Handling incoming coiled material is one of the most critical “costs” for tube, pipe, and roll form operations.
No one likes to receive expensive coiled material that is visibly damaged. Or, perhaps it looks great on the dock, but just before putting it into the tube, pipe, or roll forming mill, you notice it is damaged. These are costly events that can certainly disrupt the day. Below is a list of points to help prevent the likelihood of this happening.
First, it is imperative to have purchasing and receiving standards in place for incoming material that will match the requirements of your finished product.
The forming process of a tube, pipe, or roll form mill can “iron out” some imperfections of incoming material. However, these machines cannot work miracles, and the old adage, “junk in…junk out,” is so true when it comes to safeguarding the quality of incoming material.
Look for the following noteworthy conditions when inspecting coiled material:
Stains/Rust. Normally stains from cooling or pickling operations of the master coil will not affect the formation of a tube, pipe, or roll form product. However, the stains and rusty surface areas may affect the cosmetics of the end product by obstructing the adhesion of paint or other coatings. Each situation needs to be addressed to determine if it will cause issues during secondary operations. If so, it should become a quality factor in the receiving standards of the incoming material.
Stains and Rust on Material Strip
Scale Flaking. It is acceptable to have a certain amount of flaking when forming any material, especially with hot-rolled products. However, an extreme amount of flaking could cause a number of issues:
Excessive sediment on the mill bases and bottom of coolant tanks, which could create a very unpleasant mill environment
Coolant contamination, which could accelerate tooling wear and obstruct filters and impeders on high-frequency weld lines
Weld zone contamination, resulting in weld quality issues
Drive issues between the tooling and the material
Build up on the tooling, which would affect proper formation
Coated Incoming Material. When running galvanized, aluminized, or painted product, it is important that the adhesion specifications are in line, to prevent separation of the coating from the parent material as it is formed within the machine.
Slit Edge Quality. This is especially important for tube and pipe mill operations which involve the welding process. The slit coils have spent time in transit before they reach the payoff reel that feeds the mill. It is essential that care in handling the coils be a part of the overall quality measures every organization should have in place.
Indentations. These are normally caused by improper handling, but can also occur in areas such as the entry equipment and accumulators, where the edges can be damaged as they interface with worn turnaround or support rollers. This can result in pin holes and weld failure, if the indentations are deep enough.
Laminations/Inclusions. This usually is a result of a problem in the original master coil when it is cast and rolled. These conditions can present themselves in raw coil form, however, most do not appear until after the welding or forming process.
Painted Edges/Rusty Edges. Excessive paint and rusty edges can cause weld issues. Coils that are intended for production should not have any painted or rusty edges, to ensure weld integrity, with the exception of paint used to identify rejected coils.
Painted and Rusty Edges
Excessive Burr/Rough Slit Cut/Camber/Crown. These conditions can cause problems on all forming applications. Regarding excessive burr and rough slit cut, the fin pass section on a typical tube or pipe mill can only provide minimal adjustment to the edges to make them parallel for proper presentation to the weld box. Attention must be given to burr and slit edge quality and should be part of the standards for incoming coils.
Camber and crown issues can cause major stability problems on all applications. They could result in walking of the strip throughout the mill, ripples, seam wandering, bow, marking, and twist.
Inconsistent Edge Quality
Chemistry & Rockwell. With today’s high quality end product requirements, special attention must be paid to chemistry and Rockwell parameters. The current ASTM standards for raw material may not be tight enough or could be too broad for the specialized end product applications found in the industry. Many firms conduct trials to ensure the material will survive the secondary end product fabrication and performance requirements. Information regarding the chemistry and Rockwell standards can then be provided to vendors to assure conformity.
In conclusion, once receiving standards for incoming material are in place, do not allow them to stray, no matter what outside changes present themselves. It is all too easy to deviate from the required parameters when cheaper material is offered, or when material is hard to get.
Those firms that stay focused and keep their standards in place will have the best opportunities to prosper and produce quality products that are highly favored in the marketplace.
Author: Robert A. Sladky, Vice President Tube Mill Engineering, Roll-Kraft.
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