Anti-shock and vibration protection
Shock and vibration protection is required for all sensitive products. Ficus Pax offers industrial packaging solutions such as shock-absorbing material that reduces vibrations and shocks, as well as bracing that separates and holds products in place.
What effect does vibration have on packaging?
Every mode of transportation vibrates the packages being shipped at different frequencies. To protect vibration-sensitive products, determine the natural frequency of any component that is susceptible to vibration damage and compare it to the vibration characteristics of the packaging design. When vibrations induced during transport coincide with the natural frequency of the product (or rather, the critical component in the product), resonant frequency vibration excitation occurs, resulting in the highest risk of damage.
How to Choose the Best Vibration Protection
To prevent vibration damage during shipment of most vibration-sensitive products, ensure that the packaging design does not amplify (increase) vibration at the product’s natural frequency. However, for extremely vibration-sensitive products, the packaging design may need to attenuate (decrease) the frequencies of concern.
The vibration characteristics of a specific design, like shock, should ideally be tested, but they can be estimated based on knowledge of the vibration characteristics of the cushioning material.
Material response diagrams are frequently used to show performance for a given thickness of a given material at its natural frequency. As a function of the static loading applied to the cushioning, one can estimate whether the packaging will perform in a direct coupling (unchanged vibration), amplification (increased vibration), or attenuation (decreased vibration) mode for any frequency.
Package Design Manual
First, determine the product’s fragility.
The first step in determining how much cushioning a product needs is to determine how much mechanical shock it can withstand on its own. There are several terms for this, the most common of which are “fragility” and “g-factor.”
The maximum deceleration that a product can withstand without being damaged is normally expressed in units of “g.” The lower the g-factor of a product, the more fragile it is. The table below illustrates this concept.
Typical Packaged Articles’ Approximate Fragility
|Extremely Fragile||Missile guidance systems, precision aligned test instruments||15-25 g’s|
|Very Delicate||Mechanically shock-mounted instruments and electronic equipment (Shock mounts must be firmly secure prior to packaging. They are provided for in-service protection only.)||25-40 g’s|
|Delicate||Aircraft accessories, electric typewriters, cash registers and other electronically operated office equipment||40-60 g’s|
|Moderately Delicate||Television receivers, aircraft accessories||60-85 g’s|
|Moderately Rugged||Laundry equipment, refrigerators, appliances||85-115 g’s|
|Rugged||Machinery||115 g’s and up|
A product’s fragility is best determined by subjecting it to a series of increasingly severe shocks (decelerations) in order to find the lowest severity impact that will damage the product. The product’s g-factor is determined by the greatest deceleration that did not cause damage.
It is not uncommon for a product to exhibit greater strength in one direction than another, so determining fragility levels for a product in various orientations may be necessary. Even very similar models should be tested individually, because fragility in one model is rarely safe to assume in another.
There is no replacement for fragility test data. Educated guesses about a product’s fragility are frequently detrimental to the design process. If the g-factor is overestimated and the product is unable to withstand as much shock as anticipated, the packaging will be inadequate, and significant shipping damage is likely. If the g-factor is underestimated and the product can withstand more shock than expected, the packaging will be over designed and unnecessarily expensive.
Packaging Drops and Shock Forces
Shock is the force applied to a pack as a result of a sudden change in velocity. An example of this is a truckload falling off the back onto the sidewalk. In that example, the change in velocity, which is controlled by the distance fallen and the nature of the impacting surface, indicates the severity of the shock experienced by the pack and its product. Shock occurs in many areas of the distribution chain, not only in simple drops but also in sudden stops and jolts caused by transportation rigors.
Drop tests are a common way for new packs to be tested. For specific pack weights, a range of likely drop heights has been developed over many years. The spreadsheet below illustrates this. As one might expect, lighter packs are more likely to be dropped from a greater height. This is due to a variety of factors, including their lighter weight, which makes it easier to transport more than one at a time. Because of their light weight, packs are more likely to be thrown. Heavier parcels are more likely to be carried with greater care to avoid injuring the worker, but instead of being placed on the floor, they may be dropped the final few inches to the ground.
