Automatic colouring unit

ruggedhigh-precision

General description
The colouring forehearth is a specialised forehearth system designed to introduce low‑melting boron‑based frits containing metal oxides into the glass melt to produce a wide range of colours without changing furnace batches. It is suitable for short runs and flexible production of container glass, tableware and cosmetic containers.

Provided production equipment

• Automatic frit dosing device (with cooling)
• Stirrer machine(s) for homogenisation
• Control panel with PLC and touch screen

Coloring forehearth - Technology
Systems are robust and engineered for continuous industrial operation. Key design priorities are simplicity, flexibility and reliability. The dosing and stirring equipment are adaptable to different pull rates and require limited maintenance even under heavy loads.

1. Glass heating zone and colouring frit addition

• Glass is heated to approximately 1250–1300 °C in a high‑energy melting zone with a double row of burners to melt the frit
• Frit is fed through one or two dosing tubes, air‑ or water‑cooled, to the melt

2. Stirring zone

• Melted frit is dispersed into the base glass using refractory stirrers; the number of stirrers is selected according to forehearth dimensions and required pull
• Available stirrer designs: screw or paddle
• An additional stirrer is installed before the spout to minimise colour variation during colour changes and to reduce changeover time

3. Conditioning

• Final zone conditions the glass to the correct gob temperature to ensure process stability and repeatable gobs

Critical points and solutions

• Accurate frit dosing – use of a high‑precision dosing device
• Consistent frit composition – supply of first‑quality frit
• Stable redox atmosphere – high‑quality combustion system and forehearth design
• Homogeneous mixing – properly configured stirrer arrangement
• Rapid colour change – forehearth layout and pre‑spout stirrer to minimise transition time
• Refractory life – special refractory selection and design to resist boron vapour corrosion

Automatic Frit Dosing Device (with air cooling package) - Main features

• PLC controlled dosing system with colour touch screen
• Feeding tubes equipped with thermocouples (two per tube)
• Temperature control of feeding tubes via UDC regulator
• Ground‑level installation for easy operator access and maintenance
• Robust steel structure above the forehearth

Automatic dosing & transport concept
Low‑level dosing unit feeds a main hopper that requires periodic refill; hopper sensor signals refill. Dosing device meters frit to a transport system driven by conveyor and high‑pressure air blower, conveying frit through stainless pipeline to a centrifugal dust separator and then to feeding tubes in the forehearth superstructure. PLC manages dosing rates and conveyor speed with automatic control and alarm functions.

Stirrer Machine
Mechanical stirrers provide glass and colour homogenisation. A stirrer installed before the spout improves colour change quality and reduces transition time. Detailed configurations are available on request.

Stirrer machine - selected technical details

• Vertical height: 2,275 mm – customizable
• Vertical stroke: 950 mm – customizable
• Columns: 1–5 according to forehearth size
• Rotor mass and geometry specified per application
• Speed range and torque control adjustable; screw or paddle options

Control Board

• PLC with colour touch screen to manage dosing logic, alarms and trends
• Closed‑loop control to adjust belt dosing speed with high precision
• Individual injection tube temperature regulation (Honeywell UDC 2500 or equivalent)
• Local and main cabinets for stirrer control and safety stops
• Standard alarms: injection tube overtemperature, fan and blower faults, stirrer faults, hopper level, cooling air low pressure; additional functions on request

Technical specifications

• Dosing range: 5–140 kg/h
• Main hopper (standard): 600 litres
• Main transfer device: electromagnetic vibrating channel
• Dosing transfer device: rubber belt driven by brushless motor
• Weighing: high‑precision electronic load cell
• Control: PLC with touch screen
• Feeding tubes: thermocouples and air cooling, temperature regulated by UDC
• Transport: high‑pressure air blower + stainless steel pipeline + centrifugal dust separator
• Frit melting: glass heated to 1250–1300 °C in the heating zone
• Stirrer types: screw or paddle with torque control clutch