How adhesion force, contact surface and hydraulic pressure influence cylinder selection
Selecting the correct hydraulic cylinder for an injection mold is not simply a matter of choosing the largest available bore.
When a hydraulic cylinder is used to extract a molded component or core, the cylinder must overcome the adhesion between the plastic material and the steel surface of the mold.
This makes the contact surface, the adhesion coefficient and the available hydraulic pressure critical elements of the cylinder-sizing process.
A real application analysed by the Vega Team provides a practical example of this engineering approach.
The Customer was working on an injection-molding application using PA GF40%, a glass-fiber-reinforced polyamide containing 40% glass fiber. The Customer asked the Vega Team to evaluate the appropriate cylinder bore, specifically whether a 50 mm or 63 mm bore would be suitable. The Customer was also preparing a quotation for 14 cylinders and needed to know the maximum possible oil-passage diameter for the selected V450CM configuration.
The Vega Team analysed the total surface involved and calculated the pulling force using two different adhesion coefficients.
The case demonstrates a fundamental principle:
Hydraulic-cylinder sizing for plastic-part extraction must consider the adhesion force between the molded component and the steel surface, not simply the injection pressure.
1. The Customer’s Application
The Customer contacted the Vega Team with a technical question concerning the appropriate hydraulic-cylinder bore for the application.
The material to be injected was:
PA GF40%.
The Customer had doubts about whether a 50 mm or 63 mm bore would be the correct solution.
At the same time, the project involved:
14 cylinders
and therefore the Customer also needed information about the maximum diameter that could be provided for the oil delivery passages.
The technical problem therefore had two distinct aspects:
- determining the required cylinder force;
- determining whether the hydraulic connections could provide the required oil flow.
2. Why the Plastic Material Matters
The application involved PA GF40%, meaning polyamide reinforced with 40% glass fiber.
In an extraction application, the hydraulic cylinder must overcome the forces that keep the molded component attached to the steel surface.
These forces can depend on several factors, including:
- plastic material;
- contact surface;
- adhesion;
- shrinkage;
- surface finish;
- mold geometry;
- cooling conditions.
The material is therefore an important part of the engineering analysis.
However, the adhesion coefficients used in this Customer case should be understood as specific calculation assumptions for this application, rather than universal values for every PA GF40% molding application.
3. The Total Surface Considered
The Vega Team calculated the pulling force using a total surface of approximately:
306.6 cm².
This surface was the basis for calculating the extraction load.
The basic engineering principle can be expressed as:
Pulling Force = Contact Surface × Adhesion Coefficient
The resulting force then provides the basis for selecting the hydraulic-cylinder bore and operating pressure.
4. First Scenario: 20 kg/cm² Adhesion Coefficient
The first condition considered by the Vega Team used an adhesion coefficient of:
20 kg/cm².
Using the total surface considered in the application, the technical analysis reported a pulling force of:
6,032 kgf.
This was the higher-load scenario analysed by the Vega Team.
The next step was to determine which hydraulic-cylinder bore could generate this force at an appropriate operating pressure.
5. The CM063 Solution
For the 6,032 kgf pulling force condition, the Vega Team indicated:
CM063
with a minimum working pressure of:
250 bar.
This provided the Customer with one possible solution based on the 63 mm bore class.
The important engineering point is that cylinder bore and hydraulic pressure are directly related.
A larger piston area can generate the required force at a lower hydraulic pressure.
6. The CM080 Alternative
The Vega Team also proposed an alternative solution for the same calculated pulling force:
CM080
with a minimum working pressure of:
150 bar.
The two alternatives therefore represented different combinations of:
cylinder size + hydraulic pressure
For the same required pulling force, the larger cylinder can operate at a lower hydraulic pressure.
This can be particularly relevant when the mold’s hydraulic system operates at a defined pressure level.
7. Second Scenario: 15 kg/cm² Adhesion Coefficient
The Vega Team then considered a second adhesion condition.
The adhesion coefficient was reduced to:
15 kg/cm².
Under this assumption, the calculated pulling force was:
4,599 kgf.
The reduction in the assumed adhesion coefficient therefore resulted in a lower calculated extraction force.
This illustrates how strongly the cylinder requirement can depend on the assumed adhesion conditions.
8. CM063 at 150 bar
For the 4,599 kgf pulling-force condition, the Vega Team indicated that the CM063 could be used at a minimum working pressure of:
150 bar.
