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Extruder gearbox repair

I believe that many people in the industry will encounter an embarrassing problem: the quality of foreign equipment is very good, but it is more troublesome to replace and repair; in addition to hiring foreign original technical engineers at a large price, praying that people can come early; more importantly, The long-term purchase and delivery of foreign original parts and components can make people laugh and cry; this will cause great losses to production! So is there a better solution?
One. The gearbox is the "heart" of the extruder
The heart is the source of power for the human body. The human body realizes the circulation of blood through the contraction and expansion of the heart, and the oxygen and nutrients in the blood provide a "power" guarantee for various parts of the human body.
By analogy, the gearbox is the "heart" of the extruder. The gearbox transmits power to the screw, ensuring proper operation of the extruder.
The gearbox, also known as the gearbox, is a power transmission mechanism and a reduction transmission device. The gearbox is meshed by gears of different numbers of teeth to convert the number of revolutions of the motor into the number of revolutions required by the working equipment and increase the torque. For plastic extruders, the gearbox is a key component that directly affects the overall performance of the extruder. However, most of China's extruder gearboxes are still at the level of relatively low carrying capacity or low torque levels of the older generation (eg, gearboxes with single-sided parallel drive structures), which are far behind the current international mainstream in technology. High torque gearbox (eg double-sided gear symmetrical drive gearbox).
In order to meet some high requirements such as the production of polyoxymethylene, domestic plastics manufacturers must choose foreign polyoxymethylene polymerization machines with more power and better stability.

Extruder gearbox repair

two. What should I do if the imported extruder gearbox is broken?
What should I do if the imported extruder gearbox is broken? This problem seems to be very simple: the gearbox is broken, of course, the original factory to repair, and then change a gearbox.
Indeed, in theory it should be handled this way. However, the reality is not so simple: for most plastics manufacturers, production is a continuous, large-scale process; they want the gearbox to be repaired as early as possible with as little impact as possible on production.
1. Foreign original factory replacement maintenance costs are high and long
However, foreign large-scale extruder suppliers are not located in China due to the headquarters and factories, and most of them set up offices in first-tier cities in China; when plastic production or processing plants have large problems such as broken gear boxes, the staff of the office are generally For sales engineers, they can't handle such problems; they have to contact foreign technical personnel to solve the problem, so that things that can be solved in one day can take 4 or 5 days, which seriously affects normal production.
The screw extrusion system is maintained in two ways: daily maintenance and regular maintenance:
(1) Routine maintenance is a routine routine work that does not take up the working hours of the equipment and is usually completed during driving. The focus is on cleaning the machine, lubricating the moving parts, tightening the loose threaded parts, checking and adjusting the motor in time, controlling the instrument, working parts and piping, etc.
(2) Regular maintenance is generally stopped after the continuous operation of the extruder is 2500-5000h. The machine needs to disassemble, measure, and identify the wear of the main parts, replace the parts that have reached the specified wear limit, and repair the damaged parts.
(3) Do not allow empty cars to run, so as to avoid screwing of the screw and barrel.
(4) If an abnormal sound occurs during the operation of the extruder, stop immediately and inspect or repair.
(5) Strictly prevent metal or other debris from falling into the hopper to avoid damage to the screw and barrel. In order to prevent iron debris from entering the barrel, a magnetically absorbing part or a magnetic frame may be placed at the feeding port of the material to prevent the impurities from falling into the material.
(6) Pay attention to the clean production environment, do not let the garbage impurities mix into the material to block the filter plate, affect the product output, quality and increase the resistance of the machine head.
(7) 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 machine head. The small screw should be hung in the air or placed in a special wooden box and leveled with wooden blocks to avoid deformation or bumping of the screw.
(8) Regularly calibrate the temperature control instrument to check the correctness of the adjustment and the sensitivity of the control.
(9) The gearbox maintenance of the extruder is the same as that of the general standard reducer. Mainly to check the wear and failure of gears, bearings and so on. The gearbox should use the lubricating oil specified in the machine manual, and add the oil according to the specified oil level. The oil is too small, the lubrication is insufficient, and the service life of the parts is reduced. The oil is too much, the heat is large, the energy consumption is high, and the oil is easy to deteriorate. Also, the lubrication is invalidated, resulting in damage to the parts. The oil leakage part of the gearbox should be replaced in time to ensure the amount of lubricant.
(10) The inner wall of the cooling water pipe attached to the extruder is easy to scale and the outside is easily corroded and rusted. Care should be taken during maintenance. Excessive scale will block the pipeline and will not reach the cooling effect. If the corrosion is serious, water leakage will occur. Therefore, measures such as descaling and anti-corrosion and cooling should be taken during maintenance.
(11) For the DC motor that drives the screw to rotate, it is important to check the brush wear and contact. The insulation resistance of the motor should be measured frequently. In addition, check the connection wires and other components for rust and take protective measures.

