Roller chains have evolved a long way since Leonardo da Vinci sketched his ideas in the 16th century and Hans Renold invented bush roller chain in 1880. Jon Severn takes a look at some of the latest developments in power transmission and conveyor chains, as well as chain attachments and chain-monitoring sensors.
Chain transmission systems have been eclipsed by timing belts for many applications today, thanks to the developments in materials and tooth form that have resulted in stronger and more reliable toothed belts with higher efficiencies. But for applications in harsh environments or where there is limited space available to transmit the required power, roller chains still have a role to play. Moreover, this is an area where product development is continuing, even though Leonardo da Vinci sketched roller chains in the 16th century and they have been mass-produced since the late 19th century.
Recent developments have focused on both power transmission and conveyor chains, often targeting applications in extreme environments - where elevated temperatures and corrosive substances are encountered - as well as those where cleanliness is important, such as in the food and beverage industries.
For the majority of applications, however, the main drawback with roller chain is wear in the chain and sprockets, which leads to the chain lengthening (often misleadingly referred to as 'stretching') and, eventually, the need to replace the chain and maybe the sprockets too. In a bid to combat this problem, companies such as Eriks have been investigating ways to improve the wear characteristics of roller chains.
Eriks' Fenner Plus range of transmission roller chains, for example features solid rollers that are manufactured to have an extremely high surface hardness that improves wear resistance. This results in longer life for the chain in less demanding applications, as well as better performance in hostile environments (Fig.1).
Shot-peened plates help further in extending the chain's life, as this process relieves the stresses built up during manufacture and reduces the likelihood of fatigue failures. In addition, since the chain plates are punched progressively, hole concentricity and the accuracy of both the diameter and pitch are maintained along the entire length of the chain. This ensures quiet and accurate meshing with the sprockets and eases pin extraction when splitting the chain.
Another feature that helps to minimise wear is the case-hardened chain pins, and the Fenner Plus chain is also delivered with a wax lubricant applied so that it can be used straight from the box. Since debris cannot adhere to the dry wax finish, this helps to protect against premature failure. Precision grinding of the chain pins gives a high-grade surface that helps to retain the wax lubricant and extend the life of the chain.
A lubrication-free version of Fenner Plus chain is also available with sintered bushes that retain lubricant, thereby negating the need for external lubrication and avoiding the problems associated with maintenance teams failing to adhere to relubrication regimes. An added benefit of using sintered bushes is that the chain can operate at linear speeds of up to 2.5m/s - which is more than twice the speed of a composite bush chain.
To complement the Fenner Plus chain, Fenner Plus sprockets are manufactured from C45, a 0.45 per cent plain carbon steel that is suitable for through-hardening. The teeth are flame-hardened to just below the tooth root, helping to improve the chain and sprocket life by up to 50 per cent.
Eriks is not alone in offering chains with oil-impregnated sintered rollers; Tsubakimoto Chain has a similar range, plus this company also supplies chains manufactured from a combination of engineered plastic and stainless steel. These are said to protect food products and packaging from marking and contamination, and reduce the expense associated with continual lubrication with costly food-grade lubricants in food and beverage processing plants.
According to Tsubakimoto, a de-palletising machine at one of the UK's largest butter processing sites uses Tsubaki corrosion-protected drive chain to overcome issues relating to lubrication and corrosion. The company imports over 26000 tonnes of butter into the UK every year, with the butter arriving on pallets holding 50 blocks each.
Machines in the butter processing plant are washed down using high-pressure salt water at 70°C after each shift. Thanks to its sintered, oil-impregnated rollers and protective finish, the Tsubaki Lambda WP chain requires no external lubrication or other protection against corrosion.
For its PC grade of non-lubricated chain aimed at lighter-duty applications, Tsubakimoto uses an engineering plastic for the inner links and stainless steel for the side plates and pins (Fig.2). This chain has no rollers; instead it relies on the self-lubricating properties of the engineering plastic. PC chain also has the added advantage of being 50 per cent lighter than all-stainless steel chain, which results in easier handling and installation.
Available in drive, conveyor and attachment variations, the PC chains provides high resistance to water, acids, alkalis and food ingredients. Tsubakimoto also manufactures specialist types of chain in various materials, offering a variety of properties to solve application-specific problems. These include a titanium-based engineering plastic combination chain for increased acid resistance and the KV series for operation in temperatures up to 140°C. The UMW and E series PC chains have lower magnetic properties than all-stainless versions, discharging static electricity built up during use to avoid interference with products and systems, especially in the electronics industry.
