What Is an Extrusion Machine?

Extruder belongs to the category of plastic machinery and originated in the 18th century.

Extruder

The extruder originated in the 18th century. The manual piston extruder for seamless lead pipes manufactured by Joseph Bramah (England) in 1795 is considered to be the first extruder in the world. Since then, during the first 50 years of the 19th century, extruders were basically only suitable for the production of lead pipes, macaroni and other food processing, brick making and ceramics industries. During the development of a manufacturing method, the first clear record was a patent filed by R. Brooman in 1845 for the production of Goodyear rubber wires with an extruder. H. Goodwave Bewlgy subsequently modified the extruder and used it in 1851 to cover the copper wire of the first submarine cable between Dover and Calais. In 1879, the British M. Gray obtained the first patent on Archimedes spiral screw extruder. Over the next 25 years, extrusion methods became more important, and electric-operated extruders quickly replaced conventional manual extruders. In 1935, German machine maker Paul Troestar produced an extruder for thermoplastics. In 1939 they developed the plastic extruder into a current stage-the modern single screw extruder stage.

Single screw extruder principle

The single screw is generally divided into three sections on the effective length, and the effective length of the three sections is determined according to the diameter of the screw and the depth of the screw, which is generally divided by one third each.

The last thread of the material mouth is called the conveying section: the material is required to be plasticized here, but it must be preheated and compacted. In the past, the old extrusion theory believed that the material was loose. Later, it was proved that the material is actually The solid plug means that the material here is a solid like a plug after being squeezed, so as long as it completes the conveying task, it is its function.

The second section is called the compression section. At this time, the volume of the screw groove gradually decreases from large to small, and the temperature must reach the degree of plasticization of the material. Here, the compression is generated by the conveying section three, and the compression is here one. 3 1, some machines also have changes, the plasticized material enters the third stage.

The third section is the metering section, where the material maintains the plasticizing temperature, just like

The energy saving of the extruder can be divided into two parts: one is the power part and the other is the heating part.

Energy saving of the power part: Most of the inverters are used. The energy saving method is to save the remaining energy consumption of the motor. For example, the actual power of the motor is 50Hz, and you only need 30Hz to produce it in production. wasted,

In the extruder, in general, the most basic and versatile is a single screw extruder. It mainly includes six parts: transmission, feeding device, barrel, screw, head and die.

The auxiliary equipment of the plastic extrusion unit mainly includes a pay-off device, a straightening device, a preheating device, a cooling device, a traction device, a meter counter, a spark tester, and a take-up device. The use of the extruder unit is different, and the optional auxiliary equipment is also different.

Plastic extruder is divided into

When making different plastic products, the operating points of the extruder are different, but there are similarities. The following briefly introduces the same operating steps when extruding various products and the main points of the extruder that should be noted.

1. Preparations before driving

Used for

The screw extrusion system is maintained in two ways: daily maintenance and regular maintenance:

Daily maintenance is a regular routine work that does not take up equipment operation hours, and is usually completed during driving. The focus is to clean the machine, lubricate all moving parts, fasten loose threads, check and adjust the motor, control instruments, various working parts and pipelines in a timely manner.

Regular maintenance is generally carried out after the extruder is continuously operated for 2500-5000h. The machine needs to be disassembled, inspected, measured and identified for the wear of the main parts, replaced parts that have reached the prescribed wear limit, and repaired damaged parts.

(3) The empty car is not allowed to run.

If abnormal noise occurs during the operation of the extruder, stop it immediately for inspection or repair.

Prevent metal or other debris from falling into the hopper to prevent damage to the screw and barrel. In order to prevent iron debris from entering the barrel, a magnetic absorption component or a magnetic frame can be installed at the material inlet of the barrel to prevent the debris from falling into the material. The material must be sieved in advance.

Pay attention to the clean environment of the production. Do not mix the trash impurities into the material to block the filter plate, which will affect the product output, quality and increase the resistance of the machine head.