- Drops are less likely to occur in unitized loads than in single packs.
- Packs are frequently dropped from lower heights, but the likelihood of a pack being dropped from three feet more than once is low.
- Because light packs are likely to be carried in a variety of orientations, their behavior when dropped is unpredictable.
- Heavier packs have a 50% chance of landing on their base.
- Handholds reduce the likelihood of a high drop height by making it easier to lower the pack to the ground.
- Labels like “Fragile” and “Handle with Care” have little effect on cutting damage.
- Address labels increase the likelihood of the pack being dropped with the label on top.
- A corner or edge drop causes the most damage to the pack.
- Drops onto the flat faces cause the most damage to the product.
- The shock can harm the product within a pack without causing significant damage to the pack.
- Rather than stiffening the outer pack, the normal solution is to improve the internal cushioning.
Drops and shocks normally cause damage to the pack, reducing its protection and containment capabilities. The chart below depicts the percentage likelihood of a specific drop height for a variety of pack weights. Naturally, this is only a broad generalization of all possible distribution cycles. The flat sections of the graphs represent areas where mechanical handling is likely to replace manual handling.
Calculating the fragility factor of a product
One of the most common methods for determining a product’s fragility is to take repeated drop samples and measure the drop height at which damage begins to occur. However, quantifying fragility as a drop height is only useful if the pack contains no additional cushioning protection. It is useful for products that may experience drops in use, such as handheld calculators, telephones, and personal computers. It should be noted that calculating an efficient cushioning system for a specific product is impossible without knowledge of the product’s fragility and areas of weakness. When subjected to a shock, “G” levels are commonly used to quantify an object’s tendency to break. The drop height used to determine the G level is usually greater than the likely drop height of the packed product.
Dynamic cushioning curves, which are available for most cushioning materials, can be used to estimate cushioning thickness.
The following information is required to perform these calculations using dynamic cushioning curves:
- Product dimensions and weight
- Product brittleness, as measured by G’s Expected drop height
Locate the curve that crosses the desired critical acceleration line twice to use a dynamic cushioning curve (see the spreadsheet above). The required foam thickness and static load range can then be calculated.
The minimum and maximum static loads are represented by the two points where the critical acceleration line crosses. Typically, a static load near the minimum point of the curve is chosen, but designing with higher static loads reduces cushion material area.
Understanding shock and fragility factors will aid in the comprehension of many shipping damages. A compressor motor assembly, for example, weighs 15 kilograms in a refrigerator shipped by road. The designer felt safe attaching this assembly to the frame with three fasteners capable of holding 120 kilograms, providing an adequate safety factor. However, during transportation, the refrigerator experiences a 10 G shock, and the motor behaves as if it were 150 kilograms in weight. Because the three mounting fasteners can only support a combined weight of 120 kilogrammes, they may shear off. The sidewall of the refrigerator, with a bearing area of 1.5 square meters, and the shipping box can distribute the load of a unit that suddenly weighs ten times more. The refrigerator is accepted at the receiver’s warehouse and by the retailer because there is no external evidence of damage. Only when a final customer plugs it in does the problem become apparent.
All good manufacturers are aware of the fragility factor in their products. In many instances, they will redesign products with low G levels, knowing that the savings in protective materials and the goodwill generated by satisfied customers will more than repay the cost of added engineering. Fragility may be greatly dependent on how the force is transmitted to the product. An egg on a flat surface has a fragility of 35 to 50 g, depending on the axis of impact. If the egg is supported on a conforming surface, its fragility can exceed 150 g.
Cushioning Against Shock
Any material that deflects under a load can be used as a cushioning material. The cushioning material reduces the peak G level experienced by the product when compared to the shock pulse felt at the package surface by deforming. Cellulosic, polymers, and long fibers, such as animal hair bonded with rubber materials and wood wool, will be the primary cushioning materials used. The most cost-effective cellulose cushioning materials are shredded paper, tissue paper, corrugated board, and molded pulp. However, such materials may not be as suitable in terms of abrasiveness and cleanliness. They can also have corrosive reactions with certain products. Molded shapes made of materials such as EPS, on the other hand, can be expensive to produce in anything other than large quantities. For small quantities, loose foam chips are usually a more cost-effective option.
