April 28, 2009
Scrap handling is one important issue that is sometimes left out of the planning stage, but if not integrated into the project properly, scrap handling can cost you operating time and money. By asking—and answering—these five questions first: Can I install the equipment in the floor space I have? Do I want to drop the scrap through the bolster or convey it away from the bolster? Do I want to convey the scrap to a central collection area or near the press at floor level? What size pit do I need and how will I collect the scrap when it gets to the remote scrap area?—you can prevent costly problems.
So, you found the money to buy a press. You've got a commitment from your best customer for 250,000 pieces a year for 12 different parts. You've gotten everything lined up: the cradle, the straightener, the feeder, the parts handling system, and your tooling source. You're ready to issue your purchase orders and get the process rolling.
But wait a minute: What will you do with the scrap?
Scrap handling is one important issue that sometimes is left out of the planning stage, but if not integrated into the project properly, scrap handling can cost you operating time and money.
Murphy's law (the original "what-can-go-wrong law") was born in a scrap barrel.
By asking—and answering—these five questions first, you can prevent costly problems and ensure a smooth ride.
The answer to this question depends primarily on the size of the press required. A 150-ton, open-back, inclinable (OBI) probably won't pose much of a problem. A single, small scrap conveyor usually can carry the scrap to a hopper behind the press. Make sure you've provided for the vibration isolation and charge ahead.
A straight-side press between 400 tons and 2,000 tons, however, will require more decisions. Naturally, large-tonnage presses mean larger bolsters using bigger or multiple dies. You will need to determine the number and type of scrap conveyors needed to get the scrap to the drop points. You will need to decide if you want to build scrap conveyors into the tooling or design enough tooling commonality to adapt what you are using to any die. Installing more than one press, also will affect your choice.
If you convey scrap away from the bolster, you must put it into a hopper near the press. This will create additional floor traffic when you exchange hoppers. You also must allow the space required for the hopper. Unless you have two hoppers side by side with a tipple chute or similar device, you may have to shut down the press while you change hoppers.
If you drop the scrap through the bolster, you may have to excavate a pit under the press or expand an existing pit. In-floor conveyor systems keep the area around the press less cluttered with equipment and scrap hoppers, and gives the operator clearer access to the press for operator attention or die changes. Because above-the-floor conveyors cannot be completely guarded, in-floor systems are also intrinsically safer. Because of excavation requirements, in-floor systems have a higher initial cost but may be more economical in the long run.
Some press designs may allow the placement of a low-profile scrap conveyor on the floor under the press. However, in most cases, the scrap clearance or requirement for scrap chutes or press skirt design makes this impractical.
This will be determined by the volume and geometry of the scrap produced. The larger the volume and the bigger the scrap, the greater the need to have a remote scrap handling area. Multiple presses (especially tandem installations) are best handled this way. If a scrap hopper is filled in 15 minutes or less, you probably have to dedicate a lift truck (and driver) to that press. This assignment of personnel and equipment, plus the continuous traffic flow, dictates using a more out-of-the-way method.
If you want to keep the scrap close to the press, you may want to use the loop pit and modify it slightly so that one conveyor brings the scrap out from under the press and another conveyor takes it at a right angle up to the hoppers. This will reduce the amount of excavation required and will not interfere with the feed equipment or the finished-parts handling at the other end of the press.
The next step is selecting the size and type of scrap conveyor. Once you have done this, you can determine the pit dimensions. If you will be conveying the scrap below the floor underneath other presses, or to a remote scrap handling area, these dimensions are critical. If scrap is conveyed from multiple presses, the conveyor must be sized for the total scrap load.
The headroom required probably will be dictated by the amount that the press or presses extend below the floor or by the design of the scrap chutes. The pit design must allow for the installation and maintenance of the conveyor (see Figure 1). At minimum, the pit should be deep enough and have enough headroom for maintenance personnel to move beside the conveyor comfortably. You will need access to the entire length of the conveyor. Long conveyors are built in sections, so provisions must be made for joining the sections once they are in the pit.
The press manufacturer, press design, and the options needed will determine the pit dimensions and space needed. It must be custom-designed to meet each project's parameters.
The common method of doing this is to incorporate tipple chutes, indexing chutes, or pant-leg shuttles. Which type of chute you choose will depend on the size of your final scrap container and the overall economy of the system (see Moveable Scrap Dispensing Chutes sidebar).
Movable scrap chutes can be an important addition to scrap conveyors, providing uninterrupted operation of a press or bank of presses, thus increasing productivity. They can segregate different materials, increasing your scrap's value, and can evenly distribute the scrap in large containers, making it easier and more efficient to haul the scrap away.
Segregation. If you stamp parts from different materials (mild steel, stainless, galvanized, aluminum, and so forth), separating the scrap will greatly increase its value, considering that scrap is also a commodity. Sorting scrap by metal type can add significantly to your bottom line.
Access. You have to run your plant efficiently and safely to generate the most profit. This is easier to accomplish with the most access to your equipment, the least lift truck traffic, and the fewest interruptions to your press operating cycles. Scrap handling can affect all of these parameters.
Lowered Costs. The best way to ensure that you are installing the most economical system (considering both the initial purchase cost and operating costs) is to select your suppliers early in the project and let them work with you as part of a team to provide the best solutions. If you need an architect, make sure he talks to your conveyor supplier before finalizing the design for any pits or scrap rooms. Make sure your press supplier knows how you intend to handle the scrap so that the proper options can be included. Know what clearances are required around your feed and part handling equipment.
Each supplier has the experience of many previous installations from which to draw. Use their experience to determine your best options. Your success is important not only to you, but also to your customers and your suppliers to strengthen the manufacturing economy.
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