When the extruder needs to be stopped for a long time, it should be coated with anti-rust grease on the working surface of the screw, barrel, and head. The small screw should be suspended in the air or placed in a special wooden box, and leveled with a wooden block to avoid deformation or injury of the screw.

Regularly adjust the temperature control instrument to check the correctness of the adjustment and the sensitivity of the control.

The maintenance of the gearbox of the extruder is the same as the general standard gearbox. It is mainly to check the wear and failure of gears and bearings. The gearbox should use the lubricating oil specified in the machine manual, and add oil at the specified oil level. Too little oil, insufficient lubrication, and reduce the service life of the parts; too much oil, large heat, high energy consumption, and easy oil deterioration. , Also makes the lubrication invalid, resulting in damage to the parts. The oil leakage of the reduction gear box should be replaced in time to ensure the amount of lubricant.

The inner wall of the cooling water pipe attached to the extruder is prone to scaling and the exterior is corroding and rusting. Careful inspection should be done during maintenance. Excessive scale will block the pipeline, fail to achieve the cooling effect, and serious corrosion will leak water. Therefore, descaling and anticorrosive and cooling measures must be taken during maintenance.

For DC motors that drive the screw, check the brush wear and contact conditions, and measure the insulation resistance of the motor above the specified value. In addition, check the connection lines and other parts for rust and take protective measures.

Specify someone to be responsible for equipment maintenance. And detailed records of each maintenance and repair are included in the factory equipment management file.

China's conventional extruders and production lines are gradually gaining popularity in the international market with excellent cost performance. At the same time, China has continuously innovated in the field of advanced extrusion technology, and has developed a variety of new extrusion products. Precision extrusion technology to meet the needs of high precision processing

Melt gear pump

Precision extrusion molding can eliminate the need for subsequent processing methods and better meet the needs of product applications, while achieving the purpose of reducing material costs and improving product quality. Today, to meet the needs of precision direct extrusion of plastic products, a variety of mature technologies have been introduced to the market. Polymers

Extruder is a common

Extruder feed roller wear

Because the extruder is made of metal and has high hardness, it will be subject to vibration impact and other combined forces during the production and operation process, which will cause the parts to form gaps and cause wear. Traditional repair methods include surfacing, thermal spraying, and brushing. However, several methods have certain disadvantages: surfacing will cause the surface of the part to reach a very high temperature, causing the part to deform or crack, affecting dimensional accuracy and normal use. It can also cause fracture when it is severe; although the brush crossing has no thermal influence, the thickness of the crossing layer cannot be too thick, the pollution is serious, and the application is also greatly restricted. Western countries are more applied to the above problems

In order to protect the box of the twin screw extruder transmission box, the following points must be done:

After 500 hours of first use, change the lubricant once;

The extruder is lubricated with original medium-pressure gear oil of the brand No. 150;

The oil level during normal operation is not lower than the center line of the oil level.

Change the oil every 3000 hours after use;

When changing the oil, clean the box and the oil filter. After changing, clarify the lubricating oil used this time, refill the clean lubricating oil into the box, clean the box once, then release it, and then put it in a new one. Lubricant

Regular monthly use should be cleaned for normal use

Common problems and treatment of screw extruder In the use of machinery and equipment, it is inevitable to have one or other problems, so it is very important to be able to find problems and find solutions in time. Here we analyze some common problems of screw extruder and discuss the best treatment methods.

1. Common problems and processing methods of extruder

1. The phenomenon of "missing material" and screw heating occurs without feeding.

1.1 Reasons and methods

1.1.1 The reamer is severely worn. The gap between the reamer and the inner wall of the mud tank is too large, or the helix angle of the reamer blade is incorrect. When replacing the reamer, care should be taken to maintain the gap of 3 to 5 mm, and the reamer blade should be made according to the designed angle.

1.1.2 The surface of the reamer blade is too rough, and the friction between the mud and the blade is too large. Therefore, do not build up the reamer in groups, and replace all of them at one time. It should be performed step by step and replaced in batches to ensure smooth out. brick.

