MMC is an Advanced Combustion Control System conceived and designed by engineers at Therser to enhance the performance of Gas Fired, Industrial Intermittent Kilns. Unlike other Kiln Combustion Control Systems, where the control philosophy is fixed at the Kiln design stage; MMC uniquely combines multiple combustion control modes in to one Flexible and Advanced Combustion Control Package capable of independently controlling multiple Temperature Control Zones.
Whilst multiple different combustion control modes can be incorporated into one powerful MMC Control System; typically, the control modes shown opposite (fig 1) are usually sufficient for the optimum firing of most products. Control modes types can be programmed in to the firing cycle in any order and sequence. Switching between each control mode is fully automatic and “bumpless”.
|Fig 1. Typical MMC Combustion Control Modes:|
|Mode #||Primary Mode:||Secondary Mode|
|1||High / Low with Ratio Control||Excess Air with bias Control|
|2||Fixed Air with Modulating Gas||---|
|3||Pulse Firing with Ratio Control||Excess Air with bias Control|
|4||Modulating On-Ratio control||Excess Air with bias Control|
Utilisation of MMC On A New Kiln For A UK Aerospace Manufacturing Company
The demand for newer more efficient and eco-friendly commercial jet engines, together with the introduction of new environmental regulations forcing airline operators to retire and replace older operationally inefficient aircraft, has spurred a rapid and sustained growth in the aerospace industry and especially in the production of commercial jet engines.
The manufacture of a modern commercial jet engine is complex, requiring many high-performance precision cast parts in which the internal section of the casting can only be precisely formed using a Preformed Ceramic Core; for example, in the casting of turbine blades. To eliminate damage and distortion during sintering / firing, large ceramic cores are normally supported using a profiled setter, whilst smaller, more detailed precision ceramic cores are normally supported in a powder in refractory “saggers” (boxes).
Preformed ceramic cores with complex and delicate shapes, typical of those used for high performance precision cast parts require de-binding and sintering in a kiln that will heat treat the product over several days.
Most traditional gas fired kilns will not be able to perform and maintain the complex and demanding firing parameters required by core manufactures unless fitted with Therser’s unique MMC system.
Field Trials – Challenges:
Relatively Dense Set Kiln Car Loading Pattern (fig 2).
Densely set loading patterns, especially product contained in refractory saggers can be difficult to heat uniformly at the same heating rates resulting in large temperature differentials across the saggers causing product deformation, thermal stress cracks and loss of ware.
The combustion control system must be capable of:
- Very long and close temperature tolerances in early pre-heat portion of the firing cycle for products fired in saggers supported in granular (30 hours to 600 ºC):
- The Combustion Control System must be capable of precise “Low Temperature Hold Control” over long periods whilst maintaining minimal deviation, effective turbulence, high mass flow and uniform heat transfer to the product, as well as controlling oxygen levels.
- Binder Removal
- Dimensional Stability
- Pre-Formed Ceramic Cores
- MMC Programming and Code for Bumpless Switching between different Firing Modes was satisfactory achieved.
- Control System and Device Communications interface and Control was effective.
- “Low Temperature Hold Control and Slow Ramp Rates” were effective and drift / deviation was not experienced
- The technology has now been applied to several UK ceramic core manufacturers. They have increased product yield. This led to some existing kilns being converted to Therser’s MMC system and also to an additional investment in two new kilns to increase capacity.
- Yield and productivity benefits from the technology are now being applied to help new and existing ceramic manufacturing customers in tableware, sanitaryware and heavy clay.