Sludge and varnish: the hidden productivity killers of injection moulding operations

In an output-intensive industry, productivity is a priority and any unplanned downtime caused by equipment breakdown will impact directly on the manufacturer’s bottom line. Not only will customer delivery deadlines be at risk, but there is the added cost of machine repair along with expensive shift workers standing idle while this takes place.

At the heart of these machines lies the hydraulic system with hydraulic fluid playing a vital but often underestimated role. As multiple surveys carried out by hydraulic equipment manufacturers and other industry bodies reveal, 50% to 70% of mechanical failures are related to ‘improper hydraulic fluid condition’. These failures can be as a result of a build-up of what are often called the ‘hidden killers’ of productivity - sludge and varnish.

Gaining notoriety as the hidden killers, whilst most standard Oil Condition Monitoring (OCM) tests like Total Acid Number or Viscosity can help screen for problems such as ineffective corrosion-protection, helping to pre-empt hydraulic system failures, they cannot detect the build-up of sludge and varnish. The reason being that soft contaminants don’t typically impact the bulk chemistry of the hydraulic fluid making them difficult to measure.

Equipment failures can then result from reduction of the spool-to-bore clearances in valves leading to valve malfunction, the clogging of a suction strainer that will lead to pump failure or damage to seals and o-rings leading to oil leaks and cylinder problems.

"As multiple surveys carried out by hydraulic equipment manufacturers and other industry bodies reveal, 50% to 70% of mechanical failures are related to ‘improper hydraulic fluid condition’. These failures can be as a result of a build-up of what are often called the ‘hidden killers’ of productivity - sludge and varnish."

The resulting unplanned repair downtime and oil change can have a financial impact on the manufacturer. Additionally, short oil drain intervals are costly not only in terms of the oil cost but also oil waste cost.

Poor-quality hydraulic fluids are more susceptible to this problem as they readily oxidise in the presence of yellow metals, water and air contamination. In addition, they contain additives that are not thermally stable and so decompose at elevated temperatures. The best way to avoid this is to use a high-quality hydraulic fluid which has high oxidation resistance and excellent thermal stability helping to mitigate risk of sludge and varnish build up , lowering the operator’s total cost of ownership² .

Shell Lubricants’ Tellus range of hydraulic fluids has been specifically formulated to meet the demands of hydraulic systems by resisting thermal and chemical breakdown, which adversely affect a fluid’s lubricating performance. Shell Tellus can provide better reliability and system cleanliness compared to competitor products having achieved excellent results in the industry standard thermal stability test of hydraulic oils - ASTM D2070³. This test method evaluates the thermal stability of a hydraulic oil in the presence of copper and steel at 135 °C.

Many of Shell’s customers that operate plastics injection moulding machines have reaped the benefits of switching to the Shell Tellus range. For example, an electrical appliance manufacturer based in Jiangsu Province, China, which owns 13 plastics injection moulding machines, was experiencing problems caused by blocked filters. The Shell technical team investigated and discovered an excess formation of sludge, which meant that the oxidation stability and filterability performance of the machine’s hydraulic fluid was not effective. Switching to Shell Tellus S2 M 46, the company no longer experienced blocked filters and was also able to significantly extend the oil-drain interval from 8,000 to 24,000 hours. As a result, it reported total annual savings of USD$126,140⁴.

This underlines how effective hydraulic fluids, like those in the Shell Tellus range, can provide equipment reliability and system cleanliness that in turn protects against these ‘hidden killers’ mitigating breakdown risk and its associated costs. 

^{1 Source: multiple surveys by industry bodies including additive companies, filter manufactures, hydraulic equipment manufacturers. One source includes Parker Hannifin GmbH Bulletin: HY30-3248/ UK: Hydraulic Fluids for Parker Axial Piston Pumps Series PV
2 Total Cost of Ownership (TCO) is defined by Shell Lubricants as the total amount spent on industrial equipment, including cost of acquisition and operation over its entire working life, including costs of lost production during equipment downtime
3 *Test method ASTM D2070 was carried out under third-party laboratory conditions. Shell Tellus S2 MX 46 was tested against 17 competitor oils. Each oil was heated to 135 degrees Celsius for a period of 168 hours together with catalyst rods of copper and steel. The precipitated deposits were weighed, with weight loss recorded, along with total sludge and acid number change. Shell Lubricants is able to provide a copy of the ASTM D 2070 report on request.
4 The savings indicated are specific to the calculation date and mentioned site . These calculations may vary from site to site and from time to time, depending on, for example, the application, the operating conditions, the current product being used, the condition of the equipment and the maintenance practices.
5 Source: multiple surveys by industry bodies including additive companies, filter manufactures, hydraulic equipment manufacturers. One source includes Parker Hannifin GmbH Bulletin: HY30-3248/ UK: Hydraulic Fluids for Parker Axial Piston Pumps Series PV}