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Ageing Ovens

Wallace Multi-Cell Ageing Chamber - O7E

Introduction

The Cell method of ageing rubber and PVC consists of subjecting test pieces to controlled deterioration by air at high temperature and at atmospheric pressure so that the physical properties can be measured and compared with those of unaged test pieces.This method has the advantage that individual compounds are aged in separate cells which prevents contamination from migration of sulphur, antioxidants, peroxides, plasticisers and other volatile products.Normally a temperature of 70°C is the highest that can be regarded as providing satisfactory uniform ageing for natural rubber. Temperatures such as 100°C, 150°C and 250°C are sometimes used with synthetic rubbers.

The Ageing Oven

The oven consists of a cast aluminium block containing seven cylindrical vertical cells, each 7.5cm in diameter by 30.5cm long. Pre-heated air of the correct operating temperature is forced into the bottom of each cell through a calibrated opening from a manifold in the base ensuring even distribution through all the cells. The air flow is indicated by a flowmeter and a control valve is fitted. Air flow is provided by a diaphragm pump driven by an induction motor. Air is discharged to the atmosphere through the covers at the top of each cell to ensure that no feedback contamination occurs. Double top covers are fitted to the top of each cell to provide adequate thermal insulation. The inner cover of each cell is fitted with a vertical spindle carrying two adjustable spiders on which specimens are suspended. The oven has been designed as a unit complete with its own stand so that it will not occupy valuable bench space. Castor wheels are fitted to allow the oven to be moved by one person. The manifold in the base is easily accessible for cleaning.

Control Module

The control module is located on the side of the oven. It houses the temperature controller, the air pump, filter, air flow regulator and air flow indicator. These items are all easily accessible for servicing.

Temperature Control

The oven has a temperature range of 60°C - 25O°C. A PlD* temperature controller with digital display is fitted. The software is programmable with up to eight separate steps which allows tests of many years duration to be selected if required. The ramping facility controls the rate of temperature rise and so can be used to generate temperature gradient steps. An RS 485 or RS 232C communication option with serial interface is available to allow connection to PC or Data Logger. Power supply interruptions can occur and may cause the cell temperature to fall below an acceptable level. The high and low alarms on the temperature controller can abort the test if the temperature goes outside its operating band. The cell block is fitted with two thermostats in series which will turn off the power if the temperature exceeds approximately 280°C. This will prevent any possibility of thermal runaway.

* PID stands for Proportional, Integral, Derivative terms. The temperature controller continually refines its terms to bring the process variable ever closer to the set point.

Air Flow Regulation

The air flow is regulated by a valve positioned on the top of the control module. The air flow rate is indicated by a Flow Meter reading from 1 - 10 C.F.H.

Specifications

The Ageing Oven O7E conforms to National and International Standards. See the table below for a run-down of this product's specifications.