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the feature industry this month is....
Wax Manufacturers
One of my recent construction millwright contract jobs was at a wax factory. It's interesting that a place looking at least as high-tech as an oil refinery produces something as familiar as waxes. Mind you, there is some connection between oil refineries and wax factories: the raw ingredients!
There's lots of piping systems in a wax factory. Pipes always lead to pumps, and pump maintenance is a common millwright job in any kind of industry. During use, seals wear, leaks develop, and the pump needs work. This quick lesson is about the simplest kind of pump sealing: 'packing', or 'stuffing'.
On the outside of the pump proper, there will be a "stuffing box", with a "packing chamber" to contain the packing material which does the actual seal; a "gland follower" which presses the packing into the seal area, and "gland bolts" to hold it on. Sometimes there is an additional part, called a "lantern ring", which goes in the packing chamber between rings of packing, positioned under a plug in the stuffing box housing. It is a ring with radial holes, through which more lube can be added to the stuffing box, or flushing or cooling can be applied to the central packing. The packing itself is frequently layers of lubricated asbestos rope, although you may also see a more inflexible material, even metal, being used in special applications. Most of the time, though, the packing will arrive in the form of a large roll of rope or felt in the appropriate thickness, which the millwright must cut into rings of the right size to fit around the shaft. The rings are then inserted into the stuffing chamber, with the cut joints staggered. Sealing is then accomplished by squeezing the packing against the chamber's OD and the shaft by tightening up gland follower.
Quiz Question:
The stuffing box method is not a complete (positive) seal. Can you explain why this should be so?
There are many types of wax. In the case of one type, petroleum wax, the raw material is a by-product of crude oil refining called slack wax. They remove the oil component with heat and solvents; the wax component crystallizes out when cooled. It is further separated by filtering, then the solvent is removed by distillation. Percolating the wax through clay removes unwanted colours. (Solvent and clay are reused; separated oil is sold for other purposes). The manufacturer will then blend the refined paraffin waxes for specific properties desired in the final product, such as melting point; and then may convert the liquid wax into slabs, granules, pellets, or whatever form they wish to sell. Other types of wax such as natural beeswax, although starting with different raw ingredients, will share many of the same manufacturing steps for purification and blending. It's an impressively complex process for such a familiar item as wax, but there are more uses for wax than you would at first think.
Here are a few links to sites related to wax manufacturing:
The European Wax Federation has a page detailing many types of wax and their various (sometimes surprising) uses: http://www.wax.org/wax1/pages/f_waxes.htm
The International Group is a manufacturer of wax, and has a site detailing its products and answering exactly "what is wax": http://www.igiwax.com/
The Petrowax site tells you a lot more about the steps in turning slack wax into final product: http://www.petrowax.com/
The Magnum Machine & Manufacturing company makes the equipment that manufacturers use in their factories. Check out this very millwright-ish link for their wax products page, pictures of production presses, chill plates, etc: http://www.magnummm.com/
All stuffing box seal arrangements must have what is termed "controlled leakage". This means that when correctly installed, a certain number of drops per minute will still be able to find their way through the packing material. It would be impossible as well as incorrect to attempt to eliminate the controlled leakage by overtightening the gland follower. This would put excessive load on the motor--the pump could even be stopped completely by the clamp-like action of overtight packing. A stronger motor can overcome more resistance, but there must always be controlled leakage. Also, many materials used for packing come impregnated with lubricant, and are able to absorb additional lube. As a rule of thumb, lube may be 30% of the packing material. If squeezed too hard by the gland, the lube will actually get squeezed out causing excessive friction, heat, and wear to the pump and shaft.
See you on the next monthly update of the Construction Millwright Feature Page!
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