Wooden Pallets | Classifications, Sizes, Specifications, Bearing Capacity Calculation

Induction

Wooden pallets are versatile tools that are used in various industries for different purposes. They play a crucial role in the transportation, storage, and handling of goods.  These versatile platforms are used across various sectors, including manufacturing, warehousing, and retail.

In this article, we will provide you with a comprehensive guide to understanding wooden pallets, including their classifications, Different sizes of pallets, specifications of wooden pallets, bearing capacity calculation with examples, and also discuss general designs of pallets.

Wooden pallets are flat structures that consist of a platform and a base, usually made of wood bars, wood blocks, and wood boards. Wooden pallets can be reused, recycled, repaired, or re-manufactured depending on their condition and quality. They can also be customized to meet specific requirements of different industries or applications. Wooden pallets are widely used because they are relatively cheap, durable, easy to handle, and environmentally friendly.

Classification of Pallets:

Wooden pallets can be categorized based on their design and construction. Each type is suited for specific applications and load requirements. Wooden pallets can be classified according to different criteria, such as:

Type of wood used for pallet
Number of entries points to an excess of pallets type of design or type of deck

Classification based on the type of design or deck of the pallets: Here we can be broadly classified into three categories:

a)Stringer pallets or open decks pallets

b)Block pallets or Solid decks pallets

c) Reversible pallets

Stringer pallets or open deck pallets: These pallets have multiple parallel boards known as stringers running the full length of the pallet. Open deck pallets have gaps between the deck boards, which makes them lighter and cheaper. However, they cannot be used for small items that may fall through the gaps. These are commonly used in warehouses and are known for their strength and durability.

Block pallets or Solid deck pallets: Block pallets are designed with blocks between the top and bottom deck boards. i.e. Solid deck pallets have a continuous sheet of wood or metal without any gaps or spaces. These blocks serve as additional support to bear heavy loads and increase the pallet’s overall load-bearing capacity. Block pallets are generally used in industries that require heavy-duty pallets such as automotive, construction, and manufacturing. They are more suitable for small items and hygienic applications

Reversible Pallets: Reversible pallets have identical top and bottom decks, allowing for full reversibility. This feature enables them to be used in both downward and upward shipping processes, resulting in cost savings and increased efficiency.

Classification based on the number of entry points to excess pallet

Wooden pallets are designed to facilitate the movement of goods in various stages of the supply chain. The platform is where the goods are placed, while the base provides support and allows forklifts or other lifting devices to access the pallet from different sides. Wooden pallets can have two-way or four-way entry points for excess forklift forks.

Two-way Entry Pallets: These pallets have openings on only two sides, allowing for entry with a forklift truck or pallet jack from either the front or back. Two-way entry pallets are popular in retail and warehouse operations where accessibility from multiple directions is not required.

Four-way Entry Pallets: These pallets are designed with openings on all four sides, enabling forklifts or pallet jacks to enter from any direction. Four-way entry pallets provide versatility and accessibility, making them ideal for industries with complex logistics requirements.

Classification based on the type of wood used for pallet

The type of wood used for pallet construction is crucial for its strength, weight-bearing capacity, and resistance to environmental factors. Common wood types include hardwood and softwood. Wooden pallets can be made of hardwood or softwood.

Hardwood pallets: They are made from dense woods and usually have exceptional strength and longevity, making them suitable for heavy-duty applications. Some common hardwood species used for pallets are oak, maple, birch, ash, and beech.

Softwood pallets: These pallets are constructed from less dense woods like pine, spruce, fir, and cedar. They are more affordable and lighter, making them ideal for lighter loads and one-way shipments.

Specifications of Wooden Pallets:

Wooden pallets must meet certain specifications to ensure their quality, safety, performance, and compatibility with different systems and equipment. Some of these specifications include:

Moisture content:

The moisture content of wooden pallets affects their weight, strength, durability, and susceptibility to mold and insects. The ideal moisture content for wooden pallets is between 15% to 25%. Too high or too low moisture content can cause warping, cracking, shrinking, or swelling of the wood.

Fasteners:

The fasteners used to join the boards and blocks of wooden pallets include nails, screws, staples, and bolts. The type, size, number, and placement of fasteners affect the strength, stiffness, and durability of wooden pallets. The fasteners should be corrosion-resistant, smooth, and flush with the wood surface. They should also be compatible with the wood species and the intended use of the pallet.

Heat and Fumigation treatment:

To enhance durability and prevent decay, wooden pallets can undergo various treatments, such as heat treatment (HT) or chemical treatment (CT). Heat treatment is a process of exposing wooden pallets to high temperatures (at least 56°C or 133°F) for a minimum of 30 minutes to kill any pests or pathogens that may be present in the wood. Heat treatment is required for wooden pallets that are used for international trade to comply with the phytosanitary regulations of the International Plant Protection Convention (IPPC). Heat-treated wooden pallets are marked with the IPPC logo and the letters HT.

Heat treatment of wooden pallets is required while shipment to and from Europe as per ISPM15 standard.

ISPM 15 defines a standard that is not intended to provide ongoing protection from contaminating pests or organisms. It describes three approaches to eliminating the likelihood of pests and contaminants.

These are:

Heat Treatment (HT)
Remove moisture by Kiln Drying
Fumigation for wood packaging material by using Methyl bromide (MB)

There are stringent regulations for each of these methods which ensures that pests, diseases, and contaminants are all eliminated.

