News & Press Releases

Vacuum Heating & Brazing Systems

 

Upgrade or Replace?

 

With the advent of NADCAP and AMS 2750D compliance being placed upon them by their customers, companies using vacuum heating and brazing equipment for aerospace applications will be asking themselves whether it is more cost-effective to upgrade an existing system or to perhaps replace it
with a new one.

A number of factors should be considered before making the upgrade or replace decision. There are
both “up-front” costs and operating costs that need to be evaluated. There are five mainareas of the
typical vacuum heating or brazing system that need to be reviewed so as to make a proper determination as to whether to upgrade or replace an existing system:

A. The Vacuum Vessel or Chamber
B. The Power Control System
C. The Vacuum Pumping Components
D. Trending/Data Storage & Reporting Devices
E. The Furnace “Hot Zone”

Let’s look at each area of the vacuum heating system and see what information is required and
how it can be obtained:

Integrity of the Vacuum Vessel or Chamber

There are a considerable number of vacuum heating and brazing systems in operation that were supplied
in the 70’s and 80’s – some even older! These systems have been producing quality product for many years. Many of these systems utilize a water-cooled vacuum vessel – either of a rectangular or cylindrical design. Over the years, the internal structure of the vessel may have been compromised due to a build up
of rust or water-born contaminates, leading to areas of the vessel that are running “hot”. There may also
be areas of the vessel that have developed a reduction in wall thickness due to oxidation – the ultimate indication of this is a water leak in the chamber wall.

Determining if the vessel water passages are restricted One method is to utilize an Infrared laser thermometer. With the furnace “ON” and water being circulated thru the vessel, measure the temperature of the external vessel wall at various locations. The areas near the water inlet to the vessel should be the “coldest”, while the areas near the water outlet from the vessel should be the “hottest”. If there are sections of the vessel that produce temperatures above the water outlet zone, this could be an indication of an area that is receiving little or no water cooling – perhaps due to a build up of rust or contaminants.

Determining if the vessel wall thickness has become compromised There are two common ways to do this – utilize an electronic thickness gauge or similar device, or perform the “drill and fill” empirical method. Modern electronic thickness gauges can provide extremely accurate measurements of the remaining wall thickness of various metals. If the metal of the vessel or chamber wall has suffered erosion over the years, the reduced wall thickness can be determined by either of the methods mentioned above. (Note: Build up inside the water passages of a system is dependent upon a number of factors: the materials used to construct the vessel; the type of water cooling/ recirculating system being used; the quality of the water being used to cool the equipment; etc.)

Power Control System Many older vacuum heating and brazing units utilized a mechanical means of controlling the various “trim” areas within a furnace. It was oftentimes necessary for an operator to manually adjust (or “trim”) a number of rheostats based upon the meter readings or sensor indications within a particular area of the hot zone. This was a labor intensive procedure and lent itself to the possibility of lengthy cycle times and/or “human error”. Today’s control systems are completely automatic – “hands off” operation is achieved by using electronic controllers that make use of computerized programs (or “recipes”) for the various components to be heated or brazed. It is possible to upgrade only this portion of the vacuum heating or brazing system. Replacing an old manual control system will often result in significant savings in that it will generally reduce cycle time and can eliminate any “human errors” that might be due to incorrect or badly timed manual adjustments. A fast return on investment (ROI) can result from the increased production and reduction in rejects.

 

Vacuum Pumping Components Diffusion pumps, mechanical blowers and hold pumps, when properly maintained, generally provide many, many years of reliable service. The determining factor as to whether a vacuum pumping system should be repaired or replaced can usually be found in the maintenance records for the individual components. Most often, it is more cost-effective to rebuild the existing vacuum pumping components.

The exceptions to this rule would be: 1) the need to reduce the present pump-down time, and 2) the inability to obtain parts for an obsolete pump. If the current pump-down time can be reduced significantly
by the upsizing of the vacuum pumps, the additional production that can be attained may cost-justify this investment. This “ROI” (“Return-On-Investment”) calculation is relatively simple – be sure to include the cost
of the “lost production” that will result due to the time required to install the bigger pumps.

If you cannot obtain parts for an “old dog”, the decision to replace it becomes simple – and one best made before it breaks down in the middle of a critical production run.

 

 

 

The Furnace “Hot Zone”

The heating elements, metal shielding and insulation materials that comprise the furnace “hot zone” are generally designed for a specific application at the time the system is originally engineered. The power components are sized and selected to “match” the heating elements. Over a period of time, the elements may become dirty or damaged due to the heating process and/or operator considerations. It is sometimes necessary to repair or replace sections of the hot zone – this is ordinarily done by the maintenance crew
on an “as-required” basis. Replacement of a complete hot zone may become cost-justified when the number of “patched” areas reaches a significant portion of the hot zone. As a rule of thumb, when you
find it necessary to make a third patch to the heating elements within an individual trim zone of the
furnace, you should begin to plan for the replacement of the entire hot zone at the next convenient time.

Trending/Data Storage and Reporting Devices

Perhaps the areas of AMS2750D and NADCAP that have the most impact on existing vacuum heating and brazing systems are the trending and data storage and reporting requirements. If you were to summarize AMS2750D in one word, it would be “documentation”. While existing paper chart recorders and manual record- keeping systems may still be used for these purposes, the availability of electronic trending / data - retention and recording devices will generally enable the vacuum heating customer to “survive” a NADCAP audit with far fewer “headaches”. Present day, readily-available computer hardware and custom software has been designed to take into account the data and format that an auditor will want to see and verify. In general, if the existing trending/data storage and reporting system is more than five to six years old (a “lifetime” in the world of electronics!) it will be well-worth the cost to upgrade and replace this portion of the system.

Summary

If your customers are beginning to specify “NADCAP” or AMS 2750D in their purchase orders, and your vacuum heating or brazing system has some “age” to it, you will want to consider each of the five main areas of the system when making the determination as to whether to upgrade or replace your system. Consider not only the “up-front” costs but also the ongoing operational costs when making your “ROI” calculations.

 

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