A Customer Case on Hardness, Pressure, Preload and Mold Conditions
When a self-locking hydraulic cylinder fails, the most obvious question is often:
Why did the cylinder break?
The answer, however, is rarely found by looking only at the broken component.
A proper failure analysis must consider the complete application: operating pressure, preload, mold geometry, slide weight, cylinder orientation, number of cycles, assembly conditions and the characteristics of the locking components.
A real Customer application analyzed by the Vega Team provides an interesting example of this approach.
The Customer reported a broken metal component inside a V260CF self-locking hydraulic cylinder. The cylinder had been installed on a new mold and had completed fewer than 25,000 cycles before the failure occurred.
The Vega Team inspected the cylinder, checked the components and carried out a metallographic hardness test on the locking component. The measured hardness was 51.5–52 HRC, within Vega’s specified range of 48–52 HRC.
The initial investigation therefore did not identify an obvious manufacturing non-conformity.
This case demonstrates an important engineering principle:
A broken component does not automatically mean that the component was defective. The complete operating environment must be investigated before the root cause can be established.
1. The Customer’s Problem
The Customer reported that a metal component had broken inside a V260CF self-locking hydraulic cylinder.
The cylinder was returned for inspection and repair, while the Customer also questioned whether the failure should be considered a warranty issue.
This created two separate technical objectives:
- restore the cylinder to operation as quickly as possible;
- determine the actual cause of the failure.
These two objectives should not be confused.
A cylinder can be repaired while the root-cause investigation is still underway.
The technical investigation requires additional information about the application and operating conditions.
2. The First Vega Team Inspection
After receiving the cylinder, the Vega Team inspected the internal components.
At this stage, the actual cause of the failure was not clear.
The components were checked against the relevant drawings and construction specifications, and no obvious non-conformity was identified.
This is an important step in any failure investigation.
Before assuming that a component failed because of a material or manufacturing defect, the investigation should verify:
- geometry;
- dimensions;
- material;
- heat treatment;
- hardness;
- assembly conditions;
- operating conditions.
In this case, the initial inspection did not reveal an evident manufacturing problem.
3. Metallographic Hardness Testing
The Vega Team sent the locking component to a metallographic laboratory to verify its hardness.
The measured value was:
51.5–52 HRC
The specified Vega range was:
48–52 HRC.
The measured value was therefore within the specified range.
This is an important finding because it indicates that the locking component was not outside the specified hardness range.
However, a correct hardness value does not by itself identify the cause of a fracture.
It only confirms that the measured hardness was compliant.
The operating conditions still had to be investigated.
4. Why Hardness Is Only One Part of the Investigation
A mechanical component can be correctly manufactured and correctly heat-treated but still fail if the application generates unexpected loads.
For this reason, failure analysis should distinguish between:
component conformity
and
application conformity.
The first concerns the cylinder itself.
The second concerns the way the cylinder is installed and operated.
The Vega Team therefore requested additional information about the complete mold and operating conditions.
5. Operating Hydraulic Pressure
One of the first questions concerned the hydraulic pressure used by the Customer.
The Customer reported a typical pressure of:
2,200 psi
which is approximately:
152 bar.
The Customer also confirmed that pressure was maintained during the injection phase.
This information is important because a self-locking cylinder in an injection mold can be subjected to significant forces while the mold is under injection pressure.
The analysis therefore cannot focus only on the pressure used to move the cylinder.
The conditions during the holding/locking phase must also be considered.
6. Movement Pressure Versus Holding Conditions
There are two fundamentally different operating situations:
Cylinder movement
Hydraulic pressure is used to move the piston and rod into the required position.
Mold injection
The mold component must remain accurately positioned while injection pressure acts on the mold.
A mechanical-locking hydraulic cylinder is designed specifically to provide mechanical holding rather than relying exclusively on hydraulic pressure.
Vega’s current self-locking technology uses a mechanical locking system between the rod and cylinder body. The system is designed for applications where mold components must remain mechanically locked and withstand injection forces.
7. The Importance of Preload
The Vega Team also requested information about the preload.
The Customer reported a preload of approximately:
0.002–0.003 in
or approximately:
0.05–0.076 mm.
The Vega Team subsequently confirmed that the working pressure and preload were within the expected parameters.
Preload is an important parameter in mold applications because it can help eliminate small clearances between the moving mold component and the surrounding mold structure.
8. Why Preload Matters in Injection Molding
During injection, pressure is exerted on the mold components.
Even very small movements can become important when the mold contains a precision sliding component.
