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Wearsurfacing with PTA: tips for the first-time user.

Once you've decided to invest in an automated plasma-transferred-arc (PTA) system, you'll probably start wondering how to get the earliest possible return on that investment. This will be especially true if you're making the switch from a manual wearsurfacing method to PTA.

You likely decided to invest in PTA to increase wearsurfacing productivity, improve deposit quality, and reduce material and labor costs. To gain the maximum value from each of these benefits, you should follow a few simple rules. These relate to locating and installing your system properly, training your operators sufficiently, and preparing to take advantage of the much higher productivity that PTA systems deliver.

Any wearsurfacing method requires common sense and a basic knowledge of the process before you can use it successfully. Since PTA is more sophisticated than manual wearsurfacing, you'll need to be even more prepared to take full advantage of its benefits.

Since PTA equipment is automated, it can wearsurface parts faster, with higher quality deposits. This means reduced material waste and less need for expensive touch-up grinding.

Another advantage of PTA is its ability to deposit a greater variety of inexpensive alloys. PTA can usually deposit the most cost-effective alloy for a particular application because, pound for pound, powder alloys are generally less costly than rod or wire. Also, you'll have a greater selection to choose from because many powder alloys are unavailable in rod or wire form.

Install PTA properly

The installation of your new PTA system is important to its performance. You will be better off to have the manufacturer install your first system and train your people. This will help to avoid a potentially poor installation and a lot of wasted time in troubleshooting during startup. It also gives your operators a chance to learn and develop good wearsurfacing techniques from experts.

Things to watch out for during installation and operation of any arc wearsurfacing equipment also apply to PTA. Most of these are simply matters of good common sense.

For example, make sure that your new PTA system has the proper ventilation. Cooling fans cannot do their job if they are backed up against a wall. Also, proper grounding of the unit and access to electrical power are primary considerations.

You will do well to locate the unit away from drafts. Even a minor draft from an open door can affect the arc column. If that happens, your system may not perform properly.

Safety is an important consideration when installing your system. Keep PTA equipment away from chlorinated solvent vapors. They can combine with ultra violet radiation given off by the plasma arc to form a deadly gas. Make sure you provide adequate shielding for operators and others working near the system. PTA generates more UV radiation than other wearsurfacing arcs of the same intensity so it provides the potential for more frequent incidences of arc burn or flash if proper safety procedures aren't followed.

Know the process

Most fears of the first-time PTA user stem from not understanding the technology of the process. No matter how advanced the PTA system may appear, it is still shielded arc-type wearsurfacing equipment. And, like any other system, you need to know how it operates and how it's controlled.

Who will you train to operate the new PTA system? Your most experienced operators may not be good choices, especially if they've only been exposed to manual methods. They might be too set in their ways and reluctant to give up some control to a machine. Overriding the capabilities of the machine will reduce its productivity. You will reduce its productivity. You will probably be better off by training fresh new faces who will be more flexible in accepting the capabilities of an automated system.

The amount of training required normally depends on the complexity of the parts being wearsurfaced. A one-day session will usually give your operators the basics for wearsurfacing a simple flat part. For more complex applications, a two- or three-day trainig period may be desirable.

The operator of a PTA system needs to be more aware of wearsurfacing procedures and materials than with some other processes. For example, a semiautomatic TIG process requires that an operator know consumable feed rates, oscillation, amperage, arc voltage, and shield gas flow rate. When operating a PTA system, he needs to know those values plus powder-gas and center-gas flow rates.

With a PTA system, you should monitor the consistency of consumables. PTA generally utilizes alloys in powder form and particle size can vary from bottle to bottle. This may require minor adjustments to maintain a consistent deposit. Also, it's important to make sure that your powder alloys are kept dry.

The biggest mistake

The biggest mistake most first-time users make is trying to go into production before their operators are comfortable with the system. It pay s to give your operators several days to familiarize themselves with the process. This is especially true if they've worked with manual processes in the past. With PTA, you're virtually taking the torch "out of their hands." The functions that they previously judged from sense and experience are now precisely controlled with buttoms and knobs. Operators have to feel comfortable reaching for those knobs and must appreciate the new degree of control they have as a result.

It's a good idea to let your operators practice on simulated production parts. You might think it's costly to pay them to practice, but it's probably much cheaper than reworking defective production parts. If you provide an adequate training period, your operators will feel comfortable with the system more quickly.

Operating tips

Once your system is installed and your operators are confident in their ability to operate it, the following tips will help you to boost productivity.

First, prepare the work for wearsurfacing. Surface preparation for PTA is almost identical to that of other methods. Do not attempt to wearsurface on dirty, rusty, oily, or greasy surfaces. Preheat your parts to 200 F to 300 F to eliminate moisture if they have been stored in a damp area or below the ambient temperature. Depending on the application and alloy being applied, you may have to preheat the part surface to several hundred degrees to ensure a good deposit bond. Remember that preheating, interpass temperatures, cooling rate, and post heat treatment are critical to all forms of wearsurfacing, including PTA.

Second, make sure your operators know the importance of running the system at recommended speeds. With an arc temperature of about 30,000 F, you run the risk of melting the workpiece if you're not working fast enough. With PTA, more parts are probably ruined by working too slow than too fast.

Third, use a good welding-grade gas. The PTA process can use any of several inert gasses. Regardless of which gas is used, it must be moisture-free to avoid spatter. Make sure your gas is dry before beginning the wearsurfacing operation.

Fourth, there should be adequate consumables on hand to finish a particular job. Restarting a PTA job is more difficult than with some other wearsurfacing methods. So, he flexible and finish a run of parts before breaking for lunch.

Finally, adequate safety precautions must be observed when operating a PTA system. Simply stated, watch out for the arc! The PTA arc column is larger with more surface area than the arc in some other processes. Be aware and cautious of the arc at all times. Develop and use good shielding techniques (a number 12 shield glass is recommended). Common-sense practices make PTA as safe to operate as most other wearsurfacing methods.

Productivity hints

Schedule your work for the greatest productivity. An idle machine isn't producing, and you're not getting any return on your investment. Proper scheduling means preheating parts in advance, having materials and gasses readily available, and maintaining a good work flow.

It's a good idea to have commonly needed spare parts on hand. The lack of an inexpensive part can hold up your entire operation. Also, because most parts are not directly interchangeable between PTA systems, make sure your manufacturer can supply parts quickly if needed.

Taking the little bit of extra care necessary to ensure that your system is installed properly and operated correctly by well-trained personnel will pay handsome dividends in terms of quality production and long, trouble-free operation. For more information on PTA wearsurfacing, circle E36.
COPYRIGHT 1984 Nelson Publishing
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Copyright 1984 Gale, Cengage Learning. All rights reserved.

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Title Annotation:plasma-transferred-arc
Author:Shubert, Gary
Publication:Tooling & Production
Date:Nov 1, 1984
Previous Article:Tips on finishing problem parts.
Next Article:Post-show report: highlights of IMTS-84.

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