Lead Screws Play Role in Case Packer Retrofit
- Wednesday, 01 February 2006
In the industrial automation market, an increase in speed results in an increase in production rates. Increased production rates, in turn, lead to increased profit.
With case packing machines — whereby a machine or person moves a product down a conveyor to be packaged — it is important for manufacturers to move a large volume of products in a short amount of time. The case packer must not only be fast, but also cost-efficient and durable enough to ensure a long lifespan. Over the past few years, RPT Motion, a provider of custom modular linear motion systems based in Quebec, Canada, has experienced an increasing demand for case packers and other linear motion solutions from manufacturing customers.
A key segment of RPT’s business is based upon updating existing subsystems on machinery with higher-performance linear motion to increase production rates and reliability. Although speed is a critical component for linear motion applications, size plays a significant role as well — that is, increasing speed without affecting the dimensions of a machine or sub-assembly.
Recently, RPT Motion teamed up with Kerk Motion Products, a manufacturer of non-ball lead screws, for a retrofit project involving a major tissue manufacturer whose operation was getting bottlenecked at the case packing stage. The manufacturer was looking to add a second case packer to its process in order to increase the speed and prevent the slowdown of its current production.
The first obstacle was that the existing system, which had a two-position lane changer powered by a pneumatic cylinder, wouldn’t provide the four required positions or the higher speeds. In order to service the four lanes, a stroke in excess of 40" was required and the lane changer needed to index, on average, every 10 seconds or less while maximizing time available for product flow.
The ball screw and nut did not fit into the existing design with a fast enough pitch to suit the higher speeds. It hit its limits and did not allow the high linear speeds needed. To tackle this motion control challenge, RPT teamed with Kerk to design and provide a motion system to feed the required four lanes (two lanes in each of two case packers). The two companies collaborated to include a Kerk screw and nut in the RPT modular slide system, creating a high-speed, servo-powered system, with an anti-backlash lead screw assembly.
The new system featured Kerk’s VHD lead screws. In order to meet the high speeds required in the lane changer, RPT chose a 2.4" travel per revolution screw of ¾" nominal diameter, which proved to have approximately the same efficiency as a ball-nut configuration.
The servo-powered system achieved the speeds necessary to accommodate the second case sorter and subsequently eliminate the manufacturer’s bottleneck — within the confines of the system’s original dimensions.
The use of the self-lubricating screw was instrumental in combating environmental challenges. Since airborne tissue-paper dust is regularly generated in the cartoning and case packing area, almost everything eventually gets covered in a light layer of dust. Grease, which captures dust and creates a harmful, abrasive paste, is eliminated in this process, as the screw does not require grease to operate.