Methods of drying wood for transport boxes

Wood is unique for its strength, lightness, insulation and flexibility. It is widely used in construction, furniture making, paper making and many other areas. However, when a tree is felled, it usually has a high moisture content, which makes it unstable and unsuitable for many applications.

Drying is the process by which wood is gradually dehydrated to reduce its moisture content to an acceptable level for a particular application. As a result, it becomes more stable, less prone to shrinkage, cracking and deformation.

We distinguish between the three most popular drying methods – air, chamber and pressure-vacuum. In this article we will discuss each of them and focus on their advantages and disadvantages. Finally, we will describe the method used at Danpol to produce our products, which is stricter than the standard accepted standards in order to achieve the highest quality products.

Advantages of drying wood

Drying reduces the moisture content, which makes the wood more stable and less susceptible to deformations such as shrinking, cracking or twisting. It also allows its mechanical properties to be adjusted. It enables the hardness, strength and elasticity of the wood to be adapted in a controlled way to specific requirements, and also reduces its weight. This allows the wood to retain its dimensions and shape, which is crucial in the construction and manufacture of wooden products such as transport crates.

The high moisture content of wood encourages the growth of mould, fungi and bacteria, which can lead to wood decay and reduce its quality. Wood also contains nutrients such as carbohydrates, which are necessary for their growth and reproduction. Drying removes the moisture necessary for the growth of these micro-organisms and cuts them off from food.

The high moisture content and availability of nutrients attract not only micro-organisms, but also a wide range of insects that penetrate it through its surface by gnawing, digging tunnels, or creating entrance holes. Once the insects get inside the wood, they settle there and start feeding which leads to their reproduction and spread. They mainly feed on cellulose hemicellulose and lingnine, which leads to j degradation of the wood. Dried wood deprives them of this opportunity, making it unattractive to insects.

Wood drying process

Drying wood is a key step in transforming raw wood into a durable and useful material. It aims to reduce the moisture content of the wood to an acceptable level, which is usually below 20%. There are several different methods of seasoning, each with its own advantages and disadvantages, as we will discuss briefly below.

Air drying (seasoning)

This is the traditional method of drying, which involves leaving the wood outside, exposed to the weather. The time it takes depends on several factors such as the type of wood, its thickness and climatic conditions. The process usually takes from several months to several years. Although it is the oldest drying technique, it is still used in many parts of the world.

Advantages:

Low cost: no sophisticated infrastructure or complex equipment required.
Eco-friendliness: it is environmentally friendly as it does not use electricity, fossil fuels or chemicals, which is good for the environment.
Optimal for some wood species: air drying may be optimal for some low-density species that are not prone to cracking or twisting during drying

Disadvantages:

Long drying time: air drying is much slower than drying in kilns, which means that the wood remains outside for a long period of time and is therefore exposed to changing weather conditions
Low Moisture Control: Air drying does not allow precise moisture control, which can result in uneven moisture content in the wood.
Risk of Defects: As a result of improper air drying, wood is susceptible to various types of defects, such as cracks, warping, resin leakage, knot loosening, discolouration and deformation, which reduce the quality and value of the wood.
Sensitivity to Contaminants: Air-dried wood is exposed to contaminants such as dust, bird droppings and other substances that can affect its quality.

Chamber drying

Chamber drying is a more advanced method of drying wood that is widely used in the timber industry. The wood is placed in a special drying chamber where parameters such as temperature, humidity and air circulation are controlled. The water in the wood is removed gradually by heating and air circulation. This method is effective and provides precise control over the drying process, making it widely used where precision and high quality wood are crucial.

Advantages:

Precise moisture control: chamber drying enables precise control of the wood’s moisture content. This process achieves a set moisture content at a level that ensures the durability, stability and strength of the wood.
Shorter lead times: chamber drying is much faster than air drying, which affects production efficiency.
Higher quality of the final product: chamber drying minimises the occurrence of defects such as cracks, warps or twists in the wood and other deformations, which has a positive impact on the quality of wood products.
Minimising the impact of atmospheric conditions: the process takes place under controlled conditions in the drying chamber, which minimises the impact of changing atmospheric conditions on the quality of the wood.
Cost-effectiveness: although it requires investment in drying chambers and energy, it can be more economical in the long term than other drying methods.

Disadvantages:

Investment cost: the relevant equipment must be purchased
Wymaga Energii: proces ten wymaga dostarczenia energii do komory suszarniczej

Pressure-vacuum drying

Pressure-vacuum drying is an advanced wood drying technology that uses controlled changes in pressure and vacuum to remove moisture from wood. It is one of the fastest and most precise drying methods.

Advantages:

Faster drying process: it is faster than traditional drying methods. Pressure and vacuum allow the boiling point of water to be lowered, which speeds up the process of evaporating moisture from the wood.
Precise moisture control: This method enables very precise control of the moisture content of the wood. Thanks to controlled pressures and temperatures, the wood reaches a certain moisture content.
Minimising the occurrence of defects: reduces the occurrence of wood defects such as cracks, warping and twists.
Energy saving: Compared to chamber drying, it uses less energy because it allows the drying temperature to be lowered.

Disadvantages:

High investment costs: pressure-vacuum drying equipment is expensive and requires a significant initial investment, which can be a challenge for smaller companies.
Complex drying process: the process requires specialised know-how, experience and advanced equipment and technology.

suszarnia komorowa drewna danpol skrzynie transportowe

Wood drying at Danpol

Danpol is a company with a long tradition in the production of wooden packaging, transport boxes and pallets. We provide our customers with products of the highest quality, which is guaranteed by subjecting wood to thermal treatment in accordance with IPPC requirements.

Our main tool in the drying process is a chamber dryer, which allows us to achieve the appropriate moisture content of the raw material we use for timber production. At Danpol, we regularly improve the wood drying process in order to meet the strict phytosanitary standards in the ISPM-15 standard.

IPPC certificate and ISPM-15 standard

The ISPM-15 standard is a regulation developed by the International Plant Protection Organisation, which specifies the requirements for the treatment of wood for the creation of wood packaging to transport goods through various countries. Above all, the application of the ISPM-15 standard is intended to prevent the spread of diseases and wood-dwelling insects that are a potential threat to the biota of other environments.

The IPPC certificate is issued for timber that meets the ISPM-15 standard. All pallets and sawn timber that have undergone heat treatment are marked with the IPPC mark with additional symbols indicating the identification code of the operator responsible for the fumigation process, the name of the country, the certification number and, if the timber has undergone suitable heat treatment, it will be marked with the HT symbol.

The ISPM-15 standard assumes that proper drying of the wood in the drying chamber takes place when the wood reaches a temperature of 56°C and this is maintained for a minimum of 30min. This is a key part of the drying process, as this temperature allows potential pests and fungi that may be in the wood to be destroyed.

Longer drying time for perfect results

Although the temperatures in our drying chambers are equal to those required and the thermal treatment maintains the time specified in the ISPM-15 standard, at Danpol we leave the thermally treated timber in our chambers for a longer period of time in order to achieve a better drying effect, thereby eliminating the risk of damp areas forming inside the raw material.

Methods of drying wood for transport boxes

Advantages of drying wood