Before and after you buff...
Successful truck tire retreaders know that preparing a casing for retreading is an exact science. The visual inspection of a used truck tire is not enough to make sure all the flaws and nail holes have been detected.
Non-destructive testing (NDT) also is required. With computer-controlled NDT machinery, a retreader can produce a final product that often provides more miles than a new tire.
And at less expense. According to the 2013 Modern Tire Dealer Facts Issue, the average price of a new truck tire is $425; the average price of a retreaded truck tire, including the casing, is $230.
“Shearography falls within the NDT category,” says David Stevens, managing director of the Tire Retread & Repair Information Bureau (TRIB). “Some people say, ‘That’s an NDT machine,’ and some say, ‘That’s a shearography machine,’ but basically you’re talking about looking inside the tire without destroying it.”
In many retreading operations, shearography is the NDT method of choice, but it’s not the only one. Here are some of the companies that supply NDT equipment, which helps raise your professional standards and makes you a more viable supplier.
Steinbichler Vision Systems Inc.
“Shearography is a very sensitive, laser-based inspection technology similar to holography,” says Rainer Huber, NDT product manager at Steinbichler Vision Systems, manufacturers of the Intact Tire Test System.
“We use the technology to find air bubbles and separations in casings for tire retreading. Tires with major air bubbles inside are not valid for retreading, because they would fail during usage.”
A separation inside a tire creates a space, and over time air migrates into it. To detect the air bubbles and other flaws, the casing (without the rim) is put into the Intact’s vacuum chamber for under-pressure loading. One measurement is taken at standard ambient pressure, and then the pressure is reduced by 5%. This is a minor change, says Huber, but it increases the diameter of any air bubbles in tread separations.
“The increasing air bubbles deform the tire’s surface by microns,” says Huber (a micron is one-millionth of a meter). “That surface deformation can be measured using shearography.”
Michelin Retread Technologies Inc.
According to Mary Ann Kotlarich, commercial public relations director at Michelin North America Inc., Michelin supplies complete retread processes to its franchisees, including shearography, through its Michelin Retread Technologies (MRT) subsidiary. Called the Casing Integrity Analyzer (CIA) system, this proprietary equipment, imaging and analysis system for casing inspection is only available to MRT franchisees.
MRT has shearography equipment in 100% of its plants and requires its use on all casings after initial inspection. One of them is Valley Tire Co. Inc., which has one MRT facility in Charleroi, Pa.
“In our system, we have NDTs [grazing light/electronic liner inspection, advanced X-ray] for the initial inspection,” says Jim Stankiewicz, president of Valley Tire Co. Inc. “We buff next and then we put them into the shearography. We have two Michelin shearographs.”
Stankiewicz has been an MRT retreader since 2007. He says every operator has to be certified on each piece of equipment.
“Our shearographs will pick up normal separations,” says Stankiewicz. “It’s automated and does everything — rolls the tires in, closes the doors, reads eight different segments on a tire and gives you printouts. The operators know what to look for and it’s all computerized.”
Marangoni Tread North America Inc.
According to Giampaolo Brioschi, product marketing manager for Marangoni Tread North America, a division of Marangoni SpA, the Marangoni ITT 3000 SFERA is the company’s most technical and sophisticated piece of tire inspection equipment offered.
“The ITT 3000 SFERA is an NDT machine based on the technology of vacuum chamber shearography. The machine has been designed to identify any belt and tread separations before the buffing procedure. The inspection system is integrated in a complete measuring head with laser diode.”
Brioschi says the ITT 3000 SFERA’s principle of testing is based on a comparison between a first interference image of the tire surface and a second interference image of the deformed state at decreased pressure. The difference between these two conditions is processed and then displayed on a video screen.
The SFERA, developed by Marangoni SpA, can be used both for the first and final inspection of the tire, he says. “That’s the only way to be sure about the quality of the retreaded tire casing.”
Goodyear Tire & Rubber Co.
“The Goodyear Tire & Rubber Co. does not mandate the use of shearography,” says Todd Labbe, general manager, commercial retread, Goodyear Commercial Tire Systems. “We do offer shearography equipment for our Goodyear Authorized Retreader Network, but only a few of our retreaders use it on a regular basis as part of their process.”
Labbe says Goodyear has conducted evaluations for detecting separations via shearography and differometric images, both of which have demonstrated the ability to detect some separations in casings.
“However, neither technology detects separations of all sizes and locations within a tire in the retread production environment. There also can be some difficulty in reading the images, which can result in the rejection of good casings.”
Labbe says that shearography is only a small part of the tire inspection process, and it is valid only for indicating possible separations in the tire. It will not work in an area that has been punctured, as this disrupts the vacuum that needs to be part of the system for indicating a separation.
“Shearography has not been found to be fool-proof and may be prone to ‘false-positives’ (i.e. the indication of a separation when none exists) and therefore, may actually cause an increase in the rejection rate of sound tires.”
At Goodyear’s Wingfoot Commercial Tire Systems retread facilities, electronic discharge devices find nail-hole casing penetrations that can be difficult to detect visually. Wingfoot retreaders also use a multi-level pressure system to detect weak or broken cords in the upper sidewalls of casings that have not been detectable via other inspection methods, such as X-ray.
“Inspection will continue to be an important part of the retread process, and is a step in the process that technicians should never skip.”
