May 2019

the point at which the chain connects with the sprocket on the lower strand. However, this method of lubrication is considered to be error- prone because of the human factor involved and is therefore only used on the odd occasion as opposed to use for continuous operation. In drip lubrication, the oil is dripped into the space between the inner and outer plates of the chain by a drip oiler. It is important to check the oil in the reservoir on a regular basis and to make sure that the lubricant flows at the required frequency. This is generally in the region of four to twenty drops per minute, depending on the speed of the application. Also particularly important here is the application point of the oil: the oil will only be able to penetrate between the inner and outer plates and reach the bearing surfaces if it is delivered to the edges of the chain. This type of lubrication is especially recommended for chain speeds between 1.5 to 8 m/s. In bath lubrication, the lower strand of the chain is run through an oil bath in the drive enclosure. The oil level needs to cover the lowest point of the chain whilst operation is in progress. Another form of bath lubrication is the so-called centrifugal disc, in which an oil bath is used but the chain runs above the oil. A disc picks up the oil from the sump and delivers it to the chain via baffle plates. The plates need to have circumferential speeds between 180 and 2240 metres per minute. Bath lubrication is particularly suitable for speeds ranging from 4 to 8 m/s. The fourth type of lubrication is forced-feed lubrication in combination with an oil bath, in which a constant supply of oil is delivered to the chain via a tube. In this method it is important to check that the nozzle holes from which the oil comes are aligned with the edges of the chain. The spray tube needs to be positioned so that the oil is delivered to a point on the chain just before the drive sprocket comes into action. This ensures that the oil is centrifuged by the chain and the impact of the rollers on the teeth of the sprocket is damped. Forced-feed lubrication is particularly suitable for providing effective cooling and shock absorption for high speeds. Special chains without lubrication Although there are different types of lubricant and lubrication, there are some applications for which lubrication is generally difficult and undesirable. In many industries, e.g. the food, paper and electronics industries, the possible contamination of the end product by lubricant is not acceptable. This problem can be solved with maintenance-free chains which manage without lubrication for the duration of their entire working lives and which are certified for use for specific applications. The Syno chain, for example, is a solution which has been developed by Renold for use with zero external lubrication. A sintered bush was developed for this purpose, featuring a lubricant which is only delivered to the friction surface when the chain is running. The moment the application stops, the lubricant returns to the bush and there is no possibility of product contamination. This so- called “dry-to-touch” surface of chains such as the Renold Syno is suitable for most applications in which additional lubrication is not allowed to be used. These chains have their limitations, however, when it comes to speeds over 3 m/s and high surface pressure in the joint. Chains with sinter bearing bushes should not be used in dusty environments either, because the dust draws the lubricant out of the joints. In applications involving mainly frozen food, the use of standard chains is not possible without restrictions because of the increased risk of corrosion due to melt water. The effective solution here is to use chains with polymer inner links. In this case the inner link is made of special plastics, while the pins and the outer link plates are made of stainless steel. In most cases these chains do not need any bushes or rollers at all, with the entire inner link being made as a single piece requiring no lubricants. When it comes to choosing a plastic chain, it is essential to bear in mind that although it offers distinct advantages in terms of hygiene and weight, it is not as strong as a standard chain. As a new alternative, rust- free chains with brass bushes are now also offered. These permit higher levels of surface pressure than chains with plastic inner links, but they require a film of water in the joint for lubrication. In the food segment with dry ambient conditions, nickel-plated chains with sintered metal bushes containing approved lubricants are also an option, similar to the Syno previously mentioned above. Focus on: Seals, Bearings & Lubrication Process, Controls & Plant May 2019 www.pwemag.co.uk Plant & Works Engineering | 27