Leakage of oil pressure in machines is a common fault phenomenon, that affects the system’s normal operation and product quality for injection molding machines.
The oil pressure leakage of injection molding machines is the result of the coupling of multiple factors, and needs to be solved comprehensively from the aspects of hydraulic system buffer design, seal selection, precise control of process parameters and manufacturing process upgrade. Evidence shows that optimizing heat treatment can eliminate coolant leakage economically and efficiently, while hydraulic shock and seal failure require targeted improvement of structural design.
Internal leakage of oil pressure elements for injection molding machine reasons and their solutions can be analyzed as below:
Internal leakage of oil pressure element for injection molding machine reasons
Leakage of oil pressure in injection molding machines reasons
Hydraulic shock causes pipeline rupture
When the injection molding machine opens and closes the mold, the electro-hydraulic valve frequently changes direction. The instantaneous hydraulic shock can cause the system pressure to surge to several times the normal working pressure (normal working pressure is 7 MPa), causing the copper pipe joint to burst and leak oil.
The hydraulic shock energy exceeds the oil pipe’s bearing limit, causing oil loss and shutdown.
Seal failure
- Reciprocating seal leakage: The higher the surface roughness of the seal, the greater the leakage; the leakage is highest at low speed and zero at the critical speed. The sealing pressure is constant in injection molding applications (6.90 MPa).
- O-ring dynamic leakage: In reciprocating motion, the leakage is proportional to the square of the movement speed and is affected by the oil viscosity and material hardness. When the material hardness is insufficient, it is easy to deform and fail under high pressure (statically can withstand 280 kg/cm², but dynamic leakage is significant).
- Plug seal failure: Under high-pressure hydraulic oil, the uneven distribution of contact pressure leads to a decrease in sealing performance, especially the inertial force generated by the hydraulic pressure rise rate will aggravate the leakage.
Improper process parameters
- When the melt temperature is too high or the injection pressure is too high, the melt fluidity increases and it is easy to leak from the parting surface to form flashing. When the clamping force is insufficient, the melt expansion force will push the mold open.
- Wrong parameter settings (such as insufficient injection pressure) will lead to short shots, while coolant leakage will extend the cooling time (from 22 seconds to 39 seconds) and aggravate defects.
Structural gaps and manufacturing defects
The radial gap between the screw and the housing (about 1 mm) causes oil retention, resulting in 60% of the gap being filled with oil film, but there is still leakage at the rear.
When the cooling channel density is insufficient, the coolant leaks from the pores, affecting the mold temperature control and causing short shots.
Solution of leakage of oil pressure in machines
Suppress hydraulic shock
Add damping holes, throttle valves or increase the diameter of the oil pipe to shorten the length of the pipeline to absorb the impact energy.
Optimize seal design
- Select high-hardness O-ring materials (reduce dynamic leakage)
and control the surface roughness of the seal - Optimize the plug contact pressure distribution and reduce the hydraulic pressure rise rate.
Adjust process parameters
- Control the melt temperature (recommended 180–230°C), reasonably match the injection pressure (such as 60 bar) and the clamping force.
- Avoid low-speed movement and ensure that the critical speed is reached to eliminate leakage.
Improve manufacturing process
- Solution + aging treatment (SAT) of metal printing molds to increase hardness (from HV 189 to HV 546) and reduce porosity (pore size is significantly reduced), thereby eliminating coolant leakage
- This method saves 38% production time and 46% cost compared to high-density parameter molds
Structural optimization
Reduce the radial clearance of the screw and use oil film filling to reduce leakage.
Improve the design of mold exhaust system to prevent the melt from flowing into the exhaust channel.
Impact of leakage
Production defects
Leakage causes defects such as flash, short shots, and black spots, which require additional cleaning or scrapping.
Decreased efficiency
Coolant leakage nearly doubles the cooling time (e.g. 22 seconds → 39 seconds), slowing down the production rhythm.
Increased energy consumption
Leakage in the compressor reduces volumetric efficiency and adiabatic efficiency.
Haichen injection molding machine
We are Haichen, one Chinese injection molding machine manufacturer for more than 10 years. Our injection molding machines’ quality is under CE certificate servo injection molding machines.
We adopt imported multi-layer steel wire hose, that withstands high-pressure 42mpa; high-pressure hose for oil pipelines adopts an H-type interface. Through these, we can ensure the normal operation and production efficiency of the equipment
Through the above measures, the internal leakage of the oil pressure element for the injection molding machine can be effectively reduced. And the stability and working efficiency of the system can be improved.
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Haichen have rich experience of producing plastic products, with successfully cases for your reference. We can supply complete production line as per customer’s specific demand.
Consider the above. You can choose a suitable plastic injection molding machine and mold to ensure product’s quality and production efficiency.
