Jingmen Jinjiu Gypsum Powder Co., Ltd: May 2016

For most of the sanitaryware or Chinaware manufacturers, gypsum moulds are still the main molds for slip casting method. Natural gypsum is the raw material for making gypsum moulds, the quality of gypsum powder will directly effect the performance of moulds, then effect the final quality of sanitaryware, so almost all the manufacturers or companies of sanitaryware are highly pay attention on the quality of pottery plaster of paris.
The structure of sanitaryware is complex, huge volume, thick green body, all these factors determines this industry requires gypsum powder to meet all the good standard, initial set time cannot be to fast, final set time cannot be to long, suitable bending strength and compressive strength is also very important, the water absorption rate should be proper, long life cycle for use etc. It also matters that it is not easy to be cracked and very smooth finished surface.
Generally speaking, slip casting plaster includes alpha plaster and beta plaster, but the sanitaryware industry use beta plaster most of the time. In this article we will introduce how to testing the property of beta gypsum for making Sanitaryware Ceramic Mould. All the information just for reference only.

1, Fineness and Water absoprtion rate:
The fineness of gypsum will effect moulds strength and final set time. The better fineness the more touching area gypsum and water will get, thus it is faster to dissolve in the water, this means the final set time will be faster. The fineness of the beta gypsum for sanitaryware use is 120~180 mesh. The testing method for fineness is sieving method: take 100g gypsum dry powder, pour onto the certain meshed analysis sieves, wash it with water, drying the left gypsum one sieves and weigh it you will get the fineness.

2, Set up standards for testing method:
Several factors will effect quality of gypsum moulds:
>Water quality: natural water or purified water
>Consistency: water to plaster ratio(1:1.25~1:1.55 is ok)
>Soaking time and stirring time(2~4 minutes is ok)
>Stirring rate(300~500 r/min is ok)

3, Test the flowing diameter:
We all know that by checking flowing diameter we can know the gypsum ability before knowing initial set time. If the dismeter size is too small, the gypsum slurry flowing ability will not be not good when slip casting the moulds, there will be bubble in the moulds and moulds strength will be less. if the dismeter is too large, it will be mortar leakage when casting moulds even the gypsum slurry secrete water stratification.
Testing method:
>Weigh suitable gypsum powder and water according to the consistency. Please note that pour powder into water evenly within 30 seconds and make sure water have to submerge the powder. At the same time, timing it when start pouring powder. After all powder poured in water, soak it for 2 minutes then stair it for 3 minutes, put a barrel on glass board ensureing the barrel inside is very smooth, then pull out gypsum slurry into the barrel, vertically lift the barrel quickly, when the gypsum slurry will not flow, messure the size of the diameter.

4, Test the initial set time and final set time:
When testing the diameter, use a 0.5mm thickness knife to cut the round gypsum cake, cut it every 30s at the beginning, cannot repeat or across, clean the knife each time after the cutting and make sure the round gypsum cake donot move or shake. When the scratch cannot close together, recoard the time it is the initial set time.
And after the scratch cannot close together, press the round gypsum cake with your thumb by using 50N, press it every other 30s until there is no moisture recoard the time it is the final set time.

5, Test the bending strength:
Make gypsum slurry according to the consistency, pour the slurry into metal mouds, waiting for drying for 2 hours, take out the 3 dryed gypsum and put them into the testing machine, press the bottom and when the gypsum crached recoard the number MPA.