Focus on material handling
October 11, 2005
Planning an offline band sawing system can be complicated because it can affect, and is affected by, many interrelated factors. Breaking it down to infeed, sawing, and outfeed helps to frame the planning by breaking it down to three subprocesses. Furthermore, answering 15 pertinent questions can help you tailor an efficient sawing operation to your specific facility and sawing applications.
The first step in setting up an offline band sawing system to cut tube or pipe is to analyze your manufacturing processes. A solid analysis requires answering dozens of questions about your specific operation—so many questions that many of us don't even know where to begin.
To simplify this task, you can start by thinking about three distinct processes: infeed, sawing, and outfeed. All three have space requirements, and the infeed and outfeed processes entail material handling considerations too. Key factors are the size of the material to be cut, the size of the final product, and the availability of material handling equipment such as cranes and forklifts. You also should pay attention to the balance between the speed of the operation and cutting accuracy.
Keeping all these factors in mind while answering a handful of the most commonly asked questions can get you off to a good start in setting up an efficient band sawing operation.
You need to have a staging area to hold the material as it is fed into the saw. An adequate staging area allows an operator to load a substantial amount of material onto the transfer trucks and free up the crane for other tasks.
Some configurations have transfer trucks on both sides of the infeed roller tables so that material feeds into the saw from both sides. This type of system requires some kind of squaring pop-up roller system. Other configurations load material from one side only. The rest of this article focuses on systems that feed from one side only, but you can duplicate the equipment easily for a second supply line.
Bear in mind that the size of the infeed staging area affects not only infeed equipment choices, but also your saw choices. A vertical band saw uses less floor space because the head retracts from the cutting area and the material can be top-loaded. If you were splitting a 20-foot bundle, the amount of space required would be only slightly larger than the 20-ft. length of the material. Conversely, you cannot top-load a mitering horizontal machine. You have to load the material from behind the machine, then feed it through the machine, which requires considerably more space.
The size and length of material determine the quantity, length, and spacing needed for the infeed transfer trucks. Your system requires enough transfer trucks to support the material adequately so it doesn't deflect, or bend, when it is being transported.
Most tube and pipe handling systems use cranes or forklifts to load the material onto the transfer trucks. The size, length, and quantity of the raw material determine how to use the crane or forklift efficiently. The type of transfer truck system influences the crane and forklift requirements.
A fork load system is capable of end-loading only. A crane system is capable of loading anywhere in the staging area, including side-loading, onto transfer trucks and therefore is preferable for many applications.
Two commonly used transfer truck systems are chain drag and lift-and-carry.
A chain drag system drags the material down the transfer trucks or it lifts the material in a uniform manner and carries it on chains, moving the material to the powered roller tables. This method can move material rapidly but requires backloading a storage table to hold the material until it can be fed into the saw. A lift-and-carry system moves one batch of material at a time onto the powered roller tables. The crane puts the material onto the transfer trucks and then is free for other tasks until that load of material has been delivered onto the powered roller tables. The crane returns later to load another batch of material onto the side-load magazine system.
The type of transfer system on the outfeed, or discharge, side of the sawing system is just as critical as the transfer system on the infeed side.
If the cut parts are longer than 6 feet, three rollers spaced 2 ft. apart are adequate. However, if the parts are 2 ft. long or less, the space between the rollers on the discharge table must be small enough to support more than half the weight of the material. At least two rollers must support the material at its center of gravity.
If the cut parts vary in length, the sizes of the parts determine the spacing of the side transfer trucks. The side transfer trucks must support parts in three evenly spaced places. Side transfer trucks have to move independently to ensure that material can be offloaded safely, continuously, and efficiently. If the parts vary in size, the spacing of the transfer trucks on the discharge side must vary accordingly.
Two methods are available for aligning the tube—a hard stop or a trim cut to square the material. The method you use depends on the amount of drop available and the cutting accuracies required for the finished product.
In the first method, the tubes or pipes can be moved against a hard stop before banding them into bundles. A hard stop can compromise cutting accuracy. As the material hits the hard stop, the impact can cause the stop to bend, shift, or warp, especially over time and when moving heavy material. Additionally, the stop may flex and spring back, causing the material to rebound so it is not in contact with the stop during the cutting process. If the material is longer than 12 ft. and the tolerances are ±1 in., this method may be adequate.
If you are cutting banded bundles and cutting tolerances must be less than ±1/16 in., the trim-cut method may be preferable. A shuttle vise system indexes the material and feeds it into the saw. For this application, a bidirectional vise is necessary to allow the banding to pass through the vises of the saw without getting caught.
If cutting tolerances are ±1 in., squaring the material isn't necessary.
Be aware that banding can affect the squareness of the cut. Banded material travels easily across roller tables if the crimp that secures the band is not facing downward.
If you decide to use the trim-cut method for squaring the tube, you must have some way to remove the trim-cut pieces. Two removal methods are manual and automated.
Manual removal requires an operator to stand at the output side of the saw and manually remove the trim-cut pieces. This means the saw and feed systems have to be shut off to prevent injury to the operator, thus creating an additional, time-consuming step in the work flow.
The second method is to add an automated gate that lifts, creating an opening for trim-cut pieces to fall into. With this type of system, the trimmed parts are dumped automatically into a parts container or onto a chip conveyor to remove them from the sawing area.
Doug Harris is president of HE&M Inc., P.O. Box 1148, Pryor, OK 74362, 888-729-7787, fax 918-825-4824, www.hemsaw.com.