High temperatures can be problematic for chains and lubricants but, once again, manufactures have developed specialist grades to suit. Tsubakimoto offers a heat-resistant version of its non-lube Lambda chain with an operating temperature range of 150 to 230°C (Fig.3). Typical applications for this type of chain include heat sealing in packaging, semiconductor production, steel furnaces and die casting.
Prior to heat-resistant chains being available, such applications would have required the use of standard chains with costly coatings that did not offer good wear life and necessitated the derating of the chain due to standard rollers and plates losing their strength at elevated temperatures. Of course, the need to derate chains also required the specification of larger chains than would otherwise be needed, leading to more space being required and higher energy consumption.
In tests performed at 230°C, the Tsubaki HT Lambda chain achieved about three and half times the life of standard Lambda chain, which is not designed for high-temperature operation. Importantly, although the standard chain exhibited some degradation at this high temperature, HT Lambda did not.
The lube-free performance of HT Lambda at high temperatures is the result of a construction that employs oil-impregnated bushes, specially coated pins and solid rollers, and nickel-plated inner plates.
Poor lubrication is often the root cause of premature chain failures in high-temperature environments, so it is not surprising that manufacturers are making an effort to develop lubrication-free chains. Another company active in this field is Renold, which has launched a high-temperature version of its lubrication-free Syno chain for operating in temperatures up to 200°C (Fig.4).
As with standard Syno chain, the high-temperature version features oil-impregnated sintered bushes, only this time the specially formulated lubricant is able to withstand elevated temperatures. Renold says that its high-temperature Syno chain has been used in drying ovens and industrial environments where heat is a factor.
A further interesting development from Renold is a new, smaller version of its Smartlink chain sensor, which is now available for chains down to half-inch (12.7mm) pitch. This breakthrough has been possible thanks largely to advances in the miniaturisation of electronics. Renold says that the Smartlink devices are particularly useful in applications where access is difficult, either during normal operation or maintenance.
Smartlink consists of a tiny microprocessor that is attached to the chain side plate to measure the stresses experienced by the chain as it travels through a machine. It can therefore act as an overload detector and communicate via an infrared link when the chain exceeds a predetermined load. This provides a simple warning to enable the machine to be inspected, hopefully before any serious damage is incurred. Using the infrared remote control unit, the Smartlink alarm can subsequently be reset and the system restarted.
To understand more about the working loads applied to the chain drive there is a second level of diagnostics that the Smartlink can provide. Using a handheld receiver, more detailed information about the loads can be downloaded and transferred to a Windows-based PC. This data can be analysed to determine which points in the chain drive are experiencing problems.
So far we have considered the chain itself, but another important topic for conveyor chains is attachments. Transdev has recently introduced a range of chain attachment protector clips for conveying and parts handling. These clip-on components ensure that delicate goods are protected against damage by the chain while also providing non-slip conveying (Fig.5).
Manufactured from POM (polyoxymethylene, or acetal), these durable clips feature an overlay of TPU (thermoplastic polyurethane) on the top surface that increases the contact surface, thereby improving significantly the drive between the clip and the conveyed item. Furthermore, to prevent any possible tilting or lifting of the load, the clip is profiled to ensure there are no edge-lifting pressures at the transfer points.
Suitable for use with the Wippermann 462L, 513GL and 548GLS roller chains, including the stainless steel and maintenance-free Marathon versions, the clips are said to be easy to install, highly durable and have a high load capacity, making them suitable for use in a wide variety of applications.
Another more specialist chain-based application is the Tsubaki 'gripper' chains for form, fill and vacuum-sealing wrapping applications in sectors such as food, electrical and medical packaging. Whereas conventional gripping attachments often open vertically, the Tsubaki gripper attachments open to the side as well, providing a larger opening that prevents jams and makes loading easier (Fig.6). This range is available with many variations of transmission chain, including the Lambda lube-free chain.
The Tsubaki attachments are claimed to offer excellent wear characteristics as well as the advantages associated with a design that cams open to create a wider opening. Incorporating a larger coil spring wound from square-section wire, the gripper is said to be less prone to breakage.
Tsubaki gripper chains are produced with a hard-wearing and protective nickel-plated finish as standard, suitable for general use in temperatures ranging from -10 to 150°C.