Important warning: This is a historical archive text, not a current recommendation, risk assessment or instruction for drying wood in heated petrolatum. Temperatures, tanks, heating, ventilation, lifting, petroleum-derived materials, emissions, fire and explosion protection, worker health and environmental protection must be checked against applicable regulations by authorised specialists.
This text is not an offer of petrolatum, dryers or plant-design services from Savo Kusić. The current offer focuses on windows, doors and related solutions.
Historical material and procedure
The historical text describes the use of petrolatum for drying sawn timber in construction-industry woodworking companies. Petrolatum is described as a waste product obtained during the processing of petroleum lubricating oils.
It is described as a mixture of paraffin, ceresin and purified viscous oils. At a temperature of 20o, petrolatum has a straw-yellow colour. Its specific gravity is stated as about 0.9, its melting temperature as 250o and its solidification temperature as 50o. Petrolatum consumption for drying 1m of softwood is stated as 20 to 25 kg. The text describes this method as less expensive than kiln drying.
Figure 1: Equipment for drying wood in petrolatum: 1 - Decauville track; 2 - container; 3 - crane rail; 4 - crane; 5 - ventilation along the entire building; 8 - heating registers; 9 - slag concrete; 10 - clay insulation
Historical equipment
The construction of petrolatum dryers (Figure 1) is described as very simple. A steel tank is set into a concrete pit and lined with slag wool for thermal insulation. Pipes at the bottom of the tank heat the petrolatum using steam or exhaust gases. Sawn timber is stacked in special containers that are lowered into the tank of heated petrolatum by an electric hoist.
Historical temperatures and duration
The drying time depends on temperature, which the text states may reach 140o for thin softwood material and no more than 110o for thick material. According to the stated data, 25 mm-thick softwood sawn timber dries from 45% to 15% moisture content in 3h, while material 40-45 mm thick dries in 8h. Billets with a cross-section of 100 x 100 mm dry in 22-24h, described as approximately 15-20 times faster than drying in steam chambers.
After drying, the material should be kept in a cooling room or in a warehouse for two to three days, after which it can be processed on machines.
Historical description of qualities and limitations
The historical text describes the drying quality of softwoods and coarse-pored species as fully satisfactory. It states that oak and large-section softwood produce considerable waste during petrolatum drying because of internal cracks. Petrolatum penetrates the wood to a depth of 2 mm and is said to provide an antiseptic effect, but the resulting petrolatum crust makes subsequent machining more difficult. The text also notes an uneven moisture distribution through the cross-section of the dried sawn timber, ranging from 6 to 14% depending on the wood species.