Key Process used at DBT Medical

The major raw material used

Rubber is sap from a rubber tree (hevea brasiliensis). We buy the best quality crepe rubber. The rubber sap is allowed to dry is then thoroughly washed and compressed into 25kg bales. We cut this up on our guillotine into smaller pieces.

Milling and calendering

After cutting up the bales we mill the wedges of crepe rubber on our rubber mill to soften the rubber, add the very few chemicals needed to combine with the rubber so that after curing the finished product has a memory. This means the finished product is elastic and will return to its original shape. Without these chemicals, the principle one being sulphur, the rubber sheet will simply stretch and only return limply to its original shape - like chewing gum.

We use some of the milled rubber for moulding products but our main skill is in producing sheet. To make the sheet the rubber is pre warmed on the mill and then put over our rubber calender which has 3 big rollers. Cooling water and steam are passed through the rollers to get the temperature exactly right to produce the often very fine sheet which we produce. A lot of the products we produce are one form or another of bag. Some are used for containing urine as incontinence bags or for holding air when used as a pipeline stopper. In each case it is vitally important that the sheet does not have any small pin holes.

In the process of calendering the rubber air bubbles can be trapped and these will pop creating tiny pinholes that could cause a leak. So we run a second ply on top of the first ply to ensure minimal likelihood of one air bubble sitting on the one below. For extra security, in many cases we add a third ply. We run single ply sheets as thin as 0.004” (0.1.mm) but more typically our plied sheet runs at 0.035” (0.9mm) to 0.120” (3.05mm).

The majority of products we make are 2 dimensional - typically bags of one sort or another - but we also make 3 dimensional products. We do this by fitting the still uncured sheet over a shape. The rubber will remember the shape it was when it was cured and will hold that 3 dimensional shape thereafter.

The Curing Process

Once the product is made then it needs to be ‘cooked’ to complete the process and cure the product. This is achieved either by curing in the oven or in an autoclave. Once cured it will retain the form it was in when cured.

Finishing

Connectors, non return valves or belts may be fitted. The products are then tested, packed and labelled frequently in our customers packaging, before being despatched.