October 2005 / Hybrid Cord Technolog

Hybrid cords have a different inner portion to the outer portion. The simplest hybrid is one where the inner strands of the plied structure have different (strand) twist to those of the outer strands. The inner and outer strands do not have to be made with the same fibre material. One example is to use glass strands for the centre of the cord, and aramid strands for the outside of the cord. Another example is to use a high modulus material (carbon fibre, PBO, aramid and others) in the middle and lower modulus glass (or other material) around the outside. This last combination has been demonstrated to give good performance for rubber adhesion and flex fatigue life. 

Timing belts with hybrid cords can be produced for enhanced performance in hot, cold, dry and wet (including oil) environments. This gives the potential for high modulus narrow timing belts with good environmental performance to replace equivalent metal parts, such as timing chains.

Reactive Impregnation Technology

Traditionally, glass cord is manufactured by the impregnation of glass filament with resorcinol-formaldehyde latex. The latex is cured as the strand is passed through an oven. The strand is then twisted. Several strands can be plied together into a cord. During the rubber moulding process the rubber matrix reacts with the cord to enhance the adhesive bond. There is no bonding between strands – they are simply pulled together. This can lead to weakness within the cord structure and areas of fatigue due to crack formation.

Reactive Impregnation technology does not use resorcinol-formaldehyde. Instead, a mixture of reactive chemicals is used. These are dried not cured around each glass filament. When the cord is moulded inside a rubber article, the impregnation inside the cord reacts at the same time as the external rubber.
 

The net result is to create one network throughout the cord of both rubber inside the cord and the bulk rubber matrix. The individual strands are now fully bonded.
 

These new cords give belt designers greater opportunities to overcome the the ever-increasing demands of automotive engines, and to progress the technology of synchronous belts in a cost-effective manner.
 

Polyurethane Cords
 

Cords for direct bonding to polyurethane are available. These are particularly good for reinforcing small PU belts for office goods such as ink-jet printers, scanners and photo-copiers. These cords are also capable of reinforcing large goods such as PU or PVC conveyor belts