1.1.3 The mud wall bushing is heavily worn. The gap between the blade of the reamer and the wall of the mud tank is too large, which causes too much rotary motion of the mud in the mud tank, and the mud cannot come out or enter. At this time, the new mud tank bushing should be replaced, or several parallel or inclined ribs should be installed on the inner wall of the bushing to replace the worn out grooves to prevent the ineffective rotation of the mud and increase its effectiveness Extrusion.

1..1.4 The gap between the mud press blade and the reamer is too large to suppress the mud. At this time, the blade should be adjusted or repaired and renewed so that the gap between the blade and the reamer blade is less than 10mm.

2. Mud movement bending

2.1 Reasons and methods

2.1.1 The sludge is bent to one side. This is because the centerline of the machine mouth, core tool, mud cylinder and spiral reamer is not aligned or the roll bed is installed in an inclination. Adjust the position to solve the problem.

2.1.2 S-bend appears in the mud. This is because the compression length of the neck of the machine is not enough, the main and auxiliary leaves of the first spiral reamer are not uniform, or the auxiliary leaves of the first reamer are severely worn and become smaller. As a result, only the semicircle of the main blade is pushed out during operation. . At this time, the first reamer should be replaced to repair the auxiliary blades.

3. Overload

3.1 Reasons and methods

3.1.1 The mud is too dry. At this time, the too dry mud should be pulled out first, it is better to remove the mouth and head, start the machine to drain the dry material in the mud tank, and then install and run, and appropriately increase the molding moisture within the specified range.

3.1.2 If the machine is stopped for a long time, the remaining material in the mud tank becomes dry and hard. This will not only cause severe overload, but sometimes it will fail to start. In order to prevent this from happening, when shutting down for more than 8 hours, do not shut off the water at the mouth of the machine. For the two-stage vacuum extruder, the mud in the upper cylinder should be properly supplied with water to keep it moist. Open the mud as much as possible before shutting down.

3.2 Precautions: When the motor is overloaded, the load of the motor will remain high and the clutch will slip. At this time, it is forbidden to force start to avoid damaging the related parts and even causing large accidents such as crushing the mud tank and the machine head.

4. Machine "swing"

4.1 Reasons and methods

4.1.1 "Swinging head" is a common problem of screw extruder. This is because the cutter shaft is a long cantilever shaft with poor stability. When the bearing is loose, the main shaft is bent, and the auxiliary blade of the first section of the cutter is too Hours will exacerbate the situation. If the mud cylinder is not installed correctly, the gap between the spiral reamer blade and the circumference of the mud cylinder wall is not the same, and the outer edge of the spiral reamer blade is seriously out of round, which causes the main shaft to be uneven and swing the head. It should be corrected in time and often Tighten the anchor bolts and connection bolts to prevent them from swinging.

5. Spirals appear after mud sticks are squeezed out

5.1 Reasons and methods

5.1.1 Because the sludge is affected by the spiral action of the cutter, the speed of the mud on the section of the mud tank is not consistent, the mud near the axis moves faster, the mud on the edge moves slower, and between the mud at different speeds An interface is formed, and water and air are concentrated in the voids on this surface, creating a layering phenomenon. The main reasons are the high plasticity of the mud, the excessive moisture in the molding, the high spindle speed, and the mud return phenomenon on the inner wall of the mud tank. The handling method is as follows:

(1) Raw materials with different properties should be thoroughly mixed and homogeneous, as far as possible, soaking and aging, so that the water fully penetrates into the inside of the raw material particles, and reduces the water on the surface of the raw mud.

(2) Properly reduce the molding water to increase the friction between the mud layers.