If a small gap develops between the moving component and the mold, plastic material can enter that gap and potentially create a flash or burr on the molded part.
Vega’s self-locking technology uses the mechanical locking capability of the cylinder to support preload applications. The current Vega documentation specifically describes preload as one of the applications of the self-locking system.
The mechanical lock allows the cylinder to maintain the component position with very little dependence on continuous hydraulic pressure.
9. The Number of Cycles
The Customer reported that the cylinder had completed:
less than 25,000 cycles
and that the cylinder had failed on a brand-new mold.
This is a significant piece of information.
A failure after a very high number of cycles may lead an engineer to investigate long-term fatigue, wear or progressive degradation.
A failure on a new mold after fewer than 25,000 cycles requires particular attention to:
- initial installation;
- alignment;
- preload;
- operating conditions;
- assembly;
- unexpected loads.
However, the number of cycles alone cannot establish the cause.
It is an important diagnostic parameter, not a diagnosis.
10. Slide Weight
The Customer reported that the slide weighed less than:
5 lb
or approximately:
2.27 kg.
This indicates that the static weight of the slide was relatively low.
However, the static weight of a slide is not necessarily the dominant load acting on a hydraulic cylinder.
Other forces may result from:
- injection pressure;
- friction;
- mold geometry;
- preload;
- acceleration and deceleration;
- guide friction;
- misalignment.
Therefore, slide weight must be considered together with the other application parameters.
11. Cylinder Orientation
The Customer also provided detailed information about the installation.
The cylinders were mounted vertically:
- two cylinders were installed on the top of the mold, with the piston rods pushing downward;
- two cylinders were installed on the bottom of the mold, with the piston rods pushing upward.
The Vega Team specifically requested this information because mounting orientation can be relevant when investigating a mechanical failure.
The orientation of the cylinder can affect:
- load distribution;
- slide movement;
- guide conditions;
- possible lateral forces;
- preload behavior;
- mechanical alignment.
12. Why Vega Requested the 3D Mold Model
The Vega Team requested the 3D model of the mold and the plastic component.
This request is particularly significant.
A hydraulic cylinder does not work in isolation.
To understand the actual forces acting on the cylinder, the complete mechanical system may need to be examined:
cylinder → slide → mold components → plastic part
The 3D geometry can reveal conditions that are not obvious from a simple cylinder drawing.
For example:
- cylinder alignment;
- slide geometry;
- guide arrangement;
- connection points;
- possible eccentricity;
- movement direction;
- interference;
- contact surfaces.
13. Why the Plastic Part Is Also Relevant
The Vega Team noted that the available drawing did not include the 3D model of the plastic component and requested it from the Customer.
The plastic part can be relevant because its geometry determines how the molding forces are transmitted to the moving components.
Its geometry may influence:
- contact area;
- pressure distribution;
- undercuts;
- extraction forces;
- slide loading.
Without the complete geometry, it can be difficult to reconstruct the real load path.
14. The Air-Pressure Test
The Vega Team also asked whether the Customer had tested the cylinder on the mold using air pressure.
The answer was:
No, the cylinder had not been tested with air.
This question demonstrates the importance of understanding how the cylinder was commissioned and tested before full operation.
A preliminary test under controlled conditions can sometimes help distinguish a cylinder problem from an application problem.
However, the documentation for this Customer case does not provide a complete Vega test procedure.
Therefore, the case should not be interpreted as establishing a universal requirement that every cylinder must be tested with air.
15. Was the Cylinder Manufactured Correctly?
The Vega Team checked the cylinder components and reported that they complied with the relevant drawings and construction specifications.
The metallographic test also showed that the locking component had a hardness of:
51.5–52 HRC
against a specified range of:
48–52 HRC.
These findings did not identify an obvious manufacturing non-conformity.
That does not mean that every possible failure mechanism had been eliminated.
It means that the documented checks did not identify an evident deviation in the inspected components.
16. Component Conformity Versus Application Conditions
This distinction is particularly important for hydraulic cylinders.
A component can comply perfectly with its manufacturing specifications while the application can still create unexpected loads.
For example:
correct component
does not automatically mean:
correct installation and operating conditions.
This is why professional failure analysis considers both sides.
Product
- material;
- geometry;
- hardness;
- manufacturing tolerances;
- assembly.
Application
- pressure;
- preload;
- alignment;
- slide geometry;
- mold design;
- operating cycle.
17. An Additional Question: Cylinder Assembly
The Customer also asked about the torque required to assemble the two halves of the cylinder.
The reason was that some cylinders were difficult to separate after operation.
The Customer asked whether heat, cold or simply a large amount of force should be used to separate the two halves.
