roll states will appear when the temperature of the roller is changed. The temperature is lower, the rubber material is harder, and the elasticity is high. The rubber mainly stays at the accumulation of rubber and slides, delaying the production process. The temperature is suitable, and the rubber can be normally wrapped on the roller. It has both plastic flow and moderately high elastic deformation, which is conducive to the mixing operation. As the temperature increases, the fluidity increases, the intermolecular force decreases, and the strength decreases. The film cannot be tightly wrapped on the roller, and the phenomenon of roll-off or cracking occurs. Rubber is a viscoelastic fluid enveloping the roller at a higher temperature and producing plastic flow.

 

2. After the powdered rubber material wraps the roller, in order to mix the compounding agent into the rubber as soon as possible, an appropriate amount of accumulated rubber should be kept on the roll gap. When the powder is eaten, when the rubber material enters the upper layer of the accumulated rubber, it is congested and folded due to resistance, forming crepe grooves in front of the accumulated rubber, and the powder can enter these grooves and be brought into the inside of the accumulated rubber . If there is no accumulated rubber, the compounding agent will only rub the powder into the rubber by the shear force between the rear roller and the rubber, which will not allow the powder to penetrate into the rubber and affect the mixing effect. In addition, the powder that has not been rubbed into the rubber will be squeezed by the rear roller and the rubber into a thin sheet and fall into the receiving tray. If it is a liquid compounding agent, it will stick to the back roll or flow to the receiving tray, making subsequent mixing difficult. In the process of eating powder, the amount of accumulated glue must be moderate. If there is no accumulated glue or the amount of accumulated glue is too small, on the one hand, the compounding agent only rubs into the rubber compound by the shear force between the rear roller and the rubber, and cannot penetrate into the rubber compound to affect the dispersion effect; on the other hand, it is not rubbed in The powdery compounding agent in the rubber will be squeezed by the rear roller into pieces and fall into the receiving tray. If it is a liquid compounding agent, it will stick to the rear roller or fall onto the receiving tray, causing mixing difficulties. If the accumulation of glue is excessive, a part of the rubber material will rotate and roll at the upper end of the roll gap, and cannot enter the roll gap, so that the compounding agent is not easy to mix in.

 

Third, the third stage of mixing and mixing is mixing. Due to the high viscosity of the rubber, the rubber material only flows in the circumferential direction along the rotation direction of the mill roll during mixing, and there is no axial flow. Moreover, the rubber flowing in the circumferential direction is only laminar, so it is about the thickness of the film. 1/3 of the glue layer close to the surface of the front roller can not produce flow and become a "dead layer" or "sluggish layer", as shown in the figure. In addition, the accumulated glue on the upper part of the roll gap will also form a part of the wedge-shaped "return zone". The above reasons all cause the compounding agent in the rubber compound to be unevenly dispersed.

 

Due to the high viscosity of the rubber, the fluidity of the rubber near the surface of the roller is poor, and the shear force promotes the flow of the rubber to be laminar. The compounding agent of the inner layer of about 1/3 of the thickness of the film in contact with the roller surface cannot enter, forming a "dead layer".

 

In order to compensate for the adverse effects of the accumulated rubber on the mixing, the process must be supplemented by cutting and refining, so that the rubber in the "dead layer" is continuously brought to the top of the accumulated rubber and into the "live layer", so that the left and right sides of the rubber will interact with each other. Mixing evenly can destroy the dead layer and recirculation zone, make the mixing uniform, and ensure the uniform texture.

 

2. Internal mixer technology:

1. Purpose of internal mixer:

 

It is mainly used for the plasticization and mixing of rubber, but also for the mixing of plastics, asphalt materials, linoleum materials, and synthetic resin materials. It is one of the main rubber mixing equipment in the rubber factory. Since the 1970s, although foreign rubber mixing technology and equipment have developed rapidly, for example, screw extruders are used to replace internal mixers and open mixers for plastic mixing and mixing, but they still cannot replace internal mixers. The rubber mixing equipment in the new modern factory is still dominated by internal mixers, and the mixing method still uses the two-stage mixing method.

