Hot Plate Welding

HOT PLATE WELDING:

Plastic components to be welded are partially melted by being in contact with a high temperature thermal source or a hot plate, and then welded together before they become cold and solidify.

As a method to obtain relatively firm welding with the relatively simple equipment, this method has long been used and is particularly suitable for large moldings.

1. Hot Plate Welding is a plastic welding process utilizing heat of hot plate placed between the surfaces to be joined.  

2. A heated plate is clamped between the surfaces to be joined until they soften. 

3. The plate is then withdrawn and the surfaces are brought together again under controlled pressure for a specific period. 

4. The fused surfaces are allowed to cool, forming a joint. 

5. The welding tool or heating element has built in electric heaters to prevent the plastics sticking to it.

6. Hot plates are made mainly of Aluminum alloys. 

7. A hot plate is equipped with an electric heating elements and a thermocouple providing temperature control of the plate surface.

HOT PLATE WELDING PROCESS

The equipment consists of a hot plate to simultaneously heat two surfaces to be welded and a pressurizing mechanism.

First step: Moldings to be joined are kept in contact with the hot plate to melt the welding areas.

Second step: Two molten surfaces are kept in contact each other and held until they are cooled and solidified.

Typical hot plate temperature to weld plastics ABS - 210 Deg-C - 230 Deg C

PP - 190  Deg-C   210 Deg  C

PVC - 210  Deg-C  220 Deg  C

PRESSURE BETWEEN A WORK PIECE AND A HOT PLATE

Minimum pressure to achieve close contact of the work piece with the hot plate

If the pressure is too high, the dimension can be smaller than the specification and flash may be generated.

When the welding machine is not equipped with a pressure controller, some invention on the side of jigs is required, for example the installation of stoppers.

MEASURES TO PREVENT STICKING OR THE ADHESION OF MOLTEN RESIN TO A HOT PLATE.

To use polytetrafluoroethylene (PTFE) sheets or to coat the hot plate with PTFE.

Note : Mirror finish on the surface of the hot plate is required before the coating with PTFE

FEATURES OF HOT PLATE WELDING:

MERITS

High weld strength and efficiency. The highest in all known welding processes.

Relatively large degree of freedom in the total shape of the component and in the design of welding portion.

DEMERITS

Since the transfer of heat from the hot plate to the moldings is required, processing cycle time becomes relatively long.

Measures to prevent the sticking of molten plastics to the hot plate is necessary, otherwise stringing may happen.

Advantage

1. Easily automated; 

2. High quality tight joints; 

3. Large and complex parts may be welded 

4. Hot plate provides confirming the joined surfaces. 

Disadvantage

1. Long welding cycle: up to 20 sec. for small parts and up to 30 min. for large parts; 

2. Relatively large amount of flash (excess material) forms. 

Application

1. Components of domestic electric devices (dishwashers, washing machines, vacuum cleaners) 

2. Pipes 

3. Automotive components (lights, fuel tanks, reservoirs, batteries).