I. Injection Molding Machine: The Most Complex Plastic Machinery

The injection molding machine is one of the most complex equipment in the plastic processing industry. A standard injection molding machine has bearings distributed in three completely different working areas: the mold closing unit bears the huge clamping force and impact load, the injection unit undergoes high-frequency reciprocating motion and friction wear, and the hydraulic system operates continuously under high pressure.

 

The working conditions in these three areas are vastly different. The bearings in the mold closing mechanism need to maintain rigidity under low-speed heavy loads, while the thrust bearings of the injection screw need to maintain accuracy under high-speed reciprocating motion and withstand the back pressure and axial thrust of the molten plastic. The bearings in the hydraulic pump and motor need to operate continuously under high pressure, high temperature, and high contamination oil.

 

A single unplanned shutdown of the injection molding machine not only means the loss of production during the shift but also implies that the mold being molded may be damaged - the value of a precise mold is often several times that of the injection molding machine itself. NMT's dedicated bearing solutions provide systematic precision support solutions from cylindrical roller bearings, self-aligning roller bearings to angular contact ball bearings for the different working conditions of the mold closing, injection, and hydraulic systems.

 

II. Mold Closing Unit: The Challenge of Low Speed and Heavy Load

The mold closing unit is the part of the injection molding machine that bears the largest load. During the mold closing process, the mold closing mechanism needs to apply hundreds of tons to thousands of tons of clamping force to counteract the huge bulging force of the molten plastic when it is injected into the mold. The bearings in the mold closing mechanism, under low-speed or even stationary conditions, bear extremely high static loads and continuous clamping forces.

 

The core challenge of the mold closing unit bearings

 

The clamping force is transmitted to the bearings through the mold closing mechanism, and the bearings in the mold closing mechanism bear extremely high radial and axial loads under low-speed or even stationary conditions. The lubrication state of the bearings under low-speed heavy-load conditions is extremely demanding - the rotational speed is too low, and the rolling elements cannot form a complete elastic flow lubrication film, and the rolling elements and the raceway may be in boundary lubrication or mixed lubrication states.

 

At the same time, the template undergoes slight elastic deformation under the action of the clamping force, causing the bearings to bear unbalanced loads. If the bearings do not have self-aligning ability or sufficient rigidity reserve, the unbalanced load will cause uneven wear on the raceway, accelerating fatigue spalling.

 

NMT's solution

 

NMT's self-aligning roller bearings are the ideal choice for the mold closing unit. The spherical raceway design allows the bearings to automatically adjust the contact position when the template deforms, distributing the load evenly along the length of the rolling elements, eliminating edge stress concentration. The optimized roller profile and cage design ensure that the bearings can still maintain stable guidance under extremely low rotational speeds.

 

For mold closing structures with higher rigidity requirements, NMT provides high-rigidity cylindrical roller bearing solutions, providing the maximum radial load-bearing capacity through a line-contact structure, combined with precise clearance setting, to maintain the minimum elastic deformation under low-speed heavy-load conditions.

 

III. Injection Unit: Precision and Lifespan in Reciprocating Motion

The injection unit is the part of the injection molding machine with the most frequent motion. In each injection molding cycle, the injection screw advances to inject the molten plastic into the mold, and then retreats to wait for the next batch of plasticized material. This reciprocating motion repeats thousands of times per day, posing extremely high requirements for the wear resistance and fatigue resistance of the bearings.

 

The core challenge of the injection unit bearings

 

The axial force borne by the injection screw comes from two directions: when the injection is forward, the front end of the screw is subjected to the back pressure of the molten plastic; when the plasticizing retreats, the screw is subjected to the reverse thrust generated by the friction of the material. The thrust bearings must have sufficient bearing capacity in both directions.

 

The injection unit's bearings also face temperature challenges. The temperature of the molten plastic is usually between 200°C and 350°C, and the heat is transmitted through the screw to the bearing area, causing the bearing to work at a temperature far higher than that of general industrial equipment. At high temperatures, the grease accelerates oxidation, the bearing clearance changes, and the sealing material ages more rapidly.

 

NMT's response plan

 

NMT angular contact ball bearings provide precise support for the reciprocating motion of the injection screw with high rigidity and low friction characteristics. The large contact angle design provides sufficient axial load capacity, and precise pre-tightening control ensures that the bearings have no backlash during reciprocating alternation. For the high-temperature working conditions of the injection unit, NMT provides high-temperature resistant grease and fluorine rubber seals to ensure that the bearings remain reliable for a long time at temperatures above 150°C.

 

For injection units that need to withstand extremely high axial thrust, NMT provides a thrust angular contact ball bearing solution, with multiple rows of balls to distribute the axial load, extending the service life of the bearings in heavy-load reciprocating conditions.

 

IV. Hydraulic System: Reliability in High Pressure, High Temperature, and High Pollution

The hydraulic system of the injection molding machine is the power source of the equipment, and the hydraulic pumps and hydraulic motors need to operate continuously under high pressure (usually over 20 MPa). The bearings in the hydraulic system not only bear high loads but also need to maintain accuracy in the immersion and flushing of hydraulic oil.

 

Core challenges of hydraulic system bearings

 

Hydraulic oil is both the transmission medium and the lubricant for the bearings. However, hydraulic oil is not an ideal lubricant for bearings - its viscosity is usually low, and the formed oil film thickness is limited. Under high pressure, the contact stress of the bearings increases, and the oil film thickness is insufficient to completely separate the rolling elements and raceways, increasing the risk of metal direct contact.