Extruder gearbox repair

The extruder belongs to one of the categories of plastic machinery and originated in the 18th century.
The extruder can divide the nose into a right angle head and a bevel head according to the direction of the head flow and the angle of the screw center line.
The screw extruder relies on the pressure and shear force generated by the rotation of the screw, so that the material can be fully plasticized and uniformly mixed, and formed by die molding. Plastic extruders can be broadly classified into twin-screw extruders, single-screw extruders, and rare multi-screw extruders as well as screw-free extruders.
Development History:
The extruder originated in the 18th century, and the manual piston extruder manufactured by Joseph Bramah (England) in 1795 for the production of seamless lead pipes was considered to be the world's first extruder. Since then, during the first half of the 19th century, extruders have been basically only suitable for the production of lead pipes, macaroni and other food processing, brick making and ceramic industries. In the development process as a manufacturing method, the first time clearly stated is the patent that R. Brooman applied for the production of Gutebo adhesive wire by an extruder in 1845. G. Wave's H. Bewlgy then improved the extruder and used it in 1851 to coat the copper wire of the first submarine cable between Dover and Calais. In 1879, the British M. Gray obtained the first patent using the Archimedes spiral screw extruder. In the next 25 years, the extrusion process became increasingly important, and the electric hand operated extruders gradually replaced the previous manual extruders. In 1935, German machine manufacturer Paul Troestar produced extruders for thermoplastics. In 1939 they developed the plastic extruder to a new stage – the modern single-screw extruder stage.
Mechanical principle:
Single screw extruder principle
The single screw is generally divided into three sections in the effective length. The effective length of the three sections is determined according to the diameter of the screw and the pitch of the screw. Generally, it is divided into one third.
The last thread of the material port 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 here was loose, and later proved that the material here is actually The solid plug, that is to say, the material here is a solid like a plug after being squeezed, so it is its function as long as the conveying task is completed.
The second section is called the compression section. At this time, the volume of the groove is gradually reduced from large to large, and the temperature is to reach the degree of plasticization of the material. Here, the compression is generated by the conveying section three, where it is compressed to one, which is called the compression ratio of the screw -- 3:1, some machines have also changed, and the finished plasticized material enters the third stage.
The third section is the metering section, where the material maintains the plasticizing temperature, just as accurately and quantitatively transports the melt material as the metering pump to supply the head, at which time the temperature cannot be lower than the plasticizing temperature, generally slightly higher.

