News: Replacement of Traditional Pavement Lights
At Hargreaves Foundry we make unique, handmade, original castings. We combine manufacturing skills with knowledge and experience to offer a bespoke service to our customers. Our speciality is making cast iron products, and whether these products are for engineers, artists or architects, the processes are still the same. Given cast iron's place in history many of our architectural castings are for restoration or heritage projects, although we do get some new or original designs to work on.
There is a common misconception that nobody makes certain products any longer. A case in point is cast iron Pavement Lights. Although not as common on our streets as they used to be, we still get orders for these and still make them.
The purpose of this Blog is to explain how we make cast iron Pavement Lights, the information we need and some of the technical detail that will help customers understand the different designs and their effects on the pattern making and casting processes.
We enjoy working closely with our customers who can always pick up the phone and speak to an expert about their project. All the contact details are shown at the bottom of this blog.
What do we need?
As with all castings we need a pattern. There are many factors critical to making any pattern, but in the case of Pavement Lights probably the most important detail is the size of the glass lenses. Traditionally made in 4inch by 3 inch (100mm x 75mm), they can now be obtained in several standard sizes. Bespoke sizes are available but these will cost more. We can’t make a pattern until we know which lenses need to be fitted. (You can find out more about pattern making here http://www.hargreavesfoundry.co.uk/blog/blogview/34/why-is-pattern-making-so-important)
We also need to know the overall dimensions, metal thickness required and any decoration or wording required before the pattern can be made. This information is often gleaned from originals or samples from originals. Even where an old pavement light has been damaged, corroded or broken we can usually work out precisely what the finished casting needs to look like and therefore how to make the pattern.
Making the Sand Mould
Another factor that effects how we make a Pavement Light is the overall metal thickness required. This can vary but is often subject to location and the load bearing requirements. As a rule of thumb, if the overall depth of the casting is up to two inches (50mm) we can make a single piece flat back mould from the pattern. If more than two inches (50mm) the mould will need to be made in two parts. This can have an effect on the cost as there is twice as much work in a two part mould. The reason for the difference in the moulding is to do with taper and the amount of light allowed through the Pavement Light.
Draw taper at 2° is added to patterns to allow the pattern to be lifted out of the sand mould without undercutting. Undercutting occurs if, when lifting the pattern out, sand gets trapped and breaks or damages the mould. In the case of a Pavement Light with less overall depth, the amount of taper will not affect greatly the amount of light allowed through. In this case a single, flat backed mould will do the job. Where the overall depth is greater than two inches (50mm) the amount of taper will limit how much light can get through. The answer is to make the mould in two parts, so that the taper can be reversed on the underneath section and allow the light through.
The mould is made by placing the pattern in a box then ramming sand around the pattern. The pattern when removed leaves a Pavement Light shaped cavity, which is a ‘negative’ or reverse of the pattern. The sand has additives that allow it to set hard. The surface of the mould is lined with a refractory paint to protect it from the initial inflow of hot iron. Once the iron has been poured in at 1,360°centigrade, it is left to cool and then broken out of the mould. The casting that comes out of the mould is again a ‘positive’ version, exactly like the pattern. All the sand is recycled and the pattern is available to make more moulds if required. (You can find out more about mould making here http://www.hargreavesfoundry.co.uk/blog/blogview/40/making-sand-moulds-and-cores-for-iron-casting
Pattern Ramming Up’ the mould around the pattern
Completed mould coated with refractory paint
What else do we need?
Pavement Lights often carry makers or customer names, sometimes dates etc. This kind of decoration is added at the Pattern making stage. Letters and numbers in standard fonts can be attached to the pattern. Also, in this day and age, since Mr. Health was introduced to Mr. Safety, it is common to add non-slip ridges. This was not usually the practice on originals, but something we can easily do.
Details of pattern
When the casting is broken out of the mould it needs to be fettled. Fettling is a foundry process that involves shot blasting any sand residue left from the mould off the casting and grinding off any extraneous metal, joint lines etc. Any waste or excess iron is then recycled and re-used for future castings. The casting is then ready to be primed, painted and have the glass lenses fitted.
The glass lenses are fitted into the cast iron frame using double sided adhesive tape used in the manufacture of modern double glazing units. The process is finished by brushing fine, kiln dried silicon sand mixed with cement into the edges and covering with a fine mist of water to cure.
Fitting the lenses Finished Pavement Light
• We still make bespoke cast iron Pavement Lights
• It is important to decide on the size of the glass lenses as soon as possible
• We need the overall dimensions as well as details of any design embellishments required.
• Samples of originals, even if broken or badly damaged can still be helpful to us.
Find out More
In use in construction and art for centuries, modern Cast Iron can be a sustainable, cost effective, locally sourced product for structural and aesthetic applications.
To talk about your project, contact Andy Knight, Foundry Manager at firstname.lastname@example.org Tel: 01422 399111
Contact us via Linkedin or Twitter or speak to Andy on Twitter.