Load capacity:

The load capacity of wooden pallets is the maximum weight that they can safely support without breaking or deforming. The load capacity depends on several factors, such as the type of wood, the type of design, the type of support, and the type of load. The load capacity can be determined by laboratory testing or computer modeling following different standards, such as ISO 8611, ASTM D1185, or AIAG RC9.

Bearing Capacity of Wooden Pallets

Determining the requirement of the bearing capacity of a wooden pallet is crucial to ensure the safe handling of loads. The bearing capacity of wooden pallets is the maximum load that they can withstand without collapsing or failing. The bearing capacity calculation involves considering factors such as load distribution, Static load, dynamic load carrying capability, and overall design and construction of the pallet.

For example, consider the size of the square pallet sizes 1200mm x 1200mm and load rice bags on pallets of a height of 30 layers. Each layer of bags weight is 150kgs (6 x 25kgs)

Step 1 (Load Distribution Pattern): Let’s assume the load is evenly distributed across the entire pallet surface.

Step 2 (Maximum Load): The maximum load given per layer is 150 kg with 30 layers. Hence total static load on a pallet is 4500kgs.

Step 3 (Dynamic Loading): Dynamic loading refers to the additional impact or dynamic forces that may occur during handling, stacking, or movement. These dynamic forces can increase the load on the pallet.

It is crucial to account for dynamic loading in the calculation to ensure sufficient structural strength. Consider using a safety factor to accommodate dynamic loading (e.g., multiplying the maximum load by a factor of 1.5 to 2).

In our example, we consider a safety factor of 1.8, multiply the maximum static load by the factor

i.e 4500 kg x 1.8 = 8100 kgs.

Step 4 ( Support Area): The support area of the pallet is given as 1.44 m2 (The size of the pallet is 1200mm x 1200mm).

Bearing Capacity = Maximum Load / Support Area

= 8100/1.44 = 5625 kg/m2 = 5.625 MT/m2

The bearing capacity of a given pallet can be calculated by using formulas based on the mechanical properties of the wood and the geometry of the pallet. Alternatively, it can be estimated by using tables or charts that provide empirical values for different types of pallets and loads.

One example of a formula for calculating the bearing capacity of a wooden pallet is:

Bearing capacity of wooden pallet = (F x L x E x I) / (8 x D ³)

Where:

• • F  –  safety factor (usually between 2 to 3)
  • L  –  length of the pallet in inches
  • E  –  modulus of elasticity of the wood in pounds per square inch (psi)
  • I  – moment of inertia of the cross-section of the pallet in inches to the fourth power
  • D  – deflection or sagging of the pallet in inches

How to choose the design of pallets?

The design of wooden pallets encompasses the structural layout, assembly method, and reinforcement mechanisms. The design should consider load distribution, rigidity, stability, and overall durability. Advanced designs may incorporate features like anti-slip surfaces, perimeter barriers, or integrations for secure strapping.

Wooden pallets can be designed by following some basic steps:

Determine the purpose and requirements of the pallet: What kind of goods will it carry? How much weight will it support? How will it be handled and stored? What are the environmental conditions? What are the quality standards?

Choose the type and size of the pallet: Based on the purpose and requirements, select the most suitable type and size of wooden pallet from the available options. Consider factors such as cost, availability, durability, compatibility, and aesthetics.

Choose the type and quality of wood: Based on the type and size of the pallet, select the most suitable type and quality of wood from the available options. Consider factors such as strength, stiffness, weight, moisture content, heat treatment, and fasteners.

Calculate or estimate the load capacity: Based on the type and quality of wood and the type and size of the pallet, calculate or estimate the load capacity using formulas or tables. Check if it meets or exceeds the requirements.

Draw or model the pallet: Based on all the previous steps, draw or model the pallet using software or tools. Include all dimensions, details, labels, and markings.

Test or verify the pallet: Based on all previous steps test or verify if your design meets all specifications using laboratory testing or computer modeling following relevant standards.

Standard Sizes and Dimensions of Pallets

Wooden pallets are available in various sizes to accommodate different loads and fit into various packaging systems. The most common sizes include:

Standard Pallet  48″ × 40″ ( 1200mm x 1000mm):

This is the most frequently used pallet size, with dimensions of 48 inches by 40 inches. Standard pallets are commonly used for shipping and are compatible with most industrial racking systems.

Half Pallet 48″ × 20″ ( 1200mm x 500mm):

Half pallets are smaller versions that measure 48 inches in length and 20 inches in width. They are ideal for smaller loads or when space optimization is crucial.

Square Pallet 48″ × 48″ (1200mm x 1200mm):

Square pallets, also known as industrial pallets or bulk storage pallets, have dimensions of 48 inches by 48 inches. They are generally used for larger loads and are suitable for heavy-duty applications.

Wooden pallets have different sizes and dimensions depending on the region and the industry.

The most common size in the U.S. is the 48×40 inch pallet, also known as the GMA (Grocery Manufacturer’s Association) pallet. This pallet can hold up to 4,600 pounds and weigh about 37 pounds.

Other standard sizes approved by the International Organization for Standardization (ISO) are 42×42 inches and 48×48 inches. The weight and load-bearing capacity of wooden pallets varies depending on the materials and design.

The following table shows some common wooden pallet sizes and dimensions in inches

Conclusion

Wooden pallets are versatile tools that are used in various industries for different purposes. They play a crucial role in the transportation, storage, and handling of goods.  We hope you found this article helpful and informative.