How tribological characterization helps compare self-lubricating plastic materials and select the most suitable compound for real application conditions.
When two components work in contact and are subjected to relative movement, friction and wear become fundamental parameters in material selection.
Reducing these phenomena means improving system efficiency, limiting deterioration over time and, in many applications, reducing or eliminating the need for external lubricants.
It is precisely to meet these needs that LATI develops LATILUB, the family of self-lubricating thermoplastic compounds designed for applications where sliding, contact, and component durability represent decisive requirements.
But choosing the material with the lowest friction coefficient is not enough. Tribological behavior depends on the system as a whole: material, counterpart, pressure, speed, temperature, geometry, and type of movement.
For this reason, characterization by tribometer represents an important tool in the development and selection of self-lubricating compounds.
Self-lubricating thermoplastic compounds: what they are and how they work
Self-lubricating thermoplastic compounds are materials in which specific functional additives are dispersed within the polymer matrix with the aim of controlling friction and wear generated by the relative movement between two or more surfaces.
The LATILUB range includes formulations developed using different self-lubricating systems, selected based on the required performance and the operating conditions of the application.
Solutions used include, for example:
- graphite, molybdenum disulfide, and silicone oil, to influence friction behavior;
- aramid fibers, to contribute to wear control;
- carbon fibers and ceramic fillers, to increase the PV limit;
- PTFE-based formulations
- PFAS-free alternative solutions.
The choice of formulation therefore depends on the tribological problem to be solved and the conditions in which the component will actually operate.
In other words, there is no universally best self-lubricating compound: there is a formulation more or less suitable for a specific tribological system.
Advantages of self-lubricating compounds in moving applications
One of the main advantages of self-lubricating compounds is the possibility of operating without external lubrication using oils or greases, when application conditions allow.
This can contribute to:
- reducing maintenance requirements;
- keeping systems cleaner;
- limiting the accumulation of dust and contaminants associated with the presence of traditional lubricants.
In addition to these advantages are those typical of thermoplastic materials:
- possibility of obtaining complex geometries through injection molding;
- integration of multiple functions into the same component;
- mass reduction compared to many metal solutions;
- possibility of creating components intended for technically demanding environments;
- control of friction, wear, and noise in moving applications.
Self-lubricating materials therefore find application in components such as gears, bushings, plain bearings, sliding planes, linear guides, cams, pins, automation systems, pumps, and valves, as well as in couplings between plastic and metal parts.
Friction coefficient and wear: why a single value is not enough
When talking about tribology, one of the first quantities considered is often the friction coefficient.
However, simply asking “what is the friction coefficient of this material?” is rarely sufficient to predict its behavior in a real component.
Tribological performance depends on numerous parameters, including:
- operating temperature;
- pressure or applied load;
- relative speed;
- contact geometry;
- surface finish;
- counterpart material;
- environmental conditions;
- duration and type of movement.
Even friction and wear, although closely linked, represent different phenomena.
A material characterized by a particularly low friction coefficient is not necessarily the one that also offers the lowest wear under the same conditions.
For this reason, LATI recommends using friction coefficients and wear factors primarily to compare different materials under the same test conditions, avoiding considering them automatically as absolute design values.
This is where experimental characterization plays a central role.
Tribometer: how friction and wear of plastic materials are measured
The tribometer is an instrument used to characterize the tribological behavior of materials and material pairs under controlled contact and movement conditions.
Through defined tests, it is possible to study phenomena such as friction and wear, compare different formulations, and analyze how material behavior varies by modifying the parameters of the tribological system.
The value of a tribological test derives precisely from the possibility of controlling the test conditions.
Load, speed, temperature, distance traveled, contact geometry, counterpart material, and surface characteristics must be carefully defined so that the results are significant with respect to the application to be studied.
The more the real operating conditions are known, the more it is possible to build a test capable of providing useful indications for material selection.
Rotary and linear tribological tests: what changes
The characterization possibilities of the tribometer used by LATI have recently been expanded through the introduction of a new linear module.
The system allows for tests with reciprocating linear movement to be performed alongside tests characterized by rotary movement.
In reciprocating motion, the contact repeatedly travels a certain track and the direction of movement is periodically reversed.
This configuration allows for the representation of different kinematic conditions compared to continuous rotation and for a closer study of applications where components work through back-and-forth sliding.
