Part Three of a Three-Part Series Setting Up Shop
Mold handling and the overhead hoist system.
Last month we covered shop size and bench requirements for a 50'x 50' mold repair shop that will have a MPP (mold pull pace) of approximately 25 to 30 multicavity molds per week and employ four repair technicians in a six-bench layout. The next topic to consider is mold handling.
Just as important as workbench design and by far, the one aspect of mold repair most taken for granted is the overhead hoist system. Installing a hoist system can be the single highest expenditure in constructing a repair area. And once the system is installed, you live with it forever. It's not something that you can afford to change your mind about after a year or two of operation, so give traffic flow considerable thought, and keep expansion in mind.
A Valuable Tool
A properly designed and smooth operating hoist is a valuable tool that should not be limited to just moving molds about the toolroom, but continually utilized to allow the technician to position mold plates and tooling in a more comfortable arrangement that translates into more accurate, efficient and safer repairs.
For instance, a plate leaning back and facing you at a 45-degree angle while supported by the hoist is much more comfortable to work on and allows for better control of hand tools during repairs or visual inspection of bores and tooling than if the plate was standing upright. Many times you will even lift a plate or mold to get specific areas at eye level for closer view. If the hoist is not available, mobility is not utilized, compromising many maintenance procedures.
To improve maintenance efficiency, technicians must have access to a hoist when they need it, which always seems to be when someone else has it. Standing around waiting on the hoist to become available can ultimately cost thousands of dollars in extended repair hours and lost production.
Having worked with most types of cranes/hoists available today has allowed me to develop some hard-learned opinions concerning pros and cons of different systems.
Hoist System Requirements
Some crane systems can turn a simple mold assembly into a gut-wrenching exercise in uncontrolled plate movement while others are just plain dangerous to work with. If the main function of the crane is to service a mold repair area, careful thought must be given to achieve a design that will provide the safest and most efficient workflow through all the stages of mold repair and cleaning. This includes how to handle the molds related to getting them in the shop, split and on the bench, and continuing on through three stages of mold repair—disassembly, cleaning and assembly.
Hoist System Options
I contacted several companies that specialize in designing and installing a variety of hoist/crane systems to see what they would recommend for our 50 x 50, six-bench shop. Each one wanted to sell me on the only bridge crane virtue of having the capability to move practically anything in the shop to anywhere in the shop. A couple of the salesmen were adamant about the perceived advantages of this feature, and did not seem to recognize any downside to it, aside from cost.
Listed below are the pros and cons of different systems as they pertain to repair-ing molds in a busy four- to six-man shop.
- Molds can be moved from practically any point in the shop. This means you can go from the shop entrance to a bench, from bench to bench if necessary, to a cleaning area and finally to a rack (storage) area without the need of a forklift or moveable mold tables.
- If in the business of total mold refurbishment, it makes it easy to move heavy mold plates and tooling to a mill, grinder or other machine tools right from the bench.
- If you like to periodically change the layout of a shop, it is easy to pick up the above machine tools and place them in a new position.
- There is normally only one hoist on a bridge crane for all to share. This is a potentially huge bottleneck in a busy shop, especially one cycling 30 molds or more through per week. To offset not having a hoist available, repair techs will attempt to physically move plates or tooling that should be left for the hoist. This translates to blown-out backs and nicked up or severely damaged tooling while a mold hangs on the hoist waiting for Bob to get back from lunch.
- The ability to set a mold and plates anywhere does not bode well for a shop whose employees do exactly that, clogging up walkways and impeding a smooth traffic flow.
Lack of Control
- Bridge cranes cannot be manipulated manually. All mold and mold plate positioning has to be carried out with a handset that controls hoist motors for movement (i.e. up, down, left, right, forward and backward). Safe and accurate mold assembly or disassembly relies on the technician's ability to minutely adjust plate position for absolute alignment of pins, bushings and other tooling during repairs. Six-button handsets are large; sometimes requiring both hands to operate and forcing you to take your eyes off the plate you want to assemble. Attempting to one-hand it can cause you to hit the wrong button, thus binding or tipping a plate over. Some technicians will get a mold plate close to the starting position, then attempt to swing it onto the bushings to engage the pins, which usually ends up binding the plate, and then finally tap the correct button to move the hoist in the needed direction to slide it on. Tap the wrong button and it's a train wreck.
- Since a bridge crane would span the entire length and width of our shop, the cost could end up being 50 percent more than boxing (with a steel frame) in the area over six benches and installing three monorails. According to my sources, a 50-foot span would require a minimum 24-inch I-beam to hold 5 tons (10,000 lbs.) The beam alone carries a $30,000.00 price tag.
Mono-rail (single I-beam centered over two benches set end to end, 10 feet apart)
- Monorails are positioned directly over the center of a bench. This ensures mold plates always hang inline with each other during disassembly and assembly operations. The control box is much smaller and only requires one hand to actuate two buttons, which control the up and down movement of the hoist. Linear (left or right) hoist travel is controlled manually. This greatly improves the physical control level during repairs, and allows the other hand and both eyes to focus on the movement of the plate.
Availability and Housekeeping
- No waiting for the hoist. Time is money. Every technician needs to be able to use the hoist during all stages of repair, whenever needed. There also will be fewer accidents and arguments concern-ing whose turn it is. Since molds cannot be placed randomly about the shop, aisles stay clear because molds are stored where they belong, not where it is convenient.
Cost and Upkeep
- It is considerably less expensive to install a monorail system that will service only the workbench area even with the added cost of a two-speed hoist over each bench. Supporting the monorails in the center (25 feet) will allow the use of a much smaller, and less expensive I-beam, than one that must span the entire 50 feet.
- Since the only moving/working part of the system is the hoist, annual upkeep through inspections, and long-term maintenance costs on this type system is much less.
- Monorails only service the area directly over, and usually six to eight feet past either end of the bench. This means molds must be brought to the bench via forklift.
- Plates and tooling must be off-loaded to a mobile table to be taken to the cleaning area. This could be a problem with molds more than 10,000 lbs.
Floor Post Supports
- To keep costs down, a typical 12-inch to 18-inch I-beam is usually center-supported if the wall-to-wall span is more than 40 feet long. For our shop, this means dodging three floor posts or supporting the beams from overhead if possible. Design and installing a hoist system is not a job for the plant handyman. Determine your traffic flow, then get a crane/hoist systems expert to come in and examine your existing walls, floors and overhead girders for structural issues that might cause load-bearing problems. All design wishes take a backseat to safety.
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