Source: Ulrich - Strip Steel Recoiling
Precision rerolling of strip steel products is becoming important across a host of industries.
A surprising use of precision and specialized metal strip, involves the airbag sensor for all automobiles. Each and every part has to have precise thickness control and mechanical characteristics, so that it can be reliably triggered with the precise specifications required by automobile manufacturers.
Strip Rerolling Tolerances Getting Tighter
With products needing smaller components, all of these tolerance demands get placed on the strip manufacturer to ensure ultra-precise production of material. Medical parts also are now specifying dimensional tolerances with some cases as low as .000060 inch (0.0015240mm), making precision very important.
The first requirement for producing these tight tolerances is consistency or complete control of the process. Specialized equipment is required for rolling the strip into coil, in order to achieve this level of precision, accuracy, and dimensional stability.
Multi-task computers are used to control the coil unrolling throughout the entire process until the product is ready for shipping. The screw down system response time must match during each step of the process. These reflect the input from thickness measuring gauges as a control mechanism on the overall process.
They allow the production of strip as thin as .00050 inch and can achieve tolerances 50% tighter than most standards. Effectively the mill must be able to measure the incoming material, adjust all the work rollers, verifying the dimensional accuracy of strip and the foil once it exits the mill.
In order to do this in real time, there is no choice but to use sensors and computer algorithms with servos or hydraulics to adjust all components of the system, allowing the final product to be within specific dimensional tolerances.
Prior to this level of specialization with computers, the rerolling of strip steel had to use manual screws to literally adjust strip thickness. Though that seems completely archaic in today's world, it was not very long ago when the computers were not running the factory.
Input Material Quality is Critical to Output
The underlying assumption of all of the components for an advanced rerolling line is that the material coming in is of sufficient quality and consistency that control mechanisms on the line are able to maintain a final product tolerance. If the material coming in is not sufficiently consistent or high enough quality, than the control mechanisms on the line will probably not be able to repair it.
Slower speeds have to be used during the rerolling process to achieve these tight tolerances and to allow for the material correction. There may be a number of passes required for achieving the necessary shape and level of finish on the strip or the oil.
The other considerations are the work roll size along with the surface finish, the overall mill maintenance, and the complete control of the environment. Much like integrated chip manufacturing, where every aspect of the environment is completely controlled from dust particle size in the air to humidity levels, to temperature, to the amount of light, precision rerolling and strip processing is rapidly reaching that level of overall control.
One area where rerolling and precision strip processing reaches its zenith is in foil production. Some of these foils are as thin as .000060 pitch. These measurements are confirmed with a control system that uses a non-contact beta ray gauge in order to measure the thickness tolerances as the line is running.
In order to achieve the highest level of foil, the entire operation may have to be housed completely in an airtight environment with the contamination level below a specified minimum.
Precision Strip Processing Goes Clean Room
Gone are the days when a steel strip processing and rerolling of strip steel plant was a dirty and difficult environment. The new versions for producing precision products are more or less a clean room environment.
Part of the reason for the makeover of the environment is that there are increasing burdens placed on the operators to do such things as anneaing the strip as it goes through the process.
The annealing process can be an intermediate or final anneal, which will recrystallize material so it can be rolled further into thinner gauges and provide certain temperature or temper finishes for the material.
A final anneal will be applied if the material is going to be formed further. This level of treatment requires a protective atmosphere of some type of gas which could be hydrogen, argon or specified by the customer.
Similar to the precision foil, this kind of treatment requires complete control over the environment.
Both slitting and testing for precision rerolling are similar processes to the standard slitting test in non-precision environments. But the difference with the precision rerolling is that the testing and the slitting are carried out to higher standards and perhaps with more attention to surface finishes.
The overall trend in specialty rerolling is towards increasing tolerances and increasing burdens on the strip reroller and processing facility to ensure that a low percentage of their product falls outside of the tight tolerances required by their customers.To return from this Precision Rerolling page to the Strip Metal Coil Processing Home page, click here.
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