Polymeric materials are available in a variety of resiliencies and densities. Polymeric materials include expanded polystyrene (EPS), foam polyurethane, and air bubble sheet. These materials may be more suitable in terms of cleanliness. Although cushioning polymers are not hygroscopic, some open-celled foams, such as polyurethane, can absorb liquid when wet.
Loose-fill cushioning materials are ideal for odd-shaped products, but they can settle during transit. In some cases, loose-fill cushioning materials can be reused. Loose fills made from recycled corrugated cases are being used to address environmental concerns. Foam-in-place polyurethane is labor-intensive in the packing process, but it is another versatile cushioning material that allows for the production of custom shapes.
Pre Shipment Testing Equipment
Vibration tables are used to evaluate the responses of products and packages to the various ranges of vibration that they will encounter in the field. They are classified into two types: Repetitive-shock vibration tables have an acceleration of 1.1 G, an amplitude of 1 inch, and a frequency of 4.5 hertz. These tables are used in Dangerous Goods Code tests as well as procedures recommended by ISTA and ASTM D 4169. They can also be used to determine relative scuff resistance. Variable-frequency vibration tables can be set to sweep through all common transport frequencies ranging from 3 to 100 hertz. They can represent the true distribution environment more realistically. They are also used to locate stack resonance points for stacked packages and to search for resonance weaknesses in the unpackaged product.
The ASTM specifies the following vibration tests:
- D-4782, Random Vibration Testing of Shipping Containers
- D 5112, Vibration (Horizontal Linear Sinusoidal Motion) Test of Unpacked Products and Components
- D 999, Vibration Testing of Shipping Containers
- D 1185, Pallets and Related Structures Used in Materials Handling and Shipping
- D 3580, Vibration (Vertical Sinusoidal) Test of Products
- D-4169, Shipping Container Performance Testing and System Drop Testers
The ability of all drop-test devices to produce representative drops at specific orientations and heights without rotation or other influences is their defining feature. Drop heights can be chosen from drop probability tables, ISTA or ASTM standards, or the requirement of a danger code (hazardous goods code).
The following standards describe drop tests:
- ASTM D 5276, Drop Test of Loaded Containers by Free Fall
- ASTM D 1083, Mechanical Handling of Unitized Loads, Large Shipping Cases, and Crates
- ASTM D 3071, Drop Test of Glass Aerosol Bottles
- ASTM D 5487, Standard Practice for Simulated Drop Tests of Loaded Containers by Shock Machines
- ASTM D 5265, Bridge Impact Testing
Horizontal and Inclined (Conbur) Impact Machines
The incline impact machine mimics horizontal shocks experienced during rail shipments. Impact programmers can be used to control the shock by changing the impact velocity. The effects of dynamic horizontal compression can also be evaluated using appropriate backloads.
The incline impact machine, with modifications, is also used to determine the durability of pallets for repeated forklift entries.
ISTA and ASTM pre-shipment test methods specify incline impact tests, which are described below:
- ASTM D 1185, Pallets and Related Structures
- ASTM D 880, Incline Impact Test for Shipping Containers
- ASTM D-4169, Performance Testing of Shipping Containers and Systems, is used in handling and shipping.
- Horizontal impact machines are a newer, more controllable way to generate horizontal shocks.
- The load is accelerated along a horizontal track and into a programmable backstop by these machines.
- ASTM D 4003, Programmable Horizontal Impact Testing for Shipping Containers and Systems
- ASTM D 5277, Performing Horizontal Impacts with an Inclined Impact Tester, are both standards.
Compression Test Systems
Warehouse stacking ability is directly related to compression strength. A compression test system is used to determine a package’s load-carrying capabilities. Units range in size from small enough to measure the compression strength of plastic bottles to large enough to measure the stacking strength of entire pallet loads. Fixed-plate testers tend to fail the specimen at its weakest point. Swivel platens frequently cause specimen failure at its weakest point.
