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How High Frequency Works in the Timber Industry |
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Introduction
Past day synthetic resin adhesives can take up to a few hours or days before they attain any real strength to hold two or more pieces of wood together. This lengthy setting time does not matter when the pieces are held together by nails, screws or dowels, but when there is no physical holding together of the pieces other than the adhesive, the jig or press is of necessity occupied for a long time for each article being made.
The object of R.F. heating is to raise the temperature of the glue line (adhesive) in an assembly, so reducing the time that it has to be in the jig or press.
Adding R.F. heating to the jig or press enables the glue to be cured in minutes or even seconds and results in high daily outputs.When R.F. heating is introduced to the press there can be down pressure to hold the pieces level so that tonguing and grooving is no longer necessary, thus giving a saving in wood, a saving in the time needed to put the tongues and grooves on the timber, and a saving of the investment in the machines for carrying out the tonguing and grooving operations.
Adhesives
If two pieces of flat timber are to be joined together without the use of mechanical fasteners such as nails or screws they must be stuck with some form of adhesive. This is any substance which will adhere to the materials to be joined and has sufficient strength in itself to hold the two pieces together.
The normal adhesives encountered in the woodworking industry can be divided into three groups.
- Those that set by loss of moisture.
- Those that set by cooling from a molten state.
- Those that set by a permanent chemical reaction.
Group (3) adhesives which are usually known as synthetic resins include urea-formaldehyde. The setting process is speeded up if they are either mixed with or brought into contact with a hardener or accelerator. This has the effect of speeding up the chemical reaction and reducing the setting time to hours or even minutes. Once the chemical reaction has taken place it cannot be reversed either by water or by heat, although the two together may reduce the maximum strength of the bond slightly.
In order to get the best results from R.F. heating, it is essential that the correct type of glue is used under the right conditions. It is necessary, therefore, that the user of this heating technique knows the basic principles of modern glues which are needed for any particular application; also the correct mixing percentages as either too much or too little hardener in the glue will result in longer setting times
General Principles of R.F. Heating
There are two principle means of raising the internal temperature of a non-metallic material such as wood and glue: (1) by applying heat externally or (2) generating it internally. In the first method, use is made of the thermal conductivity of the material, which is low for wood, so the outside has to be raised to a much higher temperature than the centre, unless the heat is to be applied for a very long time. Outside temperature higher than inside will cause one problem, moisture will difficult to extrude out of wood. The second method is to use R.F. heating which is also known as High Frequency of H.F. Dielectric which generates heat in the material itself. In practice the frequency employed in the wood industry is between two million and thirty million cycles per second.
When two metal plates, which are connected to a source of R.F. (H.F.) energy, so having an R.F. (H.F.) voltage on them, have a block of wood between them, heat is generated in the material itself. All materials are made up of molecules which are ‘dipole’, i.e. one end is charged positively, and the other negatively. |
Through Heating-general usage on Wood Bending and Forming
The fundamental principles of R.F.(H.F.) heating were described as above in which the material to be heated was placed between two plates or electrodes. This is the system employed in Through Heating, especially in the making of laminated shapes. |
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Glue Line Heating-general usage on Wood Board or resembling
Glue line heating is when the electrodes are either side of the glue line to be cured. It is one of the most widely used methods having the advantage that the majority of the
Energy goes into the glue line with only a small percentage into the wood.
In the attaching of wooden bearers, rails and runners to plywood or hardboard panels for the making of such sub-assemblies, as sides of bedside cabinets, dressing tables and kitchen cabinets being just a few examples, glue line heating is at the time the most popular method. |
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Stray Field Heating-general usage on irregular wood products
When the glue line is separated from the electrodes by a sheet of plywood, hardboard or chipboard, the system is known as stray field heating.
This system using the platen was originally designed for the ‘putting on’ of flat tops on articles of furniture such as bedside cabinets, tables, stools and chests of drawers being just a few examples;
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Advance Applications of R.F. Heating
Wood drying
R.F. heating is one of the ideal methods of raising the temperature of timber, so that the outside can be kept lower than the interior when its moisture content is to be reduced. By having the inside hotter than the outside there is no chance of case hardening, which normally occurs with air drying, as the moisture content of the exterior is less than that of the middle. By raising the temperature of the centre, the moisture expands and is forced to outside, so keeping the exterior damp, which allows the moisture to escape easier. The higher the initial moisture content of the timber, the softer will be the outside so allowing the internal water to get out more easily. |
Safety of KUOMING High Frequency Machines
30 years since KUOMING founded, we have accumulated for over 30 years of High Frequency technology knowledge. Our technology not only apply on Timber industry, but also apply on Metal processing, Plastic Welding, Medical instrument processing as well as on Lunch box making. All these proved that our flexibility over this technology. Safety devices have been equipped with all our machines whatever inside and outside. A microwave oven can be even more danger than ours, if one careless safety.
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Simplified Maintenance
Most of our customer used to worry about is, Is High Frequency machine difficult to maintenance? Base on this, we have improved and enhanced all our machines, whatever both at components which comply with international brand or at machine structure design. Simplified and easily maintenance is our main principle on designing all our machines. Even one technician who with general technical acknowledge will able to maintenance of our machine. What more, our patented “Variable Capacitor” is under lifetime guarantee. This is our customer-guarantee second to none |
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