Are your temperatures up to spec?

..and can you prove it to your customer? In times of recession when orders are hard to come by, companies inevitably look for the benefits of their product that will give them an edge over their competitors.

Quality and reliability are often the chosen themes - which naturally leads to questions being asked about their suppliers' manufacturing procedures. If the reliability of our product depends on the quality of a certain component, how can we be sure that it is being made exactly as it should be? It's at this point that the supplier gets a visit from the customer's quality audit team; and if he can't demonstrate conclusively that specified procedures are being followed to the letter, he could find his contract in jeopardy.

The reliability of many engineered products depends on metal components, of course - and in most cases it is accurate temperature control at critical points on the process route that determines success or failure. When business is booming, the customer's over-riding concern is to get parts so that he can continue to meet demand, and 'minor details' such as process temperatures are of little or no interest. But when the economic tide turns, the supplier must be able to show that he is doing the right thing at the right time - and in exactly the right place.

The five case studies summarised here show how infrared temperature measurement can often provide a solution - but this is usually not an area where off-the-shelf, 'point and press' portables can do the job, however tempting the price ticket. In fact, as some of these examples show, they can give incorrect and misleading results. Choosing the right system and integrating it into the production line are crucial to success, which is why it's important to have an equipment manufacturer well versed in the realities on board from the start.

At LAND, we wouldn't claim to have 'seen it all' - because there is always a new challenge around the corner - but we have certainly acquired a great deal of experience over the years in matching our technology to a wide range of production circumstances.

1. Forging

Manufacture of a safety-critical suspension part from 13-25mm diameter bar depends on a bar temperature of at least 950 °C, to avoid possible cracking or insufficient hardness. The customer - a European car manufacturer - was dissatisfied with existing temperature measurement arrangements, which were limited to a single thermocouple inside the furnace in which the bars were heated, supplemented by the ability of operators to judge bar temperature from appearance alone. Reliance on such subjective judgments is commonplace in manufacturing, but it is invariably ill-founded because - although the human eye is a good and repeatable detector - it is not calibrated and no two eyes are the same, so that quality varies from operator to operator. The system Land installed measures the temperature of each bar at the critical point - immediately before forging - and activates a warning buzzer if it is below temperature.

2. Rolling

A precious metals manufacturer needed to improve efficiency in response to the recent opening-up of the industry to Europe-wide competition. Products included blanks from which coins are stamped, consisting of strips of semi-precious and base metals that are fused together by resistance-heating to 450?C before passing them through a set of pinch rolls. Process control was limited to the heat setting of the furnace, and metallurgical analysis 'after the event' to determine whether an adequate bond had been achieved. To reduce scrap rates, the company wanted to use strip temperature as a means of varying strip speed. LAND demonstrated that the most accurate measurement position was the 'wedge' formed at the point where the strip and the roll converge - a method it has also used successfully in the continuous annealing of bright metal strip.

3. Fusing

A surgical instrument manufacturer risked losing a long-standing contract to rivals when the orthopedic tools he supplied frequently parted from their plastic handles during use. The tool was assembled by heating the stainless steel shank in an induction coil, and then inserting it into the handle using a pneumatically operated jig. Although the company knew that the shank had to be at around 350?C to achieve a successful bond, the only controllable part of the process was the heating time - and the portable infrared thermometer used to check temperatures gave inaccurate readings, resulting in a high reject rate. The system that LAND supplied takes accurate temperature readings from the correct fixed distance - something the portable could not achieve - and activates a light signal for the assembly process to continue if the temperature is within tolerance limits.

4. Heat Treatment

During the manufacture of bandsaws, the saw teeth are hardened by induction-heating to 850 °C, followed immediately by oil quenching. As in several of the other cases described here, the only means of controlling quench temperature was to adjust the speed at which the band traveled through the induction coil. There was a fair degree of 'guesstimation' involved - which was reflected in the proportion of product that had to be scrapped if metallurgical analysis showed that the carbon content of the tooth area was below the specification. The company wanted to reduce the scrap rate by measuring the temperature of the teeth as the band passed from the induction heater into the quench. As well as meeting this requirement, LAND's system showed that the line speed controls were not as accurate as had been assumed - a deficiency the company has since rectified.

5. Casting

A company casting steel cylinder liners inside a rotating mould were using a hand-held infrared thermometer to check the temperature of the mould's internal surface, which determines the rate of flow of the metal and hence the thickness of the liner. Land replaced this manual method with an automatic continuous system, eliminating the considerable loss of production time necessary for an operator to go into the safety compound surrounding the casting area to make the temperature measurement. As a consequence, productivity has increased by almost 100%, achieving the output required by management.

A final thought

Several of the companies described here were 'caught napping' with inadequate temperature measurement arrangements when the customer came calling- but there must be thousands of other cases on production lines in all parts of industry that pass without notice. It's easy to take the short-term, cynical view of course. The thousands who get away with it are the lucky ones. Why spend the money if you don't have to - especially when business is bad? Every little helps to make the bottom line look better. But there is a more positive (and potentially more profitable) approach. If you spend a few thousands to bring your temperature monitoring arrangements up to standard, you won't just cut your production costs (desirable though that is). Equally importantly, the facility you have invested in becomes a positive selling point in its own right. Instead of just rescuing the orders that you've got today, it can help you win the multi-million pound contract of tomorrow.

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