Compared with the first scenario, the same cylinder bore could therefore operate at a lower pressure because the calculated pulling force was lower.
9. CM080 at 100 bar
The Vega Team also proposed the larger:
CM080
as an alternative for the same 4,599 kgf condition.
The indicated minimum working pressure was:
100 bar.
The four documented combinations can therefore be summarized as follows:
| Adhesion coefficient | Pulling force | Cylinder | Minimum working pressure |
|---|---|---|---|
| 20 kg/cm² | 6,032 kgf | CM063 | 250 bar |
| 20 kg/cm² | 6,032 kgf | CM080 | 150 bar |
| 15 kg/cm² | 4,599 kgf | CM063 | 150 bar |
| 15 kg/cm² | 4,599 kgf | CM080 | 100 bar |
This table clearly illustrates the relationship between adhesion force, cylinder bore and hydraulic pressure in the Customer application.
10. Why Bore and Pressure Must Be Considered Together
Hydraulic-cylinder force is fundamentally related to piston area and hydraulic pressure:
F = P × A
where:
- F = hydraulic force;
- P = hydraulic pressure;
- A = effective piston area.
Therefore, for a given required force:
larger bore → larger piston area → lower pressure required
while:
smaller bore → smaller piston area → higher pressure required
The Customer case provides a practical example of this relationship.
For the higher adhesion condition, the Vega Team indicated either:
CM063 at 250 bar
or:
CM080 at 150 bar.
11. The Application Involved 14 Cylinders
The Customer was not evaluating a single hydraulic cylinder.
The project involved:
14 cylinders.
This changes the hydraulic-system design requirements significantly.
When multiple cylinders operate within the same mold, the engineer must consider not only the force generated by each cylinder, but also:
- total oil flow;
- oil-passage diameter;
- pressure losses;
- movement speed;
- hydraulic distribution;
- synchronization where applicable.
This explains why the Customer also asked the Vega Team about the maximum possible oil-passage diameter.
12. Oil-Passage Diameter
The Customer specifically asked about the maximum oil-delivery diameter for the:
V450CM 50 E O E G × 120
configuration.
The Vega Team confirmed that the standard oil-passage diameter was:
2.5 mm
while the maximum diameter that could be manufactured was:
3.5–4 mm.
This was an important technical detail because the application involved 14 cylinders.
13. Why Oil-Passage Diameter Matters
Cylinder sizing is not only about force.
A hydraulic cylinder must also receive enough oil to achieve the required movement speed.
The relationship can be summarized as:
Flow rate → cylinder speed
If the oil passages or hydraulic connections are restrictive, pressure losses can increase and the available flow to the cylinder can be reduced.
This becomes particularly relevant when multiple cylinders are supplied from the same hydraulic system.
The Customer therefore correctly identified the oil-passage diameter as an additional engineering consideration rather than treating cylinder force as the only parameter.
14. The V450CM Family
The V450CM is Vega’s heavy-duty short-stroke compact hydraulic-cylinder family.
According to Vega’s official product information, the standard range includes piston bores from 16 to 100 mm and strokes from 10 to 200 mm. The series is designed primarily for moving components such as carts, pins and plugs in plastic injection molds, as well as ejection plates. Its maximum working pressure is approximately 450 bar, with maximum delivery depending on the configuration.
This makes the V450CM particularly suitable for applications where the designer needs a combination of:
- compact dimensions;
- high hydraulic resistance;
- significant force;
- short stroke;
- robust construction.
15. The Customer’s Bore Selection Question
The Customer’s original question was very practical:
Should the application use a 50 mm or 63 mm bore?
The Vega Team’s answer demonstrates why there is not always one universal “correct” bore.
The appropriate bore depends on the combination of:
- required pulling force;
- available hydraulic pressure;
- installation space;
- hydraulic flow;
- number of cylinders;
- operating conditions.
In the documented analysis, both CM063 and CM080 were proposed under different conditions.
16. Why a Larger Cylinder Is Not Automatically Better
It may seem logical to select the largest cylinder available.
However, increasing the cylinder bore also increases:
- physical dimensions;
- oil volume per stroke;
- required installation space;
- potentially the hydraulic flow requirement.
A smaller cylinder operating at a higher pressure may therefore be preferable in one application, while a larger cylinder operating at a lower pressure may be preferable in another.
The Customer case demonstrates exactly this trade-off.
