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May 01, 2024

Assignment Task

Background

Improving durability and energy efficiency of machines are crucial from the perspectives of environmental protection and economic resource management. In this course, this is achieved via effective lubrication strategies using appropriate lubricants to manage friction and wear of moving components.

A Lubricant is a multi-component fluid. Its major component is a base fluid. Various additives are included to improve specific tribological properties of lubricants. These include friction modifiers, antiwear additives, viscosity modifiers, dispersants, antioxidants to name a few.

The complexity of lubricant formulations means potential interactions among additives may impact the performance of a lubricant.

Antiwear additives are commonly added when a rubbing contact experience mixed and/or boundary lubrication regimes. They are used to reduce wear of rubbing surfaces and are important for improving durability of machines.

Zinc dialkyldithiophosphate (ZDDP), schematically shown in Figure 1, is one of the most successful antiwear additives to- date. Under the right conditions, ZDDP can form a protective film (an antiwear film) on steel surfaces and reduce wear. It is also a very effective antioxidant.

As a lubricant is being used, contaminants and degradation products may form and accumulate. This may lead to many problems including increased lubricant viscosity which is detrimental to energy efficiency and machine life. Dispersants are surfactant-like molecules and are commonly added in a lubricant to disperse contaminants, i.e. prevents aggregate formations. One commonly used dispersant is polyiso-butylsuccinimide-polyamine (PIBSA- PAM). PIBSA-PAM contains amine, i.e. is nitrogen containing additives. Literature review shows that they may interact with ZDDP via P and/or Zn in ZDDP. Dispersants may also be surface active and compete for surface sites, similar to what is observed with organic friction modifiers.

This exercise concerns interactions between ZDDP and dispersant.

Settings

You are a product development team leader in a lubricant company, responsible for the development of high performance lubricants. Your colleagues come to you with a new dispersant they have developed and are extremely excited about it.

Your colleagues: Let’s replace what we have in our formulations with this new one! We have done some tests and it is fantastic!

Being a Mechanical Engineering graduate from Imperial College London, you understand that it is important to know how your colleagues come to this conclusion,

You: What tests have you done to check?

Your colleagues: We have checked the viscosity of fresh base oil, used base oil and used base oil with dispersant. The viscosity of the used oil with dispersant is lower than that without.

Your manager is very keen on the idea. You are however less convinced. You remember what you have learnt in your Tribology course and are aware that the new additive may interact with other additives already in your formulation and may lead to unexpected results. Since ZDDP works by forming an antiwear film to protect rubbing surfaces, it is important to check if the ZDDP film formation process is interfered by the use of the new additive. You are also concerned for the impact of the new additive on tribological performance such as friction, wear and lubricant film thickness in the contact.

Task

To make a more informed decision, you have convinced your manager to let you conduct a preliminary study that examines if the new dispersant affects the performance of ZDDP in your lubricant. Specifically, you would like to answer the following questions.

Most importantly

  • Does the dispersant interfere with the formation of ZDDP antiwear film? If so, how?
  • How does the dispersant impact on wear performance of ZDDP containing lubricant?

Secondly

  • How does the dispersant impact on friction performance of ZDDP containing lubricant?

The focus of this preliminary study will be in points (1) and (2). You would write a report to convey your decision with explanation and supporting evidence. The length of the report is 4-page maximum (Arial font size 11 minimum, at least 1 inch margin in all sides, inclusive of everything).

Brief experimental Plan

We need to first examine how ZDDP, and dispersant behave in a two-component lubricant (one additive + oil) before we investigate their interactions in a lubricant. The properties of interest and how to obtain this information are below:

  1. Surface film formation - film thickness measurements and / or wear track examination via imaging (SLIM)
  2. Wear - topographical examination of worn surfaces (optical, white light interferometry)

The plan is discussed with your laboratory team who will perform the tests. The materials systems chosen, types of tests performed and test conditions are agreed.

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