Extruder gearbox repair

Extruder energy saving:
The energy saving of the extruder can be divided into two parts: one is the power part and the other is the heating part.
Power saving: Most of the inverters are used. The energy saving method is to save the residual energy of the motor. For example, the actual power of the motor is 50Hz, and you only need 30Hz in production to produce enough. The excess energy consumption is vain. Wasted, the inverter is to change the power output of the motor to achieve energy saving.
Energy saving in heating part: Most of the energy saving in heating is energy saving by electromagnetic heater, and the energy saving rate is about 30%~70% of the old resistor ring.
work process
The plastic material enters the extruder from the hopper, and is transported forward by the rotation of the screw. During the forward movement, the material is heated by the barrel, sheared by the screw and compressed to melt the material. Thus, a change between the three states of the glassy state, the high elastic state, and the viscous flow state is achieved.
In the case of pressurization, the material in a viscous flow state is passed through a die having a certain shape, and then becomes a continuum having a cross-section and a mouth-like appearance according to the die. It is then cooled and shaped to form a glassy state, thereby obtaining the part to be processed.
 The extruder is a common plastic machinery. During the daily operation of the extruder, there are various failures in the extrusion machine, which affects the normal production of plastic machinery. Below we analyze the failure of the extruder.
Common faults and treatment methods of rod extruder
1.1, abnormal noise
(1) If it occurs in the reducer, it may be caused by damage to the bearing or poor lubrication, or it may be caused by gear wear, improper installation adjustment or poor meshing. It can be solved by replacing the bearing, improving the lubrication, replacing the gear or adjusting the meshing condition of the gear.
(2) If the noise is a sharp scraping sound, the position of the barrel should be considered to be skewed, which may cause the shaft head and the transmission sleeve to be scraped. Can be solved by adjusting the barrel.
(3) If the barrel emits noise, it may be a screw bending broom or setting the temperature too low to cause excessive friction of solid particles. It can be handled by straightening the screw or increasing the set temperature.
1.2 Abnormal vibration
If this happens at the reducer, it is caused by the wear of the bearing and the gear. It can be replaced by a replaceable bearing or gear. If it occurs at the barrel, it is because the material is mixed with hard foreign matter, and the material should be inspected for cleaning.
The main reasons and solutions for the wear of screw extruder
2.1 The main reason for the wear of the screw extruder
The normal wear of the screw and barrel of the screw extruder mainly occurs in the feeding zone and the metering zone. The main cause of wear is caused by the friction between the sliced ​​particles and the metal surface. When the temperature of the slice is softened, the wear is reduced.
The abnormal wear of the screw and the barrel will occur when the screw loop and the foreign matter are stuck. The loop knot refers to the screw being condensed by the condensed material. If the screw extruder lacks a good protection device, the strong driving force may be broken. Screws, stuck, can create unusually large resistance, causing serious damage to the surface of the screw and severe scratching of the barrel. Scratching of the barrel is difficult to repair. The barrel is designed to ensure that the service life is longer than the screw. For the normal wear of the barrel, it is generally not repaired. The method of repairing the screw thread is often used to restore the radial clearance between the barrel L and the outer diameter of the screw.
2.2 Screw wear solution
The local damage of the screw thread is repaired by surfacing the special anti-wear and anti-corrosion alloy. Inert gas shielded welding and plasma argon arc welding are generally used. Metal spray technology can also be used for repair. First, the worn outer surface of the screw is ground to a depth of about 1.5 mm, and then the alloy layer is surfacing to a sufficient size to ensure sufficient
The machining allowance, finally grinding the outer circumference of the screw and the side of the thread to the outer dimensions of the screw is the original size.
2.3 ring plugging at the screw inlet
This type of failure is mainly caused by the cooling water interruption or insufficient flow. It is necessary to check the cooling system and adjust the cooling water flow and pressure to the specified requirements.
in conclusion
(1) The natural life of the extruder is long, and its service life mainly depends on the wear of the machine and the wear of the gear box. Choose design materials and well-made extruders and speed reducers, directly off
It is tied to the use performance. Although the equipment investment is increased, the service life is prolonged, which is reasonable considering the overall economic benefits.
(2) The normal use of the screw extruder can fully exert the performance of the machine and maintain a good working condition. It must be carefully maintained to extend the life of the machine.
(3) The main failures of screw extruders are abnormal wear, foreign matter jamming, blockage of materials, wear or damage of transmission components, poor lubrication or oil leakage. In order to avoid the occurrence of faults, it is necessary to strictly manage the drying, mixing and feeding operations and the setting of the process temperature, and carry out routine maintenance, maintenance and overhaul in strict accordance with the requirements of the "Inspection of Equipment Points".

Extruder gearbox repair

Extruder feed roller wear
Since the extruder is made of metal, the hardness is high, and it is subjected to vibration shock and other compounding forces during production and operation, resulting in gaps between the components and causing wear. The traditional repair methods include surfacing, thermal spraying, brushing, etc., but several methods have certain drawbacks: surfacing will cause the surface of the part to reach a very high temperature, causing deformation or cracking of the part, affecting dimensional accuracy and normal use. In severe cases, it will lead to breakage; although the brush crossing has no heat effect, the thickness of the crossing layer should not be too thick, the pollution is serious, and the application is also greatly limited. Western countries have applied the polymer composite method to the above problems. Its comprehensive performance and mechanical processing characteristics at any time can meet the requirements and accuracy after repair, and can also reduce the shock and vibration of the equipment during operation and prolong the service life. Because the material is a "variable" relationship, when the external force impacts the material, the material will deform and absorb the external force, and expand and contract with the expansion or contraction of the bearing or other components, and always maintain a tight fit with the component to reduce the probability of wear. For the wear of large extruders, “mold” or “mating parts” can also be used for on-site repair of damaged equipment, avoiding the overall disassembly of the equipment, maximizing the fit size of the parts and meeting the production and operation requirements of the equipment.

The processing section of the feeding section of the extruder does not match the processing dimensions.
When the material of the extruder bushing is 38CrMoAlA, due to machining reasons (the positioning keyway and the mating part are not on one axis), there is a matching clearance between the side plate (material 40Cr or 45), when starting up, Leakage due to the action of the recoil of the rubber. The temperature does not exceed 100 °C. The company has previously repaired other products, only 1 to 2 days, using polymer materials to repair can solve this problem.

Extruder feed section side cover thread damage (sliding wire)
During the pre-tightening of the bolt, the bolt is deformed by the tensile stress, and its restoring stress is tightly connected with the sealing part to which it is attached, and is stretched over time, partially stretched and deformed. It becomes permanent deformation, and the stress is reduced. As a result, stress relaxation and torque drop occur, and bolt looseness occurs, causing the thread to wear the thread, and even causing damage to the internal thread of the fastened component. It is repaired with Mikawara polymer materials, which has the concession of metal, which guarantees the recovery stress after repair and ensures the use of components. At the same time, the non-metallic nature of the material itself makes it more sturdy than metal, eliminating the damage caused by loosening and ensuring the safe and continuous production of the enterprise.


Extruder gearbox repair

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