Manufacturing rotary veneer from small logs
Special thanks to the original source of https://www.aciar.gov.au/publication/guide-manufacturing-rotary-veneer-and-products-small-logs
, a veneer is a thin layer of wood usually 1–4 mm in thickness, removed from a log using a rotary peeling process. Other
forms of veneer such as sliced or sawn veneers are not discussed.The process of rotary veneer production is to remove a continuous thin ribbon of wood from a peeler billet periphery using a knife that is positioned parallel to the grain. The billet is rotated against the knife using a drive mechanism that varies in design and approach, depending on the technology being used.
Uses of rotary veneer
Rotary-peeled veneers can be used to manufacture products suitable for structural and appearance applications. Common structural applications for products manufactured from rotary-peeled veneers include structural plywood, formwork plywood for concrete construction, packaging, marine ply and laminated veneer lumber. Decorative uses for rotary-peeled veneer include architectural uses, furniture and joinery.
GENERAL OVERVIEW OF VENEER-BASED PRODUCT MANUFACTURING
Veneer-based product manufacturing typically involves three main stages: veneer manufacture (billet storage, handling and peeling); veneer clipping, drying and up-grading; and panel lay-up, pressing and finishing (Figure 1.1). Recommended practices for each stage are outlined below
Stage 1: Veneer manufacture
Grading, sorting and handling logs
◆ Select logs that meet required specifications—appropriate quality and size.
◆ Sort logs into batches based on quality, size and species.
◆ Minimise time between harvesting and processing to avoid degradation.
◆ Store logs off the ground and protect where necessary from drying and biological attack from insects.
◆ Cut logs to billets of appropriate length before peeling
Debarking, pre-conditioning and round-up
◆ Ensure billets are kept free of stones, dirt and other debris in order to avoid damage to peeler knives and other equipment.
◆ Debark and consider pre-conditioning (heating) billets prior to peeling.
The decision whether to pre-condition or not is a matter of weighing up the advantages and disadvantages for each individual peeling operation. Choose pre-conditioning conditions appropriate for the resource, equipment and target products. As a guide, hardwoods with a density of 500–700 kg/m3 are normally heated to 50–70°C, and wood with a density >700 kg/m3 to 70–90°C. It is important that the desired temperature is reached across the full radius of the billet.
◆ Round-up to produce cylindrical billets prior to peeling
◆ Choose lathe technology compatible with log resource characteristics, target products, available supporting infrastructure, labour and other economic factors. Spindleless lathes are proving to be an effective processing method foforest resources such as young fast-grown plantation hardwoods where treediameters are small (e.g. often <200 mm), billet qualities are comparatively low (at least compared to billets from mature native forests) and billets are prone to end-splitting.
◆ Adopt manufacturer’s specific instructions for lathe set-up appropriate for the resource and target products. Optimal settings are determined by a range of conditions and parameters including the lathe capacity, supporting infrastructure (e.g. billet pre-treatment), species, log size, log quality, speed of production and actual veneer quality requirements (including target thickness and thickness tolerance).
◆ Position the billet in the lathe in order to maximise the recovery of veneer. In more sophisticated operations using spindled lathes, scanning systems support the optimal positioning
Stage 2: Veneer clipping, drying and upgrading
Clipping and sorting
◆ Choose a clipping strategy that recovers the highest amount of accurately sized veneer with acceptable quality.
◆ Sort the veneers, where appropriate, according to quality, size, cross bands, long bands, fishtails, heartwood and sapwood.
◆ Separate the veneers into types that will dry at different rates, e.g. it may be necessary to separate heartwood from sapwood veneers.
◆ Determine target moisture content according to adhesive, product and market requirements.
◆ Dry the veneers as soon as possible after peeling to avoid degradation (e.g. by moulds, veneer distortion or buckling).
◆ Re-dry veneers that do not meet moisture content requirements
Grading, patching, joining, sorting
◆ Grade the veneers according to the requirements of relevant standards and/or requirements of customers.
◆ Consider upgrading veneers through composing and patching veneers. However in some cases, the preference is to patch panels instead Sort the veneers according to type—quality, sizes, mechanical properties (e.g. for modulus of elasticity (MoE) where suitable testing equipment is available and structural products are targeted), cross bands and long bands.
Stage 3: Product lay-up, pressing and finishing
◆ Prior to lay-up, ensure that the veneers are of appropriate dimension, quality
and moisture content.
◆ Use an adhesive suitable for intended product end use.
◆ Prepare and apply adhesive according to adhesive manufacturer’s instructions.
◆ Choose a construction strategy that satisfies the quality requirements of the final product but also efficiently utilises the available veneer qualities that are produced from the forest resource. That is, optimise the placement, use and
combination of the lower volume of high aesthetic quality or high mechanical quality veneers and the higher volume of lower qualities veneers. For example, the outer veneers of a panel have the most influence on the mechanical
performance of the final product with the inner core veneers having less influence. It is therefore important that veneers with the highest mechanical qualities be favoured for the product outer veneers (in particular face and back veneers) and low mechanical quality veneers be directed towards the inner core veneers.
◆ Press products according to recommended press schedules.
◆ Trim, fill and patch products.
◆ Where necessary sand and finish products.
◆ Grade and test products according to the requirements of relevant standards and/or requirements of customers