 

Classification:

 

(1) According to the shape of the rotor cross section, it is divided into: oval rotor internal mixer, cylindrical rotor internal mixer, triangular rotor internal mixer

 

(2) According to the working principle, it can be divided into: tangent rotor internal mixer, meshing rotor internal mixer

 

(3) According to the size and change of the rotor speed, it can be divided into: low speed, medium speed, high speed and single speed, double speed, variable speed internal mixer

 

(4) According to the relative speed of the rotor: asynchronous and synchronous rotor mixers

 

(5) According to the structure of the mixing chamber, it is divided into: ordinary type and inverted type internal mixer

 

(6) According to the relative gap between the rotors, it is divided into: fixed gap and adjustable gap internal mixer

 

2. Specifications and technical characteristics of the internal mixer:

 

1. Specifications

 

In the past, the working capacity of the mixing chamber and the rotating speed of the active rotor were used to express; now, the total capacity of the mixing chamber/the rotating speed of the active rotor is used to express.

 

Specification representation of domestic internal mixer:

 

XM-250/20

 

X means rubber, M means internal mixer, 250 means total capacity of internal mixer, 20 means rotor speed

 

X(S)M-75/35x70

 

X means rubber, S means plastic, M means internal mixer, 75 means total capacity of internal mixer, dual speed (35 and 70 rpm)

 

3. The overall structure of the internal mixer and the function of each part:

 

(1) Mixing part: The mixing part is mainly composed of a rotor, a mixing chamber, and a sealing device.

 

(2) Feeding part: It is mainly composed of the right feeding chamber, the bucket-shaped feeding port and the flap door (feeding door) 11. This part is mainly used for feeding and instant storage.

 

(3) Material pressing part: It is mainly composed of the upper bolt 9 and the cylinder 14 which pushes the upper bolt to reciprocate up and down. Its main function: to give a certain pressure to the rubber material, accelerate the rubber mixing process, and improve the rubber mixing Effect.

 

(4) Unloading device part: It is mainly composed of the lower top bolt 3 and the lower top bolt locking mechanism 2 installed under the mixing chamber. Its main function is to discharge the rubber after the rubber mixing is completed, that is, unloading. material. The lower top bolt can be cooled by cooling water. The ‘’ shaped surface of the lower top bolt in contact with the material should be welded with wear-resistant alloy to increase its wear resistance.

 

(5) Transmission device part: mainly composed of motor 22, elastic coupling 21, reducer 20 and toothed coupling 19, etc. Installed on the transmission base, its function: to transmit power, make the rotor rotate against the working resistance, thereby completing the rubber mixing operation.

 

(6) Base: Mainly composed of machine base, some of which are divided into main engine base and transmission base. Its function: It is used for the internal mixer, and the components of the main engine and the transmission system are installed on it.

 

(7) Heating and cooling system: mainly composed of pipes and distributors, so that cooling water or steam can be circulated in the cavity of the mixing chamber, rotor and upper and lower top plugs to control the temperature of the rubber compound. The heating and cooling system of the internal mixer imported from abroad is equipped with a temperature control device and adopts constant temperature water for heating and cooling. Function: According to the process requirements, control the temperature of the rubber compound during the rubber mixing process

 

(8) Hydraulic system: It is mainly composed of a double vane oil pump 15, a rotating oil cylinder 17, a reciprocating oil cylinder 16, pipelines and oil tanks. It is the power supply part of the unloading mechanism. Used to control the opening and closing of the lower top bolt and the lower top bolt locking mechanism.

 

(9) Pneumatic system: It is mainly composed of cylinder 14, piston 13, cylinder of the feeding door, air valve, pipeline and compressed air. It is the power supply part of the feeding and pressing mechanism. It is used to control the lifting, pressurizing and opening and closing of the flap door.

 

(10) Electric control system: It is mainly composed of a control box, an operating machine and various electrical instruments. It is the operation center of the entire machine.

 

(11) The lubrication system is mainly composed of an oil pump, an oil separator and a pipeline. The purpose is to reduce the friction of each rotating part (such as the rotating shaft, the bearing, the sealing ring friction surface of the sealing device, etc.). To increase the service life, inject lubricating oil into these friction surfaces. Function: Inject lubricating oil into each rotating part, so as to reduce the friction between the moving parts and prolong its service life.

 

4. The mixing process of the rubber material in the mixing chamber: the raw rubber and the compounding agent are added by the hopper, and first fall into the mouth of the two relatively rotating rotors. Under the pressure and friction of the top bolt, they are It is brought into the gap between the two rotors and subjected to a certain degree of kneading, and then the rubber is separated by the sharp edge of the lower top bolt, and enters the gap between the rotor and the mixing chamber wall, where it undergoes strong shearing and kneading. After refining, the two broken strands of rubber meet at the mouth of the two rotors, and then enter the gap between the two rotors, and so on.