Common problems and treatment methods of finished bricks

Hair crack

Shallow cracks appear on the surface of the brick, but there are almost no straight lines, and sometimes the cracks extend to the strip surface or the top surface. This is mostly a hidden danger left during molding, and the firing is improperly used to crack the cracks. To this end, the plasticity index of the raw materials should be appropriately reduced, the rotation speed and helix angle of the screw reamer of the brick machine should be adjusted, a separate spiral reamer should be used, and a mud stick should be added to the mud tank to reduce mud layering; Measures such as steam stirring and vacuum squeezing can reduce water and gas in the mud to eliminate stratification. In addition, the brake should be properly used for roasting, evenly discharge the moisture, and implement the front gate in stages.

Burst

When the residual moisture in the kiln brick is too high, and the initial heating temperature in the pre-tropic zone exceeds 25-35 ° C / h, the rapidly vaporized steam in the body is too late to be exhausted. When the brick slab is extruded, the higher the residual moisture, the more the situation will be. Severe, even cracking sounds can be heard at the top of the kiln. Especially after squatting fire, the temperature of the pre-tropical zone is rapid, and the moisture of the injury is not too high. The water vapor often only breaks the surface of the brick and forms a fine spider-like crack. In addition to controlling the residual moisture in the kiln billet below 8%, the preheating zone should be appropriately extended to slow the temperature rise and dehydration uniformly, and the remote gate should be slowly raised after the squatting fire and the paper burning in the round kiln to gradually increase the height.

3. Frost

A layer of white powder was produced on the brick surface. This is the residue of soluble inorganic salts such as magnesium sulfate and sodium sulfate remaining on the brick body. Because the blank contains a certain amount of crystal water, it swells after dehydration, so it will crack the surface of the brick during frost. For this reason, the content of twisted magnesium in the mud should be controlled below 3%. Strengthen pulverization, increase fineness and extend the roasting and holding time appropriately, so as to generate water-insoluble silicates, reduce or eliminate harm.

4.Mute brick

Except for mute bricks caused by underfire, invisible cracks caused during molding and too many impurities in the raw soil, invisible layering caused by uneven stirring, wet billets are heated too quickly during preheating, and have been frosted. And bricks in the pre-tropical moisture absorption condensation will form micro-cracks, resulting in mute bricks, the body suddenly formed micro-cracks, etc., may also cause mute bricks. In this regard, in addition to strengthening the processing of raw materials, removing impurities, mixing thoroughly, and improving the relevant parameters of the brick machine, care should also be taken not to burn high-temperature billets and frost billets. At the same time, it should ensure good preheating and a long enough insulation band.

5.Scorched and foamed brick surface

The reason is that the calcination zone heats up too fast, the surface layer melts and sinters quickly, blocking the pores, and the gas produced by the ongoing physical and chemical reaction has no way to go, and bubbles form on the brick surface. Therefore, the heating rate of the calcining zone should be lower than 40-70 ° C / h, especially when the green body has reached a temperature above 900 ° C, the rate of continued heating is even lower than 20 ° -30 ° C / h to prevent the brick surface from scorching. bubble.

What does the type designation on the extruder plate indicate?

In the rubber extruder standard GB / T 12783-91, the type designation on the label is described as follows:

From left to right: the first grid of plastic machinery code is S; the second grid of extruder code is J; the third grid refers to the different structural form code of the extruder. The combination of the three grids is: SJ for plastic extruder; SJP for plastic vented extruder; SJF for plastic foaming extruder; SJW for plastic feeding extruder; SJE; step plastic extruder is SJJ; twin screw plastic extruder is SJS; conical twin screw plastic extruder is SJSF; multi-screw plastic extruder is SJD. The fourth box indicates the auxiliary machine, code is F; if it is an extruder unit, the code is E. The fifth parameter refers to the screw diameter and aspect ratio. The sixth grid refers to the design order of the products, arranged in the order of letters A, B, C, etc. The first design is not marked with a design number.

For example: SJ-45X25, which means that the diameter of the plastic extruder is 45mm, and the aspect ratio of the screw is 25: 1. Not marked when the screw aspect ratio is 20: 1.