In today’s heavy clay market there is becoming a push for more product in faster lead times. This need is putting extra pressure on manufacturers especially to increase throughput times. Although kilns and sometimes driers can be the bottleneck, there is added pressure on the moulding equipment to produce clay products quicker.
These increased production rates coupled with the fact that most clay bodies will contain quantities of highly abrasive un-plastic materials are putting a great strain on the moving parts within the moulding operation. This increased strain can have an impact on the wear of these parts leading to clay products not meeting crucial dimensions and tolerances.
In general for clay bricks the production route will be either extruded, moulded, hand-made or dry press whilst for clay tiles usually extruded or extruded and then pressed/moulded. For all the different forming methods (apart from certain hand-made applications) the equipment used will be made from stainless steel, alloy steel, carbon steel and tool steel. The only other additional material that is used in production is wood for hand making moulds.
So what options are available to you to extend the life of these parts having ensured you are using the correct type of steel?
- The clay body formulation will usually contain a proportion of low plastic clays, high shale clays, sands, coarse abrasive inert minerals (like grog, quartz, ground fired bricks) to name a few which over time can abrade the steel being used reducing production optimization and eventually producing out of specification products. Companies have looked in to the use of more plastic clays but their source is becoming less available and their costs have become too expensive in some instances and may lead to further changes required in the firing cycle and even longer drying times. Alternatively, you could look in to reformulating your body recipe to remove some of the more aggressive coarse particles which aid opening the body up but this route can incur extra costs for alternate materials and extra time required to formulate and approve said changes.
- The clay body can be tacky once prepared with water and as such can adhere to the auger blades or moulding boxes and if for example a large particle of abrasive material becomes stuck there then as clay passes over it it could continually abrade the steel it is in contact with. An expensive way of trying to eliminate this would be to look at non-stick coatings of the steel. However, this is can be an expensive initial out-lay and will require continual coatings to ensure continuous coverage.
- The use of clay additives, however, has been seen to be a cost effective way of improving wear life without the need to make any significant changes to the body formulation or manufacturing process. The additives help to wet out the clay particles and lubricate them which has benefits of being able to reduce water additions, improve clay workability/plasticity allowing a smoother and easier forming of the products as the now coated coarser particles will move more freely through the forming process. As the clay is now more plastic it has been shown that the power required to extruded the clay products can be reduced putting less stress and strain on the auger blades and extruder dies. In the moulding processes this increased workability allows the bricks to be de-moulded quicker and faster and can help reduce any coatings that might be required to aid the process.
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