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August 30, 2023

ingle and Twin Screw Extruder General Knowledge Book

  •  Classification of extruders

Product code standard parameters

Note: For example, SHJM-Z40×25×800 refers to a twin-screw mixed plastic extrusion and plastic film machine with a screw diameter of 40mm, an aspect ratio of 25, and a traction roller length of 800mm.

1. “SH” category code refers to twin-screw mixing type (also written as: SHSJ, SJ refers to plastic extruder)

2. “J” group code refers to the extruder.

3. “M” refers to the type code and refers to the blown film machine

4. “Z” refers to the auxiliary code, which refers to the main unit, and “F” refers to the auxiliary aircraft.

5. “40×25×800” refers to the standard parameters, which means that the diameter of the screw is 40mm, the aspect ratio is 25, and the length of the traction roller is 800mm.

6. The last digit is the manufacturer’s identification serial number, which usually does not appear and is omitted.

  •  Functional parameters of twin-screw mixing extruder

1. “D” is diameter, an important parameter to measure the size of output.

2. “L/D” refers to the ratio of length to diameter, which directly affects the degree of plasticization and is a symbol of the purpose. Generally, for plastic modification, it is about 30-40, and 36:1 is commonly used.

Or 30:1.

3. “H”, the depth of the screw groove, refers to the size of its material-holding space.

4. “e” screw edge thickness, technically reflected in the size of the shear.

5. The gap between “6” screw and barrel is an important parameter of extruder quality, usually 0.3-2mm, skipping 5mm extruder is the warning line.

6. “N” host speed refers to its highest value, which refers to a processing adjustment scale, which greatly affects the output value and the distinction between medium, high and low speeds. (Domestic machines usually run at 500-600r/min)

Such as: max: 600r/min, low speed: 350r/min, medium speed 230-240r/min, high speed 450-600r/min.

7. “P”, motor power and heating power.

  •  Screw placement and technical settings

① Segments and functions of the screw

(1) The screw is usually divided into 5 sections: conveying section, melting section, mixing section, exhaust section, and homogenization section.

1. The conveying section, conveying materials and preventing overflow.

2. Melting section, this section undergoes heat transfer and frictional shearing to fully melt and homogenize the material.

3. The mixing section further refines and evens the size of the material components to form an ideal structure, with the function of dispersive and dispersive mixing.

4. The exhaust section discharges impurities such as water vapor and low molecular weight substances.

5. Homogenization (measurement) section, conveying and pressurizing, establishing a certain pressure so that the material at the die mouth has a certain density, while further mixing, and finally achieving smooth extrusion granulation Intention.

(2) Diffusion (distribution) and scatter mix

1. Distribution and mixing, cutting and reorganization of the melt, and uniform spatial distribution of each component, mainly through separation, stretching (generated by the replacement of compression and expansion), distortion, and fluidization

It is completed by replacing the activity under the action of stress such as activity reorientation.

2. Disperse mixing to break the components into particles or to disperse the two incompatible components to the required range. This is mainly accomplished by shear pressure and joint extension stress.

②Conveying components, threaded

Express method: such as “56/56” transport block, the previous “56” tutorial is 56MM, and the latter “56” means the length is 56MM.

Large lead, refers to the pitch of 1.5D~2D

Small lead means that the pitch is about 0.4D.

Its application rules: with the increase of the lead, the extrusion volume of the screw increases, the residence time of the material decreases, and the mixing effect decreases.

A. Where large-lead threads are used, where transportation is the main purpose, it is beneficial to increase output value; heat-sensitive polymers shorten residence time and reduce degradation; for exhaust locations, use (

Shallow grooves are also used), which increases the surface area and facilitates exhaust and evaporation.

B. Use medium-lead thread occasions, mainly mixed occasions, with a combination of different working sections that are gradually reduced, for transportation and pressurization.

C. When choosing to use a small lead thread, it is usually gradually reduced in combination. It is used in the transportation section and the homogenization metering section to pressurize, improve melting, and improve the mixture process.

Degree and extrusion are stable.

③Mixing elements, there are two types, “K” series and “M” series (dentate)

“K” series

Notation: such as K45/5/56″, which belongs to the cutting block. “K” refers to the sheet cutting block, “45” refers to the angle of the pieces, “5” refers to a total of 5 pieces, and “56” refers to the length.

The degree is 56MM, the width of the thread is 56/5=11.2mm), its parameters:

A. Direction, there are forward and reverse directions – reverse direction, which hinders the transportation of materials, extends time, increases filling and pressure, and greatly improves the mixing effect.

effect.

B. Viewpoint, usually divided into “30°, 45°, 60°, 90°”, its functions and functions:

a. When it is in the positive direction, increasing the interlacing angle will reduce the conveying capacity, prolong the residence time and improve the mixing effect, but the leakage will be easier.

