A cable tie or tie-wrap, also known as a hose tie, zap-strap or zip tie, is a type of fastener for holding items together, such as electric cables or wires. Because of their low cost and ease of use, tie-wraps are ubiquitous, finding use in a wide range of other applications. Stainless steel versions, either naked or coated with a rugged plastic, cater for exterior applications and hazardous environments.
The common tie-wrap, normally made of nylon, has a tape section with teeth that engages with a pawl in the head to form a ratchet so that, as the free end of the tape section is pulled, the tie-wrap tightens and does not come undone. Another version of the tie-wrap allows a tab to be depressed to either adjust the tension or remove the tie-wrap. Another popular design of the cable tie locking mechanism involves a metallic barb in the head slot. The metallic, e.g. stainless steel, barb is inserted after the plastic part is molded. The barb engages and cuts into the strap surface to lock the strap in place when fastened.
Another prior-art design of a tie-wrap is assembled from a plastic strap component and a double lock head component. The plastic strap is extruded continuously. The double lock head has two slots with a metal barb in each slot to lock the plastic strap inserted into the head. The plastic material in this design is typically acetal.
A typical requirement for cable ties, in addition to, for example, chemical resistance to common automotive fluids, is that a fastened cable tie should withstand prolonged exposure to elevated temperatures, (e.g. at 125° C.), if it is to be applied, for example, in or in the vicinity of the engine compartment. At the same time, such a cable tie should show good mechanical strength at low, (e.g. sub-zero), temperatures. For such high-end applications, cable ties are often molded from a polyamide composition, (e.g. a plasticized polyamide 11 composition, an elastomer-modified polyamide 66 composition, etc.). Acetal material is also used to extrude cable tie straps and injection mold cable tie heads separately due to its relatively inferior processability.
A drawback of conventional nylon cable ties is that they do not fulfill all these requirements simultaneously and, especially, do not show enough strength and impact resistance at temperatures down to −35° C. This means that various cable ties of different designs and/or made from different thermoplastic compositions need to be used for assembling an electrical harness and mounting it in various diverse environments. This concurrent use of different types of cable ties is disadvantageous from logistical, manufacturing, and economical points of view.
A cable tie has two typical failure mechanisms. First, the cable tie strap can break when the fastening load is beyond the material strength limit. Another failure mechanism involves the unlocking of the strap from the cable tie head slot, whether the cable tie uses a plastic pawl or a metallic barb. Both failure mechanisms can cause a cable tie to fail before reaching its designated loop tensile strength rating. These failure methods are also how the tie can fail above its rated load.
Since the original invention of the cable tie in 1958, many follow-up patents have emerged that mainly focus on improved manufacturing methods, new materials, or special applications. More recent patents directed to the problem of insufficient strength at different temperatures focus on reinforcing of the polymer matrix with graphene.
Another prior art method of reinforcement involves introducing strengthening fibers into the raw plastic material prior to molding the cable tie. It has also been proposed in commonly owned PCT Application No. PCT/US16/27509 to provide a reinforced cable tie with a continuous fiber roving throughout the whole body. Such glass fiber reinforced cable ties have much higher strap strength than unreinforced, but an ultra-strong locking mechanism is needed in order to fully take advantage of the increased strap strength. Moreover, a suitable locking mechanism cannot involve parts which may dig into the strap and cut the fibers, such as a metallic barb.
Many solutions to the problem of cable tie locking exist. Some involve multi-part locking mechanisms, while others are of a single piece with the cable tie strap. For example, some cable ties utilize a ratcheting pawl to lock a serrated plastic strap. In other cases, a metallic barb is used to lock a plastic strap. It is also known to use a fiberglass pin to lock a plastic strap or a ball or balls to lock a steel strap. However, none of these prior art approaches are specialized for fiber-reinforced cable ties.
Accordingly, it would be desirable to provide a simple, inexpensive locking mechanism for fiber reinforced cable ties. It would be further desirable to provide a simple, inexpensive locking mechanism which can be injection molded and match the ultimate strength of the fiber-reinforced tie without significant change to the form factor of the un-reinforced product.