How to get the most from your heavy-duty brakes
08 September 2015
As with all things mechanical, it is possible to improve the reliability and life span of heavy-duty brake systems with good specification, correct installation and correct maintenance procedures. Steve Powell offers some advice.
Once a braking system is in place it is essential that the operating loads and conditions that are specified by the manufacturer are not exceeded. Having specified the required design, getting the installation correct is essential if the braking components are going to deliver the expected long service life; the manufacturer should be able to help with this.
Ideally, heavy duty braking systems should be designed with two callipers on each disc, mounted diametrically opposite one another, in order to neutralise the braking torque reaction forces on the shaft bearings. Sufficient space should also be allowed for access to the callipers for routine inspection and maintenance as well as for pad renewal.
Following the manufacturer’s specifications is important, especially on topics such as hydraulic fluid, which should be checked for compatibility with the seals in the system. Using an incorrect grade of oil can cause seals to swell which may result in reduced braking efficiency. Alternatively, the oil seals may fail prematurely and cause a loss of oil pressure.
Having correctly assembled and installed the braking system, it is important to follow the initial running-in procedure as it can have a significant impact on the overall performance of the braking system.
The procedure normally involves two phases: the bedding-in of the pads on the disc and the pad conditioning. The former maximises the area of contact between the pads and the disc while the latter involves a gradual increase in heat generation that creates changes in the pad material which are necessary to develop the full braking potential.
Although procedures will vary between individual applications, the principle during this period is to work the brake lightly at first to remove any pad high-spots and so achieve something approaching 100 percent pad contact with the disc. After this, progressively heavier braking can be applied until the full rated duty is achieved. It is important to monitor the disc temperature throughout the bedding-in process and allow sufficient cooling time to prevent overheating.
In most cases 250°C is a safe peak braking path temperature, but this can be difficult to measure. In emergency brake applications much higher temperatures can be attained, but this type of duty brake should be allowed to cool down to near ambient temperature before re-testing.
Of course the procedures described so far involve dynamic braking systems, but if the brake is only to be used for static holding duties it is not practicable to operate it with the disc in motion. In these situations the pad/disc interface will rarely develop even 50 percent of its friction potential - often less. However, as this can be anticipated during specification it should have been allowed for in the original design.
In general, some improvements can be made to the braking efficiency by removing the high-spots on the pads to improve the total area of contact. However, if sufficient braking force is still not generated, there are some further options to consider. Firstly, it may be advisable to change pad material to a more efficient variety; secondly, it is possible to adjust the air gap in spring-applied units or increase the hydraulic pressure in direct-acting components.
Operation and maintenance
Once the new braking system has been properly bedded-in and conditioned it can be commissioned and operated on a full time basis. During the first week of normal operations it is important that a number of regular maintenance checks are made to ensure that there is no unexpected fluid leakage and that brake operation is smooth.
Having completed the running-in period, the security of all bolted connections and pipe connections should be checked, while the calliper mounting bolts should also be paint marked to provide a visual check of any movement.
With all of the necessary checks and certifications in place the braking system will finally be ready to enter regular service. From this point on, in addition to any statutory requirements, it is important to follow a regular maintenance inspection programme as stipulated by the manufacturer.
Clearly, brake pad wear needs to be monitored according to the application and any adjustments made accordingly. In some components additional monitoring equipment can be installed to provide warnings about friction pad wear and adjustment. When the brake pad is nearing the end of its service life it will need to be replaced and the procedure for this will depend on the installed design.
Within my own company’s product range, one of the features offered is 'parked off', which actively removes the spring force from the brake while it's powered off, meaning there is no force acting on the pad which could lead to unexpected closures. With hydraulic pressure applied, maintenance engineers can unwind an adjusting spindle, which releases the spring pack. When the hydraulic pressure is removed the springs have the freedom to extend without acting on the brake. At this point the spring load and hydraulic pressure are both zero and the brake has no stored energy.
This 'parked off' feature has a number of benefits. First, basic maintenance such as brake pad replacement can be carried out quickly and with a reduced risk of unexpected closure compared with conventional brake designs. Second, the brake force can be easily adjusted by setting the brake to 'parked off' and adjusting the number of shims from the end cover. Installation is considerably simplified and the brake can be installed without the need for hydraulic pressure.
Manufacturers of braking systems have designed the components to work together within strict tolerances so that they meet the required specification, including a sufficient safety margin. It is therefore advisable to replace any parts with those prescribed by the manufacturer in order to ensure continued reliable service.
While the use of third party components may have an initial cost benefit, their long term performance and reliability may be lacking. Very often, cheaper components have different chemical or mechanical properties and tolerances that lead to reduced performance and a shorter service life.
By ensuring that the correct installation and maintenance procedures are followed, operators of large industrial equipment can deliver long term cost savings to their operation. Working with the original manufacturer also ensures that the long term efficiency and reliability of this essential equipment can be sustained.
Steve Powell is product manager at Twiflex
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