What are the professional terms for blow molding processing in Shanghai

Blow molding is currently the main method for forming hollow plastic products in China. Today, we bring you some relatively obscure yet very practical Shanghai blow molding processing tips.

1) Processing temperature and screw speed

The principle is to use lower processing temperatures and faster screw speeds as much as possible, while being able to extrude smooth and uniform plastic preforms without overloading the extrusion rotation system.

2) Forming air pressure

Generally within the range of 0.2-06MPA, its size is mainly determined by the high or low melting viscosity of the plastic. Low viscosity materials such as nylon and polyethylene are easy to flow and inflate, so the air pressure during molding can be reduced; Those with high viscosity, such as polycarbonate and polyoxymethylene, require higher pressure due to poor flow and inflation ratios. The size of the formed air pressure is also related to the size of the product and the thickness of the billet wall. Generally, thin-walled and large volume products should use higher pressure, while thick walled and small volume products should use lower force. The most suitable pressure range is 0.1-0.9MPA. A series of hollow products are blow molded by increasing the pressure by 0.1MPA, and the clarity of their shape, contour, thread, pattern, text, etc. is determined by visually distinguishing them.

3) Inflation ratio

The ratio of product size to billet size, which is the multiple of billet inflation, is called the inflation ratio. When the size and quality of the billet are constant, the larger the product size, the greater the blowing ratio of the billet. Although increasing the inflation ratio can save materials, the thinning of the product wall thickness makes molding difficult, and the strength and stiffness of the product decrease; Insufficient inflation ratio leads to increased plastic consumption and reduced effective volume of the product; Wall thickness, extended cooling time, and increased cost. The general inflation ratio is 2-4 times, and a ratio of 1:2 is more suitable, as the wall thickness is more uniform at this time.

4) Mold temperature and cooling time

The higher the melting temperature of the material, the higher the mold temperature is allowed. On the contrary, the mold temperature should be lowered as much as possible. If the mold temperature is too low and the plastic cools too early, it will be difficult to deform, and the contours and patterns of the product will become unclear; If the mold temperature is too high, the cooling time will be long and the production cycle will increase; If the cooling degree is not sufficient, it is easy to cause deformation of the product during demolding, high shrinkage rate, and a dull surface.

To prevent deformation of products caused by elastic recovery of polymers, the cooling time for blow molded products in Shanghai is generally longer, accounting for one-third to two-thirds of the entire molding cycle. For products with a thickness of 1-2mm, a cooling time of only a few seconds to a dozen seconds is generally sufficient.

5) Thread

The threads processed by blow molding in Shanghai usually have a trapezoidal or semi-circular cross-section, rather than ordinary fine or coarse threads, as the latter are difficult to form. In order to facilitate the cleaning of burrs on the product, the threads can be made intermittent without affecting the use, that is, on a section of the parting surface attachment, the plastic product does not have threads.

6) Rounded corners

The corners, grooves, and reinforcing ribs of blow molded products in Shanghai should use larger arcs or spherical transitions as much as possible to facilitate molding and reduce deformation in these areas, resulting in plastic products with uniform wall thickness.

7) Demoulding slope

Due to the fact that Shanghai blow molding does not require a convex mold and has large shrinkage, the demolding slope can generally be removed even if it is zero. However, when there are ripples on the surface of the product, the demolding slope should be at least 3 degrees.