Introduction
Aluminum honeycomb panels have good properties in use, including good strength and impact resistance. It enables them to be used in a wider range of applications.
Below are 7 analyses on the causes of defective aluminum honeycomb panels in production.
1 Polyurethane Two-component Adhesive Weight Ratio Is Not Accurate (generally allowed within 5% error)
Polyurethane two-component adhesives consist of a resin (part A) and a hardener (part B). These components must be thoroughly mixed in precise proportions using accurate electronic scales to achieve optimum bonding performance. Errors in the proportions are generally within 5%, and once the error is too great, it can lead to a serious loss of adhesion.
Reasons For Inaccuracies In Weight Proportioning Include:
1 Improper operation of the scale or measuring equipment;
2 Changes in ambient temperature and humidity can affect the viscosity and weight of adhesive components;
3 The density of adhesives can vary from batch to batch.
Inaccurate Weight Ratios:
——Can lead to an imbalance in the resulting chemical reaction – if there is an excess of resin (Part A) it can result in a softer adhesive that lacks the necessary rigidity and strength; similarly, if there is an excess of hardener (Part B) it can make the adhesive brittle, leading to cracking under stress or thermal cycling.
——Insufficient Reaction Components – Incorrect ratios can result in an incomplete chemical reaction, which can cause some areas of the adhesive to remain sticky or weak, compromising the overall bond.
——Reduced durability – Adhesives can be much less tolerant of environmental factors such as moisture, temperature changes and chemicals, leading to premature failure.
2 Two-component Adhesive Mixing Is Not Sufficiently Uniform – Resulting In Insufficient Adhesion
Polyurethane adhesives need to be mixed thoroughly and evenly. Inadequate mixing can lead to insufficient or incomplete chemical reactions, which can result in poor bonding and inadequate adhesion.
Inadequate Mixing Is:
1 Inadequate mixing, or use of inappropriate mixing tools and tools with insufficient shear (e.g., round stick mixing).
2 Inaccurate mixing time, use of expired adhesives, or different mixing durations for different batches.
3 Viscosity mismatch, large differences in resin and hardener viscosities can make mixing uneven, especially if the components are not pre-conditioned to the same temperature.
The Effect Of Inadequate Mixing On Adhesion:
Incomplete Chemical Reaction – areas of inadequate mixing may contain unreacted or partially reacted components, which can lead to weak points within the adhesive layer, so that the bonding strength of the entire adhesive layer will also be affected.
Reduced Mechanical Properties – Poorly mixed adhesives may fail to form a cohesive bond, reducing the load carrying capacity and durability of the bonded joint. Areas with an excess of one component may become brittle and crack more easily under stress.
Susceptibility To Environmental Influences – Incomplete mixing can result in moisture intrusion, which can cause bonding performance to degrade over time. During temperature fluctuations, adhesives may exhibit inconsistent thermal expansion characteristics that can lead to delamination.
3 Pressurization After More Than The Opening Time – Resulting In A Decline In Adhesive Force
"opening time" (also known as "open time" or "working time") refers to the period during which an adhesive remains workable and can form an effective bond after mixing and application. For two-component adhesives used in aluminum honeycomb panels, Pressurizing the adhesive after this period has expired can lead to a significant decline in adhesive force.
Effects Of Late Pressurization On Adhesive Force:
- Curing on the Surface: Once the opening time is exceeded, the adhesive may start to cure or form a skin on its surface, which can prevent proper wetting and bonding with the substrate.
- Reduced Penetration: The adhesive’s ability to penetrate and fill surface irregularities diminishes, resulting in a weaker bond.
- Viscosity Increase: As the adhesive begins to cure, its viscosity increases, making it less able to flow and spread evenly under pressure.
- Poor Contact: Incomplete flow can lead to voids and gaps between the adhesive and the substrates, reducing the effective bonding area.
- Incomplete Cross-Linking: Pressurization after the opening time can interrupt the chemical cross-linking process essential for forming a strong adhesive bond.
- Bond Degradation: The adhesive may not achieve its full strength potential, resulting in a bond that is more susceptible to mechanical stresses and environmental factors.
4 Early Unpressurization Within The Set Pressurization Time – Resulting In Partial Cracking Of The Board
In the manufacturing of aluminum honeycomb panels, maintaining the correct pressurization time is crucial for ensuring the adhesive cures properly and the structural integrity of the panel is maintained. Early unpressurization, occurring before the adhesive has fully set, can lead to incomplete bonding and structural weaknesses, such as partial cracking of the board.
Effects of Early Unpressurization on Panel Integrity:
- Bond Weakness: Releasing pressure too early can result in the adhesive not fully curing, leading to weak bonds between the aluminum layers and honeycomb core.
- Reduced Adhesive Strength: The adhesive may not achieve its full mechanical strength, compromising the panel’s overall durability.
- Partial Cracking: The lack of sufficient adhesive strength can cause the panel to develop cracks, particularly under stress or load.
