Roll forming using spring-loaded top rolls
For certain sheet metal applications, roll forming with spring-loaded top rolls is a practical production method. This article explains the process, describes various machine configurations, and outlines the criteria for suitable applications. It also discusses product requirements that are incompatible with this process.
Roll forming using spring-loaded top rolls, in which the top rolls are not held perfectly rigid, is a practical and economical option for many applications. Spring-loaded top rolls have advantages and pitfalls depending on their use, but a well-designed spring-loaded machine will give good service for many years, be forgiving to minor changes in material thickness, and be less likely to be damaged if blanks are accidentally misfed.
This type of arrangement allows the machine to compensate for varying material thicknesses without manual adjustment. Roll grip is set for the minimum material thickness, and the springs allow the rolls to lift for heavier gauges to enter and maintain drive on the material. The spring-load pressure is accomplished by coil compression spring or cup spring washers, depending on the application and force required. Since these rolls can be adjusted to maintain a very light grip, they are suitable for forming prepainted, embossed, and polished materials.
Because spring-loaded top roll machines generally do not have any step in roll diameters and have a limited adjustment of vertical centers, the majority are used in precut applications. The most common user is a manufacturer who runs the equipment in-house for its own production needs to process 0.015-in. to 0.060-in-thick material. Typically, the manufacturer's requirements have increased over time, and roll forming in-house has become a viable option.
Sometimes operators have limited knowledge about operating or adjusting the machine. They manually feed precut blanks or monitor the machine's operation with other line equipment. Because roll set removal and change can be time-consuming, it is rarely done, and usually only for maintenance purposes.
Best-suited as a dedicated machine that produces a family of products for an OEM in the sheet metal industry, a spring loaded roll former is proven in custom applications from mirror frames to garage doors. It is widely used in the shelving and storage industries and for making appliance, wall, and roof panels.
Because of safety concerns for the operator feeding the material, these machines run 60 to 90 feet per minute (FPM) when manually fed. Automatically fed, they run up to 250 FPM in many applications. In either case, gaps must be allowed between feeding blanks during production, because the material will slow down from forming resistance and the controlled grip provided by the spring pressure.
Many times up to four roll sets are mounted on one roll former, and the operator simply feeds material into the correct roll set to make the required part. Because the springs can support the forming load of only one profile at a time, multiple strips cannot be fed into different roll sets at the same time. If this machine type is installed in an automatic line, it will have a provision to traverse perpendicular to line direction to line up roll sets with other line equipment, such as an uncoiler and cutoff.
Another variation is the panel or duplex roll former. This machine has two roll formers mounted parallel to each other on one base to form two opposing edges of a wide sheet simultaneously. One or both sides are made movable to adjust for the product's desired width range. These machines are available in spring-loaded and rigid designs from various manufacturers. The spring-loaded design is preferred if gauge thickness varies or changes frequently. This arrangement is common in the HVAC industry for ductwork applications, in which machines are capable of running 26 through 18 gauge without adjustment.
The best applications for spring-loaded roll formers will meet most of the following criteria.
- Roll sets are rarely or never changed on the machine.
- Material thickness changes are frequent and common.
- Operators have little knowledge of machine adjustments.
- Product to be formed is 2 in. tall or less.
- Expected production cannot justify the cost of a rigid, micrometer-adjusted roll mill.
Applications not well-suited to spring-loaded roll formers include:
- Products taller than 2 in.
- Gauges heavier than 14 (depending on profile form).
- Products requiring extreme dimensional accuracy.
- Production speeds in excess of 250 FPM.
- Large numbers of roll sets need to be mounted on the machine on a regular basis.
While these machines are lighter-duty versions of their rigid, micrometer-adjustable brothers, they perform very well in their intended environment. Those who look beyond the initial perception will see a time-proven, dependable, and economical design.
Rick Blum is custom machines manager of Comet Roll & Machine Co., firstname.lastname@example.org.