17. Why the Adhesion Assumption Is Critical
The difference between the two scenarios is significant:
20 kg/cm² → 6,032 kgf
15 kg/cm² → 4,599 kgf
The cylinder requirement therefore changes considerably depending on the adhesion coefficient used.
For this reason, the adhesion coefficient should be treated as an engineering assumption that needs to be supported by the specific application.
It should not be presented as a universal constant for PA GF40%.
18. From Calculation to Cylinder Selection
The engineering process used in this Customer case can be summarized as:
Step 1 — Determine the contact surface
306.6 cm²
Step 2 — Define the adhesion condition
For example:
20 kg/cm²
or:
15 kg/cm²
Step 3 — Calculate the pulling force
6,032 kgf
or:
4,599 kgf
Step 4 — Select the cylinder bore
Compare the available cylinder configurations.
Step 5 — Determine the required hydraulic pressure
For example:
CM063 → 250 bar
or:
CM080 → 150 bar
under the higher adhesion condition.
Step 6 — Verify the hydraulic circuit
Especially important when using:
14 cylinders.
19. The Importance of Application Engineering
The Customer was not simply asking Vega for a catalogue recommendation.
The question required the Vega Team to evaluate:
- material;
- contact surface;
- adhesion;
- required pulling force;
- cylinder bore;
- hydraulic pressure;
- oil-passage diameter.
This is a good example of application engineering.
The objective is not simply to identify a cylinder that exists in the catalogue.
The objective is to determine which cylinder configuration is appropriate for the actual application.
20. The Customer Was Asked to Perform Its Own Verification
At the end of the analysis, the Vega Team explicitly recommended that the Customer perform its own verification.
This is an important part of the engineering process.
The calculation provides a technical basis for cylinder selection, but the final design should always be verified against the actual mold, material, contact surfaces, operating conditions and hydraulic system.
The case therefore represents an engineering assessment, rather than a universal specification applicable to every mold using PA GF40%.
Conclusion
This Customer case demonstrates how hydraulic-cylinder sizing for plastic-part extraction should be approached from an engineering perspective.
The application involved PA GF40%, a total contact surface of approximately 306.6 cm² and 14 hydraulic cylinders. The Customer asked the Vega Team to evaluate the appropriate bore and specifically questioned the suitability of 50 mm and 63 mm cylinder configurations.
The Vega Team analysed two adhesion conditions.
With an adhesion coefficient of 20 kg/cm², the calculated pulling force was 6,032 kgf. The proposed solutions were:
CM063 at a minimum of 250 bar
or
CM080 at a minimum of 150 bar.
With an adhesion coefficient of 15 kg/cm², the calculated pulling force was 4,599 kgf, leading to:
CM063 at a minimum of 150 bar
or
CM080 at a minimum of 100 bar.
The Customer also needed to optimize the hydraulic oil passages. For the specified V450CM configuration, the Vega Team indicated a 2.5 mm standard passage and a maximum possible diameter of approximately 3.5–4 mm.
The key lesson is therefore:
The correct hydraulic cylinder cannot be selected from bore diameter alone. The engineer must consider the extraction force, adhesion coefficient, available hydraulic pressure, oil flow and the complete operating conditions of the mold.
In this case, the Vega Team demonstrated that different combinations of cylinder bore and hydraulic pressure could satisfy the calculated pulling-force requirements.
This is the essence of application engineering: turning the real mechanical requirements of an injection mold into a technically appropriate hydraulic solution.
Useful and Verified URLs
1. V450CM Heavy-Duty Short-Stroke Compact Hydraulic Cylinders
Official Vega product page for the V450CM family, including bore and stroke ranges, applications, pressure capability and hydraulic delivery information.
V450CM Heavy-Duty Short-Stroke Compact Hydraulic Cylinders
2. Hydraulic Cylinders Catalogue
Official Vega catalogue showing the hydraulic-cylinder families organized by application, including the V450CM for cart and plug movement and ejection-plate movement.
Hydraulic Cylinders Catalogue – Vega Cylinders
3. Hydraulic Cylinders for Plastic and Die-Casting Molds
Official Vega product overview containing the V450CM range and other hydraulic-cylinder families for injection-mold applications.
Hydraulic Cylinders for Plastic and Die-Casting Molds
4. How to Calculate the Correct Hydraulic Cylinder Size for Injection Molds
Vega’s technical article explaining how core-pull force, plastic adhesion and hydraulic pressure should be considered when selecting hydraulic cylinders for injection molds.
How to Calculate the Correct Hydraulic Cylinder Size for Injection Molds
