Processing

 

Contacting

The electrical contacting of the webs is done by soldering the bridges or leads. Note that the soldering temperature should be at least 350 °C to remove the insulating lacquer at the contact points. Determing whether the lacquer has benn completely removed is possible by measuring the resistance of the individual fabric web. When measuring resistance, the intrinsic resistance of the test leads has to be considered.

For contacting a web there are several ways possible:

Quick Version

For this you have to set a soldering point about 2 cm from each end of a web, which means a parallel circuit of all strants. A certain distance from the web end is necessary, because no strand should be cut between the soldering points. Using this method enables to divide a web in several circuits.

 

Heat the entire Knitted Heating Fabric

For this purpose, both litz wires have to be extracted of the fabric at the web ends. Afterwards they have to be soldered together. Alternatively, it is possible to heat the extracted litz wires, for example with a heat gun, to a temperature of 450 °C, and then complete the connection by crimping.

 

General Information

If you want to adjust the resistance of a fabric web exactly, then it is recommended to set the soldering points slightly further apart than calculated. Afterwards, the electrical resistance between the contact points is measured. If the resistance turns out to be higher than calculated, the following steps are suggested:

 

  1. resolder the soldering points, because eventually the insulation lacquer was not sufficiently removed
  2. extend one soldering point in the direction of the web center, so that the fabric length between the points is reduced

Once the resistances of the individual webs are logged, the webs may be connected by bridges.

 

The input leads should be provided with a strain relief. For Knitted Heating Fabric that will be embedded in a matrix, it is advisable to solder both the input leads and the cables, which lead to the fabric webs, on a common copper foil. To prevent the surrounding material from thermal overload, thermal insulation should be placed under the soldering points. The image depicts a piece of Teflon® foil which is glued to a wooden board.

 

 

For many matrices, it is recommended to solder a threaded bushing on this copper foil. Under the copper foil a piece of fiberglass fabric should be locally placed in order to guarantee under all circumstances the electrical insulation and to protect the litz wires from sharp edges.Tacky tape prevents the matrix from ingressing the bushing. After curing, the thread is exposed and the input lead is screwed. Of course, you can obtain the already pre-assembled threaded bushings in different sizes from us.

 

Fabrication of an electrical Panel Heating with CoTexx® Knitted Heating Fabric

  • preparing the surface (link layer) for later connection with the matrix (e.g. sanding, degreasing)
  • scissoring and positioning the Knitted Heating Fabric webs
  • attaching knit webs using hot glue nonwoven or spray adhesive
  • setting soldering points
  • measuring and logging web resistances
  • interconnecting webs to heating circuits
  • preparing electric supply
  • checking the total resistance
  • installation of the sensors
  • buildup of the remaining fabric layers
  • injection / infiltration as usual

Annotations

CoTexx® Knitted Heating Fabric is preferably suitable for processing using injection methods. Due to positioning the webs in the dry state there is no time pressure, the risk of cutting strands is smaller and small void content ensures a good heat flow.

 

If the Knitted Heating Fabric is later embedded in resin, then both sides should be covered with glass fabric. Glass fabric or NCF provides additional electrical insulation and protects the Knitted Heating Fabric against mechanical stress after curing. In order to ensure good heat transfer from the Knitted Heating Fabric to the surface to be heated, the layer thickness should not be chosen too large.

 

The method of adhering with hot glue nonwoven has numerous advantages. The Knitted Heating Fabric can be placed on the hot glue nonwoven, aligned and then bonded piece by piece without time pressure. Subsequent corrections are possible without cutting the strands by heating relevant areas again. In areas that will be soldered, no bond should take place so that the thermal insulation between fabric and surface can be layed in. When the electric contacts are complete, the knitted fabric ends will be glued.

 

Ideally, the fabric webs run parallel and do not overlap. If using extra-low voltage below 30 V and several webs are connected in parallel, then little overlap is allowed. If using a connection in series, and in particular at a high voltage, it is advisable to separate the webs by an electrical insulator such as glass fabric in the overlap region.

Hereby, a short circuit is avoided under all circumstances. For the same reason it is necessary to provide an electrical insulation between carbon fibers and the Knitted Heating Fabric or the connecting points.

 

In order not to violate the fine strands, the fabric must not come into contact with sharp edges or rough surfaces. It is also advisable to wear vinyl gloves over cotton gloves. This combination ensures that your hands are protected against the heat gun and the Knitted Heating Fabric does not stick to the cotton gloves.

 

The heating must be protected from overheating. For this purpose, temperature sensors have to be incorporated at the position with the presumably highest temperature. Normally the highest temperature prevails in the heating wires, so the sensors have to be positioned close to the Knitted Heating Fabric, but sufficiently electrically insulated (e.g. by a layer of glass fabric 200 g/m²).

 

 

Feel free to contact us for further information
hotline: 0800 6677373
telephone: +49(0)8259 8287-81
info@cotexx.com