Square Transfer vs. Automatic Hoist Lines
Q. We are a plating company about to embark on the world of e-coat and are having a hard time deciding which type of machine to buy.
Could you help us out, detailing the pros and cons between a square transfer line and an automatic hoist line?
We are a job shop, so flexibility in our process is very important, but we do not want to sacrifice productivity. R.M.R.
A. Choosing the type of machine you purchase will be the most important decision you and your company make. Since you come from the plating side of the industry, you may view e-coat as if it is another form of plating. There are some important distinctions, though.
Typically, a company decides to go with an automatic hoist or square transfer index system solely based on the number of loads estimated to process through the system, almost independently of all other pros or cons.
If your hourly production requirements for the size of tank and system exceeds 15 loads per hour, you are better off installing and operating a square transfer index system. If your hourly production requirements, are less than 12 loads, then you are better off installing and operating a hoist system. For loads of two to six, the system can be manual hoist, and if the system exceeds six loads per hour, the system should be a programmed automatic hoist. The manual hoist system provides minimum productivity, the automatic hoist system provides medium productivity and the square transfer indexing system provides the maximum productivity of all square transfer systems.
As productivity between systems increases, the flexibility of the processes decreases. The square transfer index system provides the least process flexibility, as the times and process sequences can’t be modified. All process tanks and times must be the same, whereas the automatic or manual hoist systems have more flexibility with process tanks and times.
It is crucial to keep in mind that although this process flexibility is important in plating due to variables in process and specifications, it is not as important in e-coat, because there are only one or two processes globally recognized by the electrocoat industry.
If your parts are for the automotive market, process flexibility should not play a role in the decision making process as most (if not all) automotive specifications require that you clean, zinc phosphate and e-coat the parts with fixed process sequences and ranged times, and will not allow you to deliver parts that are iron phosphate or other processes.
On the other hand, if your customers are going to demand multiple substrates, multiple pretreatments (iron phosphate, zinc phosphate, alodines, etc) and perhaps multiple colors, then process flexibility is the most important characteristic you should consider when making the decision of what type of machine to purchase and operate. In this case, a hoist system should be the choice, independent of productivity.
Additionally, a programmed hoist will have the advantage of lower investment cost over the indexing system for loads below 12 per hour, will be more maintenance intensive than the index system, and will require more floor space than the index system, as the oven cannot be installed overhead the pretreatment and e-coat system.
In experience, about 65% of the systems are index type machines, 25% are monorail and the remaining 10% divided between manual hoist and programmed hoist systems. The typical job shop in the U.S. and European markets are index type systems. Square transfer systems are the most used among custom coaters around the world.
In summary, programmed hoist are typically the best choice for low volume production requirements and are especially suited for large part sizes and low volume requirements. They are also often used for very small parts and bulk processing in barrels. Square transfer indexing systems are best suited for high production volume operations. Most reputable e-coat equipment suppliers should be able to analyze your situation and provide detailed cost, floor space requirements and process flexibility calculations specific to your needs. That analysis is very important before your decision is made.
This paper is a peer-reviewed and edited version of a presentation delivered at NASF SUR/FIN 2012 in Las Vegas, Nev., on June 13, 2012.
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