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Step-by-step Guide of Plastic Extruder Gearbox Repair


The power extruder is an important piece of equipment for the production of polypropylene pellets. And polypropylene film. because it requires a long-term continuous high-load operation. Works in a high-temperature and heavy-load environment. Therefore, the core component of the power extruder is the reducer gearbox. Quality is especially important. andWe also encounter Extruder Gearbox Repair. In the following case analysis. there is a high-power extruder in the polypropylene film production line introduced for the user. After more than 3 years of use, the situation is basically normal. But recently, the main gearbox gear damages suddenly, causing the device to shut down for many days.

During this period, engineers and technicians adopted various solutions through various efforts. And finally restored the main extruder gearbox to normal operation. But in the process of processing, there are also mistakes and detours. Therefore, through this article, let us understand 5 important points

In this content we will share a real -case about  Extruder Gearbox Repair step by step:

1.Analysis of the causes of gearbox damage

2.Gear repair process detailed explanation

3.How to reduce gearbox damage

4.KONIC provides professional gearbox repair service for you

5.Extruder gear box repair needs attention

Extruder Gearbox Repair

Analysis of the Causes of Gearbox Damage

Incident Process and Countermeasures

The water-cooled motor with a rated power of 900kw of the extruder drives the output of a gearbox with a rated power of 1058kw. It drives the twin-screw extruder to extrude molten polypropylene material. With a maximum extrusion rate of 3.5 tons/hour. There is a special lubricating oil pump system for circulating lubrication inside the gearbox. Under normal working conditions. The lubricating oil temperature is between 40 °C and 55 °C, the pressure difference between the front and rear of the oil filter is not more than 7bar. And the outlet pressure of the oil filter is not less than 3bar. When the oil temperature exceeds 80 ℃ or the oil pressure after the oil filter is lower than 0.5bar, it will interlock and stop.

The Operators found Problems

The operator found that the lubricating oil temperature of the gearbox of the extruder increased rapidly. From the normal 48 ℃ to 70 ℃. the lubricating oil filter replaces according to the operating procedures. And the lubricating oil temperature dropped to 55 °C. Two days later. The oil temperature of the gearbox rose to 76°C. The operator cleaned the breathing valve of the gearbox. And replaced the lubricating oil filter. And the temperature of the gearbox dropped to 48°C. During operation. The oil temperature of the gearbox will rise from time to time. And the pressure difference between the oil pressure before and after the filter also tends to rise many times.

damage Extruder Gearbox Repair


During the maintenance, the gearbox opens for inspection, and it founds that a group of gears damages to varying degrees and coked. The analysis causes by insufficient lubrication. Then, the lubricating oil pipeline in the gearbox inspectes and found at a high-end key point of the lubricating oil pipeline. There is no oil injection hole, which causes a group of gears here to be poorly lubricated. resulting in high-temperature coking and gear damage. And there are many gear fragments at the bottom of the gearbox. Some of which are still very clean, it should be that the gears were damaged during the initial operation of the new gearbox.

Extruder Gearbox Repair Process Detailed Explanation

When the lubricating oil temperature of the gearbox founds. It should not stop and checked out of the box in a timely manner. which will easily cause the gears in the gearbox to continue to damaged.

If it founds that there is coke inside the gearbox, it should dealt with in time. Since the lubricating oil washes down from the new opening at the high point of the lubricating oil pipeline. It enters the entire gearbox and blocks the lubricating oil pipeline. resulting in sharp damage to the gear and bearing, resulting in downtime.

damage plastic extruder gearbox
damage plastic extruder gearbox

It founds that the overpressure one-way valve in the pipeline of the lubricating oil system was in an internal leakage state. And the one-way valve connected in parallel with the filter opened after the pressure rose. It was stuck by impurities in the lubricating oil, resulting in a normally open state. After the one-way valve, the lubricating oil directly enters the gearbox without passing through the filter. and heat exchanger, which will cause the lubricating oil with gear wear impurities to circulate in the gearbox. pollute the entire gearbox and lubrication system, and cause a vicious circle. , not only aggravated gear damage but also damaged all bearings in the gearbox.

