False economies – Glass trolleys and carts

This week I'm looking into glass trolleys and carts, where costs can be saved in manufacture, and if they are really savings or a false economy. The two areas investigated are castors and bearing surfaces.

One of the key components of factory trolleys which is often overlooked in terms of its importance is the castors and their ability to carry a load of glass. A standard sized 2M long by 1.7M tall glass trolley with ledges of 200mm has a glass load capacity of around 2 tonnes. That means what when evenly balanced on a perfectly flat factory floor, each of the four castors is taking around 500kg of load.

Six inch castors vary in price from around $15 each to around $150 each. To the uninitiated two castors may look the same, and may operate the same …. for a while. The more expensive castor will be made for carrying heavier loads (like glass and windows) and most likely will have a rating.

So, is there a false economy with cheap castors?

If and when a castor fails the results could be injury to staff and damage to glass load. Injuries in the workplace have both direct and indirect costs on the business, and generally around the world these costs are on the rise as our governments implement policies to create safer workplaces. Damage to the glass load is easier to calculate, and an allowance must be made for the additional costs associated with rework, such as inconvenience for the customer and your own factory processes.

To replace a castor requires the site engineer or service company to identify the problem, remove the broken part, source and install the new part, and return the unit to the factory. I once saw "graveyards" of broken trolleys which were not being fixed. I believe this is testament to the fact that fixing broken factory equipment is a hassle and a cost that many companies can't be bothered with.

Whether the costs associated with castor replacement are simply a part replacement or involve injury and product damage I believe it's a no-brainer that the investment in good castors is money well spent. Buying cheap castors is a false economy.

The second key design decision is the bearing surface. The decision of whether to use timber (low cost), glued on foam, or a purpose designed polymer bearer. 

The costs for a 90mm x 19mm hardwood decking bearer from my local hardware store is around $10 per metre. By comparison the aluminium slotted extrusion and polymer insert bearer available from The Glass Racking Company is around $25 per metre. The polymer bearer product has been developed specifically for this purpose and has a far longer life and multiple benefits over timber. On a typical factory trolley of 2M long and 1.7M tall, assuming 5 bearers per side of the A-frame, the total meterage is 20M, so the dollar value difference is per trolley is around $300.

So, is there a false economy with timber bearing surfaces?

The timber bearers will eventually split, crack or warp and require replacement. The replacement cost will be another $200 of materials plus the time to source the materials and fix them to the trolley, plus an allowance for the inconvenience to the factory. Assuming that your factory engineer costs $50 per hour and that this job takes a total time of 2 hours, then each replacement of the timber has an actual cost to the business of $300.

We have customers using our factory trolleys which have our polymer bearing surface installed that have not done any maintenance or replacement work to the trolleys for over 10 years. How many timber replacements will be required over the life-time of the purpose built polymer?

Based on these numbers you'd have to have rocks in your head to build trolleys with timber bearers. The benefits of a polymer bearer are immediate, and the cost savings of the timber simply don't add up.

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