- Delamination: Incomplete bonding can lead to delamination, where the layers of the panel separate, severely compromising structural integrity.
- Uneven Surface: Early unpressurization can result in an uneven surface finish, with areas that did not fully bond properly.
- Bulging or Warping: Insufficient curing can lead to deformation, such as bulging or warping, as the adhesive may shrink or expand inconsistently.
- Environmental Vulnerability: Panels with incomplete curing are more susceptible to environmental factors like moisture, temperature changes, and chemical exposure, leading to accelerated degradation.
- Reduced Load-Bearing Capacity: The overall load-bearing capacity of the panel is compromised, making it unsuitable for intended structural applications.
5 Oxidation Or Oil Contamination Of Aluminum Plate Or Aluminum Honeycomb Core During Storage – Resulting In Poor Adhesion
It is important to keep the surfaces of components such as aluminum panels and honeycomb cores in optimal condition to ensure a strong bond.
When exposed to air, aluminum reacts with oxygen and can form an oxide layer, which prevents further corrosion but also hinders adhesion.
When touched with bare hands, aluminum surfaces can transfer oils and contaminants, leading to surface contamination. Or aluminum parts stored in an environment that is not climate controlled or exposed to contaminants can lead to oxidation and oil contamination.
Additionally, lubricants and cutting oils used during the manufacturing process may remain on the surface if not properly cleaned.
When these finishes or coatings may not be completely removed, the residue left behind may interfere with adhesive bonding.
Effects Of Oxidation And Oil Contamination On Adhesion:
- Oxide Layer Formation: The natural oxide layer on aluminum surfaces can prevent adhesives from adequately wetting and bonding to the substrate.
- Contaminant Barrier: Oils and other contaminants create a physical barrier that inhibits the adhesive from making direct contact with the aluminum surface.
- Weak Interfacial Bond: The presence of an oxide layer or oil film can result in a weak interfacial bond, reducing the mechanical strength of the adhesive joint.
- Adhesive Failure: Under stress, areas with poor adhesion due to contamination are prone to failure, leading to delamination or separation of the bonded components.
- Variable Bond Strength: Contaminated or oxidized areas may result in inconsistent bond strength across the surface, compromising the overall structural integrity.
- Reduced Durability: The bond may degrade more quickly over time, especially under environmental stressors such as moisture, temperature fluctuations, and mechanical loads.
6 Aluminum Plate Or Aluminum Honeycomb Core Is Not Flat – Resulting In Unevenness Or Bulging And De-gluing Of The Plate Surface
In the production process of aluminum honeycomb panels, there will be some extrusion, falling, bending and other deformation, while temperature fluctuations will cause different expansion and contraction, so any deviation from the surface flatness of the aluminum plate and the honeycomb core will lead to uneven bonding, resulting in the surface of the board bulging, uneven and deglossing (delamination) and other problems.
The Effect Of Uneven Surfaces On Adhesion, Including:
- Gaps and Voids: Non-flat surfaces can create gaps where the adhesive does not make contact with the substrate, leading to weak or no bonding in those areas.
- Variable Bond Thickness: Inconsistent surface flatness results in variable adhesive thickness, affecting the bond strength and durability.
- Localized Stress: Non-flat surfaces can create localized stress points where the bond is weaker, making these areas prone to delamination under load.
- Flexural Stresses: Uneven surfaces can introduce flexural stresses during handling and use, promoting adhesive failure.
- Bulging and Warping: Visible bulging or warping can occur, compromising the aesthetic quality of the panel and indicating underlying structural issues.
- De-Gluing: Poor adhesion due to non-flat surfaces can lead to de-gluing, where the aluminum plate separates from the honeycomb core, severely compromising structural integrity.
7 Aluminum Honeycomb Core Is Not Effectively Perforated – Resulting In Bulging And De-Gluing Of The Board Surface
When manufacturing aluminum honeycomb panels, perforation facilitates adhesive distribution and allows air and moisture to escape during the bonding process.
Ineffective perforations occur when the perforation pattern is incorrect, the size of the perforations is inconsistent, the perforator is improperly calibrated, and too few perforations are made.
Effects Of Ineffective Perforation On Panel Integrity:
- Trapped Air Pockets: Ineffective perforation can lead to trapped air pockets within the adhesive layer, resulting in weak bonds and potential voids.
- Inadequate Adhesive Flow: Without proper perforation, adhesive may not flow uniformly across the bonding surfaces, leading to uneven bonding.
- Bulging: Trapped air and moisture within the adhesive layer can cause bulging of the board surface as they try to escape during the curing process.
- De-Gluing: Areas with poor adhesion due to ineffective perforation are prone to de-gluing under stress or load, compromising structural integrity.
- Surface Irregularities: Bulging and uneven surfaces are not only visually unappealing but also indicate deeper structural issues.
- Reduced Durability: Panels with ineffective perforation are more likely to experience premature failure due to compromised bonding.
Related References
Detailed introduction of aluminum honeycomb panels
Detailed information about adhesives