Dieffenbacher plywood/Continuous press line for veneer laminated timber

Current situation of China’s plywood industry

The development of China’s plywood production, while meeting domestic and international market demand, has solved the employment of large surplus rural labour force and promoted the development of plantation forests. In addition, China has a large number of plywood enterprises. But it is difficult to keep up with the new normal of China’s economic development due to their small scale, poor equipment, backward technology, serious and low quality homogenisation of products and disorderly market competition.

China’s plywood industry is in need of upgrading

In China, with the shortage of forest resources and labour, rising timber prices, rising chemical raw material prices and transport costs, rapidly rising labour wages and safety costs, the comprehensive production costs of plywood enterprises are rising, while the profit margin of enterprises is constantly compressed. Another important reason is that in the production of plywood, it is not possible to continuously form veneers and continuous hot pressing, which severely restricts the development of plywood production in the direction of large-scale industrialisation. In addition, due to the simple production technology and backward equipment of most plywood enterprises, the quality of the plywood produced varies greatly, for example, the thickness tolerance of plywood reaches 1 to 3 mm, which is difficult to meet the market requirements for its quality.

Dieffenbacher has the longest experience in the field of continuous veneer laminate production. The company has supplied several continuous press lines for plywood/veneer laminated lumber (LVL) to customers all over the world.

Continuous press lines for plywood/veneer laminated timber

4 feet wide continuous press line with a production capacity of 80,000 to 130,000 m³/a

The process layout of the line is shown in the diagram above. The main equipment is a veneer feeder 1, a curtain coater machine 2, a veneer grouping device 3, a microwave pre-heater 4, a continuous flat press 5, a diagonal saw 6, a veneer laminate and long board stacking device 7, and a star-shaped cooler 8.

4 feet to 8 feet wide continuous press lines with a production capacity of 150,000 to 220,000 m³/a

Process layout diagram

The process layout of the line is shown in the diagram above. The total length of the line is approximately 180 m. The difference between the two lines is that the line is equipped with two parallel veneer feeding lines at the feed end. The veneer is thus conveyed to the main line of the continuous flat press, where it is automatically formed into a continuous 8 feet wide veneer. The veneers are hot pressed in the continuous flat press and then processed through the post-treatment process to produce the required specification.

Plywood produced by continuous press lines

1) Standard plywood

This is a common type of plywood. It is three or more layers of plywood pressed from rotary cut veneer or planed thin wood blanks.

2) Container baseboards

Plywood for container flooring can be manufactured from traditional tropical broadleaf timber such as Abidon and Clone.

3) Various types of plywood and new types of sandwich panels

This is a new type of plywood product developed by companies in response to market demand. For example, as the supply of timber such as Abidon has decreased significantly and prices have risen, the cost of container baseboards has increased. A Chinese company has now developed the technology to make container base boards (COSB) from specially made oriented strand board, which is a high value-added product. The central layer of this plywood product uses a single oriented strand board.

Components of a continuous press line for plywood/veneer laminates

Veneer scarfing line

The veneer scarfing line is arranged in front of the main line of the continuous press. It is used to grind the top and bottom layers of longitudinal veneer in a range of widths so that the top layers can be lapped together to form a continuous core veneer when forming the blank. The veneer grinding line generally consists of veneer feeding, veneer grinding and gluing, outfeed stacking and conveying equipment.

plywood forming lines

The fully automatic plywood forming line is shown below and the nominal size of the veneer used for forming is 4’ x 8’. 

Plywood forming line

1) Veneer feeder

This machine automatically lifts the veneer one by one in vacuum and transports it to the intermediate conveyor belt, where it is then transported to the gluing machine.

2) Curtain coater machine

This machine showering glue to the upper surface of each veneer that passes through the gluing machine. The advantages of using a curtain coater machine: the glue is evenly applied to the upper surface of the veneer, the amount of glue applied is very constant and easily adjustable, thus reducing the consumption of glue. High coating efficiency, low labour intensity, suitable for continuous line production.

Veneer pre-pressing and hot pressing process

Microwave pre-heating systems are used in the production of veneer laminates. The continuous veneer that has been assembled moves and passes through the microwave pre-heating system. The heat generated by the microwave system is concentrated in the heated core layer of the veneer, resulting in a higher core layer temperature than the surface layer of the slab material. The subsequent presses, when hot pressing the continuous veneer, create an opposite temperature gradient along the thickness of the veneer. These two are superimposed on each other, so that thick veneer laminates reach essentially the same temperature in the surface and core layers.

This graph shows the temperature gradient curve of the veneer. It shows micro-blog preheating, conventional press heating, and the effect of superimposition respectively.

A number of veneer laminate lines have been in operation using microwave technology. The line is heated by a very low intensity electromagnetic field, which has no effect on the movement of people in the area; the microwave pre-heating system has a high energy conversion rate, which greatly increases the production speed of the continuous press line.

The continuous flat pressing hot press is shown in the diagram below.

The diagram below shows a continuous flat press with a microwave pre-heating machine. The length of the continuous press is 38 to 60 m; the pressed product width is 4′, 6′ or 8′; the hot press sheet width is 1 500 to 2 650 mm. There are two drive rollers at the discharge end. The press speed is between 10 and 200 mm/s. The press inlet is compact and short; the final heating zone of the press has no high thermal requirements (the heat source can be switched off in order to cool the veggie veneer).

Advantages of continuous press lines for plywood/veneer laminates

1) Small deviations in sheet thickness and low sanding volumes.

2) No flush loss in the lateral direction of the sheet.

3) More stable sheet properties due to shorter press opening times for loading and the possibility of using fast curing adhesives.

4) Low glue consumption due to the absence of flush loss in the cross-section of the sheet and the low amount of glue applied.

5) Fewer workers required.

6) Low thermal energy consumption of the press.

7) Continuous production of plain boards whose thickness can be measured online by means of a thickness tester.

8) Less rejects because the quality of the veneer is checked prior to forming and shorter lengths of rejects are cut off (in-line thickness measurement).

9) No warping of the veneer laminate.

10) Flexible adjustment of the sheet length; the thickness of the sheets can be adjusted in the range of 5 mm to 150 mm.

The NelsonPine plant in Richmond, New Zealand, is equipped with a Dieffenbacher plywood/veneer continuous press package. The average thickness deviation per sheet (including the position of the veneer overlap) was 28 mm ± 0.15 mm for a 28 mm thick plywood sheet.

Quality is the life of an enterprise and product quality is the key to its survival. The adoption of advanced plywood production processes and machinery and equipment is a very important part of plywood enterprises to enhance and guarantee product quality. Sinoeuro Machinery is a leading brand for wood based panels machinery. Sinoeuro Machinery manufacturer is a professional manufacturer with 27 years experience for veneer peeling, plywood machinery solutions plant with factory layout and processing technology.It covers 8000squre meters,with more than 100 R&D and after sales service technicians. If you are interested in plywood making machine, you can visit these websites:

https://plymachineline.com  https://china-plywoodmachine.com

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