Pumping decorative plaster with a progressing cavity pump

Feed hopper progressing cavity pump pumps plaster

Gypsum plaster has been used as building material for at least 4000 years. Currently it is
used to make plaster boards, fibrous plaster, building decorations and moulds for many
applications.

The process of producing plaster

The gypsum (CaSO4.2H2O) is heated to remove 75% of its combined water, resulting in the formation of a harder plaster (CaSO4.½H2O). This reaction is called calcination.
Then the dry plaster powder is mixed with excess water and any additives. It can then be casted in moulds, extruded, applied as thick slurry to a surface or laminated between paper boards. The additives are used to change the density of the plaster and, in the case of plaster board, to help the plaster to mechanically bond to the cardboard.

In a manufacturing operation, excess water is added to ensure complete rehydration of
plaster back to gypsum and to provide sufficient fluidity for manufacturing processes. The
excess water is then removed either by simply leaving the plaster to dry by evaporation or
by heating it to up to 250°C for up to 60 minutes. During this time the plaster solidifies so
that it can be removed from a mould in one piece.

At a production facility of a Dutch coating manufacturer, decorative plaster is pumped with a progressing cavity pump. The worm pump is already pumping the plaster successfully for over 37 years now.

Under the mixing tank where the plaster and the other ingredients will be mixed there is a two stage progressing cavity pump. This worm pump has a rectangular suction inlet and conveyer screw on the coupling rod in the pump housing. This eccentric screw pump feeds the filling machines of the plaster. The SEW drive of the worm pump is separately mounted on a common base plate and connected with a flexible coupling to the pump.

The question

After 37 years of successful running the customer wanted the original progressive cavity pump to be replaced by an identical worm pump. It was very important that the hopper dimensions of the progressing cavity pump would be exactly the same. The hopper needed to fit exactly to the the existing production unit for the plaster. Other dimensions would cause too many, very expensive, changes.

The problem

An identical worm pump is not available anymore; even the similar hopper dimensions within the latest pump range of our former supplier are not available. Even modifying the hopper of the progressing cavity pump against a reasonable price increase can’t be done.

Process conditions

The progressing cavity pump transfers a decorative plaster with a required capacity of 15 m3/h and a manometric head of maximum 5 bar. The viscosity of the plaster is round 5000 cP with sharp edge particles of 2 till 3 mm. Dry solids content is limited to a maximum of 10%. To keep the abrasive character of the medium as low as possible we selected the pump with a maximum internal sliding velocity of 1 m/s.
The elastomers of the rotor and the stator can be fitted in NBR, which is resistant and the best suitable against an abrasive medium.

The solution

Verder has a new pump line: Verderpro progressing cavity pumps. Because it is Verder’s own engineered brand we have got the flexibility to manufacture the feed hopper rectangular pumps with an identical hopper size of any other worm pump series. This makes replacement within the production unit for plaster possible with only a reasonable investment.

For the customer this means the downtime for plaster production is as short as possible. Furthermore, only small changes to pipe work and base plate are necessary.
A second advantage of the Verderpro brand is the availability not only of stainless steel 316, but also stainless steel 304. For media that meet the resistance of SS 304 the more economic SS 304 worm pump version can be a fine alternative.

If you also have problems pumping abrasive media, contact us via the contact form.

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