How to solve woodworking dust

1. Introduction

In the modern variety of wood processing plants and wood-based panel plants are widely used in the vacuum dust collection system, it has become the development of these factories in the production of high-tech production level indispensable production equipment. Specifically, there may be as many as dozens of different types and sizes of woodworking machines in various types of wood processing plants, which produce large amounts of wood fragments of different shapes during the processing of wood Wood chips are usually shavings, wood chips, sawdust, wood fiber and wood flour, etc., the use of dust collection system can be these wood shredding materials in a timely, clean, continuous suction out to the designated location, which for It is of great significance to ensure the normal production of wood processing, improve labor productivity and improve product quality, protect the environment inside and outside the workshop, ensure the health of workers, improve the fire conditions in the workshop and prevent the surrounding environment pollution. This paper introduces the structure, working principle and characteristics of the new dust collection system.

2. Principle of Dust Collection System

Dust collection system consists of three parts: (1) pipeline system; (2) power system; (3) filtration system. These three parts are equally important for ensuring the efficiency of the dust collection system.

2.1 Determination of piping system

The piping system consists of a movable hose, straight pipe, elbow, multi-pipe, sliding baffle and throttle. The movable hoses are used to connect the machine tools. The sliding baffle is used to close the suction, throttle and conical funnel of a single machine. It is used to adjust the balance of airflow and air pressure in the multi-pass pipe. In the wood processing industry, the dust collection system in the pipeline with galvanized steel plate manufacturing.

Pipeline design should note the following:

1) in order to prevent dust accumulation in the pipeline, the pipeline must keep the wind speed is not lower than a certain value.

2) the air flow in the pipeline, due to the friction of the pipeline, will lead to lower air pressure. The pressure loss is actually a constant, which is related to the velocity of the air flow and the length of the tube.

3) due to the different pressure at the connection, the connection needs to be balanced. If unbalanced, the airflow at the sanding machine will not be sufficient.

4) the power consumption is determined by the amount of wind and wind pressure, exhaust volume, wind pressure and power consumption of the relationship shown in Figure 2. The main parameters of the fans used in the dust collection system shown in Figure 1 are: Air flow Q = 5500m3 / h; wind pressure P = 166mmH2O; speed n = 1800rpm; power N = 3.7KW. As can be seen from Figure 2, high air volume, high wind pressure, high speed will produce high energy consumption. When the air flow is determined by the minimum exhaust requirement of the woodworking machine, the reduction in energy consumption can only be achieved by reducing the pressure of the pipe; the reduction in pipe pressure is achieved by properly balancing the pressure of the piping system.

2.3 Dust collector

Dust collection system used in the dust collector can be divided into two types: (1) positive pressure dust collector, usually a standard type, the fan will blow the dust into the filter. (2) negative pressure dust collector (vacuum filter) is round or oval, by the fan suction filter. The filter in Figure 1 is a positive pressure filter.

The filter consists of three parts: (1) the bottom of the dust collector - dust treatment; (2) the central - dust filter; (3) the upper - air purification. Air and dust enter the bottom of the dust collector by the fan. Dust rises into the dust collector, while the "heavy" dust is deposited at the bottom. "fine" dust is completely attached to the bag, and air is discharged from the top of the filter through the dust collector. The filter bag can not be self cleaned. By the air back to complete, so that the dust deposited in the bottom of the filter. The fan installed at the top of the dust collector is used for air blowing.

The bottom of the dust collector is equipped with plastic bags for collecting dust. The large dust collector discharges dust through a screw or chain conveyor mounted at the bottom. And then through the pneumatic conveying device into the storage box or silo.

2.3.1 Selection of dust collection

The choice of the dust collector is based on (1) the air volume; (2) the amount of dust; (3) the type of dust to determine. The filter load is the amount of air that can be filtered by each filter bag. The load is the amount of air flow (m3 / h) per square meter of the filter bag. Since some dusts are difficult to filter completely in the bag, the dust type is an important factor in determining the load. On the dust collector if the load is an important factor. In the dust collector if the load is too high (dust collector is too small), reduce the system dust removal effect, and easy to plug; if the load is too low (dust collector is too large）, the investment is too high.

When the maximum load is determined, the load of the dust collector is calculated as follows:

Load capacity of dust collector m2 = Air flow (m3 / h) Load (m3 / h)

If the load selected in the example is 80m3 / h per square meter, then the minimum dust collector load is: Dust collector load = 5500/80 = 69m2

2.3.2 Positive pressure dust collector

The positive pressure collector is a standard dust collector. For the wood industry dust collection system in the traditional positive pressure filter maximum load of 80-100m3 / hm2, low load, large volume.

The fan in the positive pressure system is located at the inlet of the filter, so the fan uses an open straight leaf impeller to transport all the dust. The efficiency of such fans is very low (55% -65%), energy consumption. Fan per kilowatt transmission capacity of 550-650m3 / h. For a filter capacity of 50000m3 / h system, the energy consumption will reach 85KW.

2.3.3 Negative pressure dust collector

Negative pressure (vacuum) dust collectors have been used in the European wood industry for 10-15 years because of their high efficiency and compact structure and are now widely used in large production lines.

Negative pressure dust collector has a high load capacity, its range is 180-220m3 / hm2.

The fan used in the vacuum system is an air purifying centrifugal fan with a power of 85-90%. This type of fan transmission capacity of 900-1050m3 / h per kilowatt, for filtering capacity of 50000m3 / h system, the energy consumption is 50KW.

3. The characteristics of the new dust collection system

In the dust collection installed in the automatic cleaning system, when the pressure drop exceeds the specified value, the filter bag will need to clean, when the pressure back to normal, the cleaning work is over, it is through the induction bag pressure changes to achieve automatic clean. At the bottom of the filter is equipped with scraper transport device, can remove the sawdust from the rotary valve.

A conventional pneumatic dust removal piping system must be accurately calculated so that the air pressure of all the machine tools in the system is balanced and sufficient airflow is obtained. This is easy to implement in a small factory, but becomes complicated in a factory with many machine tools. The traditional piping system is very inflexible in the factory floor. When several machine tools need to be moved or repositioned, the piping system must be recalculated or changed. If the piping system does not change, it will cause clogging, or some machine suction is excessive, so that the energy consumption increases.

When a closed-loop control circuit is installed in the dust collection system to achieve the purpose of reducing energy consumption and increasing efficiency, the control system keeps the pipe at a constant vacuum by changing the speed of the fan (at the required air flow) The value means that the amount of inhalation from each machine is constant regardless of whether 50% or 100% of the machine is running. If only 50% of the machine is in production, then the energy consumption of the dust collection system will be halved. In a conventional dust collection system, if 50% of the machine is in production, another 50% of the equipment is closed and the speed of the air in the main pipe will change significantly.