Finished tires that meet OEM uniformity requirements must be specifically marked for delivery with conicity stripes and highpoint locations.
Tire manufacturers who supply tires to the OEM market face rigorous tire performance criteria. First, they must design a tire that meets the performance requirements set by the vehicle. This is a balance of rolling resistance, tire noise, wet and dry traction, treadwear, subjective handling, and ride resulting in a unique SKU. Once the engineering approval is achieved the tire moves into production where it will again face rigorous uniformity and quality specifications. To guarantee compliance tire makers will screen 100% of the cured tires gaining uniformity data on each tire. Once the uniformity data is known for the tires that pass, they must be marked in a manner that facilitates mounting to the wheel and compiled into a set of four tires for assembly to the vehicle on the production line.
High point refers to the location of the first harmonic of radial force variation (R1H). Radial force variation (RFV) is a test where an inflated tire is rolled against a wheel with force measuring capability. The tire is loaded against the wheel and fixed in position, as the tire rolls it measures the radial force exerted on the load wheel. A perfect tire will measure a constant force, say 1000 lbs. typically, this force will vary, for example, +/- 990 to 1010 lbs. = 20 lbs. of force variation. OEM’s know that excessive force variation creates a ride disturbance and set limits for the tire manufacturers. They also know that wheels will have similar variations (especially steel wheels). To minimize ride disturbance, they match mount the tire to the wheel, so the forces tend to cancel each other. Therefore, a high point mark is required. Each OEM specifies the required color and dot size.
Conicity is also measured on the same uniformity machine. It is a measure of the tire’s tendency to like a cone. Turn an empty coffee cup on its side and roll it and you will see it rolling away from a straight line. Tires will excessive conicity will be felt like a pull in the steering wheel when driving in a straight line. Automakers address this effect in two ways. One is to place tight limits on the magnitude of the force, the other is to match tires in sets so that when mounted on the car the forces offset each other. This drives the conicity striping requirement. First tires are sorted into batches by (+), (-) values then it is a manual operation where a person marks the tread face with a crayon using the guidelines set by the OEM for color and quantity.
How this can be automated:
All modern tire plants place barcodes on each tire. Each tire’s uniformity data is collected and stored on a database by barcode. This is a key enabler for automation. Tires enter the marking cell and the barcode is read, pulling the relevant data. The system then selects the specific OEM marking requirements. A robot arm then picks up the tire and presents it to an array of painting heads where the conicity stripes and high point mark are applied. Following the marking operation, the tire is presented to a vision system that verifies the markings are in the correct location, color, and quantity. Once verified the tire is placed on the exit conveyor for sorting and delivery preparation.
Benefits of automation:
Tires come off the processing line ready to ship to the respective OEM. The task of finding pallets of tires in the warehouse and having to mark them with a crayon can be eliminated freeing operators to focus on more value-added tasks. The markings are clear eliminating customer complaints of “hard to read” while staging for the tire wheel mounting operation. The OEM receives sets of tires that provide their customer’s smooth rides free of pulls and roughness.
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