Screen Changers -- Retrofits

Retrofits of Existing Lines

For retrofit line projects where another type of screen changer is being taken off and is being replaced by a HITECH™ screen changer, HITECH™ offers the following expertise.

Because the footprint of a HITECH™ screen changer is almost always smaller than that of any other type of screen changer that it is replacing, various factors are taken into consideration when designing the adapters required to fit the screen changer into an existing line:

Optimizing the flow channel diameter and length for minimal pressure drop
Maintaining the shortest distance between the screw tip and the breaker plate to minimize polymer inventory and stagnation
Whether or not there is an existing screw tip extension
Whether or not there is the possibility of moving existing equipment to shorten length of flow channels
In instances where the customer does not wish to move any existing equipment, the adapters are designed to compensate for the smaller footprint of the Hitech™ screen changer.

Advantages of a Screw Tip Extension

HITECH™ screen changers can be installed in an extrusion line with or without a screw tip extension. The drawings below illustrate both solutions. If there is no screw tip extension, a reduced flow canal is normally used to minimize the polymer inventory as much as possible.

Whenever possible, a screw tip extension is strongly recommended since it has the following advantages:

Polymer degradation is eliminated as a result of uniform velocity across the section of the material between the tip of the extruder screw and the filtration screen
The color change-over time period is reduced due to low polymer inventory between the tip of the extruder screw and the filtration screen.

The following drawings are representative of the most typical ways in which our screen changers can be retro-fitted into existing lines.

BOLT-ON ADAPTER

This illustrates the HITECH™ screen changer retro-fitted to an extruder with a bolt-on type connection:

The screen changer is marked with Balloon (1 ). The upstream adapter (2 ) is bolted to the screen changer and to the barrel flange.

Above the horizontal centerline the adapter is shown with a reduced flow channel through the adapter and into the screen changer body, which transitions to the breaker plate diameter.

Alternatively, below the horizontal centerline, we show the same installation with a screw that extends into the screen changer body . The screw can be smooth or with flights.

CLAMP TYPE ADAPTATION

screen changer clamp type retrofit adapter plastics extrusion lines

This illustrates the manner in which our HITECH™ screen changer can be retro-fitted to an extruder with a clamp type connection:

The screen changer is marked with Balloon (1). It is connected to the extruder barrel (3) with the upstream adapter (2 ) by means of a clamp(4 ).

The drawing shows both options with regard to the extruder screw:

a) Above the centerline: in instances where no screw tip extension is added, the upstream adapter is designed with a reduced flow channel to keep polymer inventory to a minimum. The adapter transitions up to the breaker plate diameter in the screen changer body.

b) Below the centerline: we illustrate the preferred method where the existing screw is extended close to the breaker plate. The extension can be smooth or with flights.

THREAD-ON RING & BOLT-ON ADAPTER

screen changer thread on ring and bolt retrofit adapter plastics extrusion line

In this illustration, the screen changer is marked with balloon (1). An upstream adapter (2 ) is bolted to the screen changer’s upstream face. The threaded end of the extruder barrel (3 ) is fitted with a ring (4 ) to which the upstream adapter is secured by means of studs and nuts (5) & (6 ).

The drawing shows both options with regard to the extruder screw:

a) Above the centerline: where no screw tip extension is added, the upstream adapter is designed with a reduced flow passage to keep minimize polymer inventory. The adapter transitions up to the breaker plate diameter in the screen changer body.

b) Below the centerline: the extruder screen is shown in the preferred method where the existing into the screen changer body. The extension can be smooth or with flights.