 

The mechanical action of the rubber in the mixing chamber:

 

1. The kneading effect between the outer surface of the rotor and the inner wall of the internal mixing chamber (especially obvious in the oval rotor internal mixer)

 

2. The mixing, stirring and squeezing action between the two rotors (especially obvious in the intermeshing internal mixer)

 

3. Shunting, shearing and exchange of upper and lower top bolts

 

4. The axial reciprocating cutting and kneading effect of the rotor

 

Production capacity and fill factor:

 

G ---Production capacity, kg/hour;

 

V1 ----Working capacity of internal mixer, liter;

 

----The specific gravity of the rubber material, kg/liter;

 

t ----The time of one rubber mixing, in minutes.

 

The working capacity V1 is calculated by the following formula: V1=VβV----total capacity of the mixing chamber (total capacity of the mixing chamber minus the volume occupied by the rotor)

 

β----The filling factor of the rubber compound

 

Methods to increase the pressure of the top bolt: (1) Increase the pressure of compressed air; (2) Lengthen the diameter of the air duct; (3) Use hydraulic pressure instead of air pressure.

 

Determination of power consumption: N=4•η•u2B/h

 

N----power consumption on the rotor unit;

 

η-the viscosity of the rubber;

 

u----Rotational linear velocity of the top of the rotor edge;

 

B----The width of the top of the rotor edge;

 

h----The gap between the top of the rotor edge and the inner wall of the mixing chamber.

 

N=Cuk+1

 

k ----The characteristic coefficient of rubber, k＜1:

 

u----The linear velocity of the top of the rotor ridge;

 

C----Coefficient.

 

The transmission mode of the internal mixer: A. The number of internal mixers driven by the motor at the same time: multiple transmissions, single transmission. B According to the rotor speed of the internal mixer: single speed, double speed, variable speed C according to the relative position of the motor and the internal mixer: left transmission, right transmission, middle transmission D according to the form of reduction mechanism: transmission with large drive gear, no large The separate transmission of the drive gear and the use of a double output shaft reducer have higher requirements for the motor.

 

(1) The instantaneous overload factor must be greater than 2.48, with overload resistance characteristics;

 

(2) Large starting torque;

 

(3) It can be forward and reverse;

 

(4) Use enclosed motors.

 

Rotor material: In the rubber mixing process, the rotor bears the friction, extrusion, corrosion, high temperature action and huge torque of the rubber. Therefore, the rotor is required to have sufficient strength and rigidity, and the surface is wear-resistant, chemical-resistant, and has good transmission. Thermal properties. The rotor material is mostly cast steel (ZG45). A layer of 5-8mm thick wear-resistant cemented carbide is welded on the top of the protruding edge, and a layer of wear-resistant cemented carbide with a thickness of 2 to 3 millimeters is also required to be welded on the rest of the working surface.

 

Rotor cooling type: (1) spiral jacket type; (2) spiral grooves on the inner surface of the rotor (GK series); (3) general forced cooling type

 

Mixing chamber: Function: It is the main working part of the mixing chamber, and it completes the kneading function of the rubber together with the rotor.

 

Material: A. The front wall is ZG45. In order to ensure its wear resistance, 2-4mm wear-resistant hard alloy can be surfacing welded on the inner wall of the mixing chamber. B. The side wall is cast iron

 

The structure of the mixing chamber: A, front and rear combined type, composed of front and rear front walls 14, 17 and left and right side walls. B. The upper and lower split type is composed of upper and lower mixing chambers and upper and lower casings. C. The opening and closing type (bright wing type) is composed of two front and rear openable and closable front walls and two side walls. D, tilt type E, flip type

 

Common materials for mixing chamber: A. The front wall is ZG45. In order to ensure its wear resistance, 2-4mm wear-resistant cemented carbide can be surfacing welded on the inner wall of the mixing chamber. B. The side wall is cast iron

 

The structure of the pressing part (top bolt): Structure: The device is installed in the upper part of the mixing chamber.

 

① Cylinder-cast iron parts, in order to avoid the piston colliding with the cylinder cover during movement, there are buffer devices on the top and bottom of the cylinder.

 

② Piston-its sealing method uses rubber skin and cast iron piston ring.

 

③Piston rod-has a certain strength and stability, and does not deform during the pressurizing process.