Having both configurations thus expands the conditions under which LATILUB compounds can be characterized.
The goal is not simply to collect more data, but to obtain information more representative of the real tribological system to be analyzed.
To further explore the meaning of this evolution from a material development perspective, we speak with Annacarla Cereti, Product Development Technician at LATI
Tribological tests on LATILUB: five questions for the LATI laboratory
Anna, let’s start with the basics: what is a tribometer and what does it allow us to understand about the behavior of a self-lubricating plastic material?
| A tribometer is a laboratory instrument used to measure friction and wear between two surfaces in contact and relative movement. In the case of a self-lubricating plastic material, it allows us to understand how easily the material slides against another surface, how much it wears down, and how effective its ability to reduce friction is without external lubricants. |
How is a tribological test set up and what are the variables that can most influence the result?
| At LATI, we use a tribometer in a pin-on-disc configuration, where a steel pin is pressed with a certain load against a plastic material disc, which rotates at a given speed. The system measures the friction coefficient and allows for the quantification of wear after a certain distance traveled. The factors influencing the test are therefore the applied load, rotation speed, temperature, surface roughness, and test duration. |
Recently, our tribometer was equipped with a new linear module. What does it allow to do compared to the previous configuration?
| In the classic pin-on-disc configuration, the movement of the disc is rotary and the pin leaves a circular track that is always traveled in the same direction during the test. The linear module allows this rotation to be transformed into a reciprocating linear movement, where the track left is a line, traveled back and forth. |
How does the possibility of performing reciprocating movement tests expand the characterization of LATILUB materials?
| Since the tribological performance of a material does not belong to the material alone, but to the entire system in which it operates, being able to perform tests in different configurations allows for the study of different systems and the acquisition of more information on the possible behavior of the material. |
From the laboratory to the real component: how can these tests help designers, molders, and developers in choosing the most suitable compound?
| The values obtained in the laboratory cannot be used as design data, but rather to compare different materials tested under similar conditions. Characterization can be done with a rotary or linear module based on the customer’s application; however, the ideal would be to create a test situation (type of contact, loads, speeds, geometry, …) as similar as possible to the real system. |
From the tribological test to the choice of compound
When facing a tribological problem, simply choosing the material with the lowest friction coefficient is rarely enough.
One must simultaneously consider:
- friction;
- wear;
- contact conditions;
- type of movement;
- speed;
- pressure or load;
- temperature;
- counterpart material;
- operating environment;
- structural requirements and expected component life.
The compound formulation therefore represents the starting point. Experimental characterization instead allows for understanding its behavior, comparing different solutions, and identifying the most promising ones for the application conditions considered.
With the introduction of the linear module, LATI further expands its analysis capabilities, adding reciprocating movement tests to rotary ones and thus increasing the possibilities of studying LATILUB materials in scenarios closer to real application needs.
The laboratory thus becomes not only a tool for verifying material properties, but a concrete support for design and compound selection.
| Do you have an application characterized by friction or wear problems? Type of movement, speed, contact load or pressure, temperature, counterpart, environmental conditions, and performance goals are fundamental pieces of information to correctly set up material selection and characterization. Contact the LATI team to further explore the choice and characterization of LATILUB compounds for your application. |
FAQ
What is a self-lubricating compound?
A self-lubricating compound is a thermoplastic material formulated with functional additives intended to control friction and wear in applications characterized by relative movement between surfaces, reducing or eliminating the need for external lubricants in certain cases.
How is the friction coefficient of a plastic material measured?
The friction coefficient can be evaluated through tribological tests performed under controlled conditions of load, speed, temperature, contact geometry, and counterpart material. The result must always be interpreted in relation to the specific test conditions.
What is the difference between friction and wear?
Friction describes the resistance to relative movement between two surfaces, while wear concerns the progressive deterioration or loss of material due to contact. A low friction coefficient does not necessarily imply low wear.
What is a tribometer used for?
A tribometer allows for the characterization of the interaction between surfaces subjected to relative movement and for comparing the behavior of different materials under defined tribological conditions.
What information is needed to choose a self-lubricating plastic material?
It is important to know at least the type of movement, speed, contact load or pressure, temperature, counterpart material, environmental conditions, component geometry, and required duration.
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