Colortronic Press Release

Choosing The Right Feeder

Accurate and repeatable dosing and blending is crucial in the manufacture of compounding and chemicals.

There is typically a wide range of equipment available and processors have to choose between volumetric or gravimetric loss in weight systems – so how to choose?

By definition, gravimetric feeders measure the weight of flow in one way or another – and then adjust the feeder output to achieve and control the desired setpoint.

Volumetric feeders – again by definition – operate by delivering a certain volume of material per unit time which is then translated into an inferred weight based flow rate. As such, volumetric feeders are simple and inexpensive – they are open loop and cannot detect or adjust to variations which may occur in the material.

Volumetric feeders can perform well if the material being used does not vary significantly and so does not warrant the additional investment in gravimetric feeding.

Where the material can vary significantly such as with flakes, fibres and powders the gravimetric feeders automatically detect any variations and continually adjust to the process conditions. Data capture/data logging is increasingly important for many customers, which is an additional benefit with the gravimetric feeder where process conditions can be printed or stored onto a PC or host system.

Feeder Types

Typically in compounding and chemical applications there are various types of feeders for the mechanical dispensing of material into the process:

  • Single screw feeders for pellets, regrinds and free flowing product
  • Single screw with agitator for medium flowing materials
  • Twin screw with agitator for non-free flowing powder and sticky materials

These feeders tend to be permanently situated in a fixed position, dosing the same materials on a day to day basis.

Where feeders or products need to be changed quickly and on a regular basis, the C-Flex flexible side walled feeder can be of benefit.

Loadcell Technology

The gravimetric feeder(s) uses a loadcell as the measuring device to determine the setpoint and actual flow rate – and then control the motor drive speed to compensate for any variation. In the main, there are two types of loadcell used in the industry – one being the analogue/strain gauge and one being the digital loadcell (CSL).

The perfect loadcell should be robust and able to quickly detect small changes in the system, have the highest possible resolution and stability and avoid drifting of calibration - regardless of the conditions, temperature and humidity.

The strain gauge can, in most cases, fulfil most of these requirements adequately at a lower initial cost. However, where difficult materials are to be dosed and consistent and repeatable results are required, the digital loadcell (CSL) has several advantages:

  • Weighing resolution of 1:10000000
  • Integrated electronic linearisation control
  • Integrated electronic temperature compensation control
  • Integrated digital filter to eliminate vibration
  • Direct digital weight data acquisition
  • Rugged construction

Control Concepts

Today more than ever, due to reduced staffing levels and cost pressures, easy to use controls are a ‘must’ to avoid unnecessary errors.

Volumetric controls are simple, due to the fact they are only controlling the motor speed but can still be costly if set up incorrectly.

The ideal control would allow the operator to directly input various parameters such as speed or percentage and have a motor speed feedback to detect problems if they occur.

Gravimetric controls are continually performing very complicated functions such as drive commands, speed pickup, weight channels, refill signals and filtering disturbances on the system etc.

In the past the control would normally be quite complicated - but new intelligent control concepts, such as the C2 Touch Control, have made the operation very simple, limiting the amount of information to a level which the operator can grasp and control via a Touch Screen. Should further details be required, the appropriate function can be selected from the general overview and shown on a full page.

The on-screen guidance instructions and the symbol design have been optimised as a result of various tests with operators, and are self-explanatory. Since very little text is necessary due to the graphical presentation, the system can be easily operated without the need to consult the manual.

All data can be recorded and stored – such as recipes, materials, suppliers - and can be recalled at any time.

Test and Evaluate

The right choice of supplier as well as the feeder options is very important. The best possible way to ensure the correct choice is to arrange a visit to the supplier’s premises and request a test be carried out using your specific materials. This will ensure the correct feeder, control and supplier is chosen to ensure trouble-free operation for many years to come.

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