Temperature Measurement


Temperature profiling in automobile manufacture

September 2020 Temperature Measurement

The automotive industry uses many materials to build cars, including metals, glass, polymers and rubber. These have evolved over time, becoming more sophisticated and they also often require heat treatment at some stage of component manufacture.

Air bags

For an air bag to function correctly, it must inflate quickly and efficiently. To aid this process, the nylon substrate of the material is coated with a low friction silicone layer. The silicone coating, as part of its application to the nylon substrate, goes through a critical thermal cure process. This is often performed in a stenter oven, where the fabric is passed through a convection oven with a very low height restriction. If the silicone is under-cured, there is a risk that the surfaces of the air bag will stick together, preventing correct inflation of the air bag. The solution:

• Using a customised Datapaq Oven Tracker system (Datapaq StenterPaq System), even this difficult varying width stenter oven can now be profiled quickly and safely.

• The system allows profiling at full process speed.

• No need for the system to sit on the material, so no risk of fabric damage or the profiler falling through the unsupported fabric.

• Repeatable thermocouple positioning across the fabric.

• Process profiling performed without downtime, maximising productivity and eliminating fabric burn.

• Uniform curing results in reduced rejects, scrap and their associated costs.

• Process traceability provides protection against costly liability and litigation issues.

Adhesives, sealants and mastics

During the paint cure process, a variety of complementary materials need to be either heat treated or cured. Many of these materials are essential to the safety of the car, so they are as important as the paint cure process and therefore, need to be profiled. High temperature structural adhesives are used to give structural strength to areas of the car that need it for side impact resistance and to achieve the safety specifications required. Adhesives are used, since there is no space for welding on B pillar flanges. Proper cure of sealants, mastic and sound deadening materials provide waterproofing/reduced road noise and prevent toxic engine gases from entering the car’s interior. Over curing can produce by-products that can affect the quality of other paint processes. The solution:

• Using a Datapaq Oven Tracker XL2 system, the correct heat treating of adhesives, as well as curing of sealants and mastics, can be assured. A standard Oven Tracker XL2 system (6- or 8-channel), with TB0090 thermal barrier is often used.

• Alternative systems (process dependent) include: OvenTrackerXL2 with dual interface (16-channel), and TB0083 thermal barrier; OvenTrackerXL2 Singlepass with long duration TB0081 barrier, for profiling all ovens in one run.

• With rework not an option in this industry, scrap costs resulting from the over curing of sealants are reduced.

• Passenger safety is improved and manufacturer liability issues relating to curing of the adhesive, are reduced.

Panel pressing

Hot forming is being increasingly adopted in the forming of structural panels for use in the production of automobiles. The key benefit is that very rigid structures can be made accurately with high strength lightweight steels. This ensures the car is both lightweight and strong, both of which are improvements required by legislation in many regions of the world. The process consists of the rapid heating of flat panels to 950°C prior to pressing them into complex shapes. Temperature uniformity of the panel prior to pressing is critical in ensuring correct forming of the product. The solution:

• The Datapaq system is used to measure the temperature uniformity of the panel through the fast heating process.

• The user can accurately measure the performance of this key process.

• The time to set up the process at each new product introduction is reduced, thus maximising production line utilisation rates.

Rubber

Natural rubber has some serious defects; it is weak, easily becomes sticky and is not very elastic. To improve the physical properties (strength and heat resistance) of the material, it is taken through a vulcanisation process. The polymeric chains of rubber undergo a cross-linking reaction, initiated by the addition of sulphur to form a stable 3D network. To increase the rate of the chemical reaction, heat is applied. Typically, a target cure schedule for the rubber is 180-200°C for two to three minutes. Measurement is very difficult, due to oven size restrictions. The solution:

• A low height, narrow thermal barrier enables Datapaq to provide a customised fit-for-purpose solution.

• Using a customised Q18 system, the user can guarantee the quality of the vulcanisation process with the desired cure schedule achieved.

• Multiple channels are available to measure oven and product temperature uniformity at different depths in the rubber.

Paint cure on bumpers

In general, profiles are performed on paint lines to measure paint cure quality on an intermittent basis – for example daily, weekly or monthly. The assumption the user makes is that the process is working correctly for the period between acceptable consecutive profile runs. Obviously the more frequent the profiles, the more confident the user will be that the process is constantly in control. The desired aim of any paint QA manager would be to have live profile data from the process at continuous intervals through each shift. The solution:

• A Datapaq system equipped with the optional TM21 radio telemetry functionality can provide real-time data from within the process.

• Ability to provide a profile system that could monitor every product cycle providing live product temperature data, via radio links, from the two coating oven lines, in real-time.

• The system continuously runs through the cure process loop, fully protected, constantly providing product temperature data from a sample bumper with thermocouples attached.

• A trial of the system in a serpentine oven showed that over 99% of all data was received over a 95 min cycle, thus proving reliability of data transmission and collection.

• A single PC and receiver can collect temperature data simultaneously from two separate Datapaq systems, running on separate bumper lines.

• Hardware only needs loading and unloading once per shift, reducing handling wear and tear on the system and the thermocouples.


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