The term unit load refers to the size of an assemblage into which a number of individual items are combined for ease of storage and handling, for example a

pallet A pallet (also called a skid) is a flat transport structure, which supports goods in a stable fashion while being lifted by a forklift, a pallet jack, a Loader (equipment), front loader, a Jack (mechanical), jacking device, or an erect cra ...

load represents a unit load which can be moved easily with a pallet jack or forklift truck, or a container load represents a unit for shipping purposes. A unit load can be packed tightly into a

warehouse A warehouse is a building for storing goods. Warehouses are used by manufacturers, importers, exporters, wholesalers, transport businesses, customs, etc. They are usually large plain buildings in industrial parks on the rural–urban fringe, out ...

rack,

intermodal container An intermodal container, often called a shipping container, or a freight container, (or simply "container") is a large metal crate designed and built for intermodal freight transport, meaning these containers can be used across different Mode ...

truck A truck or lorry is a motor vehicle designed to transport freight, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construct ...

boxcar A boxcar is the North American (Association of American Railroads, AAR) and South Australian Railways term for a Railroad car#Freight cars, railroad car that is enclosed and generally used to carry freight. The boxcar, while not the simpl ...

s, yet can be easily broken apart at a distribution point, usually a distribution center,

wholesale Wholesaling or distributing is the sale of goods or merchandise to retailers; to industrial, commercial, institutional or other professional business users; or to other wholesalers (wholesale businesses) and related subordinated services. In ...

r, or

retail store The retail format (also known as the retail formula) influences the consumer's store choice and addresses the consumer's expectations. At its most basic level, a retail format is a simple marketplace, that is; a location where goods and services ar ...

for sale to consumers or for use.

Function

Most consumer and industrial products move through the supply chain in unitized or unit load form for at least part of their distribution cycle. Unit loads make handling, storage, and distribution more efficient. They help reduce handling costs and damage by reducing individual handling. A typical unit load might consist of

corrugated fiberboard Corrugated fiberboard, corrugated cardboard, or corrugated is a type of packaging material consisting of a fluted corrugated sheet and one or two flat linerboards. It is made on "flute lamination machines" or "corrugators" and is used for maki ...

boxes stacked on a

or slip sheet and stabilized with stretch wrap,

pressure-sensitive tape Pressure-sensitive tape or pressure-sensitive adhesive tape (PSA tape) is an adhesive tape that sticks when pressure is applied without the need for a solvent (such as water) or heat for activation. It is also known in various countries as self ...

, strapping or shrink wrap. About 2 billion unit loads are in daily use in the United States.

Unit load design

There are three kinds of unit load design: component-based, systems-based, and standards-compliant. These have different applications.

Component-based design

Component-based design is the outmoded ''ad hoc'' method of unit load design. Components are sometimes over-specified to get assured performance, or tested to get inexpensive economic performance. Unit load storage and distribution systems consist of several interacting parts: *

Packaging and labeling Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a co ...

(with product) * Pallet * Handling/storage equipment * The distribution environment ( shock,

vibration Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

, etc.) Considerable knowledge exists regarding the design of each of these components: their interactions have more recently been studied. When packaging, pallet, and handling systems are designed separately at different locations by different teams, the result might be inefficient unit load systems. The consequences of independent component-based design in the supply chain can include: *Unsafe workplaces *Product damage *High packaging costs *Reduced handling efficiency *Wasted natural resources *Reduction of environmental quality

Systems-based design

Systems-based design is a proven process of unit load component cost optimization based on an understanding of how the pallet, packaging and material handling equipment interact during product distribution and storage to design the unit load component parts. A systems-based approach to unit load design uses software tools and lab testing to create a package that uses just the right amount of material to protect the product, make for safe handling and transportation and minimize the use of non-recyclable materials. Companies must now consider sustainability when determining how their packaging products will be reused or recycled at the end of their journey. By combining sustainability with unit load science, they not only create the optimal unit load, but also reduce the amount of packaging material used to transport that load, maximizing the materials that can be recycled and minimizing what goes into a landfill. Unit loads move via an unpredictable combination of many types of vehicles and storage areas, and the exact set is difficult to predict. Therefore, unit loads must be designed to travel by any such vehicles, and be stored in a wide variety of places. There are many similarities in the requirements for long-term storage and long-distance transportation of unit loads. Factors considered in unit load systems-based design include: *Distribution vibration and resonance *Load bridging and deformation *Unit load deflections *Interfacial friction and load stability *Compression stress and product protection *Vertical and horizontal stabilization Often a few inexpensive additions to the packaging can stabilize or stiffen a critical part and give good unit-load performance at a low cost.Systems Based Design Eliminates Product Damage, Pallet Enterprise, pg. 90
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Standards-compliant design

Standards permit a unit load to be designed and tested to meet a written

specification A specification often refers to a set of documented requirements to be satisfied by a material, design, product, or service. A specification is often a type of technical standard. There are different types of technical or engineering specificati ...

or test method. A unit load can be verified to comply with a standard and validated to determine that the unit load is indeed effective. Standards provide institutional memory of the many conditions in real logistic trains, and collect the best practices for design and testing unit loads. Standards also describe load requirements, so that logistic providers can plan to meet them. * Material-based standards describe proven designs for particular circumstances. These are often used to describe unit load components such as pallets, strapping, seals, caps, retaining rings and battens. * Performance testing standards describe needs and allow flexibility in the choice of materials. These are applied to particular unit load designs.

ASTM ASTM International, formerly known as American Society for Testing and Materials, is a standards organization that develops and publishes voluntary consensus technical international standards for a wide range of materials, products, systems and s ...

D4169 has standard test protocols for unit loads. These vary based on the value of the load, the expected hazards, and the distribution environment. This is a performance-based standard. Another standard for unit loads is MIL-STD-1660, a standard for ammunition unit loads. DOD unit loads generally use pallets, which unfortunately do not pack efficiently into ISO containers. They weigh less than to limit the stresses on handling equipment. They are weatherproof, and stack high. They often use steel pallets, steel straps with notched seals, outdoor plywood, and plastic film. MIL-STD-1660 mandates that loads must never be less than the width of a pallet, while permitting some overhang. The markings are LOGMARS

bar code A barcode or bar code is a method of representing data in a visual, Machine-readable data, machine-readable form. Initially, barcodes represented data by varying the widths, spacings and sizes of parallel lines. These barcodes, now commonly ref ...

s and standard inventory numbers. The standard describes major parts of the logistic path, including storage, ship, air, truck, forklift and sling (i.e. ship-to-ship and parachute). There are auxiliary standards for ship-to-ship transfers, and amphibious transfers. There are tests for stacking, transport, sling, forklift and pallet jack, impact, drop tests, tip, water-retention (i.e. weather), and safe disassembly. MIL-STD-1660 at first looks like overdesign to commercial unit-load designers. However, similar marking standards, safety, stability, volumetric efficiency, weight limits and impact resistance are routinely needed in commercial logistics. Sling handling is routine for small ports and noncontainer transports. Weatherproofness could be optional. It is sometimes valuable, and the baggies are cheap. High, standardized stacking could be optional as well. It is expensive, but sometimes valuable for rackless and military customers.

References

External links

Virginia Tech Center For Unit Load Design
{{Authority control Packaging Shipping containers