What is Electrolysis and galvanic corrosion?
Galvanic Corrosion is the corrosion that occurs when two dissimilar metals are used together in a structure and exposed to an electrolyte (salt water, chemical, petrol) and the less noble of the 2 metals will corrode. For example; aluminum sheet with steel fasteners on a boat. Some pairings of metals are more at risk of galvanic corrosion. Check a galvanic series or chart.
Electrolysis is the acceleration of the galvanic corrosion when electricity is introduced to the metals in question. Connected by an external electrical source, the less noble metal experiences accelerated galvanic corrosion.
while both processes involve metals and electrolytes, their dependence on an external voltage source distinguishes them.
Protection of products from potential damage during transit and storage is one of the most important requirements for packaging today. The use of resilient energy absorbing materials such as PLASTAZOTE foam to protect products from shocks and vibration during transit is well known and is commonly termed 'cushion packaging'. Cushion packaging represents the most widespread use of such materials in protective packaging, although less demanding uses are also found in space filling, bracing, and load spreading.
The primary function of a cushion system is to reduce the severity of the shock experienced by a packaged article through mishandling to a level at which damage is highly improbable. This is achieved by allowing the article to have limited but controlled freedom of movement within its container during impact.
Controlled movement results from compression of the cushion system through conversion of the kinetic energy of the packaged article. The cushion compression allows the deceleration of the article to take place over a longer period and a greater distance than for the corresponding uncushioned system, resulting in a lower level of transmitted shock.
Internal damage suffered by an article on impact is caused by the action of inertial forces (which are proportional to the decelerations experienced) on the internal structure of the packaged article. External damage depends not only on the forces at impact but also on the area, positioning, and physical properties of the cushioning and internal fittings within a pack.
The reduction of transmitted shock and resultant inertial forces offered by a suitably designed PLASTAZOTE foam cushion system can therefore virtually eliminate likely damage during transit. The resilient properties also offer the ability to protect against repeated impacts - an important factor in most transit operations.
Protection from the effects of vibration is normally a secondary but often important function of foam cushioning systems. PLASTAZOTE foam offers excellent protection through its inherent damping properties.
Provided the principles of design explained in this booklet are used, then designers can be assured that cost and performance-effective packages will result.
Designing for Effective Cushioning
Before looking at the design process in detail, some essential concepts and characteristics are discussed.
Suitability
PLASTAZOTE foam is generally best suited to the protection of high-value delicate goods weighing several kilograms or more.
Dynamic Cushioning Curves
Dynamic cushioning curves are often used to characterize the shock protection capabilities of cushioning materials. The dynamic performance of PLASTAZOTE foam is fully characterized in this way in this booklet. An example is shown in Figure 1. The curves show the level of shock transmitted by the cushion to the packaged article for a given cushion thickness and drop height as the cushion loading is varied. These curves are generated by measuring the peak deceleration of a series of falling weights when dropped onto foam samples from a predetermined height and closely resemble the conditions experienced by a cushioned article when dropped from the same height.
The peak deceleration (measured in terms of gravitational acceleration units and referred to as peak 'G') is simply plotted as a function of cushion loading (measured in terms of the static load exerted by the packaged article at rest) to obtain a dynamic cushion curve.
Dynamic Working Range
When absorbing impact energy, most compressible cushioning materials exhibit similar behaviour to that shown in Figure 1. At a given drop height, a minimum value of peak 'G' is found at a particular static loading. At much lower static loadings, the impact energy is insufficient to compress the cushion, and the packaged article effectively comes to an abrupt halt, suffering high peak deceleration. At much higher static loadings, the impact energy rapidly compresses the cushion until it 'bottoms out' on the surface below, at which stage the packaged article again comes to an abrupt halt.
In practice, a cushioning material is generally designed to operate at a static loading close to the minimum of a dynamic cushioning curve. Here, the cushion operates most effectively and is subject to less variation in performance as operating conditions change.
Repeated Impact Characteristics
Most resilient cushioning materials, including PLASTAZOTE foam, exhibit a marginal change in properties known as fatigue when subjected to a succession of impacts. Dynamic data for such materials is therefore usually presented not only for the first but for subsequent impacts. After three impacts, fatigue effects are considerably reduced, and for cases where multiple impacts are likely, this condition can be safely used for design purposes.
The use of first impact performance curves for general design purposes is widespread, and much practical testing of complete packages has resulted in many design procedures recommending the use of first impact performance curves only. This is due to the cushioning contributions of outer containers and impacted surfaces, which are ignored during foam testing, and which effectively add a safety margin for actual use.
