Tire cords- placing demands on wire and cable manufacturers

In a recent blog, we looked at the automotive industry from the perspective of machine tools. It takes little imagination to understand why these instruments are critical components of the car-manufacturing process, given that shaped or molded material is essential for many components of the vehicle. But there is another, equally integral component shared by all automobiles, albeit one less immediately obvious visually (because it’s hidden). That is, wiring.

Cars contain a lot of wires, of numerous different types: copper wires for powering vehicles, aluminum wires for weight reduction and high-voltage applications, multi-conductor cables for connecting sensors and switches, twisted pair wiring for communication and data transmission, high-temperature wiring for wires near heat sources, and many more. And tire wires, the specific subject of this blog.

Making tires

When it comes to tire manufacturing, the domain is varied. One size doesn’t fit all. Tires, the touchpoint between a vehicle and the road surface, support the weight of the automobile and provide a primary control surface as it moves. Since that weight places unique demands on the tire, it’s easy to understand the point about variance. A small car typically weighs around 2,500 lbs.; a large one 4,500 lbs. A tractor, in contrast, generally weighs around 15,500 lbs. (or 7 tons). A fully loaded bus can weigh over 36,000 lbs., doubling even that. As such, it’s easy to understand that not only variety but also accuracy in the tire manufacturing process is critical.

Tires are complex, highly engineered products and building them to the required quality involves several different steps. Broadly, these are:

  • Material selection – of the main components; natural rubber, synthetic rubber, fabric, and steel wires.
  • Inner liner – made of synthetic rubber serves as a barrier preventing air escape.
  • Bead area – steel wires are coated with brass and wound into rings form a tight seal between the tire and the wheel rim.
  • Tire body – layers of fabric coated with adhesive form the tire’s body, on top of which “steel belts” (steel wires coated with brass to improve adhesion and resist corrosion) are placed.
  • Tread creation – specialized rubber is formed into specific patterns depending on the tire’s specific purpose.
  • Curing – the tire (sited on a mold) is heated and subjected to high pressure, a process known as vulcanization, to chemically bond the materials together and give the tire its final form.

For our purposes, the takeaway from this overview of the manufacturing process is to demonstrate and understand the centrality of wires and how they are formed throughout.

Wire and cable in tire manufacturing

That established, let’s look further. Manufacturing wires and cables for tire cord is, perhaps not surprisingly, a specialized process (which is to say that it’s not directly comparable, say, to manufacturing electronic equipment wires). It must produce the high-strength steel wires necessary for the construction of safe, reliable, and high-quality automobile tires. It’s primary the steel cords in the tires that provide the strength and stability necessary for a tire to be able to ensure the required degree of performance and safety.

So, how are tire wires manufactured? Again generally, via the following steps.

  1. Raw materials are selected, for tire cord primarily high carbon steel wire. This is made from steel alloy treated with specific chemicals to increase its strength and flexibility. The wires can also be given a zinc coating (known as hot-dip galvanizing) to increase their resistance to corrosion.
  2. The wires are then drawn, perhaps the key step, through a series of drawing dies to reduce their diameter down to the necessary size. The drawing process itself also improves the tire wires strength and flexibility and must be undertaken with full attention to accuracy as the wires must meet their required specification.
  3. Several of the now manufactured (drawn) steel wires are grouped together to form strands. The arrangement of strands created here is based on the specific requirements of the tire cord in question.
  4. Next, multiple strands are twisted together to create a cable structure which, of course, adds further strength and flexibility to the tire cable. This process is known as winding.
  5. The cable is heat treated to relieve stresses, enhance properties, and reach its desired tensile strength. It is also lubricated to reduce friction and improve performance.
  6. Lastly, the cable’s diameter is measured and, if necessary, adjusted as diameter control must be precise to meet the specific requirements of tire reinforcement.

Keep in mind the point we made earlier in this blog; that the quality and specifications of tire cord will vary based on the type of tire being produced (e.g., passenger car tires, truck tires, or specialty tires for industrial or agricultural use). The specific manufacturing process used for each will be designed to produce cords that meet the exact requirements of the tire application in question, considering factors such as load-bearing capacity, durability, and vehicle performance in various conditions.

The importance of measurement systems in tire manufacturing

If we look at the tire manufacturing process described in the section above, we can immediately see the centrality of step 2; the drawing (or building) of the wires that form the basis of the ultimately completed tire cord itself. Getting this drawing process right is the key step in ensuring that the resulting tire meets the required standard.

For manufacturers, “getting the drawing process right” means as much anything else being able to rely on the accuracy of their drawing dies. If these are out of specification, then a range of issues from wire breaks to compromised results that don’t meet their required specification will negatively impact the tire. Since for wire manufacturers profitability depends entirely on converting as much raw material to saleable output as possible, and as quickly as possible too, issues in the drawing process represent a serious threat to their financial performance.

Thus, if a drawing die is damaged or deformed in some way, even at a very minute level, the tire wire will be compromised, and not produced to the required specification. This will render it unusable. To avoid this scenario, it’s critical that drawing dies are measured, and on an ongoing basis. Cameras are one way to achieve this, with light directed into the die measurements can be taken as it is turned to capture key metrics including diameter, cone angle, bearing, ovality, and others and make adjustments as necessary (usually die replacement) based on the findings.

A good example of such an approach is the CU11 series from Conoptica, an advanced solution in the field of drawing die measurement. The product makes it possible to produce an objective bearing asymmetry measurement where until now the only option has been to use a microscope with a skilled operator to assess whether the bearing was symmetric or not. Uniquely, the CU11 series provides access to both inclination and variation data.

Measuring the die is a quick process – from a few seconds to a couple of minutes – and it allows machine operators to determine whether a die can continue to be used or needs to be replaced. Given that for tire manufactures issues such as wire breaking or poor quality can cost thousands in lost sales or devalued product, the alternative isn’t appealing.  There’s also an environmental benefit to reducing “scrap” wire (wire that’s been drawn but can’t be used). Scrap wires have, when made, still consumed energy in the manufacturing process and accurate wire measurement thus increases sustainability.

About Conoptica

A leading source of high accuracy measurement systems for the wire and cable industry is Conoptica, which offers a variety of measurement systems suitable for dies of different sizes. They enable the accurate measurement of dies, so that you can track consistency and take appropriate actions – avoiding excessive quality deterioration and enabling better management of your die stocks.

Conoptica is the market leader for measurement equipment in the wire & cable industry and has been providing high tech camera-based measurement solutions since 1993. We make sure that the metal working industry has access to key quantitative data about their products and tools.