Racking up a win

Jon Lawson

Giant circular gear rack manufactured for malt beer or whisky kiln vessel

Recently, an expert in the supply of precision-engineered parts was tasked with supplying the first of two giant 44m gear racks for use on germinating kiln vessels (GKV) for a malt producer based in the UK. The second gear rack will be delivered by the end of 2017.

Halifax Rack & Screw (HRS) manufactured the rack in 54 separate curved sections that come together to form a complete 26m outside diameter circular gear rack, which drives the turntable/floor of the GKV.

The gear rack is part of a multi-million pound project to construct a total of four GKVs. HRS is working closely with the project’s main contractor, Don Valley Engineering, a specialist UK-based provider of process plant and support services to the malting industry.

Steve Benn from HRS comments: “There aren’t many companies in the world that are capable of cutting a gear rack of this size, let alone one that is curved. At our manufacturing facility in Brighouse, we’ve one of the largest dedicated rack-cutting facilities in the world. We’ve cut bigger teeth than this in the past, but on this project, it’s the sheer size of the circle that posed the biggest challenge. We’re also fortunate that we have a flexible, highly skilled, experienced workforce that is capable of producing custom racks of this nature in a fast turnaround time.”

The racks for the GKV are made from medium carbon steel (C45) and coated (hot dip galvanised) to provide corrosion resistance against the harsh conditions of the malt germination process. The racks were manufactured in 100mm square sections to Grade 8 accuracy. The gear teeth (pitch of 18 mod) were cut as straight pieces and then each of the 54 sections of rack were rolled and bent to the precise curvature required. The mating pinions were then corrected for the resulting angular tooth form on the rack. The outside radius of the rack is 12,749mm (outside diameter 26m).

The malting process and GKVs

The process cycle for malting can be divided into three stages.

Steeping is where the moisture content of the barley is raised by immersion in water resulting in the start of the natural germination process.

The steeped barley is then transferred to germination units where germination continues, enzymes are produced to partially break down the starchy material and a rootlet is formed. This green malt is then transferred to a kiln where the controlled drying and curing process halts germination and imparts the final colour to the malt required for its final use as either beer or whisky.

Circular germinating kiln vessels (GKVs) provide improved airflow, good energy usage, clean conditions, a faster and simpler vessel construction and a rotating stainless steel floor that is driven by the gear rack.

The turntable and floor are rotated continuously but slowly (only once or twice a day). The germinating grain is therefore kept loose for between four to six days, depending on the final malt type.

A combination of heat and air flow is then applied to halt the germinating process at the precise time.