Calculation of raw material requirements for plywood
plywood raw materials
(1) Timber requirements
Loss (process loss and technical organization loss) coefficient:
The loss of each process can be calculated according to the sequence of the process flow:
1. Surface processing of plywood:
Process loss coefficient I1=δ/SΦ×100%;
In the formula: I1——Process loss coefficient of plywood surface processing
δ——Surface machining allowance (mm), single-sided sanding δ=0.1~0.15 (mm)
Single-sided scratching δ=0.15~0.20 (mm)
SΦ——The thickness of the hot-pressed plywood (mm)
Then I1=0.15/3×100%=5%
The loss of technical organization is included in the trimming process and considered together.
2. Trimming:
Process loss coefficient I2 = (F end - F already) / F end × 100%;
In the formula: I2 ——the process loss coefficient when the plywood is trimmed;
The end of F - the area of the plywood without trimming (m²)
F has - finished plywood width after trimming (m²)
The trimming allowance is usually taken as 60mm
Then I2=(1.890*0.975-1.830*0.915)/ 1.890*0.975×100%=9.13%
Take I2=10%
Technical organization loss △1,2=3%.
3. Hot pressing:
Process loss coefficient I3=(∑S - SΦ)/∑S×100%;
In the formula: I3——compression loss coefficient of plywood during hot pressing;
∑S——Plywood slab thickness (mm)
SΦ——The thickness of the extruded plywood (mm), measured after leaving the press for 24 hours.
I3=15%
Technical organization loss △3=0.5%
4. Dry veneer processing (finishing, grading, repairing):
The process loss factor I4=10%, and the technical organization loss (△4) is included in I4.
5. Veneer drying:
Process loss factor I5=8%, technical organization loss △5=0.4%.
6. Wood segment rotary cutting:
Usually, the process loss coefficient I6=25%, and the technical organization loss △6=2% is caused by the centering deviation.
7. Log truncation:
Process loss factor: I7=4%, I7 includes technical organization loss (△7).
After the loss coefficient of each process is determined, the required amount of raw materials for this process can be calculated from the following formula:
Qn=(m³/per shift)
In the formula: Qn——the required amount of raw materials for this process (m³/per shift);
Qn-1——The required amount of raw materials for the previous step in the calculation process. Since the calculation is performed backwards, it is actually the next process in the process flow; (m³/per shift)
In——the process loss coefficient of the process;
△n——Technical loss coefficient of this process.
The calculation of each process is as follows:
① Number of finished products in storage
Q into = Q has (1-Io)
In the formula: Qcheng——the quantity of finished plywood in storage (m³/per shift)
Qhas - processed plywood to be inspected, Qhas = Qcp (m³/per shift)
Io ——Sampling inspection percentage (1% for ordinary plywood, 4% for export board).
Qcheng = Q has (I-Io)=17.6099*(1-1%)=17.4338 (m³/per shift)
② The amount of plywood without surface treatment
Q not 1=Q already/(1-I1)=17.6099/(1-5%)=18.5367 (m³/per shift)
③ The amount of plywood without trimming
Q not = Q not 1/(1-I2-△1,2)= 18.5367/(1-0.1-0.03)=21.3066 (m³/per shift)
④ The volume of blanks before hot pressing (that is, the number of dry veneers after dry repair)
Q dry 1= Q not/(1-I3-△3)= 21.3066/(1-0.15-0.005)=25.2149 (m³/per shift)
⑤ The amount of veneer after drying
Q dry = Q dry 1/(1-I4)= 25.2149/(1-10%)=28.0166 (m³/per shift)
⑥ Amount of wet veneer before drying
Q wet = Q dry/(1-I5-△5)= 28.0166/(1-8%-0.4%)=30.5858 (m³/per shift)
⑦ Wood segment volume for peeling
Q wood = Q wet/(1-I6-△6)= 30.5858/(1-25%-2%)=41.8984 (m³/per shift)
⑧ Log requirement
Q original = Q wood/(1-I7)= 41.8984/(1-4%)=43.6442 (m³/per shift)
The material η of the plywood can then be calculated as:
η=Qcheng/Qoriginal×100%=17.4338/43.6442=39.95%
And the amount of logs consumed per 1 cubic meter of finished product can also be obtained:
K= Q Yuan/Q Cheng=43.6442/17.4338=2.50 (m3/m3)
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