About Diffuse and Dispersive Blending

For example, distributed blending is more effective with large viewpoints, and diffuse blending is at viewpoint 45. is the best, followed by 30. , the worst is 60. .

b. In the reverse direction, increasing the angle of view will reduce the effective restraint of the polymer, but it will be easier to leak.

C. The width of the helix is usually 7mm, 11mm, 11.2mm, 14mm, 19mm, etc. This is one of the most important parameters to measure the cutting size and mixing size. The width

The larger the shear, the greater the mixing and the smaller the mixing; the smaller the width, the smaller the shearing and the greater mixing. For diffuse blending and diffuse blending, diffuse blending is more effective as the width increases

As the width increases, the efficiency of dispersive mixing increases; the smaller the width, the ratio of the effective flow rate in the axial direction and the effective flow rate in the radial direction increases.

D. Number of heads, usually single head, double head, triple head. Its function:

a. In the forward direction, the fewer the number of heads, the greater the extrusion conveying ability, the greater the torque, the better the mixing performance, but the less shearing effect.

b. In the reverse direction, the fewer the number of heads, the smaller the extrusion and conveying capacity, and the better the mixing performance.

c. The two-head thread can be mainly used for extrusion, which is evenly heated and short, and has good self-cleaning function (commonly used).

d. Three-head thread, which can flexibly select the pressure and temperature distribution of the material at the corner of the machine, the fiber addition is stable, and the exhaust surface renewal effect is good, but the output value is low.

“M” series: tooth shape, mainly to disrupt the material flow, and can accelerate the homogenization of materials. The more teeth the stronger the blend. ——But pay attention when using, high shear damage

sex. (Indications, such as “M80” in China and Taiwan, SME45/45 of “WP”, ZB45/ of “BERSTDRFF”

3/11)

  • Screw arrangement and temperature setting of each section of the screw

1. Physical change characteristics of plastics and temperature setting criteria:

⑴Physical change characteristics of plastics:

A Amorphous plastic

Gradually added with temperature has three physical properties such as:

High elastic state                   Viscous flow state

Tg                         

(glass transition temperature)

 Tf                       

(melting temperature)

 Td

 (differentiation temperature)

Its melting takes place under viscous dissipation due to shearing action.

Bcrystalline plastic,

With the gradual increase of temperature, there are two physical characteristics, and the changes are relatively sudden, such as:

Tm

(melting temperature)

Td

(differentiation temperature)

Its melting experience: the formation and rupture of solid bed, forming many particles floating in the melt, and then gradually melting.

⑵Temperature setting criteria:

①The melting point and ratio of each component of the blended alloy: the melting point of the blended component is used as the basis, and the melting point of the continuous phase is used as the adjustment scale.

② Thermal properties of plastics, such as melting heat absorption and heat release, thermal degradation process and thermal oxidation difficulty.

③ Within the range of the melting point of each component of the plastic, the activity function and shape change.

Such as PC/ABS (6:4), PC: melting point is about 230 degrees, decomposition point is about 350 degrees; ABS: melting point is about 180~190 degrees, decomposition point is about 245-290 degrees – so PC/ABS processing temperature is 230-250 Degree – taking into account other additives, such as compatibilizers, thermal stability of lubricants, etc.

⑶ The source of material temperature increase:

1. The shearing of the screw and the friction between the material particles generate heat – most of them.

2. Heat transfer from the cylinder.

(2) Screw arrangement and temperature setting of each section

The function of screw combination:

①Transport materials

②Supply shearing—the energy required to obtain physical and chemical changes in the processed materials to scatter and spread the components.

③Build pressure

Analysis of the melting process of material particles:

Free transport and preheating of polymers – full or partial filling of solid plugs – solid friction, dissipation and generation of solid dense “island” structures – solid rare “island” structures – molding extrusion.

Screw layout segmentation and temperature setting:

1. Transport section

A. The screw arrangement ideas are:

a Deep groove forward thread

b Medium screw groove and large lead forward thread, and the volume of the screw groove changes from large to small, that is, the thread lead changes from large to small.

B. Temperature setting ideas

a It should not be too high, which will affect the transportation and shearing of materials in this section; it should not be too low, the screw will be overstressed or stuck

b Usually slightly closer to melting, arranged in gradients.

2. Melting section

A. Screw arrangement:

The purpose of the material in this section is to make the processed material obtain the energy required for physical change and partial chemical change, so that the components are evenly distributed and start to scatter, so that

The components are homogenized and the viscosities are similar. It is usually required that the material undergoes greater shear and heat transfer in the barrel to melt it – usually with kneading blocks, shear elements or reverse threads,

And pay attention to the coordination of placement.