 

④Heavy hammer-that is, the upper top bolt, which is a pressing part that directly contacts the rubber material.

 

The main function of the pressurizing cylinder is to provide the power of the upper bolt to move up and down, and to provide the pressure of the upper bolt to pressurize the material.

 

Top bolt safety device: In order to prevent the heavy hammer from breaking and causing the heavy hammer to fall into the mixing chamber and cause a major mechanical accident, certain safety measures must be adopted. ①Increase the size of the pin hole on the piston rod. ② Install stop pins on the upper part of the mixing chamber. ③Welded stopper on the cooling water pipe.

 

The structure of the feeding part: The device is installed in the upper part of the mixing chamber, and is mainly composed of a feeding hopper, a flap door, a rear door, and a stuffing box.

 

Unloading part form: ⑴, sliding type ⑵, swing falling type (3) flip type

 

The sealing device form of the internal mixer: 1. End face seal 2. Labyrinth seal 3. Reverse thread seal 4. Packing seal

 

(1) External pressure end face sealing device:

 

A. Classification and compression methods are divided into bolt spring compression type, shift fork spring compression type, shift fork hydraulic cylinder compression type.

 

B. Structure and sealing principle:

 

a. Bolt spring compression type: under the action of the spring pressure mechanism, the contact surface of the rotating ring and the compression ring produces a certain pressure to prevent the leakage of materials. It is used for low-pressure and low-speed internal mixers, with simple structure, reliable sealing and long service life, but requires good maintenance during use.

 

b. The advantages of shifting fork hydraulic cylinder compression type (FYH for short) are: the working surface of each sealing ring is under constant pressure, and the specific pressure of the sealing surface remains quite stable. At the same time, it can be adjusted while working, the sealing is reliable, and the maintenance is convenient.

 

C. The structure of the shift fork spring compression type: similar to the shift fork hydraulic cylinder compression type, that is, the oil cylinder in the figure is replaced with a spring. Simple structure, low pressure, suitable for small and medium-sized internal mixers and inverted internal mixers.

 

(2) The internal pressure end-face contact type automatic sealing device mainly relies on the pressure of the mixing chamber when the rubber is extruded to make the inner sealing ring always press on the outer sealing ring to achieve a good sealing effect. This kind of sealing device can automatically adjust the compression degree of the inner sealing ring by the pressure change of the rubber material, and the sealing effect is better. It is suitable for the sealing device on the high-pressure fast internal mixer.

 

(3) Reverse thread and end face composite automatic sealing device When the material is exposed from the mixing chamber, the reverse thread can return it to the inside of the mixing chamber as much as possible.

 

(4) Reverse thread labyrinth compound sealing device: The device has a simple structure and is easy to manufacture and maintain. However, if the rotor sinks and the two labyrinth rings are in contact, the labyrinth will wear out quickly. When the rotor bearing becomes a sliding bearing, this kind of sealing device is not suitable

 

(5) External pressure labyrinth sealing device: The sealing principle is: when the material in the mixing chamber leaks out, it takes a long and narrow path to reach the contact surface of the inner and outer sealing rings, which acts as a "labyrinth". The sealing device can meet the needs of high-pressure and rapid mixing, but the structure is complicated, and the loading and unloading, adjustment and maintenance workload is relatively large. For example, the GK type internal mixer adopts this sealing device.

 

(6) Double reverse thread packing compound sealing device This kind of sealing device has a simple structure, and the packing can be replaced by disassembling the gland. However, the filler wear is severe and the service life is not long, so it needs to be replaced frequently. The effect is better only when the material is under medium pressure.

 

Auxiliary system of internal mixer: carbon black pneumatic conveying system; carbon black weighing and feeding system; oil conveying, storage, weighing, and oil injection system; rubber guiding, weighing and feeding system; computer intelligent control system.

 

Auxiliary system of internal mixer: Mainly has A tablet press: The currently commonly used tablet presses have two forms: open mixer tableting or twin-screw extrusion tableting.

 

And B film cooling unit: The rubber material after tableting must be cooled. The purpose of cooling is to reduce the temperature of the film and apply a release agent to avoid mutual adhesion and self-sulfurization when the film is stored. After the plasticized rubber or mixed rubber is discharged by the tablet press or extrusion tablet press, spray or immerse the soap release agent, cool, cut (or fold) the laminated sheets and park them for the next process. The currently available film cooling unit device is a rack-type film cooling device. There are two forms: floor-standing or overhead. Overhead