High-precision colouring unit

automatic

General
Colouring forehearths provide controlled addition and melting of boron‑based colouring frit to produce a wide range of glass colours with short production runs. Glass Service supplies complete systems tailored to pull rate, colour range and production type (containers, tableware, cosmetic containers).

Included equipment

• The automatic frit dosing device
• The stirrer machine
• The control panel with PLC and touch screen

System concepts
Systems are built for continuous operation with emphasis on simplicity, flexibility and reliability. The automatic dosing and stirring units adapt to various pull rates and require limited maintenance under heavy use. Glass Service has supplied installations to multiple customers internationally.

Coloring Forehearth — Process overview
1. Glass heating zone and colouring frit addition

• Glass is heated to 1250–1300 °C using a double row of burners to ensure melting of the colouring frit.
• Frit is introduced via one or two dosing tubes, which can be air‑ or water‑cooled.

2. Stirring zone

• Refractory stirrers (screw or paddle) mix melted frit into the base glass; the number and layout depend on forehearth dimensions and pull.
• A stirrer installed before the spout reduces colour variation during changes and shortens changeover time.

3. Conditioning

• Final zone conditions the glass to the correct gob temperature for forming.

Critical points — Issue / Solution

• Accurate dosing of the frit — Use a reliable dosing device technology.
• Constant chemical composition of the frit — Use first‑quality frit.
• Constant redox atmosphere — Require a high‑quality combustion system and forehearth design.
• Homogenous mixing — Apply effective mixing technology (stirrers).
• Conditioning — Ensure correct mixing and thermal control.
• Rapid colour change — Forehearth design and the pre‑spout stirrer reduce changeover time.
• Long life of refractories — Special refractory design resists boron vapour corrosion.

Automatic frit dosing device — concept and features
Glass Service installs the dosing unit at low level and conveys frit pneumatically to the forehearth. Key elements:

• Main hopper (standard 600 litres) with level sensor and alarm for refill.
• Dosing system delivers measured frit amounts to the transport system; PLC with colour touch screen controls dosing and belt speed.
• Pneumatic transport via high‑pressure blower and stainless steel pipeline to a centrifugal dust separator and feeding tubes into the forehearth.
• Feeding tubes fitted with thermocouples and cooling air; positioning at ground level simplifies access and maintenance.

Automatic dosing — technical data

• Dosing flow range: 5 kg/h (min) to 140 kg/h (max)
• Main hopper volume (standard): 600 litres
• Main transfer device: electromagnetic vibrating channel
• Dosing transfer device: special rubber belt driven by brushless motor
• Scale: electronic strain gauge high precision
• Electronic control: automatic by touch screen PLC

Stirrer machine

• Used for glass and colour homogenization; configurations depend on forehearth dimensions and pull.
• Typical data: vertical height and stroke customizable; 1–5 columns; screw or paddle rotors; torque control clutch for protection.

Control board — main characteristics and alarms

• PLC with colour touch screen manages dosing logic, belt speed LOOP control, settings, trends, alarms and calibration.
• Temperature regulation of injection tubes via Honeywell UDC regulators; external tube temperature shown on Honeywell DC displays.
• Local feeder cabinet enables manual stop of stirrers for safety and maintenance.
• Default alarms: high injection tube temperature, fan motor, stirrer motors, blower motor, hopper frit level, cooling air low pressure, plus configurable alarms on request.

Technical specifications

• Process: dosing of boron‑based frit into forehearth; frit melts at 1250–1300 °C and is mixed into base glass.
• Dosing flow range: 5–140 kg/h.
• Main hopper: 600 litres (standard).
• Transfer: electromagnetic vibrating channel and rubber belt drive with brushless motor.
• Scale: high‑precision electronic strain gauge.
• Controls: PLC with colour touch screen (automatic control, trends, alarms, calibration).
• Feeding tubes: air‑ or water‑cooled with thermocouples and temperature control.
• Mixing: refractory stirrers (screw or paddle) with torque protection.
• Forehearth refractory: special design to resist boron vapour corrosion.
• Accessibility: dosing unit at ground level for easy operator access and maintenance.