The Vega Team explained that the V260 did not have a specified assembly torque.
The two bodies were assembled using a wrench, while larger cylinders could require a wrench with an extension.
18. Why Large Cylinders Can Be Difficult to Disassemble
The Vega Team explained that after a cylinder has operated for a long period, considerable force may be required during disassembly.
For larger bore cylinders, a wrench extension may be necessary, and in some situations the combined effort of two or three people may be required.
The communication also mentions a historical example in which a large cylinder used for a long period on a die-casting mold could not be opened even after using a blowtorch.
This historical example should not be confused with the Customer’s failure.
It was cited as general practical experience concerning cylinder disassembly, not as the identified cause of the broken component.
19. Why a Failure Investigation Must Avoid Premature Conclusions
When a component breaks, it is tempting to immediately select a cause:
- defective material;
- excessive pressure;
- incorrect preload;
- incorrect assembly;
- excessive load;
- fatigue;
- misalignment.
A professional investigation should instead collect evidence before reaching a conclusion.
In this case, the Vega Team requested information concerning:
- hydraulic pressure;
- pressure during injection;
- number of cycles;
- slide weight;
- mounting orientation;
- preload;
- mold 3D geometry;
- plastic component geometry;
- component hardness.
This is a classic failure-analysis approach.
20. A General Failure-Analysis Procedure
The Customer case provides a useful methodology for investigating hydraulic-cylinder failures.
Step 1 — Identify the failed component
Determine exactly which component has broken.
Step 2 — Document the fracture
Record photographs, fracture location and component condition.
Step 3 — Inspect the component
Check dimensions, geometry and visible damage.
Step 4 — Verify material and hardness
Compare measured values with the technical specification.
Step 5 — Reconstruct operating conditions
Check pressure, preload, temperature, cycles and operating sequence.
Step 6 — Check installation
Review orientation, alignment, guides and connections.
Step 7 — Analyze the mold
Use the 3D mold model when necessary.
Step 8 — Analyze the molded component
Check how the geometry transfers loads to the moving mechanism.
Step 9 — Compare the complete data set
Only after all these steps should a root-cause hypothesis be established.
21. Why 3D Geometry Can Be Decisive
The 3D mold model is not only a design tool.
It can also become a diagnostic tool.
It allows the engineering team to investigate:
- cylinder axis;
- slide movement;
- guide arrangement;
- connection geometry;
- possible eccentric loads;
- clearances;
- contact surfaces.
In this case, the Vega Team explicitly requested the 3D mold and plastic-part drawings because the available information was not sufficient to understand the cause of the failure.
22. Why Pressure Alone Cannot Explain the Failure
The Customer was operating at approximately 2,200 psi, with pressure maintained during the injection phase.
It would therefore be tempting to conclude that pressure caused the failure.
But the Vega Team specifically stated that the working pressure and preload were in line with the expected parameters.
This is an important engineering lesson:
A parameter should only be considered abnormal after it has been compared with the relevant specification.
A pressure value by itself is neither “safe” nor “dangerous” without knowing the cylinder and application requirements.
23. The Importance of Cycle Count
The cylinder failed after fewer than 25,000 cycles.
Cycle count is an important parameter when evaluating:
- fatigue;
- wear;
- repeated loading;
- component life.
However, cycle count cannot be interpreted independently.
Two cylinders can experience the same number of cycles while being subjected to completely different load histories.
For this reason, the number of cycles should always be evaluated together with the actual operating conditions.
24. Mechanical Locking in Injection Molds
The V260CF belongs to Vega’s mechanical-locking cylinder technology.
The basic principle is to mechanically lock the rod to the cylinder body once the required position is reached.
Vega’s current V270CG series uses a similar mechanical-locking concept and is designed for accurately moving and locking carts, pins and plugs in plastic injection molds, particularly where the component must withstand injection pressure.
The current V270CG is available in standard bore sizes from 30 to 84 mm and strokes from 30 to 150 mm, according to Vega’s current product documentation.
25. How the Mechanical Locking System Works
Vega’s current documentation explains that the rod-piston assembly incorporates a floating piston and high-resistance floating sectors.
When the rod reaches the locking position, the geometry of the piston causes the sectors to expand into a groove in the cylinder body.
The load is then transferred mechanically through the locking components and reinforced cylinder body rather than relying exclusively on hydraulic pressure.
This principle is particularly useful in injection molds where the mold component must remain accurately positioned while injection pressure is applied.
26. Mechanical Locking and Preload
The same mechanical-locking principle also makes it possible to apply preload.