 

Pollutants in the hydraulic system are another threat. During long-term circulation, hydraulic oil may mix with metal particles, sealing debris, and external dust, which enter the bearings under the drive of high-pressure oil, accelerating the wear of the raceways.

 

NMT's response plan

 

NMT hydraulic system-specific bearings use high-purity bearing steel and special heat treatment processes to maintain sufficient hardness and fatigue resistance under high-pressure heavy-load conditions. The optimized raceway contour design ensures uniform contact stress distribution, even in the boundary lubrication state with insufficient oil film thickness, delaying the initiation of fatigue cracks.

 

For the polluted environment of the hydraulic system, NMT provides a strengthened sealing bearing solution to effectively prevent pollutant intrusion. At the same time, NMT recommends installing efficient filters in the hydraulic system to control the cleanliness of the oil to NAS 7 or better, to extend the service life of the bearings.

 

V. Typical Failure Modes and Prevention of Injection Molding Machine Bearings

Fatigue spalling caused by clamping force

 

The bearings of the clamping unit accumulate fatigue damage on the sub-surface of the raceway under the continuous clamping force. Preventive measures include: selecting bearings with sufficient rated load, ensuring uniform distribution of clamping force, and regular inspection of template parallelism and clamping force balance.

 

Wear caused by reciprocating motion

 

The bearings of the injection unit may experience abnormal wear on the raceway surface due to insufficient lubrication or contamination during high-speed reciprocating motion. Preventive measures include: selecting bearing materials with excellent anti-wear performance, ensuring adequate lubrication, and regular replacement of hydraulic oil and filters.

 

Lubrication failure caused by high temperature

 

The high-temperature environment of the injection unit and the hydraulic system accelerates oxidation of the grease, reduces viscosity, and thins the oil film. Preventive measures include: selecting high-temperature resistant grease, considering heat dissipation channels in the bearing housing design, and using forced cooling when necessary.

 

Retention ring damage caused by impact load

 

The impact load during the clamping action and injection action may cause additional stress on the retention ring. Preventive measures include: selecting high-strength retention ring materials, setting reasonable acceleration and deceleration curves in the control system, and avoiding mechanical hard impact.

 

VI. NMT Injection Molding Machine Bearings Selection and Technical Support

NMT's understanding of injection molding machine bearings goes beyond the traditional mode of "providing bearings", extending to the engineering service dimension of "participating in injection molding machine design": Molding unit selection: Based on the locking force, template weight, and molding speed, the most suitable types, sizes, and clearance groups of self-aligning roller bearings or cylindrical roller bearings are recommended.

 

Injection unit selection: According to the injection pressure, screw diameter, and reciprocating frequency, the most suitable angular contact ball bearings or thrust bearings scheme is recommended, along with suggestions for preload and clearance settings.

 

Hydraulic system selection: Based on the system pressure, flow rate, and cleanliness requirements of the oil, suitable hydraulic pump and motor bearing schemes are recommended, along with suggestions for lubricants.

 

High-temperature sealing solution: For the high-temperature environment of the injection unit and hydraulic system, suitable sealing materials (such as fluororubber) and high-temperature lubricants are recommended.

 

VII. Core application map of NMT injection molding machine bearings

Molding unit: Crosshead guide bearing, mold locking cylinder ear shaft bearing, template support bearing. NMT self-aligning roller bearings and cylindrical roller bearings provide high rigidity and anti-bias load capacity under low-speed heavy-load conditions.

 

Injection unit: Injection screw thrust bearing, injection seat moving guide bearing. NMT angular contact ball bearings and thrust bearings provide high precision and low friction support in high-speed reciprocating motion.

 

Hydraulic system: Variable pump bearing, hydraulic motor bearing, directional valve valve core support bearing. NMT hydraulic special bearings maintain long-term reliability in high-pressure, high-temperature, and high-contamination environments.

 

Ejection unit: Ejection cylinder bearing, ejection rod guide bearing. NMT bearings maintain stable motion accuracy in frequent start-stop and impact loads.

 

VIII. Lifetime value of NMT injection molding machine bearings

The downtime cost of injection molding machines is extremely high - not only does it result in the loss of production during the shift, but it also poses the risk of mold damage and the time cost of re-tuning. The reliability of injection molding machine bearings directly determines whether equipment managers can advance the maintenance cycle from "emergency repair" to "planned maintenance".

 

NMT injection molding machine bearing solutions cover the bearing requirements of every critical rotating part of the injection molding machine, from the anti-bias load self-aligning roller bearings of the molding unit, to the high rigidity angular contact ball bearings of the injection unit, and to the high-temperature resistant sealing bearings of the hydraulic system.

 

In the molding unit, NMT self-aligning roller bearings' spherical raceways automatically compensate for template deformation. In the injection unit, NMT angular contact ball bearings' precise preload ensures the positioning accuracy of reciprocating motion. In the hydraulic system, NMT sealing bearings maintain long-term reliability in high-pressure, high-temperature, and high-contamination environments.

 

Choosing NMT injection molding machine-specific bearings is to select a verified precise support solution for each of the three systems of the injection molding machine - ensuring each mold locking is tight, each injection is precisely measured, and each molding cycle is stable and reliable.