Geogrid Tips: Punching and Stretching Process

2025-12-18

Punching and stretching process is a unique physical processing technology that first punches holes and then stretches them, which is the core technology for manufacturing Biaxially Oriented Polypropylene Geogrids. (Regarding of ASTM D6637)

The following are the detailed steps of this process:

Raw Material Preparation and Extruding

(1) Mix high polymer polymers (PP or HDPE)

[if necessary, mix with appropriate ultraviolet and aging-resistant additives]

(2) Melt and plasticize the raw materials and then extrude through a T-shaped die to form a sheet with a smooth surface and uniform thickness.
Punching

Use precise punching molds to make regular holes on the preheated sheet. Then these holes are usually arranged neatly.
Stretching

It is the key to achieving high strength for geogrid. Stretching is carried out within a specific temperature range (above the glass transition temperature and below the melting point).

(1) Longitudinal Stretching (MD):

The punched sheet is passed through a series of preheating rollers and stretching rollers of different speeds.

The line speed of the latter set of rollers is much greater than that of the former set. In the softened state due to heating, the sheet is stretched in the machine direction (MD).

At this time, the circular holes on the sheet are stretched into elliptical or nearly rectangular shapes.

(2) Lateral Stretching (CD):

The sheet material after stretching longitudinal will be immediately sent into the width expansion machine.

The two sides of the sheet are held by special clamps or needle chains, which run along the width expansion track with angle between the tracks gradually increasing. So it greatly widening the sheet in the lateral direction (CD).

During the lateral stretching process, the longitudinal and the lateral ribs are both have stretching and thinning process. And the elliptical holes eventually become neat rectangular or square grids.
Shaping and Cooling

After the stretched, the geogrid is immediately transferred to the cooling shaping process and rapidly cooled with current tension. Subsequently, the tension is released and the product is coiled.