Wax Elements

A wax element is a simple negative feedback controller. The wax element operates as a sensor, controller and actuator in a closed control loop.

Overview

FROM THERMAL ACTUATORS TO THERMOSTATIC ELEMENTS

Wax elements, also known as thermal actuators, thermal wax elements or thermostatic elements, are widely used technologies in automobiles. As well as for oil, fuel and even air flow control, they feature prominently in engine cooling systems – an essential component in a car.

Wax thermostats are well proven in the automotive sector. We can produce them in high volume which makes them a cost-efficient product.

Basic structure

HOW IT WORKS

A wax element is designed as a metal cup with an encapsulated wax with a steel pin.

Rising temperature increases the inner pressure of the closed wax-chamber. The inner pressure acts on a steel pin, which acts as a working piston and converts the pressure into mechanical force.

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With a mechanical thermostat, the wax reacts to the fluid temperature of the surrounding fluid. With an electrical thermostat, the wax reacts to the temperature of an electrical heat source inside the wax element, as well the fluid temperature. They are available with a standard cap, a standard cap with a platform, or a double cap.

Synthetic wax

COMPOUNDS AND TEMPERATURES

The compound is based on different melting ranges

Each application needs individual wax mixing to define the Start To Open (STO) temperature, and the Fully Open Temperature (FTO)

Synthetic wax can be mixed with additives such as graphite or copper to accelerate the response time

Internal sealing methods

RUBBER BAG &ANNUAL SEAL

In terms of internal sealing methods, wax elements come in two types for automotive applications: rubber-bag and annular seal. A third type, using a membrane seal, is used for non-automotive applications with a lower stroke only.
All three types have different characteristics shown in the diagram (sent) for STO, FTO and Hysteresis (between opening and closing curve.)

Technical Specification

STO FTO

Characteristic of three types of wax elements

Characteristic of three types of wax elements

IN MORE DETAIL

RESPONSE CHARACTERISTICS OF MECHANICAL THERMOSTATS

Response characteristic of mechanical thermostats for two types of wax elements used in automotive applications.

Rubber-bag type elements are widely used for mechanical thermostats. They are cost effective due to their simple design and good performance. They also have an especially fast reaction time by using additives in the wax.

Wax elements with a membrane design can be used with high proportion accelerators. They have the lowest hysteresis available and a small diameter.

An annular seal type is used for electrical thermostats and features a compact design. They have good damping capabilities as well as good failure behaviour if thermally overloaded. Wax elements that use an annular seal have a small diameter and are longer which gives a better flow.