The Hawkinson NDT by Hawkinson Companies, a division of Branick Industries Inc., uses electrical impulses to detect casing flaws. It is a high-voltage tire inspector that the company says is standard equipment for many retreaders. The Hawkinson NDT’s electrical impulses detect nails, nail holes, cuts, tears and bad repairs that are not visible to the naked eye.
“The big difference between the Hawkinson NDT and a shearograph is that the NDT works on a high-voltage system,” says Calvin Sperr, general manager at Hawkinson. “It finds any type of penetration in the tire whether it be a nail hole or some type of puncture to the tire that would cause problems after retreading. A shearography machine runs under a vacuum system which looks for separations in the belt package in the tire.”
The Hawkinson NDT inspects casings prior to buffing and can test up to 200 tires per day. Since it is independent from buffing, it does not slow down the retreading process, notes the company. The unit also can be used to inspect tires after buffing, after repairs and at final inspection after retreading.
Sperr says retreaders also use the NDT before shearography because if there is a nail hole, it must be repaired first.
“Shearography runs under vacuum and punctures have to be sealed up, otherwise the pump is not able to create the proper vacuum to correctly flex the sidewall of the tire.”
The Hawkinson NDT machine has been used by tire remanufacturers such as Michelin Retread Technologies, Bridgestone Bandag LLC and Wingfoot Commercial Tire Systems for nearly 30 years.
Bridgestone Bandag Tire Solutions LLC
The Bandag 7450 Insight Casing Analyzer uses shearography to scan crown/beads/sidewalls and locate ply failures. The company says that when Bandag dealers upgraded their casing inspection capabilities with this new technology, fleets started to notice improvements in retread reliability. (The unit is only available to Bandag franchisees.)
Flaws will show up on the unit’s monitor. The operator can select any section of the tire for further investigation. A truck tire can be completely scanned in minutes, and no lifting is required of the operator. The result is a dynamic image that shows the surface of the crown, bead, sidewall or inner liner. Any measured change will be displayed and may indicate a defect in the casing.
Continental Commercial Vehicle Tire
The Continental Commercial Vehicle Tire business unit of Continental AG recommends that its retreaders invest in pressure testing equipment in addition to conventional shearography. The company suggests using shearography as the final method of performing casing inspection to verify radial sidewall strength.
“Also known as a ‘boom box’ for the loud sound made if a tire ruptures at the highest inflation stage, the Mattuezzi G100 machine recommended by Continental’s ContiLifeCycle retread process engineers utilizes three stages of visual inspections,” says John Barnes, Continental’s manager of ContiLifeCycle activities in the Americas.
Different inflation pressures are used during the three inspection stages, which are measured at 25 psi, 65 psi and 115 psi. The pressure levels are adjustable.
At the 25 to 65 psi levels measured by the G100, distinct ripples or waves can sometimes be detected in the casing’s sidewall, which indicates a weakened or broken steel body ply section.
“A casing sidewall section of this type could rupture under operating conditions, something that no retreader — or fleet — wants to experience. Inspecting a casing under pressure as the final step can help identify tread and casing separations, missed repairs, other tire deformities and off-center treads. Some of these deformities can be missed, even with conventional shearography.”
Barnes says the result of this pressure testing is the peace of mind offered to both fleets and installers that the casing has been proven sound at operating inflation and the retreader has taken multiple steps against zipper ruptures.
“A casing rupture at these inflation pressures can be deadly, so we encourage our retreaders to make the additional investment in the G100 or similar pressure testing equipment.”
Barnes says that because of the increased focus on safety and non-destructive testing in recent years, most reputable retreaders are aware of the need for complete and thorough inspections. Advocacy for safety by industry groups has made shearography, inflation cages and advanced training in retread practices fairly commonplace. However, Barnes said they may not realize that the extra step of pressure testing is a quick and affordable process.
“Continental’s ContiLifeCycle retread process engineers estimate that carrying out pressure testing takes only an additional two minutes per tire, and costs only an additional 74 cents per retread. It’s well worth the investment. Continental helps our ContiTread licensed retreaders to obtain this equipment at an affordable cost, which pays off in terms of safety to their employees and their customers.” ■
The ITT 3000 SFERA from Marangoni SpA provides “bead-to-bead” inspection without turning the tire. In addition, the non-destructive inspection shearography machine offers an automatic loading and unloading system.
The Intact Tire Test System from Steinbichler Vision Systems Inc. horizontally loads truck tires into its vacuum chamber and measures the tires in eight sectors to detect flaws. The company says it can detect 95% of faults.
Retreading trend: Marangoni pioneered shearography
Marangoni Tread North America Inc., a division of Marangoni SpA, says it was a pioneer in producing shearography inspection equipment in 1998. According to Giampaolo Brioschi, product marketing manager, the market for shearographs was strong when the new technology was introduced, and in recent years it has become more stable.
“Our research and development department is continuously and fully committed to improve and to find out innovative solutions in such an important sector as tire casing inspection,” says Brioschi.
According to Rainer Huber, NDT product manager at Steinbichler Vision Systems Inc., two major retreading trends today are making the use of shearography systems increasingly necessary.
“First, casings are becoming harder to source due to weaknesses in the new tire market,” says Huber. “Due to the growth of new tire manufacturers getting involved in retreading, they strive to retain ‘their’ casings within their own systems.
“Second, there has been a new focus in recent years on quality among medium-sized retreaders, and that is becoming ever more important. Both customers and the competitive business environment demand this. To retreaders who continue to believe that they can’t afford investments of around $130,000, an investment in shearography has always been crowned with economic success for those who have taken the step.”