May 2019

surface and the chain roller. These normally only need minimal lubrication because they are not exposed to much friction or movement. Nevertheless, when it comes to troubleshooting, time and again it turns out that lubricant has been applied particularly generously here. Which chain lubricant is the most suitable for each application depends on a variety of factors. The conditions in the surrounding area, for example, play an important role in the choice of lubricant. If there is a large amount of dust in the ambient air, such as lime, talc or flour, for example, initial lubrication with a waxy grease should be the preferred option. This has the disadvantage, however, that the chain joint is often not reached on relubrication. Waxy lubricants should therefore be specifically used where relubrication is difficult or even impossible and there is a risk of the lubricant being drawn out of the joint by dust because of the nature of conditions in the surrounding area. The operating temperature also plays an important role. Table 1 shows the optimum lubrication viscosity for each temperature range. Mineral oils are suitable for most applications. However, if grease lubrication is required, it is particularly important to heat the grease until it reaches a liquid state and then to immerse the chain into it until no more air bubbles are seen. Chains lubricated using this method need regular cleaning and relubrication. Chain temperatures in excess of 100 degrees Celsius should be avoided as a general rule because of lubricant limitations. used for the standard relubrication of chains, because removing the chain and hot-dipping it again is too complicated for all but a few applications. As a general rule, oil with a viscosity of 150 to 450 cSt is recommended. In many cases lo wer viscosities provide insufficient lubrication effect where there is high surface pressure in the joint, whereas higher viscosities seldom reach the chain joint between the pin and the bush. Correct chain lubrication Given the design of a chain, lubrication products are required to pass through a narrow gap between the plates. Most suitable for the purpose are liquid lubrication products without thinners, which are capable of being applied so that sufficient quantities get into the chain joints. However, this procedure alone involves plenty of potential for errors. One of the most common lubrication errors is in the treatment of the 26 | Plant & Works Engineering www.pwemag.co.uk May 2019 Process, Controls & Plant Focus on: Seals, Bearings & Lubrication In special cases chains can be used in temperatures of up to 250 degrees for some applications and deliver good performance. This requires the use of special oils for high temperature applications. One good means of improving the effectiveness of the lubrication and its cooling effect is to use forced-feed lubrication with a higher oil volume (up to 4.5 litres per minute per chain strand) and to provide a method for the external cooling of the oil. For very high temperatures (e.g. oven chains), graphite or molybdenum disulphide can be used as an admixture in support of the oil or in spray form. Dry lubricants are often used in these cases because relubrication is difficult and has an adverse effect on the product in the oven. The four types of lubrication There are four general methods of lubricating chains: manual, drip, oil bath and oil flow. The choice of method depends on the operating speed of the chain and the power transmitted. In manual lubrication, the lubricant is applied to the chain by brush, oil can or spray can. This tends to be little used in the industry because the manual work involves considerable time and effort. Although it varies from application to application, it can generally be assumed that the procedure needs to be repeated at least every eight operating hours. The quantity of oil and frequency must be sufficient to keep the chain wet and it is essential to make sure that the new, clean oil is able to penetrate into the joints in order to lubricate the bearings. This means that the oil needs to be directed into the spaces between the inner and outer plates, ideally at $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ Table 1: Lubricant viscosity for different temperature ranges