1-1. SHINKOLITE PX

• Grade : PX
• Size : 2.763 m (108")(flexible length)
• Color : Standard colors and special requests

1-2. Heat-Forming Process

• 1-2-1. Molds

  A mold used for the morning or acrylic sheet is usually made from wood, plastic, or aluminum. The selection of the mold material is dependent upon the anticipated number of parts to be produced before a design change is expected and the capital investment funds available for tooling. Two ways of controlling mold temperature, which is usually kept between 50-80°C (122°F-176°F) are by electric heating coils and built in piping for hot water. The selection, if any, depends on availability and cost of either energy source. In the sanitary ware application for acrylic sheet, most molds are preheated in the oven prior to the start up of a thermoforming session. This lessens the chance of a sheet failure resulting from a cooling cycle which is too rapid after the heating and forming of a sheet. Specialcare should be taken to properly preheat the clamping area of the mold, a surface area which is too cold in this area will cause the sheet to pull away from the clamp resulting in a wasted sheet. In the construction of the mold, it is necessary to be sure there is sufficient draw or gradient between the male and female mold to assure a quick and clean demolding or releasing process. Usually this difference is 2/100 to 5/100 for a male mold and 1/100 to 2/100 for a female mold. In the round radius at the bottom of the mold a minimum of 25mm (1 inch) for each 5mm (.200) in thickness. The minimum radius of a round part is proportional to the original sheet thickness and depth of the draw.

  
  
• 1-2-2. Heating Equipment

  The following type of equipment is used to heat acrylic sheet. It is most important to be able to control the heat and to heat the sheet completely through.

  1. Natural Air Circulating Oven

     This oven has a shelf for suspending a sheet of acrylic over nichrome wires buried in the bottom which heats the surrounding air. The hot air rises and heats the sheet. This is a simple oven and allows little control of the heating area.

     
     

     Fig. 2-1. Natural Air Circulating Oven

     

     
     
  2. Forced Air Circulating Oven

     This oven has more temperature control and is especially suitable for heating thicker sheet. It is ideal to use this oven in the 140°C-200°C (284°F-39°2F) range with a plus or minus 3°C (5°F).

     
     

     Fig. 2-2. Forced Air Circulating Oven

     

     Example	Measure	Circulated air volume	Heater capacity
     	0.4m3	20m3/minute	6~7KW
     	0.6	30	8~9
     	1.0	50	10~11
     	1.5	80	13~14
     	2.0	110	17~18

  3. Electric Infrared Ray Heating Oven

     This oven uses a high temperature radiant heater, the advantage being the ability to have your point of source of heat further away from the acrylic sheet. This higher heat range can be the cause for many problems in thermal forming, with the chief problem being that of heating the top and bottom of the sheet quickly, but the center not as much.
     A cure for this is to keep a lower voltage and heat over a longer period of time. Another effective technique is to raise the temperature step by step.

     
     

     Fig. 2-3. Electric Infrared Heating Oven

     

     
     
• 2-2-3. Forming Installation

  This is a working process to put the heated and softened on a forming mold, to clamp it, and to vacuum form it. It is important during this process to make sure you have no air leaks or vacuum leaks.

  1. Vacuum Forming Machine

     This machine is the heart of the acrylic thermal forming process. The clamping, heating, pressing, vacuuming, blowing, and cooling are all part of this machine. In order to more efficiently control the heating of each sheet of acrylic the machine must be larger in size than the largest sheet size you anticipate using.

     
     

     Fig. 2-4. Vacuum Forming Machine

     

  2. Traditional Forming Methods

     The sheet is inserted into the oven, heated and withdrawn, placed on the mold and formed. The disadvantage of this system is the amount of time needed for moving the sheet in and out of the oven. The General Forming Methods are shown below.

     
     

     Fig. 2-5. Straight forming

     

     
     

     Fig. 2-6. Snapping Back

     

     
     

     Fig. 2-7. Plug Assist Reverse Drawing

     

Basic ways of forming

1. Press forming
2. Blow forming
3. Vacuum forming

Any complicated forming comes from these forming combination.

2-3. Fiberglass Process

As all fiberglassing of vacuum formed acrylic sheet is done on the back side, care should be taken to protect the surface side of the acrylic sheet during this and further production stages. Normally a masking tape is on the top lip of the part. Other procedures such as clean soft cushion material should be used to pad the jig frame. Two types of glassing techniques are used.

• 2-3-1. Hand-lay Method

  This is for a small production line of small parts. As always, the most important aspect of this method is to remove the air from the laminate via a squeegee or a roller.

• 2-3-2. Spray-up Method

  This is the most commonly used method for the reinforcing of acrylic sheet. The mixing of resins, fiberglass and catalyst are important to assure a proper cure. Perhaps the biggest danger in this process is the improper catalyzation of the laminate. Blistering could occur if the ratios are out of the proper percentage levels. The thorough removal of air, particularly in the radius areas is also important to prevent later delamination problems in the part.