Wednesday, 21 October 2009

Karl Mayer News | Comfortable children’s seats made from 3D warp-knitted textiles

A seat construction made from manufactured-to-shape, warp-knitted spacer textiles produced on the HDR 6 EL

Checking-off towns by their car licence plates, counting the number of cars, or constantly feeding them sweets are just some of the tricks used by parents to keep their children happy on long journeys, but they usually forget the glaringly obvious – the comfort and well-being of their little passengers. The build-up of heat inside the car is the main reason for children becoming fractious, especially on long journeys to holiday destinations.
Whereas dad’s driving seat is fully climate-controlled to maintain his concentration levels, the children usually end up by feeling hot and sticky - but spacer textiles are on hand to solve the problem.

Spacer textiles produce comfortable seats
The perception of heat and moisture by passengers in the car can be described by means of the thermophysiological seat comfort. Basically, this property relates to climatic perception, and includes factors such as thermal transmission during the journey, including when sitting down, as well as moisture transport and buffering. Using ventilation effects between the seat and the body to create a pleasant microclimate is the best way of achieving optimum values.
Various test methods are used at the Hohenstein Institutes to measure the extent to which these are successful. Four physiologically determined parameters are used to describe the climatic seat comfort: initial heat flow as a perception of warmth immediately after sitting down, breathability, which is expressed in terms of the resistance to water vapour transmission, thermal insulation, and water vapour buffering, which is a measure of the amount of water vapour absorbed by the seat until it feels damp. The values for the climatic comfort indicators are determined at the Hohenstein Institutes using the upholstery tester and the skin model, and enable physiological construction principles to be drawn up for car seats. One of these indicates that warp-knitted spacer textiles are better lining materials than foams. 3D warp-knitted textiles are clearly superior for moisture buffering. The textile spacers are also better for use as interior cushioning, and exhibit a 3.7 times lower resistance to water vapour transmission than moulded foam. This value cannot be achieved by a rubber-coated fibrous web either. /1/

Manufactured-to-shape, warp-knitted spacer textiles
Spacer textiles for producing comfortable seats can be produced extremely economically and flexibly on KARL MAYER’s HighDistance® machine. This well-known manufacturer has made a breakthrough in designing 3D textile products using this high-speed, double-bar raschel machine, i.e. it is now possible to produce articles whose contours match the shape of the end product during the actual manufacturing process. This ready-to-use principle will be described in detail for the production of a children‘s car seat.
The basic principles of contouring products to match the end-use lie with the interaction between guide bars GB 4 and GB 5. These two yarn laying elements operate in the pile zone and are threaded with yarns in blocks for manufactured-to-shape production. They make up the full working width when arranged next to each other. If the distance between the two pile guide bars is reduced, the knitted width is reduced and, in the same way, increasing the distance between them increases the horizontal measurement of the textile (Fig/ download , right). The incremental width and height movements, which the guide bars execute towards and away from each other, are decisive for producing the contours. The shog movement per guide bar can be executed in the horizontal direction, i.e. along the needles – with a maximum path of 60 mm (30 needles) per stitch course – and without restriction in the production direction above the stitch courses. The gradient of the contours is produced by the specific coordinates of the shogging steps that are fixed by the lapping. If these alternate from being long in one direction and almost zero in the other direction, abrupt directional changes occur in the outline of the silhouette and the contours are flatter, i.e. staircase-shaped. Thus the outlines are worked course by course according to the structural plan to suit the intended end-use. An example of this is shown with all the details in the ‘Patterns’ section of this issue.
The pattern shown follows the shape of the child’s seat. The spacer textile is roughly 20 mm thick, has a specific resilience, and was produced professionally by an upholstery company – the result is a comfortable ride for children on long journeys.
/1/ Functional textiles for optimising climatic comfort on car seats, Paper presented by Prof. Dr. K. H. Umbach, Hohenstein Institutes, at the Annual Conference of the Forschungskuratorium Textil (Textile Research Council), 10.11.2004