Functional Testing Solutions For Brake Calipers

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The brakes are the most important safety feature of any vehicle, and the calipers are one of the most important components of the braking system. They apply the force necessary to slow and stop the vehicle. Producing quality calipers that stand the test of time, wear & tear and is essential to safe operation. If the calipers aren’t working, the car will just keep on going—even when one doesn’t want it to.

History

Disc brakes came on the commercial vehicle market in the 1950s. They represented an improvement over older drum brakes, which were prone to overheating and deteriorating performance over a short amount of time. Nearly all cars and trucks known have front-end disc brakes; some less expensive models still use drum brakes on the rear axle.

The standard brake caliper contains metal plates on both the outside and inside face of the rotor. The plates are faced with brake pads, which are the point of contact between the calipers and the rotors. When you depress the brake pedal, brake fluid flows through a master cylinder, which is linked to a piston housed within the calipers. The piston presses against the pads and forces them against the rotors. The action of friction slows down the rotor and the wheel.

Floating and Fixed

Floating calipers have their hydraulic pistons on the inboard side of the rotor; they move in and out as the brake pedal is depressed. Fixed calipers have their pistons set up on both sides of the rotor and apply pressure directly from both sides, allowing them smoother operation and more braking power; the floaters, however, are less tolerant of any defects or warping of the rotors.

Construction

Brake calipers can be one or two pieces and contain pistons or cylinders made of aluminum or steel. Two-piece designs are less expensive to manufacture, but have some disadvantages, which includes flex, less present in one-piece designs. Brake calipers hold the brake pads and have channels that accept the hydraulic brake fluid that activates the piston to push the brake pad against the rotor.

Materials

Most brake calipers consist of aluminum, as aluminum is very strong, but a light material that can handle the constant wear that exists in the braking system. Minimizing weight is crucial to the design of any vehicle and using forged or cast aluminum brake calipers helps accomplish this goal. Sometimes magnesium alloy is used, but it is expensive and often reserved for race cars. The brake rotors are made of a harder metal, as the friction against the rotor face during braking can bend or warp lighter metals.

The InterTech Solution for Testing Brake Calipers

Here’s one example of a turnkey system designed and built by InterTech Development Company in the USA. Do bear in mind that this technology is now available in India to best ensure that your products are tested with a robust and reliable system while ensuring that your parts meet the standard and quality requirements of your Customers.

brake-caliper-testing-system-test-stand

brake-caliper-testing-system-test-stand

 

Features

Components are leak tested to a 3 sccm. limit at 5 psig.

Piston retraction is gaged within a 0.010˝ window after venting down from 200 psig.

An InterTech M-1075 Mass Flow Leak Detector controls the leak test cycle.

Benefits

Reliability: System operates in a fail-safe mode with self-check features.

SPC Capabilities: Test results may be transmitted via RS232 interface or stored on disk.

Measurement Capabilities: Test R&R meets QS9000 requirements.

The Brake Caliper Functional Test Cell automatically tests and marks r.h. and l.h. calipers at a rate of 211 pph.

 

Follow the InterTech India blog for more solutions on leak and functional testing. For sales enquiries, you may contact us at;

Mobile: +91 994 032 0718

eMail: ajay@intertechdevelopment.com

Land phone: +91 44 4211 2525

Sales & Support: Chennai, India

 

 

 

Source: eHow.co.uk & eHow.com

InterTechdevelopment.com

 

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Leak Testing 101 – Part 4

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In parts onetwo, and three of this “Leak Testing 101” series, we discussed three methods of dry-air leak testing—pressure decay, differential pressure decay, and mass-flow leak testing—including the pitfalls and hidden costs inherent in two-step pressure testing methods and the higher accuracy of single point measurement mass-flow leak testing techniques.

 Is mass-flow leak testing always the best leak testing method? Absolutely not. When accuracy and cycle time requirements are not that stringent, pressure decay testing or differential pressure decay testing can be a better application match because test instrumentation does not require as much specialization and related cost. At the other extreme, when very small leaks of less than 0.01 standard cubic centimeters per minute (sccm) must be detected, helium mass spectrometer leak testing methods may be required. It is the only reliable method when an application requires detecting leaks as small as 10–4 standard cubic centimeters per second (sccs) or less.

There are several different helium leak detection methods:

Sniffer—The test item is pressurized with helium and an operator moves a sniffer probe connected to the mass spectrometer to localize the leak. This method is slow, nonquantitative but has the advantage of localizing the leak.