Vega’s current documentation explains that a preload configuration can be used to compensate for small clearances between the mold components.
This can help prevent the formation of unwanted gaps during injection and therefore reduce the risk of plastic flash.
The Customer case is particularly interesting in this context because preload was one of the parameters specifically investigated by the Vega Team.
27. What This Case Teaches Mold Designers
The case shows that selecting a self-locking cylinder is only one part of the engineering process.
The designer must also consider:
- cylinder orientation;
- slide weight;
- mold geometry;
- preload;
- injection pressure;
- cylinder alignment;
- operating sequence;
- number of cycles.
The Vega Team’s request for all these parameters demonstrates the importance of analyzing the cylinder as part of the mold system, rather than as an independent component.
28. The Most Important Lesson: Do Not Invent a Root Cause
The available documentation does not contain a final technical report establishing one definitive root cause for the failure.
The Vega Team initially stated that there was not enough information to explain the problem.
At the same time, the documented investigation established that:
- the inspected components complied with the drawings and construction specifications;
- the locking component hardness was 51.5–52 HRC, within the specified 48–52 HRC range;
- working pressure and preload were reported as being within Vega’s parameters.
Therefore, it would not be technically correct to claim that the documentation proves a specific root cause.
And this is itself an important lesson in engineering failure analysis.
29. A Better Way to Investigate Hydraulic-Cylinder Failures
A professional investigation should move through three levels.
Level 1 — The component
Is the cylinder manufactured according to specification?
Check:
- material;
- hardness;
- dimensions;
- geometry;
- heat treatment.
Level 2 — The operating conditions
Is the cylinder being operated within its intended parameters?
Check:
- pressure;
- preload;
- temperature;
- speed;
- cycles;
- hydraulic fluid.
Level 3 — The application
Is the mold generating unexpected loads?
Check:
- alignment;
- guides;
- slide geometry;
- mold structure;
- plastic-part geometry;
- mounting arrangement.
Only when all three levels have been investigated can the root cause be established with confidence.
Conclusion
The Customer case involving a damaged V260CF self-locking hydraulic cylinder is an excellent example of why hydraulic-cylinder failures should be investigated systematically.
The Customer reported a broken internal metal component and believed that the problem could potentially be a warranty issue.
The Vega Team inspected the cylinder and found that the components complied with the relevant drawings and construction specifications.
A metallographic hardness test showed a value of 51.5–52 HRC, within the specified 48–52 HRC range.
The Customer also reported:
- approximately 2,200 psi operating pressure;
- pressure maintained during injection;
- fewer than 25,000 cycles;
- slide weight below 5 lb;
- vertical cylinder installation;
- approximately 0.002–0.003 in preload.
The Vega Team also requested the 3D geometry of the mold and plastic component because the cylinder could not be analyzed independently from the application.
Most importantly, the documented investigation does not establish a definitive root cause.
That distinction is essential.
A good failure analysis does not force a conclusion when the evidence is insufficient. It identifies what has been verified, what has been ruled out, and what additional information is still required.
For self-locking hydraulic cylinders used in injection molds, this means analyzing the complete system:
cylinder → locking mechanism → preload → slide → mold → injection pressure → plastic component.
This approach allows mold builders and hydraulic-cylinder manufacturers to distinguish between a component non-conformity and a problem originating from the application.
Useful and Verified URLs
1. Mechanical-Locking Hydraulic Cylinders
Official Vega page explaining the mechanical-locking technology and its application in plastic injection molds.
Mechanical-Locking Hydraulic Cylinders – Vega Cylinders
2. Self-Locking Hydraulic Cylinders
Official Vega technical page explaining how the self-locking system works, including the mechanical locking principle and preload application.
Self-Locking Hydraulic Cylinders – Vega Cylinders
3. V270CG Self-Locking Hydraulic Cylinder
Official product page for the current V270CG self-locking hydraulic cylinder, including bore and stroke options and integrated end-stroke sensing.
V270CG Self-Locking Hydraulic Cylinder – Vega Cylinders
4. Hydraulic Cylinders for Molds
Official Vega category covering hydraulic cylinders for plastic injection and die-casting molds, including the Mechanical-Locking category.
Hydraulic Cylinders for Molds – Vega Cylinders
5. Hydraulic Cylinders Catalog
Official Vega catalog page with the different cylinder families organized by application, including Mechanical Locking.
Hydraulic Cylinders Catalog – Vega Cylinders
6. Custom Hydraulic Cylinders
Official Vega page for custom hydraulic-cylinder solutions when a standard configuration does not meet the application requirements.