B. Temperature setting

a Glass fiber system, the temperature is too low, the resin is half-melted, and the coating of the glass fiber in the rear section is poor; the temperature is too high, the resin flow increases, the tempering and shearing effects become smaller, and even high temperature occurs

Degradation, its setting criteria:

1. According to different base materials and glass fiber content;

2. Deduct the heat input by screw shearing, which is slightly higher than the melting point of the base material;

3. Melt activity in the latter part of the melting section (that is, the glass fiber inlet).

b Filling system (provide strong shear to make the filler fully dispersed), the melting section is 10~20°C higher than the melting point of the base material (as high as possible), so that the material is fully melted and evenly distributed.

c For flame retardant systems (protect the flame retardant), the temperature should be as low as possible, especially for white materials.

d Glass fiber reinforced flame retardant system, the set temperature is between the previous two, based on the basic melting point of the material.

e Alloy system, based on two sets of melting temperatures, consider the proportion of components and the thermal sensitivity of the components, etc., and adjust the temperature appropriately

3. Mixing section

A. Arrangement of screw components

The purpose of the material arriving in this section is:

1. Refine and disperse to form the ideal scale and structure.

2. Pay attention to protect the ideal structure of the product from being damaged.

There are usually two typical ideas: 1. Reinforced type, two-headed and three-headed combination; 2. High-shear and high-splitting flow with both dispersion and dispersion, with the kneading block as the main body and the threaded block as the auxiliary salty

High shear. — Better method: combination of kneading blocks with different thicknesses and different angles, plus conveying screw blocks – to make the materials loose due to high shear and save time and return

Mix, but guaranteed not to degrade.

B. Temperature setting

a Glass fiber system, if the temperature is too low, the material flow function is poor, the viscosity is high, the friction becomes larger, the heat generation is high, and local overheating will occur; the temperature is too high, the resin is degraded, and the shear degree

The dispersion and variation of small glass fibers are poor, and the setting criteria are:

1. It varies according to the base material and glass fiber content.

2. Keep it slightly within the melting point range of the base material.

3. Determine based on the glossiness of the product strip.

b Filling system (provide strong shear to make the filler fully dispersed), the mixing section is 10~20°C higher than the melting point of the base material (as high as possible), so that the material is fully melted and evenly distributed

cloth to ensure that the mixture is in a fluid condition.

c flame retardant system, (protect the flame retardant) the blending temperature is on the low side, especially for white materials, keep it as low as possible.

d Glass fiber reinforced flame retardant system, the temperature setting is based on the basic melting of the material to protect the flame retardant.

e Combination is based on the melting temperature of the components, and is adjusted by considering the proportion of the components and the thermal sensitivity of the components.

4. Exhaust section

Screw combination placement

Usually, at the inlet of the exhaust port, a reverse thread salty reverse kneading block is set up to seal the melt, which is high pressure; a large lead thread element is used to form a low filling degree and a high pressure.

Understand the melt layer, expose the material freely on the surface or use multi-head small lead threads to increase the renewal speed of the melt surface, which is conducive to gas removal and evaporation ——General idea

Path: reverse thread (R-LH) or reverse roller block (KG) + transport thread + large lead or multi-head small lead thread.

5. Homogenization (material quantity) section

A screw combination

Small thread block lead mutations or small screw groove mutations are used to achieve pressurization and reduce the length of the back pressure section. At the same time, attention is paid to the use of single-head threads and wide helix threads to improve the discharge capacity.

Prevent material from popping up.

B temperature setting,

To appropriately lower the temperature, but the high temperature of the die is conducive to discharge.

On the basis of the temperature of the melting section, the temperature should be appropriately lowered. The criterion is: based on the degree of gloss reduction.

  • Speed question

The higher the rotation speed, the greater the shear, and the dispersed phase will be evenly dispersed in the matrix; the larger the shear, the finer the size of the dispersed phase, but the rotation speed is too high, and the friction will easily lead to thermal degradation.

The residence time becomes shorter and the mixing becomes uneven.

The lower the rotation speed, the smaller the shear, the dispersion is uneven, and the residence time is long, which is not good for easily decomposed polymers.

The rotation speed and screw structure are both related to shear dispersion, so it is necessary to consider both as a whole.

⑴Fiber reinforcement type affects the length and diameter of glass fiber, affects the loose wrapping of resin and glass fiber, and thus affects the reinforcement effect.

⑵ For alloys, it is necessary to consider the formation and damage of the structure between resins due to rotational speed shearing. For example, PC/ABS alloy belongs to the “sea island” structure similar to sponge.

(3) For flame retardants, it is necessary to consider the thermal properties of flame retardants, such as melting heat absorption and heat release, thermal degradation process and thermal oxidation difficulty. Single and twin screw extruder