Accumulation—The test item is placed in a chamber and charged with helium. Helium leaking from the part accumulates in the chamber and after a certain amount of time, a sniffer probe checks for the presence of helium, i.e., a leak. While apparently inexpensive, this method has a number of shortcomings: presence of tracer gas from prior tests, lack of adequate circulation in the chamber, and long test times due to background effects. As a result, it will be difficult to provide quantitative testing with this method.

Vacuum leak testing with helium—Figure 1 shows how helium mass spectrometer leak testing proceeds. The part is pressurized with helium and the chamber is evacuated down to less than 0.1 mbar absolute to eliminate background effects. The presence of helium leaking into the chamber is then detected by the mass spectrometer.

Helium Mass Spectrometry Method of Leak Testing

Figure 1: Test item is pressurized with helium within a test chamber. The chmber is evacuated, drawing helium out of the leaking test item. Mass spectromter then samples the vacuum chamber.

Equipment costs, maintenance costs, extra time required to evacuate helium from test fixturing in between test cycles, and ever rising helium costs makes this method the method of last resort. Typical applications include: heating, ventilating, and air conditioning (HVAC) components; pace makers; aluminum wheels; and airbag components.

For these type applications where leaks of 10–4 sccs or less must be detected for product integrity or safety, helium has its well-deserved place in the repertoire of best-match leak test techniques to consider.

In the next part of this Leak Testing 101 series we will discuss miscellaneous other testing techniques including: hydrogen ultrasonic, bubble testing, and air under water.

If you would like specific questions on best practices for leak testing (and other testing topics) answered in future articles, please send me your questions at jhoffmann@intertechdevelopment.com.

 

Note:  The above article has been reproduced from an article written by the author for Quality Digest

 

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Leak testing 101 – Part 2

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In part one of this series, we considered the pros and cons of pressure-decay testing. In part two, we’ll take a close look at a leak-testing method called “differential pressure decay.”

This method is similar to simple pressure-decay testing discussed in part one.A more accurate variant of the pressure-decay method, differential pressure testing involves pressurizing a reference volume along with a test part. The pressure differential between the non-leaking reference volume and the test item is then measured by a transducer over time, as shown in figure 1. This method requires measuring pressure at two points in time to obtain a pressure change reading. It is an indirect method of measuring leakage rate because the time and pressure data must be converted into leakage rate. This method allows you to use a higher-resolution pressure transducer.

Differential Pressure Decay Method of Leak Testing

Differential Pressure Decay

Figure 1: With valves 1 and 2 open, the test item and reference volume are pressurized and then isolated by closing valve 1. The reference volume is then isolated from the test item by closing valve 2. The transducer reads the pressure differential between the reference volume and test item twice over time.

A down side to this method is that the larger the volume, the smaller the change in pressure for a given leak rate, resulting in longer test times as test volume increases. All temperature effects are the same as for pressure decay.

Differential pressure-decay testing is widely used. Unfortunately, in many instances it is the default choice of manufacturing and quality engineers who don’t understand the true cost of this type of testing. They could eliminate these hidden costs by using mass-flow leak detectors, another dry air-leak testing method that will be discussed in part three.

Moreover, the indirect nature of the test process and the time needed to track pressure changes and take two measurements create inherently longer testing times. This means a greater probability of measurement error exists than for methods that require only one measurement. The probability of measurement error is directly related to the interval length between the two measurements. These factors are what lead many technicians to use mass-flow leak testing.

That said, it should be noted that for many applications at pressures in excess of 150 psig, differential pressure-decay leak testing remains the method of choice. Granted, test cycle times are slower than with single-measurement leak test methods, however, this drawback is outweighed by the lower costs for instrumentation. Basically, choosing between pressure decay or differential pressure-decay test methods involves a trade-off between cycle time and instrument cost.

In part three of “Leak Testing 101,” we will discuss the mass-flow leak testing method: how it works, and the pros and cons vis-à-vis helium and pressure-decay testing. I’ll explain how to implement this technique to get accurate gauge repeatability and reproducibility (R&R).

If you would like specific questions on best practices for leak testing (and other testing topics) answered in future articles, please send me your questions at jhoffmann@intertechdevelopment.com.

Note:  The above article has been reproduced from an article written by the author for Quality Digest
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Roundtable Questions and Answers regarding Testing & Inspection in the Medical Device Industry

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Testing & Inspection in the Medical Device Industry

Some key questions addressed in this online session with Jacques Hoffmann include:

  • What are the common missteps OEMs make when planning a testing solution for their medical devices?
  • How early in the product development lifecycle should testing come into play?
  • When dealing with supply partners, what best practices should OEMs follow to inspect the product?
  • Any thoughts/comments on testing, inspection, or another related area that you would like to share with medical device manufacturers to aid them?

Check out this link for complete details on this session.

 

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