Extruder Gearbox Repair Need to Consider

Most of the extruder gearboxes in China are still at the level of the old generation. With relatively low bearing capacity or low torque level. (such as gearboxes with one-sided parallel drive structure). which are far behind the current international mainstream high-tech gearboxes. Torque gearboxes (e.g. double-sided gear symmetrical drive gearboxes). In order to meet some high requirements. such as the production of polyoxymethylene. domestic plastic manufacturers must choose foreign polyoxymethylene polymerizers. with more power and better stability.

What should I do if the imported extruder gearbox brokes?

This problem seems to be very simple: the gearbox brokes, of course, the original factory has to repair it. and if it fails, replace it with a gearbox. Indeed, in theory, this should do. However, the reality is not so simple. For most plastics manufacturers, production is a continuous, high-volume process. They want the gearbox to repair as early as possible with as little impact on production as possible.

The replacement and maintenance costs of foreign original factories are high and the time is long.

However, because the headquarters. factories of foreign large-scale extruder suppliers are generally not located in China. At most they set up offices in first-tier cities in China. when plastic production or processing plants have broken gearboxes, etc. When there is a big problem. The personnel in the office are generally sales engineers. cannot handle such problems. this requires contacting relevant foreign technical personnel to solve the problem, so that things that can solve in one day may take 4 or 5 days. , thus seriously affecting normal production.

Reliable Domestic High Torque Extruder Gearbox

The replacement and maintenance of well-known domestic manufacturers is a new solution. Comparison of before and after gearbox maintenance. With the rapid development of domestic machinery. Although high-torque extruders. (such as polyoxymethylene polymerizers, etc.) may not be available in China at present. Some key parts such as gearboxes Parts have been able to replace foreign parts. This provides a better solution for problems such as imported extruder gearboxes!

Extruder Gearbox Repair

Domestic gearbox suppliers redesign and process gears, gear shafts. All internal parts in the box on the basis of the original box, and replace all severely worn bearings and oil seals in the gearbox. In addition, the gearbox supplier also redesigned a new replacement gearbox. According to the installation size of the original gearbox.

How to Reduce Gearbox Damage ?

Modified the unreasonable design of its bearing directly wearing the output shaft. Using a bearing with an inner ring to make the output shaft It will not be directly worn. The small radial force on the output shaft in the original design changes to zero radial force, which improves the design. After the gearbox installing. The installation size of the original gearbox is completely restored, the operation is stable. The vibration is small, the noise meets the user’s requirements. The full-load operation reaches the bearing capacity of the original gearbox.

After assembly and trial and two fine adjustments, the new gearbox finally reached a better state. After various load tests, the inspection is normal, and it can run normally under the monitoring state.

Extruder Gearbox Repair Needs Attention

Do not blindly believe in the reliability of imported gearboxes. During the warranty period, a foreign person must be present. At least once to confirm the status after the trial operation and solve problems in time.

When the temperature of the gearbox lubricating oil rises repeatedly, it must stop in time for a thorough inspection. If the cause is not identified, it cannot start without reliable measures.

At present, the domestic laser fusion technology is not suitable for the repair of the inner gear of the heavy-duty gearbox.

Whether the equipment can be properly operated and used has a great influence on whether the equipment can run for a long time.


The repair of the high-power extruder gearbox is still quite difficult in China at present. Therefore, the inspection before the operation of the equipment. The monitoring during the operation should make the equipment operate normally as much as possible. Before the operation, it is necessary to confirm whether the lubrication system is perfect. During operation, it is necessary to monitor whether the lubrication system is normal. The temperature, pressure, and regular sampling and analysis of the quality of the lubricating oil. It uses as monitoring methods. Once any abnormal phenomenon found, it should stop and checked in time.

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