Types of Screen Changer for Plastic Machines
Screen Pack Assembly
Screen pack with breaker plate used to remove any contamination. For more details on screen pack, breaker Plate and sources of contamination you can visit article: “Screen Pack and Breaker Plate for Plastic Extruder Machine”
Today’s topic is how the screens are changed and what are the methods to change the screen?
When it’s a need to change the screen?
Every plastic (extruder) machines have a load meter. Pressure increases with the blockage of screen. As screen blocks slowly with time after continuous use pressure began to rise and this rise in pressure can be noted by a pressure transducer/Gauge or by load meter. A pressure meter is used in auto screen changer and an upper limit of pressure is set. When melt pressure reach or cross that point auto screen changer get active and change the screen automatically. While in case of manual a liver connected to screen pack is used to change the blocked screen.
Types of Screen changer
In early days a pack of screen is bolted at the end of (Screw and Barrel) extruder and start of die some time an adapter is used between plastic machine (Extruder) and Die. Removal and then placing a new screen pack when need to be changed is much time consuming, difficult and an experienced person is required to perform this. To overcome these situations mainly to save time different types of screen changer are being used. Screen changer can be categorize by following:
Manual Screen Changer with a liver
Two screens are attached at the end of liver in such a way that if someone push the liver upward then upper screen comes at the front of extruder and when downs the liver then second screen comes in the front. At this time blocked screen is changed with new one. In these types of changers machines need to be stopped. It is the cheap equipment need less capital cost.
Auto Screen Changers:
Auto screen changers are further divided into categories
Screen Changers with Hydraulic Arm
In these hydraulic type screen changer a hydraulic oil cylinder piston assembly is used to change the screen. It is also further divided into types like single and double piston. Single screen and two screens on a cylinder piston assembly.
Rotary Screen Changers
Rotary screen changer consist of a wheel with number of screens on it. It rotates in such a way that a single screen comes in front of extruder. It have advantages that process not need to be stopped to change the screen but its capital cost is high.
Continuous Screen passing in front of machine head
In this type a screen in belt like shape pass and continuous moves one side to other removing the contaminants. This type of screen changer is not very common.