Lay Out Design
Planning the Surface Heater for Fiber Composites
Auslegung
Design of the Heating Area
Arrangement of the Heating Fabric Segments
There are always several options for assembling heating fabric strips to form a heating area.
The simplest design variant is the series connection of all strips. The total resistance is obtained by adding the individual resistances.
If this resistance is too high and the maximum power would therefore not be reached at a specified voltage, the resistance can be reduced by connecting several heating fields in parallel (e.g. the three fields highlighted in color in the pictures on the right). In order to guarantee that all fields produce the same amount of heat, they must have the same resistance.
Using Excel During Lay Out Design
Our Excel spreadsheet will also assist you during the design process. Enter basic data on the used Knitted Heating Fabric version as well as on the voltage source, heat requirement and heating area and the heating field will be divided automatically into sections. The position of the solder points will also be calculated. Please contact us and we will send you the tool.
Surface Heating for Moulds:
Can We Support You with the Lay Out Design?
Whether and how CoTexx® Knitted Heating Fabric can be used in your project – this is a crucial question in the design process. We are happy to give you our evaluation.
To do so we need some information about your project, which you can send us preferably by email:
- What should be heated?
- Size of the heating area
- Surface temperature
- Material of the matrix (epoxy resin, polyester resin, silicone, …)
- if known, the heat requirement in W/m² (or the heating-up time)
- Ideally, a picture, drawing or sketch with the marked heating area
- Key data of an existing power supply or the intended operating voltage
Scheme of Design Process
If you want to manually perform a preliminary design, then the following procedure is recommended. The following steps are already integrated in the Excel spreadsheet mentioned above.
Specify the specific heat demand (W/m²):
Experience value: 600 – 1500 W/m² (depending on the heating temperature and the heating gradient)
G
Derive required heating power (W):
Product of specific heat demand and heated area
G
Specify power supply:
Depending on the required performance and security aspects
G
Calculate the optimal total resistance of the heating:
With the help of Ohm’s law and the specifications of voltage U and current I, the resistance R opt=U/I results
G
Lay out of CoTexx surface heating:
Select width, number and interconnections of the Knitted Heating Fabric segments in such a way that the total resistance R real is as close as possible to R opt
Comments on the Heating Power
The heat demand mainly depends on the heating temperature, the thermal insulation of the system and the heat conduction properties of the matrix . A high temperature level goes along with a higher heat flow to the environment. A first guideline for heated moulds in the fiber composite industry is an output of 1000 – 1500 W / m² during the heat up phase.
Some processes require a high heating gradient. If it is ensured by correctly placed temperature sensors that none of the components such as matrix (e.g., silicone / epoxy resin) or insulating are overheated, the system can also be operated with even higher electric power. Specific heating outputs in the range of 5 kW/m² and more are possible depending on the application.
Comments on the Power Supply
Small heating areas (max. 1.5 m²) tend to mean small resistances (in the case of series connection). As a result, the formula
P=U²/R
indicates high heating outputs even with low voltage (DC voltage up to max. 60V).
CoTexx® Knitted Heating Fabric can be operated with higher voltages, but this requires increased safety precautions. The advantages of a higher voltage include high heating power with large resistances (less number of parallel connections required), low ohmic losses despite small conductor cross-sections in the supply lines and inexpensive power supplies.
At an operating voltage greater than 50 V AC or 70 V DC, the safety guidelines of the Low Voltage Directive must be observed. It is advisable to install separate circuits for the connected resistance heaters, which are separately protected by ground fault circuit interrupters.