manufacturing process of chinese plywood
TRANSCRIPT
CHINESE PLYWOODMANUFACTURING PROCESS
• Shanghai Yishan Market Research Co.• China Phoenix Woods International• E-mail: [email protected]
www.Chinapwi.com
Making Plywood
Grading and Inspection Trimming and Sanding Hot Pressing Cold Pre-pressing
Log Processing Log Conditioning Lathing Veneers Drying Face veneers grading
Glue Spreading
Assembly
Core Logs Core Veneers Lathing Core Veneers Drying Core veneers Splicing
Packing
1. Face/back veneers manufacturing: Imported logs for face veneers are shipped to the veneer mills’ storage yard
On arrival at the mills’ storage yard, logs are sorted and stored according to species, diameter, length and end-use. The logs for face veneers are mainly Okoume from Africa,
Meranti from SEA, Birch from Russia, Obeche from Burma, Red Oak and Maple from North America, and poplar from local
plantation.
Peeling, Reeling and Clipping
In China in most cases, plywood face veneer is rotary-cut.
The log emerges from the barker after having been stripped of its bark.
The logs are conditioned using steam or hot water to improve peel quality.
At the lathe, a sharp blade peels the log, now called a block, into a continuous sheet of veneer.
The green veneer is clipped to size.
Face Veneers Drying
The veneers need to be dried after peeling. Some are dried by kiln but in North part of China most of the veneers are left outside to dry in the air.
The veneers’ moisture content is around 8-15% after drying.
Face Veneers’ Grade Selection And Packing
When the veneers are dry enough, they are graded and packed, then sold to plywood mills.
The rotary-cut veneers are mainly cut to 4x8 size. The sliced veneers are mainly sold by small components.
SlicingSome species like red oak, cherry and maple, are mainly plain-sliced in China. For the thin veneers (below 0.40mm) they can be laid up to the platform when they are still wet. But for the thick veneers (above 0.5mm they need to be spliced by machines before using.
2. Core Veneers – Peeling, Reeling and Clipping
In China people use species like poplar, paulownia, birch and sometimes mixed tropicals for core materials.
The core veneers are mainly cut to 1250 x 830mm size. Thickness is normally between 1.2mm to 2.6mm.
Core veneers drying
Most of the core veneers are air dried. Some mills use machines like hot pressers to dry them in winter.
Core Veneers Grade Selection And Packing
When the core veneers are dried to 8-15%, they can be graded and sold to plywood mills.
3. Platforms Manufacturing
The glue can be MR, Melamine and WBP.In China the hand roller spreader is a widely used method of glue Application.
The assembly of the plywood prior to pressing entails the jointing of the narrow strips of veneers, which are taped (not egde-glued in China) so as to make sheets of the rqeuired size (mainly 4x8).
Glue is applied to the innerplies or core, which in turn, are laid between the outer veneers ready for bonding. This operatioin accounts for a large share of the manual labor employed in the production process.
4. Cold Pressing And Platform’s Repairing
When the veneers are laid-up as assembly platform sheet, they are fed into hydraulic presses first (no heat) for cold pressing. After that they will be repaired. The repairing is to cut the overlaps of the crossbands, fill in the splits with putty etc..
5. Curing Hot Pressing And Cooling
Then the platform are subject to heat and pressure in the hot press until the glue is cured. The hot pressing time and temperature depend on the thickness and glue. The heating of the platens isgenerally by hot water or steam.
6. Platform Further Repairing And InspectionAfter hot pressing the platform will be inspected piece by piece to avoid delamination problem. They also need to be further repaired. The platform needs to be stored for 3 to 7 days so the moisture can come out and the formaldehyde emission can be lower.
7. Platform’s Calibration
The platform will be calibrated first. This is a very importation step. After calibration the platform is ready for face and back’s lay-up. Usually before the platform goes through the glue speader it needs to be painted. This is to avoid telegraphing.
8. Face/back Laid-up
1. Platform is painted and then goes through the glue spreader.
2. Face back lay- up
5. Final polishing3. Reparing before hot pressing 4. Final Hot Pressing
* Face Reparing Before Hot Pressing
• Before hot pressing the faces need to be repaired carefully. For P/S face and back it needs much more work. The repairing is to cut the overlaps, filling in the splits and open knots with putty.
9. P/S Face/back Plywood ManufacturingThe P/S veneers are small strips and they can be laid-up on the platform when they are wet. After hot pressing the face veneers can be dry because they are very thin (usually below 0.3mm).
10. Trimming And Grade Selection
Primary finishing, which entails the trimming, upgrading of the Plywood after pressing, is undertaken so as to enhance the marketability of the product.
Some Chinese Plywood Quality Problems And Resolutions
Due to: 1. Poor banding materials2. Rough loading and
unloading etc..
Due to:1. Lacking of glue2. Glue is dry when hot
pressing3. Large overlaps4. Too much putty 5. Wrong pressing time,
temperature or pressure 6. Short core
Due to:1. Poor structure2. High moisture
content etc.
Due to:1.High moisture
content2. Excessive salt in
the glue etc.3. Storage problem
Poor Package Moldy Panels
Delaminations Warpage
The Formaldehyde Emission LevelStandard Product(s) Test Method Numerical Value ~E1333 (ppm)CARB-P1 HWPW E1333 0.08 ppm 0.08
" PB " 0.18 ppm 0.18" MDF " 0.21 ppm 0.21
CARB-P2 HWPW E1333 0.05 ppm 0.05" PB " 0.09 ppm 0.09" MDF " 0.11 ppm 0.11
E1 HWPW EN 717-1 0.12 mg/m3 0.14" PB " " 0.14" PB, MDF EN 120 8 mg / 100g 0.10
F*** All JIS A1460 0.5 mg/L 0.07F**** All JIS A1460 0.3 mg/L 0.04
China HWPW GB 18580-2001 1.5 mg/L 0.14" PB GB 18580-2001 90 mg/100 g 0.14
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