Compression tests can be dynamic, utilizing hydraulically or mechanically driven platforms, or static, utilizing a dead load stacked on a subject container and the system being observed over time. Most pre-shipment testing procedures require compression tests, which are described in:
- ASTM D 642, Compression Test for Shipping Containers
- ASTM D 2659, “Column Crush Properties of Blown Thermoplastic Containers,”
- ASTM D 4577, Compression Testing of Shipping Containers Under Consolidated Load.
ASTM D 4332 specifies recommended standard atmospheric conditions.
Shock machines are used to create fragility boundary curves and G levels for calculating cushioning requirements or assessing the design fragility of a product. A shock machine is made up of a rigid table that can be lifted and lowered onto a programming device. Different G levels, pulse durations, and pulse shapes (sine, square wave, etc.) can be achieved by controlling the programming device and the drop height.
The following are descriptions of shock machine tests:
- Mechanical Shock Fragility of Products Using Shock Machines, ASTM D 3332
- Transmitted Shock Characteristics of Foam-in-Place Cushioning Materials, ASTM D 4168
- Standard Practice for Simulated Drop Tests of Loaded Containers Using Shock Machines, ASTM D 5487
Summary of ASTM D 4169 distribution testing elements
To use the procedure, first determine the nature of the distribution environment you want to simulate in the laboratory, as well as the shipping unit for each stage of the journey. Unlike the ISTA procedure, the ASTM procedure involves testing the actual unit being shipped, which may differ at different points of distribution. For example, a unit load could be used as the test unit for part of the gramme, and an individual container could be used for the rest.
The test method then selects the elements representing the identified shipping environment and the “private assurance level.” A decision must be made as to what constitutes an unacceptable level of damage. The test procedure describes various shipping modes or elements and allows for the introduction of atmospheric factors at any time during the test programme.
When evaluating a new shipping container, the entire sequential test would be performed. Where the package response to a single condition is required, only that element must be executed. The operator can create a custom sequence or use one of the 18 predesigned sequences that describe the most common distribution cycles.The ASTM procedure can simulate more distribution hazards and in a more realistic manner than the ISTA methods. ASTM also offers useful design information. Establishing a tory capable of performing ASTM D 4169 tests, on the other hand, is orders of magnitude more expensive than ISTA, and skilled operators are required to test and interpret data. There is also some disagreement about the select sequences and their levels. Furthermore, the sophistication of the ASTM D 4169 approach is not required for all shipping problems.
Pre Shipment testing is an important tool for developing a suitable button package or resolving specific problems. Whatever tests are used, the damage observed in the laboratory should resemble that seen in the field. One common misconception is that a specific time or exposure in the laboratory is equivalent to a specific number of kilometers or miles in the field. Finally, it should be understood that a successful shipping history is the ultimate and true test.
Other Test Methods and Standard Practices
The following are selected other standards related to packaging materials:
- ASTM D 6198, Standard Guide for Transport Package Design
- ASTM D 4649, Selection of Stretch, Shrink, and Net Wrap Materials
- ASTM D 5118, Fabrication of Fiberboard Shipping Boxes
- ASTM D 5168, Fabrication and Closure of Triple-Wall Corrugated Fibrous Containers
- ASTM D 4919, Testing of Hazardous Materials Packaging
- ASTM D 3951, Commercial Packaging
- ASTM D 1974, Methods of Closing, Sealing and Reinforcing Fiberboard Boxes
The level of protection required is determined by the nature of the goods being transported. Materials made of steel or other durable materials will require more shock and vibration protection than fragile or dangerous goods. There are several methods for shielding your goods from shock and vibration.
Each of these solutions has its own set of benefits and drawbacks. The appropriate type of protection is determined by what you are shipping, how it will be shipped, and several other factors. We have various types of protections at Ficus Pax that can be used for a wide variety of different types of goods.
Do you have any concerns about how to protect your equipment during shipment? Ficus Pax, specializes in innovative packaging solutions, can assist you in ensuring that your machinery travels safely and comfortably to your customer’s location. To learn more about our services, please contact us.