Challenges for sustainability development and environmental health led to a deep reconsideration of the methods of generating and using energy, raising the bar also for PU application in insulation technologies.
In fact, due to their harmful effects on the stratospheric layer of Ozone, some raw materials are progressive replaced with “greener” ones, while performance requirements in terms of energy efficiency and fire resistance are becoming stricter.
Building, cold chain and appliance industries are thus constantly aiming at tailoring conventional low density rigid polyurethane formulation to each specific product.
In this scenario, temperature control is fundamental to guarantee the high quality of the finished product, playing a strategic role for the chemical reaction and the cycle times (and for increasing productivity too).
Why?
- New blowing agents require precise temperature control, being the evaporation rate strictly connected to the cell size and consequently to the insulation properties of the foam.
- New formulations are becoming faster (cream time 5-6s) to speed up the demoulding and cycle times, and temperature control heavily influences the reactivity of the foam.
- Higher Polyol viscosity is common, making the cooling function more difficult
Which are the common temperature variation factors?
Factors that can determine a change in temperature can come both from the environment and the equipment.
Here some examples:
- Critical environment conditions
- Modification of existing raw chemicals distribution system (e.g. to add one dosing unit)
- Chemicals heating by shear forces generated by mixhead injectors, high pressure pumps and high pressure piping
- Improvement of current storage temperature control system due to formulation change
- Increase of the line productivity with faster chemicals consumption
Cannon solutions for temperature control
Depending on the specific characteristics of customers’ production process, Cannon has developed different solutions aimed to grant the best quality foam into the finished product.
Cooling system performances
The conventional Cannon cooling system is made of a water jacket on the machine daytanks and one nested tubes heat exchanger on the return line from mixing head.
In typical conditions with cold water supplied at 10-12°C, the system takes out 1°C from 10 kg of material in 1 minute of low pressure recirculation.
1 to 3 additional heat exchangers can be added in series and/or parallel in case of better performance requirements.
In case of specific requests, or whether the nested tubes heat exchangers are not considered sufficient, the alternative proposal includes a gasketed plates heat exchanger.
This solution can provide 5x times the cooling performances.
Independent Thermoregulation System
When the dosing unit is serving operating lines for most of the time (e.g. distance between shots less than 1 minute), can be necessary to include an independent thermoregulation system.
The material is unable to pass through the return line and be cooled down, then needs a dedicated system to perform this activity made up of an independent circuit for the heat exchanger(s) fed by a low pressure gear pump and piping connections.
This system is typically coupled with gasketed plates heat exchangers because of the high amount of material being consumed by the production line.
The solution can be implemented either on new lines or integrated in existing ones, through a dedicated machine modification.
High pressure heat exchangers
The most effective solution in terms of temperature control is the installation of high pressure heat exchangers close to the injection points.
The system is made up of high pressure heat exchangers and a dedicated chiller unit.