Article | REF: AM3694 V1

Water-assisted injection

Author: Jean-Luc DREYER

Publication date: April 10, 2007

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ABSTRACT

The implementation of the water-injection process is strictly identical to that of the gas-assisted injection. Although some differences do exist, the objective remains the same, that is to say, the fabrication of hollow bodies. Yet water-assisted injection are, for the time being, smaller. Nowadays water-assisted injection applications compensate for certain deficiencies in the gas-assisted injection process, in particular in the case of heat exchanges. However, the process is increasingly used and applications exist in varied sectors such as toys, household appliances, medicine, DIY, furnishing and automobile.

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 INTRODUCTION

The water-assisted injection (WAI) process is paradoxically older than gas-assisted injection (GAI). . Indeed, the first patent describing water-assisted injection dates back to 1938 (figure 1 ).

Detail of water-assisted injection patent (doc. IKV)
Figure 1  -  Detail of water-assisted injection patent (doc. IKV)

The process is exactly the same as for gas-assisted injection molding. Although there are significant differences, the final objective remains the same: to produce hollow bodies.

For the time being, water-assisted injection molding applications are more limited, with the sole aim of reducing cycle times.

Unlike nitrogen, water is inexpensive and readily available.

Of course, all the advantages of gas-assisted injection are there:

  • increased rigidity by creating a tube effect, up to 80 mm in diameter;

  • reduction in part mass ;

  • reduced closing force in case of partial filling ;

  • reduced shrinkage ;

  • increase in stiffness at equivalent quadratic moment.

Today, water-assisted injection makes up for some of the shortcomings of gas-assisted injection, particularly in the field of heat exchange.

Even more than gas-assisted injection molding, water-assisted injection molding is a process in which every stage must be optimized, from part design to choice of material, and from tooling selection to injection press selection. It only takes one neglected parameter to risk random production, or even poor quality. Material suppliers have formulated specific resins to delay crystallization phenomena.

The process is becoming increasingly popular, with applications in fields as varied as toys, household appliances, medical devices, DIY, furniture and automobiles.

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Water-assisted injection